SPE 117410

Main Tendencies of the Sweep Efficiency Improvement Evolution in Russia

A.N.Shandrygin, SPE, Schlumberger, and A.Lutfullin, State Reserves Committee “SRC Rosnedra”

Copyright 2008, Society of Petroleum Engineers

This paper was prepared for presentation at the 2008 SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA, 21–24 September 2008.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been
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Abstract
The sweep efficiency enhancement technologies applied in Russia were analyzed. It was shown that the most common sweep
efficiency enhancement techniques are sidetracking, non-stationary flooding and different flow-diverting technologies, based
on chemicals injection, restricted by volume. In some cases, hydraulic fracturing can be considered also as a means to
improve the sweep efficiency by treatment. The case histories of all treatment techniques specified in the paper are presented
and trends of their development in the future are identified.
Introduction
The problem of enhanced oil recovery is particularly pointed in Russia today: for the last 25-30 years the tendency is from
slow to steady decline of oil recovery factors in the fields. Within last 5-6 years the oil recovery factor in Russia has become
more or less stable and can be estimated for Russian fields as 34-36 %37.
The decrease of oil recovery factor in the country can be explained by the change of the so the called “structure of oil
reserves”, specifically by increase of the share of oil reserves and production volumes from regions with more complex
terrain and climatic conditions and fields with more complex geological conditions: low productive formations and deep-
seated accumulations. For the last decades the share of Western Siberian fields has been significantly increased in the total oil
production, while production share of European part and Urals area has dropped, i.e. developed regions with good
infrastructure (map with main Russian hydrocarbon basins is in Appendix A). Adverse climatic and geological conditions
stipulated the development of fields with less dense well spacing and consolidation of the large number of productive
formations in single production targets. All this inevitably results in a sweep efficiency and oil recovery factor decrease.
It is necessary to mention that in the former Soviet Union a lot of attention has been paid to oil recovery problems since the
end of 70-s (the review of EOR used in the former Soviet Union and Russia has been presented in the paper37).
Unfortunately, the economic shocks during the period of the well-known events in the end of 90-s caused the catastrophic
reduction of EOR application. The oil industry restructuring seriously affected the scale of EOR operations. Start-up shops
and newly-made oil companies needed to develop and get a profit rapidly and couldn’t support expensive EOR projects.
Unfortunately, for the last ten years there was no official statistics on EOR application and efficiency available in Russia.
According to different estimates8,52, the number of projects with actual EOR implemented, such as gas injection, WAG,
thermal EOR techniques has significantly reduced, and incremental oil production due to their application is insignificant in
the overall oil production (Fig.1). It is significant that chemical flooding came to naught also during last 20 years and
chemical EOR constitutes practically the so called “Flow Diverting Technologies” or “Flow Deviating Technologies” (FDT).
These technologies are based on injection of insignificant volume of special agents into injectors for “redistribution” of
injectivity profiles between layers, “smoothing” water displacement front in heterogeneous formation and as a result the
enhancement of sweep efficiency. Together with flow diverting technologies other techniques in Russia are applied to
improve the sweep efficiency which is not really correctly referred to EOR techniques. In some cases these technologies may
include massive hydraulic fracturing, sidetracking and some other sweep efficiency improvement techniques which in the
common world practice are referred to the reservoir and water management. Total incremental oil production due to
traditional EOR doesn’t exceed 2.8-3.0 MMtons while FDT and other techniques of formation stimulation and bottomhole
zone treatments bring about 44-45 MMtons (Fig.1). Part of this oil production related to well stimulation while the other one
was connected with the sweep efficiency enhancement.
2 SPE 117410

50

Additional oil production per year, MMton

45

40

35

30 Others
Gas
25
Chemical
20 Thermal

15

10

0
1970 1975 1980 1985 1990 1996 2001 2006
years

Fig.1 Incremental oil production dynamics over time

The objective of the current paper is to provide an analysis of the sweep efficiency enhancement techniques applied today, to
evaluate their efficiency and determine the main trends of their development. The main stimulation technique in Russia is
flooding, and therefore, hereafter we will review the sweep efficiency during flooding. Gas flooding, WAG, and thermal
techniques which improve both the displacement efficiency and sweep efficiency will stay outside the scope of this paper (the
current status of the application of these techniques in Russia is presented in paper37).
Quantitatively the «sweep efficiency» is expressed in terms of a ratio of the swept zone of the oil-saturated reservoir volume
to the overall oil-saturated reservoir volume. Quite often, the sweep efficiency for the field development efficiency analysis is
a product of its constituent efficiencies. One of the most common approaches is a sweep efficiency presented in form of two
efficiencies: areal (or lateral) and vertical sweep efficiencies. There was a different understanding of the sweep efficiency in
Russia in its time - in form of several different efficiencies, reflecting geological and technological effects on the sweep
efficiency. In general, all these efficiencies were grouped in two main sweep efficiencies: “sweep efficiency by
displacement” and “sweep efficiency by flooding”. The first one was the share of interconnected oil-saturated reservoir
volumes with the well spacing applied to the overall oil-saturated reservoir volume, i.е. it determined the reservoir pore space
volume (reservoir voidage) involved in the flow to the overall pore space volume of the reservoir. The second one was
calculated as the share of the oil displaced from all interconnected oil-saturated volumes of the reservoir with the well
spacing applied. Thus, the first type of the efficiency determined how the applied well spacing (its density and geometry)
provided the development of separate unconnected and blind zones of the reservoir. The second efficiency showed how well
the heterogeneous formation is drained and if the volume of the agent injected is sufficient for formation flushing.
As a matter of fact all techniques of sweep efficiency enhancement are targeted at changing one of the efficiencies, i.е.
whether to bring into the development the reservoir volumes earlier not connected to wells, or to improve the process of the
oil displacement from formation zones heterogeneous but connected to wells. It seems that all existing techniques of the
sweep efficiency enhancement can be combined into four groups:
- Well spacing.
- Massive (interpenetrating) treatments of the near-wellbore zone.
- Flooding management.
- Flow Diverting Technologies.

First two groups of techniques are aimed mainly at bringing into the development the unconnected zones of discontinuous
formations, whereas the other two – to improve the sweep efficiency of connected but heterogeneous reservoirs.
“Well spacing”
It is quite obvious that a well spacing and, first of all, a well density is one of the main factors which determines the sweep
efficiency of the reservoir. To determine the optimal well spacing and its density is the issue of technological and technical-
economic calculations of the field development design, and the studies of the well spacing type and density effects on the
sweep efficiency and oil recovery factor for different field development options form an integral part of the field
development plans. That is why there is a lot of materials with theoretical and field data on the sweep efficiency relations to
the well density obtained from the fields in different regions of Russia15, 30, 36. In numerous papers there is a description of
different technological solutions to improve the sweep efficiency by well spacing transformation, transfer of injection zones
and spots, isolation of the inflow and injection intervals, etc. However, in this particular case all these field management
SPE 117410 3

solutions, excluding the non-stationary flooding techniques, will stay outside the framework of the given paper. The
experience of the sweep efficiency enhancement by drilling new infill wells during the field development; sidetracking and
horizontal well drilling will be analyzed.
Sweep efficiency enhancement by horizontal drilling
Horizontal wells certainly can be considered as one of the tools to improve the sweep efficiency, since they have the
significant borehole extension in productive formation and provide considerably greater contact with formation, than the
vertical wells. Due to horizontal drilling the sweep efficiency can be greatly improved in the reservoirs with the gas caps and
bottom waters and also in naturally-fractured carbonate reservoirs. The effect from horizontal drilling in the reservoirs with
extensive gas-oil and water-oil zones is determined not only by the “geometrical factor” (significant reservoir coverage by
horizontal hole), but also by the possibility to significantly reduce water and gas cones effect due to decreasing of pressure
drawdown. Thereby, together with the current production parameters improvement (watercut and gas factors decrease), the
oil production is increasing, especially in the near-contact zones. Sweep efficiency enhancement due to horizontal drilling in
fractured carbonate reservoirs is achieved by providing greater contact of the main reservoir filtration channels – fractures
with borehole walls. At rational technological regimes of the well operations it is possible to bring in the drainage larger
reservoir volumes. And, finally, due to horizontal well drilling it is possible to bring into the development low-productive
zones of the formation, which by economic reasons can not be developed by the vertical wells.
The annual number of horizontal wells put on production is steadily growing (Fig.2) and in 2007 it was about 400 units. The
annual production from horizontal wells put on production in 2007 was more than 4 MMtons of oil. Horizontal wells are
used in the fields with different characteristics and designed to cover various issues, including the problems of sweep
efficiency enhancement by treatments as specified above. Single horizontal wells and horizontal well patterns are applied in
the areas penetrated by vertical and deviated wells. In this paper we will give some examples of horizontal wells applied to
improve the sweep efficiency under various conditions of the development.

400 4.5

350 4.0
wells number
oil production 3.5
300

oil production, MMtons

horizontal wells number

3.0
250
2.5
200
2.0
150
1.5

100
1.0

50 0.5

0 0.0
1995
1995 1998 2001 2004 2007
year

Fig.2 Horizontal wells drilling dynamics over time

The effectiveness of the sweep efficiency enhancement by horizontal wells as «pure» field experiment can be demonstrated
by two Western-Siberian fields: Lokosovskoye and Southern-Lokosovskoye. The Cretaceous formations BV5 and BV 6 and
Jurassic formation JV1 are targets of the development in the small-scale Southern-Lokosovskoye field. Average net oil pay of
the targets is from 4.5 to 10 m, permeability from 7 to 200 mD, net to gross ratio – 0.35- 0.76. The considerable area of the
development targets is in the water-oil zones. Herein, Southern-Lokosovskoye can be considered as the «fragment» of the
larger Lokosovskoye field. Therefore, the productive formations of Lokosovskoe field are better developed and have greater
thicknesses, smaller ratio of water-oil and pure oil zones and some better reservoir properties. The development of Southern-
Lokosovskoye field was performed by systems of both vertical and horizontal wells, while the targets of Lokosovskoye field
were mainly penetrated by vertical wells. Horizontal wells in Southern-Lokosovskoye field allowed to ensure not only the
high flow rates, than those in the vertical wells (6-7 times), but also to provide greater coverage by the flooding. Thus, at
worse reservoir properties and development conditions of the Southern-Lokosovskoye field, the expected oil recovery factor
can be 8-10 % higher than in the development targets of the Lokosovskoye field.
4 SPE 117410

As an example of the efficiency enhancement of the oil rim development and sweep efficiency enhancement due to
horizontal well drilling it will be worthwhile to mention horizontal well drilling and operation project - the most famous in
Russia – Fedorovskoye field (Western Siberia)7. The oil accumulation of АS4-8 formations of this field is a fine oil rim
between the gas cap and bottom water, average net pay is 5.6 m with the distance between GWC and OWC - 12 m. In the
course of the reservoir production test different patterns of vertical well location 400х400 m and 600х600 m were applied.
However, the efficiency of these patterns was low due to significant breakthroughs water from the bottom water zone and gas
from the gas cap in the vertical producers. To improve the parameters of the field development more than 200 horizontal
wells were drilled with the length of a horizontal section up to 500 m. Despite the complications occurred during the
horizontal wells operation, in general, their application was efficient. The average initial flow rate in horizontal wells per
years was from 45 to 55 tons/day and exceeded the flow rate of vertical wells 1.3-2.5 times. Therefore, the watercut in
horizontal wells reduced 1.1-1.2 times with gas factors similar to vertical holes. Specific volume of the cumulative oil
production per one horizontal well exceeded the values of vertical wells 2.2-2.3 times. Thus, the sweep efficiency increased
as well.
Horizontal wells were widely used to improve the field development efficiency and the oil recovery factor in some fields with
low-productive carbonate formations in Volga-Urals region. Horizontal drilling was widely used for carbonate fields
development in Udmurtiya since 1994 (the first well in Mishkinskoe field was drilled in 1992)43. Today about one hundred
horizontal wells have been drilled in many carbonate fields in Udmurtiya region (Mishkinskoe, Gremikhinskoe, Kezskoe,
Yuzhno-Kiengopskoe and others). The main characteristics of these fields are: pay zones consist of stacks of thin layers
(fraction – units meters), low and mid permeability formation (dozen-hundreds mD), high viscosity oil (30-150 mPa*s), as a
rule, the bottom water drive. So, the horizontal wells (with average length 100-400 m) were selected to mainly increase PI
and improve the sweep efficiency by intersecting poorly-drained zone and layers. In some cases high viscosity oil was
produced under hot water flooding. Average rate of horizontal wells was in range of several tons/day to 20 tons/day or 3-7
times higher than in the nearest vertical wells.
Horizontal wells have been drilled also in the carbonate formations of the Tatarstan Republic: Novo-Elkhovskoe,
Romashkinskoye, Bukharskoe and other fields. In this respect the multilateral horizontal drilling experience in some blocks
of Romashkinskoye field will be of interest. In 2006 two two-lateral horizontal wells with total length 300 m were drilled in
Tournaisian formation in one of the blocks of the fields. The average rate of these wells was about 10 tons/day or 4.5 times
higher than in the nearest vertical wells. The other example of the multilateral horizontal well is block №3 of this field31.
As of the beginning of 2006, in this rather small-scale deposit, 6 horizontal branched wells – two-lateral wells with holes
separated in planes were producing together with vertical wells. The usage of these wells allowed having greater sweep
efficiency from the treatment, ensure equal pressure distribution and OWC elevation. As a result, the growth of the sweep
efficiency is expected to be 12 % and the oil recovery factor increase from 36 to 48 %.
Several examples from the tens of implemented horizontal drilling projects clearly demonstrate the capacities of the sweep
efficiency enhancement by applying this technique. Besides, as it will be demonstrated below, sidetracking with horizontal
completion is used quite efficiently for different purposes, including the sweep efficiency improvement. At the same time
horizontal wells can not be considered as a cure-all solution applied in all cases and fields. There are some examples of rather
low horizontal drilling efficiency due to different reasons: not considering the geological structure of the formation and its
heterogeneity, considerable well interference with drainage of specific volumes in the offset wells, etc. Therefore, the
possibility of horizontal drilling application in each specific case shall be validated by technical-economic calculations of the
field development parameters or parameters of its separate blocks and deposits.
Down-spacing technique (infill wells drilling)
Down-spacing in the process of the field development was widely used in the fields in almost all oil-producing regions of
Russia. In most cases the infill drilling was effective, though there were some failures to improve the sweep efficiency by the
infill wells. Certainly, the efficiency of a given stimulation technique depends on many factors, including geological structure
of the field, properties (first of all heterogeneity and discontinuity) formations, implemented system of the development, type
and density of the well spacing, reservoir depletion as of the beginning of the infill drilling.
Classical «pure» field experiment to evaluate the well density effect on the sweep efficiency by infill drilling was conducted
at the Arlanskoye field (the Republic of Bashkortostan)47. Two pilot areas with similar reservoir properties within the pilot
block were selected in Novokhazinskaya area of this field in mid 60-s годов. Through the section of productive strata of the
block 4 sandstone strata of low Carbon with different reservoir properties and heterogeneity type were distinguished. This
allowed to determine the well density effect on the reservoir production in the single production zone. In the northern and
southern pilot areas well spacing patterns similar by type but different in density were used: 17.7 and 10.4 hectare/well. The
oil recovery factor by the end of the flooding in the blocks was 59.7 and 54.1 %, i.е. the difference with oil recovery factor,
and consequently the sweep efficiency was 5.6 points. In the Cherlaksky block of the same field the experiments on the
down-spacing had been performed at the stage of high watercut in wells (88 % as of the beginning of the experiment). The
down-spacing was performed in two stages with 12 wells drilled at stage 1 (one third of wells earlier producing in the field),
4 wells at the second stage. Thus, the well density had changed from 16 to 7.5 hectare/well. By converting 5 producers to
SPE 117410 5

injection the line-drive flooding was changed to the spot waterflooding. By increasing the well density and changing the
direction of filtration flows the oil recovery factor increased from 32 to 55 %.
The accumulations of B2+B3 formations of the low Carbon in the Krasnoyarsky field (Samara region)38 is an example of
positive down-spacing effect when developing the accumulations under conditions of natural water-drive. Oil accumulations
of these formations were initially recovered by 63 wells, drilled in the central part of the accumulation in 5-line rows with
well density 20 hectare/well (the well density for the whole reservoir is 37 hectare/well). The oil was displaced by formation
edge waters. The infill drilling was started in early 70-s with water cut 72 % and suspended in 1991. In total 31 wells were
drilled, of which 26 designed as infill wells in the central zone of the penetration, and 5 – in separate edge zones, not
completely involved by displacement. The well density in the whole accumulation had increased up to 25 hectare /well, and
in the initially drilled zone up to 14 from 20 hectare /well. Due to this the sweep efficiency increased by 10.2 %, and oil
recovery factor increased from 0.546 to 0.648.
Infill drilling was widely applied during the field exploitations in Western Siberia. The distinctive characteristic of these
fields was the large size of oil productive areas, presence of a big number of zones with different reservoir properties,
significant heterogeneity and discontinuity of productive formation reservoirs, etc. The development of these fields required
drilling of a big number of wells. Well productivity and recovery of oil reserves from different zones could vary to a large
extent due to the differences in geological-physical characteristics. As a rule, together with the development of separate thick
formations, one production zone included several formations with similar or relatively similar characteristics. Different line-
drive (basically three lines) and dispersed (five, seven – and nine spots) flooding (injection) systems with well density from
16 to 49 hectare/well (basically 25 hectare/well) were applied. In many cases the infill drilling was used to ensure the
increased recovery of the oil reserves and to improve the existing system of the development.
Some most representative results of the infill drilling are described in this paper. During the period of 1983 to 1995 there
were 230 infill wells drilled in Neocomian formation BV8 of the Aganskoye field due to this the incremental oil production
was 15,171 MMtons15. Since 1986 and for the next 10 years the infill drilling had been performed in two sites of the Severo-
Varyeganskoye field: Jurassic formation JV1 and Neocomian formation BV1. In the first one about 240 wells were drilled,
and in the second one– 30. Due to drilling this type of wells the incremental production was 9 and 0,9 MMtons of oil
respectively and the recoverable reserves per one well in separate zones of the JV 1 formation were from 24,5 to 51,5 Mtons,
as for formation BV1 about 28 Mtons. It should be noted that the efficiency of the infill drilling in both cases was quite high,
notwithstanding that the initial watercut of the infill wells in formation BV1 was 64-79 %, while in JV 1 formation wells it
was within the limits 12-30 %. Infill wells were used to recovery the reserves from discontinuous part and edge zones of the
BV8 formation in Povkhovskoye field. Due to this in some parts of the central zone of the formation the well density was
increased from 16 to 9 ha/well. By 1995 288 infill wells were drilled, which produced 5.3 MMtons of oil. However, by that
time the marginal barrel of production in new infill wells became less due to bad quality drilling. The considerable volume of
infill drilling was performed in Fedorovskoye gas-oil field. Due to infill drilling together with cyclic formation treatments in
4 blocks of Fedorovskoye field the incremental oil production was 6.7 MMtons, and in 9 blocks of Mokhovskoye field – 14.6
MMtons (it is characteristic that in 3 other blocks there was no effect observed).
The infill drilling in the Neocomian formation BV10 of the Mamontovskoye field (one of the largest in Western Siberia)
showed interesting results. In the beginning the formation was penetrated with line three-row flooding with well spacing
750х750 m and with increased distance in the first line of rows up to 900 m, i.е. between the rows of injection and first rows
of production wells. Due to initially wide well spacing and insufficient treatment of production wells the infill drilling of the
initial well spacing was performed with the transformation of it in “block-closed” water flooding system*) by organizing
lateral and cross-sectional water flooding. The well density of the block-closed system was 1.8 times higher than the initial
well density. The total well stock for down-spacing and block-closed system organization in the zone included 1235 wells.
Since, during the well spacing transformation the combined effect was obtained from moving to the block-close system and
down-spacing it makes sense to mention the results of additional well drilling in the first line of rows. 201 producers had
been drilled in the first line and that is 25 % of the overall infill well stock. The average cumulative oil production from the
infill wells was 45 thous.t, with more than 40 % of these wells each produced more than 30 Mtons of oil, including one third
of wells (12 %) with cumulative oil production 100-300 Mtons. It is quite natural that in the blocks of the zone which are in
continuous production the cumulative oil production was 4 -6 times less than in the infill wells drilled at the same time as the
main well spacing was organized. The distinctive feature was that in separate wells of the first line which were brought into
the development 20-25 years ago the average flow rates were 18 tons/day, with water cut 59 %.
At the same time in separate oil fields of Western Siberia less significant infill drilling effect was produced. The low
efficiency of the infill drilling was observed in the Zapadno-Surgutskoye field. From 1984 to 1994 around 490 infill wells
were drilled in Neocomian formations of the BS formations. For the first two years after the drilling had started the annual oil
production per one infill well was 7.4 Mtons, however, within next 4-5 years this figure dropped dramatically up to 1.7
Mtons and in 1994 it was only 1.2 Mtons.
*)
block-closed water is a reformed three row system with transformation of some producers into injectors to create closed blocks with three
producers row surrounded by several injectors
6 SPE 117410

Still, it should be noted that an example of Zapadno-Surgutskoye and some other fields of Western Siberia are rather an
exception than a rule. At the same time, amazingly good infill drilling effects suggest that probably, the initial well spacing
used in these fields was too wide or there were possibilities to bring less number of formations in a single production zone
development. Nevertheless, to our opinion, the down-spacing at good consideration of all geological and technological
factors is one of the most efficient ways to improve the sweep efficiency of the formation. For sure, the selection of the infill
well count and location is an issue of technical-and-economic evaluation of their efficiency.
In recent years due to the technology development and cost reduction of the side-track drilling there is a possibility to have a
wide application of this technique to solve different field development issues, including the infill drilling by sidetracks
instead of drilling the infill wells.
Sweep efficiency enhancement by sidetracking
By no means unimportant factor for the down-spacing, together with purely economic benefits of the side tracks (ST) is the
possibility of targeting separate ST in zones of residual oil reserves, their «spot» application in zones of high concentration of
residual reserves.
The sidetracking activities had increased significantly in Russia for the last ten years (Fig.3) and the number of sidetracks
drilled in 2007 was 940-960 units. With that, a little more than 60 % of this number was drilled in the fields of «ОАО
Surgutneftegaz» company in Surgutsky region (Western Siberia). The national incremental production due to sidetracking
completed in 2007 was about 4 mln.t.

1000 4.5

900 4.0

800 sidetracks number

3.5
oil production

oil production, MMtons

700
3.0
sidetracks number

600
2.5
500
2.0
400
1.5
300
1.0
200
] 0.5
100

0 0.0
1995
1995 1998 2001 2004 2007
year

Fig.3 Sidetracks drilling dynamics over time

It should be noted that the number of sidetracks with horizontal completion and also so called low-angle holes sidetracks
(extended borehole penetrating the formation at a high angle) had increased significantly especially over the last years.
Double and triple-hole drilling of horizontal sidetracks had started in 2001 and in 2003 it was the first time when four
horizontal sidetracks were drilled in one well34. At the present time the number of horizontal sidetracks put on-stream is
exceeding the number of deviated wells. And that is quite explainable, since the sidetracks are widely used in both oil and
gas-oil fields and designed for additional development of residual reserves under various geological conditions. The analysis
of data given in some papers26,32,34,40,45 shows that the extraction of residual oil reserves by the sidetracks from the oil field
formations is achieved by two factors. The first one is an oil extraction from the layers in the watered zones of the reservoirs
by sidetracks directly drilled in these zones. The second mechanism of the sweep efficiency enhancement is the redistribution
of flows in the formation and bringing-in the residual oil from the reservoir pockets to the reservoir flow with its further
production in the offset wells. Together with specified mechanisms of residual oil stimulation some part of undeveloped
reserves is extracted by the sidetracks from the contract area in the gas-oil fields: oil-water and gas-oil contacts.
The sidetracking efficiency for residual oil production and sweep efficiency enhancement can be analyzed based on
sidetracking and production data from the fields of “OAO Surgutneftegaz” presented in papers26,32,34. From 1994 till 2004
the sidetracks were drilled in 1106 wells in 89 oil accumulations in 25 fields of this company. The fields had different
geological structure and physical reservoir properties and fluid saturation. From the total number of wells deviated holes had
been drilled in 251 wells and horizontal sidetracks in 810 wells with horizontal length from 22 to 580 m, in 38 and 5 wells –
SPE 117410 7

two and three horizontal holes, respectively, and in 2 wells – four horizontal sidetracks. The sidetracks had been drilled in
highly watered and low rate wells. The average production rate of the sidetracks had increased from 7.3 to 33.8 tons/day over
the last ten years. With that, in 2004-2005, the flow rate in horizontal sidetracks was 42.2 tons/day, while in deviated
sidetracks it was 10.7 tons/day. For the last 10 years of sidetrack application the incremental oil production from the
reviewed fields was 13.8 MMtons of oil, with 75 % of incremental production from horizontal sidetracks and 8 % from wells
with several horizontal sidetracks.
The main application of the sidetracks was aimed at additional development of residual oil in highly watered mature oil
reservoirs, change of the reservoir drive by the sidetracking in highly watered deposits, development of low-productive beds
by significant enhancement of the well productivity and additional development of residual oil from near-contact zones of
gas-oil reservoirs and reservoirs with bottom waters.
The analysis delivered by the authors in paper34 based on 637 sidetracks which were drilled to extract residual reserves from
the watered zones of long-producing deposits showed that specific incremental oil production in one well with sidetrack was
11 Mtons, and the predicted production as of the end of operations was about 31 Mtons. It is characteristic that specific
production in one horizontal sidetrack was already 1.5 times higher than in deviated sidetrack (predicted ratio is 3.7).
Evaluation of the sidetrack effect on the production in 1470 offset wells allowed making the conclusions that at relatively low
flow rates of the sidetracks (up to 35-40 tons/day) no flow rate decrease had been observed in the offset wells, assuming
insignificant drop of the water cut. At higher rates of the sidetracks some deterioration of the offset well performance was
observed during the startup of the sidetrack operations with their following recovery to the initial level. Offset well
observations allowed making the conclusion on the possibility of the incremental oil production from these wells due to
redistribution of the flows after the sidetrack commissioning. Thus, incremental total production in several appraisal wells in
some fields was about 12 Mtons in average. Therefore, residual oil from watered zones was extracted directly by the
sidetracks, and, partially, by offset wells due to the change of filtration flows in the reservoir.
Application of the sidetracks together with physical-chemical formation treatments is able to increase the efficiency of this
type of treatment. It was specified in the operation analysis performed in 58 blocks of different fields with 1147 wells,
including 179 sidetracks, which was described in papers26,34. The sidetrack commissioning allowed increasing the efficiency
of so called physical-chemical treatment 1.2-1.8 times.
Sidetracking results in the beds of Jurassic (JS1 and JS2) and Achimov (BS16-20) sediments in Western Siberia can illustrate
the sweep efficiency enhancement in low-permeable reservoirs. The operation results from 149 blocks in BS16-20, JS1 and JS2
formations with 284 sidetracks drilled are presented in paper*8. The average initial flow rate in these wells was about 40
tons/day. With that, no significant sidetrack effect was observed in the offset wells. The flow rates of the sidetracks had
reduced with time, with the flow rate reduction in BS16-20 formations due to the growing waterflood level, while in JS
formations it was due to pressure drop in the drainage zones. Nevertheless, cumulative production in 284 holes as of the date
of analysis was 4.5 MMtons, with expected figure in the future – 10.2 MMtons.
The most vivid example of the efficiency enhancement of the oil production from the oil rims is the Lyantorskoye oil-gas
field. The massive reservoir of this field is presented by small thickness (5.9 m) of the oil rim between the gas cap (average
thickness 6.8 m) and water-saturated zone (thickness 21 m). Productive formations of the fields are characterized by the high
level of heterogeneity and discontinuity. Initially the field was developed with nine-spot water-flooding pattern, with well
density 16 hectare/well. Gas and water breakthroughs were observed in production wells in the process of the field
development and, as the result the ambiguous nature of the current reservoir volume saturation was observed. Both deviated
and horizontal sidetracks were applied for additional residual oil production. Generally the sidetrack application was
successful, though its efficiency to a large extent was determined by geological-physical parameters and formation structure
in the zone of sidetrack targeting and also by the level of the reserves depletion in these zones. It is worthy of note that it was
possible to extract some part of residual oil reserves from gas-oil (under the gas cup) and gas-water-oil (the rim between gas
and bottom waters) zones due to the sidetrack application. The field development experience pointed at the benefit of the
low-angle (not horizontal) profile targeting of the sidetracks.
Thus, the experience of the sidetrack drilling and operations accumulated to date in many Russian fields shows that the
sidetrack application (especially with horizontal section) is one of the most efficient ways to improve the sweep efficiency
(and oil recovery factor respectively) under various conditions of the field development.

Massive treatments of the near-wellbore zone

From currently existing formation bottom-hole stimulation techniques, probably only the hydraulic treatment can increase the
well productivity and ensure the treatment of the distant reservoir zones.
8 SPE 117410

Hydraulic fracturing as a means to improve the sweep efficiency

There are polar opinions regarding the possibility to apply hydraulic fracturing not only as a flow stimulation technique but
as a means to enhance the sweep efficiency. To our opinion it is necessary to distinguish two aspects in this issue: purely
technological and technical-economic one. From technological aspect, certainly, hydraulic fracturing is first of all considered
to be a flow stimulation and well productivity enhancement technique. At the same time, in very heterogeneous and
discontinuous formations with corresponding size of the fracture «wings» the hydraulic fracturing might provide the
additional sweep efficiency due to connecting undrained layers and lenses (schematic sketch in Fig.4). However, in some
cases the same so called massive or bulky fracturing (with a large proppant volume and with a big length of the fracture
«wings» respectively) can cause the enhancement of the sweep efficiency as well. Thus, in case of line-well placement the
hydraulic fracturing with fracture direction across the well lines might decrease the lateral sweep efficiency due to the change
of the water flow direction in the area between the lines of injectors and producers with predominant water flowing to the
fracture tips. For areal flooding systems with corresponding length the hydraulic fracture distorts the flow line in the pattern
spot.

Producer Injector Producer Producer Injector Producer

Fracture

Without hydraulic fracturing With hydraulic fracturing

Fig.4 Simplified scheme of connection of undrained layers by hydraulic fracture

From technical and economic point of view hydraulic fracturing in low permeable formations, obviously, ensures the sweep
efficiency enhancement by flooding, since it allows at acceptable profitability to place wells in the zones of lower net
reservoir thicknesses, and to increase the productive life of the well (or to ensure higher cumulative oil production in these
wells).
Hydraulic fracturing has been considered as a technique used to improve the sweep efficiency in many Western Siberian
fields*2. Among them the most interesting fracturing results were observed in Aganskoye, Vatinskoye, Povkhovskoye and
some other fields. Intensive fracturing operations in production zone BV18-21 of Aganskoye field started in 1994. Formations
constituting this zone had considerable discontinuity and heterogeneity. The majority of hydraulic fracturing performed made
it possible to improve the well rates, in average, 8-9 times: from 5 to 42 tons/day15. It is characteristic that the flow rate
increase due to hydraulic fracturing did not effect the operation of the offset wells and energy state of the reservoir. Besides,
the watercut increased only by some percent units. All these allowed making the conclusions on the absence of well
interference and incremental oil production not due to formation drainage in the offset area but due to bringing into the
development separate interlayers and lenses. Hydraulic fracturing in Vatinskoye field allowed bringing into the development
earlier undrained oil reserves of the zone AV13+AV2 (Neocomian formations) and zone BV22-JV1 (Achimov and Jurassic
formations). The distinctive feature is that due to discontinuity of the formation and thin-layer reservoir the pockets close to
the water injection line were detected in these zones. After hydraulic fracturing the average increase of the flow rate was 1.7-
2 times, no «dagger» flooding was observed and, moreover, in wells with high watercut the hydraulic fracturing did not cause
the sharp increase of the watercut. The experience of bringing into the development the passive oil reserves of the edge zones
in formation BV8 of the Povkhovskoye field performed in early 90-s seems to be of interest. According to the data provided
in the paper15 due to 147 fracturings performed out of 26.3 MMtons of passive oil reserves of these zones it was possible to
bring into the development about 3 MMtons, with 1.6 MMtons of incremental oil produced and to reduce the delay in
recovery rate of the edge zones in the central part of the formation by 2.5-3 times. Optimistic predictions indicated the oil
recovery enhancement in this zone by 20-24 %. The analysis of the fracturing technological efficiency performed in this field
directly showed the efficiency of oil reserves recovery from the well treated zones and the dynamics of their watercut as from
SPE 117410 9

the fracturing design (first of all, the proppant volume and parameters) and geological structure of the formation (its
impermeability or discontinuity, sand content and thickness).
At the present time a number of fields in Yugansky region (Western Siberia) with low permeable formations can not be
developed without hydraulic fracturing application due to the low flow rates. Such fields as: Priobskoye, Prirazlomnoye,
Malobalykskoye, Obminskoye and some other fields3,20. Thereby, «RN-Yuganskneftegaz» LLC ( «Rosneft» OSJC
subsidiary) considers hydraulic fracturing not only as a means of the oil flow stimulation in separate wells but also as a
process to regulate the development of the whole field with the low-productive reservoirs and to increase the oil recovery
factor3. Thus, from 1992 to 2004 in one of the largest fields of the country – Priobskoye (on northern license territory) more
than 1300 frac jobs were performed (including 500 well jobs performed in new wells drilled), as a result, up to 50 % of the
total oil production was ensured20. According to the data from the same paper the slow moving oil reserves from the pockets
were brought into the development due to hydraulic fracturing application, and frac job performance had insignificant effect
on the water cut movement with permanent production and watercut control. It is characteristic that in the southern license
territory of the Priobskoye field (ОАО «Gazprom neft») the development system was formed with respect to the frac jobs
performed and injection well located along the direction of the rock stress development.
Active reservoir treatments to improve the oil recovery by integrated application of hydraulic fracturing and enhanced oil
recovery techniques can now be considered as one of the perspective directions of the field development in ОАО
«Surgutneftegaz»27. Integrated application of hydraulic fracturing and enhanced oil recovery techniques (as a rule, physical-
chemical) is based on formation treatment through injection and production wells following the most efficient simulated
option. With that, the enhanced oil recovery techniques can be performed in hydraulically treated wells or in nearest wells.
Hydraulic fracturing is used for improving the well productivity and the sweep efficiency. It is interesting that in the result of
hydraulic fracturing performed in injection wells it was possible to achieve incremental oil production 30 % higher than after
hydraulic fracturing performed in the production wells28. This can be explained by more intensive treatment of the pockets
with slow-moving oil reserves located away from wells, connecting a bigger number of low-permeable interlayers and also
creating higher filtration rates and by that decreasing the residual oil saturation in already flushed zones of the formations.
Thus, the hydraulic fracturing experience accumulated to date in many different regions of Russia indicates the possibility of
its application as the sweep efficiency enhancement technique.

“Hydrodynamic methods”
The influence of the changes of well operation conditions on the fluids flow pattern in formation is considered in Russia as
“Hydrodynamic EOR methods”. The following technologies can be included in “hydrodynamic EOR methods” category:
- flow path (streams directions) change;
- cycling formation pressure change;
- forced (accelerated) liquid production.
Each of these types of the influence is aimed at recovery one or another type of residual oil from a reservoir. For instance,
the flow path change method allows collecting the oil from the stagnant zones of the reservoir. The cycling formation
pressure change provides the drainage of the low permeable zone of the formation (porous matrix in case of fractured porous
reservoir) during pressure variations. Both of these methods can be carried out by temporally injectors or/and producers
shutdown or water injected volume alteration. Forced liquid production method is based on “stripping effect”, i.e “residual oil
saturation -capillary number” dependence.
As it was mentioned before, the so called hydrodynamic EOR in a wider sense should be referred to a reservoir management
rather than to EOR. In the context of the reservoir management they can certainly be reviewed as the means to improve the
sweep efficiency by flooding.
“Сycling water flooding with the flow path changing” developed in 1964 and has been used in many Russian fields in
Western Siberia, Volgo Urals and Timan Pechora areas. In 1970-1980 this method was applied in some fields of Volgo-Ural
province: Pokrovskoe (1.3 % of recovery increase), Bavlinskoe (5 % of recovery), Alakaevskoe (4 % of recovery),
Lyalikovskoe (400 Mtons of incremental oil production with decreased water cut) and many others. One of the biggest fields
in the world - Romashkinskoe field (The Republic of Tatarstan) gives the most vivid example of this technology
implementation. Cycling water flooding started in several blocks of the field in 1972 with various modifications: 1-
shutdown of the rows of injection wells (or groups of injectors) for a period from 1 month to 1 year, 2- temporally separate
injectors shutoff or the injected water volume decrease21. Methods of the flow path change in addition to cycling water
flooding have been used since 1986 and were based on the switching on of the new injection well rows. The complementary
impaction of the so called “pulsed injection” began in some blocks of the field in 1989. It consisted of production wells
shutdown during the cycles of water injection and injection stopping in production cycles. As a result of these impacts the
oil recovery increased in ten blocks of the field in range from 1.8 to 10.0 %. Today all injectors in Devonian reservoir of
the field are operated in a cycling regime. Cycling pressure change and cycling water flooding are being actively used in the
10 SPE 117410

oil fields of Volgo Urals hydrocarbons basin and, first of all, in the Republic of Tatarstan and the Repuiblic of
Bashkortostan. In these regions the “hydrodynamic EOR” provides 40-50 % of the current oil production from some mature
fields2,10,33.
Up to 7 % of the producers and 36 % of the injectors were involved in cycling watering at the other giant oil field - Samotlor
(Western Siberia) 15. Widely non-stationary flooding was applied in early 90-s in the large-size Fedorovskoye gas-oil field.
The filtration flow change in formations was used by continuous shut-down of injection wells and cyclic water injections in
the injection wells. In total the operation had been performed in 12 blocks of Mokhovskaya and 3 blocks of Eastern-
Mokhovskaya areas. As it was written before, together non-stationary treatments new infill production and injection wells
were brought into the operation in Mokhovskaya area, therefore the effect of 14,6 mln.t. of incremental oil production was
mainly due to the treatment preformed (it is typical that in 3 blocks no effect was observed). Due to production stimulation
and non-stationary drainage in blocks of Eastern-Mokhovskaya area the incremental oil production was 0,7 mln.t. With that
the most efficient was the switching-off some of the injection wells in the blocks (for 1-1,5 years) keeping the water volume
injected into the block with continuous shut-down period of the high-watercut production wells (up to 4-11 months). Cyclic
water injection was less efficient, and no effect was observed when insignificant pressure change occurred in production and
injection zones. Non-stationary flooding, including cyclic flooding and directional change of filtration flows was actively
applied for additional development of heterogeneous formations of the other Western Siberian fields. About 8-10 %
additional oil produced due to these methods was declared for some Western Siberian oil fields 33, 46.
The forced liquid production method has been used in several mature fields in Samarskaya region since the end of 90-s6. The
main effect of the forced liquid production in these fields appears as the water cut decreases in highly watered wells. It is
characteristic, that a temporary shut-down of the forced production in these fields resulted in the watercut increase.
Incremental oil recovery from these fields can reach several units according to predicted calculation. Of course, together with
residual oil saturation decrease at high rates, some effect can be also referred to bringing in the production the undrained oil
reserves, and therefore some sweep efficiency improvement.
Thus, the experience of non-stationary flooding application in different Russian fields indicates the possibility of the sweep
efficiency enhancement by changing the flow direction and cyclic reservoir flooding. At the same time, non-stationary
flooding can be considered as some additional reservoir stimulation techniques together with other techniques of the sweep
efficiency enhancement and oil recovery factor increase.

“Flow Diverting Technologies” (FDT)

“Flow Diverting Technologies” – FDT (sometimes, they are considered as a variety of physiochemical treatments) are based
on the injection of insignificant volume of special agents into injectors for reduction of high layers flow properties
(sometimes down to blockage of these layers) and thereby for “redistribution” of injectivity profiles between layers and
“smoothing” water displacement front in formation. FDT are mainly used under high water cut conditions, although in some
cases they are applied not only for mature fields. These technologies have been actively used in Russia since 1980-s and
nowadays almost all chemical flooding projects in the country are connected with them.
There is a variety of FDT types and agents applied for these technologies. All flow diverting technologies can be devided in
several groups by nature of their influence on the reservoirs:
- blockage due to gel formation;
- blockage due to precipitation through chemical reaction;
- blockage due to particles plugging;
- decreasing of formation permeability by bacteria metabolites;
- increase of displacement agent viscosity.
FDT can also be classified according to the type of agents applied. About 100 of existing agents applied in FDT can be
categorized as:
-gels;
-polymers and mixtures on the basis of polymers;
-agents reacting with formation fluids;
-agents forming emulsion;
- fluids containing particles;
- microbiology;
- high viscosity systems.
By now tens thousand wells in Russia has been treated with FDT on the whole. For the large fields the number of well
treatments can be run up to hundreds per year. As an illustration some most interesting examples from hundreds of FDT
projects are presented in Table B-1 (Appendix B). Consolidated estimate of the efficiency of different FDT applied is
SPE 117410 11

complicated by a considerable diversity of the field structure and characteristics where they were applied. Comprehensive
evaluation of FDT results in Russia shows that the effectiveness of these methods varies greatly. The “specific oil
production” value depends a lot on the oil field parameters and changes in wide ranges (Table B-1):
- blockage due to gel formation: 13 - 5400 tons per 1 treated well (on average 2000-2500 tons) or 400-500 tons per 1 ton of
agent;
- blockage due to precipitation through chemical reaction: 800 - 4500 tons per 1 treated well (single instance 32500 tons) or
3-180 tons per 1 ton of agent;
- blockage due to particles plugging: 900 - 1200 tons per 1 ton of agent;
- increase of displacement agent viscosity: 820 - 2200 tons per 1 treated well (single instance 14500 tons) or 191-1550 tons
per 1 ton of agent;
- decreasing of formation permeability by bacteria metabolites: 288-1080 tons per 1 treated well for carbonate and 512-2756
tons per 1 treated well for clastic formation.
From data specified it is seen that, as a rule, the effectiveness of FDT implementation is estimated as the ratio of produced oil
and injected agent or as the incremental oil production per one treated well. First of all, such estimation approach rides the
use of FDT in some separate zones of the fields and not for the field as a whole. Sometimes, the incremental recovery in
these zones is calculated as well. However, such evaluations can be inaccurate even in cases of limited and separated zones
because of various reasons and insignificant reservoir volume involved in the process. Besides, in most cases FDT
effectiveness is determined by the so called “characteristics methods” which are based on the function “cumulative oil
production vs. cumulative liquid production”. The incremental oil production is calculated as the difference between the
actual cumulative oil production and predicted “characteristics” for the same value of the cumulative liquid production. The
actual characteristic desribes the whole period of the reservoir development including the period of FDT implementation
while the same period of time in predicted “characteristics” is determined as extrapolated trend of the actual “characteristics”
curve before the FDT starts. Of course, sometimes the accuracy of this calculation method is relatively poor.
To our opinion, together with numerous examples of high FDT efficiency there are quite a number of results with overrated
calculated effect. As it was mentioned above, treatments of different technological character can occur in the process of the
field development which can change the well performance parameters, much more significant than those resulted from
formation bottom-hole treatments performed by FDT. Besides, in many cases FDT could not produce any effect due to
conditions of their application: structure and geological-physical characteristics of the formation, well count status,
implemented system of the development.

Limitations for FDT application

Geological restrictions of the specified techniques clearly demonstrate the following figures, representing the modeling
results of the oil displacement from the stratified reservoir with different parameters of the interlayers.
The calculations were performed using commercial simulator in two-phase structure for the element of the 5-spot flooding
system. In the first case a two-layered reservoir with different permeabilities of the layers and share of their thickness in the
net pay of the formation has been reviewed. In the second case 3-layer reservoir with similar thicknesses and different
permeability of the layers was reviewed. Meanwhile, the possibilities of the sweep efficiency enhancement by FDT
application were studied at more favorable conditions. Within a layer the reservoir was taken as homogenous, thus the lateral
sweep efficiency had improved. In the main set of calculations the layers were separated with each others by impermeable
streaks, i.e were disconnected. Relative phase permeabilities used in the simulation are in Appendix C. Oil water viscosity
ration was 3. Both cases with isolation of high permeable layer and with permeability decrease in zone with radius 50 m
around well were simulated. Permeabilities of the separate layers were decreased proportionally and with considerable cut
down of the permeability in the high permeable layer.
Results of the calculations (Fig5-7) demonstrate that FDT can be effective only in the presence of high permeable thin layers
in formation: with permeability a sequence higher than permeability of other streaks and thickness equal to 10-20 % of
formation thickness). The blocking of high permeable layers allows to decrease the water cut and the volume of injected and
produced water. It is reasonable that early isolation of high conductive layers cause better effect as related to the water cut but
somehow reduces the final sweep efficiency because of the trapping some part of residual oil in these layers. The
effectiveness of FDT diminishes with increase of the portion of high permeable thickness in formation and decrease of the
layers permeability ratio. The decrease of high permeable layer permeability instead of its blocking slightly improves FDT
effectiveness but can’t change situation dramatically. Small additional decrease of the cumulative volume of injected and
produced water can be provided if permeability of the high permeable layer is reduced more seriously than permeability of
low permeable layers (Fig.6).
12 SPE 117410

1 1

0.9 0.9
0.8 0.8
0.7 0.7
sweep efficiency

sweep efficiency
0.6 0.6
0.5 without treatment 0.5 without treatment

0.4 treatment by Wc=50 % treatment by Wc=50 %

0.4
0.3 treatment by Wc=75 % treatment by Wc=75 %
0.3
0.2 0.2
0.1 0.1
0 0
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
a) total injected water, PV b) total injected water, PV

1 1

0.9 0.9
0.8 0.8

0.7 0.7
sweep efficiency

sweep efficiency
0.6 0.6

0.5 without treatment 0.5 without treatment

0.4 treatment by Wc=50 % treatment by Wc=50 %

0.4
treatment by Wc=75 % treatment by Wc=75 %
0.3 0.3
0.2 0.2
0.1 0.1
0 0
0 1 2 3 4 5 6 0 1 2 3 4
c)
total injected water, PV d) total injected water, PV

1
1
0.9
0.9
0.8
0.8
0.7
sweep efficiency

0.7
sweep efficiency

0.6 0.6
0.5
0.5
0.4 without treatment
0.4 without treatment
treatment by Wc=50 %
0.3 treatment by Wc=50 %
0.3
treatment by Wc=75 %
0.2 treatment by Wc=75 %
0.2
0.1 0.1
0 0
0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3
e) f)
total injected water, PV total injected water, PV

Рис.5 Sweep efficiency vs. accumulated volume of injected water for various parameters of layers of formation – permeability ratio
of high and low permeable layers (К) and volume portion of high permeable layer (α): a) К=10, α= 0.1; b) К=10, α= 0.2; с) К=5, α=
0.1; d) К=5, α= 0.3; e) К=2.5, α= 0.2; f) К=2.5, α= 0.4;

The efficiency from FDT application is more reduced when several layers present in the formation are distributed according
to some law of partition (normal or logarithmic-normal, etc.) without any significant difference in permeabilities of the
layers. Finally, the presence of hydrodynamic connection between layers with different permeability even in separate point of
formation can bring the FDT effectiveness to naught because of water crossflow into low permeable layers from high
permeable streak. The results of simulation of 3-layered formation with high permeable layer and “interconnection windows”
show this effect (Fig.7). The details of the simulation are presented in Appendix C. Even massive treatments with
significant radius of the treated zone can’t improve the sweep efficiency of the formation with full interconnected layers
(Appendix C).
SPE 117410 13

0.9

0.8

0.7

sweep efficiency
0.6

0.5

0.4 without treatment

0.3 Kh/Kl=1.0
Kh/Kl=0.5
0.2

0.1

0
0 0.5 1 1.5 2 2.5 3
total injected water, PV

Fig.6 Sweep efficiency vs. cumulative injected water for various ratio of permeability of high and low permeable layers in near
wellbore zone of injector: Kh/Kl=1 – reduction of high permeable layers permeability in 5 times while low permeable layer – in 2
times; Kh/Kl=0.5 – reduction of high permeable layers permeability in 10 times while low permeable layer – in 2 times;

180000
0.9

160000
0.8
cumullative oil production, PV

140000
0.7

0.6
120000

0.5
100000
Base Case with interlink
with interlink wc 0
0.4
80000
with interlink wc 60
0.3
60000 Base Case w/o interlink
50m w/o interlink wc 0
0.2
40000
50m w/o interlink wc 60

0.1
20000

0
00 0.5
100000 1.0
200000 1.5
300000 2.0
400000 3.0
500000 4.0
600000

cumullative liquid production, PV

Fig.6 Total oil production (PV) vs. total liquid production (PV) for the formations with disconnected (isolated) each others and
interconnected (through the high permeable “windows”) layers and treatment of well by various water cut

Conclusions

• The experience of the oil field development improvement by flooding and sweep efficiency enhancement has been
accumulated in Russia to date.
• Flow-diverting technologies based on different agents injection in the injection wells, infill drilling, non-stationary
flooding were used as the main sweep efficiency enhancement techniques. Lately, horizontal wells are used more often for
the field development which are at the same time the elements of the sweep efficiency enhancement. To our opinion,
sidetracking and horizontal drilling have distinctive excellence as compared to the other techniques of the sweep efficiency
enhancement. Down-spacing can also have good results at specific conditions. However, the efficiency of the infill wells
application is decreasing as the sidetracking technology is improving. Therefore, infill drilling can be applied in cases when
residual oil stimulation in watered zones is required at the time when wells of the main stock continue to drain their reserves
and can not be used for the sidetracking.
14 SPE 117410

• As for flow-diverting technologies, then together with the a distinct effect from their application in many cases the
efficiency is not obvious. The treatment is performed in a highly restricted zone of the formation. Not without reason in many
cases the treatment effect is evaluated in form of some specific parameters (as per well-job or the volume of injected
chemical) and is not reviewed for the whole formation. Besides, very often the reservoir development effect is “recorded” as
the result of the flow-diverting techniques performed (including the change of technological regimes of the well operations,
well commissioning and shutting-in of the well, etc.). Indeed, FDT will be widely applied in the future because of their
simplicity, low costs and as effective means of the water cut reduction. Nevertheless, to our opinion, they can’t be considered
as principal methods applied for the whole formation volume treatment and significant improvement of the sweep efficiency.
• Hydraulic fracturing can be recognized as the sweep efficiency enhancement technique. With that, it is necessary to
consider both technological and technical-economic aspects of this sweep efficiency enhancement technique. By
technological aspect one should understand the possibility of bringing into the development the undrained blind zones and
isolated interlayers of the formations. From technical-economic point of view the hydraulic fracturing in low-permeable
formation certainly facilitates the sweep efficiency enhancement by flooding allowing at acceptable profitability to place
wells in low–productive zones of the formations and to increase the profitable life of the well (or provide higher cumulative
oil production in these wells). At the same time, during the treatments it’s necessary to consider the current water flooding
system and formation parameters to exclude an artificial areal heterogeneity due to hydraulic fracturing.
• Based on all points mentioned above we can predict the higher rate of sidetrack application in the future as a means
to improve the sweep efficiency enhancement (including horizontal and multilateral wells), further development of the flow-
diverting technologies with the possible reduction of the number of recipes and agents applied. The volume of horizontal
drilling and hydraulic fracturing will be still growing.

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*)
Oil Industry Journal– in Russian
16 SPE 117410

Appendix A

6
3
2
1
4
5

North
Caucasia
Administrative districts on territory of
Volga Urals basin:
1 - Republic of Bashkortostan, 2- Republic of
Tatarstan; 3 - Republic of Udmurtia; 4- Samara
region; 5 –Orenburg region; 6 – Perm region

Fig.A-1 Russian hydrocarbons basins map

Appendix B

Table B-1 – DFT implementation results

Type of Type of Agent Number of Additional oil Period
*) Field (region or area)
reagent influence composition treatments production of time
871 tons/ Nartovskoe (Republic of 1986-
110
treated well Bashkortostan) 1991
Ammonia precipitation 24% ammonia
14 Novokhazinskii block of
water growth solution 1986-
45 13 tons/tons Arlanskoe field (Republic of
1989
Bashkortostan)
Lokosovskoe, Ur’evskoe,
Potochnoe, Las-Eganskoe,
4180 tons/
218 Pokachevskoe, Uzhno- 1986
treated well
Pokachevskoe (Western
Siberia)
5400 tons/ Samotlorskoe (Western
123 1986
treated well Siberia)

2731 tons/ Fedorovskoe (Western

91 1988
treated well Siberia)

2477 tons/
PDS
12,13,16,17,44 13 Talinskoe (Western Siberia) 1990
treated well
(polymer- polymer+
disperse gel disperse 785 tons/ Povkhovskoe (Western
8 1990
particles particles treated well Siberia)
system)
Romashkinskoe, Novo-
2188 tons/
492 Elkhovskoe, Bavlinskoe 1981
treated well
(Republic of Tatarstan)
Chetyrmanskoe, Arlanskoe,
Sataevskoe, Serafimovskoe,
1457 tons/ Igrovskoe, Uzhno-
21 1986
treated well Maksimovskoe,
Shkapovskoe, Voyadinskoe
(Republic of Bashkortostan)
Abdrakhmanovskii block of
1148 tons/
67 Romashkinskoe field 1987
treated well
(Republic of Tatarstan)
SPE 117410 17

Abdrakhmanovskii block of
33 tons/
4 Romashkinskoe field 80-90-s
treated well
9, 13, 41, 44 wood meal +mud (Republic of Tatarstan)
VDS gel
powder 3965-7830
Samotlorskoe, AV and BV
tons/ treated 90-s
formation (EWestern Siberia)
well
843 tons/
13 Balykskoe (Western Siberia) 90-s
treated well
12,13
Polymer Abdrakhmanovskii block of
viscosity 826 tons/
(polyacrylamid polyacrylamide 3 Romashkinskoe field 80-90-s
increase treated well
e) (Republic of Tatarstan)
2214 tons/ Nartovskoe (Republic of
7 80-90-s
treated well Bashkortostan)
Novokhazinskii block of
Alumino- precipitation addional 5
14 Alumino-chloride - Arlanskoe (Republic of 1995
chloride growth Mtons of oil
Bashkortostan)
Biopolymer 157 tons/ Nartovskoe (Republic of
12 gel polymer 14 90-s
“Simusan” treated well Bashkortostan)

Alkali-silicate precipitation alkali-silicate 2525 tons/ Nartovskoe (Republic of 1986-

12 40
solution growth solution treated well Bashkortostan) 1991

Abdrakhmanovskii block of
1060 tons/
90 Romashkinskoe field 1993
Viscous- treated well
44 gel polymer (Republic of Tatarstan)
elastic liquid
Deryuznekovskoe (Samara
609 721 tons/tons 1988
region)
1500-2500
Uzen (Kazakhstan) 1992
tons/tons
1236 tons/ Bobrovskoe (Orenburg
1993
treated well region)
Polymer
gel polymer - Barsukovskoe,
“Temposcrin” 5000 tons/
Novopurpeyiskoe (Western 1995
treated well
Siberia)
2000 tons/ Ust-Balykskoe (Western
1997
treated well Siberia)
17 tons/tons Arlanskii block of Arlanskoe
8 710 tons/ field (Republic of
Liquid glass
Liquid glass treated well Bashkortostan)
+HCI+ 1993-
gel +HCI+ 23.54
polyacrylamid Berezo-Nikolskii block of 1995
19,44 polyacrylamide tons/tons,
e 3 Arlanskoe field (Republic of
4020 tons/
Bashkortostan)
treated well
41, 49 1730 tons/ Mamontovskoe ( Western
SSS 5
precipitation sulphate- soda treated well Siberia)
(sulphate- 90-s
growth system 2143 tons/ Yuzhno-Balykskoe (Western
soda system) 9
treated well Siberia)
1137 tons/ Yuzhno-Balykskoe, AS
treated well formation (Western Siberia)
Surfactant 1394 Petelenskoe, BS formation 1993-
emulsion surfactant
“Ekstract-700” tons/tons (Western Siberia) 1995
1833 Malo-Balykskoe, AS
tons/tons formation (Western Siberia)
Arlanskii block of Arlanskoe
1 - field (Republic of
Liquid glass
Liquid glass Bashkortostan)
+HCI+ waste of 1993-
+HCI+ gel 12,51
19 chemicals plant Berezo-Nikolskii block of 1995
chemicals tons/tons
“Kaustik” 2 Arlanskoe field (Republic of
1645 tons/
Bashkortostan)
treated well
precipitation NaSiO3+electrol 180 tons/tons, 90-s-
41 Samotlorskoe (Western
OS growth, yte (СaCI2, - 5001 tons/ early
Siberia)
SiO2 NaCI) treated well 2000
precipitation
90-s-
44 growth, NaSO4+electroly 4164 tons/ Samotlorskoe (Western
SS - early
gipsum te treated well Siberia)
2000
CaSO5
Polyatomic precipitation polyatomic 454 tons/ Several fields in Republic of
25 - 1994
alcohol growth alcohol treated well Bashkortostan
44
“ODS” precipitation NaSiO4+electrol
4557 tons/ Samotlorskoe (Western
(disperse growth + yte (СaCI2, - 90-s
treated well Siberia)
system for particles NaCI)+ wood
18 SPE 117410

precipitation plugging meal

growth)
9, 44
“GеОs”
(gel- precipitation NaSiO3+electrol
3559 tons/ Samotlorskoe (Western
precipitation growth, yte (СaCI2, - 90-s-
treated well Siberia)
growth SiO2 NaCI)
mixture)
25 precipitation aluminum 1678 tons/ Several fields in Republic of
Nepheline - 1995
growth silicate natrium treated well Bashkortostan
1551 Orlyanskoe (Republic of
9 80-s
tons/tons Bashkortostan)
Sosnovskoe (Republic of
15 191 tons/tons 80-90-s
Bashkortostan)
39 viscosity Romashkinskoe, bobikovskii
Polymer polymer
increase 3 493 tons/tons formation (Republic of 1981
Tatarstan)
14500 Novo-Khazinskii block of
16 tons/ treated Arlanskoe field (Republic of 80-s
well Bashkortostan
Novo-Khazinskii block of
polymer + viscosity polymer + 950 tons/
12 9 Arlanskoe field (Republic of 80-s
surfactant increase surfactant treated well
Bashkortostan
Novo-Khazinskii block of
2000 tons/
93 Arlanskoe field (Republic of 80-90-s
treated well
Bashkortostan
35,44 Arlanskii and Berezo-Nikolskii
SAS 1600 tons/
precipitation silicate alkali 63 blocks of Arlanskoe field 80-90-s
(silicate alkali treated well
growth solution (Republic of Bashkortostan)
solution)
1700 tons/ Mancharovskoe (Republic of
14 80-90-s
treated well Bashkortostan)
1800 tons/ Igrovskoe ( Republic of
4 80-90-s
treated well Bashkortostan)
1100 tons/ Серафимовское Republic of
17 80-90-s
44 treated well Bashkortostan)
APS (alkaline
Alkaline polymer 1200 tons/ Nartovskoe (Republic of
polymer gel 19 80-90-s
solution treated well Bashkortostan)
solution)
700 tons/ Nartovskoe (Republic of
65 80-90-s
treated well Bashkortostan)
1400 tons/ Arlanskoe (Republic of
7
1,35 viscosity hydrolyzed treated well Bashkortostan)
Lignine 80-90-s
increase lignine+ alkaline 1000 tons/
2 Volostnovskoe
treated well
SST (sulfate
precipitation sulfate waste Mamontovskoe (Western
waste)+КОP-1 30 139 tons/tons 90-s
9, 49 growth “SZhK”+acid Siberia)
Yuzhno-Balykskoe (Western
9 72 tons/tons 90-s
Siberia)
Ust’-Balykskoe (Western
SST (sulfate 3 125 tons/tons 90-s
precipitation sulfate waste Siberia)
waste)+CaCI2
9, 49 growth “SZhK”+acid Ust’-Balykskoe (Western
4 33 tons/tons 90-s
Severo-Salymskoe (Siberia)
Pravdinskoe (Western
6 12 tons/tons 90-s
Siberia)
sulfate waste Pravdinskoe (Western
SST (sulfate 1 3 tons/tons
precipitation “SZhK”+acid + Siberia)
waste)+СaCI2
9, 49 growth ammonia-tar Ust’-Balykskoe (Western
+HB 2 30 tons/tons
liquor Siberia)
SSS (sulfate
soda precipitation sulfate
12 136 tons/tons Aganskoe (Western Siberia)
system)+CaCI growth soda+acid
49
2
aluminate +
4 40-60 Several fields in Pravdinskoe 1990-
“GALKA” gel carbamide + -
tons/tons Western Siberia 1992
additions
aluminium
sulphate +
29 gel+ 4400 tons/ Sutorminskoe (Western
AF-12+gel carbamide + - 90-s
surfactant treated well Siberia)
surfactant (АF-
12)
SPE 117410 19

“ShPSK”
(alkaline
slurry + alkaline 1258 tons/ Var’eganskoe (Western 2000-
polymer gel 43
+ polyacrylamide treated well Siberia) 2003
culture
41,51
system)
Swelling 1152 tons/ Nurlatskoe (Republic of
24 gel polymer 1 90-s
polymer treated well Tatarstan)
Koshilskoe,
924 tons/ 2000-
46 Khokhryakovskoe,
“ShPSK-2” treated well 2001
Permyakovskoe
(alkaline slurry + alkaline
Megionskoe, Vatinskoe,
polymer gel + polyacrylamide 1929 tons/
75 Severo-Pokurskoe, Yuzhno-
culture +methacin treated well 2000-
41,42 Aganskoe ( Western Siberia)
system) 2003
1312 tons/ Var’eganskoe (Western
43
treated well Siberia)
“GFE”
Abdrakhmanovskii block of
(hydrophobic Surfactant + oil 400 tons/
emulsion 11 Romashkinskoe field 1998
emulsion wetting agent treated well
44 (Republic of Tatarstan)
эмульсия)
Liquid glass+ Abdrakhmanovskii block of
19, liquid glass+ 401 tons/
chloric acid gel+ПАВ 1 Romashkinskoe field 1998
44 chloric acid treated well
(Republic of Tatarstan)
Abdrakhmanovskii block of
44 viscosity polyglycol + 5559 tons/
“HTI” 4 Romashkinskoe field 1984
increase isopropyl alcohol treated well
(Republic of Tatarstan)
rubber grit Abdrakhmanovskii block of
Rubber grit particles 7336 tons/
44 +chemicals 4 Romashkinskoe field 1996
+chemicals plugging treated well
“slamel” (Republic of Tatarstan)
Abdrakhmanovskii block of
44 1369 tons/
Biopolymers gel polymer 14 Romashkinskoe field 1996
treated well
(Republic of Tatarstan)
Silicate- Abdrakhmanovskii block of
19, polymer +liquid 373 tons/
polymer gel gel 16 Romashkinskoe field 1995
44 glass treated well
(Republic of Tatarstan)
Alkine waste Alkine waste of
Abdrakhmanovskii block of
of viscosity caprolactam 120 tons/
2 Romashkinskoe field 1995
caprolactam increase production treated well
41 (Republic of Tatarstan)
production (ShPSK)+GOK
Abdrakhmanovskii block of
44 oxyethyl- 4265 tons/
OEC gel 17 Romashkinskoe field 1986
cellulose treated well
(Republic of Tatarstan)
CDS (colloidal Olyoxyethylene Abdrakhmanovskii block of
1688 tons/
disperse gel glycol + mud 2 Romashkinskoe field 1993
treated well
system) powder (Republic of Tatarstan)
Abdrakhmanovskii block of
19, 44 particles 911 tons/
Rubber rubber grit 27 Romashkinskoe field 1991
plugging treated well
(Republic of Tatarstan)
Alkylated Abdrakhmanovskii block of
precipitation 32428 tons/
sulphuric acid sulphuric acid 9 Romashkinskoe field 1974
19, 44 growth treated well
(Republic of Tatarstan)
SPS (cross- Abdrakhmanovskii block of
viscosity 686 tons/
linked polymer 21 Romashkinskoe field 1996
39,44 increase treated well
polymer) (Republic of Tatarstan)

”ShDZh”(alkin precipitation Buzov’yazovskoe,

water cut
e “distillered” growth, “distillered” liquid Urshakskoe (Republic of 90-s
50 decreasing
liquid gipsum Tatarstan)

288-1080
ton/treated
Decreasing IAI (“active silt” Romashkinskoe, Bavlinskoe,
68 well for
of formation produced from Novo-Elokhovskoe 90-s and
“IAI” “active producers carbonate
23 permeability biological (Republic of Bashkortostan) early
silt” 54 injectors 512-2756
by bacteria treatment Tayimurzinskoe, Arlanskoe 2000-s
tons/treated
metabolites facilities) (Republic of Tatarstan)
well for clastic
formation
1375 Pokamasovskoe (Western
8 90-s
tons/tons Siberia)
“BP-
1230 Severo-Pokurskoe, formation
92”biopolymer gel biopolymer 13
48 tons/tons BV-6 (Western Siberia)
Severo-Pokurskoe, formation
13 577 tons/tons 90-s
BV-8 (Western Siberia)
20 SPE 117410

9 682 tons/tons Yuzhno-Aganskoe

11 714 tons/tons Vatinskoe (Western Siberia) 90-s

*)
tons/treated well – 1 ton of additional oil per 1 treated well; tons/tons – 1 ton of additional oil per 1 ton of injected agent

Appendix С
Simulation details and calculation results
Simulation was done jointly with D.Klemin – Schlumberger employer with the use of commercial simulator. The formation
consisting of three layers with each layer 10 m thick was examined. We simulated the displacement of oil by water in sector
model representing a quarter of 5-spot flooding block with distance between producer and injector 500 m. Two-phase flow
with oil water viscosity ratio equal 3.0 was evaluated. Phase permeabilities are shown in Fig.C-1. Two cases were
examined: 1- disconnected layers and 2- layers interconnected through the “high permeable windows” as it is shown in
Fig.C-2. Permeability of high permeable layer was 200 mD, low permeable layers - 50 and 40 mD, “high permeable
windows” - 200 mD. It was assumed that injector treatment should decrease the permeability of the high and low
permeable layers 10 and 1.2 times correspondingly.
Water cut and cumulative oil and water production in cases of oil displacement from formations with disconnected and
interconnected (through ‘windows”) layers are presented in Fig.C-3 and C-5. Water saturation distribution from these cases
is presented in Fig.C-4, C-6 and C-7. As you can see from these figures the reduction of permeability around the injector
can’t significantly decrease the water cut value because of the hydrodynamic connection between layers with different
permeability. Water saturation distribution in low permeable layer is the same as in case of flooding without injector
treatment, but the displacement front delays a little bit. In case of full hydrodynamic contact between layers (Fig.8) the water
cut dynamics can’t be changed by the treatment due to intensive water crossflows from high-permeable to low-permeable
layers.
1
relative phase permeability

0.8

0.6
water
oil
0.4

0.2

0
0 0.2 0.4 0.6 0.8 1
water saturatioin

Fig.C-1 Oil and water relative phase permeability

Fig.C-2 Permeability distribution: layer with high permeability - at the left, layer with low permeability - at the right
SPE 117410 21

0.9 400000

0.8 350000
Total Production, sm3

oil, without treatment

0.7
300000 water, without treatment

Total production, m3
0.6
oil, treatment by Wc=60 %
250000
0.5 water, treatment by Wc=60 %

0.4 200000

0.3 150000
without treatment
0.2
treatment by Wc=60 % 100000
0.1
treatment by Wc=1 %
50000
0
0 1000 2000 3000 4000 5000 0
Time, days 0 1000 2000 3000 4000 5000
Time, days

Fig.C-3 Water cut and cumulative oil and water production vs. time (disconnected layers)

a b

c d

Fig.C-4 Water saturation distribution in disconnected layers: а) layer with high permeability, time t1; b), с) и d) layer with low
permeability, time t1, t2 и t3; by t1<t2<t3
22 SPE 117410

350000

1 water, without treatment

300000
0.9 oil, without treatment
water, treatment by Wc=60 %

total production, м3
0.8 250000
oil, treatment by Wc=60 %
0.7
200000
0.6
water cut

0.5 150000
0.4
without treatment
0.3 100000
treatment by Wc=60 %
0.2
treatment by Wc=1 % 50000
0.1
0 0
0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000
Time, days time, days

Fig.C-5 Water cut and cumulative oil and water production vs. time (interconnected layers)

a b

c d

Fig.C-6 Water saturation distribution in interconnected layers: а) layer with high permeability, time t1; b), с) и d) layer with low
permeability, time t1, t2 и t3; by t1<t2<t3
SPE 117410 23

a b

Fig.C-7 Water saturation distribution in layer with low permeability after injector treatment case with interconnected layers): а)
time t1; b ) time t2 ; by t1<t2

1
0.9
0.8
0.7
water cut

0.6
0.5
without treatment
0.4 treated zone 10 m
0.3 treated zone 50 m
treated zone 200 m
0.2
0.1
0
0 1000 2000 3000 4000 5000
Time, days

Fig.C-8 Water cut vs. Time for various radius of treated zone around injector