Disc Contents © IPA, 2006 - 2nd Annual Convention Proceedings, 1973

Contents
195

Search PROCEEDlNGS INDONESIAN P E T R O L E U M ASSOCIATION

Second Annual Convention June 1973

GEOLOGY OF THE ATTAKA OIL FIELD

EAST KALIMANTAN, INDONESIA
C.M. SCHWARTZ *
G.H. LAUGHBAUM, JR. f
B.S. SAMSU **
J.D. ARMSTRONG *

Abstract The Attaka field is the first commercial efforts which have been directeu roward the
offshore oil' field to be discovered in Kalimantan, shelf and shallow sea areas around Indonesir
Indonesia, After its discovery in 1970 and the dril- have now been rewarded with the discovery of
ling of confirmation wells during 1970 and 1971, a several large offshore oil and gas fields. One of
development programme involving 50 welIs from six
these is the Attaka field in the Kutel basin in
platforms was begun. The field is 12 miles off-shore
from the East KaIimantan coast in 200 ft of water. East Kalimantan (Figure l), and in fact thir
field is the largest offshore field in Indonesia.
Areal and vertical closures of the Attaka structure
are 26 square miles and 600 ft respectively, and the The first wells in the Kutei basin were drilled
areal extent of oil accumulation is some 9.8 square along the coast on surface anticlines late in
miles. The Attaka structure is located in the Tertiary the nineteenth century. Oil and gas were
Kutei basin which contains Early Tertiary to Quater- discovered in sands of Miocene age in several
nary sediments, and the oil in the Attaka field is in of the structures ; commercial quantities being
numerous deltaic sands deposited during a Late
present in t h e Sanga-Sanga, Sambodja and
Miocene advance of the ancestral Mahakam River
delta. Klandasan culminations. The several hundred
development wells subsequently drilled on
Seismic velocity and well velocity survey data indi- these structures have produced a cumulative
cate the presence of a low velocity region more or 300 million barrels of oil. Clearly the Kutai
less coincident with the limits of oil and gas accumu- basin was petroliferous and it seemed to offer
lation on the crest of the Attaka structure. Use of good prospects for further discoveries in the
lower RMS stacking velocities in this crestal area in adjoining offshore shelf area.
comparison with the RMS stacking velocities requi-
red on the flanks produces continuous seismic events
in the crestal area. The diminished interval velocities Offshore reconnaissance seismic surveys con-
on the crest may be due to the presence of oil and duted independently by Japex Indonesia Lirni-
gas. ted and Union Oil Company of Indonesia late
in 1968 and early in 1969 located the Attaka
Gravity of the Attaka oil ranges 'from 35' to 43' structure. Because the structure straddled the
API and its sulphur content is 0.1% by weight. boundary between contract areas held by the
Production rates from individual completions range two companies, an operating unit, the first in
from 400 to 4300 barrels of oil per day and by late South East Asia was formed to permit joint
1973 or early 1974 when all wells are on stream the
production rate will be about lOQ,OO barrels of oil exploration of the structure. Union and Japex
per day.. contributed equal portions of their respective
contract areas to the' 112 square-mile Attaka
Unit and the u n i t agreement specified that all
INTdODUCTION exploration, development and production costs
Oil has been produced from numerous fieids would be borne equally by the companies.
in Indonesia since the latter part of the nine- Union was designated operator for the Unit.
teenth century and until t h e last few years
most o f this production was from onshore The Attaka Oil field is located in 200 feet of
fields. Recently, however, there has been an water 12 miles offshore from the East Kaii-
upsurge in the exploration of offshore areas *) Union Oil Company of Indonesia.
and it is signifidant that the not inconsiderable * *) Pertamina Unit IV, Balikpapan, Indonesia
 LOCATION MAP
SOUTH EAST ASIA
ATTAKA FIELD

0 500 1000

SCALE IN M I L E S
A U S T R A L I A

FIGURE I
 197

mantan coast and the name of the field basins i n Kalimantan which lie along the
derives from a small patch reef 15 miles t o eastern margin of the cratonised Paleozoic and
the east of the Attaka structure. The discove- Mesozoic rocks of the Sunda Shield (Figure
ry well, Attaka No. l A , was spudded in May 2). The basin covers approximately 40,000
1970, reaching a total depth of 11,659 ft in square miles, 5% being offshore and it con-
August 1970. I t tested oil and gas from six tains up t o 25,000 ft of Tertiary sediments.
zones at a combined rate of 11,330 barrels of T o the north, the Kutei basin is bordered,by
low sulphur oil per day and 2 6 million cubic the pre-Tertiary basement rocks of the Ku-
feet of gas per day. Subsequently the confir- ching High dnd its southeasterly plunging spur
mation wells (Attaka Nos. 2 - 7 ) , drilled the Mangkalihat Ridge.
during the period October 1970 to February
197 1, established the existence of oil reserves North of the Mangkalihat Ridge is the Tara-
sufficient for a programme of development kan basin. T o the southwest and south, the
and production, Development of the field sediments of the Kutei basin are continuous
commenced in April 1971 and the drilling of with those of the Barito platfrom, the Barito
50 wells from six platforms will be finished basin and t@e Paternoster platform (Figure 3).
late in 1973 or early 1974. Pre-Tertiary basement rocks of the Meratus
mountains separate the Barito basin from the Pa-
The oil produced from Attaka occurs in nu- ternoster platform. East of the Kutei basin 1s
merous sandstone bodies individually up to the Makassar trough ; a present-day marine
150 f t thick, between the depths of 200 and basin with water depths up to 8000 ft.
7800 f t and production is expected to reach
100,OO barrels of oil per day on completion Positive Bouger gravity values over the thick
of the development programme. Despite the Tertiary deposts in the Kutei basin in compa-
rather formidable logistical and communicati- rison with the negative Bouger values over the
on probelms in this remote area, the field was thinner Tertiary section in the Barito basin
placed on production only 27 months after its suggest that oceanic crust may underlie part
discovery. of t h e Kutei basin. Similarly the strongly
positive isostatic gravity anomaly over t h e
All exploration, development and production Makassar trough indicates that the simatic
within. the Attaka Unit is carried out under rocks, which probably comprise basement for
the provisions of separate .Production Sharing a thin veneer of sediments in the trough, are
Contracts between Pertamina (Perusahaan Per- above their level of isostatic adjustment. Whe-
tambangan Minjak dan Gas Bumi Negara), the ther this is the result of tensional rifting and
Indonesian State-owned oil company, and Uni- the relative spreading of Sulawesi away from
on, and between Pertamina and Japex. Costs Kalimantan, or whether it is due to compressi-
incurred in the exploration and development ve stress is uncertain.
of the Attaka field are shared equally by
Union and Japex and production is also sha- The Kutei basin seems to have been initiated
red equally. Sharring of production with Per- in the Early Tertiary and it received sediments
tamina is governed by the terms of each throughout the Tertiary and Quaternary. Stra-
company’s respective Production Sharing Con- tigraphic data indicate that in general the
tract with Pertamina. basin filled from the west towards the east ;
the axis of maximum sediment thickness de-
I t is the object of this paper to present a posited during each of the Tertiary Stages
summary of our understanding of the geology shifting progressiveIy eastwards with time (Fi-
of the Attaka oil field as a contribution gure 3).
towards a greater understanding of the geolo-
gy of East Kalimantan Tertiary Kutei basin. Thus t h e Attaka structure is located in a
subsiding Tertiary-Quaternary basin in which
KUTEI BASIN the sediments are pro-grading eastwards onto
The Kutei basin is one of several Tertiary the thin veneer of deep-sea sediments of the
 I I I. I I I
120-

MAJOR STRUCTURAL
ELEMENTS
OF KALIMANTAN
I I I If I

00
KALIMANTAN
_,- -- -

FIGURE 2
 REGIONAL N-S & E-W STRATIGRAPHIC CROSS-SECTIONS
EAST KALIMANTAN

KUTEI BASIN
PATE RNOS T E R ATTAKA FIELD TARAKAN
PLAT FORM BASIN

LATE
I
.
I.......

ATTAKA FIELD
17--1
OLIGOCENE .
& EOCENE --~o,ooo'

FIGURE 3
2 00

Makassar trough. During this pro-gradational gas, the shallower sands in general being gas
process, deltas ancestral t o t h e present-day reservoirs without any oil.
Mahakam River delta advanced and were
transgressed a number of times, and the oil- Benthonic foraminifera are present throughout
bearing sandstones of the Attaka field were the Attaka succession b u t are most abundant
deposited during the most recent of the major in Unit 111 and in the uppermost few hundred
regressive cycles in the Late Miocene (Figure feet of Unit 11. Abundance of benthonic fora-
3). minifera diminishes markedly in the middle
pArt of Unit 11, but increases slightly again in
STRATIGRAPHY OF ATTAKA FIELD Unit I. Pelagic foraminifera, are uncommon in
The oil and gas-bearing sandstones occur bet- the Attaka succession. Also uncommon are
ween the depths of 600 ft and 7800 ft in the nannoplankton, the calcareous algae which
Attaka structure and t h e discussion of the recently have become increasingly significant
stratigraphy of the field is restricted t o this for establishing local and regional Tertiary
interval. Below 7800 f t the section consists correlations. Ages of the Attaka deposts are
largely of siltstone with some thin beds of based partly on the sparse pelagic foraminifera
limestone and sandstone and is of Middle and nannoplankton which are present, but
Miocene age to the depth reached by drilling primarily on the comparison of the species of
to date. benthonic foraminifera at Attaka with bentho-
nic foraminifera in adjacent areas where ages
At Attaka there are three main rock units can be determined from nannoplankton and
(Figure 4) : pelagic foraminifera.

Unit I below about 6200 ft consists of silt- Salinity of the formation water in the sand-
stones with a few sandstone beds up to 40 f t stones varies considerably. The sands in Unit
thick. The sand are very-fine to fine-grained, I, in the lowermost and uppermost few hun-
friable, well sorted and are porous and per- dred feet of Unit 11, and in Unit 111 all have
meable. Many of the sands present in this formation water with salinities in the range of
interval are oil and gas-bearing. 17,004 to 38,000 prn NaCl. Between 4600 ft.
and 5800 ft in Unit 11, however, the salinities
Unit 11 between 4000 and 6200 f t contains of the formation waters range from 5000 t o
numerous sandstone bodies, individually up to 12,000 ppm. Most of the Attaka oil resehoirs
150 ft thick, interbedded with siltstones and a contain formation water with salinities greater
few thin limestones and coals. The sands are than20,OOO ppm whereas 4nly minimal accu-
mostly fine-grained, friable, porous and per- mulations of oil and gas exist in t h e sands
meable although some of the sands in the with low-salinity water.
middle part of the unit are less well sorted
and contain grains ranging up to pebble size. Unit I1 sediments were deposited during the
Most of the Attaka oil and gas reservoirs are regression of a Late Miocene delta over the
in the uppermost and lowermost few hundred organically rich pro-delta and shelf deposits of
feet of this interval. Sands are individually Unit I. The sandstones with high-salinity for-
discontinuous (Figures 5, 6) although common mation water i n t h e basal and uppermost
fluid interfaces in some parts o f ' the field portions of Unit II are inferred to have been
indicate that there is some form of connection deposited i n delta front, mixed distributary
between them. Figure 5 is a stratigraphic mouth, and marine strand-line environments.
cross-section of the uppermost several hundred The siltstones and interbedded sandstones
feet of Unit 11. with low-salinity formation water were deposi-
ted in similar environments but also intlude
Unit 111 above 4000 f t consists of siltstones sediments deposited on the delta plain and in
and mudstones with some limestones and the distributaries landward from the delta
sandstones and a few beds of coal. Several of front. That the formation waters are connate
the sands in this interval also contain oil and is suggested b p the occurrence pattern and the
 FORMATION WATER ABUNDANCEOF
AGE ( X 1oooppm) FAC IES
iSALiNl
I /
20 I40
P t E ISTOCENE
i 301 SHELF
'LEISTOCENE
AND
PL I O C E NE AND

P R O - DELTA

DELTA F R O N ~
LATE DELTA P L A I N
UNIT It, AND
2,200FT. DELTA F R O N l
MIOCENE
DELTA F R O N I

PRO-DELTA

AND

SHELF

FIGURE 4
202

STRUCTURE CONTOURS RT MARKER

FIGURE 5
 STRATIGRAPHIC CROSS-SECTION OF M A I N PAY INTERVAL IN ATTAKA FIELD
NO.4 F-1 6-1 c-5 NO.6

B'
RKER

COAL
0 2000 3000 4000
VERTICAL EXAGGERATION 25X LlMESlOWE
FEET
- SAWDSIONE

FIGUM 6
 204

types of t h e benthonic foraminifera that are sits in the central part of the basin comprise
present in the section. The Unit 111 sediments mostly terriguous detritus whereas carbonate
include limestones, shelf and pro-delta siltsto- sedimentation was common on the surroun-
nes and mudstones, and some delta-front and ding platforms and highs and along the shelf
strand-line sand. edge. Isopach data indicate that the axis of
maximum sediment thickness deposited during
STRUCTURE OF ATTAKA FIELD each of the Tertiary Stages shifted progressive-
The Attaka structure is a symmetrical. antic- ly eastwards with time.
line with flank dips up to 100 and an axial
trend of 10' west of north (Figure 7). Areal The most eastward encroachment of one of
and vertical closures are 26 square miles and the Kutei basin deltas took place, in Late
600 ft respectively and in some reservoirs up Miocene time when a deltaic complex progra-
t o 70% of the vertical closure is occupied by ded over the East Kalimantan shelf to the
the columns of oil and gas. Attaka lmation (Figure8). Deltaic sedimenta-
tion terminated in the Attaka area towardsthe
The structure is transected b y a series of end of the Late Miocene, either by lateral
major normal faults oriented northwst-south- shift of the delta or transgression of t h e Makas-
east. All of these faults are downthrown to sar Sea. Pliocene and Quaternary sediments
the northeast and their throws range from 500 at Attaka were deposited in prodelta and
to 1000 ft. The fault which is best controlled shelf envirbnme nt s.
by data f r o m wells is NWIII and its throw
increases with depth. At a depth of 7000 f t The Attaka structure was a slightly positive
the throw is80G900ft whereas at depths of element during the Late Miocene deltaic re-
2000 ft - 3000 ft the throw is 400 - 500 ft. gression. There is evidence that the major
Growth on these faults is indicated, although normal faults at Attaka underwent some
most of their movement appears to have growth during sedimentation of the Unit II
taken place after depositi.on of the main inver- sands although displaced gas/oil and oillwater
Val of Attaka sands in Unit 11. In the crestal contacts suggest that most of the movement
area of the structure where there is adequate on these faults was confined to the time after
well control, it is possible t o map a number of deposition of those. sands and also after the
smaller. normal faults antithetical t o fault migration of oil and gas into them.
NWIII. Throws of these faults are about 100
ft. SEISMIC DATA
Several seismic surveys have been carried out
That t h e structure was a slightly positive over the Attaka Structure and two aspects of
element during the Late Miocene and Pliocene the resultant data are of particular interest.
is $evidenced by the thinning of sands on the
crest of the structure. F o r example, the sands Firstly, some early seismic lines over the crest
comprising the main pay interval of the field of the structure (Figures 9, 10) showed a
in the upper part of Unit I1 are best develo- strong shallow reflection a t about. 26 seconds.
ped o n t h e flanks o f t h e structure in the Considerable interest has recently been gene-
vicinities of the F and C platforms and are rated in the petroleum industry by Craft
thinner on the crest of the structure between (1972) and others regarding seismic amplitude
Platforms A and B. anomalies (hot spots) created b y gas bearing
zones. Drilling ultimately established that the
DEPOSITIONAL HISTORY OF ATTAKA reflection a t , 26 secondsin Attaka was from a
SUCCESSION series of gas bearing sands and this reflection
Sedimentation began in the Kutei basin early appears to be an example of the hot spot
in t h e Tertiary following a phase of Late phenomenon.
Cretaceous Early Tertiary folding, and detritus
was shed eastward from the Sunda Shield and Secondly o n the crest of the structure there is
Kuching High throughout the Tertiary. Depo- an area of low seismic energy where reflect-
STRUCTURE CONTOURS ON 44-7
FIGURE 7
206
 207

STRUCTURE CONTOURS ON 44-7 SAND

POOR RECORD

FIGURE 9
 h,
0
M
1 A
N. WEST S. EAST

0.0 -0.0

1.0 -1.0

2.0 -2.0

3.0 -3.0

4.0 .4.0

5.0 -5-0

FIGURE I0
 209

ior,s have poor continuity. This low energy increase at the rate of 0.44 pounds per square
area underlies the strong reflector a t . 26 se- inch per foot of depth and the geothermal
conds and it more or less coincides with the gradient is approximately 80’ + 2’ per 100
limits of oil and gas accumulation of the field feet of depth below sea level. Reservoir and
(Figures 11-13). A low velocity zone on the crude oil properties are summarized on the
crest of the structure with RMS velocities accompanying Table.
200-250 ft/sec. lower than those on the flanks
was recognized by laterally continuous veloc- Several sands contain gas without oil and
ity. analyses of the seismic data. Existence of some of these will be completed t o provide a
this reduced velocity region in the crestal area supply for fuel and gas lift if required. Asso-
was subsequently confirmed b y velocity sur- ciated solution gas is used for fuel. No com-
veys in wells drilled o n the structure. pletions will be in gas caps since this gas is
Continuity of the reflections in the low being conserved as reservoir energy. The areas
energy area was improved by the use of the low of accumulation for the various reservoirs vary
RMS velocities in the 2 4 fold CDP stacking from 500 to 500 acres and vertical columns
.echniques and by increasing the amplitude of the are from 5 0 t o 4 7 0 ft.
low energy events (Figures 1 1-13). Calculations
indicate that velocities in the gas sands between DEVELOPMENT - COMPLETIONS - PRO-
.26 seconds and 1.4 seconds must be a b o u t DUC TI ON
2500 feet per second in order to produce the
Based on a spacing requirement of 140 t o 220
observed crestal average velocities.
acres per completion, 50 wells will be drilled
Considering these two aspects of the seismic from six platforms. The platforms are set in
data, it seems that the low energy/poor record 200 f t of water and are designed to withstand
area on the crest of the structure is the result 35 foot waves and 100 mph winds. The holes
of (1) attenuation of seismic energy by the are deviated up to a maximum of 55O and
shallow gas sand and (2) the fact that average total measured depth for such wells is about
crestal velocities are lower than flank veloci- 12,000 f t . When drilling is finished late in
ties because of the presence of highly porous 1973, over 100 miles of hole will have been
oil and gas bearing sands. drilled and cased. A typical casing programme
for the wells is 20” casing a t 700 f t , 13 3/8”
The deterioration in reflection quality and the to 3500 f t (measured depth) and 9 5/8” to
diminution of velocities across the crest of the the total depth.
structure are the result of the presence of gas
and oil in the structure and it is logical t o At present 40 dual completions and 9 single
speculate that these aspects of the data were completions are planned. Most wells will be
some indication of the presence of gas and oil. completed with 3%” tubing. The use of dual
or single packers with sliding sleeves gives
RESERVOIR AND CRUDE OIL CHARAC- optimum flexibility ena,bling sustained produc-
TERISTICS. tion by maximizing the time between work-
The oil produced at Attaka is from 34 sand- overs and permitting the opening of sleeves in
stone reservoirs between the depths of 2000 the event that a primary campleted reservoir
and 7800ft. Most of the reservoirs are very- develops a high GOR or becomes water cut.
fine to fine-grained, friable, well sorted sand- In several instances, compatible reservoirs are
stones with minimal amounts of matrix and comingled to optimize production rates and t o
cement. Porossities and permeablities range up ad eq ua t ely drain producing reservoirs .
t o 35% and 4 - 5 darcies. E-logs indicate that
most reservoirs have gas caps although some Individual production rates vary from 400
oil zones are undersaturated. Solution gas/oil BOPD t o 4300 BOPD per tubing string. A
ratios range from 275 t o 750 SCF/STB. Gravi- ,total of 84 completions for oil production is
ties of the oil produced range from 35’ to planned and these should result i n a field
43’ API and sulphur content of the oil avera- production rate of about 100,000 barrels of
ges 0.1% b y weight. Subsurface fluid pressures oil per day by late 1973.
210

STRUCTURE CONTOURS ON 44-7 SAND

FIGURE I I
 21 I

PROCESSING - HANDLING for three stages of separation before the oil

goes into storage.
First stage separation of gas, oil and water At present, three 500,000 barrel floating roof
occurs on each well platform, Oil and gas are storage tanks are available and a fourth is under
then moved separately to a production plat- construction. For tanker loading, oil is trans-
form through an 8” or 10” oil line, and a 10” ferred through a 30” pipeline to a buoy (Single
or 12” gas line. On the production platform, Buoy Mooring), anchored 4.84 miles offshore,
crude oil is comingled and shipped through an in 92 ft of water. Tankers up to 125,OO DWT
18” pipeline to the onshore Santan Terminal are loaded at the buoy through two 16”
facilities, 15 mile away (Figure 14 ). At San- floating hoses. The maximum loading rate is
tan, two 50,000 BPD process trains are used 30,OO barrels per hour.

T A B L E

ATTAKA FIELD - RESERVOIR AND CRUDE OIL PROPERTIES

Depths of Oil Reservoirs feet 2000 to 7600

Reservoir Pres‘sure psia 900 to 3340
Normal Hydrostatic Gradient psilfoot 0.44
Reservoir Temperature OF 120 to 230
Geothermal Gradient OF 800 + 2O ] 100 feet
Gravity of Oil OAPI 35 to 43
Formation Volume Factor B/B 1.31 to 1.45
GasOil Ratio (solution) cu ftjbbl 275 to 750
Oil Viscosity at Reservoir
pressures and temperatures cen tipoise - 5 6 to .33
Viscosity 63 72OF centipoise 1.36 to 1.98
Colour of Oil greenish to dark brown
Pour Point OF Below 32
Flash Point OF Below 75
Ash Wt % .0002
Sulphur Wt% 0.1
212

&---
KMA 8&
T EAST
0.0

1.0

2.0

3.0

4.0

5-0
 21 3

1
K
WEST --
0.0 0.0

1.0

2.0 2.11

3.0 3.0

4.0 44

5-0 5.0
 N
I
P

UNION - JAPEX - PERTAMINA

ATTAKA FIELD
EAST KALIMANTAN - INDONESIA
SCHEMATIC OF P R O D U C T I O N A N D TERMINAL FACILITIES

FIGURE 14
 215

ILLUSTRATIONS

Figure 1 Location Map

Figure 2 Major Structural Elements of East Kalimantan
Figure 3 Diagrammatic Regional North-South and East-West cross-sections of East
Kalimantan
Figure 4 Attaka Field - Stratigraphic Column
Figure 5 Structure Contour Map of R t Marker showing location of stratigraphio
cross-section in Figure 6.
Figure 6 Stratigraphic cross-section of main pay interval in Attaka Field (see Figure 5
for location of section)
Figure 7 Attaka Structure - structure contour map of 44-7 sand and Attaka Field
Composite Log showing R t Marker and 44-7 sand
Figure 8 Three dimensional diagrammatic sketch of East Kalimantan offshore shelf
area.
Figure 9 Map of Attaka Structure showing location of seismic section KM 11
Figure 10 Seismic section KM 11
Figure 11 Map of Attaka Structure showing location of Seismic Section KMA 8
Figure 12 Seismic Section KMA 8 using incorrect crestal RMS velocities
Figure 13 Seismic Section KMA 8 using correct crestal RMS velocities
Figure 14 Attaka Field - Schematic diagram of Production and Terminal facilities

TODD, Donald F. & PULUNGGONO,

A . (1971) : T h e Sunda Basinal
Area, a paper presented at the Ame-
rican Association of Petroleum Geo-
logists Convention, Houston, March
1971.