Chapter Five Well Correlation
地层对比
5.1 Introduction (简 介）
Correlation or stratigraphic correlation is a geological term referring to the process
by which two or more geological intervals are equated even through they are spatially
separated. The International Stratigraphic Guide subdivides it as follows:
“ there are different kinds of correlation depending on the feature to be
emphasized: lithologic correlation; a correlation of two fossil - bearing beds
demonstrates correspondence in their fossil content and in their biostratigraphic
position; and chronocorrelation demonstrates correspondence in age and in
Chronostratigraphic position.”
Correlation is a principal task for many geologists, particularly in the oil and gas
industry, but also in mining and hydrogeology. Cuttings, cores and well logs constitute
the main data used for correlation, with well logs playing a special role because they
are long, continuous recordings. Additionally, they are useful because they are
unbiased physical measurements and often available in a large number of wells in a
field or a basin.
Chapter Five Well Correlation
地层对比
5.1 Introduction (简 介）
Most conventional open-hole logs including electrical, neulear and
accoustic logs are primarily sensitive to the properties of the rocks and
fluid they contain. In fact, most of them are more sensitive to the fluids,
and the lithological signal is often only secondary. Nevertheless, if
these logs are used for well correlation, an essentially lithostratigraphic
correlation will be obtained. Many geologists prefer to use just the GR
log or a combination of GR logs with SP logs, because they they are
commonly available and they carry a relatively strong lithological signal.
5.2 The scale of stratigraphic correlation and well logs chosen
(地层对比规模及测井曲线的选择）
The stratigraphic correlation can be divided into the four scale as follow:
① The worldwide scale;
② the regional scale;
③ the basin (or depression) scale; and
④ The oilfield scale.
The correlation at worldwide and regional scale is done by methods of absolute age
dating and/or analysis of fossil assemblage. They are not used commonly for
petroleum geologists. Generally exploring petroleum geologists commonly use
correlation at basin (or depression) scale to build up stratigraphic framework in a basin
or depression in a basin, and development geologists commonly use correlation at
oilfield scale to do reservoir zonation in oilfield.
The target of correlation at basin (or depression) scale is building up stratigraphic
succession in the scale of basin or depression firstly. Secondly, studying distribution of
the formation, and further, studying tectonic and depositional evolution in the basin or
depression. 建立地层层序；揭示地层展布规律，研究构造和沉积演化
5.2 The scale of stratigraphic correlation and well logs chosen
(地层对比规模及测井曲线的选择）
The correlation at basin (or depression) scale is generally lithologic
correlation done at exploring stage. Well logs and seismic profile is
important tool to do the work. The combination of GR curve and SP in
association with conventional resistivity curve (commonly base lateral
electrode array with 2.5 meter electrode spacing, recorded R2.5) in the
scale of 1:500) commonly are used to do the correlation because GR
and SP logs is very sensitive to the lithology, can be used to identify
permeable and impermeable rock, and R2.5 is sensitive to the fluids, can
be used to correct affection of fluids.
5.2 The scale of stratigraphic correlation and well logs chosen
(地层对比规模及测井曲线的选择）
The target of correlation at oilfield scale is firstly to build up detailed stratigraphic
succession in hydrocarbon reservoir assemblage in oilfield, the minimal reservoir unit
divided is called as “single sandstone unit”. Secondly, to study the distribution of the
“single sandstone unit” , barrier bed and interbed so as to serve the strategic decision in
oilfield development management. 建立油田内主力含油层系精细地层层序，落实
到“单砂体”。研究各“单砂体”及隔、夹层的宏、微观非均质性，为油田开发
管理优化决策服务。
As single sandstone unit is demanded to be divided for the reservoir correlation
, then, higher precision in correlation is needed. Therefore, the combinational logs in
reservoir interval with the scale of 1:200 will be used for reservoir correlation in our
country.
There are much more kinds of logs with greater scale （1：200）in combinational
logs (including lithology, porosity and resistivity logs, further also other new logs, such
as diplog, image and NMR logs etc.). Their resolution of formation is higher, it is better
tool for reservoir correlation.
5.2 The method of stratigraphic correlation
(地层对比方法）
The petroleum geologist must have knowledge on regional geology, correct
geological concept, richness of correlation of experience and skill , can apply the
correct correlation method to do the works.
1. Several correlation concepts
(1) The concept of similarity
The concept of “similarity” is the base of stratigraphic correlation. The closer two
wells is apart from, it is shown that the more similar the deposition conditions is, and
the greater the similarity of the strata is. This kind of “similarity” was reflected on log
curves with the similarity of amplitude, shape ,thickness and association etc.
The respects of the four will be concerned when "similarity" was be used to do the
stratigraphic correlation, as follow: ① type well; ② reference horizon (or key
horizon/bed); ③ sedimentary cycle; and ④ the rule of facies change (correlation by use
of rule of facies change)
“相似性”是地层对比的基础。二口井相距越近，一般来说其沉积条件越近，沉积岩层相似程度
越大。反映在测井曲线上就是测井曲线在“幅度，形态，厚度及组合”等诸方面近似。
利用“相似性”概念进行对比，需要从四个方面入手：（1）标准井；（2）标准层；（3）沉积
旋回；（4）相变规律（相控对比）。
① Type well
The type well play the important role, which is equivalent to typical
section in the study of stratigraphy from outcrop.
The type well define: “ it is the well, which is the most complete in
stratigraphic succession exposed, strata of the most thick, without strata
loss and abnormal thinning or thickening caused by fault and erosion,
with good quality and complete logging series, with system analysis
data of core and test, clear of chronostratigraphy ”
The type well is relative, it is chosen in the the process of
stratigraphic correlation. In this sense, the stratigraphic correlation is a
repetitive process constantly .
Stratigraphic correlation is from the nearest wells, which is called as
“ type well or standard well ” to begins to be done from near to far.
标准井的作用相当于野外露头地层研究中的典型剖面
标准井：揭露地层最全，地层最厚，无断层，剥蚀而造成的地层缺失，减薄或异常增厚；有质
量良好，系列完整的测井资料，有系统取芯及系统的分析化验资料，年代地层清楚的井。
标准井是相对而言的，是在地层对比过程中不断选择的。从这个意义上来讲，地层对比是一个反
复的过程。
地层对比是由距“标准井或称为典型井”最近的井开始，“由近及远”地对比。
② Reference horizon (or key horizon/bed)
Reference horizon define: it is the horizon, which lithological
feature is obvious, steady on lithology, the thinner in thickness, the
farther horizontal extension and easy to identify on the log curves.
Generally, the Reference horizon is isochronal (等时的）.
Reference horizon can be divided into “main reference horizon” and
“ secondary reference horizon ” according to difficulty to identify and
distribution range.
The more the reference horizon is and the more obvious the features
is, the more reliable the stratigraphic correlation is.
标准层是指岩性特征突出，岩性稳定，厚度较薄，横向延伸远且变化小，且
在测井曲线上易于识别的层段。一般标准层具有等时特征。
根据标准层的易于识别程度和稳定分布范围的不同，可分为“主要标准层”
和“辅助标准层”。在地层划分对比中，标准层越多，特征越明显，小层划分对
比的结果越可靠。
Delta front depositional subfacies
三角洲前缘沉积亚相
The reference horizon with the feature of high resistivity mudstones of three in the
Shanghe oilfield between sandstone package 3 and 4.
商河油田沙二中，三四砂层组之间“三高阻”泥岩段
③ Sedimentary cycle
Cycle is geologic record left in the strata with periodic variation due
to periodic variation of geologic agent. 旋回是由于地质营力周期性变化而在
地层中留下的记录
Cycle exhibits periodic variation in the strata features (such as
lithology, thickness of bed, color, fossil, and lithology association etc.).
All of these features can be expressed on the log curves except for rock
color. Therefore, cycle can be studied comprehensively by log curve
combined with lithology, rock composition and texture, thickness and
fossil. These features can be analyzed and plotted cyclic curve.
Corresponding relation between the cyclic curve and logging curve also
should be analyzed and transgressive – regressive (T - R ) turn point can
be determined by log curve. then, the cycle in different scale can be
determined.
Iron
Lith.
fossil
Cycle
bedding
color
curve
cycle RT/SP restore
logs coeffi.
The right figure is an example
to determine different scale cycle
curve by comprehensive analysis of
lithology, fossil, the rock chemical
feature and logging curve. It is
shown that there is regressive
cycle (reverse cycle) which
contains three sandstone packages.
Gastro.
fish
右图是运用岩性、电性、古生物、 plant
岩石化学资料综合分析编制成的旋回曲 purplish
red
gray
线。表示三个油层沉积剖面是一反旋回 green
gray
black
Iron
Lith.
fossil
Cycle
From the bottom to the up for the plot, it
bedding
color
curve
cycle RT/SP restore
logs coeffi.
has changed for lithology from the fine to
coarse in grain, increased for sandstone bed
numbers and for single sandstone bed
thickness, magnitude of planktonic organism
(浮游生物)(like as: Ostracoda -介形虫;
Conchostracan -叶肢介) will decrease; the
mudstone color has changed from grey and
grey black to the purplish red (紫红）.
Geochemical indicators suggest that the the
weak restore, restore condition has ben
transformed into the oxidation condition. All
Gastro.
the these have be reflected that the water fish
depth has be changed from deep to shallow. plant
由下至上岩性由细变粗，砂岩层增多；单 purplish
层厚度增大；古生物中介形虫、叶肢介等浮游 red
生物由多到少；泥岩颜色由灰黑，灰色到绿色 gray
green
至上部出现紫红色；地球化学指标显示由还原 gray
black
至弱还原至氧化。反映了湖水由深至较深至较
浅变化。
Iron
Lith.
fossil
Cycle
bedding
color
curve
cycle RT/SP restore
logs coeffi.
According to the change of
features above concerned, secondary
order cycle of three ( I, II and III , see
right figure )can be determined on the
background of the first order cycle
exhibited as regressive cycle (reverse
cycle).
在大的反旋回背景上，可以划分为由 Gastro.
fish
下而上的I、II、III共3个次一级的反旋回。
plant
purplish
red
gray
green
gray
black
Delta front depositional subfacies
三角洲前缘沉积亚相
The reference horizon with the feature of high resistivity mudstones of three in the
Shanghe oilfield between sandstone package 3 and 4.
商河油田沙二中，三四砂层组之间“三高阻”泥岩段
④ The rule of facies change (correla. controlled by rule of facies change)
The connection between the vertical and lateral changes of facies observed
in outcrop and subsurface is made by Walther‘s Law. This is a fundamental
principle of stratigraphy, which allows the geologist to visualize predictable
lateral changes of facies based on the vertical profiles observed in 1D sections
such as small outcrops, core, or well logs. As discussed by Miall (1997), vertical
changes in litho- and biofacies have long been used to reconstruct
paleogeography and temporal (短期变化）changes in depositional environments
and, with the aid of Walther’s Law, to interpret lateral shifts of these
environments. As a note of caution (需要注意的是）, however, such
interpretations are only valid within relatively conformable successions of
genetically related strata. Vertical changes across sequence bounding
unconformities potentially reflect major shifts of facies between successions that
are genetically unrelated, and therefore such changes should not used to
reconstruct the paleogeography of one particular time slice in the stratigraphic
record.
Walther's Law (Middleton, 1973): in a conformable succession the only facies that can
occur together in vertical succession are those that can occur side by side in nature.
Walther's Law (Bates and Jackson, 1987): only those facies and facies-areas can be
superimposed which can be observe beside each other at the present time.
Walther's Law (Posamentier and Allen, 1999): the same succession that is present
vertically also is present horizontal unless there is a break in sedimentation.
In other words, a vertical change of facies implies a corresponding latoral shift of facies
within a relatively conformable succession of genetically related strata.
C D G
E- F
B
A
A
B
C
D Walther's Law Sketch
E
F
A: marine limestone; B: brackish water marine shale; C: coal; D: clay;
G E:fresh water limestone; F: bottom shale; G: bottom sandstone;
A prograding delta is a good
illustration of theWalther's Law
concept. The deltaic depositional
system includes prodelta, delta front,
and delta plain facies, which occur
side by side in that order and the
products of which occur together in
the same order in vertical succession.
Use of the depositional system
concept enables predictions to be
made about the stratigraphy at larger
scales, because it permits
interpretations of the rocks in terms
of broad paleoenviromental
and paleogeographic reconstructions.
FIGURE : Sequence stratigraphic vs. lithostratigraphic frameworks,
starting from the same set of facies data.
1. The reconstruction of paleodepositional environments via facies
analysis is an important pre-requisite for sequence stratigraphic
interpretations. The nature of stratigraphic contacts (scoured,
conformable) also needs to be assessed via sedimentological analysis.
2. The sequence stratigraphic framework is constructed by
correlating the key sequence stratigraphic surfaces. All sequence
stratigraphic surfaces shown on the cross section are good
chronostratigraphic markers (low diachroneity - 低穿时性), with the
exception of the transgressive wave-ravinement （波浪侵蚀面） surface
which is highly diachronous.
3. Sequence stratigraphic cross section, showing key surfaces, within-
trend facies contacts, and paleodepositional environments. Within-trend
fades contacts, marking lateral changes of fades, are placed on the cross-
section after the sequence stratigraphic framework is constructed.
Facies codes: A--meandering system; B--braided system; C--estuary-
mouth complex; D--central estuary; E--delta plain; F--upper delta
front; G--lower delta front--prodelta.
4. Lithostratigraphic cross-section. Three main lithostratigraphic units
(e.g., formations) may be defined:
A--a sandstone-dominated unit;
B and C - mudstone-dominated units, with silty and sandy interbeds.
Formations B and C are separated by Formation A . Additional
lithostratigraphic units (e.g., members--subdivisions of units A, B, C)
may be defined as a function of variations in lithology and color.
东营凹陷牛庄－六户洼陷沙三段三角洲前积对比图
5.3 The procedure of stratigraphic correlation
(地层对比过程）
The general procedure of stratigraphic correlation is as follow:
1. The hierarchy of rock - time stratigraphic units should be determined by
lithology and unconformity (furture, including, reference horizon, cycle and facies ) in
correlation at basin (or depression) scale . The hierarchy of rock - time stratigraphic
units include Bed, Member, Formation, Group, Supergroup etc.
2. The stratigraphic correlation was carried out according to lithology and
lithology association , reference horizon, sedimentary cycle and facies. It was carried
out on type well-centered, and was done from the near to far.
3. The strata units of Formation and Member can be correlated by lithology , the
first order sedimentary cycle and unconformity. The strata units of Bed and sandstone
packages can be correlated between the wells according to the lithology, reference
horizon, the secondary order sedimentary cycle and facies.
4. if correlation lines is inconsistency with each other, the geological cause must
been analyzed.
5.3 The skill of stratigraphic correlation
(地层对比技巧）
1. The hierarchy of sedimentary cycle and
reference horizon can be identified by use of logs
curve of SP / GR / COND / ML / R0.5 etc. The
reference horizon used commonly is : thick
mudstone interval, oil shale like comb on
conductivity curves, thin coal, thin volcanic tuff (凝
灰岩段 ) interval with high resistivity and high GR,
thin limestone interval.
2. the logs plot will be shifted to correlate
between wells follow procedure as : (1)from upper
to down firstly, then, from down to upper
repetitively ; (2)The first easy ,and the difficult; The
first near, and far; (3) The large interval, and small
interval.
coal
limestone
Oil shale with high AC , high GR and low DEN
C81
Thin volcanic tuff interval
with high AC , high GR and low DEN
C82
Exercise Four: correlation by use of log curve
1. The purpose and significance (目的和意义)
The correlation by use of log curve is the base of studying the formation
properties and structural forms in oilfield, also is the base of doing reservoir
correlation so as to study oil pool and to serve determination of oil development
strategy. This exercise will make the students master the basic method of
stratigraphic correlation.
2. Demands of this exercise
(1) To determine position of different intervals ( A,B,C intervals ) from different
wells on the section.
(2) To find out the position of fault, to determine fault throw, and fault type.
3. The Procedure (作法)
(1) To be familiar with data given ( the features of lithology and log
curve from type well ) and to find out reference horizons on the type well.
(2) To determine the location of each layer, and mark on the each well
according to the features of lithology and log curve from each well by
correlation to the adjacent well follow the correlation principle of “ the first
near and far”.
(3) If fault was met in the procedure of correlation, the position of fault
point should be marked on the well with the special symbol. Then, fault will
be drawn according to the loss or thinning of formation.
(4) The formation equated of the same fault block will be connected by
correlated line.
4. The data known (资料)
NO.1 of well is a type well on the profile. The lithology and reference
horizon has been marked
5. The principle of identifying fault (断层识别原则)
(1) The loss of formation or repetition of strata successions ;
(2) Thinning or thickening of strata succession;
(3) Changed abruptly in the elevation of reference horizon;
Exercise Five: Reservoir correlation by use of log curve
1. The purpose and significance (目的和意义)
The detailed correlation for reservoir sandstone by use of log curve is the base
of studying the heterogeneity of “stack sandstone body complex”, revealing
distribution of the “single sandstone unit” in the “stack sandstone body complex”, so
as to serve determination of oil development strategy, to enhance oil recovery.
2. Demands of this exercise
To do detailed reservoir sandstone correlation, to find out position of each
“single sandstone unit” 对所给资料进行细分对比，找出每一个砂层的对应位置。
3. The Procedure (作法)
(1) To be familiar with and to master the position of each reference horizon and
logging features of every sandstone layer on the given wells.
(2) to correlate with adjacent wells from near to far step by step accordiong to
the logging features of every sandstone layer on the given wells
(3) the top and bottom boundary of single sandstone unit equated on the
different wells will be connected by line, and recorded by use of number of
sandstone units. 用曲线将各井相同砂层顶、底界面连起来，并写上砂层号。
4. The data known (资料)
Two profiles have been given as follow.
The End
