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Scientific Journal of Earth Science December 2013, Volume 3,
Issue 4, PP.100-106
Study on Tight Sandstone Reservoir
Characteristics of Sha-3 Member in Shuangtaizi
Structural Belt of Liaohe Depression Zhufu Shao
1, Jianhua Zhong 1, 2
, Bao Liu 3, Gangshan Lin
1, Lihong Fan
1
1. School of Geosciences, China University of petroleum, Qingdao
266580, China
2. Guangzhou Institute of Geochemistry, Chinese Academy of
Sciences, Guangzhou 510640, China
Email: [email protected]
Abstract
The reservoir characteristics and diagenesis are studied based
on test results of conventional and casting thin sections,
granularity,
mercury injection, X-ray diffraction, scanning electron
microscope and cathodoluminescence according to basic data. The
results
show that Sha-3 Member reservoir in Shuangtaizi structural belt
of Liaohe Depression is very tight with a large buried depth,
low
porosity and permeability and poor correlation. The reservoir
space types of target stratum are mainly intergranular and
intercrystalline dissolution secondary pores and intergranular
residual compacted primary pores, as well as intragranular
dissolution pores with development of fewer fractures. The
reservoir is strongly compacted with the development of
argillaceous,
siliceous, calcitic and ferruginous cementation. Metasomatism is
mainly the replacement of quartz and feldspar by carbonate
minerals. The Sha-3 Member reservoir is in the middle diagenetic
stage A-B, and the middle stage A can be divided into
sub-stages
A1 and A2 by 3200m as the dividing line.
Keywords: Liaohe; Shuangtaizi; Sha-3 Member; Tight Sandstone;
Reservoir Characteristics
1. Introduction
The western Liaohe sag, located in the west of Liaohe
depression, is a dustpan-shaped continental fault basin
developed in Meso-Cenozoic. The sag is made up of western slope
belt, transition zone of slope and sub-sag, the
central uplift belt, sub-sag belt and eastern actic region
distributed in turn from west to east. The north region is high
and narrow while the southern part is low and wide. It covers an
area of 2560 km2 at a buried depth of more than
8400m in basement. The Paleogene series develops initial
rifting, strong fault depression and block-faulting
depression in this basin, and the sedimentary strata shows
multi-cycle. Shuangtaizi structural belt is located in the
south of western sag, neighboring Qingshui sub-sag in the east
and transition zone of slope and sub-sag in the west [1-5]
(Fig. 1). The 3-Member of Shahejie Formation (Sha-3 Member for
short) is a period of strong fault depression,
with steep slope, deep water body and rich provenance. The
Shuangtaizi area develops mainly the gravity-flow
depositional system, including fan delta, sublacustrine fan,
semi-deep lake and deep lake. The midfan subfacies in
the sublacustrine fan may be further divided into braided
channel, inter-channel and channel front microfacies [2, 6-9]
.
It develops large sets of inter-beds of grey, dark grey and
beige mudstone and thick-layer lump white glutenite, at a
buried depth of more than 3000 meters.
The Sha-4 and -3 Members of the Qingshui sub-sag are rich in
hydrocarbon source rocks with relatively high
thermal evolution of organic materials. Good
source-reservoir-cap matching conditions are formed because of
the
direct contact between sand body and source rocks in Sha-3
Member of Shuangtaizi area. However, due to low
reservoir physical property value and large buried depth, this
area is a typical tight sand reservoir, especially when
the buried depth is over 3500m. In addition to fast changes of
sand bodies and high reservoir heterogeneity, it is
necessary to have a detailed study on the tight sandstone
reservoir in this area in order for a preference of favorable
zones.
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FIGURE 1 LOCATION MAP OF RESEARCH AREA
2 Reservoir characteristics
2.1 Petrological characteristics
The Sha-3 Member of Shuangtaizi area has multiple rock types and
complex lithology [7]
. Through observation to a
large quantity of cores and identification to rock slices, we
found that Sha-3 Member developed large sets of
interbeds of thick-bed conglomerate, sandstone and dark
mudstone, including boulder conglomerate, medium-coarse
conglomerate, sandy conglomerate, conglomeratic sandstone,
pebbly sandstone, middle-fine sandstone and
mudstone. Some special structures such as convolution bedding,
crumpled deformation and liquefied sandstone veins,
developed in sandstone, which shows gravity flow deposition
characteristics. Compositional and textural maturities
of the Member are low. Its reservoir lithology is represented by
feldspar lithic sandstone, minor lithic feldspar
sandstone and a small amount of feldspar sandstone and lithic
sandstone (Fig. 2). It is composed mainly of volcanic
rock and metamorphic rock as well as small amount mudstone. Its
particles, mostly in subangular-subrounded shape,
present medium to poor separation, with fairly poor rounding.
The particle contact types are point-line and line
contacts, while the cementation types are porous and contact
cements. The quantitative analyses on the whole rock
mineral diffraction of four wells, namely, Shuang 51, Shuang
216, Shuangshen 3 and Shuang 225, show that there
are low contents of clay and carbonate minerals which are mainly
quartz and feldspar.
FIGURE 2 TRIANGULAR DIAGRAM OF SANDSTONE COMPOSITION IN SHA-3
MEMBER IN SHUANGTAIZI AREA
TABLE 1 QUANTITATIVE ANALYSIS RESULTS OF WHOLE ROCK MINERAL
DIFFRACTION OF FOUR WELLS FROM WORK AREA
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Mineral
Well
Quartz Potash
Feldspar
Plagioclase Calcite Dolomite Clay
Shuang 52 58.2 11. 22.7 1.5 3.1 4.9
Shuangshen 3 55.3 12.4 24.8 0.8 2.0 4.9
Shuang 216 57.6 10.5 23.0 1.3 2.4 5.2
Shuang 225 60.9 9.3 19.4 3.0 2.2 5.0
2.2 Physical properties of the reservoir
The physical property analysis data of 24 wells in Shuangtaizi
area were collected, including 665 porosity data and
498 permeability data. The statistical results show that the
porosity ranges from 3.4 to 24.7% on an average of 13.3%
(fig. 3), while the permeability changes mainly between 0.09 and
334mD on an average of 4mD. 80 percent of the
porosity data points are less than 15% and 80 percent of the
permeability data points are less than 8mD. As shown in
Figure 4, the reservoir is mainly characterized by low porosity
and permeability. Although permeability increases
with porosity, it changes greatly in a poor correlation.
2.3 Space types of the reservoir
The pore is a significant component of clastic rocks and an
important place of oil and gas storage and migration. The
space, except clastic particle, matrix, cement, and authigenic
mineral in rock, can be collectively called pore space [10]
.
FIGURE 3 POROSITY AND PERMEABILITY DISTRIBUTIONS OF SHA-3 MEMBER
IN SHUANGTAIZI AREA
In analyses of general and casting thin sections, scanning
electron microscope, and cathodoluminescence, it is found
that Sha-3 Member in Shuangtaizi area has various types of
reservoir space, mainly including intergranular pores,
intercrystal pores, and intragranular pores. Also it has a few
of micro-pores, casting pores, and fractures. The
intergranular pores include three types: (1) primary
intergranular pores, which are the residual primary pores
because
of mechanical compaction and interstitial material filling; (2)
intergranular dissolution pores, which are the
intergranular dissolved pores after dissolution of interstitial
materials (mainly carbonate cement and quartz); and (3)
a small quantity of pores that are formed with edge dissolution
and pressure solution of clastic particles. The
intragranular pores are mainly dissolution ones unstable
minerals in clastic particles, while the intragranular pores in
this area are mainly the dissolved ones formed by felspar
particles, and sometimes oversized casting film pores occur.
Because of the target stratums large buried depth and strong
diagenesis, there are a small quantity of fractures which
can be divided into tectonic compaction and diagenetic shrinkage
fractures developing in the reservoir. Although
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they only account for 5%, they act as reservoir space and
connection channels. In this area, the reservoir space is a
network system integrated with aforementioned intergranular
pores, intragranular pores and fractures. Although there
is a good porosity in a local area, the data analyses of
permeability and mercury injection show that the reservoir
bound water saturation is generally high in target stratum.
Nonuniform pore structure and poor-throat connectivity in
this area cause poor physical properties and tight reservoir as
a whole.
3 Characteristics of diagenesis
Diagenesis refers to all the changes of rock before the hard
sedimentary rock changes into metamorphic rock or
sustaining weathering in the process of loose deposited
sediments changing into hard dimentary rocks. The research
of clastic rock diagenesis is an important basis to reasonably
explain the advantageous pore development zone and
the formation mechanism of oil and gas reservoir space, and is
also a foundation to deepen geological theory of
clastic rock reservoir.
3.1 Main types of diagenesis
With data analyses of conventional and casting thin sections,
scanning electron microscope, and
cathodoluminescence, the results show that the main types of
diagenesis of Sha-3 Member in Shuangtaizi area
include compaction, pressure solution, cementation, metasomatism
and dissolution (corrosion). They have a
significant effect on the development of reservoir pores, and
lead to the periodical change of longitudinal reservoir
physical properties directly [11-12]
.
3.1.1 Compaction
After sediments undergo mechanical compaction, clastic particles
will rearrange in a free stacking state to a close or
tightest stacking state. These particles deform due to
compression, and even rigid mineral grains are fractured or
crushed. The influence factors of compaction include
composition, granularity, separation and rounding, buried
depth and formation pressure of particles.
The microscopic observation shows that the target stratum of
study area is generally located in the strong compaction
belt, where granules present a line contact (Fig. 4a).The
reservoir can be divided into upper and lower sections by
3200 meters as a dividing line. The clastic particles in upper
section are mainly in line contact relation (about 40%).
Besides types of transitional contact relation, spot-line and
line-spot contacts are also common. More than 80% of
contacts between clastic particles in the lower section are line
contacts, and only few transitional contact relations
can be seen. This shows that compaction intensifies gradually
with depth.
3.1.2 Cementation
Results of analyses on thin sections show that the sum of
reservoir cement (remaining nowadays) and secondary
porosity in the target stratum of study area is generally less
than 20%, which illustrates the highest pore loss caused
by cementation may not exceed 20%. There are many different
types of cementation in different stages. Five
common types of cementation are: clay mineral cementation,
siliceous cementation, carbonates cementation, feldspar
cementation, and pyrite cementation.
(1) Clay mineral cementation
The clay mineral cementation can be specially divided into
cementations of kaolinite, chlorite, and illite clay mineral.
Various kinds of clay minerals exist in particle-coating,
pore-lining or pore-filling forms. The mineral content in
mixed layers of illite and montmorillonite varies
insignificantly with depth, and chlorite content has an
unobvious
increase with depth. Nevertheless, at the depth of 3100m, illite
content increases while kaolinite content decreases
significantly (Fig. 4b). It indicates that illite may transform
into kaolinite suddenly at this depth. Meanwhile, iron-
and magnesium-rich diagenetic environment suitable for chlorite
deposition is not common.
(2) Siliceous cementation
Quartz is the most common siliceous cement in the target stratum
of study area. It displays not only in authigenic
enlarged edge cement of clastic quartz, but also in microcrystal
granule filled in pores. And the secondary
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enlargement quartz in the target stratum can come to Level
three, revealing quite fierce diagenesis (Fig. 4c).
FIGURE 4 RESERVOIR DIAGENETIC FEATURES OF SHA-3 MEMBER IN
SHUANGTAIZI AREA
(a. Well Shuang 227: 3960.82m, line contact for clastic
particles; b. Well Shuang 213: 3629m, illite cementation; c.
Well Shuang 213: 2777.14m, secondary enlargement for quartz; d.
Well Shuang 213: 3631.81m, dolomite
crystal-stock cementation)
(3) Carbonate cementation
The buried depth of the target stratum is mostly over 2600m. The
carbonate cements in reservoir forms in the late
cementation, mainly including iron calcite and iron dolomite in
crystal-stock cementation form (Fig. 4d). They often
replace clasts and other components, and fill fractures and
pores in the later stage. The carbonate mineral content has
an increase with depth.
(4) Feldspar cementation
Authigenic feldspar is also a common authigenic mineral in the
clastic rocks, which exits in forms of authigenic
enlarged-edge clastic feldspar or small idiomorphic crystal in
matrix.
(5) Pyrite cementation.
Pyrite cement is the product in the strong reducing medium
conditions, and came into being at various stages of the
diagenesis. The pyrites forming in the syngenetic period or
early diagenetic stage present mostly in the strawberry
shape, while the pyrite forming at the diagenetic stage is
grain- and nodular-shaped. The pyrite in the target stratum
of study area is generally strawberry-shaped, and it is the
cement in the early diagenesis.
3.1.3 Metasomatism
Metasomatism refers to a phenomenon that primary minerals in
clastic rocks are replaced by epigenetic ones. In
essence, the dissolution of replaced minerals and the deposition
of replacing minerals occur simultaneously, and the
placed minerals are replaced gradually. The most remarkable
behavior in the target stratum of study area is the
metasomatism of different rock structure components by
(iron-containing) carbonate minerals in the late stage. It
may occur in clay cement of the edge and the inside of particle
or inter-particle.
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3.1.4 Dissolution
Dissolution refers to the dissolution of underground water to
rock components, and it starts with particle surface or
the crack of particle and interstitial material till to the
particle and interstitial material inside gradually. Dissolution
is
an important way to improve porosity and permeability conditions
of sandstone reservoir.
Corrosion to feldspar particles is the most common dissolution
in the target stratum of study area, and the dissolution
of other structural components is sporadic. With the buried
depth, more and more feldspar components are dissolved,
causing precipitation of derivative minerals. The quantitative
analysis of X-ray diffraction reveals that total quantity
of feldspar decreases with depth gradually while the clay
minerals increase with the depth. This shows the
dissolution process of feldspar.
3.2 Division of diagenetic stage
3.2.1 Sequence of diagenetic evolution
According to the diagenesis types and depth relationship, the
sequence of diagenesis can be roughly determined as
follows: early carbonate cementation, authigenic clay mineral
cementation and strawberry-shaped pyrite cementation
early carbonate and feldspar dissolutionquartzs secondary
enlargement, cementation of microcrystalline quartz
and authigenic clay mineral (kaolinite), and feldspars
authigenic enlargementlate carbonate cementation
dissolution of late carbonate, feldspar and other cements. It
should be noted that the compaction has been continuing
during the entire process of diagenetic evolution sequence.
Early carbonate cementation not only inhibits compaction,
but also provides material source for later dissolution.
3.2.2 Division of diagenetic stage
According to comprehensive various analyses and test data in
target area of the study area, as well as previous
relevant studies, the diagenetic stage of target stratum is
divided in this paper. The items for comprehensive studies
include pore types, particle contact relationship, dissolution
features, sandstone authigenic mineral characteristics,
argillaceous rock compositions, vitrinite reflectance, organic
material pyrolysis peak temperature, paleo-temperature,
buried depth, etc.. Sha-3 Member of study area is located
generally below 2500m. Its diagenetic stage is equivalent
to stage A-B of the middle diagenetic phase according to its
current diagenetic features. Stage A can be further
subdivided into sub-stages A1 and A2 by 3200m as the dividing
line roughly. The diagenetic features of the two
sub-stages are quite different (Fig. 5).
FIGURE 5 DIVISION CHART FOR DIAGENETIC STAGE OF SHA-3 MEMBER IN
SHUANGTAIZI STRUCTURAL BELT
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4 Conclusions
(1) The reservoir lithology is very complicated for Sha-3 Member
in the Shuangtaizi structural belt of Liaohe
Depression. Its particle grade varies from boulder conglomerate
to siltstone. The member has lower compositional
maturity and structural maturity, poor reservoir physical
property, poor porosity and permeability correlation, but
strong heterogeneity.
(2) The Sha-3 Member reservoir develops mainly secondary
dissolution pores, as well as intergranular primary pores.
Dissolution pores include intergranular (intragranular) pores,
grain dissolution pores, and cement dissolution pores.
(3) The main reservoir diagenesis includes compaction,
cementation, metasomatism and dissolution. Calcium, silica,
iron, and argillaceous cements coexist. The dissolution occurs
mainly in the feldspar and carbonate cements, and
develops mainly the replacement of carbonate minerals towards
quartz and feldspar.
(4) The target stratum presents a diagenetic sequence, namely,
early cementation, early dissolution, authigenic
enlargement of quartz and feldspar, late cementation and late
dissolution. The diagenetic stage is equivalent to stage
A-B of the middle diagenetic phase, where, Stage A can be
subdivided again into sub-stages A1 and A2 at 3200
meters as the dividing line.
REFERENCES
[1] Tong Hengmao, Mi Rongsan, Yu tiancai, et al. The strike-slip
tectonization in the Western Liaohe Depression, Bohai Basin.
Acta
Geological Sinica, 2008, 82(8): 1017-1026
[2] Zhang Zhen, Bao Zhidong, Tong Hengmao, et al. Sedimentary
facie sang facies model of the 3rd member of Shahejie formation
in
the Western Sag, Liaohe Fault Basin. Geological Journal of China
Universities,2009, 15(3): 387-397
[3] Sun Hongbin and Zhang Fenglian. Structural-sedimentary
evolution characteristics of Paleogene in Liaohe
Depression.Lithologic
Reservoirs, 2008, 20(2): 60-66
[4] Meng Yuanlin,Gao Jianjun,Niu Jiayu,et al. Controls of the
fan-delta sedimentary microfacies on the diageneses in the south
of
western Liaohe Depression, Bohai Bay Basin. Petroleum
Exploration and Development, 2006, 33(1): 36-38
[5] Liao Chengjun, Zhang Fugong and Li Minggui. Reserches on
diagenesis of gravity flow body of Sha 3rd member in tertiary
in
Western Depression of Liaohe Basin. The South Petroleum Geology,
2004, 17(3): 17-20
[6] Meng Yuanlin, Gao Jianjun, Liu Delai, et al. Diagenetic
facies analysis and anomalously high porosity zone prediction of
the
Yuanyang area in the Liaohe Depression. Journal of Jilin
University(Earth Science Edition), 2006, 36(2): 227-233
[7] Er Chuang, Niu Jiayu, Gu Jiayu, et al. Main sediment types
and genesis of the third member of Shahejie formation(E2s3) in
the
Shuangtaizi Structural Belt, West Sag, Liaohe. Acta Geologica
Sinica, 2011,85(6):1028-1037
[8] Sun Suqing. Sedimetary characteristics and controlling
factors of Xibaqian fan of Shahejie formation, West Depression,
Liaohe
Basin[J]. Journal Of Palaeogeography, 2001, 3(2): 92-98
[9] Tian Wenyuan, Li Xiaoguang, Ning Songhua, et al. Study on
palaeogene sedimentary source in the south of Western
Depression,
Liaohe oilfield. Special Oil and Gas Reservoirs, 2010, 17(1):
45-48
[10] Ju Juncheng, Zhang Fenglian, Yu Guofan, et al. Depositional
characteristics and hydrocarbon accumulation of the third member
of
Shahejie formation reservoir in the southern West Depression,
Liaohe Basin. Journal of Palaeogeography, 2001, 17(1): 45-48
[11] Cui Xiangdong, Chen Zhenyan, Shen Weizhou, et al. Division
of diagenetic stage and its major control factors in clastic
rock
reservoirs of palaeogene middeep strata of Shuangtaizi River
mouth area. Journal of Oil and Gas Technology(J.JPI), 2006,
28(3):
42-46
[12] Sun Hongbin and Zhang Fenglian. Sandstone reservoirs
characteristics of the paleogene in Western Depression of Liaohe
Rift.
Journal of Palaeogeography, 2002, 4(3): 83-92