shale gas reservoir characterisation_a typical case in the southern sichuan basin of china

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Shale gas reservoir characterisation: A typical case in the southern Sichuan

Basin of China

Shangbin Chena,b,*, Yanming Zhua,b, Hongyan Wangc, Honglin Liuc, Wei Weic, Junhua Fanga

a School of Resources and Earth Science, China University of Mining and Technology, Xuzhou, Jiangsu 221116, Chinab Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, the Ministry of Education, China University of Mining and Technology,

Xuzhou, Jiangsu 221116, Chinac Langfang Branch, Petro China Exploration and Development Research Institute, Lang fang 065007, China

a r t i c l e i n f o

Article history:

Received 27 May 2011

Received in revised form

31 August 2011

Accepted 4 September 2011

Available online 4 October 2011

Keywords:

Shale gas

Reservoir characterisation

Southern Sichuan Basin

China

a b s t r a c t

The Lower Silurian Longmaxi Formation is an organic-rich (black) mudrock that is widely considered to

be a potential shale gas reservoir in the southern Sichuan Basin (the Yangtze plate) in Southwest China

A case study is presented to characterise the shale gas reservoir using a workow to evaluate its char-

acteristics. A typical characterisation of a gas shale reservoir was determined using basset sample

analysis (geochemical, petrographical, mineralogical, and petrophysical) through a series of tests. The

results show that the Lower Silurian Longmaxi Formation shale reservoir is characterised by organic

geochemistry and mineralogical, petrophysical and gas adsorption. Analysis of the data demonstrates

that the reservoir properties of the rock in this region are rich and that the bottom group of the Longmaxi

Formation has the greatest potential for gas production due to higher thermal maturity, total organic

carbon (TOC) enrichment, better porosity and improved fracture potential. These results will provide

a basis for further evaluation of the hydrocarbon potential of the Longmaxi Formation shale in the

Sichuan Basin and for identifying areas with exploration potential.

2011 Elsevier Ltd. All rights reserved

1. Introduction

With the severe energy shortage and high energy prices, shale

gas has recently been the focus of exploration in many countries

(Canada, Australia, Europe and other countries) [1], especially in

China. It is also an effective way to cope with the climate change

and to promote Chinas economic growth and the energy security

[2,3]. The global distribution of shale gas is not uniform. China is

known as one of countries that is relatively rich in shale gas

resources[4]. The recoverable shale gas resources are predicated to

be approximately 26 1012 m3 in China, which is close to the

28 1012 m3 in the USA[5]. To date, the exploration and devel-opment of shale gas reservoirs has lead to success in production in

the USA[6,7]. This success has resulted through a combination of

scientic study, engineering innovation, new technology and, in

some cases, persistence and risk taking. The related concepts and

technologies are now mature, and lessons can be drawn from the

experience of similar basins worldwide. However, basin (e.g.,

Texas) conditions are ideal and probably unrepeatable, and it is

difcult to arbitrarily apply a single genetic model of productive

shale gas in the USA to China. Consequently, a peculiar exploration

activity is required to ascertain the viability of subsequent devel-

opment projects. The development of shale gas has depended on

a combination of geological, geochemical, and engineering studies

[6]. Geological and geochemical evaluations are the most basic

tasks in the exploration and development of shale gas reservoirs

projects. Geological analysis has been identied and, to a certain

extent, has characterised the reservoir portions of shale

Geochemical data have proven essential for explaining shale

potential and observed patterns of productivity. Therefore, theLongmaxi Formation, in the southern Sichuan Basin, was analysed

in this study as a case of shale gas reservoir characterisation

because any high quality source rock should produce high quality

gas shale in theory, which often shows stratigraphic continuity and

a relatively simple structural architecture.

The Lower Silurian Longmaxi Formation in the southernSichuan

Basin has been studied as a source rock for many years[8e11]. This

area has become a potential hotspot as a shale gas system and has

been studied by several researchers in recent years [12e16]

Nevertheless, there are few authentic wells drilled for character-

ising the Silurian Longmaxi shale in detail. Changxin-1 is a shallow

* Corresponding author. School of Resources and Earth Science, China University

of Mining and Technology, Xuzhou, Jiangsu 221116, China. Tel.: 86 13585390796;

fax: 86 051683590998.

E-mail address: [email protected](S.B. Chen).

Contents lists available atSciVerse ScienceDirect

Energy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m/ l o c a t e / e n e r g y

0360-5442/$e see front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.energy.2011.09.001

Energy 36 (2011) 6609e6616
mailto:[email protected]://www.sciencedirect.com/science/journal/03605442http://www.elsevier.com/locate/energyhttp://dx.doi.org/10.1016/j.energy.2011.09.001http://dx.doi.org/10.1016/j.energy.2011.09.001http://dx.doi.org/10.1016/j.energy.2011.09.001http://dx.doi.org/10.1016/j.energy.2011.09.001http://dx.doi.org/10.1016/j.energy.2011.09.001http://dx.doi.org/10.1016/j.energy.2011.09.001http://www.elsevier.com/locate/energyhttp://www.sciencedirect.com/science/journal/03605442mailto:[email protected]



bored well completed in 2009 that was the rst shale gas well in

China. The well is located at Shuanghe town in Changning county,

which is within in the study area. China has now entered a new

basic research and exploration-development stage [17,18], and

some research and exploration works focussing on shale gas

reservoir conditions and favourable area evaluation have been

conducted in recent years. A robust characterisation of a gas shale

reservoir basically starts from geochemical, petrographical,

mineralogical and petrophysical analysis. The total organic carbon

(TOC) content/richness, thermal maturity, gas content, and litho-

logic (reservoir quality) data (mineral matter, porosity, perme-

ability and thickness) are also key parameters [6,7,19]. However,

special wells (or production history) to assess the reservoir are still

limited. Therefore, this study investigated the reservoir based on

collected basset samples.

2. Regional framework

The Changning-Xingwen region investigated in this study is

located at the margin of the southern Sichuan Basin. The Sichuan

Basin, located in the west of the Yangtze metaplatform tectoni-

cally, is a large tectonically stable and old oil-gas-bearing super-

imposed basin encompassing approximately 180 thousand square

kilometres in Southwest China. The strata is South China-type

stratigraphic, with a complete regional sedimentary rock

exposed from a Presinian system to a Quaternary system, whose

sedimentary cover thickness is approximately 6000e12,000 m

from the Paleozoic to Cenozoic. The total residual thickness of the

Silurian layer is approximately 0e1200 m in the southern Sichuan

Basin.

The Sichuan Basin is a prolic hydrocarbon region and is

currently Chinas largest gas-producing region. This basin has been

subject to petroleum and gas exploration for more than 50 years,

and several oil and gas elds have been found [20,21]. Great

breakthroughs have been made in oil and gas exploration in recent

years [22]. There are 106 gas elds and 14 oil elds with proven gas

reserves totalling 840 billion cubic metres (bcm) and an annual gas

and crude production reaching 12 bcm and 145 thousand tons,

respectively, in the basin [20]. These huge reserves are a conse-

quence of six different sourcerocks, ranging from the Cambrian and

Silurian through the Permian to the Triassic: the Lower Cambrian

(marine shale), Lower Silurian (marine shale), Lower Permian

(marine carbonate), Upper Permian (coal measures), Lower Jurassic

(lacustrine mudstone) and Upper Triassic (lacustrine and coal-

bearing mudstone), which can be summarised as four Lowers

and two Uppers. Dark pelitic rock and argillaceous limestone

constitute the four Lowers, and black pelitic rock and coal rock

constitute the two Uppers. The former four sets are mainly source

rocks in the basin [20,23,24]. Of the four formations, the Lower

Silurian marine shale (Longmaxi Formation) is more widespread

(Fig.1). The Longmaxi Formation (shale) distribution is determined

based on the depositional environment and the subsequent

erosional events related to the tectonic history.

A generalised Paleozoic stratigraphy for the southern Sichuan

Basin is shown in Fig. 2. An analysis shows that the Longmaxi

Formation is formed in a neritic shelf with a biased, stagnant

Fig. 1. Isopach map of the Longmaxi Formation in the southern Sichuan Basin (modied from[16]).

S.B. Chen et al. / Energy 36 (2011) 6609e66166610



marine sedimentary environment. The shale gas reservoir charac-

terised in this study is at the bottom group, called the Longmaxi

black shale, which is the most organically rich part of the Lower

Silurian. The Longmaxi Formation is present with a range of

229.2e672.5 m in thickness in the southern Sichuan Basin. The

lateral extent and thickness of the Longmaxi Formation (strati-

graphic) is stable in the Changning-Xingwen area, and the thick-

ness ranges from 200 to 300 m on the basis ofeld investigation

[16,25]. The stratigraphy consists of black shale, black and dark/

grey shale, dark grey shale, and silty mudstone, mainly comprising

carbonaceous and clay shale. The bottom of the Longmaxi Forma-

tion is rich in carbonaceous and various graptolites, and it has

widely distributed dispersions and berry-like grains of pyrite, even

if obvious stratication is spread on part of the layer.

3. Materials and methods

3.1. Samples and experimental protocol

There are a few wells that had been drilled previously to

discover conventional hydrocarbon-bearing (sandstone) layers in

the Silurian and Ordovician as the source rock, but not with the

specic aim of characterising this unconventional shale gas reser-

voir. Therefore, it is difcult to collect cores to better dene the

shale gas reservoir through experiments. This study, then, relied on

basset samples instead of cores. The fresh basset samples are

representative of a great extent in the main zone of interest. The

samples are necessary just to describe the unconventional reser-

voirs in terms of mineralogical, geochemical and petrophysica

characteristics. A relatively complete experimental program was

conducted and is listed inTable 1.

3.2. Experimental analysis description

To evaluate this unconventional hydrocarbon system, it is

important to understand the various organic and inorganic

geochemical processes controlling the generation, storage and

access to the trapped gas[19]. Organic geochemistry is essential todene the amount of gas generated by the shale system. The key

Fig. 2. Paleozoic stratigraphic column of the Sichuan Basin.

Table 1

Experimental program.

Test projects Laboratory

Mineralogy: X-ray diffraction Key Laboratory of Coalbed Methane

Resources and Reservoir Formation Process,

the Ministry of Education, China University

of Mining and Technology

Organic thermal maturity

Mercury (Hg) intrusion tests

Methane adsorption tests

Petrophysical analyses (Porosity)

Organic geochemistry (TOC) Petroleum Geology Experimental Center of

Research Institute of Petroleum Exploration

and Development, Zhongyuan

Oileld Branch

S.B. Chen et al. / Energy 36 (2011) 6609e6616 6611



factors affecting the total volume of hydrocarbons are the original

TOC and the kerogen type. In this study, the geochemical param-

eters include the determination of organic matter richness

(present-day TOC), a description of the organic matter type

(kerogen optical analyses - maceral composition), and determina-

tion of the thermal maturity (kerogen optical analyses - vitrinite

reectance). The type of organic matter can be determined visually

by means of transmitted light microscopy. The approach for the

maturity determination was optical. Vitrinite reectance is the

most common optical method, and it is performed through

a microscopic inspection of kerogen and an analysis of the reec-

tivity of the particles via a photomultiplier.

The mineralogical composition of the bulk powder samples and

the clay fraction was determined using X-Ray Diffraction (XRD). The

bulk mineralogy provides a quantitative estimate of the crystalline

components that are present in the shale and is related both to the

petrophysical and the friability properties of the rock itself. The

methodology is unable to reveal the non-crystalline components.

The TOC is obtained from the geochemical analyses, and the

percentages of minerals are corrected to approach 100% consid-

ering the TOC.

To evaluate this unconventional hydrocarbon system, it is

important to understand its porosity. A quantity of 200e

300 g of

gas shale material was necessary for this step. The samples were

weighed and the bulk volume was measured by mercury immer-

sion. The bulk density was then calculated. The sample was then

crushed, and the grain volume and grain density were measured.

A sorption analysis of gas shale is a critical element of reservoir

analysis. The volume of gasthat can be stored in the sorbed state is

a function of pressure and temperature. Because shale reservoirs

have microporous materials that have a small external surface

area, such as organic matter in mudrocks, the Type I (Langmuir)

adsorption isotherm is adaptive. The tests were conducted at the

reservoir temperature and pressures. The parameter of the Lang-

muir isotherm was calculated by tting the experimental data.

The Langmuir isotherm[26]can be written as: VE VLP/(PLP),

where VE is the volume of absorbed gas per unit volume of thereservoir in equilibrium at pressureP, VLis the Langmuir volume

(based on monolayer adsorption), which is the maximum sorption

(storage) capacity of the sample (absorbent) at innite pressure,P

is the gas pressure, and PLis the Langmuir pressure, which is the

pressure at which the total volume absorbed (storage capacity)

(VE) is equal to one half of the Langmuir volume. The gas

absorption tests were conducted on samples with different

amounts of TOC.

4. Results and discussion

4.1. Geochemical characterisation

A geochemical analysis was performed on basset samples rep-resenting approximately 270 m of the Lower Silurian Longmaxi

Formation, especially the bottom group. A relatively complete

geochemical characterisation of the Longmaxi Formation has been

revealed.

4.1.1. Organic carbon content

The TOC contents for the 75 samples measured in this study

range between 0.29 and 5.35% for the entire formation with a mean

value of 1.96%. Twenty-eight values among all samples are greater

than 2.0%, with mean value of 3.38%, which are mainly distributed

at the bottom of Longmaxi Formation. The rst shallow well

(Changxin-1) has cored a 153-m-thick black shale at the bottom of

the Longmaxi Formation, including a 10-m-thick carbonaceous

shale of the Upper Ordovician Wufeng Formation. The mean TOC of

the upper 110 m is 2%, whereas the mean TOC of 110e153 m is 6%

[27]. The accumulated thickness with a TOC much more than 2% is

80 m, which is similar to our test results.

The values increase with burial depth especially in the bottom

50 m (Fig. 3). A comprehensive analysis indicates that the TOC

values increase from the top to bottom of the Longmaxi Formation,

and the thickness is 50 m, at least, with 2.0% TOC values vertically.

The TOC value of the top layer is relatively poor.

The TOC must be the loss amount in the basset samples for

weathering. Ma et al. [28] conducted substantial experimental

research in both well samples and Earth surface (basset) samples

from Jianghan Basin in the Lower Yangtze region and the Guizhou-

Guangxi area. They concludedthat the loss ranged from 50% to 80%.

According to that result, the adjusted TOC values ranged from 0.44

to 8.03% (mean value 3.93%) by selecting a minimum of 50% as the

adjusted factor. Thus, the Longmaxi Formation, with its high

organic carbon content, is favourable for generating shale gas.

4.1.2. Organic matter type

The maceral and the carbon isotope of kerogen are favourable

classication parameters for source rock [29]. According to these

methods, the organic matter was classied as four types: sapropelic

(I), humic-sapropelic (II1), sapropelic-humic (II2) and humic (III)

(Table 2).

Some studies of the organic matter type of the Longmaxi

Formation have been conducted in this study area and adjacent

areas. The Kerogen d13C content of the Longmaxi Formation in the

southern Sichuan Basin has been reported by many scholars:30&

[26], 29.67& and 30.51&, respectively, in the Jianshen-1 well

[30]; and between 29.3& and 29.8& with a mean value

of29.6& [16]in Changning. In the southern Sichuan Basin and

northern part of the Guizhou province, the Kerogend13C content of

the Longmaxi Formation ranges from 28.7& to 30.4&, with

a mean value of29.4& [31]. From this perspective, the organic

matter type is I. Furthermore, although there are differences

between the maceral, other studies have also demonstrated the

organic matter type is I [29,32,33]. The source material of theorganic matter was composed mainly of varieties of algae (major

component), zooplankton, and fungi, forming a mostly amorphous

organic maceral [26,31,33]. Thus, the comprehensive analysis

through pre-existing studies shows that the organic matter type of

the Lower Silurian Longmaxi Formation is sapropelic (I), which has

a strong generation capability.

4.1.3. Thermal maturity

The thermal maturity was measured in 29 samples through

a microscopicinspection(by reected lightmicroscopy) in thisstudy.

The parameter is vitrinite-like material reectance (Rom), also called

marine vitrinite, which is derived in the marine sediment below the

Permian strata. The vitrinite-like material reectance can be the

Early Paleozoic maturity index [34]. Zhong etal. [35] established therelationshipbetween thevitrinite-like materialreectance(Rom)and

the equivalent vitrinite reectance (Ro). The relationship between

RomandRois shown in the following equations:

Ro 1.042Rom 0.052 (0.30% < Rom < 1.40%),

Ro 4.162Rom 4.327 (1.40% Rom < 1.60%),

Ro 2.092Rom 1.079 (1.60% < Rom < 3.0%).

Using the above arithmetic relationship, the vitrinite-like

material reectance (Rom) has been transferred into equivalent

vitrinite reectance (Ro), which was used for the reservoir evalua-

tion. The equivalent vitrinite reectance values were determined




between 1.85% and 3.3% with mean value of 2.69%, which showed

that the thermal maturity was at the (high) over-mature stage

(Ro>2.0%). The thermal maturity parameters suggest that the

Longmaxi Formation is in the (dry) gas generation window in the

study area. In the over-mature thermal stage, the source rock

mainly generates dry gas based on the principle of methaneaccompanied with a small amount of gas condensate.

Research [36]has shown that large quantities of gas may still

potentially be generated, primarily from the secondary cracking of

in-situ oils in the thermally over-mature areas. Similar to the Bar-

nett Shale, the principal source of gas in the prolic Newark East

Field is considered to be the secondary cracking of oil and bitumen

[7,37]. Consequently, the Longmaxi Formation has the greatest

potential for gas production due to the higher thermal maturity in

the area.

4.2. Mineralogical characterisation of the Longmaxi Formation

The mineralogical analyses were performed on the same

samples utilised for the TOCdetermination.The gas shale interval is

characterised by a marked heterogeneity over short distances. The

270-m-thick interval can be subdivided into multiple layers. This

paper employed the X-ray diffraction technique to qualitatively and

quantitatively analyse 39 samples collected from the southern

Sichuan Basin (Changning-Xingwen area), in the hope of nding

certain features of the Longmaxi shale mineral composition. Theresults show that the Longmaxi Formation has an extremely

complex mineral composition and that clay, quartz and calcite are

the main mineral compositions of the Longmaxi Formation, with

Table 2

Organic matter type classied by the maceral and the carbon isotope of kerogen

[29].

Organic matter type Carbon isotope

of kerogen(d13C) (&)

Maceral of kerogen

(TI value)

Sapropelic type (I) 80

Humic-sapropelic

type (II1)

29e27 40e80

Sapropelic-humic

type (II2)

27e25 0e40

Humic type (III) >e25



a mean content of 53.39% (range 16.8%e70.10%), 29.15% (range

16.2%e75.2%) and 5.46% (range 0.2%e19.3%), respectively. The

other mineral compositions are feldspar, dolomite, gypsum, pyrite,

siderite, chlorite, halloysite and traces of undistinguished amor-

phous substances, of which the average content was less than 5%. It

is suggested that all samples contain clay minerals composed of

illite, kaolinite, illite and a montmorillonite mixed layer. Illite is the

most common of the clay minerals, and it has the highest content,

ranging from 10.3% to 41.3% with a mean value of 24.49%. The

samples also contain kaolinite, illite, illite and a montmorillonite

mixed layer with ranges of 1.1%e18.1% (11.11%), 2.5%e10.4% (3.92%)

and 3.92% (2.5%e10.4%), respectively.

Clay minerals were also favourable for the formation and

development of the shale gas reservoir. The bottom of the Long-

maxi Formation, especially, which had a low content of illite and

chlorite and high porosity, is an important horizon for explorationand development. Because a reduced sedimentary environment

favours organic matter enrichment and preservation, it provides

good deposition conditions for shale gas. In addition, pyrite, in the

form of diagenetic crystals, was quite abundant, and pyrite abun-

dance is closely related to the presence of organic matter.

The formation is a lithologically complex interval of low

permeability that requires articial stimulation to produce, which

is closely correlated with the brittle mineral content. The thickness

of the bottom group of the Longmaxi Formation is more than 30 m,

and the quartz (brittle mineral) content is more than 50%.

Therefore, the bottom group of the Longmaxi Formation is the ideal

horizon for the exploration and development of the shale gas. The

mineral composition of a shale gas reservoir has important effects

on the shale gas, such as its adsorption and storage, fracture eval-

uation, seepage ow migration, and fracture-made seams. Theoverall composition is similarto that of the Barnett shales [37], with

a lower quartz content.

4.3. Petrophysical characterisation (porosity)

The integration of total porosity data (free gas potential) with

sorbed gas capacities provides a measure of the maximum poten-

tial gas capacity, which is used to determine the economic feasi-

bility of the shale gas reservoir[7]. A mercury porosimetry analysis

revealed that total the porosity ranges between 1.71% and 12.75%

for the 16 samples (Table 3) with a mean value of 4.3%.

In general, compaction reduces mudrock porosity with greater

burial depth and its associated higher temperatures and subse-

quent diagenesis [38]. However, the porosity increases with

increasing burial depth (Fig. 4), which must be related to the

mineral composition of the samples. The porosity has a signicant

positive correlation with the brittle mineral (including quartz and

calcite) content (R2 0.82, p < 0.01, Fig. 5) and a signicant

negative correlation with the clay mineral content (R2 0.81,

p < 0.01,Fig. 6). This correlation indicates that the brittle minerals

are primarily responsible for the porosity of the mudrocks and

shales. The organic matter secondarily contributes to the porosity

because the microporosity associated with the organic fraction

could not be measured (



4.4. Gas sorption capacity

To estimate the gas sorption capacity in situ, this study con-

ducted a methane adsorption experiment from 10 different depth

samples. The TOC of the 10 samples ranged from 1.07% to 4.67%.

Methane adsorption was measured at equilibrium pressure at

approximately 7 MPa and under reservoir temperature (30

C) atmoisture equilibration. The results show that the high-pressure

methane adsorption capacities (the adsorbed gas amount) for the

moisture-equilibrated Longmaxi shale samples varied from

0.42 cm3/g in the organic-poor sample (sample sx58, TOC 1.21%) to

1.13 cm3/g for the organic-rich sample (sample sx36, TOC 4.67%)

(Table 4). The Longmaxi had lower sorbed gas capacities, with

a mean value of 0.637 cm3/g. The methane isotherms showed

a Langmuir-type isotherm up to 8 MPa. From the isotherms, the gas

sorption increased rapidly at relatively low pressures, whereas the

sorption sites were continuously lled. The steep initial slope of the

isotherm was caused by the overlapping adsorption potential

between the pore walls, with the adsorbate gas molecule diameter

only slightly smaller than the pores [39]. The isotherm features

suggest the pores were accessible at lower pressures, althoughmicropores are the majority in Longmaxi.

The analysis also indicates that the sorption capacity increases

from the top to the bottom of the Longmaxi Formation, with

a maximum value of 1.13 cm3/g (Fig. 7). It is suggested that the

reservoir has a more promising sorption capacity at the bottom of

the Longmaxi Formation.Fig. 8shows a positive correlation (linear

relationship) between the TOC concentrations and the Langmuir

volume, which represents the volume of adsorbed gas capacities

(R2 0.58, p < 0.05). The results indicate that the organic matter

was in part responsible for adsorbing the gas, a conclusion similar

to that obtained by Ross and Bustin [7]. The greater sorbed gas

capacities of the moisture-equilibrated samples with increasing

TOC are due to micropores associated with the organic fraction

onto which the gas can adsorb. (the shale porosity of microporous

materials is classied according to size using the IUPAC classica-

tion: micropores (50 nm)).

5. Conclusions and future developments

The organic matter type of the Lower Silurian Longmax

Formation is sapropelic (I), which has strong generation potential. A

comprehensive analysis indicates that the TOC values increase from

the top to the bottom of the Longmaxi Formation, and there is a 50-

m-thick layer with high organic carbon (TOC values of 2%), which

favour the generation of shale gas. The Longmaxi Formation has the

greatest potential for gas production due to the higher therma

maturity in the region. Therefore, the Longmaxi Formation (espe-

cially the lower bench) has good shale gas potential in the southern

Sichuan Basin due to its high organic content, sapropelic quality

and high thermal maturity.The mineral composition of the shale gas reservoir has impor-

tant effects on the storage and development of shale gas. A more

than 30-m thickness at the bottom of the Longmaxi Formation has

a quartz content of more than 50%, which is an ideal geologic

horizon for the exploration and development of shale gas. The

porosity increases with the burial depth. The porosity has a signif-

icant positive correlation with the brittle mineral content and

a signicant negative correlation with the clay mineral content

Analysis also indicates that the sorption capacity of the shale gas

reservoir is strong at the bottom part of the Longmaxi Formation

Consequently, the bottom group of the Longmaxi Formation is the

ideal horizon for the exploration and development of shale gas in

the early stage.

Now that an integrated methodology to characterise a shale gas(unconventional) reservoir has been settled and tested, the work-

ow can be employed at other regions to produce an assessment o

the potential in an area of interest characterised by a substantia

vertical and lateral heterogeneity. Shale gas represents a potentially

enormous amount of unconventional gas resources in China. It is

suggested that research efforts should be enhanced and strategic

surveys and optimisation should be conducted as soon as possible

More wells should be drilled to acquire more accurate and detailed

data of the reservoir.

Acknowledgements

The authors would like to sincerely thank various organisations

for the continuous supply of funds; this work was jointly supported

Table 4

Sorbed gas capacities, TOC, and equilibrium moisture contents of Longmaxi

Formation samples taken from the study area, Langmuir volumes determined at

7 MPa.

Sample # TOC (%) Moisture (%) Langmuir volume(cm3/g)

sh13 1.07 1.79 0.47

sh08 1.18 1.96 0.51

sh05 1.11 2.17 0.43

sh03 1.28 1.75 0.84sx58 1.21 1.81 0.42

sx56 1.37 1.93 0.52

sx48 2.33 2.45 0.95

sx47 2.35 2.08 0.52

sx44 2.46 2.02 0.58

sx36 4.67 3.87 1.13

Fig. 7. Sorption capacity variation of the Longmaxi Formation in vertical.

Fig. 8. Correlation between sorption capacity and TOC content.

S.B. Chen et al. / Energy 36 (2011) 6609e6616 6615



by the Natural Science Foundation of China (No. 41072117), the

Major State Basic Research Development Program of China (973

Program) (No. 2012CB214702), and the Major Program of the

National Natural Science Foundation of China (No. 40730422).

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shale gas reservoir characterisation_a typical case in the southern sichuan basin of china

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