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Coexistence mechanism of multi-types of reservoir pressure in the Malang depression of the Santanghu basin, China Hao Xu a,n , Dazhen Tang a , Junfeng Zhang b a The Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education, China University of Geosciences (Beijing), Beijing 100083, China b PetroChina Exploration and Production Company, Beijing 100007, China article info Article history: Received 31 July 2012 Accepted 26 April 2013 Available online 15 May 2013 Keywords: reservoir pressure coexistence mechanism reservoir heterogeneity volcanic rock structure uplift Santanghu basin abstract This paper focuses on the distribution and coexistence mechanism of the various pressure systems in the Malang depression of the Santanghu basin, northeast of the Xinjiang Uyghur Autonomous Region, China. According to the classication standard of formation pressure, The calculated pressure coefcient showed that the Xishanyao Formation (J 2 x) is underpressured, the reservoirs of the Lucaogou Formation (P 1 l) are both normally and overpressured, and the Upper Pennsylvanian (C 2 ) presents the coexistence of a normally pressured system and an underpressured system. The permeability of the Xishanyao Formation (J 2 x) improve from the southwest to the northeast of the basin, resulting in a relatively easy uid supply to the reservoirs, and the pressure coefcient increases gradually. Tectonic uplift had a signicant inuence on the decrease in the reservoir pressure. However, a difference in sourcereservoir assemblages caused a difference in uid recharge and original pressure in reservoirs during hydrocarbon accumulation. The difference in reservoir connectivity causes a difference in the uid supply during later tectonic movement, nally leading to the formation of different pressure systems. Thus, the basic mechanism for the coexistence mechanism of the various pressure regimes in this area is the disequilibrium of the uid supply under the restriction of oil accumulation conditions. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Abnormal pressure is a common geological phenomenon in the petroliferous basins worldwide. In recent years, consistent with the discovery of the coexistence of abnormal underpressure, normal pressure and overpressure in numerous basins in China and other countries (Belitz and Bredehoeft, 1988; Corbet and Bethke, 1992; Bachu and Underschultz, 1995; Karsten and Stefan, 2001; Liu and Xie, 2002; Dai et al., 2003; Raymond, 2005; Wang and Chen, 2007), the distribution and controlling factors of these different pressure regimes has generated interest among petroleum geologists and engineers (Luo and Vasseur, 1992; Parks and Toth, 1995; Xie et al., 2003; Jeirani and Mohebbi, 2006; Kabir and Izgec, 2009). Previous investigation has been carried out on the genetic mechanism of low pressure and high pressure systems (Powley, 1980; Law and Dickinson, 1985; Hunt, 1990; Hao et al., 1995; Warbrick and Osborne, 1998; Neuzil, 2000; Hao, 2005; Xu et al., 2009). However, few studies explain why the various pressure types of regimes could coexist in the same basin and even in the same formation. The Santanghu basin lies in the northeast of the Xinjiang Uyghur Autonomous Region, China (Fig. 1). During more than 10 years of exploration and development, three series of main oil-bearing strata have been discovered in this area (Li and Zhang, 2000). However, the Malang depression of the Santanghu basin shows that multiple pressure systems coexist and that multiple types of reservoirs were produced together. The reservoirs are characterized by complex lithology and a high degree of heterogeneity. Previous investigations in this area have focused on the background geologic, hydrocarbon accumulations, reservoir characteristics and formation mechanisms of low-pressure Jurassic reservoirs (Tang, 1998; Li and Zhang, 2000; Sun et al., 2001; Liu and Liu, 2004; Zhang et al., 2009; Xu et al., 2010; Wen et al., 2011). Multidisciplinary and systematic studies on the above- mentioned issues are still required. This paper presents a comprehen- sive study of the distribution and reservoir properties, uid recharge and tectonic evolution of the Malang depression to ascertain the mechanism of coexistence of the various pressure types of reservoirs and to guide the exploration and development of oil reservoirs. 2. Geologic background The Santanghu basin presents two uplifts and one depression and can be divided into three tectonic units: the NE thrust fold belt, the central depression and the SW thrust fold belt. The central depression belt consists of four uplifts and ve Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/petrol Journal of Petroleum Science and Engineering 0920-4105/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.petrol.2013.04.017 n Corresponding author. Tel.: +86 10 82320106; fax: +86 10 82326850. E-mail address: [email protected] (H. Xu). Journal of Petroleum Science and Engineering 108 (2013) 279287

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Page 1: Journal of Petroleum Science and Engineering Hao... · mechanism of coexistence of the various pressure types of reservoirs and to guide the exploration and development of oil reservoirs

Journal of Petroleum Science and Engineering 108 (2013) 279–287

Contents lists available at ScienceDirect

Journal of Petroleum Science and Engineering

0920-41http://d

n CorrE-m

journal homepage: www.elsevier.com/locate/petrol

Coexistence mechanism of multi-types of reservoir pressure in theMalang depression of the Santanghu basin, China

Hao Xu a,n, Dazhen Tang a, Junfeng Zhang b

a The Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education, China University of Geosciences(Beijing), Beijing 100083, Chinab PetroChina Exploration and Production Company, Beijing 100007, China

a r t i c l e i n f o

Article history:Received 31 July 2012Accepted 26 April 2013Available online 15 May 2013

Keywords:reservoir pressurecoexistence mechanismreservoir heterogeneityvolcanic rockstructure upliftSantanghu basin

05/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.petrol.2013.04.017

esponding author. Tel.: +86 10 82320106; faxail address: [email protected] (H. Xu).

a b s t r a c t

This paper focuses on the distribution and coexistence mechanism of the various pressure systems in theMalang depression of the Santanghu basin, northeast of the Xinjiang Uyghur Autonomous Region, China.According to the classification standard of formation pressure, The calculated pressure coefficientshowed that the Xishanyao Formation (J2x) is underpressured, the reservoirs of the Lucaogou Formation(P1l) are both normally and overpressured, and the Upper Pennsylvanian (C2) presents the coexistence ofa normally pressured system and an underpressured system. The permeability of the XishanyaoFormation (J2x) improve from the southwest to the northeast of the basin, resulting in a relatively easyfluid supply to the reservoirs, and the pressure coefficient increases gradually. Tectonic uplift had asignificant influence on the decrease in the reservoir pressure. However, a difference in source–reservoirassemblages caused a difference in fluid recharge and original pressure in reservoirs during hydrocarbonaccumulation. The difference in reservoir connectivity causes a difference in the fluid supply during latertectonic movement, finally leading to the formation of different pressure systems. Thus, the basicmechanism for the coexistence mechanism of the various pressure regimes in this area is thedisequilibrium of the fluid supply under the restriction of oil accumulation conditions.

& 2013 Elsevier B.V. All rights reserved.

1. Introduction

Abnormal pressure is a common geological phenomenon in thepetroliferous basins worldwide. In recent years, consistent with thediscovery of the coexistence of abnormal underpressure, normalpressure and overpressure in numerous basins in China and othercountries (Belitz and Bredehoeft, 1988; Corbet and Bethke, 1992;Bachu and Underschultz, 1995; Karsten and Stefan, 2001; Liu andXie, 2002; Dai et al., 2003; Raymond, 2005; Wang and Chen, 2007),the distribution and controlling factors of these different pressureregimes has generated interest among petroleum geologists andengineers (Luo and Vasseur, 1992; Parks and Toth, 1995; Xie et al.,2003; Jeirani and Mohebbi, 2006; Kabir and Izgec, 2009). Previousinvestigation has been carried out on the genetic mechanism oflow pressure and high pressure systems (Powley, 1980; Law andDickinson, 1985; Hunt, 1990; Hao et al., 1995; Warbrick andOsborne, 1998; Neuzil, 2000; Hao, 2005; Xu et al., 2009). However,few studies explain why the various pressure types of regimescould coexist in the same basin and even in the same formation.

The Santanghu basin lies in the northeast of the Xinjiang UyghurAutonomous Region, China (Fig. 1). During more than 10 years of

ll rights reserved.

: +86 10 82326850.

exploration and development, three series of main oil-bearing stratahave been discovered in this area (Li and Zhang, 2000). However, theMalang depression of the Santanghu basin shows that multiplepressure systems coexist and that multiple types of reservoirs wereproduced together. The reservoirs are characterized by complexlithology and a high degree of heterogeneity. Previous investigationsin this area have focused on the background geologic, hydrocarbonaccumulations, reservoir characteristics and formation mechanisms oflow-pressure Jurassic reservoirs (Tang, 1998; Li and Zhang, 2000; Sunet al., 2001; Liu and Liu, 2004; Zhang et al., 2009; Xu et al., 2010; Wenet al., 2011). Multidisciplinary and systematic studies on the above-mentioned issues are still required. This paper presents a comprehen-sive study of the distribution and reservoir properties, fluid rechargeand tectonic evolution of the Malang depression to ascertain themechanism of coexistence of the various pressure types of reservoirsand to guide the exploration and development of oil reservoirs.

2. Geologic background

The Santanghu basin presents two uplifts and one depressionand can be divided into three tectonic units: the NE thrustfold belt, the central depression and the SW thrust fold belt.The central depression belt consists of four uplifts and five

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H. Xu et al. / Journal of Petroleum Science and Engineering 108 (2013) 279–287280

depressions, of which the Malang depression is the main areastudied in this work (Fig. 1).

The basement of the basin is of Pennsylvanian and Permian ages,and the caprock is largely of middle Cenozoic age (Xu et al., 2010). ThePennsylvanian strata consist mainly of marine mudstone and volcanicrock. The overlying strata of the Pennsylvanian strata is the Permianlacustrine mudstone, marl and volcanic rock. The Triassic and Jurassicstrata consist of fluvial and lacustrine deposits (Li and Zhang, 2000).The discovered oil reservoirs mainly exist in the volcanic rock of UpperPennsylvanian (C2), the mudstone and marl of Lucaogou Formation(P2l) of the Upper Permian and the fine sandstone of Middle Jurassic

Fig. 1. Location map of the Malang depression of the Santanghu basin, China.

Fig. 2. Schematic stratigraphy of the Malan

Xishanyao Formation (J2x). The source rock includes the marinemudstone of Upper Pennsylvanian and the lacustrine mudstone andmarl of Lucaogou Formation, respectively (Fig. 2). So, the LucaogouFormation (P2l) is the self-generation and self-storage reservoirs,while, the volcanic rock of Upper Pennsylvanian (C2) and the MiddleJurassic Xishanyao Formation (J2x) are the lower-generation andupper-storage reservoirs.

The structural evolution of the Santanghu basin can be dividedinto multiple stages, including extension after late Permian oro-genesis, compression at the end of Triassic, and subsidence in theearly to middle Jurassic and late Jurassic, and early Cretaceouscompression (Sun et al., 2001). In terms of the whole basin'sevolution, the two tectonic movements during the late Hercynianand late Yanshanian periods were the largest, and have thegreatest influence on the formation pressure.

3. Materials and methods

Reservoir pressure data derived from drill stem tests (DST) andpermeability test data in 30 wells in the Santanghu basin werecompiled. These data were taken from sandstone reservoirs in theXishanyao Formation (J2x), marl reservoirs in the Lucaogou Formation(P1l) and volcanic reservoirs in the Upper Pennsylvanian Formation(C2), which are the main targets for hydrocarbon exploration in thearea (Table 1). Water data from the different pressure reservoirs werecollected to represent a retained hydrogeological condition. To revealthe difference of different pressure reservoirs, observation and thedescription of core and slice were carried out.

4. Distribution characteristics of pressure systems

According to the classification standard of formation pressure, thereservoir whose pressure coefficient is less than 0.9 is a under-pressured system, whose pressure coefficient is between 0.9 and 1.1

g depression in the Santanghu basin.

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H. Xu et al. / Journal of Petroleum Science and Engineering 108 (2013) 279–287 281

is a normally pressured system, and whose pressure coefficient ismore than 1.1 is a underpressured system (Breeze, 1975; Fertl et al.,1994; Belonin and Slavin, 1998). The results show that the under-pressure in the J2x is the most significant, its calculated pressurecoefficient ranges from 0.63 to 0.84, and the pressure measurementsin the wells generally below the hydrostatic level. The calculated

Table 1Values of pressures and pressure coefficients measured in the D

Well Formation Pressure(Mpa)

M24 J2x 11.42M24 J2x 15.08M24 J2x 16.17M24 J2x 15.23M17 J2x 8.30M17 J2x 4.21M1 J2x 9.70M2 J2x 5.20M3 J2x 11.58M3 J2x 6.33M201 J2x 11.39M201 J2x 9.03M13 J2x 15.08M29 J2x 10.27M29 J2x 8.51M8 J2x 4.53N101 J2x 9.46N101 J2x 11.75N101 J2x 11.75N101 J2x 8.50M12 J2x 10.48M4 J2x 7.95M20 J2x 18.19M25 J2x 16.47M17 P2l 29.82M17 P2l 23.25M11 P2l 25.90M1 P2l 27.46M15 P2l 24.69M16 P2l 27.36M16 P2l 27.39M16 P2l 24.91M25 P2l 25.79M15 P2l 30.21M2 P2l 34.27M6 P2l 32.57M6 P2l 37.34M6 P2l 25.72M29 P2l 49.20M10 P2l 28.29M9 P2l 28.29M9 P2l 53.39Tc3 P2l 19.24M18 C2 13.73M18 C2 14.31M17 C2 22.05M17 C2 26.14M17 C2 14.89M20 C2 19.18M20 C2 13.39M21 C2 10.18M23 C2 12.28M23 C2 17.55M23 C2 19.83M19 C2 18.83M19 C2 10.87M19 C2 11.33M8 C2 17.42M801 C2 19.13Tc3 C2 33.86Tc3 C2 29.58M203 C2 5.23M26 C2 37.66M27 C2 10.96M31 C2 30.04

pressure coefficient of the P1l reservoirs ranges from 0.92 to 1.17,falling into the normal to high pressure range. Finally, the pressurecoefficient of the Upper Pennsylvanian (C2) ranges from 0.66 to 1.08,presenting two sets of pressure systems (normal pressure and lowpressure). In general, the reservoir pressure and pressure coefficientincrease with an increase of the buried depth in this area, which

STs in the Malang depression of Santanghu basin.

Pressure coefficient Depth(m)

0.8 1326.80.81 1733.50.81 1856.30.75 1889.00.84 919.20.83 467.70.63 1540.00.71 660.80.71 1500.00.72 816.30.71 1427.20.71 1175.50.77 1819.00.68 1220.00.7 1011.70.84 539.20.71 1187.70.72 1495.20.69 1583.00.73 1081.10.63 1550.00.66 1118.30.81 2075.00.73 2103.60.92 3000.50.94 2294.41.12 2170.01.16 2235.01.01 2268.51.1 2301.41.1 2310.01.11 2076.91.12 2177.01.01 2739.01.05 3100.01.08 2809.51.08 3290.01.07 2237.51.07 4274.01.17 2241.01.17 2250.01.16 4310.51.03 1738.81 1276.70.99 1340.30.9 2275.10.99 2454.80.96 1445.90.86 2058.60.69 1792.90.91 1035.30.66 1728.30.85 1918.80.87 2103.00.7 2512.00.7 1436.70.72 1451.50.89 1810.60.9 1964.01.08 2908.60.94 2939.60.68 713.00.94 3710.00.72 1421.31.04 2676.7

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H. Xu et al. / Journal of Petroleum Science and Engineering 108 (2013) 279–287282

indicates that the burial depth has great influence on the pressuresystem (Fig. 3).

The pressure coefficient of J2x generally increases from the SWthrust fold belt to NE thrust fold belt (Fig. 4), while the pressurecoefficient of P2l increases from the NE thrust fold belt to SWthrust fold belt (Fig. 5). In the Upper Pennsylvanian (C2), thepressure coefficient has no obvious trend.

Fig. 4. Pressure distribution counter of the Jurassic Xishanyao Formation in theMalang depression of the Santanghu basin.

5. The influence of fluid recharge on reservoir pressure

For the different pressure types, the pressure has a directrelationship with the relative content of fluid in the pores. Whenthe fluid is more than the capacity of pore volume and cannot bedischarged, it will produce high pressure (Michael and Bachu,2001; Webster et al., 2011). Conversely, if the amount of fluid inthe pore is low and cannot receive recharge, it produces lowpressure (Xu et al., 2009).

Hydrochemical characteristics can reveal the evolution of flowsystems and sealing properties of reservoirs (Xu et al., 2010, 2011a,2011b). Seventy-five water samples from the different pressurereservoirs are all of the CaCl2, MgCl2 and NaHCO3 type, representinga retained hydrogeological condition, which suggests that all thepressure systems are closed and that fluids have not flowed into orout of the reservoir (Hunt, 1990; Chilingar et al., 2002). Fluids in theclosed reservoirs of Santanghu basin are mainly originated from thehydrocarbon injection, therefore, the difficulty of hydrocarbon injec-tion will directly affect the reservoir pressure. The hydrocarboninjection in the lower-generation and upper-storage mode requires alarger hydrocarbon generating quantity and a higher displacementpressure than that in the self-generation and self-storage mode.Therefore, during structural reformation, a reservoir with a lower-generation and upper-storage mode will easily form a low pressuresystem, and a reservoir with a self-generation and self-storage modewill easily form normal and high pressure systems.

The hydrocarbon in the sandstone reservoirs of J2x and the volcanicrock reservoirs of C2 come from the mudstone of P2l and C2,respectively. The reservoirs of P2l belong to the self-generation andself-storage mode. The difference of the source–reservoir assemblagecauses the difference in fluid supply during hydrocarbon accumula-tion, finally leading to the formation of the different pressure systems.

The main cause of the high reservoir pressure in the P2lFormation (southwest of the Santanghu basin), is that this forma-tion has a greater thickness and burial depth and a higherhydrocarbon generation capacity (Fig. 6) (Liu and Liu, 2004).

0

1000

2000

3000

4000

5000

6000

0 10 20 40 5030 60

Dep

th (

m)

Pressure (Mpa)

Xishanyao FormationLucaogou FormationUpper Pennsylvanian

Fig. 3. Values of pressures (a) and pressure coefficients (b) measu

6. The influence of reservoir characteristics on reservoirpressure

6.1. Jurassic

The reservoirs of J2x in the Malang depression can be classifiedas low porosity and low permeability, having an average porosityof 11% and a permeability of 0.1�10−3–1�10−3 μm2. The variationcoefficient of permeability is the ratio of standard deviation andaverage value of permeability in the single layer, and the perme-ability ratio is the ratio of maximum and minimum, value, whichare the key parameters reflecting reservoir heterogeneity (Sunet al., 2007). These parameters range from 0.51 to 3 and from 10.2to 223.6, respectively, indicating that the reservoir heterogeneityof J2x is high. The variation coefficient of permeability andpermeability ratio have a trend opposite to the pressure coefficient(Fig. 7), which shows that reservoir heterogeneity is more sub-stantial, fluid recharge is more difficult, and the pressure coeffi-cient is lower. The sedimentary characteristics had a significanteffect on reservoir heterogeneity (Daniela and Claiton, 2010). TheJ2x was a set of braided river deltaic sediments, which originated

0

1000

2000

3000

4000

5000

6000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Dep

th (

m)

Pressure coefficient

Xishanyao FormationLucaogou Formation

Upper Pennsylvanian Underpressure line

red in the DSTs in the Malang depression of Santanghu basin.

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H. Xu et al. / Journal of Petroleum Science and Engineering 108 (2013) 279–287 283

from the southwest of the basin (Tang, 1998; Wen et al., 2011). Inthe south, the reservoir heterogeneity is significant because of theshort transport distance. Reservoir heterogeneity weakenstowards the northeast, and connectivity of the reservoir is alsoimproved, resulting in a relatively easy fluid supply to thereservoirs; therefore, the pressure coefficient increases gradually.

Fig. 6. Cross section A–A′ showing the stratigraphic distribution and er

0.7

0.8

0.9

y = -0.0006x + 0.7553

R2 = 0.54270.5

0.6

0 50 100 150 200 250

Pres

sure

coe

ffic

ient

Variation coefficient

Fig. 7. Relationship of the variation coefficient (a) and the rank difference (b) wi

Fig. 5. Pressure distribution counter of the Permian Lucaogou Fo

6.2. Permian

Based on the observations of cores and thin sections, thereservoir porosity of the Permian includes matrix pores andfractures. Matrix pores are mainly micropores, which have poorreservoir characteristics. The complex and various fractures

osion thickness in the Malang depression of the Santanghu basin.

0.7

0.8

0.9

y = -0.0584x + 0.7847

R2 = 0.5868

0.5

0.6

0 1 2 3 4

Pres

sure

coe

ffic

ient

Rank difference

th the pressure coefficient in the Malang depression of the Santanghu basin.

rmation in the Malang depression of the Santanghu basin.

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represent the main reservoir spaces of hydrocarbons. The width ofthe fractures ranges largely from 5 μm to 20 μm, which accountsfor 58.8%, followed by widths ranging from 20 μm to 60 μm(Fig. 8). Additionally, on the basis of the experimental results,the permeability of the fractures ranges from 10.4 to 14.5�10−3 μm2. However, the reservoir characteristics have no obviousrelationship with the distribution of pressure, probably becausethe Permian reservoirs are self-generation and self-storage reser-voirs and have more fluid recharge.

6.3. Pennsylvanian

The logging, cores and thin sections show that the Pennsylva-nian volcanic reservoirs include primary pores (vesicular andintergranular pores) (Lenhardt and Götz, 2011), secondary pores,

Table 2Characteristics of Pennsylvanian reservoirs in different pressure systems of the Malang

Well Depth(m)

Pressurecoefficient

Pore and fracture property

M26 3797–3817 0.92–0.94 Under the influence of faultsof volcanic rock are develop

M21 1122–1141 0.91 The matrix porosity of the vare 2 stages of fractures in thand the other is filled with

M23 1802–1835 0.66 The cores have no fractures,filled with zeolite.

Fig. 8. Histogram of fracture width of Lucaogou Formation in the Malang depressionof the Santanghu basin.

and fractures (dissolved pores, dissolution fractures and structurefractures), which are closely related to the reservoirs' pressure(Table 2). Isolated reservoir spaces, including pores and filledfractures, have lower reservoir pressure because of their difficultyin being recharged during tectonic uplifting. The open reservoirspaces, including the unfilled secondary interconnected pores andfractures, have normal reservoir pressure. It was easier to berecharged by fluids during tectonic uplift. Exploration results alsoshow that the degree of fracture development also has a goodconsistent relationship with well production rates.

7. Influence of tectonic uplift-erosion on reservoir pressure

Numerical simulation and case analysis indicate that duringuplift-erosion, the pressure drop of the strata in a closed statecaused by pore rebound and a decrease in fluid temperature haspositive correlation with erosion thickness. Tectonic uplift-erosionin the late Yanshanian period caused the pressure decrease of theJurassic reservoirs in the Santanghu basin to 11.6–17.1 MPa, whichis the main reason for the low pressure in the Jurassic reservoirs(Xu et al., 2010).

The influence of tectonic uplift-erosion on Permian reservoirpressure also occurred in the late Yanshanian period. During thisstage, with substantial fractures forming, pores rebounding andtemperatures dropping, reservoir pressure decreased. However,due to a high initial pressure caused by hydrocarbon generationand productivity of the source rocks which are still in thehydrocarbon generation stage (Xu et al., 2010), the Permianreservoirs are characterized by normal to high pressure.

depression (Santanghu basin).

Cores and rockthin section

around the well, the fracturesed.

olcanic rock is very low. Theree cores, the one stage is open,

calcite.

several micro-fractures are

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Table 2 (continued )

Well Depth(m)

Pressurecoefficient

Pore and fracture property Cores and rockthin section

2190–2240 0.84 The vesicles and several fractures are filled with zeolite.

M19 1520–1570 0.70–0.72 Cross-cutting micro-fractures are filled with zeolite. Thereare a few of vesicles and dissolved pores in the volcanicrock, and the vesicles are partially filled with zeolite.

M20 1877–1896 0.69 The volcanic rock has no fractures, the vesicles are filledwith zeolite.

M27 1478–1512 0.72 Vesicles and dissolved pores are developed

M17 1535–1547 0.96 Network fractures developed, and the cores arefragmented. There are many vesicles and dissolvation poresin the volcanic rock.

2541–2550 0.99 Dissolved pores, micro-fractures, vertical fractures and highangle fractures are developed.

M18 1326–1353 0.99 Vertical fractures and low angle fractures are developed.

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Two stages of tectonic uplift had significant influence on thepressure of the Pennsylvanian volcanic reservoirs. The first stagetook place in the late Permian, with maximum erosion in theeastern Malang depression exceeding 800 m (Fig. 6), which causeddecrease of pressure in the isolated Pennsylvanian Formationreservoirs. The second stage took place in the Late Cretaceous.In this period, the Santanghu basin underwent tectonic uplift,,with maximum erosion in the eastern Malang depressionapproaching 1200 m (Xu et al., 2010), causing the formationpressure of the isolated system to decrease substantially again.During this period, a large number of open fractures were alsogenerated, which resulted in normally pressure of reservoirs, withgood connectivity.

8. Conclusions

(1)

Oil reservoirs in the Malang depression of the Santanghu basininclude three series of pressure systems: the Jurassic lowpressure system, the Permian normal-high pressure systemand the Pennsylvanian low-normal pressure system. Amongthese systems, a difference in source–reservoir assemblagecauses a difference in fluid supply in reservoirs during hydro-carbon accumulation, leading to the formation of differentpressure systems.

(2)

As a consequence of the nature of sedimentary system,reservoir heterogeneity of the J2x weakens from the southwestto the northeast of the basin, resulting in a relatively easy fluidsupply to the reservoirs and the pressure coefficient increasesgradually.

(3)

Connectivity of the Pennsylvanian volcanic reservoir is closelyrelated to the reservoir pressure. Isolated reservoirs usuallypresent low pressure systems and open reservoirs usuallypresent normal pressure systems.

(4)

Two stages of tectonic uplift during the Late Cretaceous andLate Permian caused the pressure of Pennsylvanian andPermian reservoirs to decrease. Tectonic uplift during the LateCretaceous caused the pressure of the Jurassic reservoirs todecrease. However, due to a higher initial pressure and fluidrecharge, the Permian reservoirs now present normal to highpressure systems. The closed reservoirs of the Pennsylvanianand Jurassic present low pressure system due to lack of fluidrecharge. The open reservoirs of Pennsylvanian present nor-mal pressure system because of the recharge of fluid.

Acknowledgments

This project was supported by the National Natural ScienceFoundation of China (40802027), the Key Project of the NationalScience & Technology (2011ZX05034), and the Risk InnovationFoundation of PetroChina Co. Ltd. (0706d01040102).

References

Bachu, S., Underschultz, J.R., 1995. Large-scale underpressuring in theMississippian-Cretaceous succession, southwestern Alberta basin. Am. Assoc.Pet. Geol. Bull. 79, 989–1004.

Belitz, K., Bredehoeft, J.D., 1988. Hydrodynamics of Denver basin: explanation ofsubnormal fluid pressures. Am. Assoc. Pet. Geol. Bull. 72, 416–424.

Belonin, M.D., Slavin, V.I., 1998. Abnormally high formation pressure in petroleumregions of Russia and other countries of commonwealth of Independent States(CIS). In: Law, B.E., Ulmishek, G.F., Slavin, V.I. (Eds.), Abnormal pressures inhydrocarbon environments, 70. AAPG Memoir, Tulsa, OK, USA, pp. 115–121.

Breeze, A.F., 1975. Abnormal–subnormal Pressure Relationships in the MorrowSands of Northwestern Oklahoma. University Oklahoma p. 122. (M.Sc. thesis,Unpublished).

Chilingar, G.V., Serebryakov, V.A., Robertson, J.O., 2002. Origin and Prediction ofAbnormal Formation Pressures. Gulf Professional Publishing, The Netherlandsp. 233.

Corbet, T.F., Bethke, C.M., 1992. Disequilibrium fluid pressures and groundwaterflow in the Western Canada sedimentary basin. J. Geophys. Res. 97, 7203–7217.

Dai, L.C., Liu, Z., Zhao, Y., Zhang, S.W., Cai, J.G., 2003. Study on characteristics andorigin of abnormal high pressure and abnormal low pressure in Jiyangdepression. Earth Sci. Front. 10, 159. (in Chinese with English abstract).

Daniela, E.B., Claiton, M.S., 2010. Facies architecture and heterogeneity of thefluvialeaeolian reservoirs of the Sergi Formation (Upper Jurassic), Recôncavobasin, NE Brazil. Mar. Pet. Geol. 27, 1885–1897.

Fertl, W.H., Chapman, R.E., Hotz, R.F., 1994. Developments in Petroleum Science 38:Studies in Abnormal Pressures. Elsevier Science, The Netherlands pp. 12–16.

Hao, F., 2005. Kinetics of Hydrocarbon Generation and Mechanisms of PetroleumAccumulation in Overpressured Basins. Science Press, Beijing p. 406. (inChinese with English abstract).

Hao, F., Sun, Y.C., Li, S.T., Zhang, Q.M., 1995. Overpressure retardation of organic-matter maturation and hydrocarbon generation: a case study from theYinggehai and Qiongdongnan basins, offshore South China Sea. Am. Assoc.Pet. Geol. Bull. 79, 551–562.

Hunt, J.M., 1990. Generation and migration of petroleum from abnormally pres-sured fluid compartments. Am. Assoc. Pet. Geol. Bull. 75, 328–330.

Jeirani, Z., Mohebbi, A., 2006. Estimating the initial pressure, permeability andskin factor of oil reservoirs using artificial neural networks. J. Pet. Sci. Eng. 50,11–20.

Kabir, C.S., Izgec, B., 2009. Diagnosis of reservoir compartmentalization frommeasured pressure/rate data during primary depletion. J. Pet. Sci. Eng. 69,271–282.

Karsten, M., Stefan, B., 2001. Fluids and pressure distributions in the foreland-basinsuccession in The West-Central part of the Alberta basin, Canada: evidence forpermeability barriers and hydrocarbon generation and migration. Am. Assoc.Pet. Geol. Bull. 85, 1231–1252.

Law, B.E., Dickinson, W.W., 1985. Conceptual model for origin of abnormallypressured gas accumulations in low-permeability reservoirs. Am. Assoc. Pet.Geol. Bull. 69, 1295–1304.

Lenhardt, N., Götz, A.E., 2011. Volcanic settings and their reservoir potential: anoutcrop analog study on the Miocene Tepoztlán Formation, Central Mexico. J.Volcanol. Geothermal Res. 204, 66–75.

Li, W.M., Zhang, R.Y., 2000. Reservoir characteristics of composite petroleum systemin Santsnghu basin. Xinjiang Pet. Geol. 21, 275–278. (in Chinese with Englishabstract).

Liu, X.F., Xie, X.N., 2002. Origin and characteristics of under pressure systems inDongying depression. Oil Gas Geol. 23, 66–69. (in Chinese with Englishabstract).

Liu, Y.L., Liu, Y.Q., 2004. The distribution and significance of Lucaogou Formation ofPermian in Santanghu basin. Northwestern Geol. 37, 36–41. (in Chinese withEnglish abstract).

Luo, X.R., Vasseur, G., 1992. Contributions of compaction and aquathermal pressur-ing to geopressure and the influence of environmental conditions. Am. Assoc.Pet. Geol. Bull. 76, 1550–1559.

Michael, K., Bachu, S., 2001. Fluids and pressure distributions in the foreland basinsuccession in the west central Part of the Alberta basin, Canada: evidence forPermeability Barriers and Hydrocarbon Generation and Migration. Am. Assoc.Pet. Geol. Bull. 85, 1231–1252.

Neuzil, C.E., 2000. Osmotic generation of ‘anomalous’ fluid pressures in geologicalenvironments. Nature 403, 182–184.

Parks, K.P., Toth, J., 1995. Field evidence for erosion-induced underpressuring inUpper Cretaceous and Tertiary strata, west central Alberta, Canada. Bull. Can.Pet. Geol. 43, 281–292.

Powley, D., 1980. Normal and abnormal pressure. Lecture presented to AAPGAdvanced Exploration Schools, 1980–1987.

Raymond, P., 2005. A dynamic model for the Permian Panhandle and Hugotonfields, western Anadarko basin. Am. Assoc. Pet. Geol. Bull. 89, 921–938.

Sun, Z.M., Xiong, B.X., Li, Y.L., Qiang, H.H., 2001. Structural characteristics andfavorable belt for hydrocarbon exploration in Santanghu basin. Pet. Geol. Exp.23, 23–26. (in Chinese with English abstract).

Sun, S.W., Shu, L.S., Zeng, Y.W., Cao, J., Feng, Z.Q., 2007. Porosity–permeability andtextural heterogeneity of reservoir sandstones from the Lower CretaceousPutaohua Member Of Yaojia Formation, Weixing Oilfield, Songliao Basin,Northeast China. Mar. Pet. Geol. 24, 109–127.

Tang, Y., 1998. Reservoir characteristic of Xishanyao Formation of Middle Jurassic inNiujuanhu oilfield, Santanghu basin. Xinjiang Pet. Geol. 19, 493–497. (inChinese with English abstract).

Wang, Z.L, Chen, H.L., 2007. Distribution evolution of Upper Paleozoic fluid pressureand their effect on hydrocarbon accumulation in Shenmu-Yulin area. Sci. China(Ser. D) 37, 49–60.

Warbrick, R.E., Osborne, M.J., 1998. Mechanisms that generate abnormal pressure:an overview. In: Law, B.E., Ulmishek, G.F., Slavin, V.I. (Eds.), Abnormal Pressurein Hydrocarbon Environments, 70. AAPG Memoir, Tulsa, OK, USA, pp. 13–43.

Webster, M., O’Connor, S., Pindar, B., Swarbrick, R., 2011. Overpressures in theTaranaki basin: distribution, causes, and implications for exploration. Am.Assoc. Pet. Geol. Bull. 95, 339–370.

Wen, J., Yu, J.Y., Wang, L.Q., Zhang, Z.J., Wu, M.E., Yao, M.D., Luo, W., 2011.Sedimentary facies study on Ⅱ sand group of Jurassic Xishanyao Formation ofthe east region of Niujuanhu oilfield in Santanghu basin. J. Oil Gas Technol. 33,168–171. (in Chinese with English abstract).

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H. Xu et al. / Journal of Petroleum Science and Engineering 108 (2013) 279–287 287

Xie, X., Jiao, J.J., Tang, Z., Zheng, C., 2003. Evolution of abnormally low pressure andits implications for the hydrocarbon system in the southeast uplift zone ofSongliao basin, China. Am. Assoc. Pet. Geol. Bull. 87, 99–119.

Xu, H., Tang, D.Z., Zhang, J.F., Yin, W., Zhang, W.Z., Lin, W.J., 2011a. Factors affect-ing the development of the pressure differential in Upper Paleozoic gasreservoirs in the Sulige and Yulin areas of the Ordos basin, China. Int. J. CoalGeol. 85, 103–111.

Xu, H., Tang, D.Z., Zhang, J.F., Yin, W., Chen, X.Z., 2011b. Formation mechanism of low-pressure reservoir in Huatugou oilfield of Qaidam basin. J. Earth Sci. 22, 632–639.

Xu, H., Zhang, J.F., Jia, C.Z., Tang, D.Z., Yin, W., 2010. Influence of tectonic uplift-Erosion on formation pressure. Pet. Sci. 7, 477–484.

Xu, H., Zhang, J.F., Tang, D.Z., Yin, W., Chen, Y.P., Lin, W.J., 2009. The study status andtendency of low pressure. Adv. Earth Sci. 24, 506–511. (in Chinese with Englishabstract).

Zhang, J, Jia, C.Z., Xu, H., Tang, D.Z., Yang, F., Liu, Y.H., 2009. Controlling functionof feldspar dissolution for abnormal low-pressure in Jurassic reservoir ofSantanghu basin. Acta Petrolei Sinica 30, 33–37. (in Chinese with Englishabstract).