Pet.Sci.(2014)11:81-88 81 DOI 10.1007/s12182-014-0319-4

,QÀXHQFHRIPHDQGHULQJULYHUVDQGVWRQH DUFKLWHFWXUHRQZDWHUÀRRGLQJPHFKDQLVPV a case study of the M-I layer in the Kumkol 2LO¿HOG.D]DNKVWDQ

Wang Jincai, Zhao Lun , Zhang Xiangzhong, Tian Zhongyuan, Chen Xi and He Ling PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China

© China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2014

Abstract: In order to explore the influence of sandstone architecture on waterflooding mechanisms XVLQJWKHDUFKLWHFWXUHPHWKRGDQGWDNLQJDVDQH[DPSOHWKH0,OD\HURIWKH.XPNRORLO¿HOGLQWKH6RXWK Turgay Basin, Kazakhstan, we portrayed the architecture features of different types of sandstones and quantitatively characterized heterogeneities in a single sand body in meandering river facies. Based on the ZDWHUÀRRGLQJFKDUDFWHULVWLFVRISRLQWEDUVDQGDQGRYHUEDQNVDQGDFFRUGLQJWRZDWHUÀRRGHGLQWHUSUHWDWLRQ UHVXOWVLQZHOOVDQGQXPHULFDOVLPXODWLRQUHVXOWVRIZHOOJURXSVZH¿QDOO\DQDO\]HGWKHUHPDLQLQJ oil potential of the meandering river sandstone and pointed out its development directions at the high water cut stage. The result shows that because lateral accretion shale beds are developed inside single sand bodies, the point bar sand is a semi-connected body. The overbank sand is thin sandstone with poor connectivity, small area and fast lateral changes. The heterogeneity of the overbank sand is stronger than WKHSRLQWEDUVDQG7KHVDQGVWRQHDUFKLWHFWXUHVFRQWUROWKHZDWHUÀRRGLQJFKDUDFWHULVWLFV,QPHDQGHULQJ ULYHUVDQGVWRQHVWKHERWWRPRIWKHSRLQWEDUVDQGLVVWURQJO\ZDWHUÀRRGHGZKLOHWKHWRSRIWKHSRLQWEDU VDQGDQGPRVWRIWKHRYHUEDQNVDQGDUHRQO\ZHDNO\ZDWHUÀRRGHGRUXQÀRRGHG7KHWKLFNQHVVSHUFHQWDJH RIXQÀRRGHG]RQHDQGZHDNO\ZDWHUÀRRGHG]RQHLQSRLQWEDUVDQGLVDQGWKHUHPDLQLQJRLOLQLWVWRS part is the main direction for future development.

Key words:0HDQGHULQJULYHUSRLQWEDUVDQGRYHUEDQNVDQGDUFKLWHFWXUHFKDUDFWHULVWLFVZDWHUÀRRGLQJ characteristics

1 Introduction and evaluate reservoir heterogeneities. The research emphasis IURPRYHUVHDVVFKRODUVKDVEHHQPDLQO\RQÀXYLDOGHSRVLWLRQ The study of sandstone architecture began on meandering and modern sedimentary architecture (Miall and Jones, channel architecture in the 1980s by Miall (Miall, 1985), 2003; Scott et al, 2013; Fabuel-Perez et al, 2009; Davies and who proposed that some physical surfaces develop in channel Gibling, 2010), and in China, researchers obtained successful sands, with different formation mechanisms and different results on macro-sedimentary structures in sandstone hierarchies. These physical surfaces are flow barriers in reservoirs (Tan et al, 2013; Zheng et al, 2013; He et al, 2013), sandstone and cause the segregation of the remaining oil. carbonate reservoirs (Lin et al, 2004; Yang et al, 2010; Hu et After that, the method of sandstone architecture was widely al, 2012), deep-water turbidite reservoirs (Liu et al, 2013) and applied (Miall, 2002; 2006; Jiao et al, 2005; Kjemperud et al, ¿QHFKDUDFWHUL]DWLRQRIÀXYLDOUHVHUYRLUKHWHURJHQHLWLHVEDVHG 2008; Wu et al, 2008). The key point of sandstone architecture on architecture methods (Zeng, 2010). study is to recognize the subsurface palaeochannels. With Currently, many sandstone oilfields have been in the the appearance of the seismic sedimentology (Zeng et al, late development stage with high water cut and high degree 1998), seismic data are gradually becoming an important of recovery, and the remaining oil is highly fragmented mean to analyze the palaeochannels (Hart, 2008; Pranter but locally aggregated (Li et al, 2005; Zhong et al, 2010). et al, 2007; Zhang et al, 2011). The essence of sandstone 7KHUHIRUH¿QHO\FKDUDFWHUL]LQJKHWHURJHQHLWLHVLQVDQGERGLHV architecture research is to characterize sedimentary structures and subdividing sand bodies are of great significance for characterization of remaining oil distribution and enhancement *Corresponding author. email: [email protected] of oil recovery. We analyzed much published research and Received February 28, 2013 found that little research focused on the relationship between 82 Pet.Sci.(2014)11:81-88 architecture characteristics and waterflooding mechanisms. )LJ 7KHRLO¿HOGLVDODUJHDQWLFOLQDOVDQGVWRQHUHVHUYRLU In this study, we take meandering river sandstones of the M-I with moderate-strong edge and bottom water belonging to the OD\HURIWKH.XPNRORLO¿HOGLQ.D]DNKVWDQDVDUHVHDUFKXQLW lithologic-structural trap type. The target layers are the M-I using reservoir architecture methods we analyzed the internal and M-II zone sandstones of the lower Cretaceous Aryskum KHWHURJHQHLWLHVDQGTXDQWLWDWLYHO\HYDOXDWHGWKHZDWHUÀRRGLQJ Formation and the J zone sandstones (including secondary characteristics of single sand bodies, and we made it clear that layers J-I, J-II, J-III) of the upper Jurassic Kumkol Formation. VDQGVWRQHDUFKLWHFWXUHFRQWUROVZDWHUÀRRGLQJFKDUDFWHULVWLFV The M-I zone consists of meandering river deposits and the The research results have been successfully used in the M-II zone consists of braided river deposits, while J zone is development of the Kumkol oilfield, which will be very from delta front sedimentation. The reservoir has medium useful guidance for the future development of old oilfields properties with its porosity of 24%-30% and its permeability with high water cuts. of 170-800 mD. The oilfield has been in production since 1990, with reserves recovery of 47% and integrated water cut 2LO¿HOGVXPPDU\ RILQ7KHRLO¿HOGKDVHQWHUHGWKHKLJKZDWHUFXW The South Turgay Basin is located in the central part in and high recovery degree stage, but the daily oil production Kazakhstan, and is a Mesozoic rift basin which developed of new wells is about 1-206 t, with an average value of 30 t, from the Hercynian basement with the Karatau strike-slip fault and the integrated water cut is about 0-98% with an average developed within it (Yin et al, 2012). The Kumkol oilfield YDOXHRIZKLFKLQGLFDWHGWKDWZDWHUÀRRGLQJGLVWULEXWLRQ is located at the south depression of the South Turgay Basin within the oil layer is extremely heterogeneous.

01020 30km Tabakbulak

Sarylan Ashchisay

Aksay Graben

Uplift

Uplift Bozingen

Aryskum

Akshabulak

Graben

Graben

Graben Uplift

Uplift Graben

Oilfield Outcrop structure

Fault Strike-slip fault

Study area (Kumkol oilfield)

Fig. 17KHVWUXFWXUDOORFDWLRQPDSRIWKH.XPNRORLO¿HOG 3 Sedimentary microfacies and sandstone well. The lateral accretion shale beds are developed inside a single sand body, with a thickness of 0.2-0.6 m and gamma architecture of single sand bodies ray and micro-inverse resistivity logging curves are retured The M-I zone is divided into the M-I-1 and M-I-2 (Fig. 2(a)). Overbank sand is a thin sandstone layer with a secondary layers, in which five microfacies are developed: WKLFNQHVVRIDERXWPDQGLWVWRSDQGERWWRPDUHDOOXYLDOÀDW point bar, abandoned channel, final channel, overbank and PXGVWRQHVZLWKWKHORJJLQJFXUYHVEHLQJ¿QJHUVKDSHG )LJ DOOXYLDOÀDW3RLQWEDUVDQGDQGRYHUEDQNVDQGDUHWKHPDLQ  E $EDQGRQHGFKDQQHOVDQG¿QDOFKDQQHOVDUHWZRIRUPV reservoirs. RIRQHULYHUDWGLIIHUHQWSHULRGV7KH¿QDOFKDQQHOLVWKHODWH active waterway which will be abandoned eventually. In 3.1 Recognition of different types of single sand WKH.XPNRORLO¿HOGWKHDEDQGRQHGFKDQQHOVDUHDEDQGRQHG bodies gradually, and their bottoms are earlier depositional point bar sands and are about 2-4 m in thickness, while the mid- Integrating well logging and core data, single sand bodies VHFWLRQVDUH¿OOHGZLWKPXGDQGVLOWZLWKDWKLFNQHVVRIDERXW were recognized according to vertical deposition and planar 2-3 m. In logging curves, the part below abandoned channel distribution characteristics. Point bar sand is developed with shows a box shape, while abandoned channel itself shows positive rhythm features, with a thickness of 6-7 m in a single serrated shape or near shale line serrated shape (Fig. 2(c)). Pet.Sci.(2014)11:81-88 83

SP SP LLD SP LLD 140 253 MPZ 100 125 0586 162 010 mV mV ȍ.m mV ȍ.m Lithology 15U 5.5 Lithology Lithology GR GR LLS GR LLS 75 150 0 5 48 017 415 . API ȍ m API ȍ.m API ȍ.m

(b) Overbank sand, well 5007 (c) Abandoned(final) channel, well 101 (a) Point bar, well 1101

Coarse sandstone Fine sandstone Siltstone Muddy siltstone Mudstone

Fig. 2 Vertical characteristics of meandering river single sand bodies MPZ: micro electric resistivity; LLD: deep lateral resistivity; LLS: shallow lateral resistivity

In plane view, a point bar looks like a lens on the sand abandoned type, in which point bars developed in different thickness map, and the sand is thick and becomes thin at times are mutually superimposed and form complex channel abandoned (final) channel with a thickness of 1.5-2.5 m. sand bodies. It is of great importance to determine the Overbank sand develops far away from the main channel with boundary of point bars as well as to calculate the parameters a thickness of less than 2 m. The relative distance from the of point bars in architecture research. We selected a local top of single sand body to the top of layer is low in point bar complex channel sand body belt to semiquantitatively- VDQGZKLOHKLJKLQDEDQGRQHG ¿QDO FKDQQHO quantitatively characterize the point bar sand (Fig. 4). The parameters of the lateral accretion shale beds and the lateral 3.2 Sedimentary microfacies distribution of single accretion sand bodies were calculated. sand bodies in plane Firstly, the bankfull channel depth (h) of 6-7 m can be derived according to point bar sand thickness in a single well. From depositional outcrop and modern deposition, well Then, the single channel width (W) and single meandering logging and core data as well as seismic data, the planar belt width (W ) can be estimated using empirical formulas distribution characteristics of single sand bodies in different m of high-bending meandering rivers (Eqs. (1) and (2)) from sedimentary microfacies can be analyzed. In the M-I-1 layer, Leeder (1973). The result shows that W is about 100-140 m, DEDQGRQHGFKDQQHOVDQG¿QDOFKDQQHOVZHUHLGHQWL¿HG while W is about 800-1,100 m. in the plane view (Fig. 3), while in the M-I-2 layer those m numbers are 51 and 2 respectively. Because of the low (1) accommodation/sediment supply (A/S) ratio, the meandering log(:K ) 1.54log( ) 0.83 river frequently migrates, forming complex channel sand body 7.44 1.01 (2) belts. Point bar sand is bounded by abandoned channels and is ::m  WKHPDLQERG\RIWKHPHDQGHULQJULYHUZLWKÀDNHGLVWULEXWLRQ After that, the point bar width (W ) can be calculated and average thickness of about 6.5 m. The appearance of d according to an empirical formula (Eq. (3)) on the relationship abandoned (final) channels represents the end of the point between W and W presented by Wu et al (2008) with a value bars. Muddy deposits in abandoned (final) channels divide d of 600-800 m. point bars of different periods into independent units. When the river energy becomes weak, overbank sands are deposited (3) as thin sandstones at the side of the point bar approaching ::d 0.8531ln 2.4531 the alluvial flats. The overbank sands are poor reservoirs And then, the dip of the lateral accretion shale beds ( ) can developed outside the point bar sands, with small distribution ı be estimated by empirical formula (Eq. (4)) (Wu et al, 2008) areas and poor connectivity. with a value of 5º-6º. 3.3 Inside architecture and heterogeneity of single sand bodies :K 1.5 / tan(V )  (4)

In the research on meandering river sandstone Finally, the horizontal spacing of lateral accretion shale beds architecture, many scholars mainly characterized point bar of 50-60 m can be estimated through Eq. (5). sand according to modern depositional models of meandering rivers (Constantine et al, 2010; Pranter et al, 2007; Yue et al, /+ /tan(V ) (5) 2008), and established a geological concept model as well as summarizing empirical formulas for calculating architecture in which H is the thickness of a lateral accretion body, i.e., parameters, which have already reached a semiquantitative- vertical extension length, normally H=2h/3. quantitative degree, whereas studies on abandoned (final) The analysis of point bar sand architecture shows that channels and overbank sands are rare. We comprehensively when point bar sand deposits, lateral accretion shale beds analyzed the architecture and heterogeneity of all kinds of are deposited inclined to abandoned channels in single sand meandering river sandstones. bodies with the lateral migration of the river, and these shale The channels in this oilfield belongs to the frequent beds divide the point bar sand into several inclined lateral 84 Pet.Sci.(2014)11:81-88

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2014 2008 2004 2007 2003 Point bar Abandoned channel 2002

Final channel Overbank sand 5144000 Floodplain Well 5144000

692001 696001 700001 704001

Fig. 3 Sedimentary microfacies distribution map of a single sand body of the M-I-1 layer accretion sand bodies. The dip of the lateral accretion shale and mudstones, distributed parallel to the river bed, with poor beds is 5º-6º and their vertical occurrence frequency is 1-2. connectivity (Fig. 5(b)). Lateral accretion shale beds make the point bar sand only The architecture characteristics of meandering river a semi-connected body in the vertical direction. Single single sand bodies reveal both the internal heterogeneities sand bodies have independent, superimposed and cutting- and the spatial contact characteristics between different sand superimposed contacts with each other (Fig. 5(a)). Because ERGLHVZKLFKDUHUHÀHFWHGE\UHVHUYRLUSK\VLFDOSURSHUWLHV the characteristics of subsurface palaeogeological bodies are In the point bar sand, the average porosity value is 26%, very complicated, quantitative characterization of point bar and the average permeability value is 746 mD as well as the sand is only approximate. average variation coefficient is 1.29, with high degree of The part below abandoned channels which act as the heterogeneity. While in overbank sand, the average porosity boundary of the point bar is earlier formed point bar sand, value is 24% and the average permeability value is 319 mD ZKLOHDEDQGRQHGFKDQQHOVDUH¿OOHGZLWK¿QHGHSRVLWVWDNHQ DVZHOODVWKHDYHUDJHYDULDWLRQFRHI¿FLHQWLVZLWKSRRU by overbank flood due to relatively low water energy. The reservoir physical properties. Therefore, the heterogeneity abandoned channels divide point bars of different periods of overbank sand is stronger than point bar sand. Analyzing into disconnected or weakly connected units (Fig. 5(a)). from architecture elements, point bar is a semi-connected 2YHUEDQNVDQGVGHSRVLWZKHQZDWHURYHUÀRZVWKHULYHUEDQN body consisting of lateral accretion sand bodies and lateral and are mainly thin interbeds of fine sandstones, siltstones accretion shale beds, and abandoned channel is a barrier Pet.Sci.(2014)11:81-88 85

4021 4031 337 342 346 W 137 233 236 143 147 2046 4016 333 4022 302 343 11 231 102 201 144 2045 1013 A 2037 334 338

232 138 2044 1012 2036 1008 3008 134 335 A’ 4034

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1014 2042 1006 1010 2034 2026 2020 Wd 323 4033 2041 7 1009 2033 1005 2025 2048 2019 3002 3001 B 1003 4013 1004 2024 2032 1002 2018 2012

Point bar Abandoned channel Overbank sand

Fig. 4 Distribution map of local complex meandering sand bodies belt (Location seen in Fig. 3)

A A’ 102 201 2044 1012 2036 1008 SP GR LLSLLD GR N0.5M LLD SP GR LLSLLD SP GR LLSLLD SP GR LLS SP GR LLD N0.5M 1080 1080

1090 1100 1080 1080 1090 1090

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1084

1084 1094 (b) Overbank sand

Point bar Abandoned channel Overbank sand Lateral accretion shale beds

Fig. 5 Spatial architecture characteristics of meandering river single sand bodies (Location seen in Fig. 4) LLD: deep lateral resistivity; LLS: shallow lateral resistivity; N0.5M: micro lateral resistivity body consisting of fine deposits, while overbank sand is 4 Waterflooding characteristics and FRPSRVHGRI¿QHVLOWVDQGVZLWKSRRUSK\VLFDOSURSHUWLHV7KH architecture study shows that sandstone architecture controls controlling factors of single sand bodies its physical properties and heterogeneities. In meandering Waterflooding characteristics reflect the heterogeneity river sandstones, the heterogeneity degree of overbank sand inside sandstone, and single sand bodies from different is higher than that of point bar (Table 1). RULJLQVKDYHYDULRXVZDWHUÀRRGLQJFKDUDFWHULVWLFV The interpretation results of waterflooded zones of Table 1 Reservoir heterogeneities of meandering river single sand bodies meandering river single sand bodies in 367 wells show that WKHERWWRPRISRLQWEDUVDQGLVVWURQJO\ZDWHUÀRRGHGZKLOH Point bar Overbank sand its top is moderately waterflooded, weakly waterflooded, Porosity, % 26.0 24.0 or unflooded (Fig. 6(a)) with a low development degree. Permeability, mD 746 319 2YHUEDQNVDQGLVPRVWO\ZHDNO\ZDWHUÀRRGHGRUXQÀRRGHG (Fig. 5(b)), and the waterflood development degree is low. Variation 1.29 1.64 Water cut analysis in different levels of waterflooded zones FRHI¿FLHQW of single sand bodies shows that because the heterogeneity of Architecture Lateral accretion sand bodies, Fine-silty sand with poor overbank sand is relatively greater than that of the point bar elements Lateral accretion shale beds physical properties VDQGWKHDYHUDJHǻSw (the difference between initial water 86 Pet.Sci.(2014)11:81-88

S GR Res. LLS 1 iw 0 S S -65 0 1.5 6.51 w 0 1 iw 0 GR Res. ILD S 50 125 2.5 3.51 w 0

(b) Overbank sand, well 2117ST

(a) Point bar, well 4016

Oil Water Weak waterflooded Moderate and strong waterflooded

Sw: Current water saturation Siw: Initial water saturation

Fig. 6:DWHUÀRRGLQJFKDUDFWHULVWLFVRIPHDQGHULQJULYHUVLQJOHVDQGERGLHV LLS: shallow lateral resistivity; ILD: deep induction resistivity; Res.: logging interpretation result

saturation Siw and current water saturation Sw) in overbank properties, and its bottom would be strongly waterflooded sand is lower than that in point bar sand (Table 2). when injected water comes in, forming obvious advantageous passages. While the top of point bar sand is obstructed Table 2 Water cut analysis in different levels of waterflooded zones of by lateral accretion shale beds, it is difficult for injected single sand bodies water to sweep. Therefore, the top of the point bar sand is an advantageous area for producing remaining oil (Fig. Point bar sand Overbank sand 7(a)). Overbank sand is thin sandstone with poor physical Oil Weak Moderate Strong Oil Weak Moderate Strong properties, consisting of fine-silt sands and interbedded with alluvial flats. Therefore, overbank sand has narrow Sw 0.44 0.53 0.56 0.62 0.47 0.55 0.62 0.64 extension in plane view, fast lateral changes and poor Siw 0.43 0.36 0.27 0.25 0.45 0.35 0.35 0.32 connectivity, and the sweeping of injected water is greatly affected by the connectivity between different sand bodies, ǻS w 0.01 0.17 0.29 0.37 0.02 0.20 0.27 0.32 with low waterflooding degree (Fig. 7(b)). All these show (SwíSiw) that sandstone architecture controls its waterflooding characteristics. The heterogeneity inside single sand bodies shows The interpretation results of waterflooded zones in that several inclined lateral accretion shale beds divide the sidetracking wells confirmed that sandstone architecture point bar sand into lateral accretion sand bodies, which controls waterflooding characteristics. The sand of the are connected at the bottom and disconnected or weakly M-I-1 and M-I-2 layers in well 2117 was point bar sand connected at the top. The point bar sand has good physical and overbank sand respectively, which were interpreted as

(a) Point bar sand

(b) Overbank sand

Unwaterflooded Weak waterflooded Moderate-strong waterflooded Muddy deposits

Lateral accretion shale beds Injection well Production well

Fig. 7:DWHUÀRRGLQJSDWWHUQVRIPHDQGHULQJULYHUVLQJOHVDQGERGLHV Pet.Sci.(2014)11:81-88 87 original oil layers in 2000. In 2009, well 2117ST was drilled are better than those of the lower part. The reason why the about 18 m away from well 2117 as its sidetracking well. In lower part is waterflooded strongly while the upper part is well 2117ST, the middle-lower part of the point bar sand in waterflooded moderately is that lateral accretion shale beds WKH0,OD\HULVDVWURQJO\ZDWHUÀRRGHG]RQHDQGWKHWRS form barriers to the injected water flowing at the bottom SDUWLVDPRGHUDWHO\ZDWHUÀRRGHG]RQHZLWKDWKLFNQHVVRI of the moderately waterflooded zone. The M-I-2 layer is m. In logging curves, this point bar sand has anti-rhythmic a weakly waterflooded zone that reflects poor physical characteristics and the physical properties of the top part properties in architecture characteristics (Fig. 8).

2117 2117ST SP GR Res. ILD 75 150 50 150 14.5 Res. LLS 5 GR 15 0 10 M

H

1100 M-II-1 L

M-II-2

Point bar sand Overbank sand Lateral accretion shale beds Dry layer

Oil layer L Weak waterflooded M Moderate waterflooded H Strong waterflooded

LLS: shallow lateral resistivity; ILD: deep induction resistivity; Res.: logging interpretation result Fig. 8:DWHUÀRRGHGVLWXDWLRQRIROGZHOOVDQGVLGHWUDFNLQJZHOOV ,QRUGHUWRIXUWKHUYHULI\WKHLQÀXHQFHRIODWHUDODFFUHWLRQ its wide distribution area, point bar sand has great potential shale beds on remaining oil accumulation in point bar sand, for late development. While in overbank sand, the thickness the 302 well group is selected to build a 3D geological SHUFHQWDJHRIXQÀRRGHG]RQHDQGZHDNO\ZDWHUÀRRGHG]RQH mechanism model, in which the relative position between is 58%, and the strongly waterflooded zone is only 20.8%, injection well and oil well is perpendicular to the trend with a low waterflooding degree. However, overbank sand of lateral accretion shale beds. Based on this, numerical develops only at the places where the point bar approaches simulation was carried out to explore the influence of alluvial flats, with small area and low geological reserves, sandstone architecture on the sweep of injected water at so it has little development potential (Fig. 10). Therefore, the high water cut stage. The study shows that due to the IURPWKHGLVWULEXWLRQDQGZDWHUÀRRGHGVLWXDWLRQRIDOONLQGV existence of lateral accretion beds in the point bar sand, the of sands in meandering river, the top of point bar sand is the injected water is obstructed and the bottom of the sand body main direction for late stage development potential. forms obvious advantageous passages. The bottom of point bar sand is seriously waterflooded, while its top is weakly Unwaterflooded Weak waterflooded Moderate waterflooded Strong waterflooded waterflooded or unflooded, therefore the remaining oil is 100% mainly distributed at the top of the reservoir (Fig. 9). 30.5 80% 45.4 302 9.2 4022 60% 19.8 11.6 40% 22.3 40.6 20% 20.8

0% Oil saturation Point bar Overbank sand 0.15 0.28 0.42 0.55 0.69 Fig. 106WDWLVWLFVRIZDWHUÀRRGLQJIRUPHDQGHULQJULYHUVLQJOHVDQGERGLHV Fig. 9 Numerical simulation of the oil saturation of the point bar sand in the well group 302 (Fw=90%) 5 Conclusions 7KHWKLFNQHVVVWDWLVWLFVRIZDWHUÀRRGHG]RQHVDWGLIIHUHQW 1) The channels of the M-I zone in the Kumkol oilfield levels of meandering river single sand bodies in 367 belong to the frequently abandoned type, forming wide wells show that the thickness of the unflooded zones and complex channel belts in plane view. Lateral accretion shale weakly waterflooded zones is 40% and that of the strongly beds are developed inside the single point bar sand body, waterflooded zones is 41% in point bar sand. Because of inclined to the abandoned channels. The dip, horizontal 88 Pet.Sci.(2014)11:81-88 spacing and thickness of lateral accretion shale beds are 5°- Li Y, Wang D P and Liu J M. Remaining oil enrichment areas in ƒPDQGPUHVSHFWLYHO\7KHDEDQGRQHG ¿QDO  continental waterflooding reservoirs. Petroleum Exploration and channel is the boundary of the point bar and its bottom is Development. 2005. 32(3): 91-96 (in Chinese) earlier deposited point bar sands, while it is filled with fine Lin C S, Wang Q H, Xiao J X, et al. Depositional sequence architecture shale deposits. Overbank sand is thin sandstone with poor DQG¿OOLQJUHVSRQVHPRGHORIWKH&UHWDFHRXVLQWKH.XTD'HSUHVVLRQ Tarim Basin. Science in China Series D: Earth Sciences. 2004. reservoir physical properties. 47(Supp II): 86-96 2) The waterflooded interpretation of sidetracking Liu L, Zhang T S, Zhao X M, et al. Sedimentary architecture models of wells and numerical simulation results show that sandstone deepwater turbidite channel systems in the Niger Delta continental architecture controls waterflooding characteristics. When slope, West Africa. Petroleum Science. 2013. 10(2): 139-148 the water injection direction is perpendicular to the trend of Mia ll A D. Architectural-element analysis: A new method of facies lateral accretion shale beds, the bottom of the point bar sand analysis applied to fluvial deposits. Earth Science Reviews. 1985. LV¿UVWWRIRUPDGYDQWDJHRXVSDVVDJHVIRUWKHLQMHFWHGZDWHU 22(4): 261-308 and is seriously waterflooded, while its top part is weakly 0LDOO$'$UFKLWHFWXUHDQGVHTXHQFHVWUDWLJUDSK\RI3OHLVWRFHQHÀXYLDO waterflooded or unflooded because injected water cannot systems in the Malay Basin, based on seismic time-slice analysis. sweep the top section effectively. Overbank sand is weakly AAPG Bulletin. 2002. 86(7): 1201-1216 waterflooded or unflooded with poor reservoir physical Miall A D. Reconstructing the architecture and sequence stratigraphy of WKHSUHVHUYHGÀXYLDOUHFRUGDVDWRROIRUUHVHUYRLUGHYHORSPHQW$ properties. reality check. AAPG Bulletin. 2006. 90(7): 989-1002 3) The thickness statistics of waterflooded zones at Mia ll A D and Jones B G. Fluvial architecture of the Hawkesbury different levels of meandering river single sand bodies sandstone (Triassic), Near Sydney, Australia. Journal of Sedimentary in 367 wells in the Kumkol oilfield show that 40% of the Research. 2003. 73(4): 531-545 reservoir is weakly waterflooded or unflooded in point bar Pranter M J, Ellison A I, Cole R D, et al. Analysis and modeling of sand. The remaining oil is mainly distributed at the top of the LQWHUPHGLDWHVFDOHUHVHUYRLUKHWHURJHQHLW\EDVHGRQDÀXYLDOSRLQW point bar sand, which will be the main target for the future bar outcrop analog, Williams Fork Formation, Piceance Basin, development. In overbank sand, although 58% of reservoir is Colorado. AAPG Bulletin. 2007. 91(7): 1025-1051 XQÀRRGHGRUZHDNO\ZDWHUÀRRGHGWKHGHYHORSPHQWSRWHQWLDO Scott A, Hurst A and Vigorito M. Outcrop-based reservoir is low due to its small distribution area. characterization of a kilometer-scale sand-injectite complex. AAPG Bulletin. 2013. 97(2): 309-343 Acknowledgements Tan X C, Xia Q S, Chen J S, et al. Basin-scale sand deposition in the Upper Triassic Xujiahe Formation of the Sichuan Basin, Southwest This study is funded by the Major Program of PetroChina China: Sedimentary framework and conceptual model. Journal of (2011E-2506). Earth Science. 2013. 24(1): 89-103 Wu S H, Yue D L, Liu J M, et al. Hierarchy modeling of subsurface References palaeochannel reservoir architecture. Science in China Series D: Con stantine J A, McLean S R and Dunne T. A mechanism of chute cutoff Earth Sciences. 2008. 51(Supp II): 126-137 DORQJODUJHPHDQGHULQJULYHUVZLWKXQLIRUPÀRRGSODLQWRSRJUDSK\ Yan g X F, Lin C S, Yang H J, et al. Depositional architecture of the late GSA Bulletin. 2010. 122(5/6): 855-869 Ordovician drowned carbonate platform margin and its responses Davies N S and Gibling M R. Paleozoic vegetation and the Siluro- WRVHDOHYHOÀXFWXDWLRQLQWKHQRUWKHUQVORSHRIWKH7D]KRQJUHJLRQ 'HYRQLDQULVHRIÀXYLDOODWHUDODFFUHWLRQVHWV*HRORJ\   Tarim Basin. Petroleum Science. 2010. 7(3): 323-336 51-54 Yin W, Fan Z F, Zheng J Z, et al. Characteristics of strike-slip inversion Fab uel-Perez I, Hodgetts D and Redfern J. A new approach for outcrop structures of the Karatau fault and their petroleum geological FKDUDFWHUL]DWLRQDQGJHRVWDWLVWLFDODQDO\VLVRIDORZVLQXRVLW\ÀXYLDO significances in the South Turgay Basin, Kazakhstan. Petroleum dominated succession using digital outcrop models: Upper Triassic Science. 2012. 9(4): 444-454 Oukaimeden Sandstone Formation, central High Atlas, Morocco. Yue D L, Wu S H, Tan H Q, et al. An anatomy of paleochannel reservoir AAPG Bulletin. 2009. 93(6): 795-827 architecture of meandering river reservoir—a case study of Guantao Har t B S. Channel detection in 3-D seismic data using sweetness. AAPG )RUPDWLRQWKHZHVWWKEORFNRIWKH*XGRQJRLO¿HOG(DUWK6FLHQFH Bulletin. 2008. 92(6): 733-742 Frontiers. 2008. 15(1): 101-109 (in Chinese) He M, Jin Z K, Li T D, et al. Sedimentary microfacies and sand body Zen g H L, Henry S C and Riola J P. Stratal slicing; part II, real 3-D architectural analysis of Karamay Formation of Triassic in District I seismic data. Geophysics. 1998. 63(2): 514-522 ,,,.DUDPD\2LO¿HOG$FWD*HRORJLFD6LQLFD (QJOLVK(GLWLRQ  Zen g X P. Application of reservoir structure research in the fine 87(Supp): 554 exploitation of oilfields. Petroleum Exploration and Development. Hu X L, Fan T L, Gao Z Q, et al. Combination patterns and depositional 2010. 37(4): 483-489 (in Chinese) characteristics of Ordovician carbonate banks in the western Tarim Zha ng J H, Liu Z, Zhu B H, et al. Fluvial reservoir characterization Basin, China. Acta Geologica Sinica (English Edition). 2012. 86(4): and identification: A case study from Laohekou Oilfield. Applied 894-911 Geophysics. 2011. 8(3): 181-188 Jiao Y Q, Yan J X, Li S T, et al. Architectural units and heterogeneity Zheng Q F, Cao C Q and Zhang M Y. Sedimentary features of the of channel reservoirs in the Karamay Formation, outcrop area of Permian-Triassic boundary sequence of the Meishan section in .DUDPD\RLO¿HOG-XQJJDU%DVLQQRUWKZHVW&KLQD$$3*%XOOHWLQ Changxing County, Zhejiang Province. Science in China (Earth 2005. 89(4): 529-545 Sciences). 2013. 56(6): 956-969 Kje mperud A V, Schomacker E R and Cross T A. Architecture and Zho ng Y H, Zhao L, Liu Z B, et al. Using a support vector machine stratigraphy of alluvial deposits, Morrison Formation (Upper method to predict the development indices of very high water cut Jurassic), Utah. AAPG Bulletin. 2008. 92(8): 1055-1076 RLO¿HOGV3HWUROHXP6FLHQFH   Leeder M R. Fluviatile fining-upwards cycles and the magnitude of palaeochannels. Geological Magzine. 1973. 110(3): 265-276 (Edited by Hao Jie)