The genesis and prediction of dolomite reservoir in reef-shoal of Changxing Formation-Feixianguan Formation in Sichuan Basin

Journal of Petroleum Science and Engineering 178 (2019) 324–335

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The genesis and prediction of dolomite reservoir in reef-shoal of Changxing Formation-Feixianguan Formation in Sichuan Basin

T

Jingao Zhoua,b,∗, Hongying Dengb, Zhou Yub, Qi Guoc, Ru Zhangc, Jianyong Zhangb, Wenzheng Lib a

Key Laboratory of Carbonate Reservoir, China National Petroleum Corporation, China Petrochina Hangzhou Institute of Geology, China c China University of Petroleum, Beijing, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Sichuan basin Changxing formation Feixianguan formation Reservoir genesis Reservoir predict

In the past 20 years, great exploration achievements and new progresses have been made in Permian Changxing Formation(abbreviated as C.F.) and Triassic Feixianguan Formation(abbreviated as F.F.)in Sichuan Basin. The main results and progress include: (1)several gas fields, such as Puguang gasfield, Longgang gasfield, and so on are found; (2)C.F. and F.F. contain 3 third order sequence; (3)the reservoir mainly develop in reef shoal microfacies of platform margin; (4)the gasfields are lithologic pools distributed along platform margin. Although many common views have been achieved, the divergence of reservoir formation is still remained. Based on the study of petrology and diagenesis combined with the analysis datas, the basic reservoir characteristics, pore types and their genesis, dolomization and its influence of the C.F. and F.F. have been clarified in the paper. It is pointed out that the main lithology of the reef shoal dolomite reservoir in C. F. is residual bioclastic dolostone, residual reef framework dolostone and fine-medium crystalline dolostone. The reservoir spaces are dissloved pores and vugs,which formation is closely related to early meteoric water dissolution and shallow burial dolomization. The main lithology of oolitic dolomite reservoir in F.F. is residual oolitic micrite dolostone, residual oolitic silty-fine dolostone and fine crystal dolostone. The storege is mainly intergranular pore, oolitic moldic and their enlarged pore. The mineral composition of oolitic, early freshwater dissolution and dolomization are the main controlling factors of reservoir formation. It is predicted that the platform edge is the favorable distribution area of reef shoal and oolitic shoal dolomite reservoir.

1. Introduction In the past 20 years, great exploration achievements had been made in Permian Changxing Formation(P3ch, abbreviate as C.F.) and Triassic Feixianguan Formation (T1f, abbreviate as F.F.)in Sichuan Basin. Firstly, many large gas fields such as Dukouhe gasfield, Tieshanpo gasfield, Luojiazhai gasfield(Ran et al., 2005) and Puguang gasfield(Ma et al., 2005) had been discovered in the eastern platform edge of the Kaijiang-Liangping trough(wang Yigangang, 1998). With the breakthrough of well LG 1 in 2006, a number of large gas fields such as Longgang gasfield, Yuanba gasfield and Jianmen gasfield were found continuously along the western platform edge of Kaijiang-Liangping trough. It is believed that potential gas reserves of both edges along Kaijiang-Liangping trough would be reached to 1 × 1012 m3. This shows a great prospect of gas exploration of the C.F. and the F.F. reef shoal in Sichuan Basin. Also, the understanding of “paleogeography

∗

controls facies, facies controls reservoir, reservoir controls pool " and “one reef one pool, one shoal one pool” had been formed (Du et al., 2011). In the meantime, new research progresses had been made. Firstly, Chen Hongde (1999) established a brief sequence framework of Permian and Triassic, and Wang Yigang (2002), Zhou Jingao (2012), Xing Fengcun (2014) made a sequence subdivision of C.F. and F.F.. Secondly, Wang Shenghai (1992), Wang Yigang (2007) identified the trough of Kaijiang-Liangping and laid a foundation of lithofacies and paleogeography setting. Then, more researches of sedimentary facies were made by Xu Shiqi (2004), Ma Yongsheng (2006), Wei Guoqi (2006), Li Fengjie (2009), Zhou Jingao (2012), Guo Tonglou (2011) and Guo Xusheng (2010). Thirdly, Fan Jiasong (1982), Wang Yigang (2002), Yang Yu (2002), Wang Xingzhi (2002), Xu Shiqi (2004), Ma Yongsheng (2007), et al. paid great attention to the reef complex of C.F. and the oolitic shaol of F.F. as well as their distribution. Fourthly, many scholars made efforts to understand the reservoir origin. For examples,

Corresponding author. Key Laboratory of Carbonate Reservoir, China National Petroleum. Corporation, China. E-mail address: [email protected] (J. Zhou).

https://doi.org/10.1016/j.petrol.2019.03.020 Received 30 October 2018; Received in revised form 22 February 2019; Accepted 7 March 2019 Available online 12 March 2019 0920-4105/ © 2019 Published by Elsevier B.V.

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trough(Fig. 3). In the late Feixianguan period, the whole Sichuan basin became a broad and gentle carbonate platform and gradually evolved into an evaporative tidal flat environment because the KaijiangLiangping trough and the Yanting-Tongchuan platform depression were filled by sediments. According to our research, Six facices and sixteen subfacies have been identified based on the carbonate sedimentary mold(Wilson, 1975; Tucker, 1990). Their features can be summarized as Table 1. Whether it is Changxing period or Feixianguan period or Feixianguan period, the platform edges were favorable facies for the development of reef shoal and oolitic shoal. High quality reef shoal and oolitic shoal dolomite reservoirs mentioned below all developed in the platform margin.

Wang Yigang (2002) thought that mixed water dolomitization and buried dissolution are key factors of reservoir formation, and Chen Gengsheng (2005) and Yang Xiaoping (2006) suggested that seepagereflux dolomitization and buried dissolution are controlling factors, and Huang Sijing (2006,2007) emphasized the buried dolomitization. Of course, with further study, we found that facies and dissolution play a significant role in reservoir forming(Zhou Jingao,2012, 2015a, 2015b; Zhao et al., 2006; Shen et al., 2015). Although many progresses have been made, the divergence of reservoir forming is still remained. Due to the thought of reservoir forming is the basis of reservoir prediction, so, we focus on the reservoir characteristics, especially on the genesis and prediction in this paper in order to provide more details to understand the reservoir origin and reservoir prediction, to enhance the gas exploration effectively.

3. Reservoir characteristics 2. Background According to the exploration and research results, a variety of reservoir types were developed in the C.F. and the F.F.. But the high quality reservoirs are all reef shoal and oolitic shoal dolomite. The C. F. contains reef shoal dolomite reservoir, while the F.F. contains oolitic shoal dolomite reservoir. The differences between the two are explained below.

Sichuan basin, a large superimposed basin with area of 20 × 104km2, is located in the southwestern of China. Its basement is composed of volcanic and metamorphic rocks. Sedimentary cover has bilayer structure. Marine facies of the Edicarian to the middle Triassic which consists of carbonates, evaporates and shales. And the Late Triassic to the Quaternary continental clastic rocks are overlying marine facies. Only the Permian C.F. and the Triassic F. F. will be discussed in the paper. The C.F. consists of three sections which names as P3ch1, P3ch2 and P3ch3 from bottom to top. The P3ch1 is mainly a set of gray-dark gray micritic limestone with chert bands or nodules. The P3ch2 and the P3ch3 sections are gray medium-thick layer of bioclastic micrite, bioclastic limestone, reef framework limestone and dolomite. The F.F. consists of four lithologic sections which names T1f1, T1f2, T1f3 and T1f4 from bottom to top. The T1f1 section is argillaceous limestone and micritic limestone with oolitic dolomite, the T1f2 section is oolitic dolomite, the T1f3 section is micritic limestone with thin layer oolitic limestone, the T1f4 section is mainly argillaceous dolomite, anhydrite and mudstone. Vertically, the C.F. and the F.F. can be divided into 3 third order sequences(Fig. 1). The P3ch1 section is Transgressive system tract(TST), the P3ch2 and P3ch3 section are Highstand system tract(HST), which constitutes Sequence I. The T1f1 section (TST) and the T1f2 section (HST) constitute Sequence II. The T1f3 section (TST) and T1f4 section (HST) constitute Sequence III. The reef shoal dolomite reservoirs are mainly located in the P3ch2 and the P3ch3 section, while the oolitic shoal dolomite reservoirs are distributed in the T1f2 section. They are all located in the Highstand System Tract of platform edge. In the late Permian, the regional tension of Sichuan Basin was generated due to the Emei Taphrogenesis(Luo Zhili, 1981). Thus it caused and formed the paleogeographical background of three uplifts combined with three depressions. The three uplifts are Wanyuan-Kaixian uplift, JiangeYingshan uplift, Chengdu-Luzhou uplift. Meanwhile, the three depressions include Chengkou-Exi trough, Kaijiang-Liangping trough and Yanting-Tongchuan intraplatform depression. This ancient geographical patterns controlled the regional distribution of the sedimentary facies belts. During Changxing period, the three uplifts evolved into shallow water carbonate platform. The Chengkou-Exi trough and the Kaijiang-Liangping trough became deep water slope-basin environment(Yang et al., 2001). The Yanting-Tongchuan intraplatform depression became a relatively deep water intraplatform basin. Hundreds of kilometers of platform edge developed on the hinge zone of the Chengkou-Exi trough as well as the Kaijiang-Liangping trough(Fig. 2) from the early to the middle Feixianguan periods inherited the lithofacies paleogeography pattern of the Changxing period. The difference is that Wanyuan-Kaixian uplift evolved into isolated carbonate platform (previously known as evaporation platform(Wang et al., 2005)) with a salty lagoon inside. The edge of the platform is developed around the isolated platform and the western edge of the Kaijiang-Liangping

3.1. Petrological characteristics of the reservoirs The dolomite reservoir of the C.F. developed in the bioclastic shoal at the top of the organic reef vertically and distributed along the narrow platform edge on the plane. The main lithologies are crystalline dolostone, grain dolostone, residual bioclastic dolostone and residual framework dolostone. Crystalline dolostone is reformed from bioclastic shoal or reef core within reef complex by strong dolomitization and recrystallization. The dolomite crystalline is mainly subhedral-euhedral crystal with fine or medium crystal structure(Fig. 4A). These dolomites are dirty and some of them have foggy core bright edge structure(P. A.Scholle, 2003). A few remnants of bioclasts can be seen under microscope. Reservoir spaces are mainly residual dissolved pores. Their diameter ranges from 0.2 mm to 0.8 mm and plane porosity from 2% to 12%. Residual bioclastic dolostone is transformed from beach facies bioclastic limestone in the reef complex by strong burial dolomization. So, many bioresidue such as foraminifera, fusulinid, crinoid and brachiopoda (Fig. 4B)can be seen in residual bioclastic dolostone. The dolomite crystalline replaced from crinoids is huge, while those replaced from other bioclasts are generally fine. These dolomites are dirty and are usally subhedral-euhedral crystal, some of them have foggy core bright edge structure. And the dolomite crystals of cement metasomatic origin are clean and bright. The reservoir storages are mainly biological dissolution pores and biological moldics. Tectonic fractures can be seen partly. The residual framework dolostone was formed by the strong dolomitization of the reef core facies sponge-framework limestone. The identified reef-building organisms mainly include calcareous sponge, bryozoa, coral and algea. The dolomites of metasomatic origin from sponge pipe system are generally micrite. And those replaced from sponge bone and other biology are mostly silty or fine crystal. The openings are mainly biocoelomic pores, framework pores and their dissolve enlarged pores (Fig. 4C). These pores are mostly halffilled with dolomite, calcite and bitumen. The residual pore diameters are generally 0.1–0.6 mm with a maximum of 1.3 mm. The sizes of solution vugs range from 1 cm to 3 cm, plane porosity 2%–12%. The main lithology of oolitic shoal dolomite reservoir in the F.F. is crystal dolostone, residual oolitic micritic dolostone and residual oolitic fine-medium crystal dolostone. Crystal dolostone mainly consists of subhedral-euhedral dolomite with fine crystal structure, which size ranges from 0.15 mm to 0.40 mm. Most dolomite crystal facies are flat and some are curved. They are usually dirty. Sometimes foggy core bright edge structure can be seen (Fig. 4D). There are intergranular pores ranging from 0.1 mm to 0.2 mm. A few dissolution pores are 325

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Fig. 1. The stratigraphic column of the C.F. and the F.F.

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Fig. 2. Lithofacies paleogeography of Changxing period.

sometimes filled with authigenic mineral such as saddle dolomite, calcite and quartz. The residual oolitic micritic dolostone occured at the top of the sedimentary cycle and experienced strong dolomization. The oolite was replaced by the micrite-silty dolomite but the structure of ring fabric cement was well kept. Intergranular pores and oolitic moldics were well developed (Fig. 4E). Residual oolitic fine-medium crystal dolostone consists of oolites or particles. It well developed intergranular pores with a size of 0.5–2.0 mm. And the plane porosity ranges 5%–10% generally (Fig. 4F).

throat is simply slice-shaped throat. The throat diameter is between 0.1 and 0.5 μm, the porosity is from 3% to 19%, and the permeability is from 0.01mD to 100mD. The intrusive mercury curve has the shape of monoclinic, two-stage, low platform and high platform(Fig. 5 Right). It indicates that there are not only high quality reservoirs with large pore, but also poor reservoir with micropore as well as reservoir with dual porosity media.

3.2. Physical properties of the reservoir

4.1. Origin of the C.F. Reef shoal dolomite reservoir

The main storages of the reef shoal dolostone reservoir in the C.F. are mainly dissolved pores and vugs with a few biological coelom pores and reef framework pores. The throat types of reef shoal reservoir are mainly slice-shaped throat, cluster pore throat and intergranular porethroat by means of scanning electron microscope(SEM). Constricted pore throat and constricted neck throat also can be seen. The analysis datas show that the porosity of the dolomite reservoir of the C. F. is mainly between 3% and 13%. Permeability is mainly between 0.001mD-100mD, and most of them are about 1mD. The intrusive mercury curve shapes are mainly monoclinic and high platform(Fig. 5 Left). It indicates that the reservoir have various pore types and inhomogeneity of pore distribution. The main storage spaces of the oolitic shoal dolostone in the F.F. include intergranular pores, oolitic intragranular dissolved pores, oolitic moldic pores, a few vags and fractures. But some researches considered that the main storage spaces are the buried dissolved pores(Su Liping, 2005; Yang Xiaoping, 2006; Wang Siyi, 2006). The type of

The formation of reef shoal reservoir of the C.F. is mainly controlled by three factors: sedimentary microfacies, near-surface dissolution and burial dolomitization. “Facies control reservoir” is not only a typical characteristic of the C.F. reef shoal dolomite reservoir but also a general rule in the carbonate realm. Many relative cases had been reported. For example, it is considered that the Permian carbonate reservoirs in Guadalupe Mountains and Midland Basin of Texas are related to oolitic shoals, reefs and bioclastic shoals, and submarine fans(Sarg J.F.,1986; Kerans, C.,1994; Mazzullo, S. J.,1994a; Mazzullo, S. J.,1994b; Kerans, C.,1999; Kerans, C.,2002; Mazzullo, S. J.,1997). In the Gulf, A. A. M. Aqrawi (1998) points that“The best reservoir conditions in the Mishrif Formation occur in rudist-bearing facies, such as rudstones and rudistid packstone/grainstones”; and Moutaz Al-Dabbas(2010) also publishs that “High porosity indicates high-energy microfacies, intraparticles especially in rudist-rich microfacies of Mishrif Formation”; which reflect the same concept. In China, the Edicarian Dengying Formation microbial reservoirs and the Cambrian Longwangmiao Formation

4. Origin of the dolomite reservoir

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Fig. 3. Lithofacies paleogeography of Feixianguan period.

Table 1 Types of facies and subfacies and their features.

Carbonate Platform

Facies

Microfacies

Lithology characteristics

restricted platform

mixed tidal flat tidal flat evaporite lagoon restricted lagoon interbeach sea intraplatform oolitic beach intraplatform reef intraplatform bioclastic beach interbeach sea oolitic beach sand beach sandy oolitic beach reef bioclastic beach gentle slope steep slope basin(trough)

terrigenous clastic, purple micritic limestone, micritic dolomite, anhydrite micritic limestone, micritic dolomite, granular micritic limestone, algal micritic dolomite, anhydrite, salt marl, micritic limestone, micritic dolomite micritic limestone, micritic dolomite oolitic limestone, arenaceous limestone, granular dolomite biolimestone, biodolomite bioclastic limestone, bioclastic dolomite micritic limestone, micritic dolomite, oolitic micritic limestone oolitic limestone, oolitic dolomite arenaceous limestone, arenaceous dolomite oolitic limestone, oolitic dolomite, arenaceous limestone, arenaceous dolomite biolimestone, biodolomite bioclastic limestone, bioclastic dolomite micritic limestone, argillaceous limestone micritic limestone, argillaceous limestone micritic limestone, argillaceous limestone, mudstone, brecciated limestone

open platform

platform margin

slope Basin (trough)

on the top of reef complex, and the reef core microfacies. The reasons are that the platform edge is located in the higher position of ancient landform with stronger hydrodynamic condition that lead to rapid growth and accumulation of reef shoal. As soon as the sea level drops, the build up will be exposed to atmosphere and be eroded and dissolved by meteoric water, which cause the formation of dissolved pores and dissolved vugs. These openings become the main storages, and also provide material foundation and seepage condition for burial dolomitization and burial dissolution.

graindolomite reservoirs in Sichuan basin, the Ordovician Lianglitage Formation reef-shoal limestone reservoirs in Tarim basin are also controlled by facies (zhou Jingao, 2015a; Zhou Jingao, 2015b; Shen et al., 2015). So, the “facies controls reservoir” has been a common view. As for the C.F. reservoirs in Sichuan Basin, taking Longgang gas field as an example, it is characterized by reef shoal. According to more than 20 well data, the dolomite reservoirs develop in platform margin reef-shoal instead of other facies, like slope, basin, intraplatform lagoon. The high quality reservoirs are closely related to the bioclastic shoal microfacies 328

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Fig. 4. The reservoir characteristics of the C.F. and the F. F. in Sichuan Basin. A: Fine-medium crystal dolomite with intercrystalline pores which are partly filled by asphalt. Well LG2, 6130.71 m Chanxing Formation, single polarized light, blue cast. B: Residual bioclastic dolomite with intergranular dissolved pores and intragranular dissolved pores. Well LG2, 4231.83 m, Chanxing Formation, single polarized light. C: Residual sponge framework dolomite with vugs and biocoelomic pores. Well Y12-2, 4795.85 m, Chanxing Formation. D: Fine crystal dolomite with intercrystalline pores and intercrystalline dissolved pores. Well LG001-1, 6012.42 m, Feixianguan Formation, single polarized light, blue cast. E: Residual oolitic dolomite with intercrystalline dissolved pores. Oolites are replaced by fine crystal dolomite. There are asphalt membrane on pore wall. Well LG 001-1, 6013.91 m, Feixianguan Formation, single polarized light, blue cast. F: Residual oolitic micritic dolomite with oolitic moldic pores and intercrystalline dissolved pores. Geopetal structure can be seen in oolite. Well LG 21, Feixianguan Formation, single polarized light, blue cast. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

frequency sea level change. Fig. 6B and C show that a large number of dissolved pores and cavities can been seen on the cores of Well LG26, Well LG2 and Well LG82. Further microstudies of thin sections under microscope indicate that these pores are mainly aragonitic bioclastic moldics, biological coelom pores and solution cavities(Fig. 6B, C). It belong to fabric selective dissolution which may support penecomtemporaneous dissolution origin(Melim, 2002; Horbury, 1989; Saller,A.H.,1989; Zhou et al., 2012). These pores are preserved after burial dolomization and become the main interstice. Burial dolomitization is very important for the preservation of

Near-surface dissolution is a key factor for the formation of the pores in reef shoal dolostone. It is associated with the high frequency sea level change and sequence boundary exposure at the end of Changxing period. Here are two examples for the near-surface dissolution. One is related to the sequence boundary exposure from outcrop of Yanggudong in northeast Sichuan. Fig. 6A shows that there are many bedding distribution dissolved cavities(3-20cm size), can be found on the upper part of C.F., about 30 m under the unconformity between the C.F and the F.F.. These vags are usually explained as the result of paleokast(Wright, V.P., 1991). The other is related to high

Fig. 5. The reservoir average capillary pressure curve of the C.F. (Left) and F.F.(Right). 329

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Fig. 6. Diagenesis Characteristics of the C.F. and the F.F. A:Middium to thick banded limestone bearing bioclasts. Bedding distributed vugs partly filled by calcite are considered as origin of near surface dissolution. The rocks are located on the upper part of the C.F. nearby the boundary of the Permian and the Triassic. Yanggongdong Profile, northeastern of Sichuan basin. B: Residual bioclastic dolomite. The crystallines present subhedral-euhedral with foggy core bright edge structure. Bioclastic moldic pores can be seen with filling of seepage silts and bitumen. Well LG12,6496 m, the C.F., single polarized, blue cast. C: Residual bioclastic dolomite. The crystallines present subhedral-euhedral with foggy core bright edge structure. Most storages are bioclastic moldic pores, some are intercrystalline pores. A few bitumen can be seen in pores. Well LG26, 5763 m, the C.F., single polarized, blue cast. D: Bioskeleton limestone. The fibrous sea water calcite cement is precipitated in the lattice holes firstly, then silty-fine crystalline dolomite, hydrocarbon filling(Black bitumen at present) thirdly, Polycrystalline calcite finally. Well LG 001-1, 6176.10 m, the C.F., single polarized light. Stained. E:. Fine crystalline dolomite, subhedral-euhedral, foggy core bright edge structure. Residual dissloved poresdeveloped. Under cathodoluminescence, dolomite emit strong orange-red light. Well LG2,6130.21 m, The C.F., CL. F: A typical upper toward shallow subsequence of the T1f2 on the western side of Kaijiang-Liangping trough. Bottom part of the subsequence consists oolitic pisolite limestone, the middle composed of oolitic limestone with weak dolomitization and a few intragranullar pores, the upper is oolitic dolostone with enlarged intergranullar pores, intragranullar pores, oolitic moldic pores and vugus. The top is sequence boundary between SQⅡ and SQⅢ. Near surface dissolution is considered as origin of the pores and vugs. Yudongliang Profile, the F.F., western Sichuan basin. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

dolomitization occurs in shallow buried environment and the supply of Mg2+ may come from seawater through thermal convection(Kohout, 1967; Mullins, 1985) and compaction. Buried corrosion can improve reservoir performance. There are three stages of buried dissolution. Stage I is related to the dissolution of organic acids during the hydrocarbon expulsion period. It mainly expanded the early pores and formed some dissolution pores, vugs and dissolved fractures. The subsequent oil filling and evolution resulted in

reservoir pores. Petrologic studies show that the dolomitization occurs after the cementation of seawater and before the first phase of hydrocarbon filling (Fig. 6D). The analysis datas of dolomite show that the Mg2+/Ca2+ ratio is high with an average of 1.056. Stable carbon and oxygen isotopes (Fig. 7) and strontium isotope (Fig. 8) show that the dolomitization fluid is related to Permian seawater. Fig. 6E shows that dolomite crystalline emits strong orange red light under the cathodoluminescence. All these characteristics reflect that the 330

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Fig. 7. Whole rock carbon and oxygen isotope distribution map of C.F.(Left) and F.F.(Right).

Fig. 8. Distribution of

87

Sr/86Sr of the C.F. and the F.F. dolomite in Longgang area.

(Fig. 6F), oolitic moldic pores are usually distributed in the intertidalsupertidal facies at the top of the shoal body while intergranular pores are distributed in the main part of the shoal body. However, the bottom of the shoal body is generally composed of oolitic limestone or pisolite limestone, which lacks pores due to tightly cementation. The key factors for the formation of oolitic intragranullar pores are the mineral composition of oolite and the early dissolution of fresh water. Early Triassic is the transition period from the aragonitic sea to the calcite sea(Moore, C. H.,1986), which can produce both aragonitic oolites and calcite oolites. The mineral stability of aragonite and calcite is different. When oolite shoal is exposed to atmosphere environment, unstable aragonitic oolite can be easily dissolved and produce dissolved pores under the action of meteoric water(Moore, C. H.,2001), at the same time, fabric calcite cements are precipitated in the neighbor. It results in a large number of oolitic intragranullar dissolved pores including oolitic moldic pores were developed, and the intergranular pores were significantly reduced or even completely filled due to the calcite cementation. Calcite oolite is relatively stable. It is not easy to dissolve under the meteoric water. No dissolution means no precipitation. So, the intergranular pores are well preserved in calcite dominated oolitic shoal body. Dolomitization is an important constructive factor for pore preservation. There are many views on the dolomitization of the F.F.(Mu et al., 1994; Chen et al., 2005; Zhao et al., 2006; Wang et al., 2007; Huang et al., 2007; Gao et al., 2007; Zheng et al., 2008). According to the comparison of the oolitic shoal dolostone between the eastern and

the existence of asphalt in these pores, vugs and cracks. StageⅡoccurred in the period that oil cracked into gas. The process may be related to thermochemical sulfate reduction(TSR) and may form some supersize solution pores(Zhu et al., 2006). Stage III was related to tectonic fractures. Some dissolution pores melted along tectonic fractures illustrate the existence of such dissolution. And the dissolved phenomenon can be observed from cores of well LG2 and well LG82. Burial dissolution could expand and transform the previous pores, whose contribution is less than 10% of total porosity and cannot form reservoir separately. 4.2. Formation of the F.F. Oolitic shoal dolomite reservoir The formation of platform marginal oolitic shoal dolomite reservoir of the F. F. is controlled by both sedimentation and diagenesis. Sedimentary facies, oolitic mineral composition, near surface dissolution and dolomitization are the key factors. "The platform edge facies control the reservoir" is an important feature of the development of oolitic shoal dolostone reservoir in the F.F.. Outcrop and drilling show that the oolitic shoal dolomite reservoir mainly developed along the platform edge. Out of platform edge, oolitic shoal dolomite reservoir did not developed although the existence of oolitic shoal. Another feature of “the sedimentary facies control the reservoir” is that the oolitic intergranular pores formed from deposition are the main interstice of the reservoir, which is also reflected in that microfacies control the pore type and pore distribution. Take the profile of Yu dong liang as an example, in an upward shallow subsequence 331

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Fig. 9. Prediction map of the C.F. reef shoal dolomite Reservoirs.

well LG 001-1 shows that the accumulation of the thickness is 23 m. Micro research shows that the dolomitization mentioned above took place by means of metasomatism, which effectively protected the original structures of rock including intergranular pores and dissolved pores formed earlier. The important result of dolomitization is to enforce the rock strength as well as reduce both pressolution and cementation so that it can save the pores. Former geologists believed that the burial dissolution is the key factor to the formation of Feixianguan reservoir(Yang et al., 2006; Wang et al., 2006; Zeng et al., 2002)12,13,52. But many petrology evidences mentioned above revealed that burial dissolution only effected in the pores formed earlier. It did improve the performance of the reservoir but it cannot form the reservoir on its own.

the western edge of the Kaijiang-Liangping trough, the dolomitization mechanism is different due to the difference of sedimentary background on both sides of the trough. The eastern side of the trough is an isolated evaporation platform and the oolitic shoal is adjacent to the anhydrite and salt layer, which has the geological condition of seepage-reflux dolomization(Adams, 1961; Illing, L.V.,1965; Land, L.S.,1973; Shinn, E.A.,1964; Scholle, P.A.,1974; Huang et al., 2006). Researches show that dolomitization occurred from the penecontemporaneous to shallow burial period, before the oil filling and after the precipitattion of fabric cement. From the well P3 located in the center of evaporating lagoon to the well Lj6 located in the platform edge, the percentage of oolite dolostone became less and less, the dolomitization became weaker, and the δ18O of oolite dolomite showed the tendency of declination (Fig. 7B). Strontium isotope is related to homologous seawater(Mu et al., 1994; Huang et al., 2007). All these evidences support the seepage reflux dolomitic model. Because of the enough fluid of high Mg2+ and the comparatively completed dolomitization, the thickness of dolomite reservoir was usually thicker, ranging from 50 m to 60 m, and the largest thickness of Puguang area reaches to 200 m. The F.F. oolitic shoal is adjacent to micrite limestone in the west side of the trough, which lacks the background of seepage reflux of high Mg2+ brine. The shoal body start dolomitization only when it is exposed to meteoric atmosphere by the sea level falls or sedimentary self-cycle. According to the analysis data, 41 samples show the ratio of Mg2+/Ca2+ in dolomite is generally low, in the range of 0.833–1.085 and at the average of 0.985. Strontium isotope is same as homologous seawater(Fig. 8). And the cathodoluminescence is dim. These indicates that the dolomitization may be carried out by capillary concentration and the source of Mg2+ is mainly provided by the sea water brought by tidal(Sibley, D.F. Land, L.S.,1983; Zenger, D.H.,1980; Sibley, D.F.,1987). Because of the short time exposure of the shoal body, the dolomitization is comparatively weaker. Dolostone is lentoid and its thickness is small. The thickness of dolomite in Yudongliang area varies from 6 m to 8 m and

5. Reservoir prediction 5.1. The prediction of the C.F. Reef shoal dolomite reservoir The analysis of reservoir genesis state that the reef shoal dolomite reservoir of C.F. developed in platform edge. To be specifically, it developed in the shoal microface on the top of reef shoal complex, especially on the top of third reef cycle. So, finding out reef shoal body means finding the reservoir. Also the formation of the reservoir could be affected by the meteoric dissolution and dolomitization which was related to the ancient higher landform. Based on this specialty we found the predict method by combining the sedimentary facies and paleogeomorphology: Using the seismic amplitude attributes to predict the distribution of reef shoal body,while using the seismic layer-leveling and time-thickness method to reconstruct paleogeomorphology. Then, we can foretell that the high quality reservoirs are distributed in higher paleogeomorphology reef shoals with strong dolomitization; that poor quality reservoir are lied on lower paleogeomorphology reef soals with weak dolomitization or not. The prediction result is shown as Fig. 9 332

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Fig. 10. Prediction map of the F.F. oolitic shoal dolomite Reservoir.

with the favorable area of 4000 Km2. It shows that the distribution of high quality reservoirs(yellow zone) is similar to the platform margin. And the poor quality reservoir distribute as same as intraplatform reef shoal(red zone) and intraplatform bioclastic shoal facies(green zone).

lithologies of oolitic shoal dolomite reservoirs in F.F. are mainly residual oolitic micrite dolostone, residual oolitic silty-fine crystalline dolostone and fine crystalline dolostone. The main storages are intergranular pores, intragranular pores and their expanding pores and vugs. The porosity varied from 3% to 19%, and the permeability varied from 0.01mD to 100mD. The formation of the C.F. platform margin reef shoal dolomite reservoirs and the F.F. oolitic shoal dolomite reservoirs is controlled by both sedimentary facies and diagenesis. The “facies control on reservoir” is the key factor, which is the basis formation of the primary pores such as reef framework pores, biocoelomic pores and oolitic intergranular pores. Near surface dissolution is an important factor for the formation of secondary pores such as biological moldic pores, oolitic intragranular pores and vugs. The dolomitization not only increases the strength of the rock but also reduces the presdissolution and buried cementation, which is beneficial to the preservation of pores. Otherwise, buried corrosion also improves the reservoirs. The platform edge is the favorable distribution area of reef shoal and oolitic shoal dolomite reservoirs. According to the comprehensive prediction of geology and geophysics, the distribution area of the C.F. reef shoal dolostone reservoir is about 4000 Km2 and the area of F.F. oolitic shoal dolostone reservoir covers 5000 Km2. It is the direction for future exploration.

5.2. The predict of the F.F. Oolitic shoal dolomite reservoir The reservoir prediction method of the F.F. is similar to the C.F.. The oolitic shoal is determined by using “bright spot”, which is moderate to strong seismic amplitude attributes reflection. After calibration between well logging and thin sections, logging datas and seismic attributes are used to predict the percentage of dolomite on the plane. The oolite shoal which contains more than 85% dolomite is the favorable reservoir. So it is predicted that the favorable distribution area of oolitic shoal dolostone reservoir is about 5000 Km2 (Fig. 10). As Fig. 10, the oolitic shoal dolomite reservoir mainly developed in the Longgang platform edge on the west side of Kaijiang-Liangping trench and in the isolated evaporation platform edge on the east side. The reservoir thickness of Longgang platform edge varied from 20 m to 50 m. Meanwhile, the reservoir thickness of isolated platform edge varied from 50 m to 100 m, the thickest thickness reaches to 300 m. That revealed the eastern platform edge reservoir is better than the western. 6. Conclusion

Acknowledgements The main lithologies of reef shoal dolomite reservoirs in C.F. are residual bioclastic dolostone, residual reef framework dolostone and fine-medium crystalline dolostone. Organic matter is stored in solution pores, the porosity varied from 3% to 13%, and the permeability mainly varied from 0.001mD to 100mD with the 1mD as main value. The main

We are grateful to PetroChina who funds our research projectsand to the Key Laboratory of Carbonate Reservoir, China National Petroleum Corporation who provides equipment and services for experimental analysis. We really appreciate Dr. Zhang Jianyong, Master 333

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Hao Yi, Master Gu Mingfeng, Master Pan Liyin, Master Zhang Jie, Dr. Li Chang who made contributions to the accomplishment of all projects, including outcrop survey, logging interpretation, facies analysis and diagenesis. We thank Moore, C. H. for his helpful suggestions of diagenesis during the thin section discussion. We are truly grateful to Dr. Tahar AIFA for his advices, and to the editors and reviewers. Thanks all.

daxian-xuanhan area, sichuan province, south China and constraint for the reservoirs of natural gas. Earth Sci. Front. 14 (1), 182–192. Mazzullo, S.J., 1994a. Dolomitization of peri-platform carbonates (lower permian, leonardian), Midland Basin, Texas. Carbonates Evaporites 9, 95–112. Mazzullo, S.J., 1994b. Lithification and porosity evolution in Permian peri-platform limestones, Midland Basin, Texas. Carbonates Evaporites 9, 151–171. Mazzullo, S.J., S, L., 1997. Montgomery. Permian ‘‘Wolfcamp’’limestone reservoirs; powell ranch field, eastern Midland Basin: discussion and reply. AAPG (Am. Assoc. Pet. Geol.) Bull. 81, 1750–1755. Melim, L.A., westphal, H., Swart, P.K., Eberli, G.P., Munnecke, A., 2002. Questioning carbonate diagenetic paradigms: evidence from the Neogene of the Bahamas. Mar. Geol. 185, 27–53. Moore, C.H., 2001. Carbonate Reservoirs: Porosity Evolution and Diagenesis in a Sequence Stratigraphic Framework. Elsevier, Amsterdam, pp. 444. Moore, C.H., Chowdhury, A., Heydari, E., 1986. Variation of ooid mineralogy in Jurassic Smackover Limestone as control of ultimate diagenetic potential. AAPG (Am. Assoc. Pet. Geol.) Bull. 70, 622–628. Moutaz, Al-Dabbas, Jassim, Al-Jassim, Saad, Al-Jumaily, 2010. Depositional environments and porosity distribution in regressive limestone reservoirs of the Mishrif Formation, Southern Iraq. Arab J Geosci 3, 67–78. Mu, Shuguang, Zhou, Mao, Hua, Yongchuan, 1994. Dolomite genetic types in feixianuan formation of lower triassic series in northeast area of sichuan. Nat. Gas. Ind. 14 (3), 23–27. Mullins, H.T., Wise Jr., , Land, L.S., 1985. Authigenic dolomite in Bahamian peri-platform slope sediment. Geology v13, 292–295. Ran, Longhui, Chen, Gengsheng, Xu, Fenren, 2005. Discovery and exploration of Luojiazhai gas field, Sichuan basin. Mar. Origin Petrol. Geol. 10 (1), 43–47. Saller, A.H., Moore Jr., C.H., 1989. Meteoric diagenesis, marine diagenesis, and microporosity in pleistocene and oligocenes, enewetak atoll, Marshall Islands. Sediment. Geol. 63, 253–272. Sarg, J.F., Lehmann, P.J., 1986. Facies and Stratigraphy of Lower–Upper San Andres Shelf Crest and Outer Shelf and Lower Grayburg Inner Shelf, Publication, vols. 86–25. Permian Basin Section SEPM, Midland, Texas, pp. 9–35. Scholle, P.A., Kinsman, D.J.J., 1974. Aragonite and high-Mg calcite caliche from the Persian Gulf—a modern analog for the Permian of Texas and New Mexico. J. Sediment. Petrol. 42, 195–204. Scholle, P.A., Ulmer-Scholle, D.S., 2003. A Color Guid to the Petrography of Carbonate Rocks: Grains, Textures, Porosity, Diagenesis. AAPG Memoir. Shen, Anjiang, Zhao, Wenzhi, Hu, Anping, She, Min, Chen, Yana, Wang, Xiaofang, 2015. Major factors controlling the development of marine carbonate reservoirs. Petrol. Explor. Dev. 42 (5), 545–554. Shinn, E.A., Ginsburg, R.N., 1964. Formation of recent dolomite in Florida and the Bahamas (abs.). Amer. Assoc. Petrol. Geol. 48, 547. Sibley, D.F., Gregg, J.M., 1987. Classification of dolomite rock textures. J. Sediment. Res. 57, 967–975. Su, Liping, Luo, Ping, Luo, Zhong, et al., 2005. Characteristics of Feixianguan Formation oolitic shoal reservoirs in northeast Sichuan basin. Nat. Gas. Ind. 25 (6), 14–17. Tucker, M.E., Wright, V.P., 1990. Carbonate Sedimentology. Blackwell scientific publication, Oxford, pp. 482. Wang, Shenghai, Qiang, Zitong, 1992. Upper permian jiangshuigou reef in huaying mountains,SichuanI. Oil Gas Geol. 13 (2), p147–154. Wang, Yigang, Wen, Yingchu, Zhang, Fan, et al., 1998. Distribution law of the organic reefs in Changxing Formation of upper permian in east Sichuan. Gas Ind. 18 (6), 10–15. Wang, Xingzhi, Zhang, Fan, Ma, Qing, Yang, Manping, Wang, Yigang, Wen, Yingchu, Yang, Yu, Zhang, Jing, 2002. The characteristics of reef and bank and the fluctuation of sea-level in Feixianguan period of late permian-early triassic, east Sichuan basin. Acta Sedimentol. Sin. 20 (2), 249–254. Wang, Yigang, Liu, Huayi, Wen, Yingchu, Yang, Yu, Zhang, Jing, 2002. Distribution Law, exploration method and prospectiveness prediction of the oolitic beach reservoirs Feixianguan Formation in Northeast Sichuan Basin. Nat. Gas. Ind. 22 (s), 14–19. Wang, Yigang, Zhang, Jing, Liu, Xinggang, et al., 2005. Sedimentary facies of evaporative carbonate platform of the Feixianguan Formation of lower trassic in northeastern Sichuan basin. J. Palaeogeogr. 7 (3), 354–372. Wang, Siyi, Wang, Xingzhi, Zhang, Fan, et al., 2006. R eservoir characteristics of Feixianguan Formation in Gaofengchang area, east Sichan. Nat. Gas Explor. Dev. 29 (1), 6–9. Wang, Yigang, Wen, Yingchu, Hong, Haitao, Xia, Maolong, He, Yanting, Song, Shujun, 2007. Diagenesis of triassic Feixianguan Formation in Sichuan basin southwest China. Acta Sediment. Sin. 25 (6), 831–839. Wilson, J.L., 1975. Carbonate Facies in Geologic History. Springer Verlag, New York, pp. p471. Wright, V.P., 1991. Paleokarst: types, recognition, controls and associations. In: Wright, V.P., Esteban, M., Smart, P.L. (Eds.), Paleokarsts and Plaokarst Reservoirs: P.R.I.S. Occasional Publication Series No.2. university of Reading, Reading, pp. 56–88. Xing, Fengcun, Wang, longzhang, Lu, Yongchao, 2014. Oolitic shoals outcropping illustration of the Feixianguan Formation in the jiwangdong section, xuanhan county, northeastern Sichuan basin. In: Li Sitian, Jiao Yongquan. Outcrop Depositional System Research of the Carbonate Platform Margin Belts and Reservoir Modeling. Geological Publishing house, Beijing, pp. P255. Xu, Shiqi, Hong, Haitao, Zhang, Guang rong, He, Zhihui, Hu, Hengzhi, Chen, Sha, 2004. Main controlling factor analysis on oolitic reservoir development of lower triassicn Feixianguan Formation in Sichuan basin. Nat.Gas.Explor.Dev 27 (1), 1–3. Yang, Yu, Wang, Yigang, Wen, Yingchu, 2001. The sedimentary facies and the distribution of oolitic reservoir in Feixianguan Formation in northeastern Sichuan basin. Nat. Gas Explor. Dev. 24 (3), 18–21.

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.petrol.2019.03.020. References Adams, J.E., Rhodes, M.L., 1961. Dolomitization by seepage refluxion. Bull. Am. Assoc. Pet. Geol. 44, 1912–1920. Aqrawi, A.M., Thehni, G.A., Sherwani, G.H., Kareem, B.M.A., 1998. Mid-cretaceous rudist-bearing carbonats oF the Mishrif Formation:an impoirtant reservior sequence in the mesopotamian basin, Iraq. J. Pet. Geol. 21 (1), 57–82. Chen, Hongde, Qin, Jianxiong, Wang, Chengshan, Shou, Jianfeng, LI, Xianghui, 1999. Sequence-based lithofacies and paleogeographic characteristics and evolution of permian in south China. Acta Sedimentol. Sin. 17 (4), 509–520. Chen, Gengsheng, Zeng, Wei, Yang, yu, et al., 2005. Discussion on dolomization genesis of Feixianguan Formation in notheast Sichuan basin. Nat. Gas Explor. Dev. 25 (4), 40–41. Du, Jinhu, et al., 2011. Natural Gas Exploration of Permian-Triassic Reef & Oolite in Sichuan Basin. Petroleum Industry Press. Fan, Jiasong, Zhang, Wei, Xing, Ma, Zhang, Yinben, Liu, Huaibo, 1982. The upper permian reffs in lichuan district, west hubei. Cjin. J. Geol. 3, 274–282. Gao, Meisheng, Zheng, Rongcai, Wen, Huaguo, et al., 2007. Lithology characteristics of dolomite in the lower triassic Feixianguan Formation of the NE Sichuan basin. J. Chengdu Univ. Technol. (Sci. Technol. Ed.) 34 (3). Guo, Xusheng, 2010. Litho-paleogeographic evolution in the Middle-Late Triassic in western Sichuan Province and its significance for petroleum exploration. Oil Gas Geol. 27 (1), 99–105. Guo, Tonglou, 2011. Sequence strata of the platform edge in the Changxing and Feixianguan formations in the Yuanba area, northeastern Sichuan Basin and their control on reservoir. Acta Pet. Sin. 32 (3), 387–394. Guoqi, Wei, Chen, Gengsheng, Yang, Wei, Yang, Yu, Jia, Dong, Zhang, Lin, Xiao, Ancheng, Chen, Hanlin, Wu, Shixiang, Jin, Hui, Shen, Juehong, 2006. Preliminary study of the boundary of Kaijiang-Liangping trough in northern Sichuan basin and its characteristics. Oil Gas Geol. 27 (1), 99–105. Horbury, A.D., Adams, A.E., 1989. Meteoric phreatic diagenesis in cyclic late Dianantian carbonates, northwest England. Sediment. Geol. 65, 319–344. Huang, Sijing, Hairuo, Qing, Pei, Changrong, et al., 2006. Strontium concentration isotope composition and dolomitization fluids in the Feixianguan Formation of triassic, eastern sichuan of China. Acta Sediment. Sin. 22 (8), 2123–2132. Huang, Sijing, Hairuo, Qing, Hu, Zuowei, Wang, Chunmei, Xiaoyong, Hao, Zou, Mingliang, Wang, Qingdong, 2007. The diagenesis and dolomitization of the Feixianguan carbonates of Triassic in NE Sichuan Basin: an overview. Adv.Earth.Sci 22 (5), 495–503. Illing, L.V., Wells, A.J., Taylor, J.C.M., 1965. Penecontemparaneous dolomite in the Persian Gulf. In: In: Pray, L.C., Murray, R.C. (Eds.), Dolomitization and Limestone diagenesis.—Soc. Econ. Paleont. Min, vol. 13. Spec. Pub, pp. 89–111. Kerans, C., Kempter, K., 2002. Hierarchical Stratigraphic Analysis of a Carbonate Platform, Permian of the Guadalupe Mountains. AAPG Discovery Series 5, CD-ROM. Kerans, C., Tinker, S., 1999. Extrinsic stratigraphic controls on development of the Capitan Reef complex. In: In: Saller, A.H., Harris, P.M., Kirkland, B.L., Mazzullo, S.J. (Eds.), Geologic Framework of the Capitan Reef, vol. 65. Society for Sedimentary Geology (SEPM), pp. 15–36. Kerans, C., Lucia, F.J., Senger, R.K., 1994. Integrated characterization of carbonate ramp reservoirs using Permian San Andres Formation outcrop analogs. AAPG (Am. Assoc. Pet. Geol.) Bull. 78, 181–216. Kohout, F.A., Howard, Klein, 1967. Effect of pulse recharge on the zone of diflusion in the Biscayncaquifer. Bull. Int. Assoc. Sci. Hydrol. 70, 252–270. Land, L.S., 1973. Contemporaneous dolomitization of Middle Pleistocene reefs by meteoric water, North Jamaica. Bull. Mar. Sci. 23, 64–92. Land, L.S., 1983. Dolomitization. Amer. Ass. Petrol. Geol., Contin. Educ. Courses Notes 24, 1–20. LI, Fengjie, Liu, Dianhe, Zheng, Rongcai, Zhao, Junxing, 2009. The sequence stratigraphics characteristics of upper permian in the northeastern Sichuan basin. Acta Sediment. Sin. 27 (6), 1116–1123. Luo, Zhili, 1981. The influence of Taphrogenesis on the formation of petroleum and other mineral resources since late Paleozoic in southwest China. Acta Geol. Sichuan 2, 1. Ma, Yongsheng, Fu, Qiang, Guo, Tonglou, et al., 2005. Pool forming pattern and process of the upper permian - lower triassic in the Puguang gasfield, northeast Sichuan basin, China. Petrol. Geol.Exp 27 (5), 455–461. Ma, Yongsheng, Mou, Chuanlong, Tan, Qinyin, Qian, Yu, 2006. A discussion on KaijiangLiangping ocean trough. Oil Gas Geol. 27 (3), 326–331. Ma, Yongsheng, Mao, Chuanlong, Tan, Qinyin, Qian, Tu, Wang, Ruihua, 2007. Reef-bank features of permian Changxing Formation and triassic Feixianguan Formation in the

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Journal of Petroleum Science and Engineering 178 (2019) 324–335

J. Zhou, et al.

lower triassic feixianguan oolitic beach reservoir in isolated platform, northern Sichuan basin. Mar. Origin Petrol. Geol. 17 (2), 57–62. Zhou, Jingao, Xu, Chunchun, Yao, Genshun, et al., 2015a. Genesis and evolution of lower cambrain Longwangmiao Formation reservoirs, Sichuan basin, SW chian. Petrol. Explor. Dev. 42 (2), 158–166. Zhou, Jingao, Yao, Genshun, Yang, Guang, 2015b. Genesis mechanism of the sinian cambrian reservoirs in the anyue gas field,Sichuan basin. Nat. Gas. Ind. 35 (3), 36–44. Zhu, Guangyou, Zhang, Shuichang, Liang, Yingbo, et al., 2006. Dissolution and alteration of the deep carbonate reservoir by TSR: an important type of deep-buried highquality carbonate reservoirs in Sichuan Basin. Acta Petrol. Sin. 22 (8), 2182–2194.

Yang, Yu, Zeng, Yunxian, Liu, Wei, 2002. Oolitic reservoir distribution relative to the control of Feixianguan deposition in the northeast part of Sichuan. Nat.Gas.Explor.Dev. 25 (3), 31–39. Yang, Xiaoping, Zhao, Wenzhi, Cao, Hong, et al., 2006. Formation and distribution of Triassic Feixianguan oolitic bank favorable reservoir in the NE Sichuan Basin. Petrol. Explor. Dev. 33 (1), 17–21. Zeng, Wei, Huang, Xianping, Yang, Yu, Wang, Xingzhi, 2002. Burial dissolution of Feixianguan Formation reservoirs in northeast Sichuan basin. Nat. Gas. Ind. 26 (11), 4–6. Concepts and models of dolomitization. Zenger, D.H., Dunham, J.B., Ethington, R.L. (Eds.), Soc. Econ. Paleontol. Mineral. Spec. Publ. 28, 320. Zhao, Wenzhi, Wang, Zecheng, Wang, Yigang, 2006. Formation mechanism of highly effective gas pools in the Feixianguan Formation in the NE Sichuan Basin. Geol. Rev. 52 (5), 708–717. Zheng, Rongcai, Geng, Wei, Zheng, Chao, et al., 2008. Genesis of dolostone reservoir of Feixianguan Formation in lower triassic of northeast Sichuan basin. Acta Petrol. Sin. 29 (6). Zhou, Jingao, Guo, Qingxin, Shen, Anjiang, et al., 2012. Characteristics and genesis of

Jingao Zhou experiences more than 30 years in sedimentology and reservoir of carbonate. He received a M.S. from southwest institute of petroleum in 2004, and gained a Ph.D. in 2013 from Southwest petroleum university. Now, he is a Prof. of Petrochina Hangzhou institute of geology, also one of key researchers of Key Laboratory of Carbonate Reservoir CNPC.

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