Table of Content

28 April 2019, Volume 40 Issue 2

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Petroleum Geology

Growth of strike-slip zone in the southern Bohai Bay Basin and its significances for hydrocarbon accumulation

Zhou Xinhuai, Zhang Xintao, Niu Chengmin, Liu Hao, Huang Jiangbo

2019, 40(2):  215-222.  doi:10.11743/ogg20190201

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Tanlu strike-slip fault zone transverses the Huanghekou Sag and Laixi structural belt in the southern Bohai Bay Basin.We studied the characteristics and genetic mechanism of faults within the strike-slip zone,as well as its controlling effect on hydrocarbon accumulation,by using variance slicing,3D visualization and fine seismic interpretation technologies.The results show that there are two kinds of fault systems in the strike-slip fault zone in the southern Bohai Bay Basin:the "aerial ladder" type and the "palisade" type.The fault evolution has experienced three stages including sinistral strike-slip in the Mesozoic,extension-strike-slip in the Paleogene and intensive dextral strike-slip in the Neogene.The strike-slip belt not only controls the formation of traps,but also affects the distribution of sedimentary system in medium-to-deep layers as well as the horizons of hydrocarbon accumulation.According to the characteristics of hydrocarbon enrichment at different structural locations,four types of hydrocarbon accumulation patterns within the strike-slip belt were established,namely the transfer-station,meshwork-carpet,composite and ladder types,which have contributed to the successive discovery of large-or medium-sized oil and gas fields in recent years and will serve as a practical guidance for future hydrocarbon exploration.

Ramp zone types and their hydrocarbon distribution characteristics in the Bohai Bay Basin

Zhao Shan, Liu Hua, Jiang Youlu, Wang Yongshi, Hao Xuefeng, Zhang Cong

2019, 40(2):  223-235.  doi:10.11743/ogg20190202

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The ramp zone of the petroliferous basin is a favorable area for hydrocarbon accumulation.To identify the distribution of oil and gas in the ramp zones of various kinds is of great significance for oil and gas exploration.Taking the Bohai Bay Basin as an example,we divided its ramps into three types,namely the simple type,transitional type and complex type,based on the basement geometry of the ramps under the impact of tectonic zonation.The simple type of ramp zone is characterized by weak tectonic activity and one-way dipping basement geometry with a small dip; structural-litho-logic and lithologic reservoirs are dominant in this type,and its hydrocarbon enrichment concentrates in one single layer and most hydrocarbons accumulate in early periods with a typical "line-styled" hydrocarbon distribution.The transitional type features stronger tectonic movement and the two-way dipping basement geometry,and the structural and structural-lithologic reservoirs are dominant in this type,with a small number of stratigraphic reservoirs.Hydrocarbons enrich in multiple layers through migration along faults and sand body,resulting in a ladder-shaped reservoir distribution.While the complex ramp zone features strong tectonic activity and three-way dipping basement geometry.The structural and structu-ral-lithologic reservoirs are dominant,with a large number of stratigraphic reservoirs.The hydrocarbons enrich in multiple layers,leading to a "comb-shaped" reservoir distribution.

Favorable interval for shale oil prospecting in coring Well L69 in the Paleogene Es^3L in Zhanhua Sag,Jiyang Depression,Bohai Bay Basin

Li Zhiming, Tao Guoliang, Li Maowen, Jiang Qigui, Cao Tingting, Liu Peng, Qian Menhui, Xie Xiaomin, Li Zheng

2019, 40(2):  236-247.  doi:10.11743/ogg20190203

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This paper aims to identify the favorable interval for shale oil prospecting in the cored interval of the lower section of the third member of the Shahejie Formation (Es^3L) from Well L69 in Zhanhua Sag,Jiyang Depression,Bohai Bay Basin.To study their oil content and occurrence,typical lithofacies samples from the cored intervals of Es^3L in wells with commercial shale oil production,Well L69 and Well XYS9,were comparatively analyzed with routine Rock-Eval pyrolysis method and thermal desorption method,and the favorable interval for shale oil prospecting and factors affecting shale oil production were assessed.Results show that the total content of free oil,especially the content of free oil S_1-1 after light hydrocarbon correction,for the organic-rich lamellar argillaceous limestones at a depth of 3 040.35m to 3 072.10m in Well L69,is obviously lower than that of cored interval with commercial shale oil production in Well XYS9,and the average Oil Saturation Index(OSI) is only 67 mg/g,both of which indicate no exploration potential for shale oil.The total content of free oil,especially the content of free oil S_1-1 after light hydrocarbon correction,for organic-rich lamellar argillaceous limestones at a depth of 3 116.90m to 3 126.70m in Well L69,is obviously lower than that of cored interval of the Es^3(L) with commercial shale oil production from Well XYS9,though the OSIs are usually larger than 100mg/g with an average of 204mg/g,suggesting a lower shale oil exploration potential.The total content of free oil,especially the content of free oil S_1-1 after light hydrocarbon correction,and the OSI of organic-rich laminar argillaceous limestones and calcareous mudstones at a depth of 2 994.10m to 3 010.90m in Well XYS9,are similar or almost equal to those of the cored interval of the Es^3(L) with commercial shale oil production from Well XYS9; characterized by developed micro-fractures,abnormal pressure,high contents of brittle minerals and contribution of mature oil migration,the cored interval at the depth of 2 994.10m to 3 010.90m should be a favorable interval for shale oil exploration.

Characters of hydrocarbon generation and accumulation of salt-lake facies in Dongpu Sag,Bohai Bay Basin

Xu Tianwu, Zhang Hong'an, Li Jidong, Zhao Wei

2019, 40(2):  248-261.  doi:10.11743/ogg20190204

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Hydrocarbon generation and accumulation in salt lakes are a typical petroleum geological phenomenon in the world,especially in the Mesozoic and Cenozoic continental strata of China.In order to advance research in this field,this paper discusses the research progress of Dongpu Sag in the Bohai Bay Basin,eastern China.The hydrocarbon generation and accumulation characteristics of salt-lake source rocks were analyzed through systematic geological and geochemical studies of source rocks and crude oils,providing clues for future regional deployments of exploration.Results show that the typical salt-lake source rocks were developed spatially in the north of the sag,specifically the lower section of the third member(Es^4(U)) and the upper section of the fourth member(Es^4(U)) of the Shahejie Formation vertically.Its lithology is shale featuring early hydrocarbon generation and expulsion,with a "double-layered" structure,i.e.the lower layer dominated by organic matters and clay minerals and the upper one dominated by pyrites and calcites.The hydrocarbon accumulation in salt lakes of Dongpu Sag develops along with the growth of both conventional and unconventional petroleum reservoirs.The conventional ones are characterized by "ordered distribution and differential enrichment",while the deve-lopment of unconventional oil and gas reservoirs is closely related to the organic-rich salt-lake source rocks,reflecting the control of organic-rich salt-lake source rocks on hydrocarbon accumulation.It is recommended that further regional exploration should be focused on the two organic-rich source rock areas,the Es^4(U) and the Es^4(U),and exploration of various petroleum reservoirs should be carried out.These understandings are of referential significance for the geological research of oil and gas and the exploration in other saline lacustrine basins.

Genetic model of transtensional faults in Dongying Depression,Bohai Bay Basin, and its controls over hydrocarbon accumulation

Zhang Weizhong, Zhang Yunyin, Zha Ming, Qu Zhipeng, Yu Jingqiang, Zhang Lin, He Chang

2019, 40(2):  262-270.  doi:10.11743/ogg20190205

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Study on the structural characteristics of transtensional faults and their controls on hydrocarbon accumulation is of great significance to the fine reservoir evaluation in the highly-explored areas of eastern China.The genetic model of transtensional faults in the Dongying Depression,Bohai Bay Basin,was studied,and the accumulation model controlled by transtensional faults in this area was established,on the basis of the geometrical and evolutionary characteristics of the transtensional faults.Research shows that,the transtensional faults in the Dongying Depression can be divided into three types,the broom-shaped,en echelon and juxtaposition faults.The broom-shaped transtensional faults are characterized by early extension and later transformation,with the structural style evolving from a single fault to a broom-shaped fault zone.While the juxtaposition transtensional faults feature early transformation and later extension,with its structural style evolving from the en echelon to the juxtaposition type.The en echelon transtensional faults are characterized by simultaneous transformation and extension,with its structural style evolving from a single fault at early stages to the en echelon fault zone.The differential evolution of transtensional faults leads to the model of controls over hydrocarbon accumulation with open-close coupling,providing a guidance for the fine exploration and development of reservoirs in transtensional basins.

Characteristics and controlling factors of effective reservoirs of Mesozoic low-permeability clastic rocks in Gaoqing Region,Dongying Depression, Bohai Bay Basin,China

Wang Ya, Yang Shaochun, Lu Yan, Ma Baoquan, Zhao Yongfu, Wang Yongchao

2019, 40(2):  271-283.  doi:10.11743/ogg20190206

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The Mesozoic effective reservoirs in Gaoqing Region,Dongying Depression show strong heterogeneity and complex diagenetic evolution.In order to gain insight into the petrological characteristics and physical properties of the effective Mesozoic reservoirs and clearly demonstrate the controlling factors for the growth of effective reservoirs,tests including the thin section,scanning electron microscope(SEM),cathodoluminescence,high pressure mercury intrusion and fluid inclusion were performed,and a comparative study on pore structure and diagenesis characteristics between effective and non-effective reservoirs was carried out.Results indicate that,the Mesozoic effective reservoirs in Gaoqing Region are characterized by well-developed secondary pores,relatively good physical properties and strong heterogeneity of pore structure with a bimodal distribution of mesopore throats and micropore throats.Compared with non-effective reservoirs,the porosity reduction rate in effective reservoirs significantly decreases due to compaction and cementation,while the porosity enlargement rate with dissolution increases largely.The development of Mesozoic effective reservoirs in Gaoqing Region is controlled by multiple factors.Well-sorted sandstones with high content of rigid particles weaken the porosity reduction owing to compaction,and help compose the material basis of effective reservoirs.Early carbonate cements in effective reservoirs have the ability of "anti-compaction and pore-preserving".The relatively open water-rock system is favorable for dissolution,and inhibits the mid-stage calcite cementation.The leaching dissolution and organic acid dissolution,the dominant mechanisms for diagenetic modification,function to effectively improve the macroscopic reservoir quality and microscopic pore structures.The micro-fractures generated by faulting can improve the seepage capacity of effective reservoirs,and profoundly control the distribution of oil and gas in the Mesozoic.

Genesis and accumulation models of sulfur-rich heavy oil in Laizhou Bay Sag,Bohai Sea

Tang Guomin, Wang Feilong, Wang Qingbin, Wan Lin, Yan Ge

2019, 40(2):  284-293.  doi:10.11743/ogg20190207

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In Bohai Sea,large-scale high-sulfuric oilfields are only found in Laizhou Bay Sag.The crude oil properties in this area are complex,and the source and genesis of oil here are not clearly understood.We made a detailed study on the hydrocarbon sources and genesis of oilfields in Laizhou Bay Say by means of geochemical analysis and basin simulation,and incorporating a large number of experimental data.The results show that (1) there are two sets of effective source rocks developed in the sag,namely the Es³ and Es⁴.Oils in the steep slope belt and central tectonic belt were derived from Es⁴ source rocks in the main sag,while oils in the gentle slope belt originated from the Es⁴ source rocks both in the main sag and in the south subsag.(2) During Es⁴ sedimentary period,the waters of Laizhou Bay Sag were not connected,so that the south subsag waters were prone to become saline to produce sulfur-rich kerogens.Thus,the distribution of Es⁴ source rocks in the south subsag controls the distribution of high-sulfuric oil,serving as the major controlling factor for generating high-sulfuric oil.In addition,microbial degradation can lead to the thickening of crude oil,and cause the relative enrichment of sulfur in crude oil.(3) Kenli 16-1 oilfield is characteristic of late-stage hydrocarbon accumulation,with a hydrocarbon accumulation model of saline lacustrine basins featuring early generation,early expulsion,and dual-sag hydrocarbon charge.Meanwhile,the accumulation model of deep reservoirs is a typical example of a distal source charge through long distance oil migration along unconformity laterals,different from that of the shallow reservoirs.The Palaeogene formations in the southern south subsag and high reservoir quality buried-hill formations are regarded as favorable plays for hydrocarbon accumulation,which can be targeted for further oil and gas exploration.

Quality differences between dolomite and tight sandstone reservoirs

Wei Xinshan, Chen Juanping, Lyu Qiqi, Zhao Xiaohui, Jia Ya'ni

2019, 40(2):  294-301.  doi:10.11743/ogg20190208

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The quality parameters of dolomite and tight sandstone reservoirs are a randomly distributed continuum.Their pore structures and physical parameters are complex and changeable,and are thus hard to be characterized.With the help of techniques such as thin section casting,mercury injection,nuclear magnetic resonance(NMR),and measurements of porosity and permeability,and a large number of data for natural gas exploration and development,we focused the study on analyzing and comparing the macroscopic and microscopic characteristics of the parameters of the reservoir quality.Results show that the quality parameters of dolomite and tight sandstone reservoirs are normally distributed in a pyramidal data structure.The proportion of conventional reservoirs is generally ranging from 15% to 20%,which are the "sweet spots" of the sandstone or tight dolomite reservoirs.The microscopic pores are well developed with good pore-throat connectivity and uniform distribution in the tight sandstone reservoirs.The reservoir porosity and permeability are of good relationship,showing relatively high porosity and low permeability.The tight dolomite reservoirs,however,are characterized by unfavorable factors including poor pore-throat connectivity and poor relationship of porosity and permeability,while having certain favorable factors of its kind including relatively high permeability,low irreducible water saturation,low displacement pressure,and better development of fracture networks.These favorable factors keep the natural gases flow well in tight dolomite reservoirs,indicating great potentials for the exploration and development of hydrocarbons.Carbonate deposits are well developed in China,so the exploration of tight dolomite gas reservoirs and study on their accumulation conditions should be strengthened.

Differences and origin of micro-pore throat characteristics for tight sandstone reservoir of Yanchang Formation,Ordos Basin

Gao Hui, Zhugeng Bolun, Wang Xuanyi, Shi Hua, Wang Minglei, He Mengqing, Dou Liangbin, Wang Chen

2019, 40(2):  302-312.  doi:10.11743/ogg20190209

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By adopting quantitative evaluation of pore throat parameters under different depositional and diagenetic conditions,and with reference to the test results of physical property,casting section,SEM,constant speed mercury injection,particle size and X diffraction,the pore throat types of Chang 8 reservoir of Heshui Region and Chang 6 reservoir of Xuecha Region in Ordos Basin were analyzed,contrasted and reasons for how they were formed were revealed.Results show that the pores are better developed in Chang 8 reservoir in Heshui Region,with a high quantity of intergranular,dissolved,intercrystalline and micro pores,as well as necking down throats with weak compaction,tube-shaped throats with dissolution and clay cementation; while pores are less developed in terms of both types and range in Chang 6 reservoir of Xuecha Region,with high quantity of lamellar and curved lamellar throats with compaction.For the two studied reservoirs,the differences in pore parameters are not as significant as those in throat parameters.Compared to Chang 6 reservoir,Chang 8 reservoir developed better and larger throats with apparent differences,bigger pore-throat ratio,and wider distribution of throats that are conducive to permeability.Under the condition of same permeability,the average throat radius,main flow throat radius and pore-throat ratio of Chang 8 reservoir are all bigger than those of Chang 6 reservoir.It can be concluded that the hydrodynamic conditions in sediments,particle size,detrital component,interstitials,diagenesis types and their respective influence degrees,are the main reasons for the differences in the development of pores,throat types and pore throat parameters.

Origin and distribution of formation water in tight sandstone reservoirs in the northeastern Ordos Basin

Chen Zhaobing, Yang Youyun, Shao Jinhui, Zhu Yushuang, Chen Xinjing, Shi Lei, Meng Di

2019, 40(2):  313-325.  doi:10.11743/ogg20190210

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The chemical features,genesis,spatial distribution characteristics and controlling factors of the formation water in Shenmu gas field,northeastern Ordos Basin,were studied by the analysis of seismic,drilling and logging,as well as performance data combined with test analysis of mercury injection,gas-water relative permeability,physical and hydrochemical properties.Since the studied area is located in the transitional area from water to gas,the formation water herein is of "V-shaped" CaCl₂ type,with low salinity"acid water" and high salinity conventional formation water being dominant.Vertically,the differential distribution of formation water are mainly caused by the differences of deposition,lithofacies and distance from gas source for various formations.Multiple tight limestones distributed in the Benxi and Taiyuan Formations have blocked the entry of hydrocarbons into reservoirs,leading to a low degree of gas charging for the original reservoirs and relatively high enrichment of formation water.The Shiqianfeng Formation,located far away from gas source,is in short of hydrocarbon supply with incomplete gas displacement of water.The Shanxi Formation is a self-sourced indi-genous play,which has a high degree of gas charging and low quantity of water produced.Horizontally,influenced by the "west-dipping" structural movement of the basin in the Late Cretaceous,the northeastern Ordos Basin uplifted as a whole along with the secondary adjustment of water/gas contact,producing more gas-bearing horizons and continuously increa-sing the height of gas columns; meanwhile,the pressure in the gas reservoir decreased,and the formation water at the basin margin invaded into bed laterally,leading to the pattern of "multiple gas layers,low gas yield and water-gas co-production",characterized by the ever-increasing formation water scale and water production from west to east with a gradual increase of salinity.The results provide some basis for prediction of the spatial distribution and genesis of gas and water at the margin of the Ordos Basin.

Main controlling factors for organic matter enrichment in Chang 7 member of the Yanchang Formation,Ordos Basin

Yuan Wei, Liu Guangdi, Xu Liming, Niu Xiaobing

2019, 40(2):  326-334.  doi:10.11743/ogg20190211

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The TOC content of organic-rich shales in Chang 7 member of the Yanchang Formation in Ordos Basin is abnormally high.The organic matter enrichment is essentially controlled by a combination of paleostructures,paleoclimate,paleosedimentary environments and events.We have analyzed these controlling factors and discussed their roles in the formation of organic-rich shales of the study area.The results show that the strong tectonic activity in the depositional period of Chang 7 member played a very important role in its enrichment of organic matter.Firstly,it led to a wide-scale subsi-dence of the whole basin and to an expansion of the lake water surface,producing more accommodation space.Furthermore,it induced multi-stage volcanic and submerged hydrothermal activities,and thereby delivered a large amount of nutrients to the lake.Sufficient growth space,rich nutrients supply and suitable climatic conditions have made aquatic orga-nisms flourish(the lacustrine primary productivity was extremely high),which has provided a rich material basis for the formation of organic-rich shales.Although the oxydic-suboxydic bottom-water environment in Chang 7 sedimentary period is not ideal to the preservation of organic matter,a large number of organic matters are still preserved due to adequate influx,resulting in the enrichment of organic matter in the sediments.

Characterization of braided river reservoir architecture of the Upper Paleozoic He 8 member on Fugu Tianshengqiao outcrop,eastern Ordos Basin

Chen Dongyang, Wang Feng, Chen Hongde, Wei Xinshan, Sun Shi, Zhu Shengxian

2019, 40(2):  335-345.  doi:10.11743/ogg20190212

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The major gas pay zone lies in the 8th member of the Upper Paleozoic Lower Shihezi Formation(He 8 member),eastern part of Sulige region,Ordos basin.Its reservoir architecture acts as a predominant geological factor for oil/gas distribution.Targeting at Tianshengqiao outcrop in Fugu county in eastern Ordos Basin,similar to eastern Sulige region in provenance and sedimentary setting,we finely studied the architecture of the outcropped sand body,which can offer critical information for the establishment of geological model of eastern Sulige region.Based on the outcrop survey,pe-trographic investigation,architecture analysis and fine measurement of sand body volume,combined with the sedimentary and petrologic analyses,we recognized twelve types of lithofacies in the braided river deposits of He 8 member.Six levels of architecture interfaces were classified within the reservoirs,namely composite channel-belt,single channel-belt,single sand body,silty layer accompanied with accretion,bed set,single bed and laminae.Six reservoir architecture units are indentified,that is,channel filling(CH),longitudinal bar(LB),diagonal bar(DB),transverse bar(TB),abandoned channel(ACH) and overflow deposits(OF).Among these,sand bar is a dominant reservoir architecture unit.The thickness of longitudinal bar ranges between 2.5m and 5.8m with the width/thickness ratio varying from 27.6 to 37.7; the thickness of diagonal bar ranges between 2.2m and 6m with a width/thickness ratio varying from 38.4 to 42.1; while the thickness of transverse bar ranges between 1.5m and 3.6m with a width/thickness ratio varying from 47.0 to 61.8.Based on the analyses of different architecture units,we summed up the spatial superimposition patterns of the reservoir,established the 3D architecture model of braided river composite sand body in the He 8 member of Tianshengqiao outcrop in Fugu county,both of which will provide geological evidences in the fine description of He 8 member in eastern Sulige region.

Characteristics of newly discovered crude oil in the Weihe Basin and its petroleum geological significance

Li Yuhong, Gao Gang, Wang Xingyun, Qu Tong, Han Wei, Gong Zhenqi, Zhang Wen, Dang Wenlong

2019, 40(2):  346-353.  doi:10.11743/ogg20190213

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The unexpected production of oil from the geothermal wells in the Weihe Basin breaks the conclusion of history that there is no oil distributed in the region.We made a systematic study of the crude oil in terms of its physical property,group composition,content of saturated hydrocarbon,composition of sterane and terpane,as well as carbon isotope composition of saturated hydrocarbon monomer,with a view to explore the characteristics of crude oil and its petroleum geolo-gical significance for the basin.The results show that the crude oil compositions are predominated by saturated hydrocarbons,followed by arene and asphaltene,and with the colloid coming last,thus it belongs to a kind of low-sulfur crude oil with light colloid and normal content of wax.Its saturated hydrocarbon chromatogram is bimodal,with the main peaks corresponding to C₁₅ and C₂₂,and the CPI and OEP values are 0.93 and 0.90 respectively.The organic matters of the crude oil are high in maturity,and mainly sourced from planktons,followed by certain higher plants and algaes.The carbon isotope value of low n-alkanes (C₁₄-C₂₂) decreases from -27.1‰ to -30.3‰ along with the increase of carbon number.When the carbon number is higher than C₂₂,the carbon isotope value varies between -29.3‰ and -30.4 ‰.In addition,the carbon isotope values of pristane (Pr) and phytane (Ph) are relatively heavy at 26.1‰ and 24.9‰,respectively.Higher content of gammacerane indicates that the organic matters are produced in an environment of higher salinity.Compared with the adjacent areas,the crude oil has a great difference with that from the Permian,the Triassic Yanchang Formation and the Jurassic in the Ordos Basin in terms of geochemistry and origin.The newly discovered crude oil indicates that the Weihe Basin may still have source rocks undiscovered,which is of great significance to guide the petroleum exploration of the basin.At the same time,it is also of referential meaning for oil and gas survey in the unexplored sequences in Ordos Basin.

Age and petroleum geological implications of prolific formations in Ha'ri Depression Well YHC1,Yin'e Basin

Chen Zhipeng, Ren Zhanli, Cui Junping, Qi Kai, Zhang Yuanyuan, Yu Chunyong, Ren Wenbo, Yang Guiling, Liu Runchuan

2019, 40(2):  354-368.  doi:10.11743/ogg20190214

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There have always been controversial opinions about the age of prolific formations in Ha'ri Depression Well YHC1,Yin'e Basin and the location of unconformity surface between the Cretaceous and Permian.To sort out such controversies,we studied the age of prolific formations in the region and the exact location of the boundary line,based on previous research.The micro-fossils,U-Pb zircon dating of volcanic rocks,mineral compositions and seismic reflection cha-racteristics were analyzed for this purpose.Results show that the sporopollen assemblages of the prolific formations and layers above Well YHC1 can be compared with those of the Lower Cretaceous in Wells Ha1 and Chacan1.The U-Pb zircon ages of the volcanic rocks under the prolific formations are ranging from 131.8Ma to 132.6Ma,indicating that the volca-nic rocks are products of Early Cretaceous eruptions.The mineral compositions of prolific formations are consistent with those of the Lower Cretaceous,but very different from those of the Permian.In addition,both the prolific formations and the volcanic rocks are located within the faulted depression,which is seen from the seismic reflection profile.To sum up,the prolific formations discovered in Ha'ri Depression Well YHC1should fall in the category of the Lower Cretaceous,and the unconformity surface between the Cretaceous and Permian should be located at the bottom of the Bayingebi Formation volcanic rocks.This study is of great significance to hydrocarbon evaluation and exploration in the research zones,and marks brigh prospects for oil/gas exploration in the Lower Cretaceous Yin'e Basin.

Sedimentary facies model and favorable reservoir distribution of the Middle Permian in Sichuan Basin

Li Rong, Hu Mingyi, Yang Wei, Liu Mancang

2019, 40(2):  369-379.  doi:10.11743/ogg20190215

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Some breakthroughs have been made in the exploration of the Middle Permian Qixia and Maokou Formations in the Sichuan Basin in recent years,indicating great prospects for gas explorationin the Middle Permian of this area.Previous studies focused on sedimentary facies and reservoirs of the Middle Permian in this area,but there are many differences in terms of the types and model of sedimentary facies of the Middle Permian Qixia and Maokou Formations.This has restricted the prediction of favorable reservoir distribution.Therefore,we carried out facies marker analysis including petrologic feature,sedimentary structure and biological fossil,based on the comprehensive study of some latest drilling and seismic data.The results show that the major sedimentary facies of the Middle Permian Qixia and Maokou Formations include platform margin,open-platform and intra-platform sag,among which the carbonate platform is dominant in the lower Qixia Formation of the Middle Permian,while rimmed platform and isolated intra-platform sag dominate the middle and upper Qixia Formation as well as in the Maokou Formation.The reservoirs of the study area are mainly marginal-platform and intra-platform shoals,concentrating in highstand system tracts.The marginal-platform shoal reservoirs mainly occur in areas including Ya'an-Mianzhu and Jiange-Guangyuan during the Sq1-HST period,and Ya'an-Mianzhu-Guangyuan area during the Sq2-HST period;the intra-platform shoal reservoirs are mainly distributed in the Gaoshiti-Moxi block in the central Sichuan Basin during the Sq1-HST and Sq2-HST periods,and Weiyuan-Zigong area during the Sq2-HST period.The intra-platform shoal reservoirs in Gaishiti-Moxi block during the Sq2-HST period are distributed in the form of strips due to the joint influences of paleokarst and tectonic hydrothermal fluids.The marginal-platform and intra-platform shoals are widely distributed in the Middle Permian of Sichuan Basin,and have bright prospects for hydrocarbon exploration.

Provenance and sedimentary system of the Jurassic successions in the front of Longmen Mountain in western Sichuan Basin

Deng Li, Liu Junlong, Qian Yugui, Zhang Shihua, Wang Tianyun, Yu Haiyue

2019, 40(2):  380-391.  doi:10.11743/ogg20190216

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Proximal sedimentary system in foothill belt of foreland basin has become a hot and hard topic in sedimentology in recent years.During the Jurassic depositional period,a set of proximalcoarse-grained sedimentary systemwas developed in the foothill belt of Longmen Mountain in the western Sichuan Basin.We analyzed the provenance features and sedimentary system evolution in different periods using an integrated dataset of seismic,well logging,core and outcrop data.The results show that:(1) during the Jurassic,there were 5 provenances in the minor axis and near-major axis directions in the foothill belt of Longmen Mountain; (2) in the Early Jurassic,alluvial fan-meandering river delta-shore-shallow lake-semi-deep lake system dominated this area,while in the Middle and Late Jurassic,alluvial fan-braided river delta-shore-shallow lake system were developed well here; (3) three types of sedimentary models can be identified in the foothill belt of Longmen Mountain,namely the Early,Middle,and Late Jurassic sedimentary models.This study canprovide theoretical guidance and data support for the exploration of the tight sand gas reservoirs in the foothill belt of Longmen Mountain,and deepen our understanding of the proximal coarse-grained alluvial reservoirs.

Types of mound-shoal complex of the Lower Cambrian Xiaoerbulake Formation in Tarim Basin,northwest China,and its implications for exploration

Qiao Zhanfeng, Shen Anjiang, Ni Xinfeng, Zhu Yongjin, Yan Wei, Zheng Jianfeng, Huang Lili, Sun Xiaowei

2019, 40(2):  392-402.  doi:10.11743/ogg20190217

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Based on the observation of cores and thin sections,as well as the detailed survey of outcrops,the ramp mound-shoal complexes of the Lower Cambrian Xiaoerbulake Formation of Tarim Basin can be divided into four types:grain beach,mound shoal,shoal flat,and platform inner flat,in accordance with their differences in geomorphology,sediment category,and sedimentary features.The grain-beach type complex,occurring in relatively flat platform settings in the Tazhong-Badong area,is characteristic of high-energy oolites and intraclastic grainstones growth in slices.The mound-shoal type complex,occurring in ramp settings in the Keping-Bachu area,is characterized by the prosperity of microbial mounds and algae-intraclastic grainstone shoals,displaying a feature of large shoals interspersed by small mounds.The shoal-flat type complex usually occurs in Aksu area with absence of microbial mounds and widespread grain beaches and tidal flats.The platform-inner-flat type complex is developed in the Lunnan-Yaha area,characterized by "isolated platform" with a steep eastern slope (filled with high-energy mound shoal deposits) and a relatively gentle western slope (dominated by low-energy microbial mounds or mats).Reservoirs in different mound-shoal complexes developed distinctive features.The grain-beach and shoal-flat types usually develop Type Ⅱ reservoirs with consistent distribution over large areas; while the mound-shoal and platform-inner-flat types tend to develop Type Ⅰ reservoirs,which are blocky and high-quality reservoirs,and may distribute in a large scale.In conclusion,lithologic traps should be a focus of exploration in the Tazhong-Badong area.While much attention should be paid to those tectonically stable traps with good preservation conditions in the Keping area,the high-energy mound-shoal complexes should be the exploration target in the Lunnan-Yaha area.

Sedimentary microfacies and setting of the Upper Ordovician carbonates in the Yubei area,Tarim Basin

Cai Xiyao, Gao Xiaopeng, Li Huili, Zhao Yi

2019, 40(2):  403-412.  doi:10.11743/ogg20190218

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We studied the microfacies types and sedimentary settings of carbonate rocks of the Upper Ordovician Qrebake and Lianglitage Formations from 12 wells of the Yubei area,by means of microfacies analysis.Eight kinds of carbonate microfacies have been identified based on the microscopic observation of grains,biological assemblies,matrix and structural characteristics.Based on how the microfacies types are associated to each other,combined with drilling and logging data,as well as seismic profile,palaeontological and geochemical analyses,we believed that the Upper Ordovician carbonate rocks are mainly developed in the sedimentary environments of open platform,platform margin and marginal-platform slope.The sedimentary facies in the Late Ordovician differ from the east to the west.The boundary is delineated along Well YB5-Well SH2-the south of Well PSB2,with marginal-platform slope-continental shelf facies in the east,and carbonate platform facies in the center and the west.In conclusion,the Upper Ordovician in the Yubei area has evolved from open platform,to platform margin,to marginal-platform slope,and then to continental shelf facies in vertical sequence,and the variation of sedimentary environments in the area is mainly controlled by regional tectonic movements.

Inverted rate of boundary faults along Fulongquan fault depression, Songliao Basin

Zhang Meihua, Wang Chunhua, Luan Ying

2019, 40(2):  413-422.  doi:10.11743/ogg20190219

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The boundary faults of basin are generally synsedimentary faults,which are characterized as having relatively short period of activity with intermittency and relatively long stratum deposition.The two factors together determine the stratigraphic distribution of fault depression basins.This paper analyzed the theoretical model of synsedimentary faults.Results show that the thickness of the gentle slope zones of the fault depression is equivalent to that of the footwall of the boundary fault,and at the footwall,the strata corresponding to the upper wall are usually absent.The thickness of strata in the gentle slope zone can replace that of the footwall of the boundary fault,and a virtual footwall thickness framework can be established,then the boundary faults can be studied quantitatively by means of displacement-distance graphs.Fulongquan fault depression locating in the southeast of Songliao Basin,a half-graben basin with faulting in the east and overlapping in the west,develops four boundary faults controlling four sub-sags in turn,and the activity intensity and inversion degree of these boundary faults are different.It has experienced three main structural movement,fault depression,depression,and inversion,corresponding to the three active phases of boundary faults,intense activity,inactivity,and inverting activity.The structural inverdion wich happened in the end of the Cretaceous,functions to reactivate the boundary faults and form hydrocarbon migration paths;hence the deep hydrocarbons migrated upward to the shallower traps,and the secondary hydrocarbon reserviors are thus produced.The quantitarive study about the inverted rate of each bondary fault,combined with the study of hydrocarbon accumulation patterns in Fulongquan fault depression,indicates that the areas with mrdium inverted rate are the most conducive in the generation and preservation of secondary hydrocarbon reservoirs.

Water control completion of horizontal wells in Ahdeb oilfield and an integrated coupling model

Xue Heng, Huang Zuxi, Wang Hehua, An Yongsheng, Liu Fei, Cheng Yi, He Bing, Liu Ka

2019, 40(2):  423-429.  doi:10.11743/ogg20190220

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The major beds in upper Ahdeb oilfield are developed with success through an early stage horizontal well flooding-production method.However in the current stage,the observed high water cut in many producers has affected the stable production seriously.Therefore,it is urgent to study the water control of horizontal wells.In observing that the horizontal well water breakthrough is caused by active edge or injected water in high-permeability layers or fault fissures,we set up a serious of completion schemes to achieve water control of horizontal wells based on an integrated analysis of encountered reservoirs in drilling,and an newly established numerical model of integrated wellbore-reservoir coupling suitable for simulating screen,central tube,and ICD water control completion.In the modeling,the variable mass flows in horizontal wellbores under multiple forces have been considered to increase the match between the single-well simulation results and the real water cut performance.The results show that the ICD and central tube completion measures are more effective in water control when the water breaks through in the heel section,with the water cut decreasing from 49.8% to 37.8% and 35.0% respectively.In order to achieve efficient water control,the flow-limiting range of the water control completion devices should be slightly longer than that of water breakthrough section.The application of water control devices before water breakthrough of horizontal wells will lower the cumulative water cut during the whole production life to the maximal degree,and in turn this will increase the cumulative production for single wells.

Study and application of online diversion acidizing technology in injection wells in ultra-low permeability reservoirs

Deng Zhiying, Zhang Suiwang, Song Zhaojie, Wang Erzhen, Yang Qianlong, Wu Wenchao

2019, 40(2):  430-435.  doi:10.11743/ogg20190221

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Acidification is one of the most effective injection stimulation methods in the ultra-low permeability reservoirs.These reservoirs however,are usually characterized with poor physical property and high heterogeneity,leading to an unnecessarily long operation period,low efficiency,and insufficient effectively-operating distance for conventional acidification measures,as well as fluid fingering and secondary damage to the reservoir during the acidizing process.In this regard,we studied the Triassic ultra-low permeability reservoir in the Huanjiang oilfield,Ordos Basin,proposed the online diversion acidizing technology and developed COA-1S achelating acid system and COA-1P,a new water soluble diversion agent.After a large number of laboratory experiments,we found that,compared with the conventional acidizing method,this new technology is more retardant,compatible,water-soluble,and better at chelating and temporary blocking.In-situ pilot test has shown that the homogeneity of the water absorption profile has increased from 28.5% to 50.9%,that is,the water injectivity index doubled after the implementation of this technology.Meanwhile,its characteristics of "zero well shut-off and depressurization,zero impact on the tubing strings,and zero flow-back",allows this technology to simplify the operation process of diversion and acidification,reduce the risks in security and environment protection,and thus can be recommended as a new acidification technology for stimulating injection of wells in the ultra-low permeability reservoirs.

An approach to calculate developed reserves in gas drive fractured-vuggy reservoirs in Tahe oilfield

Zhu Guiliang, Sun Jianfang, Liu Zhongchun

2019, 40(2):  436-442,450.  doi:10.11743/ogg20190222

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The reservoir space in the fractured-vuggy reservoirs of Tahe Oilfield is diverse in type and size,and spatially discontinuous,typical features for massive oil pools,and different from that of conventional laminar sandstone reservoirs.The gas injection measure for oil recovery enhancement is remarkable in Tahe oilfield.To characterize the massive reservoirs featuring numerous fractures,cavities and other features of heterogeneity in the Tahe oilfield,we proposed an categorization and calculation method of developed reserves through gas drive.Based on PDA production data analysis,the calculation method for total developed reserves of a well group is established by fitting flow reforming pressure and material balance time curves.For weathering crust,underground river,and fault karst,the calculation method of areal sweep efficiency is presented based on the form factor correction coefficient,and calculation method for the vertical drainage efficiency is also proposed based on the 3D distribution of fractured-vuggy reservoirs revealed by seismic cube energy attri-bute.In addition,based on the total developed reserves for a well group,cumulative production before gas flooding,areal sweep efficiency,form factor correction coefficient for irregular well patterns,and vertical drainage efficiency of reserves,the calculation method for gas drive developed reserves of well groups with various well patterns under different karst settings is established.This method has been applied to the Tahe oilfield for in-situ gas injection case studies,which has laid a solid foundation for the optimization of gas drive well group patterns,the calculation of developed reserves in gas drive well groups,and potential EOR analysis of gas injection.

An approach to recognize interwell reservoir connectivity based on production data

Wang Renyi

2019, 40(2):  443-450.  doi:10.11743/ogg20190223

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Characterization of interwell reservoir connectivity is the most important and fundamental research work to understand water flooding oilfield.Although the commonly used reservoir engineering,numerical simulation and geochemical methods may improve the reliability of interwell reservoir connectivity characterization,they are heavily dependent on extensive collection of geological data and long period observation of well performance through production cycle,which are either expensive or time consuming.The interaction between injectors,producers,and interwell reservoir is a complex nonlinear dynamic system.The production data of oil and water reflect certain aspect of the system,which may hint into the characters of interwell reservoir connectivity.The multivariable facies distribution reconstruction can be applied to resolve the dynamic characteristics of the system based on the multivariable production data of oil and water wells.Thus the reservoir connectivity can be characterized by calculating correlation dimensions of chaotic attractor of the injection-production dynamic system.The amount of work required by this approach is small,and it works well in the application to WR oilfield,with conclusion being consistent with actual production.The approach is clear and simple both in theory and in algorithm.Without complicated mathematical models or parameters of static geological models,it has initiated a new way to quantitatively characterize interwell reservoir connectivity.