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Exploration progress and outlook for lithostratigraphic reservoirs of CNPC overseas
DOU Lirong, LI Zhi, YANG Zi, ZHANG Xingyang, KANG Hailiang, ZHANG Mingjun, ZHANG Liangjie, DING Liangbo
2023, Vol.35(6): 1–9
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2071 )
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631
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Characteristics of hydrocarbon accumulation in deep-water depositional system in offshore East Africa
SHI Buqing, DING Liangbo, MA Hongxia, SUN Hui, ZHANG Ying, XU Xiaoyong, WANG Hongping, FAN Guozhang
2023, Vol.35(6): 10–17
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1920 )
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388
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Key techniques of high-resolution processing of desert seismic data and its application in Agedem area,Niger
SU Qin, ZENG Huahui, XU Xingrong, WANG Deying, MENG Huijie
2023, Vol.35(6): 18–28
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1709 )
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235
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Accumulation model and favorable area prediction of structural-lithologic composite reservoirs in block W,the slope zone of Oriente Basin,South America
MA Wenjie, WAGN Jingchun, TIAN Zuoji, MA Zhongzhen, WAN Xuepeng, LIN Jincheng, XU Xianglin, ZHOU Yubing
2023, Vol.35(6): 29–36
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1662 )
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250
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Classification and categorization method of overseas lithologic reservoir reserves
XIA Mingjun, SHAO Xinjun, YANG Hua, WANG Zhongsheng, LI Zhiyu, ZHANG Chaoqian, YUAN Ruier, FA Guifang
2023, Vol.35(6): 37–44
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1522 )
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551
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Evolution of Senegal Basin and exploration prospects of lithologic reservoirs
LI Hengxuan, WEN Zhixin, SONG Chengpeng, LIU Zuodong, JI Tianyu, SHEN Yiping, GENG Ke
2023, Vol.35(6): 45–53
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1614 )
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228
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Hydrocarbon accumulation rules and exploration technologies of Carboniferous subsalt carbonate reservoirs in the eastern margin of Pre-Caspian Basin
WANG Xueke, WANG Zhen, JI Zhifeng, YIN Wei, JIANG Ren, HOU Yu, ZHANG Yiqiong
2023, Vol.35(6): 54–62
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1628 )
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246
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Characteristics and controlling factors of high porosity and permeability limestone reservoirs of Cretaceous Cenomanian in the western United Arab Emirates
LUO Beiwei, YIN Jiquan, HU Guangcheng, CHEN Hua, KANG Jingcheng, XIAO Meng, ZHU Qiuying, DUAN Haigang
2023, Vol.35(6): 63–71
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1482 )
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241
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Identification of carbonate dissolution valleys filled with mudstones of Cretaceous in block A,Oman Basin
FAN Rui, LIU Hui, YANG Peiguang, SUN Xing, MA Hui, HAO Fei, ZHANG Shanshan
2023, Vol.35(6): 72–81
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1321 )
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211
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Exploration potential of lithologic reservoirs of Cretaceous AG Formation in Fula Sag,Muglad Basin,Africa
LIU Jiguo, ZHOU Hongpu, QIN Yanqun, ZOU Quan, ZHENG Fengyun, LI Zaohong, XIAO Gaojie
2023, Vol.35(6): 82–91
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1284 )
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209
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Main controlling factors and hydrocarbon accumulation models of structurallithologic reservoirs above source kitchen in rift basins in South Sudan
MA Feng, PANG Wenzhu, ZHAO Wenguang, ZHANG Bin, ZHAO Yanjun, XUE Luo, ZHENG Xi, CHEN Bintao
2023, Vol.35(6): 92–105
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1279 )
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255
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Deep-water sedimentary characteristics and sequence boundary identification of Middle Eocene in Rovuma Basin,East Africa
SUN Hui, FAN Guozhang, WANG Hongping, DING Liangbo, ZUO Guoping, MA Hongxia, PANG Xu, XU Xiaoyong
2023, Vol.35(6): 106–116
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1189 )
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225
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Determination of effective permeability of granitic buried-hill fractured reservoirs in Bongor Basin,Chad
GUO Haifeng, XIAO Kunye, CHENG Xiaodong, DU Yebo, DU Xudong, NI Guohui, LI Xianbing, JI Ran
2023, Vol.35(6): 117–126
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1126 )
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168
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Characteristics and prediction methods of igneous rocks in complex carbonate oilfields in Santos Basin,Brazil
LIU Yaming, WANG Dandan, TIAN Zuoji, ZHANG Zhiwei, WANG Tongkui, WANG Chaofeng, YANG Xiaofa, ZHOU Yubing
2023, Vol.35(6): 127–137
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1138 )
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Hydrocarbon accumulation conditions and favorable zones of lithologic reservoirs of Miocene Gumai Formation in block J,South Sumatra Basin
HONG Guoliang, WANG Hongjun, ZHU Houqin, BAI Zhenhua, WANG Wenwen
2023, Vol.35(6): 138–146
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1139 )
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Characteristics and new prediction methods of Jurassic subsalt carbonate reservoirs in the eastern right bank of Amu Darya,Central Asia
TANG Yuzhe, CHAI Hui, WANG Hongjun, ZHANG Liangjie, CHEN Pengyu, ZHANG Wenqi, JIANG Lingzhi, PAN Xingming
2023, Vol.35(6): 147–158
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Exploration progress and outlook for lithostratigraphic reservoirs of CNPC overseas
DOU Lirong, LI Zhi, YANG Zi, ZHANG Xingyang, KANG Hailiang, ZHANG Mingjun, ZHANG Liangjie, DING Liangbo
2023, Vol.35(6): 1–9
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2071 )
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631
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doi: https://doi.org/10.12108/yxyqc.20230601
Through analyzing a large number of overseas exploration cases in the past 30 years of CNPC“going out”,the current exploration status,distribution characteristics and exploration models of lithostratigraphic reservoirs were systematically summarized,and the exploration potential of global lithostratigraphic reservoirs and outlook for lithostratigraphic reservoirs of CNPC overseas were pointed out. The results show that:（1）The exploration of global lithostratigraphic reservoirs has gone through four stages,and is currently in a mature stage of development. The large-scale deep-water sediments and reefs have become the main areas for discovering giant lithostratigraphic oil and gas fields.（2）Lithostratigraphic reservoirs newly discovered by CNPC overseas exploration and global lithostratigraphic reservoirs are mainly distributed in composite traps,mainly developed in foreland,rift and passive continental margin basins,The former has the largest reserves found in rift basins,followed by foreland basin,while the latter has the largest reserves in foreland basin,rift basins was the second.（3）CNPC overseas has implemented the same deployment and integrated exploration strategy for structural and lithostratigraphic oil and gas reservoirs,forming three distinctive exploration models:Stereoscopic exploration for multiple lithostratigraphic reservoirs,discovered high abundance lithologic reservoirs in lower combination,high buried hill reservoirs and low buried hill-lithologic complex reservoirs in Bongor Basin of Chad,and channel,fan delta,subaqueous fan and buried hill reservoirs in South Turgai Basin of Kazakhstan;High resolution 3D seismic exploration for complex lithologic bodies,discovered large gentle slope reef-beach complex gas reservoirs in Amu Darya Basin of Turkmenistan,giant lacustrine reef-beach oil fields in Santos Basin of Brazil,and deep-water turbidite sandstone biogas reservoirs in Rakhine sub-basin of Myanmar;Geology and engineering integration exploration for thin layer low amplitude structural-lithologic complex,discovered low amplitude structural-lithologic complex oil reservoirs in Oriente Basin of South America and thin layer reef-beach oil reservoirs in the Oman sub-basin of Middle East.（4）The exploration of global lithostratigraphic reservoirs will expand from mature exploration areas to frontier areas with low exploration levels,and from onshore to deep-water and ultra deep-water areas. The deep-water sedimentary bodies,subaqueous fans,and reefs in passive continental margin basins will be the hotspots of lithostratigraphic reservoir exploration. Subaqueous fans and burial hills in rift basins,composite traps related to reefs in foreland and passive continental margin basins will be the main targets of lithostratigraphic reservoirs exploration for CNPC overseas,which have favorable prospects for exploration.
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Characteristics of hydrocarbon accumulation in deep-water depositional system in offshore East Africa
SHI Buqing, DING Liangbo, MA Hongxia, SUN Hui, ZHANG Ying, XU Xiaoyong, WANG Hongping, FAN Guozhang
2023, Vol.35(6): 10–17
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1920 )
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388
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doi: https://doi.org/10.12108/yxyqc.20230602
Using high quality 3D seismic and logging data,Paleocene-Oligocene deep-water depositional system in Rovuma Basin and Upper Cretaceous deep-water depositional system in Zambezi Depression were studied,and the hydrocarbon accumulation conditions of both deep-water depositional systems were compared. The results show that:（1）Channel and lobe sands are large-scale favorable reservoirs in Paleocene-Oligocene deepwater depositional system in Rovuma Basin,and the reconstruction of contour current is the key factor for the formation of high-quality reservoirs.（2）Typical deep-water deposits,such as channels,lobes,block transport deposits,are developed in Upper Cretaceous in Zambezi Depression,while large scale drifts possibly are highquality reservoirs.（3）A large amount of hydrocarbon was potentially accumulated in Upper Cretaceous deepwater sands in Zambezi Depression,which was generated from Lower Cretaceous shale of restricted marine environment. Reservoirs were capped by widely distributed HST shale,and lithologic traps could be assumed by up dip pinch-out. With good conditions for hydrocarbon accumulation,it is a favorable area for next oil and gas exploration.
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Key techniques of high-resolution processing of desert seismic data and its application in Agedem area,Niger
SU Qin, ZENG Huahui, XU Xingrong, WANG Deying, MENG Huijie
2023, Vol.35(6): 18–28
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1709 )
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doi: https://doi.org/10.12108/yxyqc.20230603
A seismic data processing method was proposed to address the severe high-frequency energy absorption and attenuation of seismic reflection waves by surface sand dunes,which results in low resolution,weak energy,and narrow frequency bandwidth in seismic data from desert areas. The method combines three approaches:nearsurface pre-stack Q compensation with micro-logging constraints,pre-stack depth Q migration,and post-stack compressive sensing frequency extrapolation based on well constraints. The method was tested on data from Agedem area in Niger. The results show that:（1）After applying the micro-logging constrained Q compensation method,the seismic data from Agedem area in Niger showed higher signal-to-noise ratio,improved resolution,smoother continuous reflection axes,enhanced effective information energy,and clearer depiction of small structures. The frequency bandwidth was expanded from 35 Hz to 70 Hz,and the main frequency increased from 30 Hz to 45 Hz.（2）The Q pre-stack depth migration eliminated the attenuation and dispersion caused by non-elastic factors and formation absorption during seismic wave propagation,ensuring imaging accuracy.（3）The results of compressive sensing frequency extrapolation method based on well-constrained data showed better matching with synthetic well records than that of unconstrained extrapolation processing,resulting in improved fidelity. It further enhanced weak signal energy and recovered the energy loss caused by severe absorption attenuation. The positioning accuracy of the 20-40 ms interval in Agedem area of Niger was improved,and the problem of false horizons at 180 ms after unconstrained processing was resolved.（4）The combined method achieved favorable results in Agedem area of Niger. The processed seismic data exhibited clear fault structures,crisp fault section waves,and easily identifiable small fault segments. After calibration with well logging data of well DB1,the correlation coefficient for the entire well section exceeded 0.92.
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Accumulation model and favorable area prediction of structural-lithologic composite reservoirs in block W,the slope zone of Oriente Basin,South America
MA Wenjie, WAGN Jingchun, TIAN Zuoji, MA Zhongzhen, WAN Xuepeng, LIN Jincheng, XU Xianglin, ZHOU Yubing
2023, Vol.35(6): 29–36
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1662 )
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doi: https://doi.org/10.12108/yxyqc.20230604
Through core observation,seismic interpretation,reservoir inversion,crude oil geochemical analysis,oil-source correlation,and oil and gas migration tracing analysis,the accumulation rules of typical structurallithologic composite reservoirs in block W of the slope zone of Oriente Basin in South America were analyzed,and the further favorable exploration directions were pointed out. The results show that:（1）the structurallithologic composite reservoirs in block W of the slope zone of Oriente Basin are generally characterized by westsouthwest dipping monoclinic structures,with local nose uplifts. The target layer of the oil reservoirs is M1ss member of Cretaceous Napo Formation. The sand bodies are NW-SE trending,with a large reservoir thickness and good physical properties.（2）Reservoir distribution is controlled by the sandbars in estuaries,the NW-SE extends shale belt and stable west-southwest dipping nose uplifts background joint control the trap formation and the spatial distribution of effective oil migration pathway controls reservoir formation.（3）There are three stages for structural-lithologic reservoir formation,including the early conventional crude oil filling stage,the middle stage for crude oil degradation,and late stage of conventional crude oil mixing.（4）The southwest part of the two shale belts in southern area of block W is favorable for structural-lithologic traps.
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Classification and categorization method of overseas lithologic reservoir reserves
XIA Mingjun, SHAO Xinjun, YANG Hua, WANG Zhongsheng, LI Zhiyu, ZHANG Chaoqian, YUAN Ruier, FA Guifang
2023, Vol.35(6): 37–44
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551
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doi: https://doi.org/10.12108/yxyqc.20230605
In order to standardize overseas oil reserves evaluation,a method for classifying and categorizing overseas lithologic reservoir reserves,determining lithologic boundary,o il bearing area and effective thickness was proposed. The results show that:（1）Reserves classified as P generally require a development plan approved by the company or the government of the resources country. P1 reserves are calculated based on wells with commercial production or commercial test flow rates,and their area is usually determined by the drainage area of the production wells and the range limited by the known gas bottom or the known oil top and oil bottom. The reserves within half the distance from the P1 reserves boundary to lithologic boundary are P2 reserves,and the reserves within the range from P2 reserves boundary to lithologic boundary are P3 reserves. If there is no oil water contact within the trap or cannot be determined yet,P3 reserves should be determined based on the spill point of the trap. If there are significant changes in lithologies or reservoir physical properties,P2 reserves can be determined by extrapolating one development well spacing based on P1 reserves,and P3 reserves can be determined by extrapolating one development well spacing based on P2 reserves.（2）When the distance from a class P reserve well to the pinchout line of a permeable reservoir is no more than 3-4 times the development well spacing,for medium to high porosity and permeability reservoirs,the pinchout line can be directly determined as the lithologic boundary,while for low porosity and permeability reservoirs,the minimum effective thickness contour line that can meet the class P reserve standard is determined as the lithologic boundary. The oil and gas bearing area should be comprehensively delineated by lithology boundaries,oil（gas）water contact,tight layer sealing zones,etc,the wells within the area should meet the class P reserve standard. For oil and gas reservoirs with identified fluid interfaces,the fluid interfaces used to delineate oil and gas bearing area should be confirmed by drilling and coring data or testing data. For oil and gas reservoirs with unidentified fluid interfaces,the oil and gas bearing area should be determined by extrapolating the lowest confirmed bottom boundary of the oil and gas producing layer or the effective thickness value through testing.（3）The determination of the effective thickness of P1 reserves should have reliable formation testing data or sufficient logging data and have demonstrated its production capacity. The determination of the effective thickness of P2 reserves usually lacks conclusive testing data and has not confirmed its production capacity. Due to the uncertainty in rock physical interpretation,there is significant uncertainty in the effective thickness of P3 reserves.（4）It is recommended to use the volumetric method for evaluating lithologic reservoir reserves. The application example in TP oilfield in Ecuador has confirmed the effectiveness of the classification and categorization of lithologic reservoir reserves and reserves evaluation method.
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Evolution of Senegal Basin and exploration prospects of lithologic reservoirs
LI Hengxuan, WEN Zhixin, SONG Chengpeng, LIU Zuodong, JI Tianyu, SHEN Yiping, GENG Ke
2023, Vol.35(6): 45–53
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doi: https://doi.org/10.12108/yxyqc.20230606
Passive continental margin basins have low exploration degree and high potential,and Senegal Basin is one of the exploration hotspots of passive continental margin basins in recent years. Based on plate tectonic evolution,the evolution process of Senegal Basin was restored using seismic and geologic data,and the exploration prospects of lithologic reservoirs were analyzed. The results show that:（1）The Senegal Basin can be divided into three evolution stages,incluing intra-continental rift during the Middle Triassic rift,inter-continental rift during the Late Triassic to Early Jurassic transition,and passive continental margin during the Middle Jurassic to the present drift. Controlled by paleostructure and paleoclimate,the rift sediments are thin and buried deeply,mainly in continental red beds stratigraphic sequence. Evaporite facies develop widely in intercontinental rift. The drifting sequence deposits with large thickness and deep-water sedimentary system are important reservoirs in discovered oil and gas fields.（2）The Lower Cretaceous Albian delta sand bodies were mainly developed in the deep-water area of the Middle sub-basin,and the Lower Cretaceous fault-lithologic reservoirs were formed by lateral or vertical migration of oil and gas. The Upper Cretaceous Cenomanian-Maastrichtian turbidity fan sand bodies were developed in the ultra-deep water area,and the oil and gas migrated upward to form Upper Cretaceous submarine fan lithologic reservoirs. Miocene turbidite fan sand bodies were mainly developed in Mauritania and Casamance salt basins,salt diapirs have important effects on oil and gas migration and sealing,forming salt structure related oil and gas reservoirs.（3）Combined with the discovered law of oil and gas accumulation,the Upper Cretaceous submarine fan reservoirs may be developed in Mauritania and Casamance subbasins without drilled wells,while the reef-shoal reservoirs may be developed in the carbonate platform of the entire basin shelf,and they are the next key exploration areas.
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Hydrocarbon accumulation rules and exploration technologies of Carboniferous subsalt carbonate reservoirs in the eastern margin of Pre-Caspian Basin
WANG Xueke, WANG Zhen, JI Zhifeng, YIN Wei, JIANG Ren, HOU Yu, ZHANG Yiqiong
2023, Vol.35(6): 54–62
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doi: https://doi.org/10.12108/yxyqc.20230607
Based on seismic,drilling and thin section data,seismic wave impedance reservoir inversion technology was used to study the characteristics and hydrocarbon accumulation rules of Carboniferous subsalt carbonate reservoirs in the eastern margin of Pre-Caspian Basin,and the next risk exploration direction was pointed out.The results show that:（1）Carboniferous subsalt carbonate reservoirs in the eastern margin of Pre-Caspian Basin can be divided into limestones,dolomites,dolomitic limestones,calcareous dolomites,silicified siliceous rocks. The reservoir porosity is 4%-12%,and the permeability is generally less than 1 mD,belonging to lowmedium porosity and low permeability vug-pore reservoirs.（2）Lithologic reservoirs are mainly developed in Aknol structural belt in the study area,without uniform oil-water contact. The oil layers are distributed in thin layers,with poor correlation and continuity. High-quality reservoirs are mostly high growth rate beach bodies in the upper part of high-frequency third-order sequence cycles and karst reservoirs near unconformity surfaces.（3）The seismic wave impedance reservoir inversion technology based on the initial model constrained by horizon and logging was used to predict thin carbonate reservoirs,which can more clearly show the horizontal and vertical distribution characteristics of KT-Ⅰ and KT-Ⅱ reservoir groups. The favorable reservoirs in the study area are mainly developed in G1 and G4 sublayers at the top of KT-Ⅱ reservoir group.
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Characteristics and controlling factors of high porosity and permeability limestone reservoirs of Cretaceous Cenomanian in the western United Arab Emirates
LUO Beiwei, YIN Jiquan, HU Guangcheng, CHEN Hua, KANG Jingcheng, XIAO Meng, ZHU Qiuying, DUAN Haigang
2023, Vol.35(6): 63–71
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doi: https://doi.org/10.12108/yxyqc.20230608
By using methods such as core and thin section analysis,nuclear magnetic resonance and micro-CT testing,isochronous tracing under sequence framework and paleogeomorphic restoration,a systematic analysis was conducted on the sedimentary characteristics,sequence,sedimentary evolution characteristics and diagenesis of high porosity and permeability limestone reservoirs of Cretaceous Cenomanian in the western United Arab Emirates,and the controlling factors of high porosity and permeability reservoirs were studied from the aspects of structure,sedimentation and diagenesis. The results show that:（1）The high porosity and permeability limestone reservoirs of Cenomanian in the western United Arab Emirates are mainly developed in Mishrif Formation,with the lithologies mainly consisting of sparite rudist limestone,sparite bioclastic limestone,and micrite bioclastic limestone. The reservoirs space is mainly composed of biological cavities,moldic pores and intergranular dissolved pores. The Mishrif Formation is generally characterized by carbonate ramp sedimentation,three types of subfacies including inner ramp,middle ramp and outer ramp,and six types of microfacies including rudistid reefs,high-energy shoals,front/back shoals and inter-shoals,lagoons can be identified. High porosity and permeability reservoirs are mainly developed in rudistid reefs and high-energy shoals. The porosity and permeability of limestone reservoirs in rudistid reefs are 20%-34% and 150-2 000 mD,respectively,while the porosity and permeability of limestone reservoirs in high-energy shoals are 25%-33% and 40-370 mD,respectively.（2）From bottom to top,the Mishrif Formation in the study area can be divided into three third-order sequences SQ1-SQ3 and seven systems tracts. The SQ1-SQ2 sequences are mainly composed of highstand systems tract,with rudistid reefs and high-energy shoals broadly developed. The SQ3 sequence is composed of highstand systems tract and transgressive systems tract,with high-energy shoals well developed in high parts of ancient landform and beeter properties.（3）The pore development of the high porosity and permeability reservoirs of Mishrif Formation in the study area is afffacted by multi-stage of diagenesis,including constructive diagenesis dominated by contemporaneous atmospheric freshwater dissolution and maintenance diagenesis related to hydrocarbon filling.（4）The high porosity and permeability reservoirs of Mishrif Formation in the study area are controlled by multiple geological factors such as sedimentary facies,sequence framework,paleogeomorphology and diagenetic effects,and the sedimentary facies was setted as the main factors. The distribution and evolution of sedimentary facies in Mishrif Formation was controlled by HST during SQ1 and SQ2,while influenced by the inherited paleogeomorphology during the SQ3.
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Identification of carbonate dissolution valleys filled with mudstones of Cretaceous in block A,Oman Basin
FAN Rui, LIU Hui, YANG Peiguang, SUN Xing, MA Hui, HAO Fei, ZHANG Shanshan
2023, Vol.35(6): 72–81
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doi: https://doi.org/10.12108/yxyqc.20230609
Based on seismic data,drilling and logging data,the seismic reflection characteristics and the distribution rules of carbonate dissolution valleys filled with mudstones of Cretaceous in block A of Oman Basin were studied by using seismic forward modeling and attributes,and the hydrocarbon accumulation model was determined. The results show that:（1）A dissolution valleys system filled with mudstones is developed in the west and middle of block A,Oman Basin,which is characterized by concave features,discontinuous reflection and weak amplitude. The dissolution valleys with depth greater than 3 m and width greater than 10 m could be identified using available seismic data.（2）By optimizing seismic attribute,it is found that Euler curvature could suppress the influence of dense faults and the effect of dissolution valleys identification is better than coherence and regular curvature attributes.（3）Combination traps of dissolution valleys filled with mudstones are identified whose total area is 80.66 km2 by the new identification technology. In addition,good oil and gas shows was revealed by a new well,confirming the reliability of this technology.
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Exploration potential of lithologic reservoirs of Cretaceous AG Formation in Fula Sag,Muglad Basin,Africa
LIU Jiguo, ZHOU Hongpu, QIN Yanqun, ZOU Quan, ZHENG Fengyun, LI Zaohong, XIAO Gaojie
2023, Vol.35(6): 82–91
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doi: https://doi.org/10.12108/yxyqc.20230610
Referring to the domestic exploration theory and technology of lithologic oil and gas reservoirs in fault basins,sequence stratigraphy analysis method was used to carry out multi-scale sequence stratigraphy division,geochemical analysis of source rocks,research on hydrocarbon accumulation rules,favorable zone division and potential evaluation of Fula Sag in Muglad Basin of Central African Rift System. The results show that:（1）Five third-order sequences can be identified based on the sea level changes,and the flooding surface is the most favorable vertical location for lithologic reservoirs.（2）There are three major provenance systems in AG Formation in the study area. Fula-west steep slope belt is short-axis with rapid deposition and narrow distribution of facies zones. Braided river delta system is continuously developed with wide distribution in the northeastern part of the study area,and braided river delta system is limited developed in the southeastern part at the later period. The delta front and beach bar in shore-shallow lacustrine are the most favorable sedimentary facies for lithologic reservoirs.（3）Grey-dark mudstones developed in AG2 member（SQ4 sequence）of AG Formation are mainly deposited in shallow lake to semi-deep lake environment. The kerogen is type Ⅰ-Ⅱ1,the average total organic carbon（TOC）content is 3.41%,and the hydrocarbon generation potential（S1+ S2）is greater than 8 mg/g,which are good-excellent source rocks and the material basis for the forming of structural-lithologic reservoirs.（4）The AG Formation can be divided into seven lithologic reservoirs zones,among which the northern Fula-Moga slope zone has favorable conditions for hydrocarbon accumulation and great exploration potential.
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Main controlling factors and hydrocarbon accumulation models of structurallithologic reservoirs above source kitchen in rift basins in South Sudan
MA Feng, PANG Wenzhu, ZHAO Wenguang, ZHANG Bin, ZHAO Yanjun, XUE Luo, ZHENG Xi, CHEN Bintao
2023, Vol.35(6): 92–105
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doi: https://doi.org/10.12108/yxyqc.20230611
Based on drilling,logging and 3D seismic data,core analysis,well correlation,oil and gas migration and accumulation simulation,seismic inversion and multi-information superposition methods were used to analyze the main controlling factors of structural-lithologic reservoirs above source kitchen in Melut and Muglad rift basins in South Sudan from three aspects:oil source conditions,reservoir and cap-rock assemblage and migration systems,and hydrocarbon accumulation models were discussed. The results show that:（1）The Melut and Muglad basins both developed high-quality source rocks in the I stage rifting period of the Early Cretaceous with large thickness,wide area,good organic matter type and moderate maturity,providing good oil source conditions. The Paleogene Yabus Formation and Neogene Jimidi Formation in Melut Basin,and Cretaceous Aradeiba Formation in Muglad Basin developed delta facies and fluvial deposits,and the microfacies sand bodies of river channels and underwater distributary channels had moderate sand content and sandstone thickness,and sealing zones in floodplains and underwater distributary bays are locally developed.The sand-mud interlayer reservoir and cap assemblage formed on multiple sources,and the reservoir and cap-rock assemblage and its vertical sedimentary evolution controlled the formation of large-scale structural-lithologic traps. The boundary-controlled basin faults and the depression-controlling faults in the slope area of the basin margin were the main vertical migration channels of oil and gas connecting the main source rock and the target layer above source kitchen. The multi-stage unconformities and sand-rich strata above source kitchen formed multiple lateral dominant migration paths（transport ridges）. The coupling of the source faults and transport ridges controlled the favorable zones of the structural-lithologic reservoirs above the source kitchen in Melut and Muglad basins.（2）The Yabus Formation,Jimidi Formation in Melut Basin and Aradeiba Formation in Muglad Basin have the petroleum geological conditions for the formation of scale structural-lithologic reservoirs above source kitchen,and the accumula-tion models are vertical migration of fault,vertical migration of fault and lateral migration of unconformity plane,and vertical migration of fault and lateral migration of connected sandbodies.
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Deep-water sedimentary characteristics and sequence boundary identification of Middle Eocene in Rovuma Basin,East Africa
SUN Hui, FAN Guozhang, WANG Hongping, DING Liangbo, ZUO Guoping, MA Hongxia, PANG Xu, XU Xiaoyong
2023, Vol.35(6): 106–116
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doi: https://doi.org/10.12108/yxyqc.20230612
Guided by the classic model of sequence stratigraphy,using core,welllog,mudlog and seismic data,the characteristics of the third-order and fourth-order sequence boundaries of Middle Eocene in the deep-water area of Rovuma Basin in East Africa were summarized. Corresponding to channel-lobe complexes in deep-water depo-sits,sedimentary subfacies and microfacies were divided. Based on this,the evolution laws of deep-water deposits and the influence of sedimentary microfacies on reservoirs were explored. The results show that:（1）The top boundary of the third-order sequence of Middle Eocene in Rovuma Basin is located at the top of the condensed section and occasional carbonate debris flow,and the bottom boundary is located at the bottom of the gravity flow that migrates southward in stages. The fourth-order sequence is determined by the top boundary of the bathyal deposit and the sedimentary interface with good continuity on the seismic section,but can only be interpreted within the distribution range of the channel-lobe complexes.（2）Two sedimentary facies,including channel complex and lobe complex,have been identified in deep-water deposits in the study area. The two sedimentary facies can be subdivided into four subfacies:composite channel,lobe,crevasse splay,and overbank/drift deposits. There are nine microfacies,including channel axis/edge filling,internal natural levee,mass transport deposits（MTD）,channel bottom lag deposit,lobe element main body/edge,crevasse splay,and overbank/drift deposits. Both crevasse splay and overbank/drift deposits are distributed in the northern part of the composite channel,and the crevasse splay affected by bottom flow is in a northward divergent vein shape.（3）The evolution of deep-water depo-sits of Middle Eocene in the study area can be divided into four stages,namely SQ1-SQ4 in sequence,showing a process of progradational deposition and retrograde deposition as a whole. Affected by the interaction between gravity flow and bottom current,the channel-lobe complexes gradually migrated southward.（4）The development of reservoirs in the research area is mainly controlled by sedimentary microfacies. The main body of the lobe element and the axis of the channel developed high-quality reservoirs. The reservoirs are the most developed and the physical properties are the best in the main body of the lobe element,with a porosity of 13.00%-21.00% and a permeability of 5.0-118.0 mD. The reservoir properties at the axis of the channel are secondary,with a poro-sity of 13.00%-19.00% and a permeability of 0.8-23.0 m D. The reservoir properties of overbank/drift deposits are poor,and the reservoirs in the crevasse splay are not developed.
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Determination of effective permeability of granitic buried-hill fractured reservoirs in Bongor Basin,Chad
GUO Haifeng, XIAO Kunye, CHENG Xiaodong, DU Yebo, DU Xudong, NI Guohui, LI Xianbing, JI Ran
2023, Vol.35(6): 117–126
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doi: https://doi.org/10.12108/yxyqc.20230613
A new effective permeability calculation method was proposed for the granitic buried-hill reservoirs in Bongor Basin of Chad based on drilling,logging,and oil testing data. Apparent effective permeability was derived from well testing results,serving as labeled data for the sample dataset. The method relies primarily on domain knowledge and mechanism-driven models,and is supplemented by machine learning to establish feature logs. The dual-prediction model XGBoost+KNN was employed to calculate apparent effective permeability,with SHAP values used for model interpretability analysis. The results show that:（1）Permeability indicator logs,namely apparent acoustic impedance and porosity,were utilized to select 26 effective testing intervals from19 wells,based on their intersection with production index. The well testing results were converted into apparent permeability values,ranging from 0.01 to 1 601.50 m D,resulting in a dataset comprising 51 348 depth data points and 14 input logs. The sample dataset adequately covers the main buried hill zones and incorporates input log response characteristics from diverse lithologies,reservoir qualities,and well testing production performance,thus achieving sufficient representativeness.（2）The XGBoost model effectively uses various logs,inclu-ding the apparent acoustic impedance log,normalized depth log representing the vertical zoning characteristics of buried-hill reservoirs,density log,window average of natural gamma ray log,acoustic log,neutron log,window average of neutron-density porosity difference log,deep and shallow resistivity log,and window standard deviation of natural gamma ray log. The model’s predictions exhibit consistency with qualitative understanding of buried-hill reservoir quality and demonstrate higher accuracy compared to the KNN model.（3）The granitic buried-hill reservoirs of Bongor Basin,Chad,with effective permeability greater than 1.00 m D,are classified as effective reservoirs,while those exceeding 50.00 mD are considered good reservoirs. The calculated results using the proposed method are consistent with the well testing results.
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Characteristics and prediction methods of igneous rocks in complex carbonate oilfields in Santos Basin,Brazil
LIU Yaming, WANG Dandan, TIAN Zuoji, ZHANG Zhiwei, WANG Tongkui, WANG Chaofeng, YANG Xiaofa, ZHOU Yubing
2023, Vol.35(6): 127–137
Abstract
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doi: https://doi.org/10.12108/yxyqc.20230614
Based on cores,analytical tests,well logging and seismic data,the stages,lithology and lithofacies,geophysical characteristics and volcanic edifices of igneous rocks in Santos Basin of Brazil were studied by means of combination of geology and geophysics,and the development characteristics of igneous rocks in Eastern oilfield was analyzed. The results show that:（1）The Santos Basin developed five stages of magmatic activities,namely Valanginian-Hauterivian eruptive rocks,Barremian-Early Aptian eruptive rocks,Aptian eruptive rocks,Campanian intrusive rocks,and Eocene intrusive rocks and eruptive rocks. There are two eruption models,incluing subaerial eruption and subaqueous eruption,two types of volcanic edifices,including fissure type and central type,and six types of rock facies,including volcanic channel facies,volcanic neck facies,overflow facies,cataclastic facies,subvolcanic facies and volcanic sedimentary facies.（2）The distribution prediction of igneous rocks in Eastern oilfield has been realized according to the prediction method of region determination by volcanic edifice,source determination by volcanic channel,facies determination by seismic reflection characteristics,qualitative determination by multiple attributes and quantitative determination by pre-stack inversion. Intrusive rocks are mainly distributed in the central part of the study area,and eruptive rocks are mainly distributed in the northwest and east part of the study area. The results were confirmed by drilling and the coincidence rate reached 95%.（3）Hydrocarbon accumulation in basins with igneous rocks is closely related to the formation and evolution of igneous rocks. Igneous rocks have both constructive and destructive effects on hydrocarbon accumulation,and they are of great significance for oil and gas exploration.
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Hydrocarbon accumulation conditions and favorable zones of lithologic reservoirs of Miocene Gumai Formation in block J,South Sumatra Basin
HONG Guoliang, WANG Hongjun, ZHU Houqin, BAI Zhenhua, WANG Wenwen
2023, Vol.35(6): 138–146
Abstract
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doi: https://doi.org/10.12108/yxyqc.20230615
Lithologic reservoirs are developed in the lower member of Miocene Gumai Formation in South Sumatra Basin. Based on logging,mud logging and seismic data,combined with regional setting,the hydrocarbon accumulation conditions and main controlling factors of the lower member of Miocene Gumai Formation in block J of South Sumatra Basin were studied,and the favorable zones were predicted. The results show that:（1）Oil and gas in block J of South Sumatra Basin mainly come from the eastern Betara hydrocarbon generation sag,and there are three sets of source rock developed,namely,the source rocks in the lower member of Talang Akar Formation,the source rocks in the upper member of Talang Akar Formation,and the source rocks in Gumai Formation. Among them,the marine continental transitional source rocks developed in the lower member of Talang Akar Formation are the best,mainly type Ⅰ or Ⅱ kerogen,containing a large number of coal seams. The TOC content is mainly 0.5%-2.0%,hydrogen index（HI）is mainly 100-350 mg/g,and the average oxygen index（OI）is 30 mg/g.（2）The lower member of Gumai Formation in block J developed a set of sedimentary systems from east to west,including proximal delta front,distal delta front,and prodelta. The proximal delta front in the eastern part of the block is mainly composed of thick sandstone,while the distal delta front in the western part is mainly composed of mudstone with thin sandstone. Massive medium to fine sandstones are the main reservoir rocks,with widely developed argillaceous bands,which are underwater distributary channels and overbank in the delta front.（3）The lithologic reservoirs of Gumai Formation in block J are controlled by mudstone seal and major faults. Oil and gas are mostly concentrated in distal delta front with high shale content and good sealing conditions in the western part of the block.（4）The lithologic reservoirs in the lower member of Gumai Formation in block J have a hydrocarbon accumulation model of“lower generation and upper storage,composite transport,and caprock controlled reservoir”. The W and P regions in the central part are favorable areas for lithologic reservoir exploration.
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Characteristics and new prediction methods of Jurassic subsalt carbonate reservoirs in the eastern right bank of Amu Darya,Central Asia
TANG Yuzhe, CHAI Hui, WANG Hongjun, ZHANG Liangjie, CHEN Pengyu, ZHANG Wenqi, JIANG Lingzhi, PAN Xingming
2023, Vol.35(6): 147–158
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doi: https://doi.org/10.12108/yxyqc.20230616
Based on core,thin section,and well logging data,the lithologies,reservoir space,and physical properties of Jurassic Oxfordian reservoir in the eastern right bank of Amu Darya in Central Asia were analyzed.3D seismic data were used to carry out semi-quantitative prediction of reservoir distribution and thickness through methods such as forward seismic modeling,waveform clustering,frequency-division RGB fusion and ensemble learning. The results show that:（1）The lithologies of Jurassic Oxfordian reservoir in the eastern right bank of Amu Darya are mainly bioclastic limestone,grainstone and micritic limestone,and the reservoirs are characterized by fractured-vuggy type. The reservoir space is dominated by biological framework pores,intragranular pores and fractures,and fractures provide a channel for later dissolution fluids. The average thickness of the reservoir is 41.6 m,and the average porosity is 4.65%.（2）The reservoirs in the study area are mostly developed in the XVhp layer,and can be divided into top-type,bottom-type,and dual-type according to their distribution position in the XVhp layer. The top-type reservoirs are mainly distributed in the central and eastern parts of the study area,the bottom-type reservoirs are concentrated in the west,while the dual-type reservoirs are extensively developed in the northwest. The reservoirs in the western and northeastern parts of the study area are well developed,with a thickness of 45-75 m,mostly distributed along fault zones. The reservoirs in the southeastern part are poorly developed,with a thickness less than 30 m,and are further away from faults.（3）When using ensemble learning method to calculate the reservoir thickness in the study area,the stacking method in the heterogeneous ensemble approach was used for model computation. Outliers were eliminated using a boxplotbased method,and the predictive performance of the models was evaluated through cross-validation. The calculated reservoir thickness showed a high degree of agreement with the thickness observed in 11 wells drilled in the study area,and the correlation coefficient is 0.74.