石油实验地质

2021, 43(4): .

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Key structural periods and Permian tight gas accumulation response in Hangjinqi area, Ordos Basin

LUO Kaiping, YANG Fan, LU Yongde, LIU Zhaoqian, TANG Yong

2021, 43(4): 557-568. doi: 10.11781/sysydz202104557

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Critical tectonic period is a critical time point that characterizes the genetic connection and causal relation (accumulation response) between tectonic effect and oil/gas accumulation in large superposition basins, it is also an important "window" for analyzing accumulation evolution and accumulation regularity of oil/gas. Based on the systematic review of the tectonic evolution history of the Ordos Basin, the tectonic evolution and deformation sequence since the Mesozoic in Hangjinqi area in the northern part of Ordos Basin were studied through the constraints of apatite fission tracks and other thermal chronological indicators. Two key structural periods including J₃-K₁ and K₂-E₁ were proposed. It was believed by combining with the understanding of the Carboniferous-Permian hydrocarbon-generating and reservoir-forming histories that the J₃-K₁ was the period of design finalization in the Hangjinqi area which formed a currant NE-trending structural framework "high in the northeast and low in the southwest" during which, lithologic gas reservoirs including the Carboniferous Taiyuan and the Permian Shanxi formations, first member of the Permian Shihezi Formation to the north of the Sanyanjing-Wulan Jilin Temple-Bo'erjiang Haizi fault were formed and corresponding to the period of great amount of hydrocarbon generated and expulsed from source rocks as well as the densification of sandstones. On the other hand, the K₂-E₁ period was the major stage for fault reactivation and the formation of NE-trending tectonic trap and NW-trending fault that led to the adjustment of early lithologic gas reser-voirs in the south and the formation of structural or structural-lithologic gas reservoirs in the north. The difference of accumulation on each sides of the main fault is obvious. The southern part was formed earlier than the northern part, and was dominated by lithologic gas reservoirs yet the northern part was dominated by structural-lithological gas reservoirs. The southern gas-bearing strata are dominated by deep strata, while those in the north are both shallow and deep ones. In Paleogene, lifting in the north caused loss of gas. The key accumulation and transformation periods transformed with space and time, which transformed accumulation factors differentially and finally constrained the enrichment and depletion of natural gas.

Fault systems and their relationships to oil and gas in Dabancheng subsag, Chaiwopu Sag, Junggar Basin

YUAN Haowei, CHEN Shuping, Dai Kun, YU Hongzhou, WANG Xinpeng, WANG Yuxin, ZHAO Huaibo

2021, 43(4): 569-579. doi: 10.11781/sysydz202104569

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The Chaiwopu Sag of Junggar Basin experienced a major breakthrough in oil and gas exploration for the first time in the late 1980s, however, the exploration effect in this area is still restricted by the complexity of faults and the uneven distribution of oil and gas. As the main body of the sag, the Dabancheng subsag has been strongly extruded by the Bogda Mountain thrust belt to the south, the Yilian Habirga Mountain (abbreviated as Yishan) thrust belt to the northeast, and the Heishan Mountain to the northwest since Permian. A compressive and narrow ramp structural system superimposed by multiple stress fields was developed, which led to the complexity and particularity of fault characteristics and evolution in the Dabancheng subsag. Approaches including logging, seismic and field geological survey data were applied to study the fault systems in the subsag, including the Southern Bogda Mountain fault system, the Yishan fault system and the Heishan fault system. The Southern Bogda Mountain fault system has a shallow detachment surface, which belongs to an orogenic wedge structure with plastic detachment layers. The Yishan fault system is a basement-involved structure. The Late Hercynian, Indosinian, Yanshanian and Himalayan tectonic movements have geological records in this area, forming different scales of faults. The late Hercynian period is a breakup stage, the Indosinian-Yanshanian period is a fault-shaping period, and the Himalayan period is a fault adjustment period. The distribution of detachment belt in the Southern Bogda Mountain fault system is consistent with that of the Middle-Lower Permian source rocks. Combined with the analyses of tectonic movement period, stratigraphic characteristics and fault systems, the Southern Bogda Mountain fault system is a potential oil and gas accumulation area.

Enrichment model of shale gas in southeastern Sichuan Basin: a case study of Upper Ordovician Wufeng and Lower Silurian Longmaxi formations in Dingshan area

NI Kai, WANG Mingfa, LI Xiang

2021, 43(4): 580-588. doi: 10.11781/sysydz202104580

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Based on the understanding of the basic geological conditions of shale gas from the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in Dingshan area of the southeastern Sichuan Basin, the occurrence, migration mode and intensity of natural gas in the shale gas system were discussed according to the results of drilling, logging, fracturing test, laboratory test and structural interpretation, moreover, a shale gas enrichment mode suitable for the study area was proposed. In shale gas systems, high-angle fractures extend for a short distance, while horizontal fractures such as bedding-parallel detachment and interlayer bedding fractures extend for a long distance. As a result, the permeability in the bedding direction is much greater than that in the vertical direction. These characteristics together determined that natural gas in shale gas system was usually transported horizontally, and sometimes both horizontally and vertically. For the Qiyueshan fault zone, the burial depth of shale reservoir and the distance to Qiyueshan fault zone are the major constrains for shale gas enrichment in the Wufeng-Longmaxi formations in the study area. The Qiyueshan fault zone is a basin-controlling fault zone with fractures and associated fractures developed, and is a shale gas escaping area. In the shallow-buried area in the southeastern part, high-angle fractures were relatively developed, by which horizontal fractures were opened. The proportion of free gas was less than 60%. A normal pressure system indicates a semi-retention area for shale gas. In the middle-to deep-buried area in the northwest, high-angle fractures were relatively undeveloped, and horizontal fractures were closed. The vertical and horizontal migrations were blocked, and most of shale gas was trapped in shale reservoirs. The proportion of free gas is more than 60%. A high-to ultra-high pressure system indicates a shale gas accumulation area.

Pore structure of continental shale reservoirs in Lower Jurassic Ziliujing Formation, northeastern Sichuan Basin

FU Xiaoping, YANG Tao

2021, 43(4): 589-598. doi: 10.11781/sysydz202104589

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The accumulation and enrichment of shale gas were significantly influenced by the pore structure of shales. In this study, thin section observation, Argon ionization-scanning electron microscopy analysis, physical property test, mercury injection-N₂ adsorption combination, X-ray diffraction whole rock analysis and X-ray diffraction clay mineral analysis were carried out to study the pore structure characteristics of continental shale of Lower Jurassic Ziliujing Fromation, northeastern Sichuan Basin. Results showed that: (1) In the Ziliujing Formation of the northeastern Sichuan Basin, the pores were mainly parallel plate and slit ones, and ink bottle pores were also developed. The average value of specific surface area of shale was 4.031 m²·g^-1, the average value of total pore volume was 93.88×10^-4 mL·g^-1, and the micro pores were dominated by meso pores (2-50 nm). (2) The specific surface area of shale is positively correlated with the volume of micro pores and meso pores, but not with the volume of macro pores. In clay minerals, illite-montmorillonite and chlorite are positively correlated with shale specific surface area and micro pore volume. The TOC content of continental shale has a certain influence on the macro pore volume, and has a positive correlation with it to a certain extent. (3) The pore structures of shale are similar in the Da'anzhai section of Ziliujing Formation. According to the difference of shale pore structure, the Dongyuemiao section can be divided into two parts: the northwestern and the southeastern. The Dongyuemiao section in the southeast is similar to the Da'anzhai section in pore structures.

Existence and geological significance of pyrite in the organic-rich shale of Lower Cambrian Niutitang Formation in Upper Yangtze region

LU Zhengwei, TANG Xuan, ZHANG Tongwei, WANG Yufang, ZHANG Jiazheng, MENG Qingqiang, MA Zijie, HE Yi, SHAO Deyong

2021, 43(4): 599-610. doi: 10.11781/sysydz202104599

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The existence of pyrite provides a basis for the restoration of sedimentary and diagenetic environment, also, it can be regarded as a reference for the prediction of organic-rich shale. Shales of the Lower Cambrian Niutitang Formation drilled at three different sedimentary locations (wells Yichang EYY1, Weiyuan W001-4 and Hanzhong SNY1) in the Yangtze region have been taken as samples in this study. The pyrites founded within these samples have been analyzed with XRD, microscope, scanning electron microscope and carbon and sulfur contents. By the comparison of analytical results, it was indicated that there were four types of pyrite in these samples including framboidal, cubic automorphic, strip-shaped and irregular non-self-formed. The framboidal pyrite was mostly developed, and its particle size was relatively smaller and varied in a narrow range, reflecting the synsedimentary origin, generally has a good and positive correlation with the content of organic matter, while other types of pyrite may be diagenetically originated. The morphological differences of pyrite in shale samples from three wells indicated that the sedimentary water of well SNY1 is quiet and has the strongest reductivity. The lower part of the sedimentary water of wells W001-4 and EYY1 experienced a transformation from oxygen-poor to anaerobic, and the high-abundance pyrite in the shales of well W001-4 might be affected by hydrothermal activities in the Mianyang-Changning tension trough. Compared with calcareous shale, siliceous shale and silicic-calcareous transitional shale are more favorable for the formation of pyrite. Pyrite has a positive effect on the development and preservation of organic pores, which is beneficial to the enrichment and storage of natural gas in shale reservoirs.

Differential mechanisms of organic matter accumulation of source rocks in the Lower Cambrian Qiongzhusi Formation and implications for gas exploration fields in Sichuan Basin

YANG Yu, LUO Bing, ZHANG Benjian, XIAO Di, XIAO Wenyao, CAO Jian

2021, 43(4): 611-619. doi: 10.11781/sysydz202104611

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The marine facies highly mature natural gas system with the Lower Cambrian Qiongzhusi Formation as the source rock in the Sichuan Basin is a global model in this field. To deepen the geological understanding of high quality source rocks and the natural gas exploration areas in the Sichuan Basin, taking two hot exploration blocks in the central and northeastern parts of Sichuan Basin as examples, the differential mechanisms of organic matter accumulation in source rocks of the Qiongzhusi Formation were studied, and some gas exploration areas were identified by the means of geochemical methods from three perspectives, including paleoproductivity, redox conditions and input of terristral organic matters. The TOC of source rocks within deep-water shelf in the intracratonic rift sampled from the Gaoshi 17 and Zhongjiang 2 wells in the central Sichuan were higher than that of source rocks within the shallow-water shelf sampled from the Xiaoyangba outcrop, northeastern Sichuan. The organic matter accumulations of both sample sets were mainly controlled by redox condition, but in comparison, the source rocks in the central Sichuan Basin were formed in relative anoxic environment, which was more conducive for the preservation of organic matter than the suboxic environment in northeastern Sichuan Basin. In addition, the dilution effection by terrestrial organic matter input was particularly significant during the formation of source rocks in the northeastern Sichuan Basin, leading to poorer source rock quality. The exploration of natural gas system in the Qiongzhusi Formation still needs to be carried out closely around the intracratonic rift and its surrounding margin in the future, and the deep-water shelf area around the basin also deserves attention. Both conventional and unconventional natural gas resources should be considered.

Influence of Permian basaltic volcanic activity on coal-bearing shale reservoirs, Southern Guizhou Depression

LI Xincheng, HOU Yuguang, CHEN Zhenhong, HE Sheng, LIANG Yaqi, LIU Yukun, SONG Yingrui, YU Rui

2021, 43(4): 620-627. doi: 10.11781/sysydz202104620

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To investigate the influences of volcanic activities on shale reservoirs, a case study was carried out on the Permian Mount Emei basalt and coal-bearing shale of Longtan Formation in the Southern Guizhou Depression. Based on the analytical results of total organic carbon content, XRD, vitrinite reflectance and cryogenic nitrogen and carbon dioxide adsorptions, the effects of volcanic activities on the hydrocarbon generation, mineral composition and reservoir microstructure of coal-bearing shale were discussed. The results showed that volcanic activities had obvious effects on the hydrocarbon generation, mineral composition and pore structure of coal-bearing shale. They significantly promoted the evolution and maturation of organic matters in shale, which quickly entered the over-mature stage (R_o% increased from 2.0% to 2.88%), and accelerated the hydrocarbon generation and expulsion efficiency. With the decrease of the distance to the basalt, the contents of clastic minerals and carbonate minerals increased, the content of clay minerals decreased, and the contents of illite and chlorite changed regularly, which indicated that the evolution of shale diagenesis had also been affected to a certain extent. The heat brought by volcanic activities had an important influence on the pores of reservoirs. As it got closer to basalt, the proportion of micropores increased while the content of mesopores and macropores decreased. It was speculated that the thermal effects of volcanic activities promoted the formation of organic pores and also affected the development of inorganic pores.

Characteristics and constrains of low-permeability reservoirs in the first member of Eocene Liushagang Formation, Weixinan Sag, Beibuwan Basin

DENG Xiaoliang, YANG Xibing, YOU Li, WU Shijiu, ZHONG Jia, ZHU Peiyuan, DAI Long

2021, 43(4): 628-637. doi: 10.11781/sysydz202104628

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Reservoir analysis data such as core, thin-section, physical property and scanning electron microscope (SEM) were applied in this paper to study the reservoir characteristics and main constrains of the first member of Eocene Liushagang Formation in the Weixinan Sag, Beibuwan Basin. Reservoir features, physical properties, sedimentation, diagenesis, and the coupling of tectonics as well as hydrocarbon generation and accumulation were analyzed. Results showed that the reservoirs of the first member of Eocene Liushagang Formation in the area of this study were mainly feldspathic debris quartz sandstones and lithic quartz sandstones with low compositional and structural maturities. The reservoir space was mainly consisted of primary intergranular residual pores and secondary dissolved pores. In the northwestern and western source areas, the reservoirs mainly had moderate porosity and medium-high permeability, while those in the eastern source area had relative low porosity and low permeability. Sedimentation caused variations in grain size, sorting and argillaceous complexes. Diagenesis such as compaction, carbonate cementation and organic acid dissolution were the main controls for the physical properties of low-permeability reservoirs. The coupling of tectonics and hydrocarbon generation and accumulation controlled early hydrocarbon charging, while abnormal high pressure protected primary pores, which, combined with fractures derived from faults, improved the physical properties of low-permeability reservoirs. In the northwestern and western source areas, the shallow-buried reservoirs in the first member of Liushagang Formation had relatively strong hydrodynamic force, coarser grain size and better sorting, and showed better properties in the area with less mud. In the eastern source area close to the No. 2 fault around the main hydrocarbon-generating depression, there exist early hydrocarbon filling, strong dissolution of organic acids and partial high-pressure protection. Secondary pores and high-pressure pores were developed at 2 500-3 500 m deep, and favorable deep-burial reservoirs were formed.

Sedimentary responses of tectonic events in Miocene, western margin of South China Sea: a case study of Wan'an Basin

ZHANG Daojun, HE Yunlong, LU Biyu, WANG Yahui, LIU Juan, YANG Yunliu, XIAO Hongyi

2021, 43(4): 638-647. doi: 10.11781/sysydz202104638

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The Wan'an Basin is located on the southwestern margin of the South China Sea, and its unique tectonic position has made its filling evolution an important window to study the expansion of the southwest submarine basin and the strike-slip faults on the western margin. Based on the results of core analysis, correlation of core and seismic reflections, and seismic facies, the characteristics of the infilling of the Wan'an Basin and the sedimentary responses to tectonic events in Miocene were studied. Four main sedimentary facies related to hydrocarbon reservoirs have been developed in the basin during Miocene, including delta, turbidite fan, carbonate platform and reef. In the Early Miocene, delta facies was widespread in the study area. During the Middle Miocene, delta facies developed only in the western part of the Wan'an Basin, and carbonate platform deposits began to develop in the eastern part. And turbidite fan, sourced from the western part, began to develop in the Late Miocene. The southwestern sub-basin of the South China Sea stopped expanding at the end of the Early Miocene and the strike-slip fault activities on the western margin of the South China Sea at the end of the Middle Miocene formed two important tectonic unconformity interfaces, which played an important role in constraining the Miocene sedimentary filling in the Wan'an Basin.

Source of hydrocarbons discovered from Cambrian sub-salt dolomite in Bachu uplift area, Tarim Basin

CAO Zicheng, ZHU Xiuxiang, WU Xian, XU Qinqi, LU Qinghua, LI Jianjiao, JIANG Haijun

2021, 43(4): 648-654. doi: 10.11781/sysydz202104648

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Exploration experiences have showed that the main source rocks of the Lower Cambrian have not been developed in the Bachu uplift; however, the well MB1 in this area had a good oil and gas showing in the Lower Cambrian.To clarify the hydrocarbon source of well MB1 and evaluate the exploration potential of the Bachu uplift, the core extracts from the oil and gas display section of the Lower Cambrian Wusongge'er Formation of well MB1 were studied here by using of geochemical analysis, moreover, oil-oil and oil-source correlations have also been carried out.The saturated hydrocarbon fraction of extracts showed a typical signature which is consistent with marine crude oil in the Tarim Basin, of which the n-alkanes have a single-peak pre-peak distribution, the series is preserved intact and there was no apparent "hump" in the basline, the ratio of Pr/Ph was 0.89, the abundance of the tricyclic terpanes was higher than that of the hopanes, the C₂₇-C₂₈-C₂₉ααα20R regular steranes had a typical "V" shape, the carbon isotope value of crude oil is -30.8‰, and the trifluorene compounds were obviously override thiofluorene.It then indicates that they were derived from the saprolite-type sources with a strongly reducing sedimentary environment, moreover, the organic matters are high mature.The Lower Cambrian oil showed in well MB1 have the same origin as the Ordovician crude oil in the Yubei 1 belt, and both of them probably came from the Lower Cambrian source rocks. It was inferred that the Lower Cambrian oil and gas in well MB1 came from the peripheral Lower Cambrian source rocks or paleo-oil reservoirs, which enhanced the exploration potential of Cambrian in the Bachu uplift.

Dissolution experiments and geological implications of tight sandstones in the Xujiahe Formation of Upper Triassic, Sichuan Basin

YANG Wei, XIE Wuren, YU Lingjie, WEI Guoqi, JIN Hui, FAN Ming, SHEN Juehong, HAO Cuiguo, WANG Xiaodan, LIU Weihong

2021, 43(4): 655-663. doi: 10.11781/sysydz202104655

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The Upper Triassic Xujiahe Formation in the Sichuan Basin is a tight sandstone reservoir with developed dissolution pores, but its formation mechanism is still unclear. In this paper, three samples, including feldspathic lithic, lithic arkose and feldspathic quartz sandstones of the Xujiahe Formation, were taken as examples. Some reaction fluid similar to the organic acid component of the formation was prepared. Five kinds of temperature and pressure conditions were applied in the corrosion simulation experiments, and four understandings were obtained. Firstly, with the increase of temperature and pressure, the concentrations of K⁺ and Na⁺ ions in the reaction solution increased, the concentrations of Ca²⁺ and Mg²⁺ ions remained stable, but the concentration of Al³⁺ ions decreased significantly. Secondly, the reaction produced a small amount of quartz and a large number of kaolinite and other new minerals, and the dissolution of feldspar particles and carbonate cement produced a large number of dissolution pores, the porosity was increased and the pore structure was then improved. Thirdly, with the same temperature and pressure, the dissolution rate of feldspathic lithic sandstone was relatively higher than that of feldspathic quartz sandstone. With higher temperature and pressure (e.g. 180℃, 53 MPa), the dissolution rate of sandstone samples were significantly increased. Lastly, the results of dissolution experiments provided a reference for the reconstructing of burial sequence, diagenesis as well as pore evolution of the Xujiahe Formation and the distribution of favorable reservoirs can be predicted. The rapid dissolution of feldspar under higher temperature pressure is one of the genetic mechanisms of effective reservoir of deep clastic rock.

Genetic mechanism of pyrolytically desorbed hydrocarbon

LI Guangzhi, NING Lirong, WANG Guojian, HU Bin

2021, 43(4): 664-669. doi: 10.11781/sysydz202104664

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In the geochemical exploration for oil and gas, the test data of pyrolytically desorbed hydrocarbons have the abnormal characteristics that the relative content of olefins is higher than that of alkanes with the same carbon number, and the relative content of isoparaffins is higher than that of normal alkanes with the same carbon number, and this feature becomes more obvious with the increase of temperature of pyrolytical desorption. On the other hand, the acid hydrolyzed hydrocarbons, headspace light hydrocarbons, free hydrocarbons, and water-soluble hydrocarbons in oil and gas sources and surface samples do not have such feature. The abnormal characteristics of pyrolytically desorbed hydrocarbons have been previously explained from different aspects, but whether the organic matters contained in the samples will crack and rearrange to generate olefins under vacuum and heating conditions has not been considered. Some experiments of pyrolytical desorption temperature of surface soil samples from three regions were carried out. The correlation between pyrolytically desorbed hydrocarbons and organic carbon was discussed. Combined with the pyrolytical desorption experiments of organic matter in leaf and soil, it was inferred that the pyrolytically desorbed hydrocarbons in soil samples mainly came from the desorption of chemically adsorbed light hydrocarbons (below 160℃) and the thermal cracking of organic matter (above 160℃). The thermal action of geothermal field can promote the hydrocarbon generation of organic matter in surrounding rocks, and to a certain extent, reduce the content of organic matter and increase the content of light hydrocarbons, which can be used for further study of geothermal indicating significances of pyrolytically desorbed hydrocarbons.

The anomalies of high-precision geochemical exploration in well AT2 area of Tahe Oil Field, Tarim Basin and its geological significance for production

YANG Min, CHEN Shuyang, WANG Guojian

2021, 43(4): 670-677. doi: 10.11781/sysydz202104670

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To evaluate the hydrocarbon potential of multiple traps in the middle and up oil groups of Triassic, an intensive oil and gas geochemical exploration has been carried out in the well AT2 area of the Tahe Oil Field of the Tarim Basin by the means of hydrocarbon microseepage-based high-precision geochemical exploration techniques.The geochemical indicators selected for this study were all active ones, including soil gas, physical adsorbed hydrocarbon gas and headspace gas.Near-surface soil samples were collected by means of a 0.25 km×0.25 km measuring grid, with a 0.1 km×0.1 km measuring grid over some key traps.Soil gas methane, physical adsorbed methane, and headspace methane were selected as the representative geochemical indicators, and their geochemical anomaly features over the well AT2 area were studied.Based on which, five integrated geochemical anomaly zones (consistent with five traps) were determined.The five integrated geochemical anomaly zones were ranked using a double-factor evaluation method combining geochemical and geological exploration evaluation parameters, and the hydrocarbon-bearing potential of these traps were evaluated, providing a geochemical basis for oil and gas rolling development of the well AT2 area.

Hydrocarbon generation characteristics and significance of accumulation of Upper Paleozoic source rocks in Dongpu Sag, Bohai Bay Basin

WANG Xuejun, ZHOU Yongshui, LI Honglei, JIA Binfeng, ZHANG Yingying

2021, 43(4): 678-688. doi: 10.11781/sysydz202104678

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In order to clarify the conditions and rules of hydrocarbon accumulation of the Upper Paleozoic in the Dongpu Sag of Bohai Bay Basin, source rock evaluation, pyrolysis experiment and basin modelling were carried out in this paper, the history of hydrocarbon generation and intensity of source rocks have been quantitatively studied, consequently, the significance of hydrocarbon accumulation in this area has also been discussed. The micro-composition of the Carboniferous-Permian source rocks in the Dongpu Sag is featured by high contents of hydrogen-rich exinite and matrix vitrinite (>10%), and the source rocks have a high oil-generating potential. The hydrocarbon generation process is characterized by multiple stages and wide gas generation band. During the Yanshanian period, the Carboniferous-Permian source rocks were shallowly buried, the R_o value ranged between 0.6%-0.8%, and only a little gas has been generated. In the Himalayan period, due to the differential thermal evolution of the Paleogene deposits, from the western part of the sag to the western slope, gas generation was significantly decreased, with an average of (1-20)×10⁸ m³/km². While in deep sag of the eastern part, source rocks were deeply buried with a high thermal degree, and a large amount of gas was generated with an intensity of (60-110)×10⁸ m³/km². Past exploration results have shown that the area with a gas generation intensity greater than 40×10⁸ m³/km² is favorable for natural gas accumulation. The gas generation intensity of the Qianliyuan sub-sag ranges (60-110)×10⁸ m³/km², which has favorable conditions for the formation of primary as well as paleogenetic and new-storage coal-derived gas reservoirs, and is a favorable exploration zone for the future exploration.

Reservoir space characterization of vuggy carbonate reservoirs with multiple scales: a case study of Ma 5-7 interval, Middle Ordovician Majiagou Formation, Daniudi area, Ordos Basin

DING Xiaoqi, LIU Xin, QI Zhuangzhuang, ZHANG Wei, LIU Sihong

2021, 43(4): 689-696. doi: 10.11781/sysydz202104689

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The reservoir space of carbonate rocks is of multiple scales and genesis mechanisms, and it is difficult to accurately demonstrate the reservoir space as well as physical properties.Millimeter-, micro- and nano-scale reservoir spaces were all developed in the Ma 5-7 interval (the 7th sub-member of the 5th member) of the Ordovician Majiagou Formation in Daniudi area, Ordos Basin. In order to study the storage space and physical properties, the storage space was characterized in layers at multiple scales, and combined with the approach of logging curves, a calculation model was established for the description of pores and caves.Several conclusions were made as follow. (1) For carbonate rock reservoirs with storage space of multiple scales, we can accurately describe their storage space by the means of core rubbing for dissolved pores (>1 mm), case thin section for intercrystalline pores (>2 μm), and argon ion polishing-scanning electron microscope for submicron and nano pores (< 2 μm). (2) On the basis of multi-scale reservoir space characterization, the acoustic porosity and neutron-density porosity can be constrained, and the corresponding intercrystalline pore porosity calculation model and dissolved pore porosity calculation model can be established, which have higher calculation accuracy.

Prediction of single-well-constrained recoverable reserves in beach bar sand reservoir using different fracturing methods

SU Yinghong

2021, 43(4): 697-703. doi: 10.11781/sysydz202104697

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Single-well-constrained recoverable reserve is an important index to evaluate whether the development of beach bar sand reservoir is economically feasible. Due to the characteristics of pressure sensitive effect, start-up pressure gradient and different fracturing methods, it is difficult to apply the conventional prediction method to single-well-constrained recoverable reserve in undeveloped ultra-low permeability beach bar sand reservoirs. In this paper, based on the static and dynamic data of typical blocks, a numerical simulation model of vertical well stratified fracturing was established. The coefficients in the characterization formula of start-up pressure gradient and pressure-sensitive effect were determined by history fitting, and the influences of pressure-sensitive effect and start-up pressure gradient on production performance were analyzed. On this basis, the influence of different reservoir parameters and development parameters on the single-well-constrained recoverable reserves of elastic development with vertical-well stratified fracturing was analyzed. The main factors of single-well-constrained recoverable reserves were determined as follows: pressure coefficient, permeability, oil saturation, effective thickness, porosity, fracture length, concentration and viscosity. A vertical-well stratified fracturing model was established by multiple regression. Compared with the data from actual production wells, the relative error was 4.58%, which showed that the formula had a high accuracy and could meet the requirements of mines. Furthermore, some prediction formulas between the single-well-constrained recoverable reserves and the reservoir parameters corresponding to the volume fracturing of vertical wells, the multi-stage fracturing of horizontal wells and the volume fracturing of horizontal wells were established. The results provided a basis for evaluating the production potential of beach bar sand reservoirs.

Characterization method of heterogeneity for Chang 8 tight reservoir in Honghe oil field, southern margin of Ordos Basin

XIA Dongling, WU Yue, XIA Dongdong, GUO Xiujuan, ZOU Min

2021, 43(4): 704-712. doi: 10.11781/sysydz202104704

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Due to the complexity of accumulation conditions of Chang 8 tight reservoir in Honghe oil field, the southern margin of the Ordos Basin, the geological "sweet spots" are small and scattered, and the reservoir is remarkably heterogeneous. The Honghe 36 well block of the Honghe oil field was taken as an example in this paper, based on the main constrains for reservoir enrichment and production, three major heterogeneity characterizations, including reservoir quality, fractures and oil-enrichment, were carried out, and then combined with evaluation on productivity. A comprehensive characterization model for reservoir heterogeneity has been established, which can represent the geological characteristics of the reservoir. A classification standard for matrix reservoirs was established from the micro and macro scales to discuss the formation mechanism of reservoirs constrained by sedimentary and diagenetic factors. A characterization method for reservoir heterogeneity that "sedimentary elements constrained diagenetic facies, and diagenetic facies constrained reservoir quality" was proposed, which clarified the plane distribution of reservoirs. Based on the constrains of different grades of fracture zones on oil and gas enrichment, a multi-scale fracture zone classification scheme was established. Well logging and seismic data were combined to carry out hierarchical predictions to quantitatively characterize the multi-scale fracture zones from meter scale to kilometer scale. The oil-bearing capacity of wells was discussed, and combined with oil and water distribution pattern, an oil saturation field was established to quantitatively characterize oil-bearing heterogeneity. On this basis, three strong heterogeneity characterization results were superimposed to establish a comprehensive evaluation model for tight reservoir heterogeneity, which was used to clarify development target distribution.

Separation of steranes and hopanes by domestic X-type molecular sieves

LI Erting, XIANG Baoli, LI Ji, ROUZI Dilidaer, WANG Huitong, MA Wanyun, LIU Cuimin, ZHANG Xiaogang

2021, 43(4): 713-720. doi: 10.11781/sysydz202104713

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Abstract:
Domestic 10X-type and 13X-type molecular sieves were used for the adsorption and desorption experiments of steranes and hopanes, and their stable carbon isotopic fractionation by the two kinds of molecular sieves during separation process was discussed in detail. These two kinds of molecular sieves have various adsorption effects on different types of compounds. They both have the weakest adsorption capacities for 5α, 14α, 17α-20S steranes, 5α, 14β, 17β-20R steranes and 5α, 14β, 17β-20S steranes, followed by 5α, 14α, 17α-20R steranes, β-carotane, and gammacerane. The 13X-type molecular sieve has stronger adsorption capacity for hopanes than that of the 10X-type molecular sieve, which can be used for the separation of hopanes. The 10X-type molecular sieve has stronger adsorption capacity for steranes than that of the 13X-type molecular sieve. By controlling the amount of eluent, different configuration of steranes can be further separated. The stable carbon isotopes of steranes and hopanes showed that no carbon isotopic fractionation occurred during separation process and the repeatability was very good, indicating that domestic 10X-type and 13X-type molecular sieves can be used for steranes and hopanes separation.

Segmented prediction of TOC based on lithology: a case study of the lower sub-member of the third member of the Eocene Shahejie Formation, Dongying Sag, Bohai Bay Basin

ZHAO Linjie, LU Jianlin, WANG Baohua, LI Hao, SONG Zhenxiang, ZHANG Yanxia

2021, 43(4): 721-727. doi: 10.11781/sysydz202104721

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Abstract:
The continental mud shale has a strong heterogeneity, and the prediction of its mineral composition, TOC (total organic carbon content) and other parameters is critical for the evaluation and optimization of continental shale oil and gas abundance. To obtain the vertical distribution characteristics of these key parameters of the continental shale formation, and to ovoid the practical problems such as time-consuming experiments, high cost, and sampling difficulty etc., a research of the logging prediction method for key parameters was carried out. The lower sub-member of the third member of the Eocene Shahejie Formation (Es₃) in the Dongying Sag of the Bohai Bay Basin was employed as an example, XRD measurements and logging were carried out based on which, various TOC prediction models were selected for different lithologies, and some TOC identification templates of different lithologies were established.The constructed model was then used to perform typical predictions on the lithology and TOC of the lower sub-member of the Shahejie Formation in well Fy1.The correlation coefficient between the predicted values obtained by the segmented prediction method for TOC and the measured values appeared to be relatively high (about 0.84), indicating that the method developed here is highly feasible and can provide effective technical support for the evaluation and target optimization of continental shale oil resources.

Transfer system reform for oil and gas mineral rights and value of reserves in China

MAO Yi

2021, 43(4): 728-736. doi: 10.11781/sysydz202104728

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Abstract:
At present, in order to adapt to the reform of national oil and gas mining right system, the domestic oil and gas industry is exploring the competitive transfer of mineral rights and the exploration of reserve value, which is a new topic in China. In order to give full play to the fundamental position of market in resource allocation, and to understand the current status and existing problems of the transfer of oil and gas mineral rights, it was analyzed in this paper for the main practices of the international oil company's and our country's oil and gas mineral rights transfer, and the research progress of our country's oil and gas mineral right transfer system reform and the value of oil and gas reserves was summarized. Since the "13th Five-Year Plan", the besieged city with a high concentration of oil and gas mining rights in our country has been gradually broken, government supervision methods have been gradually changed, supporting policies and regulations have been improved day by day, and the third-party transaction service platform for block transfer has begun to operate. The value-based evaluation of oil and gas reserves is a key link in the transfer of mining rights and the paid transfer and transaction of oil and gas reserves. On the basis of systematically summarizing the valuation methods of reserves at home and abroad, taking block A in the southeastern part of Sichuan Basin as an example, the specific application of the unit reserve price method was practiced for the determination of key parameters of multiple types of oil and gas reservoirs.

2021, 43(4): 737-737.

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Abstract:

2021 Vol. 43, No. 4

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