石油实验地质

2018, 40(5): .

Abstract(274) PDF-CN(109)

Abstract:

Causes of abnormal thermal evolution and characteristics of thermal evolution in Sichuan Basin

PENG Jinning, LUO Kaiping, LIU Guangxiang, YANG Fan, YANG Jun, PAN Wenlei

2018, 40(5): 605-612. doi: 10.11781/sysydz201805605

Abstract(1268) PDF-CN(408)

Abstract:
The causes of thermal evolution anomalies in the Sichuan Basin, and the distribution of thermal fields and their main controlling factors during different geohistory periods were analyzed. The R_o-H thermal evolution profiles of typical wells and outcrops in various tectonic units in the Sichuan Basin were established to discuss the causes of vertical thermal evolution anomalies. The thermal field distributions in the Sichuan Basin from the Late Paleozoic to the Middle Triassic, the Late Triassic to the Jurassic, and at present, respectively, were obtained by a R_o gradient method, and a thermal history analysis was carried out. Some conclusions were made as follows. (1) Hydrogen generation from source rocks produced overpressure, leading to the differential inhibition of R_o and hydrocarbon cracking, which was the main cause of the "negative" anomaly of longitudinal organic matter thermal evolution in the Sichuan Basin. (2) The tectonic movements and basin properties in different periods controlled the vertical thermal evolution in the basin. At the end of middle Permian, regional extension changed the former unified low-heat field, resulting in increasing heat flow value in the fault depression, with an average geothermal gradient above 3.5℃/hm. From the Late Yanshanian to the Early Himalayan periods, the east part of the basin began to uplift, and the basin gradually shrank to the west. The peripheral thrusting action tended to decrease, and the high thermal field began to cool. The rapid uplifting and cooling effects at the end of Himalayan period formed the current low-heat field, with a geothermal gradient less than 2.5℃/hm.

Characteristics of overpressure regime in compartmentalized overpressured system within tight sandstones, Xujiahe Formation, Yuanba-Tongnanba areas, Sichuan Basin

SONG Yu, ZHANG Li, LUO Dingwen, YANG Shuo, HAO Fang, ZOU Huayao

2018, 40(5): 613-620. doi: 10.11781/sysydz201805613

Abstract(1030) PDF-CN(159)

Abstract:
Compartmentalized overpressured systems are commonly developed in tight gas sandstones. However, studies about the characteristics of overpressure regime in compartmentalized overpressured system are rarely reported in the literature. The Upper Triassic Xujiahe tight sandstone formation in the Yuanba-Tongnanba area, northeastern Sichuan Basin, is a typical compartmentalized overpressured system. In this study, an overpressure regime in a compartmentalized overpressured system was delineated based on abundant measured pressure data, and the factors controlling overpressure regime in the compartmentalized overpressured system were clarified by comprehensively analyzing the geologic and geochemical data and the structural evolution of source rocks and tight sandstones. Results show that the overpressure regime in the compartmentalized overpressured system within tight sandstones of the Xujiahe Formation were separated from each other in both vertical and horizontal distribution of sandstone intervals, or even in the same intervals, exhibiting multi-scale and multi-level features for the compartmentalized overpressured system. Natural gas filling is a primary dynamic cause for overpressure generation, and its magnitude is directly related to gas generation intensity. The generally densified sandstones formed the background of overpressure system. Locally distributed mudstones and mudstone interbeds, and highly densified sandstone interbeds formed a multi-scale and multi-level framework of the overpressure system.

Pore structure characteristics and reservoir classification of dolomite reservoirs in fourth member of Leikoupo Formation, Longmen Mountain front, western Sichuan Basin

CHEN Yulin, ZENG Yan, DUAN Yongming, WANG Qiongxian

2018, 40(5): 621-631. doi: 10.11781/sysydz201805621

Abstract(1489) PDF-CN(131)

Abstract:
The pore structure characteristics of the tidal-flat dolomite reservoirs of the fourth member of Leikoupo Formation in the Longmen Mountain front in the western Sichuan Basin were studied through core observation, casting thin films, physical property tests, capillary pressure curves and CT scanning. There are four types of reservoir:pore, fracture-pore, pore-vuggy and fracture-pore-vuggy type, which can be distinguished by displacement pressure, sorting coefficient, proportion of connected pores, coordination number and pore aspect ratio. A reservoir classification standard was established combined with reservoir space combination type. For type I reservoirs (Φ ≥ 12%), the fracture-pore type reservoir is the most favorable, while the pore type was second. For type Ⅱ reservoirs (6% ≤ Φ < 12%), the fracture-pore type and fracture-pore-vuggy type reservoirs are the most favorable, while the pore type was second. For type Ⅲ reservoirs (2% ≤ Φ < 6%), the fracture-pore type and fracture-pore-vuggy type reservoirs are favorable.

Diagenetic characteristics and their control on porosity of sandy conglomerate reservoirs in faulted basins

HAO Jie, ZHOU Lifa, YUAN Yidong, YANG Yan, LIU Yanni, CHENG Zhaozhao, LIU Ting

2018, 40(5): 632-638. doi: 10.11781/sysydz201805632

Abstract(1243) PDF-CN(148)

Abstract:
The petrography and diagenesis of sandy conglomerate reservoirs from the Shahezi Formation of the Xujiaweizi area in the Songliao Basin were studied, and the controls of diagenesis on porosity evolution were analyzed based on thin section identification, cast thin section observation, SEM and X-ray diffraction. A quantitative model was established. The results showed that the sandy conglomerate reservoirs in the Shahezi Formation are characterized by complex components, low maturity and poor physical properties. Various diagenetic effects took place in the sandy conglomerate reservoirs, among which the compaction, cementation and dissolution effects are very common and obviously influence porosity, while fracturing, metasomatism and recrystallization effects have little control on porosity. The quantitative evaluation of the relationship between diagenesis and reservoir porosity showed that compaction greatly reduced porosity, by 24.7% in average, which was the main reason for reservoir densification. Dissolution increased porosity by 4.2% in average, which delayed the densification process. Cementation filled residual intergranular pores, reducing porosity by 5.3% in average, which was also a key factor for reservoir densification. The porosity of sandy conglomerate reservoirs is the comprehensive result of early compaction, medium erosion and late cementation.

Comparative analysis and discussion of shale reservoir characteristics in the Wufeng-Longmaxi and Niutitang formations: a case study of the well JY1 in SE Sichuan Basin and well TX1 in SE Guizhou area

WANG Ruyue, HU Zongquan, NIE Haikuan, LIU Zhongbao, CHEN Qian, GAO Bo, LIU Guangxiang, GONG Dajian

2018, 40(5): 639-649. doi: 10.11781/sysydz201805639

Abstract(1466) PDF-CN(264)

Abstract:
Wells JY1 in the southeastern Sichuan Basin and TX1 in the southeastern Guizhou were used as examples for a systematic analysis of shale reservoir characteristics of the Wufeng-Longmaxi and Niutitang formations using mineralogy, organic geochemistry, pore structure, methane sorption, brittleness and fracture characteristics. (1) Organic pores with bigger pore sizes that could reach μm in the Longmaxi shale are well-developed in migrated organic matter rather than in in situ organic matter, which are the dominant reservoir spaces. However, organic pores in the Niutitang shale have lower amounts and sizes, commonly lower than 30 nm with more complicated pore structures. The inter-particle pores in the cataclastic organic-inorganic mineral masses are significant reservoir spaces and have stronger methane sorption and desorption capacities. (2) Due to the piecewise correlation between TOC content and brittleness, the developmental characteristics of pore and fracture have significant differences:when the TOC content is less than 6%, the TOC, brittleness, organic/inorganic pores and fractures had positive correlations; when the TOC content is greater than 6%, although the increase of ductility reduces the number of fractures, the lower cohesive strength, internal friction angle and more weak surfaces of interlayer fractures and cataclastic minerals favor to the development of slip fractures, which have significantly improved fracture effectiveness and reservoir space. (3) The Longmaxi, Wufeng and Niutitang shale respectively represent the characteristics of reservoir evolution under different geological conditions, i.e. with the thermal evolution, diagenesis and tectonic deformation and pressure relief, the size, scale and proportion of organic pores gradually decrease, the complexity of pore-fracture structure, methane sorption/desorption capacity and the proportion of inorganic pores and fractures in reservoir space gradually increase.

Developmental characteristics and oil control of Indosinian paleo-uplifts in West Sichuan Depression, Sichuan Basin

HU Ye, YUAN Xiaoyu, WANG Yanqing, LIU Guangxiang, SONG Xiaobo

2018, 40(5): 650-654. doi: 10.11781/sysydz201805650

Abstract(987) PDF-CN(180)

Abstract:
The paleo-uplift of a basin is of great significance for the positioning of oil and gas fields. In this paper, the characteristics of the Indosinian paleo-highs in the West Sichuan Depression of the Sichuan Basin were studied in combination with the newly completed 3D seismic and drilling data. The study showed that in the Indosinian epoch in the western Sichuan area, not only the east-westward prototype of the uplift in the Xiaoquan-Xinchang-Fenggu area, but also the north-eastward "beaded" paleohighs in front of the Longmen Mountain and in the West Sichuan Depression developed. Seismic attributes revealed that the Indosinian paleo-uplift had significant control over the distribution of fractures on the top of Leikoupo Formation and the development of karst reservoirs. Considering reservoir distribution characteristics, paleo uplift and reservoir overlap, hydrocarbon source conditions and fracture migration channels, it was concluded that in addition to large tectonic uplift zones and slope zones, the Indosinian paleo-uplifts in the West Sichuan Depression might be favorable for hydrocarbon exploration.

Evolution of Cambrian mound-beach gas reservoirs in Gucheng platform margin zone, Tarim Basin

ZHANG Junlong, FENG Zihui, LI Qiang, ZHANG Bin

2018, 40(5): 655-661. doi: 10.11781/sysydz201805655

Abstract(1191) PDF-CN(86)

Abstract:
Gas has been discovered in the Cambrian mound-beach in the Gucheng platform margin zone of the Tarim Basin for the first time, opening up a new field of oil and gas exploration. The hydrocarbon accumulation conditions of four stages of Cambrian mound-beach in the Gucheng platform margin zone were analyzed based on core observation, cast thin section examination, geochemical analysis as well as logging and seismic data of exploration well CT 1. The results showed that the gas in the Cambrian mound-beach is mainly secondary gas from paleo-oil reservoirs. Oil accumulated during the middle and late Caledonian stage, which was cracked to gas during the Himalayan period. Mound-beach reservoirs formed due to weathering, leaching or organic acid dissolution, and the reservoir pro-perties of the central part is better than that of the periphery. On the top of the first and second stages of the mound-beach, direct caprock developed and configured well with the reservoir, which is favorable for independent accumulations. In the third and fourth stages, the top of mound-beach was exposed and eroded, and the sealing ability of direct cap rock is poor. The Upper Cambrian regional cap rocks are required for a useful reservoir. Fractures in the Gucheng platform margin zone mainly formed in the Cambrian, middle Ordovician and late Ordovician periods. Later tectonic activities were weak, which is favorable for gas accumulation.

Fault belt reservoir controls in Yubei area, Tarim Basin

QIAO Guilin, ZHENG Herong, YU Tengxiao, LUO Yu, LUO Shaohui

2018, 40(5): 662-668. doi: 10.11781/sysydz201805662

Abstract(1079) PDF-CN(151)

Abstract:
The structural features and oil and gas sources of the Yubei 1 fault belt in the Yubei area of the Tarim Basin were studied to determine the main geological conditions affecting the production of the Yubei 1 Ordovician oil and gas reservoir (the cumulative oil production before shutdown). Factors considered included the tectonic position of the top surface of the Yingshan Formation (T₇⁵) where wells were located, the development characteristics of fractured and vuggy reservoirs of the Yingshan Formation, the deformation strength of the main and secon-dary thrust faults of the T₇⁵ interface, and the distance between reservoirs and faults. Combined with the main reasons for the failure of the wells YB 3 and YB 3-1 in the Yudong 3 fault belt, east of Yubei, it suggested that the structural location of T₇⁵ and high-quality reservoirs were crucial to hydrocarbon enrichment in the Ordovician in the Yubei area. The structural location was a more important controlling factor for the production of oil and gas reservoirs. However, an excessively high structural location may cause the lack of overlying strata and the exposure of faults in the Late Hercynian, which lead to unfavorable petroleum preservation conditions.

Sedimentary characteristics and controlling factors of beach-bar sandstones of the upper section of the fourth member of Shahejie Formation on the southern slope of Dongying Sag,Bohai Bay Basin

GAO Liang, SUN Bo, WANG Yanzhang

2018, 40(5): 669-675. doi: 10.11781/sysydz201805669

Abstract(901) PDF-CN(106)

Abstract:
The sedimentary characteristicsof beach-bar sandstones of the upper section of the fourth member of Shahejie Formation on the southern slope of Dongying Sag were analyzed based on logging, coring and testing data. The controlling factors for the sedimentary distribution of beach-bar sandstones were discussed according to palaeogeomorphology, sediment source, paleobathymetry and paleo-hydrodynamics restoration. The results showed that the gentle slope zone in the rift lake basin is themain factor controlling the development of large-scale beach-bar sandstones. The main beach-bar of this area has a topographic gradient between 0.5° and 2°. The micro ancient terrains and their periphery are favorable for the deposition of thick beach-bar sandstones. Sediment sources provide material for the deposition of beach-bar sandstones. When the sediment supply index is between 0.4-0.6, sandstone beach-bar is developed. While the source supply index is between 0.2-0.4, mixed beach-bar is developed. By combining elemental analysis with logging and core observation, the paleobathymetry of the study area was determined, and the depositional environment was a shallow lake environment. Palaeo water force controlled the lateral differentiation of the sand bodies.

Depositional characteristics of a shallow-water delta in a continental faulted basin: a case study of the first member of Dainan Formation, Liuwushe Subsag, Gaoyou Sag, North Jiangsu Basin

LI Wei, ZHU Xiaomin, MA Yingjun, HOU Bin, QIU Yongfeng, BO Yongde

2018, 40(5): 676-683. doi: 10.11781/sysydz201805676

Abstract(1062) PDF-CN(111)

Abstract:
The Liuwushe Subsag, located in the east of Gaoyou Sag, North Jiangsu Basin, is a Cenozoic continental faulted basin formed at the end of Late Cretaceous. The present structural pattern of the first member of Dainan Formation is dustpan shaped, with slope zone in the north, steep slope zone in the south and deep sag in the middle. However, the restoration of the burial history indicated that the paleotopography of Liuwushe Subsag was limited when the first member of Dainan Formation was deposited. The depocenter during that period was located east of the present deep sag with a much smaller range. Provenance analyses indicated that most sand bodies of the first member of Dainan Formation in the Liuwushe Subsag came from the northern slope zone rather than the southern steep slope zone. Core observation and seismic and logging data indicated that a great many underwater channel sand bodies extended from north to south in the study area. Shallow-water delta deposits also developed in a faulted basin when the activity intensity of the basin boundary fault was weak. Well logging and seismic data were used to predict the spatial distribution of sandstone or pebbly sandstone.A large number of gravity flow deposits associated with the boundary fault remobilization occurred in the steep slope zone, which was identified as one difference between the shallow-water delta system of the fault basin and that of the depression basin.

Geological characteristics of hydrocarbon migration along a strike fault: a case study of Shaojia Fault, Zhanhua Sag, Jiyang Depression

WANG Yalin

2018, 40(5): 684-690. doi: 10.11781/sysydz201805684

Abstract(1182) PDF-CN(123)

Abstract:
The ENE trending Shaojia Fault in the Shaojia Subsag, Zhanhua Sag, Jiyang Depression has been studied. We summarized some special geological conditions for hydrocarbon migration along strike faults, including strike slip properties, faults located on a structural ridge, extremely underdeveloped transport layers on both sides of a fault, sufficient oil source and underdeveloped trap, and the matching between fault end and transport layer. The above geological conditions are not likely to be present at the same time in most areas, which explains rare hydrocarbon migration along a strike fault. The relationship between bending faults in different directions, reservior (transport layer) development formation, fault combination pattern and hydrocarbon migration along a strike fault were discussed in order to summarize the favorable geological conditions for hydrocarbon migration. It was concluded that during the main migration and accumulation period in Neogene, NW trending left lateral left-step faults and NE trending right lateral right-step faults were easy to form in a tensile weak zone at the bend, and were favorable for vertical and strike migration of hydrocarbon. The contours of sand bodies presented pinnate shape, vertical "丰" shape and half pinnate and half "丰" shape toward faults. As a result, hydrocarbon could not migrate out of the fault into a carrier bed, but migrates along a strike fault. The possibility of hydrocarbon migration along a strike fault of the Shicun Fault in Dongying Sag and the Linyi Fault in Huimin Sag was discussed.

Pore characteristics and controlling factors of coal reservoirs from Jixi Basin

LIU Jinlin, LI Huaibin, ZHANG Xuebing, ZHANG Yunfeng, SHEN Jianian, WANG Jian

2018, 40(5): 691-698. doi: 10.11781/sysydz201805691

Abstract(1160) PDF-CN(98)

Abstract:
Pore structure is a core issue of coalbed methane of untraditional reservoirs, which can control preservation properties and development results. The pores and fractures of coalbeds from the Jixi Basin were quantitatively characterized by means of low temperature nitrogen adsorption, argon ion milling scanning electron microscopy and nuclear magnetic resonance. The controlling factors of organic pores and mineral pores were discussed based on spectral analysis, mineral composition and coal component analyses. The results showed that the organic pores were mainly gas pores, usually bottle shaped, and some cylinder pores open at both ends and parallel plate pores open on four sides were also observed. The NMR T₂ spectrum has two or three peaks, indicating favorable porosity and permeability. High R_o and vitrinite content enhanced organic pore development, while water blocked pore surfaces and throats. Mineral pores mainly include intergranular pores of clay minerals and dissolution pores. The pores of monomer or aggregates of kaolinite, illite, and illite/smectite provided a large amount of adsorption space. The content of kaolinite has a positive correlation with the porosity of clay minerals, and the content of illite/smectite was negative.

Accumulation conditions of large biogas fields in Levantine Basin, East Mediterranean

JIA Huaicun, KANG Hongquan, WANG Chunxiu, QIU Chunguang, YANG Huaizhong, BAI Bo

2018, 40(5): 699-704. doi: 10.11781/sysydz201805699

Abstract(1031) PDF-CN(122)

Abstract:
In recent years, a number of large biogas fields have been discovered in the Levantine Basin of the Eastern Mediterranean, becoming a new replacement for conventional oil and gas resources. The discovered biogas is mainly pure biogas produced by acetic acid fermentation based on the biochemical characteristics and biogenetic types of biogas. The summary of accumulation conditions and rules showed that the large biogas reservoirs in the study area were controlled by four geologic factors including sufficient gas source, extensive distribution of good sandstones providing efficient migration and charging pathways, constant uplift developing giant anticline traps and a favorable match between reservoir and seal. The belt of continuous uplift provides a favorable location for a giant trap and good reservoir.

Geochemical investigation of organic matter of various occurrences released via sequential treatments of two argillaceous source rock samples from fresh and saline lacustrine environments

ZHAO Yue, CAI Jingong, XIE Aobo, DONG Zhe, ZHOU Qisheng, LEI Tianzhu, YANG Yan

2018, 40(5): 705-715. doi: 10.11781/sysydz201805705

Abstract(1067) PDF-CN(179)

Abstract:
Organic matter (OM) in argillaceous source rocks occurs in various forms, and it is common for OM be bounded to minerals forming OM-mineral complexes. In order to geochemically characterize OM of different occurrences, some high quality source rocks were sampled from the lower third member (Es₃) and the upper fourth member (Es₄) of the Shahejie Formation in the Dongying Sag, and were subjected to sequential treatments as follows:solvent extraction-saponification-hydrochloric acid hydrolysis-hydrofluoric acid hydrolysis. The free, clay interlayer absorbed, carbonate-bound, and clay surface-bound OM were successively released and GC-MS analyzed. Results indicated that the mineral-bound OM accounted for approximately 10% of the total soluble OM in source rocks, and there exists distinct geochemical differences between the free and mineral-bound OM, with the latter dominated by polar fractions such as nonhydrocarbons and asphaltene. The former comprised higher proportions of light hydrocarbons, and selectively preserved biomarkers indicative of biogenic origin, like the bicyclic sesquiterpenoids in the carbonate-bound OM, indicative of input from Botryococcus braunii, and squalane in the clay surface-bound OM, indicative of input from archaea. The mineral-bound OM was also sensitive to environmental changes, and exhibited molecular differences between fresh Es³ and saline Es⁴ samples. Thus, it was concluded that comprehensive geochemical investigation of the free and mineral-bound OM in argillaceous source rocks could achieve more authentic geological interpretations. Besides, molecular characterization of hydrocarbons of various occurrences could help further elucidate OM preservation mechanisms, as well as better evaluate source rock potential.

Characteristics of rare earth elements in Lower Cambrian Qiongzhusi Formation in northeastern Sichuan Basin and its geological implications: a case study of Yangba section, Nanjiang

CAO Tingting, XU Sihuang, Wang Yue

2018, 40(5): 716-723. doi: 10.11781/sysydz201805716

Abstract(1179) PDF-CN(137)

Abstract:
The Qiongzhusi Formation is an important shale gas production layer in the Sichuan Basin. A case study was made in the Yangba section of the northeastern Sichuan Basin. Samples were collected for rare earth and trace element analyses from the Lower Cambrian Qiongzhusi Formation in the study area so as to reveal the tectonic settings, provenance features and sedimentary environment when favorable source rocks were deposited. The distribution pattern and parameter characteristics of rare earth elements indicated that the Qiongzhusi Formation had a relatively consistent material source, mainly a passive continental margin. The parent rocks were mainly composed of sedimentary rocks and granites. When carbonaceous shale was deposited at the bottom of the Qiongzhusi Formation, the content of clay minerals increased in land sourced debris.The δCe and V/Cr parameters indicated that the bottom of the Qiongzhusi Formation was deposited in an anoxic reducing environment, while the middle and upper parts were deposited in a dysoxic-suboxic environment.

Impact of igneous intrusion on the thermal evolution of source rocks with different maturities: a case study of Fangzheng Fault Depression and Suibin Sag in north-eastern China

FENG Lu, ZENG Huasen, WANG Hongwei

2018, 40(5): 724-729. doi: 10.11781/sysydz201805724

Abstract(1415) PDF-CN(101)

Abstract:
Two intruded sections, respectively from the Fangzheng Fault Depression and the Suibin Sag in the north-eastern China, were continuously sampled and geochemically analyzed in order to decipher the thermal impact of igneous intrusion on source rocks with different thermal maturities. The changes of organic matter maturity and hydrocarbon generation characteristics of source rocks affected by igneous intrusion were studied according to the geochemical indicators of the rocks. The results showed that the thermal impact of igneous intrusion is distinguishable with sample organic maturity or diagenesis phase at the time of intrusion. When a source rock in its early diagenesis phase with a low organic maturity is intruded by magma, the thermal aureole is on average the thickness of the intrusion body and the maximum enhanced maturity can be up to 2.5% R_o. In contrast, when a source rock in its middle-late diagenesis phase with a high organic maturity is intruded, the thermal aureole is on average twice the thickness of intrusion body and the maximum enhanced organic maturity can be up to 4.0% R_o. It was suggested that in the early diagenesis phase, source rock bears a high specific heat capacity and a low thermal conductivity, and the thermal impact is less; whereas in the middle-late diagenesis phase, source rock bears a low specific heat capacity and a high thermal conductivity, and the thermal impact is greater.

Quantitative influence of soluble organic matter on pore structure in transitional shale

ZHANG Qin, LIANG Feng, PANG Zhenglian, ZHOU Shangwen, LIN Wen

2018, 40(5): 730-738. doi: 10.11781/sysydz201805730

Abstract(1027) PDF-CN(111)

Abstract:
Some representative samples of the Taiyuan Formation from the eastern uplift of the Liaohe Depression were selected in order to quantitatively evaluate the influence of organic matter on pore structure in transitional shale. Methods include quantitative mineral analysis by X-ray diffraction (XRD), Rock-Eval pyrolysis, and low pressure nitrogen adsorption. Analyses were performed on aliquot samples in the natural state and after soluble organic matter (SOM) removal by treatment with hydrogen peroxide (H₂O₂). The results indicated that the crystal structure of inorganic minerals is stable and the SOM removal process oxidizes and decreases or removes pyrite and siderite from the samples. All other inorganic phases remain unaffected. Compared with marine shale, OM pores are undeveloped, and the SOM filled in inorganic pores and matrix in the form of discrete particles or as laminations in the transitional shale samples. The cumulative fraction of total SOM actually held in inorganic pores ranges from 53.06% to 90.38%, and it mainly filled in mesopores and macropores. After SOM removal, the pore volume and pore surface area of samples both increase. The cumulative increase fraction of pore volume ranges from 72.14% to 121.83% and the cumulative increase fraction of pore area ranges from 32.8% to 52.74%. The original TOC content and the SOM proportions control pore volume and pore area increase.

Comparison of organic matter pores of marine and continental facies shale in China: based on Focused Ion Beam Helium Ion Microscopy (FIB-HIM)

WANG Pengfei, LÜ Peng, JIANG Zhenxue, JIN Can, LI Xin, ZHANG Kun, HUANG Pu, WANG Yi

2018, 40(5): 739-748. doi: 10.11781/sysydz201805739

Abstract(1800) PDF-CN(178)

Abstract:
The continental shale in the Triassic Yanchang Formation in the Ordos Basin of the central and western China, and the marine shale in the Lower Silurian Longmaxi Formation and the Lower Cambrian Niutitang Formation in South China were chosen for Focused Ion Beam Helium Ion Microscope (FIB-HIM) observation in order to clarify the development characteristics of organic matter pores in marine and continental shale with different maturities. Few organic matter pores developed in the Yanchang shale, and the pore diameter is usually small. Micro-fractures are widespread in the organic matter, and a large amount of interparticle pores were present in the clay minerals of the shale. The Longmaxi shale samples developed a large number of organic matter pores, and there are many of small-diameter pores nested in large-diameter organic matter pores, which increased specific surface area and pore connectivity, and are favorable for the occurrence and migration of hydrocarbon gases in organic matter pores. The Niutitang shale samples contain a large number of interparticle pores and few organic matter pores. Organic matter pores contributed a vast majority of the effective storage space and connectivity of the pore system. The development of organic matter pores was mainly controlled by thermal evolution. Low thermal evolution (0.5% < R_o < 1.5%) can not forma large number of organic matter pores and hydrocarbon gas supply. Thermal evolution that is too high (3.0% < R_o < 4.0%) will lead to organic matter pore disappearance and hydrocarbon gas lost during geological history. The appropriate extent of thermal evolution (1.5% < R_o < 3.0%) ensures that organic matter pores are well developed, and is also important for the storage and seepage capacity for hydrocarbon gases in shale reservoirs. Therefore, for the exploration and development of highly-mature and over-mature marine shale gas in South China, the shale horizons with a moderate thermal evolution degree should be focused on.

2018, 40(5): 749-749.

Abstract(400) PDF-CN(76)

Abstract:

2018 Vol. 40, No. 5

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