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2021 Vol. 43, No. 3

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2021, 43(3): .
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Exploration prospect of shale gas with Permian transitional facies of some key areas in China
GUO Shaobin, WANG Zilong, MA Xiao
2021, 43(3): 377-385. doi: 10.11781/sysydz202103377
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The shale gas exploration of marine-continental transitional facies in China has not yet gained a significant success. To analyze and predict the exploration prospect of transitional shale gas, the distribution, organic geochemical and reservoir characteristics of transitional shale in some key areas of China were compared. The transitional shale is widely distributed in China and is characterized by the thin thickness of single layer and the rapid variation of lithology. The kerogens of transitional shale are mainly of type Ⅲ. Except for carbonaceous mudstone, the total organic content is generally low, and the hydrocarbon generation potential is the lowest. The dominant pore types of transitional shale are inorganic pores and micro-fractures, while the organic pores on the other hand were not developed. The pore volume and pore specific surface area of transitional shale are lower than those of marine shale, the reservoir space is relatively insufficient, and the gas adsorption capacity is poor. Transitional shale has a remarkable high content of clay minerals, less brittle minerals, low porosity and permeability, and poor reservoir physical properties indicating unconducive for the late-stage development. Results show that marine shale is still the most favorable area for shale gas exploration, and the exploration prospect of shale gas in transitional facies may not be regarded as good as that of continental shale gas which has a higher thermal mature degree in some aspects.
Geological conditions and exploration potential for shale gas in Upper Permian Wujiaping Formation in the region of western Hubei-eastern Chongqing
LIANG Xiwen, LI Le
2021, 43(3): 386-394. doi: 10.11781/sysydz202103386
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The Upper Permian Wujiaping Formation shale in the region of western Hubei and eastern Chongqing has been found qualified for shale gas accumulation in early exploration activities, but the potential for shale gas exploration is still unclear. Based on the core analysis and test data of well Jy3, combined with regional seismic, testing and logging data of this well and wells nearby, the shale distribution, quality, gas-bearing properties, preservation conditions and resource scale of the second member of Wujiaping Formation were discussed. The results showed that the organic-rich shale of deep-water shelf facies and slope to shallow shelf facies were developed and they appeared to be thin in the southwest and thick in the northeast. The shale was mainly composed of quartz (averages 43.10%), clay minerals (average 21.95%) and calcite (averages 17.20%). The organic matter is rich (average TOC value of 8.77%), mainly of type Ⅱ1 kerogen, high thermal maturity (average converted %Ro value of 2.06%), excellent porosity (average value of 5.59%) and good gas bearing property (total gas content averages 3.73 m3/t). The Wujiaping Formation in the Hongxing area is the most promising replacement strata and area for shale gas exploration and development, which shares the largest shale thickness, the best preservation condition, and the most abundant resource.
Gas-bearing characteristics and preservation conditions of Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in western Hubei
XU Lulu, WEN Yaru, ZHANG Yanlin, REN Zhijun, YANG Jie, WEN Jianhang, CHEN Wei, LUO Fan, DUAN Ke
2021, 43(3): 395-405. doi: 10.11781/sysydz202103395
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The Upper Ordovician Wufeng to Lower Silurian Longmaxi formations are important exploration targets for shale gas in the western Hubei province. The lithology, sedimentary facies, gas-bearing characteristics and preservation conditions of the Wufeng-Longmaxi formations were analyzed with the samples of more than 20 survey wells. The Wufeng Formation is dominated by black carbonaceous siliceous shale of deep-water siliceous argillaceous shelf facies, while the Longmaxi Formation is dominated by gray-black carbonaceous shale of deep-water argillaceous shelf facies. The Wufeng-Longmaxi formations and the lower part of Lower Silurian Xintan Formation consist of two three-level sequences, and the gas content conforms to the characteristics of TST1 > TST2 > HST2 > HST1. The gas content of the Wufeng Formation is slightly higher than that of the Longmaxi Formation. A good gas potential has been found to the north of Tianyangping Fault and the east of Xianfeng Fault. Since most wells were in the deep shelf facies area, sedimentary facies have little effect on the plane distribution of shale gas content. The studies of preservation conditions showed that both the Xintan Formation as the roof and the Ordovician as the floor have good sealing properties. The burial history of Wufeng-Longmaxi formations can be divided into four stages, and shows the characteristics of "early uplift time" and "rapid uplift rate" when compared with the Sichuan Basin. The burial depth and the distance to normal fault have certain influence on the gas content. However, the matching pattern between fault and fold is the most important factor affecting gas content. Two structural patterns are beneficial to shale gas accumulation, one is being far away from normal fault and locating at the syncline wing or core, the other is being far away from normal fault and locating at the footwall of fault and the target stratum is not connected to the fault in the up-dip direction.
Controlling factors and countermeasures for exploring large and medium-sized gas fields in Sichuan Basin
HONG Taiyuan, CHENG Zhe, XU Huaming, CHEN Qian
2021, 43(3): 406-414. doi: 10.11781/sysydz202103406
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The Sichuan Basin has been known to be rich of oil and gas resources, and after the exploration and development for more than 70 years, oil and gas reservoirs (mainly gas reservoirs) have been widely discovered in 28 strata, and the first complete gas industrial system has been built in this basin. The main constraint factors for the formation of large and medium-sized gas fields in the Sichuan Basin were discussed in this paper, and some favorable exploration targets were proposed. The enrichment of natural gas in the Sichuan Basin has several characteristics including the generation, accumulation, reservoir, preservation and migration of natural gas which were controlled by rift troughs, paleo-uplifts, erosion surfaces, cap rocks and faults, respectively. Near-source hydrocarbon supply, hydrocarbon accumulation in paleo-uplifts, effective reservoirs caused by the dissolution of carbonate rocks at the erosion surface of unconformity, regional stable preservation by cap rocks and migration through deep and large faults were the main controlling factors for natural gas enrichment. Therefore, the exploration activity for large and medium-sized gas fields was suggested to focus on 3 paleo-uplifts, 2 rifted troughs, and the basement faults in the Sichuan Basin. Through optimization, it was concluded that the Sinian to Lower Paleozoic strata, the high-energy phase band of Permian-Triassic and the Leikoupo Formation of Triassic in the marine carbonate area, the tight continental clastic rocks, the volcanic rocks in Permian and the shale gas areas are the favorable fields for further exploring for large and medium-sized gas fields.
Microscale sedimentary characteristics and distinguishing methods for deep-water sandy debris flow and turbidity flow in continental lakes: a case study of seventh member of Yanchang Formation, Ordos Basin
LI Zhiyong, XU Yunze, DENG Jing, LI Zhiming, ZHANG Jianwu, LI Yueyi
2021, 43(3): 415-423. doi: 10.11781/sysydz202103415
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Based on the results of thin section observation, grain size analysis, environmental scanning electron microscopy, whole rock mineral quantitative analysis and fluorescence element analysis, the microscale sedimentary characteristics of sedimentary sand debris flow and turbidity flow were studied in details after a systematic sampling of the seventh member of Yanchang Formation (Chang 7) of Xunyi and Yaoqu areas of Ordos Basin. The results showed that: (1) The clastic particles deposited in the sand debris flow were in a disordered arrangement, while the turbid flow deposition(section A of the Bouma sequence) has a more obvious directional arrangement, indicating the former is characterized by overall rapid transport, while the latter is characterized by traction flow, indicating a low density. Both of them contain pyrites. (2) The probability curve of the sand debris flow sandstones showed a two-stage pattern, reflecting the characteristics of traction and drainage. According to microscopic observation, its source could be shallow water or land river. The probability curve of the turbid flow sandstones shows a single stage pattern, reflecting the characteristics of gravity flow. (3) The paleoenvironment of the Chang 7 sedimentary period of Yaoqu area is dry and cold. The eluviation of sandy debris flow is weaker than that of turbid flow in most periods. (4) For elemental compositions, the Sr/Ba ratios of both sandy debris flow sandstonesand associated mudstones were lower than those of turbidity current, which indicates that it has stronger dilution effect on lake water and faster injection speed. The Sr/Cu ratios of Yaoqu area were lower than those of Xunyi area, and the relative rainfall is more abundant. In addition, the Zr content in sandy debris flow sandstones is higher than that in turbidity flow sandstones, which indicates that it had stronger debris transport capacity. (5) Through the quantitative analysis of the whole rock and clay by X-ray diffraction, there is no obvious difference in clay composition and mixed layer ratio between them, but there were differences in mineral composition of the whole rock. Since the contents of quartz and clay showed great difference, a division template of them has been established, which can quantitatively distinguish sandy debris flow sandstones, turbidity flow sandstones and the transition section.
Exploration potential and favorable direction of tight gas in Middle Jurassic Xiashaximiao Formation in Sichuan Basin
DUAN Wenshen
2021, 43(3): 424-431. doi: 10.11781/sysydz202103424
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Tight gas is an important gas-pool type for natural gas resource and output increment in China. The Middle Jurassic Xiashaximiao Formation (J2x) is an important target for the exploration of tight oil and gas in the Sichuan Basin. Based on decades of exploration practice and studies on accumulation conditions of tight gas, it was indicated that the J2x formation gas reservoir is a secondary structural lithologic gas reservoir with multiple layers, and was constrained by source, position and sedimentary facies. The major characteristics of these reservoirs are (1) the dark mudstones, carbonaceous mudstones and coal seams in the Lower Jurassic Ziliujing and Upper Triassic Xujiahe formations provided abundant natural gas sources; (2) the mud-packed sand structure formed by the combination of various channel sand bodies and shale in sedimentary systems such as alluvial fans and deltas was favorable for the enrichment of natural gas; (3) the widely distributed "estheria shale" or purple-red mud shale layer acted as regional cap rock; (4) three major paleo-uplifts and three major depressions formed after the Himalayan Movement, developed a series of structures on the top of the Xiashaximiao Formation, which was favorable for the formation of gas-bearing traps distributed throughout the basin and (5) the faults from the Upper Triassic Xujiahe Formation to the Xiashaximiao Formation provided migration channels for far-source gas reservoirs, while gas in the Ziliujing Formation could migrate to near-source reservoirs through small faults or micro-fractures. Thus a tight gas accumulationmodel of the Xiashaximiao Formation was established. The Xiashaximiao Formation possesses the foundation for forming large and medium-sized gas fields. The western part of Sichuan Basin has the largest potential for gas exploration and followed by the northern and southern parts. In the central Sichuan Basin, the reservoir-forming conditions are poorly configured and made its exploration potential poor.
Study and application of identification and description methods for lithologic traps in large braided river sheet composite channels
ZHANG Wei, HE Faqi, YAN Xiangbin, CAI Lixue
2021, 43(3): 432-442. doi: 10.11781/sysydz202103432
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The gas reservoirs in the Permian tight sandstones in the Ordos Basin are characterized by near source, tightness, large-scale area of gas reservoir, distribution along the main channel, and strong heterogeneity. Influenced by the changes in the internal physical properties of sand bodies, the difference between gas and water is not obvious, and the gas boundary is also unclear. Therefore, the trap identification and the description of this type of gas reservoir is not like those for a single trap in the ubiquitous cases. It should be focused on the distribution of the composite channel sand bodies formed by the spatial superposition of effective single sand body, so as to determine the "sweet spots" of the maximum reserve unit. A case study was made for the first member of Xiashihezi Formation of Lower Permian in the Duguijiahan trap of Hangjinqi area, northern part of Ordos Basin. The characteristics as well as identification and description methods for lithologic traps in sheet-shaped composite channels of large-scale braided rivers were discussed. Constrained by the sequence framework and based on the geological model, a well-seismic joint analysis of sedimentary facies was employed here to realize the effective prediction and description of effective sandstone reservoirs and their boundary distributions in braided river channels. A six-step evaluation of this type of trap was introduced, which could predict the effective reservoirs in sheet-shaped composite channels of braided rivers by using relatively low-resolution seismic data. With the continuous application and improvement of the technical series, the proven natural gas reserves in lithological traps of the first member of Xiashihezi Formation in the Duguijiahan trap have exceeded 100 billion cubic meters.
Prediction of tight clastic reservoirs of Upper Paleozoic in southern Ordos Basin: a case study of Zhenjing district
LU Hongmei, ZHANG Zhongpei, WANG Linlin, BIAN Changrong, SUN Yipu, LU Yingzhong
2021, 43(3): 443-451. doi: 10.11781/sysydz202103443
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It is difficult to distinguish reservoirs and non-reservoirs based on the rock's physical properties. The quality of post-stack seismic data in the loess plateau is poor, which makes it a technical bottleneck for the prediction of reservoir of the Upper Paleozoic, and the exploration in the southern Ordos Basin was then constrained. Block evaluations have indicated that the northeastern part of Zhenjing district has a good potential for exploration, with the second member of Permian Shanxi Formation and the first member of Xiashihezi Formation as the main target beds. The results of 3D seismic facies analysis in Zhenjing area are consistent with the regional sedimentary facies studies on provenance and the distribution of sand bodies, indicating that seismic data can be used for the prediction of reservoir. The distribution of sedimentary facies of a series of seismic forward modeling showed that the sand bodies distributed with a certain distance and thickness in the second member of Shanxi Formation and the first member of Xiashihezi Formation formed recognizable seismic reflections. This vertical spatial combination of stratigraphic lithology is consistent with the depositional model of regional superimposed and thick single-type sand bodies, which is the typical form of reservoir-caprock combination that has been discovered in the surrounding gas reservoirs. The reservoir prediction based on the optimal number of wave crests from the forward simulation results confirmed that the superimposed and the thick single-type sand bodies of the second member of Shanxi Member were distributed in SW-NE directions. Furthermore, the picking and interpretation of co-phase axis and the structural mapping of seismic profile were carried out, which directly delineated the distribution range and burial depth of lithologic traps in the sand bodies of the second member of Shanxi Formation, and provided drilling targets for exploration and deployment in this area.
Origin of eyeball-shaped limestone and its significance for petroleum geology
LI Ang, LUO Kaiping, LI Fengxun, PAN Wenlei, PENG Jinning, DENG Mo, LI Longlong
2021, 43(3): 452-460. doi: 10.11781/sysydz202103452
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Eyeball-shaped limestone is a kind of carbonate rock with a structure shaped as eyeball and eyelid, which is widely developed in south China. The petrological characteristics, paleo-sedimentary environment, origin and hydrocarbon geological significance of eyeball-shaped limestone were analyzed and discussed through a great deal of review and investigation on the characteristics and origin of domestic and abroad eyeball-shaped limestone. The eyeball-shaped limestone is composed of the "eyeball" of micrite-silty bioclastic limestone and the "eyelid" of argillaceous limestone or calcareous mudstone. Its origin mainly includes sedimentation and diagenesis. The "eyelid" of eyeball-shaped limestone is high-maturity to over-mature source rock with medium organic matter content deposited in deep water environment, which has good hydrocarbon generation potential. The eyeball-shaped limestone is also a set of low-porosity and low-permeability reservoir, and the storage performance of "eyelid" is obviously better than that of "eyeball". Fractures can improve the reservoir physical properties of eyeball-shaped limestone, and the reservoir with fractures has good oil and gas display.On the whole, the eyeball-shaped limestone gas reservoir is a self-generating and self-storing carbonate gas reservoir.
Influencing factors for breakthrough pressure of carbonate caprocks
ZHANG Lu, GUO Jianying, LIN Tong, XIE Zengye, YANG Chunlong, DONG Caiyuan, GUO Zeqing, HAO Aisheng
2021, 43(3): 461-467. doi: 10.11781/sysydz202103461
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In addition to traditional gypsum salt rocks and shale rocks, many studies have confirmed that carbonate rocks also work as oil and gas seals. Breakthrough pressure is a characteristic parameter for the evaluation of the sealing ability of cap rocks. Different lithology types and lengths of carbonate rocks were subjected to breakthrough pressure measurement experiments at different temperatures, results showed that lithology, permeability and fracture development have obvious effects to rock characteristics. At the same temperature, sample length does not have a good correlation with breakthrough pressure, however, at different temperatures, the breakthrough pressure of most samples gradually decreases with the increase of temperature. Therefore, formation temperature has a non-negligible effect on the sealing ability of cap rocks. It is a key factor that needs to be considered for the evaluation of the sealing capacity of cap rocks. The carbonate rock with a high argillaceous content has better sealing capacity under high geothermal conditions.
Characteristics and controlling factors of natural gas source rocks of Middle Permian Gufeng Formation in western part of Lower Yangtze Platform, China
BAI Fan
2021, 43(3): 468-475. doi: 10.11781/sysydz202103468
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Unconventional natural gas resources in the Lower Yangtze region have caused plenty of interests of the Chinese energy companies in recent years. The developing characteristics and controlling factors of natural gas source rocks in the Middle Permian Gufeng Formation were studied by analyzing the typical field profiles and boreholes. The thickness center of Gufeng Formation shale locates in the Wuhu area, and the maximum of thickness is greater than 150 m. The total organic carbon (TOC) content of shale is relatively high, mainly ranging from 1.0% to 4.0%, with an average value of about 3.4%, and there are significant differences for the TOC content of different systematic tracts. Kerogens are mainly of types Ⅱ2 and Ⅲ. The Gufeng Formation shale is in the late stage of thermal maturity, and within the range of the dry gas window. The development of organic-rich beds in the Gufeng Formation was related to volcanism and its closely associated hydrothermal fluid activities. Volcanism and hydrothermal fluid activities brought materials from deep earth to surface, which enriched water body with nutrient-rich elements, caused biological bloom and formed high productivity, thus provided a good material for good source rocks.
Depositional characteristics and evolution of Miocene deep-water channel systems in block A of Lower Congo-Congo Fan Basin, West Africa
CHEN Hua, LIN Changsong, ZHANG Zhongmin, ZHANG Demin, ZHU Yixuan, WU Gaokui, LI Ming, XU Hai, GUO Rongtao
2021, 43(3): 476-486. doi: 10.11781/sysydz202103476
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Researches on the depositional characteristics, evolution and constraining factors of deep-water channel systems are the key factors to reveal the "source-sink" process at continental margin and make big breakthroughs in deep-water hydrocarbon exploration. Based on the integrated analyses of seismic, well logging and core data, a sequence stratigraphic framework was established for the Miocene in block A of the Lower Congo-Congo Fan Basin, and then the sedimentary characteristics, evolution and constraining factors of the Miocene deep-water channel systems were purposed. The Miocene in the study area was divided into four third-order sequences, including the Lower Miocene (SQ1), the lower part of Middle Miocene (SQ2), the upper part of Middle Miocene (SQ3), and the Upper Miocene (SQ4). The Miocene deep-water channel deposits are dominated by sandstones and include four types of sedimentary units (deep-water channel deposits, levee-overbank, lobes and mass transport deposits). In the SQ1, weakly restricted-unrestricted depositional channels and lobes were formed. In the SQ2, weakly restricted erosional-depositional channels were developed. In the SQ3, erosional channels were dominant. In the SQ4, erosional isolated channels were widely recognized. Tectonic uplift, denudation, glacial climate and sea level change provided abundant sediment supplies for the development of gravity flow deposits. They might lead to the slope change of paleo-geomorphology in the study area, which further affected the strength of gravity flow and controlled the development and evolution of deep-water channel systems. Moreover, salt structures played important roles in redirecting, restricting, blocking, migrating and destroying the deep-water channels.
Hypothesis of organic-inorganic coupling causes for petroleum generation and its significance
LUO Qun, JIA Chun, OU Guangxi, LIANG Guanghe, LIU Yinhe, ZENG Pusheng, CHEN Jiayu, CUI Qian
2021, 43(3): 487-497. doi: 10.11781/sysydz202103487
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It has important theoretical and practical significance to clarify the causes and distribution of oil and gas. This paper focused on the key scientific issues in the current petroleum genesis research, guided by the general principles of global tectonics and petroleum geology. Various petroleum genesis hypotheses have been sorted out, merged, integrated and innovated, thus a hypothesis framework of organic-inorganic coupling causes for petroleum was introduced. The main factors are that oil (including natural gas) is a renewable resource with multiple origins and has huge reserves. The formation and distribution of petroleum is the result of the coupling of four pairs of hydrocarbon-forming factors, including basin and mantle uplift, deep and shallow fluids, organic and inorganic hydrocarbon generation mechanisms, deep faults and sealing conditions. The higher degree of organic-inorganic cause coupling indicates the richer the oil and gas. The basin and the area below its basement are the locations with the best degree of coupling, followed by the deep and large fault development areas with good sealing conditions in the surrounding areas of the basin. The matching of deep and large faults with sealing conditions is an important factor constraining hydrocarbon accumulation. Large-scale traps with good sealing conditions in long-term, multi-period or recent active deep and large fault development areas are the most favorable targets for major exploration successes.
Characteristics of oil and gas generation, expelling and retention of coaly source rock
YANG Heng, GONG Wenping, ZHENG Lunju
2021, 43(3): 498-506. doi: 10.11781/sysydz202103498
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To understand the effectiveness of hydrocarbon generation, expelling and retention capacities of coaly source rocks, carbonaceous mudstones and mudstones in coal layers and interlayers of different sedimentary environments and ages were selected to carry out the simulation experiments with a semi-open system operated at high tempera-ture and high pressure, and a corresponding model of evolution was established. With different depositional environments, the type Ⅱ2 coaly source rocks expelled oil in the oil generation window with gas generated. Therefore, they worked as source rocks for both of oil and gas. However, for the coaly source rocks of type Ⅲ kerogen, the generated oil was mainly retained during the oil generation window and basically did not expel. As a result, this type of source rock was regarded as source rocks of gas only. The conversion rate of hydrocarbon generation was mainly controlled by the type of organic matter, while the ability to expel hydrocarbons was controlled by lithology and organic matter abundance. For each unit mass of rock, coal rocks has much higher conversion rates than the carbonaceous mudstones and mudstones in their interlayers. In the full evolution stage of coal rock, both low-rank and high-rank coals had strong ability for hydrocarbon gas generation and oil-and-gas retention, which showed a good potential for coal bearing methane development.
Simulation of crude oil cracking and gas generation with semi-open condition, Baiyun Sag, Pearl River Mouth Basin
LONG Zulie, SHI Chuang, ZHU Junzhang, HUANG Yuping, SHI Yuling, ZHANG Xiaolong
2021, 43(3): 507-512. doi: 10.11781/sysydz202103507
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In order to study the mechanism and product compositions of oil cracking, crude oil samples from the Zhuhai Formation of the Baiyun Sag of Pearl River Mouth Basin were carried out for the high-temperature, high-pressure pyrolysis with different heating rates with the pressure close to the conditions of underground. The underground fluid was also considered to be included with a semi-open condition for the pyrolysis, the gas yields and gas composition characteristics were then analyzed. Results showed that crude oils start to crack at 365 ℃, and the cracking yield increases with the increase of temperature. At a heating rate of 20 ℃/h, the final yields (at 550 ℃) of pyrolysis gas, hydrocarbon gas and non-hydrocarbon gas were 580.13, 394.25, and 185.88 mg/g, while at a heating rate of 60 ℃/h, these values increased to 707.68, 485.77, 221.91 mg/g, respectively. The composition of hydrocarbon gases at different heating rates also varied, and these variations were assumed to be related to the difference of cracking mechanisms of crude oils at different temperatures of pyrolysis. According to the composition characteristics of pyrolytic gas products, most of the gases from crude oil cracking has a relative higher content of high molecular weight hydrocarbon gas, thus these compounds can be used as an auxiliary index to distinguish crude oil cracked gas from kerogen cracked gas.
Re-Os isotopic dating procedures for organic-rich samples
WU Luya, JIN Zhijun, CHU Zhuyin, LIU Keyu
2021, 43(3): 513-523. doi: 10.11781/sysydz202103513
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The rhenium-osmium (Re-Os) geochronometer is newly developed technology and has been regarded as a promising radiometric tool for the direct dating of the deposition of source rock, hydrocarbon generation, migration and consequent alteration (e.g., thermal cracking, thermochemical sulphate reduction), and oil-source correlation. However, the complex nature of Re-Os systems in organi-rich samples, including their relatively low elemental contents, multiple origins and occurrences, ambiguous homogenization mechanisms of 187Os/188Os and our limited understanding of the closed system of Re-Os systematics etc., often result in the relatively large uncertainties of obtained isochrones. In this paper, to improve their data quality and yield ideal Re-Os isochrons, the existing Re-Os isotopic analysis method was improved by the terms of sample selection and screening, chemical pretreatment, total analytical blank control and international reference material monitoring. Results showed that a comprehensive guide to researching working in Re-Os geochronology for petroleum system analysis can be available.
An improved column-chromatographic separation for polycyclic aromatic compounds in petroleum
LIU Xue, LI Meijun, TANG Youjun, HE Daxiang, KONAN N'Guessan Francois De Sales, SHI Shengbao, ZHU Lei
2021, 43(3): 524-531. doi: 10.11781/sysydz202103524
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The separation and preparation process of petroleum group components is the basis for the subsequent molecular composition and isotopic analysis. Due to the complex composition of isomers, the components of aromatic compounds prepared by traditional techniques still cannot meet the isotopic analysis requirements of specific compounds. Two different separating methods were used to finely separate and prepare polycyclic aromatic hydrocarbons in crude oils. The "one-step method" was to directly pass the de-asphalted crude oil samples through an alumina/silica gel chromatography column, and elute them with different ratios of petroleum ether/dichloromethane mixed solvent. The "two-step method" firstly used conventional separation methods to obtain aromatic fraction from crude oils, and then applied the aromatic fraction to a column filled with alumina and sub-fractions with different ring numbers then eluted with mixed solvent with different ratios of petroleum ether/dichloromethane. Gas chromatography-mass spectrometry (GC-MS) analysis for the sub-fractions were carried out for the comparison between the two separation methods. Results show that the "two-step method" can better realize the separation and preparation of monocyclic, bicyclic and tricyclic aromatic compounds. The mixed solvents of petroleum ether/dichloromethane of V/V: 99/1, 9/1 and 8/2 can obtain monocyclic, bicyclic and tricyclic aromatic compounds respectively.
A calculation method for the efficiency of hydrocarbon expulsion based on parameter-diagram of source rock pyrolysis
ZHANG Dongmei, ZHANG Yanyan, GUO Junjing, HU Shouzhi, LI Shuifu
2021, 43(3): 532-539. doi: 10.11781/sysydz202103532
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The efficiency of hydrocarbon expulsion acts as a key geological factor for the study of hydrocarbon expulsion of conventional oil and gas, also, it indicates the enrichment degree of unconventional oil and/or gas. Based on the method of recovering the original hydrocarbon generation potential, a method according to pyrolysis chart was proposed in this paper. A classic diagram for classifying organic matter types based on hydrogen index (IH) and maximum pyrolysis peak temperature (Tmax) was introduced in this study. The dividing line of organic matter type and the maturity trend line were evenly interpolated and gridded. The IH and Tmax data were plotted into the chart, and then traced to the left along the type line to the intersection point of maturity line Ro=0.2% as the original value of hydrocarbon generation index, thus, the hydrocarbon expulsion efficiency can be calculated. Based on the results of 66 source rock samples from the well BYHF1 of Biyang Sag, the relationship between hydrocarbon expulsion efficiency and characteristics of organic matter (ATM) was studied. In addition, the correlation between hydrocarbon expulsion efficiency and shale oil enrichment degree was studied. The results indicated that the hydrocarbon expulsion efficiency and ATM characteristics of organic matter obtained by the pyrolysis chart method were more regular than those obtained by the artificial assignment method, and it had a higher consistency with the enrichment degree of shale oil (OSI). The calculation process and results will not to be negative value or hydrocarbon expulsion efficiency greater than 100%. Therefore, it is reasonable and feasible to calculate hydrocarbon expulsion efficiency by the pyrolysis chart method, which is a complement to the original hydrocarbon generation potential recovery method.
Method of identifying and characterizing of volcanic traps and its application
YANG Shuang, LI Zhongbo, YAN Xiangbin, CAI Lixue
2021, 43(3): 540-548. doi: 10.11781/sysydz202103540
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Volcanic rocks were widely developed in sedimentary basins in China. The Songliao, Junggar and Sichuan basins have got great research successes and exploration discoveries in igneous reservoirs, which have become one of the important fields for oil and gas exploration in China. In the Changling Fault Depression of Songliao Basin, volcanic rocks are widespread in the Huoshiling and Yingcheng formations, which have a good potential for reserve and production increase. However, the results of exploration were directly dependent on the technical level of identification and characterization of volcanic traps. The conditions of hydrocarbon accumulation in volcanic traps are more severe than those in clastic traps. The physical property of reservoir and sealing effectiveness of surrounding rocks are the key factors for the effectiveness of volcanic rock traps. Based on systematically analyzing the discovered volcanic reservoirs, it was pointed out that the characterization of volcanic rock mass and volcanic reservoir were the key points for the identification of volcanic traps. In this study, taking the volcanic lithologic trap as an example, a "five-step processing" for the identification and description of volcanic lithologic trap was proposed and applied to the Longfengshan nose structural belt in practice. The drilling results showed that the characteristics of volcanic traps were consistent with the research results before drilling, which confirmed the effectiveness and reliability of traps. It also verified that the identification and description methods of volcanic traps were effective for the Changling Fault Depression and had certain guiding application value in volcanic exploration in other basins of China.
Core testing technology with T2-Pc two-dimensional nuclear magnetic resonance and its application
CHEN Yao, ZHANG Gong, ZHENG Guoqing, PENG Qing, Qin Yingyao
2021, 43(3): 549-556. doi: 10.11781/sysydz202103549
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Abstract:
As a non-destructive, efficient and non-invasive detection method, nuclear magnetic resonance (NMR) technology has always played an important role in the analysis of oil and gas cores, but the traditional nuclear magnetic resonance detection results (T2 spectrum) only reflect the size distribution characteristics of rock pores, while the connectivity of pores cannot be directly characterized. Through the improvement of experimental procedures and data processing methods of the standard nuclear magnetic T2 spectrum, the capillary pressure dimension is added in to obtain the T2-Pc two-dimensional nuclear magnetic experiment spectrum, which solves the problem that the nuclear magnetic experiment cannot reflect the pore connectivity. Practical application shows that the T2-Pc two-dimensional nuclear magnetic experiment can not only intuitively evaluate reservoir connectivity, but also obtain bound water saturation under different production pressure differentials, thus providing more reservoir information for oil and gas exploration and development.
2021, 43(3): 557-557.
Abstract(299) PDF-CN(167)
Abstract:

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