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2020 Vol. 42, No. 4

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2020, 42(4): 00-00.
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Advances in the basic study of lacustrine shale evolution and shale oil accumulation
LI Maowen, JIN Zhijun, DONG Mingzhe, MA Xiaoxiao, LI Zhiming, JIANG Qigui, BAO Yunjie, TAO Guoliang, QIAN Menhui, LIU Peng, CAO Tingting
2020, 42(4): 489-505. doi: 10.11781/sysydz202004489
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This manuscript provides a review of the recent advances in the study of fundamental processes and geological drivers involved in the lacustrine shale deposition, burial diagenesis, thermal maturation and in-situ oil accumulation, aimed at identifying key problem areas for future study. A survey of relevant literature on the sedimentology of fine-grained sediments reveals that paleoclimate changes on the global scale and tectonic evolution on the basinal scale have played a significant role in the formation of organic rich shales. Due to the strong heterogeneity in the mixed deposition of fine-grained sediments in the lacustrine setting, multiscale integration of different grain sequence sedimentary rocks is vital in the modeling of the lacustrine shale oil reservoirs. Techniques and methodologies are generally mature for characterizing and describing micropores and microfractures at various scales in the lacustrine shales. However, the current understanding of the dynamic processes in the shale diagenesis is incompatible with the high demand for predicting the key shale attributes as an effective shale oil reservoir. The processes involved in the thermal maturation, hydrocarbon generation and expulsion, as well as the physical status of oils in a shale, are generally well understood. The next logic step would be the application of these knowledges to tailor our methodologies for the classification and evaluation of shale oil resources in different tectonostratigraphic settings. While progresses have been made fairly recently in the physical constraints of the multi-phase and multiscale non-Darcy flows in the lacustrine shale, it is highly desirable to gain a better understanding of the likely modes, as well as associated temporal and spatial consequences, of hydrocarbon flows across different shale lithofacies. As the basic study of shale oil accumulation mechanisms has lagged behind the industry drilling activity, it is necessary to expedite the basic study in order to develop suitable protocols, parameters and laboratory tools for core area and "sweet-spots" delineation in a lacustrine shale play.
Characteristics and main controls of shale oil reservoirs in Lucaogou Formation, Jimsar Sag, Junggar Basin
HUO Jin, ZHI Dongming, ZHENG Menglin, TANG Yong, WANG Xiatian, CHANG Qiusheng, GUO Xuguang, DING Jing, HE Wenjun, BAO Haijuan, GAO Yang
2020, 42(4): 506-512. doi: 10.11781/sysydz202004506
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The characteristics and main controls of continental shale oil reservoirs in the Permian Lucaogou Formation in the Jimsar Sag of Junggar Basin were studied based on seismic, core and logging data. Oil was found in a large area in the Lucaogou Formation, mainly in micro and nano pore throats or bedding fractures in free or adsorbed states. There are two sweet spot layers separated by mudstones. The formation pressure and maturity of shale reservoirs gradually decrease from the sag area to the slope area, while the crude oil density gradually increases. The quality and maturity of source rocks controlled the distribution and properties of shale oil. The sedimentary microfacies controlled the distribution of shale oil. The lithology and physical properties of shale controlled the enrichment of shale oil. Hydrocarbon generation pressurization was the main driving force for shale oil accumulation.
Favorable conditions of inter-salt shale oil formation and key parameters for geological sweet spots evaluation: a case study of Eq34-10 rhythm of Qianjiang Formation in Qianjiang Sag, Jianghan Basin
LI Zhiming, QIAN Menhui, LI Maowen, JIANG Qigui, WU Shiqiang, BAO Yunjie, CAO Tingting, TAO Guoliang, LIU Peng, XU Ershe, LIU Weixin
2020, 42(4): 513-523. doi: 10.11781/sysydz202004513
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The inter-salt fine-grained sedimentary rocks of the Eq34-10 rhythm of the Qianjiang Formation in the Qianjiang Sag, Jianghan Basin, are favorable for shale oil exploration and development. They are excellent source rocks according to the analysis of cored intervals from specialized/concurrent shale oil exploration wells and the archival data. The organic matter is composed of the amorphous components of the sapropelic group, mainly of types Ⅱ1 and I, and is currently in the peak period of oil generation and expulsion. The reservoir properties are good especially for dolomites and argillaceous dolomites, and are equivalent to the reservoir properties of main shale oil production layers at home and abroad. Thick layers of salt distributed continuously above and below the inter-salt fine-grained sedimentary rocks constitute high-quality top and bottom seals of the inter-salt shale oil. The inter-salt fine-grained sedimentary rocks of the Eq34-10 rhythm developed two types of shale oil, including the lateral migration and enrichment type in the sedimentary rocks in the Wangchang anticline area, and the in situ and near-source enrichment type in the Benghu Deep Sag and the southern slope area. Some key parameters and limits for geological sweet spot evaluation for the two enrichment types were put forward. The results provided the evidence and reference for shale oil exploration and development evaluation of other inter-salt fine-grained sedimentary rocks in the Qianjiang Sag, Jianghan Basin.
Distribution and main controls for shale oil resources in USA
BAI Guoping, QIU Haihua, DENG Zhouzhou, WANG Wenyong, CHEN Jun
2020, 42(4): 524-532. doi: 10.11781/sysydz202004524
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Systematic analyses of statistical data of shale oil resources and an integrated investigation of geological elements in major shale oil basins in USA were made. They characterize the distribution features of shale oil resources and document the controlling factors for shale oil endowment in USA. The results provide insights for shale oil exploration and production in China. Recoverable shale oil resources amount to 1 51×109 bbl in USA, of which 36.5×109 bbl have already been proven with a discovery rate of 24.2%. The shale oil resources are unevenly distributed. The Permian Basin has the lion's share of the total, followed by the Gulf and Williston basins. The enrichment of shale oil resources is largely governed by the volume of high quality source rocks, the extensive top and bottom seals of shale oil plays and the scale of "sweet spots" in shale oil reservoir intervals. The former two control the total endowment of shale oil resources and the latter controls the production volume of shale oils. It is suggested that China's shale oil exploration should focus on the selection of favorable plays and their fairways in large sedimentary basins. The delineation of new "sweet spots" and the expansion of the extent of known "sweet spots" are the keys for the new breakthroughs of shale oil exploration and the increase of both shale oil production and reserves.
Prediction of low-maturity shale oil produced by in situ conversion: a case study of the first and second members of Nenjiang Formation in the Central Depression, southern Songliao Basin, Northeast China
LIU Bo, LIU Yang, LIU Yan, HE Junling, GAO Yifei, WANG Haoli, FAN Jing, FU Xiaofei
2020, 42(4): 533-544. doi: 10.11781/sysydz202004533
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The Nenjiang Formation in the Centrel Depression of the Songliao Basin consists of organic-rich low-maturity shale with a wide distribution and large thickness. In this study, the spatial heterogeneity of organic matter (OM) abundance and types was studied based on core measurements and log data. A geological model was used to predict the potential of in situ electric heating using hydrocarbon generation kinetics and heat conduction models. All members of the Nenjiang Formation are in the immature to low-maturity stage and oil-prone. The first and second members of the Nenjiang Formation (K2n1+2) contain mainly types Ⅱ1 and Ⅱ2 kerogen with alginite the dominant maceral. The shale of K2n1 has the best generation quality, and the high-quality source rocks within this member are mainly distributed in the Xinbei-Daan area of the Changling Sag. It can be inferred from the in situ electric heating simulation that the temperature rises rapidly, and reaches above 600 ℃ after 4 years of heating at 2 kW heating power. At 1 kW of heating power, it would take about 8 years. As the organic matter conversion rate approached 100% by the fifth year of heating, the maximum resource abundance was achieved. At the 2 kW heating power, the resource of the K2n1 reaches 24.5×109 t at the end of the fifth year, and 6.6×109 t of the K2n2.
Comparison of oil-bearing properties and oil mobility of shale with different lithologies in continental basins: a case study of the upper fourth member of Paleogene Shahejie Formation in Dongying Sag, Bohai Bay Basin
LI Zheng
2020, 42(4): 545-551. doi: 10.11781/sysydz202004545
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The shale in the upper part of the 4th member of Paleogene Shahejie Formation in the Dongying Sag of Bohai Bay Basin can be divided into two lithology types: calcareous mudstone and argillaceous limestone. The differences of organic matter abundance, oil-bearing properties, reservoir properties and movable shale oil in the different lithologies were investigated using X-ray diffraction, microscopic observation, geochemical analysis, porosity tests and mercury injection. The calcareous mudstone has relatively higher organic matter abundance and better oil-bearing properties than the calcareous mudstone. The calcareous mudstone has relatively higher porosity, but the pore throats are generally smaller, while the argillaceous limestone porosity is relatively lower with more large pore throats. The shale oil mobility in the calcareous mudstone and argillaceous limestone was compared using the oil saturation index, mineral adsorption capacity for crude oil and clay mineral transformation degree. The shale oil in the argillaceous limestone has better mobility than the shale oil in the calcareous mudstone.
Characteristics of nitrogen-containing compounds in shale oil and adjacent shales in well FY 1, Jiyang Depression, Bohai Bay Basin
LIU Peng, TAO Guoliang, LI Maowen, LI Zhiming, JIANG Qigui, BAO Yunjie, XU Ershe
2020, 42(4): 552-557. doi: 10.11781/sysydz202004552
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The composition of shale oil and neighboring shales with different lithofacies in well FY 1 in the Jiyang Depression of Bohai Bay Basin was analyzed with negative-ion electrospray ionization (ESI) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The molecular compositions of pyrrole nitrogen compounds were compared. The heteroatom compounds of shale oil and two core extracts were mainly N1 compounds. The high resolution mass spectrum and fingerprint details, the DBE and carbon number distribution of N1 compounds, and the average molecular weight of N1 compounds of three samples all showed that the composition of pyrrole nitrides in shale oil is similar to that of lamellar shale extracts, but different from the massive shale extracts. The ESI and FT-ICR MS has an ultra-high resolution and can effectively show the fine molecular composition differences of heteroatomic compounds in different types of samples. The analysis results can provide a reference for the near source tracing of terrestrial shale oil.
Geochemical characteristics of lacustrine shale and enrichment mechanism of organic matter in Zhanhua Sag, Bohai Bay Basin
CAO Tingting, YAO Wei, LI Zhiming, LI Zheng, LI Maowen
2020, 42(4): 558-564. doi: 10.11781/sysydz202004558
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The lacustrine shale in the lower part of the third member of Shahejie Formation (Es3) in well L69 in the Zhanhua Sag of Bohai Bay Basin was studied. The geochemical characteristics of lacustrine shale in different system tracts were analyzed in a framework of sequence stratigraphy. The evolution process of sedimentary environment and the enrichment mechanism of organic matter were clarified, which provided theoretical support for the identification of favorable targets of unconventional shale oil. The combination of logging and lithology reveals that the sequence of the lower Es3 can be divided into transgression, early highstand and late highstand system tracts from bottom to top. Productivity and preservation conditions are the controlling factors of organic matter enrichment. The higher productivity and better preservation conditions together determine that the early highstand system tract is the most favorable organic matter accumulation interval, which provides a good material basis for a good shale oil development target.
Micro-pore structure in an inter-salt shale oil reservoir and the relationship with physical properties in the fourth section of the third member of Qianjiang Formation, Qianjiang Sag, Jianghan Basin
XU Wenming, JIANG Qigui, LIU Weixin, TAO Guoliang, ZHANG Wentao, QIAN Menhui, CAO Tingting, BAO Yunjie, LI Zhiming
2020, 42(4): 565-574. doi: 10.11781/sysydz202004565
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The micro-pore structure of an inter-salt shale oil reservoir and its relationship with physical properties in the fourth section of the third member of Qianjiang Formation (Eq34) in the Qianjiang Sag of Jianghan Basin were studied using X-ray diffraction, thin section observation, conventional scanning electron microscopy (SEM), argon ion polishing SEM and three-dimensional pore reconstruction of focused ion beam, microscopy combined with quantitative analysis of mercury intrusion and nitrogen adsorption pore volume. According to the level of mineral content, the reservoir is divided into three categories: dolomitic mudstone, argillaceous dolomite and muddy dolomite. The mineral composition and structure of the reservoir are highly heterogeneous, and the conventional core-plug porosity varies greatly, ranging from 1% to 13%. The porosity of dolomitic mudstone is low, the porosity of argillaceous dolomite and muddy dolomite is high, and the porosity of mudstone with high content of glauberite is low. The reservoir microstructure changes greatly, and the dolomitic mudstone has a directional arrangement structure, mainly with elongated or flat micropores. The pore size is small, with a pore diameter of 20-50 nm, and the largest connecting throat is small, ranging from 22 to 42 nm. The argillaceous dolomite mainly contains residual intergranular pores and pores between clay layers. The pore diameter becomes larger, mainly 20 to 80 nm. The maximum connecting throat varies greatly, between 16 and 158 nm. The muddy dolomite is mainly composed of uniform grain structure, polygonal equidimensional intergranular micropores. The pore size is large, 80-180 nm. The largest connecting throat is large, at 158-196 nm. The pore connection of dolomitic mudstone, argillaceous dolomite and muddy dolomite has the characteristics of "fracture-fracture, pore-fracture, pore-pore connection", respectively. The muddy dolomite has high porosity, wide connecting throats, and favorable pore structure, indicating the best shale oil storage space.
Aryl isoprenoids and their significance for inter-salt shale oil exploration in the Jianghan Basin
MA Xiaoxiao, LI Maowen, LIU Peng, LI Zhiming, JIANG Qigui, TAO Guoliang, QIAN Menhui, BAO Yunjie, CAO Tingting, WU Shiqiang
2020, 42(4): 575-585. doi: 10.11781/sysydz202004575
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Fifteen inter-salt shale cores were collected from the well WY 11, Qianjiang Sag, Jianghan Basin, and the sampling intervals include four of the salt cycles in the Eq3 Member of the Eogene Qianjiang Formation. Bulk geochemical data were obtained by whole rock pyrolysis, and gas chromatography-mass spectrometry (GC-MS) analyses were conducted for molecular compositions of saturated and aromatic biomarkers. Our results separated the analyzed samples into two broad categories corresponding to brackish-saline and saline lacustrine settings. Inter-salt shales deposited in the brackish-saline lakes occur over large geographic areas with relatively strong water column stratification, and are characterized by the presence of abundant gammacerane and 2, 3, 6-trimethyl-aryl isoprenoid alkanes. In contrast, inter-salt shales deposited in saline lakes tend to distribute in small areas, and the presence of abundant 3, 4, 5-trimethyl-aryl isoprenoid alkanes with lower contents of gammacerane is consistent with relatively shallow water depth. High pyrolysis S1 contents, S1/w(TOC) ratios, Ts/(Ts+Tm), and 20S/(20S+20R) and (αββ/ααα+αββ) ratios of C29 steranes are good indicators for the inter-salt shales that were deposited in the brackish-saline settings and are ideal habitats for lacustrine shale oil enrichment, since the presence of organic rich lamina favor the updip, lateral oil migration along the bedding parallel microfractures. According to the common hopane and sterane parameters as well as aryl isoprenoid biomarker distributions, it is suggested that inter-salt shale oil exploration in the Jianghan Basin should be focused on organic rich shale beds in the Eq3 and Eq4 members deposited during the maximum lake expansion. More efforts were suggested to be invested in the mature source kitchens of the Banghu Sag in addition to the continuing pilot production tests in the Wangchang area.
Multi-scale characterization of the spatial distribution of movable hydrocarbon in intersalt shale of Qianjiang Formation, Qianjiang Sag, Jianghan Basin
SUN Zhongliang, WANG Furong, HAN Yuanjia, HOU Yuguang, HE Sheng, LUO Jing, ZHENG Youheng, WU Shiqiang
2020, 42(4): 586-595. doi: 10.11781/sysydz202004586
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Pore space containing mobile shale oil was more precisely characterized by comparing the change of adsorption volume of low-temperature nitrogen experiments and the change of mercury intake volume in high-pressure mercury injection experiments and the change of pore diameter using field emission scanning electron microscopy. The Eq34-10 rhythmic mobile hydrocarbon mainly occurs in dolomitic intercrystalline/intergranular pores and clay mineral interbedded pores, and movable hydrocarbon is relatively rich in lamellar shale. Low temperature nitrogen adsorption and high-pressure mercury injection measurements of pore size were spliced with pore size of 80 nm, and the results showed that movable hydrocarbon mainly occurs in the range of pore size less than 200 nm, and also occurs in the micron sized pores. Relatively more movable shale oil occurs in pores from 90 nm to 200 nm. The samples with low clay mineral content can yield movable hydrocarbon within the pores of ≤5 nm. The higher the porosity, the larger the average pore size, and the richer the movable shale oil.
Origin and significance of "sweet spots" of analcites in shale oil reservoirs in Permian Lucaogou Formation, Jimsar Sag, Junggar Basin
MA Cong, WANG Jian, PAN Xiaohui, CHEN Jun, SHANG Ling, LIU Jin
2020, 42(4): 596-603. doi: 10.11781/sysydz202004596
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As a hydrocarbon indicating mineral, analcite was always found in shale oil reservoirs and has good correspondence with "sweet spots" in the Lucaogou Formation, Jimsar Sag, Junggar Basin. The petrographic and mineralogical characteristics as well as geologic origins of analcite were studied using a polarized light microscope, whole rock XRD analysis, electron probe BSE image analysis and mineral energy spectrum, in order to discuss its significance for shale oil "sweet spots". The analcite is mainly found in sedimentory tuff and carbonate tuff with some in tuff dolomite, and the analcite rock is very rare. The occurrence of analcite in rocks is lamellar, granular, massive and vein-shaped. Analcite was formed in high salinity, alkaline, low temperature hydrothermal conditions. The diagenetic transformation of non-volcanic material during burial forms authigenic analcite. Secondary analcite was formed by reaction and dissolution of volcanic material and hydrothermal during volcanic jetting. Analcite cements in the early diagenesis protected native porosity, and afforded the formation of secondary solution pores during mid and late diagenesis which has a good correspondence with shale oil "sweet spots".
Reservoir characteristics and genesis of shale oil "sweet spots" in Lucaogou Formation, Jimsar Sag, Junggar Basin
WANG Ran, CHANG Qiusheng, QIAN Yongxin, LIU Guoliang, WAN Min, HUANG Liliang
2020, 42(4): 604-611. doi: 10.11781/sysydz202004604
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The shale oil layers of the Lucaogou Formation in the Jimsar Sag of Junggar Basin have complex lithology and strong heterogeneity. The formation of "sweet spots" is a key problem restricting exploration and development. Through core observation, thin section analysis and oil-bearing capacity analysis, the geological features of the "sweet spots" were characterized, the geological factors affecting productivity were analyzed, and the formation mechanism of movable oil pores was determined. The lithology of "sweet spots" of the Lucaogou Formation in the Jimsar Sag is mainly lithic feldspar fine sandstone, dolomitic sandstone and gypsum dolomite, with a porosity of 5.75%-11.9% and a permeability of (0.02-1.26)×10-3 μm2, of which the lithic feldspar fine sandstone made the largest contribution to pore throats. Intergranular (intragranular) pores and fractures provide storage space for "sweet spots". Shale oil yield is controlled by the pore distribution for movable oil and the contents of argillaceous, quartz and dolomite. The movable oil pores are formed under the combined action of syngenetic and quasi-syngenetic leaching and acid fluid burial dissolution. The key factor to control permeability is the connection of dissolved pores by bedding cracks. In the process of reservoir diagenesis, the coupling of hydrocarbon generation and expulsion in the reservoir space will eventually form a "sweet spot", mainly in environments such as dolomitic flat, mixed flat, lakeside beach sand and carbonate shoal which are strongly influenced by waves. This discovery can provide guidance for the exploration and development of shale oil of the same genetic type.
Characteristics and sedimentary environment of organic-rich shale in the second member of Paleogene Funing Formation, Subei Basin
DUAN Hongliang, LIU Shili, FU Qian
2020, 42(4): 612-617. doi: 10.11781/sysydz202004612
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Two sets of organic-rich shales are developed in the second member of Funing Formation (E1f2) in the Subei Basin, which are E1f2shale 1 and E1f2shale 2. They are widely distributed, with rich shows and favorable shale oil conditions. Based on core and thin section observations, and combined with systematic organic geochemistry, X-ray diffraction and trace element analyses, the characteristics and sedimentary environment of the organic-rich shales were studied. The characteristics of the E1f2shale 1 and E1f2shale 2 are totally different. The E1f2shale 1 mainly consists of dark gray blocky limestones and siliceous mudstones, with slight bedding, 2.21%-3.41% organic carbon content, and type I organic matter. The E1f2shale 2 mainly consists of dark oil shales and dolomitic mudstones, calcite mudstones, muddy dolomites and muddy limestones, with laminar bedding, 2.02%-2.99% organic carbon content, and type I organic matter. The sedimentary palaeo climate of E1f2 has experienced semi-arid, reducing, brackish water, to dry, strongly reducing, salt lake, and to warm humid, oxic, freshwater in the Subei Basin. The organic-rich shales were formed in the transition formations near the maximum flooding surface, between strongly reducing, dry and hot, saltwater environments and oxic, humid, normal water environment. The E1f2shale 2 was formed in a strongly reducing, dry and hot, salt lake environment, while the E1f2shale 1 was deposited in a strongly reducing, damp to semi-arid and brackish water environment. Sedimentary environment evolution resulted in the differences of lithology, electrical properties, and quality of hydrocarbon source rocks, occurring in the muddy shale interlayer and internal organic-rich shale.
Enrichment characteristics and main controlling factors of shale oil reservoir in the second member of Paleogene Funing Formation, Beigang Subsag, Jinhu Sag, Subei Basin
ZAN Ling
2020, 42(4): 618-624. doi: 10.11781/sysydz202004618
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The accumulation conditions were studied and the main controlling factors were determined based on the analysis of marly shale reservoirs in the second member of Paleogene Funing Formation in the Beigang Subsag, Jinhu Sag, Subei Basin. The Beigang marly shale reservoir is buried 3 660-3 735 m, in the ③-④ subsections of the second member of Funing Formation. It is a typical self-sourced oil reservoir. The reservoir is characterized by "four high values and one development", that is, high organic matter abundance, high thermal evolution degree, high brittle mineral content, high abnormal pressure and natural fracture development. The lime mudstones and marls of the ③-④ submembers of the second member of Funing Formation are high-quality source rocks. The average TOC content is 1.83%, and the average S1 value is 0.59 mg/g. The organic matter type is type Ⅰ, and the Ro value is 1.1%, indicating a high maturity. The crude oil has moderate phytane, gammacerane, pregnane and tricyclic terpane contents indicating deposition in a relatively high salinity environment. The average content of brittle minerals is 60.7%, mainly consisting of quartz, dolomite and calcite. The measured porosity is 4.24%-8.76%, with an average of 7.04%. Solution pores are developed in subsection ③, while natural fractures are developed in subsection ④. The pressure coefficient calculated by acoustic time difference is 1.3. Widespread high-quality source rocks are the material basis for shale reservoir formation. Geological "sweet spots" control the local enrichment of shale oil. High abnormal pressure is critical for the high production of shale reservoir. The marly shale reservoir in the second member of Funing Formation has a good prospect for exploration and development.
Shale oil accumulation conditions in the second member of Paleogene Funing Formation, Gaoyou Sag, Subei Basin
FU Qian, LIU Qidong, LIU Shili, DUAN Hongliang
2020, 42(4): 625-631. doi: 10.11781/sysydz202004625
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"Carbonate sandwich shale oil" is a main exploration target in the Subei Basin. The deep depression-inner slope zone of the Gaoyou Sag is a favorable area for the exploration of "carbonate sandwich shale oil" in the second member of Funing Formation (E1f2). The source rock and reservoir quality, engineering conditions and movability of each shale section of E1f2 were analyzed in order to further clarify "sweet spot" sections by using scanning electron microscopy, mercury intrusion at elevated temperature, nitrogen adsorption, CT scanning, X-ray diffraction, triaxial mechanics, multi-temperature pyrolysis and other research methods. The E1f2shale1 and E1f2shale2 in the deep depression-inner slope zone of Gaoyou Sag were deposited in a dry, hot, reducing and brackish water environment, developing favorable shale with high organic matter content. The TOC contents are 2.33% and 1.63%, respectively Kerogens are mainly of types Ⅰ and Ⅱ1, with the most favorable conditions for hydrocarbon generation. The interlamellar pores were well developed, and the reservoir space is dominated by macropores and fractures. The brittle mineral content of E1f2shale1 to E1f2shale5 is 59.1%-63.6%, and the clay minerals are dominated by illite/montmorillonite mixed layer and illite. The brittleness index of E1f2shale2 is 64.25% at most. In the range of burial depth greater than 3 500 m, the conversion of the illite/montmorillonite mixed layer to illite is obvious, and the shale brittleness and fracturing transformation conditions are better. The E1f2shale1 and E1f2shale2 in the deep depression-inner slope zone of Gaoyou Sag are exploration directions for shale oil in the Subei Basin.
Controlling factors of continental shale oil mobility and resource potential in Dongpu Sag, Bohai Bay Basin
LI Hao, LU Jianlin, WANG Baohua, LU Kun, ZHOU Yan, WANG Miao, ZHAO Linjie, SONG Zaichao
2020, 42(4): 632-638. doi: 10.11781/sysydz202004632
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Good mobility is a key to the enrichment and high production of continental shale oil. Various data including thin section observation, scanning electron microscopy (SEM), X-ray energy spectrum (EDS), rock pyrolysis, high pressure mercury injection (HPMI) experiment were integrated to investigate the occurrence characteristics and major factors controlling shale oil mobility in the third member (Es3) of Shahejie Formation in the Dongpu Sag, Bohai Bay Basin. The distribution of movable oil resources was also predicted by using basin modelling. Shale oil mainly exists in intergranular pores, intercrystalline pores, dissolution pores and connected fractures in a free state, and is enriched around fractures. Maturity and fracture development are the main controlling factors of shale oil mobility. The influence of TOC content and porosity on shale oil mobility is relatively complicated. The shale in the middle and lower Es3 in the Dongpu Sag shows a great oil potential, mainly producing medium- and high-maturity oils. Movable oil is mainly distributed at a burial depth of 3 500-4 500 m, and is located in secondary depressions and inner slopes. The Qianliyuan Subsag, Wendong Inner Slope Zone, Puwei Subsag, Liutun Subsag, and Haitongji Subsag have higher movable oil abundances, which are the main exploration targets for continental shale oils.
Pore development in lacustrine source rock evolution: interpretation based on geological samples and simulation experiments: interpretation based on geological samples and simulation experiments
HUANG Zhenkai, LI Maowen, ZHENG Lunju, TAO Guoliang, LI Zhiming, JIANG Qigui, QIAN Menhui, CAO Tingting, LI Shuangjian, WO Yujin, SUN Dongsheng
2020, 42(4): 639-645. doi: 10.11781/sysydz202004639
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By comparing the quantitative pore results of geological samples from natural evolution profiles and simulated experiment samples, it is believed that the volume changes of pores of different scales are basically similar throughout the evolution of source rocks. Macropores and mesopores have a greater impact on pore changes. They should be the main contributors to the total porosity of rocks, and there is a certain conversion relationship between pores of different sizes. Diagenetic evolution and tectonic changes are the main external factors that cause pore changes while hydrocarbon generation and expulsion processes are the internal factors. In addition, there are some differences in the pore space and size (scale) of hydrocarbon products formed by source rocks during different evolutionary stages. This is useful for determining the storage mechanism of conventional and unconventional oil and gas resources corresponding to different evolutionary stages in the shale formation.
Movable oil extraction from shale with supercritical carbon dioxide
WANG Qiang, LI Zhiming, QIAN Menhui, JIANG Qigui, CAO Tingting, LIU Peng, BAO Yunjie, TAO Guoliang
2020, 42(4): 646-652. doi: 10.11781/sysydz202004646
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Movable oil extraction experiments from the lower part of third member of Paleogene Shahejie Formation (Es3L) in the Zhanhua Sag of Jiyang Depression of Bohai Bay Basin were made to address problems on matrix shale oil exploitation. Various negative pressure and different supercritical carbon dioxide fluid pressures at strata temperature were used after fracturing in a closed system. Only traces of light hydrocarbons (< C15) can flow at strata temperature and negative pressure. The carbon number of the main components of movable oil increases with extraction time with supercritical carbon dioxide under the same strata temperature and fluid pressure, and the contents of movable oil increase with fluid pressure increase. The light and medium weight hydrocarbon components in the free state are extracted effectively and some heavy hydrocarbon components in the bound-state (adsorption and miscible state) are also extracted. It suggests that the technology of supercritical carbon dioxide has a good prospect for improving recovery efficiency of matrix shale oil.
2020, 42(4): 653-653.
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