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Seismic reflection and sedimentary characteristics of deep-water gravity flow channels on the slope of lacustrine depression basin: First member of Nenjiang Formation in LHP area, Songliao Basin
LIU Huaqing, FENG Ming, GUO Jingyi, PAN Shuxin, LI Hailiang, HONG Zhong, LIANG Sujuan, LIU Caiyan, XU Yunze
2021, Vol.33(3): 1–12
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405
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Sedimentary characteristics and diagenesis of the third member of Triassic Xujiahe Formation in Yuanba area, northeastern Sichuan Basin
ZHENG Rongchen, LI Hongtao, SHI Yunqing, XIAO Kaihua
2021, Vol.33(3): 13–26
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276 )
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(15747 KB)
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447
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Element feature and coupling model of source-to-sink system in depression lacustrine basin: A case study of Neogene Jimidi Formation in Melut Basin, South Sudan
YANG Lisha, CHEN Bintao, MA Lun, SHI Zhongsheng, XUE Luo, WANG Lei, SHI Jianglong, ZHAO Yanjun
2021, Vol.33(3): 27–38
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282 )
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(13472 KB)
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355
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Characteristics of tectonic-sedimentary evolution from Jurassic to Cretaceous in Iraq-Iran area
WANG Huan, LIU Bo, SHI Kaibo, LIU Hangyu, HAN Bo
2021, Vol.33(3): 39–53
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336 )
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(11901 KB)
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461
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Characteristics of formation water and its geological significance in Moxi-Gaoshiti area, north-central Sichuan Basin
SU Min, WU Kangjun, LI Zhijun, ZENG Dongfang, CHEN Ying, LU Keliang, ZHU Min, GONG Yanxiu
2021, Vol.33(3): 54–62
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307 )
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(2184 KB)
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335
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Sedimentary characteristics of Eocene lacustrine microbialites in western Qaidam Basin: A case study from Xiaganchaigou Formation in Xichagou and Liangdong areas
LI Xiang, WANG Jiangong, LI Fei, WANG Yulin, WU Kunyu, LI Yafeng, LI Xianming
2021, Vol.33(3): 63–73
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260 )
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(18741 KB)
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347
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Basin modeling and favorable play prediction of Neogene in Yiliping area, Qaidam Basin
FENG Dehao, LIU Chenglin, TIAN Jixian, TAI Wanxue, LI Pei, ZENG Xu, LU Zhendong, GUO Xuanhao
2021, Vol.33(3): 74–84
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352 )
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(5664 KB)
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318
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Sedimentary characteristics and main controlling factors of Paleogene beach bar in southwestern Bohai Bay Basin
ZHANG Wen, LYU Shicong, ZHAO Dalin, JIA Haisong, CAI Yueqian
2021, Vol.33(3): 85–94
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350 )
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(7284 KB)
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337
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New method for sequence division of platform facies carbonate rocks: A case study of Ordovician in Bozhong Sag
YE Tao, WANG Qingbin, DAI Liming, CHEN Rongtao, CUI Puyuan
2021, Vol.33(3): 95–103
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276 )
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287
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Application of near-surface Q compensation technology in tight gas exploration in central Sichuan Basin
LIU Huan, SU Qin, ZENG Huahui, MENG Huijie, ZHANG Xiaomei, YONG Yundong
2021, Vol.33(3): 104–112
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232 )
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(10571 KB)
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327
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Geostatistical inversion based on Gaussian mixture prior distribution
HE Dongyang, LI Haishan, HE Run, WANG Wei
2021, Vol.33(3): 113–119
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238 )
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(4562 KB)
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331
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Lithology identification based on LSTM recurrent neural network
WU Zhongyuan, ZHANG Xin, ZHANG Chunlei, WANG Haiying
2021, Vol.33(3): 120–128
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449 )
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(4788 KB)
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590
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Well-logging evaluation index system of shale oil and gas reservoir of Da'anzhai member in central Sichuan Basin
HE Xuquan, HUANG Dong, ZHAO Ailin, LI Yucong
2021, Vol.33(3): 129–137
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279 )
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(5940 KB)
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451
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New model of gas-liquid two-phase choke flow and its application
LI Nanxing, ZHANG Peng, ZHENG Rui, MA Long, YANG Chengliang
2021, Vol.33(3): 138–144
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282 )
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(1858 KB)
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381
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Spontaneous imbibition characteristics of fracturing fluid in shale gas reservoir considering chemical osmotic pressure
XU Fei
2021, Vol.33(3): 145–152
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(2315 KB)
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297
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Characteristics of solid deposition and reservoir damage of CO2 flooding in tight sandstone reservoirs
GUO Yongwei, YAN Fangping, WANG Jing, CHU Huili, YANG Jianlei, CHEN Yingchao, ZHANG Xiaoyang
2021, Vol.33(3): 153–161
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250 )
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Fractal model of effective gas diffusion coefficient based on permeability correction factor
WANG Changjin, ZHANG Sai, XU Jinglei
2021, Vol.33(3): 162–168
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315
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Efficient management of water flooding reservoirs based on Pollock streamline tracing
SUN Liang, LI Baozhu, LIU Fan
2021, Vol.33(3): 169–176
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301
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Logging evaluation and distribution characteristics of fracturing grade in shale gas reservoir: A case study from Wufeng Formation and Longmaxi Formation in X area, southern Sichuan Basin
CONG Ping, YAN Jianping, JING Cui, ZHANG Jiahao, TANG Hongming, WANG Jun, GENG Bin, WANG Min, CHAO Jing
2021, Vol.33(3): 177–188
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(6048 KB)
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Seismic reflection and sedimentary characteristics of deep-water gravity flow channels on the slope of lacustrine depression basin: First member of Nenjiang Formation in LHP area, Songliao Basin
LIU Huaqing, FENG Ming, GUO Jingyi, PAN Shuxin, LI Hailiang, HONG Zhong, LIANG Sujuan, LIU Caiyan, XU Yunze
2021, Vol.33(3): 1–12
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308 )
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doi: https://doi.org/10.12108/yxyqc.20210301
Multiple deep-water slope channels have been observed within the lacustrine Songliao Basin， northeastern China. To understandthe spatial-temporal evolution and internal structures of these channels，techniques including 90° phase rotation，stratal slicing，opacity stacks and illumination were used to study the seismic characteristics and internal structure of gravity flow channels developed on the deep-water slope of lacustrine basin of Lower Cretaceous Nen 1 member in LHP area. The results show that： （1）Nine channels within the 50 km2 LHP area were developed in Nen 1 member of the Late Cretaceous Nenjiang Formation. The depositional setting was a sublacustrine slope characterized by a gradient of 0.5‰ - 1.0‰.（2） Based on morphology，the channels were grouped into two channel systems based on size and degree of associated erosion：small meandering channels characterized by sinuosity of 1.03-1.17，which developed early and were commonly less than 40 m wide. Erosional confinement was minimal and distal avulsions were common. These channels can be described as relatively unconfined，lying down-slope of large gravity-flow systems.（3）Larger meandering channels with sinuosity of 1.04-1.45 and widths up to 500 m，were characterized by greater erosion with maximum erosional valley relief of 20 m. These channels were sufficiently large so that cross profiles could be evaluated，revealing U/V shaped section morphology. Avulsions were uncommon and levees were observed locally. These channels likely lie within the central part of associated gravity-flow systems.（4）Morphological statistics suggest that channel slope and sinuosity，depth and width are positively correlated.（5）Well data from neighboring area indicate that the channel fills were characterized by predominantly silt/fine sandstones with thickness of 10-20 m. These reservoir-prone deposits were bracketed in good quality source rocks making them favorable hydrocarbon exploration targets.（6）The Late Cretaceous global anoxic event possibly caused the abnormal climate（frequent flooding events）and then the frequent gravity flows in the Nen 1 member of lacustrine basin. The continuous subsidence increased the gradient of the paleo-lake and subsequently caused the geomorphology difference between the channels A-D and E-I.
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Sedimentary characteristics and diagenesis of the third member of Triassic Xujiahe Formation in Yuanba area, northeastern Sichuan Basin
ZHENG Rongchen, LI Hongtao, SHI Yunqing, XIAO Kaihua
2021, Vol.33(3): 13–26
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doi: https://doi.org/10.12108/yxyqc.20210302
Medium and high production commercial gas flow was found from several wells of the third member of Upper Triassic Xujiahe Formation in Yuanba area of northeastern Sichuan Basin，which shows better exploration and development potential here. The controlling factors of reservoir development of the third member of Xujiahe Formation are not clearly understood，which restricts the exploration and development deployment. The data of core observation，thin section identification and physical property analysis were used to study the reservoir characteristics and diagenesis of Xu 3 member，and the control of sedimentation and diagenesis on reservoir development was analyzed. The results show that the strata of Xu 3 member are relatively instable in thickness with the characteristics of thick in northwest and thin in southeast，and belong to progradational braided river delta deposits. Reservoir rocks，which mainly belong to calcarenaceous sandstones with the characteristics of dissolved pores， microscopic dissolved pores，have the characteristics of super-low porosity and super-low permeability with strong heterogeneity. Reservoir diagenesis mainly includes compaction，cementation，dissolution，recrystallization and fracturing. For pore development，constructive diagenesis mainly includes burial dissolution and fracturing， and compaction and calcite cementation belong to important destructive diagenesis. In Yuanba area，calcarenaceous sandstones deposited in the braided river delta plain-front are the most favorable sedimentary microfacies. For reservoir development，the burial dissolution diagenesis could be controlled by the relatively coal-rich sedimentary environment of braided river delta plain-front to a certain extent. In conclusion，the sedimentary microfacies of underwater distributary channel and plain distributary channel in braided river delta front and plain is the foundation of pore development of calcareous sandstone of Xu 3 member. Diagenesis such as burial dissolution and fracturing is conducive to the formation and improvement of reservoir pores. Therefore，the relatively developed areas of thin coal seam or coal seam interlayer in distributary channel and the relatively developed area of faults and fractures may be favorable for reservoir development district.
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Element feature and coupling model of source-to-sink system in depression lacustrine basin: A case study of Neogene Jimidi Formation in Melut Basin, South Sudan
YANG Lisha, CHEN Bintao, MA Lun, SHI Zhongsheng, XUE Luo, WANG Lei, SHI Jianglong, ZHAO Yanjun
2021, Vol.33(3): 27–38
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282 )
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doi: https://doi.org/10.12108/yxyqc.20210303
Characteristics of elements in source-to-sink system and their coupling relationships，as one of the most important method for quantitative prediction in sediments and oil/gas reservoirs，have become the research hotspots in sedimentology. In order to characterize the elements feature and coupling relationships of source-to-sink system during the deposition of Neogene Jimidi Formation in Melut Basin，well drilling and logging data analysis，and interpretation of high-resolution 3D seismic data and 2D seismic data in the basin margins were carried out，and the elements of the source-to-sink system for depression lacustrine basin were characterized. The results show that： （1）The basement in the north depression of Melut Basin was dominated by Precambrian metamorphic rocks（phyllite）and granitic gneiss. Three first-level catchments were developed in the study area during the deposition of Jimidi Formation，four types of transportation pathways，V-type，U-type，W-type and fault trough type，were found.（2）Three source-to-sink systems can be divided：Kaka-Ruman source-to-sink system in the northwest was the typical slope-type source-to-sink coupling model，where the river-shallow delta depositional system of 600 m2 was developed in the catchment；Gandool-Wengi source-to-sink system in the northeast and Tean-Ruman West source-to-sink system in the southwest were characterized by fault-slope-break，where fan deltas of 400 km2 and 112 km2 were developed respectively.（3）The quantitative analysis for elements of the source-to-sink systems in the study area showed that the total sediments inside the basin were closely relevant with area of catchments in the source area，topographic height difference and cross-sectional area of the transport channel during the depression stage in the lacustrine basins. The area of catchments was the primary influencing factor for the scales of depositional systems，and large catchments were favorable for the development of large depositional systems. Based on the results，types of depositional system and direction of sediments source for Jimidi Formation in Ruman area of Melut Basin have been confirmed and the distribution of favorable reservoir sandbodies have been predicted， which will guide the exploration deployment effectively.
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Characteristics of tectonic-sedimentary evolution from Jurassic to Cretaceous in Iraq-Iran area
WANG Huan, LIU Bo, SHI Kaibo, LIU Hangyu, HAN Bo
2021, Vol.33(3): 39–53
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doi: https://doi.org/10.12108/yxyqc.20210304
In order to clarify the characteristics of tectonic-sedimentary evolution from Jurassic to Cretaceous and its effect on hydrocarbon distribution，the horizontal distribution and vertical evolution of sedimentary facies were studied based on previous research and relevant data of oil fields. The results show that the tectonic-sedimentary evolution from Jurassic to Cretaceous is closely related to the Neo-Tethys Ocean evolution. From Mid-Jurassic Bajocian to Late Jurassic Tithonian，transgression and regression caused by periodic sea-level changes have an important effect on sedimentary characteristics. The depositional model evolved from carbonate ramp to carbonate platform，and finally filled by evaporate. In the Early Cretaceous，the opening and expansion of the South and Central Atlantic Oceans control the sedimentary evolution in this area. The depositional model evolved from the early differential carbonate ramp to two phases of alternating fluvial delta and carbonate ramp. In the Late Cretaceous，shallow-water carbonate deposits attached intra-shelf basin were developed together in Iran-Iraq area. The sedimentary model evolved into a differential ramp from the monoclinic ramp，submerged platform，and carbonate ramp + platform. The unique tectonic-sedimentary evolution from Jurassic to Cretaceous formed an ideal source-reservoir-seal assemblage in Iraq-Iran area. The tectonic evolution since the Late Cretaceous made an effective match between the timing of trap formation and hydrocarbon migration. Ideal source-reservoir-seal assemblage and perfect timing of trap formation and hydrocarbon migration constituted the most oil-rich Jurassic and Cretaceous-Neogene petroleum systems in Iraq-Iran area. The study has important guiding significance for regional tectonic-sedimentary research and hydrocarbon distribution prediction in the Middle East.
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Characteristics of formation water and its geological significance in Moxi-Gaoshiti area, north-central Sichuan Basin
SU Min, WU Kangjun, LI Zhijun, ZENG Dongfang, CHEN Ying, LU Keliang, ZHU Min, GONG Yanxiu
2021, Vol.33(3): 54–62
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doi: https://doi.org/10.12108/yxyqc.20210305
The Moxi-Gaoshiti area is the main natural gas producing area in Sichuan Basin，but the study on the formation water characteristics and its geological significance with oil and gas is still weak. Based on the theory of hydrocarbon migration and accumulation，combined with the analysis of ion composition，chemical parameters，hydrogen-oxygen isotopes of formation water，the relationship between formation water characteristics and hydrocarbon accumulation was revealed. The results show that the formation water is mainly of CaCl2 type in Longwangmiao Formation，Changxing Formation，submember of Leikoupo Formation（Lei-11 submember）and Xujiahe Formation，while mainly of CaCl2，MgCl2 and Na2 SO4 type in the second member of Jialingjiang Formation（Jia-2 member）. The salinity of formation water in Lei-11 submember and Xujiahe Formation is high，followed by Longwangmiao Formation，and low in Jia-2 member and Changxing Formation. The sodium chlorine coefficient of formation water in the five production layers ranges from 0.3 to 0.8，and the magnesium calcium coefficient ranges from 0.1 to 0.5. The desulfurization coefficient of Jia-2 member is the largest（greater than 2）， the desulfurization coefficient of Longwangmiao Formation ranges from 0.2 to 0.5， and the desulfurization coefficient of Changxing Formation and Lei-11 submember is equivalent，ranging from 0.1 to 0.8，while the desulfurization coefficient of Xujiahe Formation is 0. The natural gas has good preservation conditions in the north-central Sichuan Basin. The formation sealing of Xujiahe Formation is the best，the rock-water interaction is strong， while the formation sealing of Jia-2 member is the worst， and the rock-water interaction is weak.
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Sedimentary characteristics of Eocene lacustrine microbialites in western Qaidam Basin: A case study from Xiaganchaigou Formation in Xichagou and Liangdong areas
LI Xiang, WANG Jiangong, LI Fei, WANG Yulin, WU Kunyu, LI Yafeng, LI Xianming
2021, Vol.33(3): 63–73
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doi: https://doi.org/10.12108/yxyqc.20210306
Qaidam Basin is an excellent site to study Cenozoic lacustrine carbonate rocks，especially lacustrine microbialites. The Eocene Xiaganchaigou Formation in western Qaidam Basin contains a set of large-scale lacustrine microbialites with a close relationship with hydrocarbon resources. Based on core observation，thin section identification，scanning electron microscope，electron probe microanalysis and laser confocal analysis of outcrops， the macroscopic to microscopic characteristics of microbialites of the upper Xiaganchaigou Formation of Eocene （E32）in Xichagou and Liangdong areas of Qaidam Basin were dissected. The results show that this set of microbiolites mainly formed in the rapid lacustrine transgression stage，and developed on the hard basement such as conglomerate and siltstone，and died out in the late period due to the shrinkage of the lake basin. The lacustrine microbialites are composed of thrombolites，stromatolites and their alternating compound types，which have large lateral distribution and the outcrop can reach several kilometers. Other carbonate particles include peloids， ooids，biodetritus and aggregate grains. Microscopically，the thrombolites are characterized by cryptocrystalline cohesive framework with clotted structure，containing abundant bioclasts and a small amount of ooids and peloids between the frameworks. Stromatolite shows slow undulant laminae. The microbialites in the western Qaidam Basin are mainly developed in high energy shallow water，low energy deep water uplifts and low energy fault zone. The research results can provide a reference for Cenozoic hydrocarbon exploration in Qaidam Basin.
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Basin modeling and favorable play prediction of Neogene in Yiliping area, Qaidam Basin
FENG Dehao, LIU Chenglin, TIAN Jixian, TAI Wanxue, LI Pei, ZENG Xu, LU Zhendong, GUO Xuanhao
2021, Vol.33(3): 74–84
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352 )
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318
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doi: https://doi.org/10.12108/yxyqc.20210307
There are great potential of Neogene natural gas resources in Yiliping area，Qaidam Basin. In order to evaluate the natural gas resource potential and risk exploration area in Yiliping area，the basin and gas-bearing system modeling was carried out，and the thermal evolution history of source rocks，main gas generation center and favorable migration and accumulation directions were determined. The results show that：（1）The abundance of organic matter（TOC mass fraction is 0.2% -1.0%）of Neogene source rocks in Yiliping area is similar to that in western Qaidam Basin，which has good hydrocarbon generation potential，and the organic matter is type Ⅱ2-Ⅲ.（2）The key periods for the beginning of generating a great deal of hydrocarbons in the source rocks of lower Youshashan Formation（N21）and upper Youshashan Formation（N22）are the late Miocene and the late Pliocene， respectively，and the source rocks of Shizigou Formation（N23）are still immature to low mature.（3）The major source rock in Yiliping area is lower Youshashan Formation（N21），and the main gas generation period is Qigequan Formation（Q1+2）. The two main gas generation centers are Jianshishan-Hongsanhan No.4 structure belt and northeastern Chuanxingqiu-Tainan structure belt.（4）Hongsanhan No. 3-Hongsanhan No.4 structural belt， Eboliang No. 3-Yahu-Teginaer structural belt and Tainan-Sebei structural belt are favorable areas for natural gas accumulation. The research results indicate the direction for Neogene gas exploration in Yiliping area.
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Sedimentary characteristics and main controlling factors of Paleogene beach bar in southwestern Bohai Bay Basin
ZHANG Wen, LYU Shicong, ZHAO Dalin, JIA Haisong, CAI Yueqian
2021, Vol.33(3): 85–94
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doi: https://doi.org/10.12108/yxyqc.20210308
In order to study the sedimentary characteristics and main controlling factors of Paleogene Dongying Formation and Shahejie Formation in southwestern Bohai Bay Basin，core observation，thin section identification，well logging analysis and mercury injection test were carried out，and combined with the characteristics of paleogeomorphology，sedimentary models of beach bar and their differences were comprehensively analyzed. The results show that： （1）There are four types of beach bar，including sandy beach bar，gravel beach bar， mixed beach bar and carbonate beach bar.（2）The source supply intensity，paleogeomorphology，paleowater depth and paleowind wave jointly control the type and sedimentary characteristics of beach bar. The source supply intensity is the material basis and controls the type of beach bar sand body. The paleogeomorphology and paleowater depth control the thickness and distribution position of beach bar sand body，and paleowind wave affects the distribution form of beach bar sand body.（3）Sandy beach bar，mixed beach bar and carbonate beach bar have good physical properties and high test productivity，which are favorable targets for oil and gas exploration in the study area. The research results can provide reference for oil and gas exploration of beach bar reservoir.
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New method for sequence division of platform facies carbonate rocks: A case study of Ordovician in Bozhong Sag
YE Tao, WANG Qingbin, DAI Liming, CHEN Rongtao, CUI Puyuan
2021, Vol.33(3): 95–103
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276 )
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287
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doi: https://doi.org/10.12108/yxyqc.20210309
The traditional sequence division method based on natural gamma ray is not applicable in shallow platform，due to that the high gamma ray in mud flat corresponds to shallow water sedimentary environment. Taking Ordovician Majiagou Formation in Bozhong 21-22 structure of Bohai Sea as an example，a new sequence division method based on natural gamma-ray spectral logging was proposed，and the control of sequence on reservoir was discussed. The result shows that： （1）Weathering，uranium enrichment of reservoir and normal sedimentary shale can cause high gamma of Ordovician Majiagou Formation in Bozhong 21-22 structure.（2）In natural gammaray spectrum logging，Th/K can effectively distinguish high gamma with different genesis，which is an effective parameter for sequence division.（2）There are five third-order sequences developed in Ordovician Majiagou Formation in Bozhong 21-22 structure. The sequence in well BZ21-2-A is complete，while SQ5 is lacked in well BZ22-1-B. The corresponding relationship between sequences and reservoir shows that the fractured reservoirs are mainly distributed within 100 m of weathering crust and are not obviously controlled by the sequence boundary.While dissolved pore reservoirs are mainly concentrated near the top and bottom of SQ1-SQ2 sequence and are obviously controlled by the sequence boundary. The research results can be used for reference in the sequence division of carbonate rocks in platform facies.
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Application of near-surface Q compensation technology in tight gas exploration in central Sichuan Basin
LIU Huan, SU Qin, ZENG Huahui, MENG Huijie, ZHANG Xiaomei, YONG Yundong
2021, Vol.33(3): 104–112
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doi: https://doi.org/10.12108/yxyqc.20210310
In view of the lenticular distribution and multi-stage superimposed development characteristics of tight sandstone reservoirs in central Sichuan Basin，improving the resolution of seismic data and restoring sand body amplitude characteristics are of great significance to the exploration and development of tight sandstone gas in this area. Considering the influence of the special surface seismic conditions and the strong attenuation effects in the low velocity layer， a near-surface model was established by micro-logging constrained tomographic static correction technology to obtain the traveltime of the low velocity layer. The centroid-frequency shift method was used to estimate a near-surface Q model based on shallow reflection wave data， so as to realize near-surface Q compensation. The results show that the near-surface Q compensation technology can effectively improve the resolution of seismic data，improve the lateral continuity of seismic events，and restore the amplitude characteristics of channel sand bodies. The application of this technology is conducive to identify the contact relationship of sand bodies with strata and faults，and can provide higher-quality seismic data for subsequent interpretation.
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Geostatistical inversion based on Gaussian mixture prior distribution
HE Dongyang, LI Haishan, HE Run, WANG Wei
2021, Vol.33(3): 113–119
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238 )
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331
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doi: https://doi.org/10.12108/yxyqc.20210311
Traditional geostatistical inversion usually uses geostatistics simulation algorithms to construct the prior information of the model parameters，and then uses some optimization algorithms to obtain the posterior solutions of the model parameters under the constraints of seismic data， which ignores the influence of lithology on model parameters and requires a lot of calculation in the optimization process. Therefore，the prior distribution of model parameters was expressed as Gaussian mixture distribution influenced by discrete lithology，then the linear Gaussian mixture inversion theory was combined with sequential simulation of geostatistics，and the posterior solutions of the model parameters and discrete lithology were directly obtained by sequential sampling，which avoids the optimization process，and the inversion results have good spatial continuity and stability. Both model tests and the application of actual data show the effectiveness of the method.
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Lithology identification based on LSTM recurrent neural network
WU Zhongyuan, ZHANG Xin, ZHANG Chunlei, WANG Haiying
2021, Vol.33(3): 120–128
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449 )
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590
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doi: https://doi.org/10.12108/yxyqc.20210312
A lithology recognition method by long-short-term memory neural network（LSTM）was proposed for complex carbonate reservoirs with complex composition and diverse lithology，to overcome obstacles troubling traditional identification，and effective results were showed with a case from gas field. Due to the inadequate ability of general machine learning methods in extracting the characteristics of sedimentary sequence，the LSTM method was introduced into the improvement for lithology identification. Taking the Lower Paleozoic carbonate reservoir in eastern block of Sulige gas field as an example，six sensitive parameters were selected to construct a lithology identification model based on LSTM，such as GR，Pe，DEN，RLLD， AC and CNL. The results show that lithology identification accuracy based on LSTM increases by 1.40%-12.25% above traditional models（Naive Bayes，KNN，Decision Tree，SVM and HMM），and can provide more reliable support for the characterization and evaluation of complex carbonate reservoirs.
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Well-logging evaluation index system of shale oil and gas reservoir of Da'anzhai member in central Sichuan Basin
HE Xuquan, HUANG Dong, ZHAO Ailin, LI Yucong
2021, Vol.33(3): 129–137
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451
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doi: https://doi.org/10.12108/yxyqc.20210313
Shale of Jurassic Da'anzhai member in Sichuan Basin is mostly featured by high TOC content, large thickness, and great physical property and hydrocarbon potential, which shows great development prospect. However, some methods to calculate key parameters of porosity and organic carbon content and other well-logging evaluation standards, which have been established for conventional oil and gas reservoirs and marine shale gas reservoirs, are not applicable for assessing shale oil and gas reservoirs in this formation. Based on petrophysical experimental analysis, and combined conventional well-logging data from natural gamma ray, acoustic, and resistivity logging with new technologies including nuclear magnetic resonance logging and lithological scanning logging, a model for calculating the key parameters of TOC content, porosity, gas saturation and free hydrocarbon(S1) content was established, and an evaluation index system was developed for shale oil and gas reservoirs of Da'anzhai member in central Sichuan Basin. The calculated results by the model agreed well with ones from core analysis, and the practices showed that the calculation model and the evaluation index system have an obvious application effect. The research results can provide an effective support in sweet spot selection, well-location deployment and well-testing plan optimization in old wells for shale oil and gas reservoirs in Sichuan Basin.
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New model of gas-liquid two-phase choke flow and its application
LI Nanxing, ZHANG Peng, ZHENG Rui, MA Long, YANG Chengliang
2021, Vol.33(3): 138–144
Abstract
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282 )
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381
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doi: https://doi.org/10.12108/yxyqc.20210314
In order to obtain larger profits，it is important to choose reasonable choke size and extend the flowing period. However，the existing choke flow model is difficult to meet the demands of North Azadegan Oilfield. By using the dimensional analysis principle of Rayleigh method，least square method and multiple linear regression method based on field data，a new choke flow model suitable for North Azadegan Oilfield was established by adding the three parameters of API gravity，crude oil viscosity and water cut to the critical choke flow formula. The results show that the average relative error of the mass flow rate predicted by the new model is 1.1%， the average absolute error is 6.5%，the correlation coefficient is 0.876，and the comprehensive evaluation coefficient is 0.933. The average relative error of the predicted production rate is 2.9%，the average absolute error is 8.4%，the correlation coefficient is 0.829，and the comprehensive evaluation coefficient is 0.900. Compared with other evaluation models，the new model has higher accuracy. Field application shows that the production rate in different stages calculated by the new model has excellent consistency with the on-site production data. Not only the change trend of the production rate is more consistent，but also the average relative error and absolute error of the corresponding data are within 10%. Compared with other models，the new model is more consistent with the production characteristics of the oilfield and can meet the demands of oil well production rate calculation and prediction. The establishment of the new model provides a theoretical basis for the reasonable selection of choke size， the completion of daily production rate and the extension of the flowing period in this oilfield. Furthermore，it has reference and guiding significance for other similar oilfields.
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Spontaneous imbibition characteristics of fracturing fluid in shale gas reservoir considering chemical osmotic pressure
XU Fei
2021, Vol.33(3): 145–152
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doi: https://doi.org/10.12108/yxyqc.20210315
The chemical osmotic pressure caused by salinity difference between fracture and matrix has an important influence on shale fracturing fluid flowback and gas well productivity calculation. The driving force types of shale spontaneous imbibition were described by establishing an imbibition dynamic model considering chemical osmotic pressure. Taking Benxi Formation shale in Ordos Basin as the research object，the effects of clay minerals，salinity and surfactant on water saturation distribution curve were studied through the shale spontaneous imbibition NMR scanning experiment. The capillary pressure curve under the dual action of capillary pressure and chemical osmotic pressure was obtained with the water saturation distribution curve measured by experiment as the fitting target. The results show that with the increase of imbibition time，the water absorption of shale increases rapidly first and then gradually slows down，while the imbibition rate decreases rapidly. The higher the clay mineral contenf decreases rapidly. The higher the clay mint in shale and the greater the chemical potential difference between matrix and fracture，the stronger the imbibition driving force is，and the greater the imbibition front distance and water absorption capacity are. The surfactant can reduce the capillary pressure and cause the driving force to drop，leading to the significant weakening of imbibition effect. The modified capillary pressure curve was applied to production prediction of shale gas well，which greatly improves the calculation accuracy of the model. The results provide a method and basis for efficient development of shale gas reservoir in Ordos Basin.
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Characteristics of solid deposition and reservoir damage of CO2 flooding in tight sandstone reservoirs
GUO Yongwei, YAN Fangping, WANG Jing, CHU Huili, YANG Jianlei, CHEN Yingchao, ZHANG Xiaoyang
2021, Vol.33(3): 153–161
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doi: https://doi.org/10.12108/yxyqc.20210316
The damage of asphaltene and metal inorganic precipitation to tight reservoir is an inevitable problem in CO 2 flooding. In order to explore the damage mechanism of asphaltene and inorganic precipitation to reservoir，taking Chang 7 reservoir of Yanchang Formation in Ordos Basin as an example，on the basis of clarifying the relationship between CO2 content and asphaltene precipitation in crude oil under（non）miscible pressure，the damage characteristics of asphaltene and inorganic precipitation on reservoir during CO2 immiscible and miscible flooding were studied by long core experiment，and the damage degree of organic and inorganic precipitation on reservoir permeability and porosity was evaluated. The results show that when the CO2 content in crude oil reaches the critical value，asphaltene begins to precipitate，and the precipitation increases rapidly at first and then tends to be stable with the increase of CO 2 content. The damage degree of asphaltene precipitation to permeability and porosity under miscible pressure is greater than that under immiscible pressure. Under miscible pressure，a large number of asphaltenes are deposited in the back of long cores，while under non miscible pressure，they are mainly in the front and middle of long cores. When the asphaltene precipitation in the core reaches the maximum，the subsequent asphaltene precipitation in the core will gradually decrease，and the damage to permeability will also gradually reduce. The damage degree of inorganic precipitation to the permeability of the front and middle cores is greater under immiscible pressure，while the damage degree of inorganic precipitation to the permeability of the middle and rear cores is greater under miscible pressure. The effect of inorganic precipitation on porosity is different from that on permeability， which is closely related to dissolution and the location of inorganic precipitation. If the target reservoir is developed by immiscible flooding，the prevention focus is on inorganic precipitation， and the prevention position is near the injection end；if miscible flooding is used，the prevention focus is on organic precipitation， and the prevention position is near the production end.
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Fractal model of effective gas diffusion coefficient based on permeability correction factor
WANG Changjin, ZHANG Sai, XU Jinglei
2021, Vol.33(3): 162–168
Abstract
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doi: https://doi.org/10.12108/yxyqc.20210317
The phenomenon of gas diffusion in porous media is widespread in the fields of energy and environment，oil and gas reservoir engineering. The internal structure of real porous media is irregular and complex，and shows fractal characteristics within a certain scale. In order to explore the law of gas diffusion in porous media with fractal characteristics，the permeability correction factor and Fick's law were introduced to establish the functional relationships of effective gas diffusion coefficient with porous media structure parameters and gas parameters. The results show that the effective gas diffusion coefficient is proportional to the area fractal dimension of porous media，porosity，and maximum pore diameter，and inversely proportional to tortuous fractal dimension， gas molar mass and gas density. By comparing the effective gas diffusion coefficient predicted by fractal model with the experimental data，it can be found that the model based on permeability correction factor is more consistent with the experimental data. The new fractal model of gas diffusion coefficient can correctly describe the law of gas diffusion in porous media， which has reference significance for the development of oil and gas fields.
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Efficient management of water flooding reservoirs based on Pollock streamline tracing
SUN Liang, LI Baozhu, LIU Fan
2021, Vol.33(3): 169–176
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doi: https://doi.org/10.12108/yxyqc.20210318
Horizontal well pattern is mainly used for water flooding development of thin carbonate reservoirs in the Middle East. Currently，the problems of high water flooding degree and low water injection efficiency are becoming increasingly prominent. Therefore，a method of efficient water flooding management based on the technique of Pollock streamline tracing was proposed to evaluate water flooding index and optimize injection-production parameters. According to the streamline simulation，the dynamic well groups were determined，and the distribution factors of wells were calculated. The injection-production connectivity and the water injection efficiency were evaluated. The water flooding development effect could be improved by optimizing the injection-production policies. This method was applied to K1 reservoir，and the results show that the distribution of injected water and streamlines in well groups became more balanced. The ineffective water circulation in the linear direction of horizontal wells was obviously reduced. The water injection efficiency and conformance factor were improved. The water cut of pilot wells were decreased by more than 10% on average. This technique is of great significance to stabilizing the production of oil fields.
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Logging evaluation and distribution characteristics of fracturing grade in shale gas reservoir: A case study from Wufeng Formation and Longmaxi Formation in X area, southern Sichuan Basin
CONG Ping, YAN Jianping, JING Cui, ZHANG Jiahao, TANG Hongming, WANG Jun, GENG Bin, WANG Min, CHAO Jing
2021, Vol.33(3): 177–188
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doi: https://doi.org/10.12108/yxyqc.20210319
Shale gas reservoir is characterized by tightness and strong heterogeneity，so fracturing is needed to increase production and transformation. Therefore，the evaluation of shale fracturing grade and its distribution rule are of great guiding significance for the fracturing design. The shale formation of Wufeng Formation-Longyi1 submember in X area，southern Sichuan Basin，was taken as the research object，based on the data of core test， logging and mud logging，the indexes reflecting shale fracturing were qualitatively analyzed，and five sensitive parameters brittleness index，Poisson's ratio，Young's modulus，tensile strength and horizontal stress difference were extracted. The weight of each parameter was obtained by analytic hierarchy process to establish the quantitative and comprehensive fracturing coefficient Icr. Combined with the production data of shale gas wells，three fracturing grades Ⅰ，Ⅱ and Ⅲ were divided. Furthermore，the evaluation of fracturing grade of multiple wells and the correlation of well-connected profiles were carried out，and the formation thickness ratios of fracturing grades Ⅰ and Ⅱ were counted to analyze the distribution features of the fracturing performance in the plane. The results show that when Icr ≥0.59，the fracturing grade of shale gas reservoir is grade Ⅰ，and its fracturing performance is the best. The fracturing profile show that the grade I interval in the sublayers 1 and 2 of Wufeng Formation-Longyi1 submember accounts for a large proportion，and core description also shows that the natural fractures in this interval are the most developed and are the most suitable favorable intervals for shale gas fracturing development. The plan indicates that the areas with intervals of grade I fracturing performance with a thickness ratio of 0.8-0.9 are mainly distributed in N201，N209，N203，N208 and N211 well areas. The research results can pro-vide a key basis for effective development of X area shale gas horizontal wells.