石油实验地质

2019, 41(3): .

Abstract(165) PDF-CN(73)

Abstract:

Application of source to sink system analysis in large reservoir research: a case study of Huagang Formation, Central Inversion Belt, Xihu Depression

LIU Jinshui, LU Yongchao, QIN Lanzhi

2019, 41(3): 303-310. doi: 10.11781/sysydz201903303

Abstract(827) PDF-CN(173)

Abstract:
Detrital zircon U-Pb dating, heavy mineral assemblage, imaging logging and seismic interpretation were applied to analyze the source to sink system in the Central Inversion Belt of the Xihu Sag. The formation process of large reservoirs in the Central Inversion Belt was studied. During the depositional period of the Huagang Formation, there were three provenance areas in the Central Inversion Belt, including the Hupijiao Uplift in the north, the Haijiao Uplift in the west and the Diaoyu Island Transitional Belt in the east. Three source channels for sand import developed in the Central Inversion Belt, including the large axially channels, the incised valley channels in the west and the channels in the Diaoyu Island Transitional Belt in the east. The Central Inversion Belt has three different large sand body convergence areas in the north, center and south. On this basis, the long-distance transportation of source sand in the Hupijiao Uplift in the north and the point source input in the Haijiao Uplift in the west and the Diaoyu Island Transitional Belt were comprehensively determined.

Zircon U-Pb dating and its significance in Jiaojiang Sag, East China Sea Basin

GAO Shunli, ZHAO Hong, WANG Jianqiang, XU Xi, HOU Kaiwen, LI Xuanyue

2019, 41(3): 311-318. doi: 10.11781/sysydz201903311

Abstract(481) PDF-CN(96)

Abstract:
Using zircon U-Pb dating as the main analysis method, the age of the pre-Cenozoic sedimentary basement was determined and the sediment source in the sag during the fault depression was traced in the Jiaojiang Sag, East China Sea Shelf Basin. The pre-Cenozoic basement of Jiaojiang Sag is dominated by magmatic rocks. The age distribution of detrital zircons is complex, with the main peak age of 227 Ma, mainly formed in the late Indosinian period. The formation environment belongs to the oceanic island arc environment, which is consistent with the existing magmatic records of Lishui East Sub-Sag and Yushandang Low Uplift. The clastic zircons of the Paleocene Mingyuefeng Formation have typical magmatic characteristics, with the main zircon peak ages ranging from 140 Ma to 90 Ma. The formation environment belongs to a continental margin environment. The Paleocene provenance of Jiaojiang Sag is relatively single, which is comparable to Lishui Eastern Sub-Sag. The Yandang Low Uplift in the east of Jiaojiang Sag provides a continuous provenance supply during the Paleocene fault depression.

Reservoir forming control of “source-potential-facies-migration” in Hetaoyuan Formation of Nanyang Sag, Nanxiang Basin

LUO Jiaqun, PENG Jinning, YANG Yunfei, LIU Guilan, GUO Feifei, ZHANG Fan, YAN Yongfang

2019, 41(3): 319-325. doi: 10.11781/sysydz201903319

Abstract(378) PDF-CN(81)

Abstract:
The hydrocarbon exploration practice of the Hetaoyuan Formation in the Nanyang Sag indicates that the hydrocarbon distribution is controlled by “source-potential-facies-migration”, that is, the coordinated control of source rock, fluid potential, geologic facies and migration channel. The effect of “source control” reflects near source-controlled reservoir, the effect of “facies control” reflects high porosity and permeability, and superior facies-controlled reservoir, the effect of “potential control” reflects low interfacial potential energy-controlled reservoir, and the effect of “migration control” reflects fault and dominant sand body-controlled reservoir. According to typical oil and gas reservoir analysis, the hydrocarbon controlling pattern of the Hetaoyuan Dormation in the Nanyang Sag is “near source-low potential-superior facies” one, and hydrocarbon mainly distributed in the middle-high potential and middle facies area, as well as the middle potential-superior facies area. After meeting faults, hydrocarbon migration presented an alley lateral migration pattern in obtuse angle direction and concentrated in positive fault blocks. It is predicted that hydrocarbon accumulation in the He-3 member of the Baiqiu area is better than that of in the Weigang area, which is considered to be a favorable exploration area in the next step.

Characteristics and significance of sedimentary facies of Wufeng-Longmaxi formation shale in Weirong Shale Gas Field, southern Sichuan Basin

XIONG Liang

2019, 41(3): 326-332. doi: 10.11781/sysydz201903326

Abstract(617) PDF-CN(216)

Abstract:
The sedimentary microfacies of organic-rich shale in the Wufeng-Longmaxi formations in the Weirong Shale Gas Field of the southern Sichuan Basin were studied based on core observation, organic carbon content, biological identification, in situ gas content and well logging data. The shale from the Wufeng Formation to the first member of Longmaxi Formation mainly developed in a deep-water shelf environment. They were divided into six microfacies mostly depending on mineral composition, including clayey siliceous, siliceous-rich biological, siliceous clay, calcareous clay, calcium-rich clay and clay-rich deep-water shelf micro-focies. Vertically, the first four facies are characterized by high TOC content (≥ 3%), high porosity (≥ 5%) and high gas content (≥ 2 m³/t). The high abundance of organic matter provided a material basis for shale gas generation, and a large number of organic pores generated during hydrocarbon generation provided space for shale gas occurrence. Moreover, siliceous-rich biological shale is the most favorable facies zone and dessert zone for shale gas exploration and development, due to its high content of brittle minerals, high porosity and permeability, and easy fracturing. From the view of horizontal distribution, the west block of Weirong Shale Gas Field has a greater gas exploration potential than the east block because of greater thickness of the four favorable facies.

Overpressure in shale gas reservoirs of Wufeng-Longmaxi formations, Fuling area, southeastern Sichuan Basin

WANG Qiang, WEI Xiangfeng, WEI Fubin, YAN Jihong, WAN Li

2019, 41(3): 333-340. doi: 10.11781/sysydz201903333

Abstract(630) PDF-CN(166)

Abstract:
There commonly exists overpressure in shale gas reservoirs in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formations in marine strata in South China. Some typical wells in the Fuling Shale Gas Field were chosen to study systematically to reveal how the overpressure does on shale gas reservoirs. Overpressure is the direct shows of favorable preservation conditions for shale gas. Pressure increases when hydrocarbon generates from organic matter in thermal evolution, which is the main cause for abnormal high pressure in the region. Overpressure exists in all high yield intervals for shale gas in the Longmaxi Formation in Jiaoshiba of Fuling area. The shale reservoirs have high porosity and high gas content. The effect of overpressure on shale gas reservoirs was concluded. On the one hand, overpressure can slow down the effective stress on rock skeleton, so that the shale reservoirs preserve a relatively higher porosity, and overpressure can form shale overpressure micro-cracks, improving the seepage capacity of shale reservoirs. Overpressure indicates for high formation energy, high free gas content, and better gas content in shale gas reservoirs. On the other hand, overpressure reduces the effective stress on shale reservoirs, and the development of overpressure micro-cracks is conducive to shale fracturing.

Preservation condition differences in Jiaoshiba area, Fuling,Sichuan Basin

LI Jinlei, YIN Cheng, WANG Mingfei, YANG Shasha, LIU Xiaojing, CHEN Chao

2019, 41(3): 341-347. doi: 10.11781/sysydz201903341

Abstract(477) PDF-CN(151)

Abstract:
The preservation condition is critical to the enrichment and high yields of shale gas. Exploration and development of the Fuling shale gas indicated that the preservation condition changes horizontally in the Jiaoshiba area. This change was analyzed using core observations, FMI logging interpretations and comprehensive seismic interpretations. Different transformations of structure units after later tectonic movements explained the diversity of preservation condition. Specifically, the differences are related to fracture scale, closure, the effect of fracture superposition and the formation deformation. The size of the fault (fault distance, extension length, offset, fracture density) and the fault properties determine the basic preservation condition of structural units. The sharp angle relationship between the maximum principal stress and the direction of the fracture affects the sealing of the fracture. The larger the sharp angle, the better the sealing property. The vertical and lateral superposition of the fracture system will form a three-dimensional seepage channel, which has a great influence on the original closed environment of shale gas, and causes strong dispersion of shale gas. This causality is worthy of attention. At the same time, the dip angle of the formation is a direct reflection of the extent of the tectonic movement. As the diffusion effect in the parallel stratification direction of shale gas increases with the inclination angle, which increases gradually, it is necessary to analyze the dip angle when choosing the prime target especially in complex structural areas.

Differential tectonic deformation in the northern Qiyueshan Fault, eastern Sichuan Basin

WEI Feng, CHEN Kongquan, TUO Xiusong

2019, 41(3): 348-354. doi: 10.11781/sysydz201903348

Abstract(739) PDF-CN(116)

Abstract:
The geometrical and kinematic characteristics and fault evolution history of the Qiyueshan Fault were analyzed systematically using seismic and geological data. The profile morphology of the Qiyueshan Fault from north to south shows in turn a “Y”, “zigzag” and spade shape. The exposed fault inclination changes from northwest to southeast. The Qiyueshan Fault is characterized by a sectional structure. The structural pattern of the western periphery of the fault, from north to south, changes from “hidden thrust and fault-slip fold of the Wushan-Tuxiang segment” to “fault-spread and slip fold of the Tuxiang-Zhongxian segment”, to “basement thrust-fault-spread fold of the Zhongxian-Jiaoshi segment”, to “thrust fold of the Jiaoshi-Nanchuan segment”. The eastern periphery of the fault is characterized by thrust structural deformation. The Qiyueshan Fault was formed in the Early Yanshanian stage, and then underwent extrusion in the middle Yanshanian Movement and extension in the late Yanshanian Movement. The middle section of the fault is the most deformed. Different structural deformations lead to the obvious difference of oil and gas preservation conditions on both sides of the fault.

Characteristics and controlling factors of low-permeability reservoirs in Silurian Kepingtage Formation, 10th tectonic belt in the Tazhong area, Tarim Basin

PENG Li, WANG Zhenbiao, YANG Jianping, LU Yongchao, WANG Qian, ZHANG Shaowei, WANG Na, PENG Peng

2019, 41(3): 355-362. doi: 10.11781/sysydz201903355

Abstract(576) PDF-CN(93)

Abstract:
The basic characteristics of low-permeability reservoirs in the upper unit of Silurian Kepingtage Formation, 10th tectonic belt in the Tazhong area were investigated and the controlling factors associated with sedimentology, diagenesis and tectonism were determined based on core observation, thin section, scanning electron microscopy (SEM), cold-cathode luminescence microscopy (CL) coupled with petro-physical property testing. The results indicate that the low-permeability sandstone reservoirs are mainly composed of litharenite and sublitharenite and the studied reservoirs belong to low-porosity and low-permeability reservoirs. The reservoir space mainly includes residual primary pores, intergranular dissolution pores and tectonic microfractures. The reservoir development was controlled by sedimentology, diagenesis and tectonism. The reservoirs in tidal channel and sand-flat microfacies deposited in strong hydrodynamic environments have substantial primary pores and obviously later acidic dissolution. The resulting reservoirs have good petro-physical properties and are targets for high-quality reservoirs. The controlling factors associated with diagenesis are evidenced by porosity reduction due to compaction and cementation, whereas the reservoir petro-physical properties can be enhanced by dissolution. Microfactures induced by tectonism can improve permeability capability and play some positive role in enhancing reservoir petro-physical properties.

Densification and diagenetic facies of Donghetang Formation sandstone reservoir in Bachu-Maigaiti area, Tarim Basin

ZHANG Yongdong, ZHAO Yongqiang, MA Hongqiang

2019, 41(3): 363-371. doi: 10.11781/sysydz201903363

Abstract(783) PDF-CN(100)

Abstract:
The reservoir characteristics, diagenesis, densification mechanism and diagenetic facies of the Donghetang Formation in the Bachu-Maigaiti area of Tarim Basin were studied using detrial reservoir and sedimentation research. The Donghetang Formation mainly contains dissolution pores, characterized by extra low porosity and permeability. Through restoring the original porosity, we identified the contribution of main diagenesis to porosity. Compaction is the main reason for reservoir densification, while cementation also works in some wells. There are six types of diagenetic facies in this reservoir, namely strong compaction and strong cementation with weak dissolution facies, strong compaction and medium cementation with weak dissolution facies, strong compaction and medium cementation with medium dissolution facies, weak compaction and strong cementation with weak dissolution facies, medium compaction and strong cementation with strong dissolution facies, and medium compaction and strong cementation with weak dissolution facies. By summarizing the well logging characteristics of the six diagenetic facies reservoirs and analyzing its similarity with the wells in the non-core sandstone segments, we discriminated the diagenetic facies of 23 sandstone segments in 9 wells. The dominant diagenetic facies of the upper sandstone is in the Batan 2 well area while the lower sandstone is in the Bakai 8 well area.

Lithologic hydrocarbon accumulation characteristics of Baikouquan Formation, Madong Slope, Junggar Basin: a case of YB 4 well block, Luliang Oil Field

LIU Mingyang, ZHANG Yongbo, TAN Jianhua, LU Jianguo, SHEN Wei, TONG Ying, ZHANG Lei, LIU Changli

2019, 41(3): 372-378. doi: 10.11781/sysydz201903372

Abstract(637) PDF-CN(89)

Abstract:
In view of the unclear mechanism and distribution of lithologic reservoirs in the Baikouquan Formation on the Madong Slope of Junggger Basin in recent years, the sequence stratigraphy and sedimentary facies theory were used to analyze the characteristics and accumulation conditions of oil and gas reservoirs found in YB 4 well block. It is revealed that the lithologic reservoirs of the Baikouquan Formation in this area are mainly updip-tip-type, which are mainly controlled by four basic factors:“the development of a fan root channel or a alluvial channel sand body with an updip tip”, “debris flow plugged in upward direction”, “covered with high water level muddy caprock”, “a fault with a source of oil in the downdip direction”. Among them, the “debris flow plugging” and “high water level mud caprock” are the key controlling factors to hydrocarbon accumulation. The updip-tip-type oil and gas reservoirs are mainly distributed at the top of the T₁b₂ and the bottom of the T₁b₃, which are located in the upper part of the transgressive system tract of the Baikouquan Formation. In the future, it will be the main oil and gas exploration target in the Madong Slope area.

Multi-stage activity characteristics of small-scale strike-slip faults in superimposed basin and its identification method: a case study of Shunbei area, Tarim Basin

HUANG Cheng

2019, 41(3): 379-389. doi: 10.11781/sysydz201903379

Abstract(1700) PDF-CN(235)

Abstract:
The strike-slip faults in superimposed basins usually experienced multi-stage activities. The episodic formation and evolution of strike-slip faults match with the important tectonic transformation periods of superimposed basins. Generally speaking, strike-slip fault zones converge (or stretch) in stress fields at different tectonic stages. It will result in the formation of specific associated structural styles of near-surface tectonic layers in the same period. Finally, a complete vertical tectonic sequence is formed. If the strike-slip associated structures peculiar to each tectonic layer are taken as geological records of strike-slip fault activities in the same period, the episodic activity of the strike-slip faults can be restored step by step from the present underground geological structure, and then the active periods of faults can be determined. In addition, during the episodic slip of strike-slip faults, changes in horizontal slip direction and faulted tectonic-sedimentary geological bodies often occur. These two phenomena actually reflect the core content of the kinematic characteristics of strike-slip faults, namely, the direction and distance of slip. It can also be used as an important basis for judging the active stages of strike-slip faults. Therefore, the Tarim superimposed basin is divided into five tectonic layers on the basis of the study of basin tectonic-sedimentary evolution background. On this basis, the vertical structural sequence and main associated structural styles of strike-slip fault system in the study area are determined. The geometric and kinematic characteristics of strike-slip associated structures in different tectonic layers of Tarim superimposed basin are analyzed. Two types with seven applicability techniques for distinguishing active periods of faults based on seismic data have been formed.

Microscopic characteristics and oil content of Chang 6 tight sandstone reservoirs in Lijiachengze area, Jingbian Oil Field, Ordos Basin

CUI Weilan, HAN Huafeng, ZHANG Yong, BAI Yubin

2019, 41(3): 390-397. doi: 10.11781/sysydz201903390

Abstract(767) PDF-CN(105)

Abstract:
The microscopic characteristics and oil-bearing properties of the Chang 6 tight sandstones in Lijiachengze area of the Jingbian Oilfield were studied using the analysis and test data of cast thin sections, thin section fluorescence, scanning electron microscopy, pressure-controlled porosimetry (PCP) and rate-controlled mercury porosimetry (RCP). The results show that the rock type of the Chang 6 sandstone reservoir is fine feldspar sandstone, and the main composition is calcite, chlorite and turbidite. The pore type is varied, mainly with residual intergranular pores and various dissolution pores, and the average pore diameter is mainly distributed at 20-50 μm. The reservoir porosity and permeability are poor. Micro-cracks are locally developed, and pore structure is very complex. Combined PCP and RCP indicate pore throat radius extends from nanometers to micrometers, but there are mainly two peaks, and the pore radius is mainly smaller than 2 μm. The oil content of Chang 6 sandstones is poor, mainly with oil spot grade, and oil is mainly distributed in the residual intergranular pores and dissolution pores. For the oil-bearing sandstones with industrial oil flow wells, the lower limits of porosity, permeability and pore throat radius are 7.5%, 0.15×10^-3 μm² and 0.1 μm, respectively.

Diagenesis controls on high-quality reservoirs of the Yingcheng-Shahezi formations in the Lishu Fault Depression, Songliao Basin

HAN Zhiyan

2019, 41(3): 398-403. doi: 10.11781/sysydz201903398

Abstract(679) PDF-CN(109)

Abstract:
Through lithologic observation, thin section identification and mineral composition statistics, the high-quality sandstone reservoirs in the Cretaceous Yingcheng-Shahezi formations in different areas of the Lishu Fault Depression were studied in detail. The results showed that the high-quality reservoirs were mainly developed in sandstones with coarser grain size, higher soluble component content and lower rock debris content. The main diagenesis processes of the target layer in this area include compaction, cementation filling, dissolution and structural fissures. In the process of diagenesis, compaction and cementation reduced the pores of the reservoir, while dissolution formed a large number of secondary pores. The structural fractures were the migration channels and reservoirs of the late oil and gas. It was proposed that the reservoirs in this area have five main pore combinations such as “original pore type”, “porous dissolved type”, “dissolved pore type”, “fractured type” and “cracked type”. The main controlling factors affecting the pore development of high-quality sandstone reservoirs are sandstone fabric, dissolution and later structural fractures. The sandstone has good structure, strong dissolution, tectonic fracture and large single layer thickness, and the interval and area adjacent to the source rock are the direction and target for future exploration.

Dissolution mechanism of siliciclastic particles in Xujiahe Formation, West Sichuan Depression, Sichuan Basin

LIN Xiaobing, TIAN Jingchun, LIU Liping, LI Mintong

2019, 41(3): 404-410. doi: 10.11781/sysydz201903404

Abstract(502) PDF-CN(106)

Abstract:
The siliceous debris dissolution event in the diagenetic series of clastic rocks of the Upper Triassic Xujiahe Formation in the West Sichuan Depression were studied to establish a theoretical dissolution model. The model may be used for recognizing dissolution by means of macroscopic observation of drill cores, profiles and testing data. Results show that the dissolution of siliciclastic particles happens under acidic formation water conditions with F participation. The F component detected in inclusions should be the sum of F^-, HF₂^-, un-dissociated HF molecule, (HF)₂, among which the un-dissociated HF molecule and (HF)₂ are the main elements. The active component (HF)₂ or HF₂^-were adsorbed on the surface of silicon particles during the dissolution under the catalysis of H⁺. Material exchange and transformation of other mineral assemblages occurred at the same time, including felspar and rock debris dissolution as well as siliceous cementation, etc. The keys to recognize siliceous dissolution mainly include geochemistry characteristics, partly dissolved siliceous particles, open contact fractures between siliceous grains in tight sandstones and mineral assemblages.

Seismic geomorphological characteristics of multiple fluvial patterns in the Neogene Lower Minghuazhen Member in the Shaleitian area, Bohai Sea

TAN Mingxuan, ZHU Xiaomin, LIU Qianghu, LIU Wei, LI Shunli, ZHAO Fang

2019, 41(3): 411-419. doi: 10.11781/sysydz201903411

Abstract(634) PDF-CN(89)

Abstract:
Fluvial deposits are well developed in the lower member of Neogene Minghuazhen Formation in the Shaleitian area, Bohai Sea, which are perceived as the main targets of hydrocarbon exploration for shallow-buried reservoirs in the offshore Bohai Bay Basin. Combined with seismic geomorphological approach and satellites photographs of modern fluvial systems, straight river, low-to medium-sinuosity meandering river (sinuosity 1.2-1.8) and braided river can be well recognized from several typical slices in the study area. And the coexistence of braided and meandering rivers can be well interpreted during the deposition of the upper submember of the Lower Minghuazhen Member. According to the reconstruction of paleoslope gradient, the slope gradients of straight and meandering rivers are relatively lower, while they are particularly larger in braided rivers on a gentle-dipping slope. Within the paleodischarge estimation from the geomorphology-hydraulics relation, the bankfull discharge of braided rivers can reach 3 942 m³/s, while meandering rivers can be as low as 145 m³/s. The bankfull discharges of straight rivers are usually less than 300 m³/s. The discrimination of fluvial patterns based on slope gradient and discharge will enhance the understanding of different fluvial patterns, and will provide an important guidance of the geomorphological characteristics of multiple fluvial patterns, the coexistence of braided and meandering rivers and spatial distribution of composite fluvial sandbodies.

Geochemical characteristics and geologic significance of the Lower Jurassic basalt on the western margin of Junggar Basin

GAO Shanlin

2019, 41(3): 420-426. doi: 10.11781/sysydz201903420

Abstract(425) PDF-CN(91)

Abstract:
The geochemical characteristics of the Lower Jurassic volcanic rocks on the western margin of the Junggar Basin were analyzed. The main, trace and rare earth element data indicate that the rocks are alkaline basalts, enriched with light rare earth elements, large ion lithophile elements and high field strength elements. The trace elements show an ocean island basalt (OIB) distribution model. The basalt magma came from the depleted mantle that was not obviously contaminated by crust, and has the characteristics of continental intraplate rift volcanic rocks related to mantle plume activity. The Tubo-Hami, Dunhuang and other basins in the northwest developed Jurassic basalt of similar genesis with the western Junggar Basin. The basalt formation was related to the rising of regional asthenosphere interface and the thinning of lithosphere, providing dynamic conditions for the formation of extension basin during the early and middle Jurassic. The extension of the Jurassic basin took place earlier in the west and the south, which explained the difference of source rock distribution and hydrocarbon accumulation in the basin.

Cretaceous oil-source correlation in Guaizihu Sag, Yin'gen-E'ji'naqi Basin

WANG Ping, XIANG Liange, JIANG Haijian, CHEN Qingtang, SHI Dahai, CHEN Qianglu, WANG Jie, XU Liangfa

2019, 41(3): 427-434. doi: 10.11781/sysydz201903427

Abstract(774) PDF-CN(93)

Abstract:
Recently, high oil product was gained in the second member of the Cretaceous Bayingebi Formation (K₁b₂) in the well X in the Guaizihu Sag of Yin'gen-E'ji'naqi Basin, which revealed a bright exploration prospect. It has not obtained a quite unified understanding of petroleum source, so some research were made on the oil-source correlation,which will be helpful for the prediction of hydrocarbon reservoir and the selection of exploration direction. The analyses of composition, biomarker and carbon isotope were made with oil sand samples from the first member of Suhongtu Formation (K₁s₁), crude oil samples from the second member of Bayingebi Formation, and mudstone samples from the second member of Suhongtu Formation (K₁s₂) as well as and the second and first members of Bayingebi Formation. The geochemical features of oil sands, crude oil are close with K₁b₁ source rocks, showing high contents of C₃₀-diahopane and gammacerane, low Pr/Ph and high maturity. The good similarity reflects that K₁s₁ oil sands and K₁b₂oil are homologous, and their parent material are both from K₁b₁source rocks.

Characteristics of biomarker compounds and their implications for Lower Cambrian black shale on the northern margin of Sichuan Basin

HAN Yuyue, RAN Bo, LI Zhiwu, LIU Shugen, YE Yuehao, WANG Han, YU Xiaoxuan

2019, 41(3): 435-442. doi: 10.11781/sysydz201903435

Abstract(620) PDF-CN(101)

Abstract:
The formation of the sag in the central Sichuan Basin may have influenced the development of major reservoir and source rock formations, such as the Lower Cambrian Qiongzhusi (Niutitang) Formation. This study analyzed the organic geochemistry, including n-alkanes and isoprenoids, steranes, terpanes (hopanes series), of organic matter in the Qiongzhusi Formation on the northern margin of the Yangtze Plate to investigate the depositional environment and formation mechanism of the intracratonic sag. The results indicate that the organic matter in the study area was sourced from eukaryotic phytoplankton and bacteria. The presence of gammacerane and low pristane/phytane ratios indicates that the top of the water column contained enough oxygen to provide favorable conditions for eukaryotic phytoplankton to thrive. The presence of 4-methyl steranes, a typical molecular indicator of hydrothermal vent microbes, in the Qiongzhusi Formation suggests anaerobic organisms thrived at the bottom of the water column as a result of extension during the formation of the intracratonic sag. A paleoceanographic model of the study area was constructed. Both methane oxidizing and sulfate reducing bacteria along with other hydrothermal vent microbes may not only serve as sources of organic matter, but also promote the propagation of algae in shallow water to improve organic productivity in this ancient environment.

A novel method for quantitative analysis of diamondoids in petroleum samples

WANG Huitong, WENG Na, ZHANG Shuichang, WEI Caiyun, ZHANG Chaojun

2019, 41(3): 443-450. doi: 10.11781/sysydz201903443

Abstract(639) PDF-CN(67)

Abstract:
A new method for the quantitative analysis of diamondoid hydrocarbons in petroleum geological samples was established using comprehensive two-dimensional gas chromatography-flame ionization detector (GC×GC-FID). The process included the pretreatment of sample followed by the qualitative analysis of diamondoid hydrocarbons using two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS). The diamondoid hydrocarbons could be well separated using the orthogonal separation characteristics of GC×GC, The original separation method of saturated hydrocarbon fraction in petroleum samples was improved in this study in order to reduce the loss of low-carbon diamondoid hydrocarbons in the pretreatment process. A new pretreatment method for saturated hydrocarbon by small column chromatography was established. There were many advantages such as lower sample costs, short analysis time and little consumption of reagents. The recovery of diamondoid hydrocarbons was satisfied for chromatography quantitative analysis. Compared to the traditional internal standard semi-quantitative method by gas chromatography-mass spectrometry (GC-MS), this method had high resolution and lower requirements for internal standards. The quantitative results of diamondoids could be obtained using only one certified reference material of deuterated adamantane. Moreover, the repeatability was good. The relative standard deviation (RSD, n=7) was less than 5%, which could meet the analytical requirements of a complicated system.

Establishment of classification and evaluation criteria for tight reservoirs based on characteristics of microscopic pore throat structure and percolation: a case study of Chang 7 reservoir in Longdong area, Ordos Basin

XU Yongqiang, HE Yonghong, BU Guangping, CHEN Lin, LIU Linyu, ZHU Yushuang

2019, 41(3): 451-461. doi: 10.11781/sysydz201903451

Abstract(764) PDF-CN(122)

Abstract:
Taking the Chang 7 reservoir in the Longdong area of the Ordos Basin as an example, the microscopic pore throat characteristics were comprehensively analyzed through physical analysis, casting thin section, scanning electron microscope, CT scanning, high pressure mercury injection and constant rate mercury injection experiments. Fluid seepage was analyzed by NMR and visualized multiphase seepage experiments. Some reasonable evaluation parameters were selected to classify and evaluate tight reservoirs. The average porosity and permeability of the Chang 7 tight reservoir in the Longdong area are 9.33% and 0.18×10^-3 μm², respectively. The main pore types are feldspar dissolved pore and intergranular pore, with an average plane porosity of 1.89%. The pore throat radius is small, mainly distributed in the range of less than 1 μm. Its reservoir capacity is strong, but its connectivity is poor. The movable fluid saturation and oil displacement efficiency are mainly controlled by the fine pore throat, and the heterogeneity also has a certain influence on the oil displacement efficiency. Porosity, permeability, plane porosity, average pore throat radius, mean value coefficient, displacement pressure, movable fluid saturation and oil displacement efficiency are selected as evaluation parameters, and a multi-classification coefficient method is used to classify and establish an evaluation criteria for tight reservoirs, which are divided into Ⅰ, Ⅱ, Ⅲ and IV from good to bad.

2019, 41(3): 462-462.

Abstract(212) PDF-CN(66)

Abstract:

2019 Vol. 41, No. 3

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