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2018 Vol. 40, No. 2

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2018, 40(2): .
Abstract(358) PDF-CN(206)
Abstract:
Comparison of geological characteristics of Chang 7 shale oil in Ordos Basin and typical shale oil in North America
GAO Hui, HE Mengqing, ZHAO Pengyun, DOU Liangbin, WANG Chen
2018, 40(2): 133-140. doi: 10.11781/sysydz201802133
Abstract(1877) PDF-CN(543)
Abstract:
The Chang 7 shale oil in the Yanchang Formation of Ordos Basin was studied using X-ray diffraction, scanning electron microscopy, high pressure mercury penetration, and gas isothermal adsorption. The formation was compared with typical shale oil in North America from four aspects including geological conditions, source rock characteristics, mineral composition, and reservoir space types. The results showed that both the Chang 7 shale oil and the typical shale oil in North America were deposited in a low energy environment, and the stable sedimentary environment was beneficial to shale oil accumulation. The organic matter type and maturity of source rocks in Chang 7 and North America are similar. The TOC content of Chang 7 shale oil is 2% to 18%, which is higher than that of the Eagle Ford shale. Thus, the Chang 7 source rocks are considered to have a great potential for oil production. The brittle mineral content of Chang 7 shale oil is 69.73%, only 1.27% lower than the typical shale oil in North America, indicating that the shale of Chang 7 formation is amenable to fracturing. Compared with the typical shale oil in North America, the Chang 7 shale oil has poor porosity and permeability (0.5%-2.1% and (0.000 4-0.03)×10-3 μm2, respectively). Micro-cracks and organic pores were well developed in typical shale oil in North America, while the organic pores in Chang 7 shale oil are scattered, and the reservoir space is mainly composed of intergranular pores, intragranular pores and micro-cracks. It can be concluded that the Chang 7 shale oil has the same oil accumulation pattern and mineral composition as the typical shale oil in North America. However, the Chang 7 shale oil has poor physical properties and a dense reservoir. Therefore, it has great resource potential and high development difficulty.
Characteristics and formation mechanism of low porosity and extra-low permeability reservoirs in the Niujuanhu oil field, Santanghu Basin
WEN Jing, YANG Ming, QI Weilin, YAO Mengduo, HOU Quanzheng
2018, 40(2): 141-148. doi: 10.11781/sysydz201802141
Abstract(1449) PDF-CN(164)
Abstract:
The Xishanyao reservoir in the Niujuanhu oil field of Santanghu Basin, though shallow (usually less than 2 000 m), is a low porosity and ultra-low permeability reservoir.The reservoir characteristics and the causes for low porosity and ultra-low permeability were studied by using core and cast thin section observations, conventional high pressure mercury injection experiments, SEM, and combined with regional tectonic data. The Xishanyao Formation was mainly composed of feldspar lithic sandstones. The reservoir includes intergranular pores, dissolution pores and fractures. Sedimentation, diagenesis and tectonic effects resulted in low porosity and ultra-low permeability. During the early deposition period of Xishanyao Formation, carbonate cementation was weak due to the acidic environment of coal-bearing formations.A strong and rapid compaction occurred due to the lack of support between particles. At the same time, sedimentation also controlled the original physical properties of the reservoir from the size of particle and the content of capping agent. The compaction effect during diagenesis led to a porosity reduction of 18%, and the acidic environment also led to a large amount of kaolinite formation, quartz secondary growth and the development of late iron-rich carbonate cementation with a cementing porosity rate of about 5%. The cracks formed by tectonic stress provided channels for late stage dissolution. However, rocks have become consolidated due to early compaction. What's more, the coal seam is thin, and the acidic fluid is not enough to flow in large scale through small particles, leading to poor dissolution strength. As a result, coarse throats which have a great contribution to permeability generated little, and a reservoir with low porosity and ultra-low permeability was formed.
Mechanism and sedimentary responses of oblique faults: A case study of Jiyang Depression, Bohai Bay Basin
LI Li, ZHAO Li, DONG Dawei
2018, 40(2): 149-158. doi: 10.11781/sysydz201802149
Abstract(1298) PDF-CN(237)
Abstract:
Oblique faults played an important role in the structural deformation of superimposed basins, which resulted in oblique rifting and controlled the sedimentary system in some ways. The systematic mechanism analyses showed that three contemporaneous deformations and one multiphase deformation controlled the generation of oblique faults, including contemporaneous pure shear, simple shear, general shear, and multiphase pure shear by oblique extension/compression. The activity features of oblique faults in the Jiyang Depression ever since Mesozoic were determined on the basis of 3D seismic data interpretation, plane and section analyses of fault and kinematic parameter calculations, combined with regional tectonic evolution. The oblique faults showed reverse oblique-slip in the Indosinian compressional stress field, normal oblique-slip in the Yanshanian simple shear, and normal oblique-slip in the Himalayan extensional stress field. In addition, there were also some normal oblique-slip faults under general shear and inherited oblique-slip faults under oblique extension by stress field transformation. The activities of oblique-slip faults controlled the lateral migration and stacking of fan bodies at the margin of the basin and the dispersion and spreading of sedimentary systems. As the sedimentary response to oblique-slip, the sedimentary imbricates and inclined anticlines formed by the oblique faults' strike slipping in three dimensions were dissected. Several false appearances in judging the faults' slip direction by sedimentary fan body were discussed, which demand intensive studies on secondary structures or regional tectonic evolution.
Reservoir-forming pattern with multiple sources in second member of Shahejie Formation, Bonan Sag, Jiyang Depression, Bohai Bay Basin
ZHANG Peng, ZHANG Jingong, ZHANG Liang, YUAN Yidong, HAO Jie, YANG Yan
2018, 40(2): 159-167. doi: 10.11781/sysydz201802159
Abstract(1114) PDF-CN(207)
Abstract:
The second member of Shahejie Formation (Es2) in the Bonan Sag of Jiyang Depression has multiple hydrocarbon sources, both from top and bottom. Drilling, logging, seismic and testing data were applied in the analyses of Es2 in view of the unclear understanding of multi-source hydrocarbon accumulation models and the low overall study level of Es2. It was concluded that the hydrocarbon in the Es2 was sourced from three sets of source rocks in the upper section of the fourth member (Es4), the third member (Es3) and the first member (Es1) of Shahejie Formation. The fans and carbonate rocks at the bottom and the mudstones on the top of Es2 served as favorable reservoirs and cap rocks, respectively. Faults and unconformities formed a 3D transport system, which had a significant influence on hydrocarbon migration and accumulation. The physical properties of reservoirs restricted hydrocarbon enrichment. Two reservoir-forming patterns, ‘accumulation during the middle stage with two sources’ and ‘accumulation during the late stage with three sources’, were established according to the difference of accumulation stage and source. Lithologic, structural and structural-lithologic traps were formed with single or multiple sources under these two patterns. The major accumulation stages have a trend of being late gradually from bottom to up and from the sag center to the edge.
Relationship between porosity evolution and hydrocarbon charging in tight sandstone reservoirs in Oligocene Huagang Formation, Xihu Sag, East China Sea Basin
LIU Yong, XU Guosheng, ZENG Bing, XU Fanghao, ZHANG Wu, GAO Yao, YUAN Haifeng
2018, 40(2): 168-176. doi: 10.11781/sysydz201802168
Abstract(1067) PDF-CN(418)
Abstract:
The pore evolution of tight sandstone reservoirs in the Oligocene Huagang Formation in the central and northern parts of the central reversal structural belt in the Xihu Sag of the East China Sea Basin was recovered based on the analyses of reservoir properties, burial history and thermal evolution history, and using cast thin section identification, scanning electronic microscope, electron microprobe, fluid inclusion analyses and porosity recovery quantified calculation. The relationship between porosity evolution and hydrocarbon charging was also discussed. The results showed that the porosity evolution in the Huagang Formation can be classified into three stages:14.28% in the stage B of early diagenesis, 10.35% in the stage A of middle diagenesis, and 8.75% in the stage B of middle diagenesis, accompanied by three stages of hydrocarbon charging. The first (19-17 Ma) and second (17-7 Ma) stages of hydrocarbon charging took place before the end of stage A of middle diagenesis. The reservoirs were not tight yet, and the acidic fluid brought by hydrocarbon charging played an important role in reservoir reformation, providing favorable porosity and permeability for later hydrocarbon charging. The third stage (7-0 Ma) of massive hydrocarbon charging happened from the end of stage A to the stage B of middle diagenesis, when reservoirs compacted gradually. The third section of Huagang Formation, buried shallow and was not tight yet, showed relatively better reservoir properties and became a main charging target. It is now the most favorable hydrocarbon exploration target for the Huaguang Formation in the overall densification background.
Tectonic evolution of Xiannüshan fault and its influence on hydrocarbon traps in Changyang anticline, Western Hubei fold belt
DENG Mingzhe, HE Dengfa, ZHANG Yuying
2018, 40(2): 177-184. doi: 10.11781/sysydz201802177
Abstract(1291) PDF-CN(256)
Abstract:
The Western Hubei fold belt is an important oil and gas exploration area in South China. Located in the northeast of the fold belt, the Xiannüshan fault intersects the Changyang anticline, and has an important influence on the hydrocarbon traps in the Changyang anticline. However, the geometrical morphology and evolution history of the Xiannüshan fault has not been well studied due to the lack of accurate depth information, and the influence on hydrocarbon trap evolution was still unclear. Based on the interpretation of the latest seismic section in the central part of the fault, the quasi-three-dimensional shape and the formation process of the Xiannüshan fault were analyzed. Combined with the regional geological evolution and hydrocarbon accumulation process, the influence of the formation and evolution of faults on the preservation units in the Changyang anticline was analyzed. (1)The Xiannüshan fault belt can be divided into three parts. The northern part is dipping westwards, while the middle and southern parts are dipping eastwards. (2)The Xiannüshan fault was first formed during the Late Jurassic as a strike slip fault, pulling apart during the Late Cretaceous, and thrusted during the Middle and Late Paleogene. (3)The strike slip of the Xiannüshan fault in the Late Jurassic was favorable for hydrocarbon migration in the Changyang anticline. However, the stretching of the Xiannüshan fault in the Late Cretaceous destroyed tectonic traps in the Changyang anticline, leading to hydrocarbon loss. In areas where similar faults have occurred in the western Hubei, the potential for oil and gas exploration may have been adversely affected.
Characteristics of organic-rich shale in Wufeng-Longmaxi formations in Suiyang area of northern Guizhou and its implication to shale gas
KANG Jianwei, YAN Jianfei, YU Qian, TIAN Jingchun, MEN Yupeng, SUN Yuanyuan
2018, 40(2): 185-192. doi: 10.11781/sysydz201802185
Abstract(1173) PDF-CN(176)
Abstract:
The organic-rich shale in the Wufeng-Longmaxi formations in the northern Guizhou was deposited in tide flat, shallow or deep continental seas, respectively, with an increasing thickness from north to south. The black shale in the Jianba section in the Suiyang area of the northern Guizhou has a thickness of 33.1 m, which is obviously thicker than the other sections even though they have similar sedimentary sequences, indicating for a sedimentary depression in this area. Organic carbon content in the Wufeng-Longmaxi formations ranges from 0.53% to 6.04%, with an average value of 3.05%. The Tmax is generally higher than 500℃. The Ro ranges from 1.93% to 2.19%, with an average value of 2.07%, indicating for an over-mature stage. Brittle mineral content is high across the section, accounting for 70.5% in average. The discovery of the Jianba section sheds new light on shale gas exploration in the northern Guizhou.
Origin and source of natural gas in the Upper Paleozoic in Hangjinqi area, Ordos Basin
NI Chunhua, LIU Guangxiang, ZHU Jianhui, WU Xiaoqi, BAO Jianping
2018, 40(2): 193-199. doi: 10.11781/sysydz201802193
Abstract(1084) PDF-CN(211)
Abstract:
The analyses of the chemical composition, stable carbon and hydrogen isotopes as well as noble gas isotopes of natural gas from the Upper Paleozoic in the Hangjinqi area of Ordos Basin showed that the natural gas was mainly composed of hydrocarbon gas, which appeared to be wet gas with a dryness coefficient from 0.80 to 0.94, lower than 0.95. The δ13 C1 and δ13 C2 values range -36. 2‰--31. 7‰ and -27. 8‰--23. 3‰, respectively, and the δDCH4 values range -199‰--172‰. The carbon and hydrogen isotopes of alkane gas are generally characterized by positive sequence, indicating for an organic origin. Gas origin identification and gas-source correlation indicated that the natural gas from the Upper Paleozoic is coal-derived gas with a normal to high maturity and was sourced from coa-measure source rocks in the Taiyuan-Shanxi formations. There are some obvious differences of gas-source to the south and the north of the Boerjianghaizi Fault. The natural gas in the Shilijiahan play in the south was derived from the P1t-P1s source rocks in situ with a high maturity, whereas the natural gas in the Shiguhao play in the north was mainly sourced from the Shilijiahan area, and then suffered a certain degree of damage and escaped.
Time-space distribution of Chang 7 oil shale in southeastern Ordos Basin: Controlled by sedimentary environments and deposition rates
CHEN Yuhang, ZHU Zengwu, WANG Zhe, HUANG Wei, LI Changchun, YANG Zhiguo, XU Feng, LI Weibo
2018, 40(2): 200-209. doi: 10.11781/sysydz201802200
Abstract(1440) PDF-CN(311)
Abstract:
Abundant oil shale resources are hosted in the seventh member (Chang 7) of Triassic Yanchang Formation in the southeastern Ordos Basin. However, the previous studies mainly focused on the characteristics and generation environment of oil shale. However the enrichment regularities and controlling factors of oil shale were not clear, which restricted mining and subsequent production. A sequence stratigraphic framework was established based on the comprehensive analyses of outcrops, cores and fossil specimen to determine the sedimentary environment of Chang 7 oil shale. The controlling factors of oil shale distribution were discussed by the comprehensive analysis of sedimentary facies, organic matter sources and deposition rates. The Chang 7 oil shale in the southeastern Ordos Basin was deposited in delta and lacustrine sedimentary environment. Organic geochemical analyses showed that the organic matter in the Chang 7 oil shale originated from both terrestrial and lacustrine plants. The terrestrial organic matter was probably transported to deep lakes by gravity flows. Sedimentary facies analysis and Th/U value showed that during lake expansions, water depth increasing and associated accommodation space increasing in the transgressive system tract (TST) (Chang 73) provided a favorable environment for organic matter enrichment. However, during the late TST, the terrestrial organic matter input was lack and the organic matter was degraded in deep lakes, which led to oil yield decreasing. Additionally, hydrocarbon migrations to adjacent turbidites also led to oil yield decreasing. (La/Yb)N analysis showed that sedimentary environments and deposition rates controlled the spatial distribution of oil shale. In the deep lake close to delta-turbidite fan deposition systems, terrestrial and lacustrine organic matter inputs were bounteous and the deposition rate was moderate, which were beneficial to organic matter input and preservation, and provided a favorable environment for oil shale formation. In the area where delta-turbidite fan deposition systems developed, high deposition rates led to organic matter dilution, which was not beneficial to oil shale formation. In the deep lakes far away from delta-turbidite fan deposition systems, low deposition rates and the lack of deposit supplies were not beneficial to the input and enrichment of organic matter.
Geochemical characteristics and paleo-environmental implications of Middle Permian Qixia Formation in Wangcang, northern Sichuan
ZHANG Yunzhou, XU Shenglin, CHEN Hongde, LIN Liangbiao, DONG Yixin, YU Yu, ZHANG Yao
2018, 40(2): 210-217. doi: 10.11781/sysydz201802210
Abstract(1369) PDF-CN(405)
Abstract:
The sedimentary paleoenvironment of the Middle Permian Qixia Formation in northeastern Sichuan Basin was studied based on outcrop observations and laboratory analyses. The data correlations of the δ13C and δ18O of 19 samples from the Qixia Formation showed that there was no linear relationship between them. The samples are reliable targets for paleoenvironmental analyses since δ18O > -6‰, Mn/Sr ≤ 0.6, Fe/Sr < 3, and MgO/CaO < 0.125. The contents of terrigenous elements (Al2O3 and TiO2) are low, and are strongly and positively correlated. The ΣREE and Σ(Al2O3+TiO2) also showed a positive relationship. The characteristics of other main and trace elements indicated that the Qixia Formation was formed in a hypoxic or oxygen-depleted environment. The Sr/Ba value ranges from 21.9-261.9, indicating that the sea level was relatively high, so the terrigenous material content is low, and the terri-genous detrital sediments were controlled by paleo-water depth during sedimentation. The carbon and oxygen isotopes revealed that the ancient oceanic temperature ranged from 17.62-28.43℃, the paleosalinity ranged from 129.07-135.21, and the ratio of MgO/CaO ranged from 0.007-0.029, revealing that the paleoenvironmental climate was relatively warm and humid. Water depth fluctuated within a small range and experienced two transgressive and regressive cycles.
Dolomitization genetic mechanism of carbonate-siliciclastic mixed rock reservoir in CFD-A Tectonic Belt, Bohai Sea
ZHAO Ke, SONG Zhangqiang, DU Xuebin, YE Maosong, XIE Xinong, XU Wei
2018, 40(2): 218-225. doi: 10.11781/sysydz201802218
Abstract(1694) PDF-CN(268)
Abstract:
The mixed rock is a rock that consists of a mixed deposition of siliciclastic and carbonate. It was dominated by biogenic carbonate in the CFD-A tectonic belt in the Bohai Sea where dolomitization was found. Research on the CFD-A tectonic belt was rarely reported, especially aiming at the genetic mechanism of dolomite reservoir. Based on the observation and identification of cores and rock slices, combined with a number of geochemical tests, the characteristics and genetic mechanism of dolomitization in mixed rocks in the first and second members of Shahejie Formation at the CFD-A tectonic belt were studied. Four dolomite types were identified:dolomicrite, bioclastic-containing dolomicrite, bioclastic dolomite and sand-containing bioclastic dolomite. Further analyses showed that negative bias and positive correlation were both found in carbon and oxygen stable isotopes. Dispersed distribution and large variation were also revealed in oxygen stable isotopes. Dolomitization was found only in bioclastic and its ring cement through microscopic photos, which did not occur in interlocking cementation and bioclast filling. Lake surface fluctuation can be revealed by Mn/Fe, Sr/Ba index, indicating that the tectonic belt has suffered from fresh water leaching because of exposure. Mixed water dolomitization is the dominated genetic mechanism of dolomites in the study area.
Thermal evolution and hydrocarbon generation histories of black shale in Lower Carboniferous Baizuo Formation, Southern Guizhou Depression
SONG Yingrui, HOU Yuguang, LIU Yukun, HE Sheng, FAN Zhiwei, LIANG Yaqi
2018, 40(2): 226-232. doi: 10.11781/sysydz201802226
Abstract(1117) PDF-CN(153)
Abstract:
The thermal evolution and hydrocarbon generation histories of the Lower Carboniferous Baizuo Formation in the Southern Guizhou Depression were studied with petroleum geology, geochemical data and petroleum system simulation in order to evaluate the hydrocarbon generation potential of black shale. Results showed that the black shale of the Baizuo Formation has relatively high organic matter abundance and low hydrocarbon potential. The organic matter in the black shale is mainly of type Ⅱ2, and has reached the high-maturity and over-mature stages. The black shale entered the threshold of hydrocarbon generation during the Middle Carboniferous (about 312 Ma) and the mature stage in the early Triassic (about 238 Ma), and reached the maximum burial depth (about 9 000 m) in the early Jurassic (196 Ma), with a maximum temperature of about 200℃. They reached the oil generation peak in the Middle Permian (291-270 Ma) and the gas generation peak in the Late Triassic (262-208 Ma), respectively. The process of oil cracking to gas during the high thermal evolution provided sufficient methane gas and storage space for shale gas enrichment. However, tectonic uplift and erosion since 196 Ma had a certain destructive influence on shale gas enrichment.
Influence of microbial textures on pore characteristics of microbial dolomites: A case study of Lower Cambrian Xiaoerbulake Formation in Keping area, Tarim Basin
YU Haoyuan, CAI Chunfang, ZHENG Jianfeng, HUANG Lili, YUAN Wenfang
2018, 40(2): 233-243. doi: 10.11781/sysydz201802233
Abstract(1398) PDF-CN(171)
Abstract:
Microbial texture is an important characteristic of microbial dolomites compared to conventional carbonate rocks. Thus, studying microbial texture is the key to understand the origin and distribution of microbial dolomites. We selected thrombolite dolomite, foam spongy dolomite and stromatolite dolomite samples of the Xiaoerbulake Formation in Keping area in the northwestern Tarim Basin to test their petrophysical properties and pore structures. The test results were correlated with corresponding microbial textures to analyze their influence on pore characteristics. These samples were divided into three groups with different intensities of diagenesis alteration in order to analyze its effects. The results showed that the pore structures of microbial dolomites were closely related to their microbial textures. Sedimentation served as the dominating factor of pore structures with its controls on microbial textures, while diagenesis, under the restriction of microbial textures, changed the pore system mainly on the basis of sedimentation.
Division of high-frequency sequences of different orders in fine-grained deposits and its geologic significance: A case study of mud shale from the lower section of the third member to the upper section of the fourth member of Shahejie Formation in Dongying Sag, Bohai Bay Basin
DU Xuebin, LU Yongchao, LIU Huimin, LIU Hui, WANG Yong, XIONG Shipeng, GUO Laiyuan, LIU Zhanhong, PENG Li
2018, 40(2): 244-252. doi: 10.11781/sysydz201802244
Abstract(1359) PDF-CN(173)
Abstract:
The sequence division of mud shale is a focus in basic research. Based on lots of sensitivity parameters, using the natural gamma curves (GR) and the improved TR cycle theory, it was classified in this paper the fourth and fifth orders of sequences in mud shale. Moreover, using continuous testing data, based on the astronomical cycle theory, some parameters such as eccentricity, slope and precession were used to establish an astronomical scale for mud shale in the study area, by which the sixth and seventh orders of sequence units can be identified. Four deposition processes were concluded in the upper section of the fourth member of Shahejie Formation in well A in the Dongying Sag, Bohai Bay Basin, and quantitative calculations were made for each process to estimate the deposition rates in different units. We divided the strata from the lower section of the third member to the upper section of the fourth member of Shahejie Formation into eight fourth order and 31 fifth order units. The quantitative analyses of deposition process showed that the deposition period of the second quasisequence in the upper section of the fourth member of Shahejie Formation was the most conducive to biological development.
Geological modeling method based on sedimentary facies coupled rock type for porous carbonate reservoirs
WANG Mingchuan, DUAN Taizhong, DU Xiujuan, LIAN Peiqing, LI Yanhua, ZHANG Wenbiao
2018, 40(2): 253-259. doi: 10.11781/sysydz201802253
Abstract(1159) PDF-CN(129)
Abstract:
The quantitative characterization of petrophysical properties such as porosity, permeability, and saturation in 3D space has been a technical problem for the development of porous carbonate reservoirs. In order to establish a reliable geological model of porous carbonate reservoirs, taking reservoir F in the Zagros Basin as a prototype, a geological modeling method based on sedimentary facies coupled rock type was studied and put forward. Based on geological research, we combined well logging data with seismic data, and established a sedimentary facies model. Controlled by the sedimentary facies model, 3D distribution models of porosity and rock type were built. Then, based on the porosity-permeability mathematical model and saturation height function controlled by rock type, 3D permeability and water saturation distribution models were established by using deterministic modeling method. The results showed that the geological model established by using the proposed method was reliable, which laid a solid geological foundation for the development of reservoir F, and the method proposed in this paper could provide guidance for the geological modeling of this kind of reservoir.
Recovery of denuded strata thickness based on Milankovitch Astronomical Cycles: A case study of Qingshankou Formation in X Oilfield, Songliao Basin
ZHAO Jun, CAO Qiang, FU Xiandi, ZHANG Feifei, QIN Guoying
2018, 40(2): 260-267. doi: 10.11781/sysydz201802260
Abstract(1154) PDF-CN(347)
Abstract:
The Milankovitch Astronomical Cycles were applied to study the erosion thickness of Qingshankou Formation (K2qn) in the X Oilfield, Songliao Basin. Spectral analysis and wavelet transform revealed that the Milankovitch Cycles occurred in the K2qn. We detected the eccentricity period of 100 ka, obliquity period of 40 ka and precession period of 20 ka in the K2qn. The bandpass filtering of 42 exploratory wells in the X Oilfield showed that, the K2qn has 35 to 43 eccentricity periods of 100 ka, which proved erosion phenomenon. The erosion thickness of K2qn is 0-98 m, and gradually decreases from northeast to southwest, where non-denuded areas distribute widely. Tectonic uplift and erosion took place regionally in the X Oilfield during or at the end of the sedimentation of K2qn.
A quantitative research method on the sealing of growth faults: A case study of JX1-1 oil field in Liaozhong Sag, Liaohe Depression
TAN Lijuan, XIE Hongze, ZHANG Hui, ZHAO Juju, GUO Youyou
2018, 40(2): 268-273. doi: 10.11781/sysydz201802268
Abstract(1123) PDF-CN(127)
Abstract:
Through the analyses of the mechanism and influencing factors of the sealing of growth faults, taking the fault body as the research object, the concept of fault closure composite index (Fci) was put forward, which was the quantified product of three factors including the fault positive pressure, the muddy content of fault zone, and the cementation of debris in fault zone. Taking the JX1-1 oil field in the Liaozhong Sag as an example, a fault sealing evaluation standard was established. The fault closure composite index of 60 is regarded as a critical value. Faults can seal oil and gas well when the index is over 60. The controlling effects on hydrocarbon accumulation of the main fault in the study area, Liaozhong no.1 fault, were analyzed.
Application of stratified sampling method in core plug sampling
LÜ Zhou, WANG Yupu, LI Li, JI Weiping, HOU Xiulin, LIU Dawang, GE Zhengting, LI Yang
2018, 40(2): 274-279. doi: 10.11781/sysydz201802274
Abstract(1170) PDF-CN(313)
Abstract:
The data obtained from reservoir core experiments are the basis of geological research, logging interpretation and oil and gas reservoir engineering calculations. The selection of a sample plug is the first step in a reservoir core experiment, and its sampling accuracy has an important effect on experiment results. When the sample number is limited, the conventional random sampling cannot meet the requirements of measurement accuracy. In view of the limitations of the traditional sampling methods, this paper described the principle of a stratified sampling method, and discussed its selection criteria. Based on measured data, the Monte Carlo algorithm was implemented using Visual Basic programming, and the measurement accuracy of random sampling and stratified sampling was compared. The results showed that, the data accuracy of stratified sampling was better than that of simple random sampling under the same sampling quantity. Therefore, according to the requirements of different experiments, a selection method of core plug samples based on stratified sampling was proposed. The method can estimate sampling accuracy and design a reasonable number of samples accordingly. When the number of experiment samples is limited, the sampling accuracy can be improved effectively.
High pressure mercury injection and scanning electron microscopy applied to characterize micro-and nano-scale pore throats in tight sandstone reservoirs: A case study of the fourth member of Shahejie Formation in Yi176 block, Zhanhua Sag, Bohai Bay Basin
YAN Qiang, ZHANG Yunfeng, FU Hang, JIANG Meiling, WANG Jun, SUI Shuling, FU Han, HAO Rui, GUO Minghan
2018, 40(2): 280-287. doi: 10.11781/sysydz201802280
Abstract(1552) PDF-CN(196)
Abstract:
Thirty-two samples of tight sandstone from the fourth member of Shahejie Formation in Yi176 block, Zhanhua Sag, Bohai Bay Basin were selected for high pressure mercury injection and overpressure pore infiltration experiments. The microscopic pore throat structure and permeability of tight sandstone reservoirs, especially the flow characteristics of fluid in nano-and micro-scale throats, were discussed along with their microscopic features observed with environmental scanning electron microscopy (SEM). Experiments showed that the discharge pressure in the study area has a wide distribution. According to the distribution of pore throats and relative permeability, the reservoirs in this area were divided into 4 major types and 6 sub-categories. dv/d(logd) reflects the distribution of pore throats at all levels. Combined with the identification of the relative sizes of pore throats by environmental SEM, the pore throat system in the study area was divided into 4 categories:nano scale, micro-nano scale, nano-micro scale and micro scale, while throat was classified into nano and micro types. According to the correlation analysis, it was found that the nano-scale throats controlled permeability, while the micro throats contributed more to porosity. High pressure mercury injection not only characterizes the structural characteristics of conventional pore throats, but also reflects the size of the micro-and nano-pore throats and the fluid flow characteristics in them, which allows further detailed evaluation of reservoirs.
Reservoir properties and hydrocarbon charging threshold of Chang 8 tight sandstones in Fuxian area, Ordos Basin
DENG Yaren, REN Zhanli, MA Wenqiang, CHEN Xipan, YANG Guilin, NANKA Ewu
2018, 40(2): 288-294. doi: 10.11781/sysydz201802288
Abstract(1322) PDF-CN(262)
Abstract:
Hydrocarbon charging threshold is the basis for tight oil accumulation research. The microstructure of Chang 8 tight sandstone reservoirs in the Fuxian area of Ordos Basin is very complicated, which is a key factor influencing hydrocarbon charging. Field emission scanning electron microscopy (SEM) and CT methods were used to quantitatively study the pore-throat characteristics of tight sandstone reservoirs. Mechanical properties, well logging and effective pore-throat analyses were used to determine the hydrocarbon charging threshold of physical properties and pore-throat characteristics. The results showed that the pore size of tight reservoirs is dominated by nanometer and submicron scale, and the average pore radius is 1.2 μm. The average radius of throat is 0.1 μm, which belongs to micropore-fine throat reservoirs. It was calculated that the charging threshold of porosity of Chang 8 tight sandstone reservoirs is 4.5%, and that of permeability is 0.04×10-3 μm2. The threshold of pore-throat diameter on the source and reservoir interface is 15.77 nm, and that inside reservoir is 24 nm. We integrated that oil and gas might occur in nano-scale pores as oil bead, throat or thin film as compaction and cementation effects became stronger.
Double-factor evaluation for oil and gas geochemical anomalies: A case study of Linnan-Qianguantun areas, Jiyang Depression, Bohai Bay Basin
YANG Jun, SHEN Zhongmin, WANG Guojian, NING Lirong
2018, 40(2): 295-302. doi: 10.11781/sysydz201802295
Abstract(1051) PDF-CN(117)
Abstract:
In the past, the evaluation of geochemical anomalies often only focused on geochemical indicators, with less consideration of geological factors, so the evaluation results lacked geological support. Taking the Linnan-Qianguantun areas of Jiyang Depression as an example, some effective indicators such as acidolysis methane, headspace methane, free methane and physically adsorbed methane were identified by a single indicator anomaly. Then, the comprehensive anomaly was obtained by a superposition method. An anomaly evaluation intersection diagram was made combining geochemical indicators with the geological characteristics of the study area. The evaluation results were in good agreement with the actual results, indicating that the double-factor evaluation for oil and gas geochemical anomalies provides good prospect evaluation. It provides a technical means for the comprehensive evaluation of comprehensive anomalies.
2018, 40(2): 303-303.
Abstract(603) PDF-CN(97)
Abstract:

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