石油实验地质

2018, 40(1): .

Abstract(389) PDF-CN(267)

Abstract:

Comprehensive characterization of shale gas reservoirs: A case study from Fuling shale gas field

SUN Jian, BAO Hanyong

2018, 40(1): 1-12. doi: 10.11781/sysydz201801001

Abstract(1548) PDF-CN(1226)

Abstract:
The comprehensive characterization of shale gas reservoirs is considered as a key technology in shale gas exploration and development. It forms the basis of gas potential evaluation and is an important reference for formulating engineering technology evolution during the process of shale gas exploration and development. Compared with other countries, shale gas exploration and development in China started relatively late. Large-scale commercial development has not officially launched until the discovery of industrial gas flow of JY1 at the end of 2012. In contrast with shale gas development in North America, the geological and surface conditions are more complex in the south of China. Thus, there is limited experience for comprehensive reservoir characterization of shale gas in China. Based on the different analyses between shale gas and conventional gas reservoirs observed during four years of field practice in the Fuling shale gas field, we established a parameter system including aspects of the sedimentary environment, hydrocarbon generation potential, reservoir quality, compressibility and gas-bearing properties to identify the specific characteristics or technical means for shale gas reservoir description. Further, research suggested the typical geological characteristics of the high gas-bearing interval of Wufeng-Longmaxi formations that provide guidance for shale gas exploration and development in similar areas.

Differential pore development characteristics in various shale lithofacies of Longmaxi Formation in Jiaoshiba area, Sichuan Basin

YI Jizheng, WANG Chao

2018, 40(1): 13-19. doi: 10.11781/sysydz201801013

Abstract(1811) PDF-CN(464)

Abstract:
It is of great significance for shale gas exploration and development to understand different pore characteristics in various shale lithofacies. In this paper, the reservoir characteristics of different shale lithofacies of Longmaxi Formation in the Jiaoshiba area were studied by using X-ray diffraction, thin section analysis, cathodoluminescence, FE-SEM, high pressure mercury intrusion-gas adsorption joint test, and nuclear magnetic resonance porosity. Four preliminary conclusions were obtained:(1) Three main types of shale lithofacies were identified in the Longmaxi Formation in the Jiaoshiba area, including siliceous shale, mixed shale and argillaceous shale. (2) Organic porosity developed well in the siliceous shale, but did not develop in the mixed shale and argillaceous shale, in which inorganic pores were more developed. (3) The reservoir heterogeneity characteristics of various shale lithofacies were remarkable. The siliceous shale was the most outstanding in TOC content, porosity, pore volume, specific surface area and gas content, while the mixed shale the second, and the argillaceous shale the least. (4) When the siliceous shale was deposited, bioproductivity was high, which was conducive to the enrichment of organic matter and the development of organic porosity. The mixed shale and argillaceous shale controlled by deep-water currents and terrigenous clastic material supply showed low TOC contents and poor organic pore development.

Geological factors of well fracability in Fuling shale gas field, Sichuan Basin

HU Degao, LIU Chao

2018, 40(1): 20-24. doi: 10.11781/sysydz201801020

Abstract(1403) PDF-CN(619)

Abstract:
Brittle mineral content, brittle index and horizontal stress difference coefficient of shale reservoirs are the main factors influencing shale fracability. The ①-⑤ layers from the Wufeng Formation to the first member of Longmaxi Formation in the Fuling shale gas field have similar brittle mineral content (>50%), brittle index (>50%), and horizontal stress difference coefficient (<0.2). Therefore, the above parameters can not be used effectively to evaluate the fracability of a single well in this block. Based on a large amount of single well data, the authors assessed the influence of various geological factors on the fracability of a single well by geological factors such as burial depth, structural form and fracture development characteristics. The results showed that:(1) Burial depth is the most important geological factor affecting single well fracability, and the greater the burial depth, the greater the difficulty of reservoir fracturing; (2) Structural morphology has a more obvious effect on fracturing, and fracturing is more difficult in negative structures than in positive ones; (3) The heterogeneity of natural fractures will also lead to the increased difficulty of fracturing, the difficulty of extending seam networks, affecting the effect of reservoir reconstruction and reducing the productivity of a single well.

Field testing technology for shale gas content

XI Chuanxue, SUN Chong, FANG Fan, SHU Xiangwei, WANG Qing, ZHANG Lei

2018, 40(1): 25-29. doi: 10.11781/sysydz201801025

Abstract(1258) PDF-CN(317)

Abstract:
The in-house developed intelligent shale gas desorption system was improved. A temperature sensor was installed inside the desorption canister to monitor the interior temperature and eliminate the influence of gas volume expansion caused by temperature change on experimental results. The conventional desorption method was optimized by using the improved instrument. The high temperature desorption method at 90℃ or 110℃ as the second-order desorption temperature was proposed to shorten test time from 40 h to 12-25 h, which ensured the reliability of test results with the advantages of practicality and safety. Due to the influence of manual operation, the initial desorption rate would always be abnormally high. In this case, we advised the use of the desorption data 5 min after core sealing as the initial point when fitting gas loss curves.

Significance of shale gas genesis to the development of Guanyinqiao Member, Wufeng Formation, Fuling area, Sichuan Basin

ZHANG Boqiao, MENG Zhiyong, LIU Li, LI Kai, LIU Chao, SHU Zhiheng

2018, 40(1): 30-37. doi: 10.11781/sysydz201801030

Abstract(1305) PDF-CN(666)

Abstract:
The widely developed Guanyinqiao Member at the top of the Wufeng Formation, Fuling area shows horizontally variable lithology and thickness. There are two main views about the causes of this variability:deep water genesis theory and shallow water genesis theory. This study combined various factors, including sedimentation rate and ecological characteristics, to indicate that the Wufeng Formation was a typical deep water allochthonous deposit. Underflow deposition was the main reason why the underlying Guanyinqiao Member was well developed. Meanwhile, strong underflow sedimentation was the main cause for the lack of Guanyinqiao Member in several areas. Additionally, this work investigated the effect of Guanyinqiao Member on the evaluation of shale gas development from the sedimentary and engineering technological transformation perspectives. The horizontal distribution characteristics of Guanyinqiao Member showed the horizontal differences of three geological elements, including the active degree of underflow deposition, the micro palaeogeomorphology and the distance to source area of gas-bearing shale in the Wufeng-Longmaxi formations, Fuling area. These differences had important effects on the deposition of gas-bearing shale of the Wufeng-Longmaxi formations and the overlying Long2 Member. Therefore, the formation characteristics of Guanyinqiao Member can be used as an important evaluation index for gas-bearing shale strata exploration and development in the Wufeng-Longmaxi formations, South China. Besides, the engineering technological transformation of Guanyinqiao Member is challenging. It is located in the main zone, and should be given full consideration when optimizing the horizontal section of development well.

Well logging evaluation of pore parameters for shale gas reservoirs in Jiaoshiba area, Sichuan Basin

SHU Zhiguo, GUAN Hongmei, YU Lu, LIU Yun

2018, 40(1): 38-43. doi: 10.11781/sysydz201801038

Abstract(1399) PDF-CN(356)

Abstract:
The shale reservoirs in the Jiaoshiba area of Sichuan Basin have the characteristics of low porosity and complex pore structure. Inorganic and organic pores, and micro cracks developed in the shale reservoirs in the Wufeng and Longmaxi formations. NMR logging played an important role in evaluating the porosity and pore structure of shale reservoirs in the study area. Based on core scale logging interpretation, we correlated conventional logging data with core NMR data, and established a total porosity and effective porosity interpretation model for shale reservoirs in the Jiaoshiba area. The total porosity interpretation model was based on the optimal matching between the total porosity analysis results of core NMR experiments and logging data. The optimization indicates that the multiple linear regression method is the best, that is, the total porosity and density logging, sonic time difference and compensated neutron logging provide multivariate linear fitting. The effective porosity interpretation model was based on the positive correlation between effective porosity and density logging of core NMR experiments, and the effective porosity could be calculated by density logging. Comparisons between the calculated results of porosity and core measurements showed that the absolute errors of 91.7% of the data were <0.5%, indicating a high quality evaluation of the pore parameters of shale reservoirs in the study area.

Pore features of shale gas layer in Wufeng-Longmaxi formations in Fuling area of Sichuan Basin and the application to development

LIU Yaowen, WANG Jin, ZHANG Mengyin, CAI Jin, LU Wentao, SHEN Tong

2018, 40(1): 44-50. doi: 10.11781/sysydz201801044

Abstract(1664) PDF-CN(356)

Abstract:
Shale porosity is an important factor affecting the gas-bearing capacity of shale. The pore characteristics of the upper gas layer from the Wufeng Formation to the first member of Longmaxi Formation were studied and compared with the lower gas layer by using argon plasma scanning electron microscopy (SEM), high pressure mercury intrusion and liquid nitrogen adsorption. Results show that the organic carbon content of the lower gas layer is high, the pores in the organic matter are dominant, the pore volume is mainly >0.02 mL/g, and the BET specific surface area is mainly >20 m²/g. The organic carbon content of the upper gas layer is low, the pores are mainly micro-fissures and clay mineral pores, the pore volume is mainly distributed from 0.016-0.02 mL/g, and the specific surface area is mainly 12-20 m²/g. Combined with a single well gas content test results, we found that organic carbon content has the best correlation with gas content, followed by specific surface area and porosity. An evaluation of the gas-bearing properties of the upper gas layer was carried out. Sub-layer ⑧ was considered as the best gas layer in the upper interval, while sub-layers ⑥ and ⑦ were the next best, and sub-layer ⑨ the worst.

Low-grade fault recognition technology and its application in Wufeng-Longmaxi formations in Jiaoshiba area, Fuling, Sichuan Basin

WU Jiahe, LU Yaqiu, LIU Jie, LIANG Bang, WANG Yu, LIU Qiang

2018, 40(1): 51-57. doi: 10.11781/sysydz201801051

Abstract(1411) PDF-CN(240)

Abstract:
The development of shale gas in the Fuling area of Sichuan Basin has achieved remarkable results. However, in the practice of shale gas development the phenomenon of drilling mud loss is frequent, and low-productivity and inefficient wells occur from time to time, which is considered to be closely related to low-grade faults. The North American shale gas development zone has a simple structure, while the Fuling Jiaoshiba block is superimposed by multi-stage tectonic movements with strong deformation and complicated faults. The conventional low-grade fault recognition was mainly based on drilling and logging data. A new method combining well data with seismic data uses both dynamic and static aspects. It was based on the comprehensive utilization of 3D seismic, drilling, well logging and gas test data. Fine horizon calibration, horizontal slice, variance body, curvature and other methods were applied to identify low-grade faults, which provided an important geological basis for the deployment and adjustment of horizontal wells, drilling design and the optimization of fracturing parameters.

Evaluation of gas content in shale reservoirs and analysis of influencing factors in Fuling shale gas field

LIU Li, BAO Hanyong, LI Kai, LI Gen, ZENG Yong, ZHENG Aiwei, XIONG Hongli

2018, 40(1): 58-63. doi: 10.11781/sysydz201801058

Abstract(1474) PDF-CN(395)

Abstract:
Shale gas has various forms of occurrence, mainly in the free and adsorbed state, and the main controlling factors of shale gas in different occurrence states are quite different. Comprehensive evaluation of shale gas systems has not yet been documented. Therefore, the actual data of production characteristics of Fuling national shale gas demonstration area in the east of Sichuan Basin were studied by means of geochemical analysis, petrophysical testing, isothermal adsorption experiments and on-site desorption of shale in the Wufeng-Longmaxi formations. The main controlling factors of shale gas content in different occurrence states were identified as the following. The evaluation of shale gas content mainly includes the evaluation indexes of six categories and six parameters:direct index (measured gas content, gas detection value and gas saturation) and indirect indicators (porosity, resistivity and formation pressure) for gas qualitative and semi-quantitative evaluation system.

Vertical variation of rocks and minerals in Wufeng-Longmaxi formations in Fuling shale gas field, Sichuan Basin: A case study of well JYA

ZHANG Mengyin, LI Zheng, WANG Jin, HAN Chiyu, LIU Shuang, QIAN Hua

2018, 40(1): 64-70. doi: 10.11781/sysydz201801064

Abstract(1211) PDF-CN(291)

Abstract:
The Fuling shale gas field is the first to achieve commercial development in China. The well JYA in the Jiaoshiba area of Sichuan Basin was used as an example to study the vertical variation of rock and mineral composition based on thin section observation and scanning electron microscopy (SEM), and combined with X-ray diffraction of whole rock and organic carbon determination. The results showed that quartz and clay minerals are dominant in the Wufeng-Longmaxi shale, accounting for over 70%, followed by feldspar and carbonate, and a small amount of pyrite. From bottom to top, the contents of quartz, feldspar and pyrite gradually decrease, while that of clay minerals increases. The effects of shale mineral vertical variation on shale reservoir property, gas content and compressibility were discussed. With the increase of biogenic silicate and the reduction of clay mineral in vertical direction, the shale shows a tendency of increasing organic matter content, organic matter pore development, shale reservoir performance and shale gas content from top to bottom. At the same time, with the increase of brittle mineral content, the compressible property of shale is also gradually enhanced.

Problems of methane isothermal adsorption calculation in shale and method improvement

FANG Fan, SUN Chong, SHU Xiangwei, ZHU Zhongyun, FANG Zihe

2018, 40(1): 71-77. doi: 10.11781/sysydz201801071

Abstract(1231) PDF-CN(562)

Abstract:
The studies of isothermal adsorption of methane in shale are the basis for shale gas exploration. Some achievements have been made recently. However, a substantial proportion of the in-lab experiment curves are abnormal, and even drop down, indicating for adsorption amount decrease under high pressure. Some reasons were found based on the studies of isothermal adsorption curves, including improper calculation and simulation methods. For example, the difference between absolute and excess adsorption amounts and the influence of adsorption phase volume might be ignored. What's more, some improper methods were applied for measuring methane free volume, and equipment error also existed. A ternary Langmuir model was built based on the Langmuir isothermal adsorption equation, which took methane free volume as an unknown parameter while adsorption phase density was fixed. Free volume, Langmuir volume and Langmuir pressure were calculated with iterative method or Matlab software. Methane free volume calculated with the ternary Langmuir model has a good comparability with Helium. The simulation results obtained by this method can better correct the previous curve anomalies.

Element geochemical characteristics of the Wufeng-Longmaxi shale in Jiaoshiba area, Sichuan Basin and their significance to shale gas development

GAN Yuqing, WANG Chao, FANG Dongliang, YANG Lanfang, ZHOU Xinke, ZHANG Ping

2018, 40(1): 78-89. doi: 10.11781/sysydz201801078

Abstract(1393) PDF-CN(398)

Abstract:
A total of 85 shale core samples from wells JYA and JYD in Jiaoshiba area of Sichuan Basin were selected to test their organic carbon contents, major and trace elements. The redox conditions and paleoproductivity of the gas-bearing shale in the Wufeng-Longmaxi formations in the Jiaoshiba area were studied by analyzing the vertical variation characteristics of the major and trace elements in the profile. Meanwhile, the controls for organic matter enrichment in the Wufeng-Longmaxi formations were explored. Moreover, the impact of geochemical elements on shale compressibi-lity and gas-bearing property were studied. The organic carbon content in the high gas-bearing interval from the Wufeng Formation to the lower part of Longmaxi Formation is high with an average value of 3.07%. Compared with the common gas-bearing shale, SiO₂ and CaO contents are higher in the high gas-bearing shale, and redox-sensitive elements such as Mo, Cr, V, Ni, Th and U are enriched. The redox condition indicators such as V/Cr, V/Sc, U/Th and Ni/Co indicated that the Wufeng Formation was mostly deposited in suboxic to anoxic conditions, whereas the anoxic environment dominated during the early sedimentary stage of Longmaxi shale and evolved into aerobic conditions later on. The contents of biological productivity-related element Ba_(xs) reflected a high paleoproductivity, whereas TOC content has an obvious positive correlation with redox proxies (Mo/Al, U/Th, Ni/Co and V/Sc) in the high gas-bearing interval, suggesting that the enrichment of organic matter was predominantly controlled by redox environment. In addition, the biogenic siliceous content of high-quality gas-bearing shale is high, and the organic carbon content is positively correlated with the SiO₂ content, which is conducive to the formation of natural fractures and the later artificial fracturing. The ratio of geochemical elements in the high gas-bearing interval is significantly higher than that of common interval, indicating that there is a certain correlation between chemical element ratios and shale gas.

Characteristics and influencing factors of desorption gas in Wufeng-Longmaxi formations in Fuling area, Sichuan Basin

LI Kai, MENG Zhiyong, JI Jing, ZHENG Xiaowei, ZHANG Qian, ZOU Wei

2018, 40(1): 90-96. doi: 10.11781/sysydz201801090

Abstract(1311) PDF-CN(305)

Abstract:
Adsorption gas is the main form of shale gas, and research of the characteristics and influencing factors of desorption gas can guide the exploration and development of shale gas. The variation of desorption rate, the change of desorption gas volume and the difference of carbon isotopes were analyzed using desorption experiments of shale gas from Wufeng-Longmaxi formations in Fuling area in Sichuan Basin. The amount of natural gas desorbed within a certain time after a core is loaded into the desorber is measured and mainly reflects the amount of adsorbed gas and part of the free gas in the rock. The comparison with shale quality shows that the amount of desorbed gas is positively correlated with total organic carbon content, brittle mineral content, and the illite/smectite ratio in clay, but not related to illite content. It has a negative correlation with chlorite content. The amount of desorbed gas has a positive correlation with the micropore volume and possesses a good positive correlation with the mesopore volume, but not with the macropore volume.

Qualitative and quantitative study of micro-pore structures of Longmaxi Formation shale in Fuling area, Sichuan Basin

YANG Wenxin, LI Jiqing, ZHAO Jiangyan, HUANG Zhihong

2018, 40(1): 97-102. doi: 10.11781/sysydz201801097

Abstract(1539) PDF-CN(397)

Abstract:
The pore structure of Longmaxi shale in Fuling area of the Sichuan Basin is so complicated that conventional single test technology fails to accurately characterize the microscopic shale pores. The multi-scale microcosmic pore structure of Longmaxi shale in Fuling area was studied using SEM of an argon ion polished surface, pressure mercury-nitrogen adsorption, and nuclear magnetic resonance (NMR) analyses. The shale reservoirs in Jiaoshiba mainly contain gray black to black argillaceous siltstones and silty mudstones with three pore types:organic and inorganic pores, and micro-cracks. The pore size distribution of shale is of multiple-scales, most of which are micro pores and meso pores. Pore diameter < 20 nm accounts for over 80% of the total. Quantitative NMR analysis showed that the main layer pore radius of Longmaxi Formation shale is significantly greater than the non-main layer. The pore size distribution increased with well depth. On the plane, the areas where the pore diameter peak value of the main layer shale is > 2 nm, the porosity is > 3%, and the water saturation of < 40% showed favorable reservoir preservation conditions.

Structural features and preservation evaluation of shale gas reservoirs in the Fuling area, Sichuan Basin

LUO Bing, YU Fei, CHEN Yalin, DING Hongwei

2018, 40(1): 103-109. doi: 10.11781/sysydz201801103

Abstract(1595) PDF-CN(580)

Abstract:
The Wufeng-Longmaxi formations in the Fuling shale gas play contain abundant shale gas resources, but the multiple tectonic superimposition had an important impact on shale gas preservation conditions in the area. We systematically studied the structural features and preservation conditions of shale gas in the Fuling area by detailed structural interpretation. There are two structural systems with NE and EW trends in the area, mainly formed in the late Yanshanian. Multi-level detachment structures were developed in the study area due to multi-phase tectonic movements. The detachment structures can be vertically divided into 3 different structural deformation layers. Structural style, fracture scale, erosion extent and fracture density were used as the main evaluation indicators for structural deformation, and the Fuling area was divided into the eastern and western belts. The structural deformation of the western belt was relatively weak, and the preservation conditions were relatively better. For further clarifying the favorable areas for shale gas development, a quantitative characterization method of preservation conditions was established by means of structural deformation characterization and reservoir prediction. According to evaluation results, three target units including Jiangdong, Pingqiao and Zilichang were selected in the western belt, and two target units including Baima and Baitao were selected in the eastern belt.

Formation pressure prediction and high pressure formation mechanisms of shale reservoirs in Fuling area, Sichuan Basin

CHEN Yalin, YU Fei, LUO Bing, ZOU Xianjun

2018, 40(1): 110-117. doi: 10.11781/sysydz201801110

Abstract(1615) PDF-CN(359)

Abstract:
Formation pressure is one of the important indicators to reflect shale gas preservation conditions, and is also an important factor affecting shale gas production. In the Fuling shale gas field, which has complex structure characteristics and variable formation pressure distribution, it is particularly important to accurately predict the formation pressure in shale gas exploration and development. The Eaton method was a preferred method for the prediction of formation pressure in the Fuling shale gas field based on the systematic analysis of the existing prediction methods. Combined with the geologic characteristics of Fuling area, the established method for normal compaction trend (NCT) lines was improved through vertical segmentation, plane partitioning and multi-well combination. It improved the accuracy of single well pressure prediction. The accuracy of 3D formation pressure prediction was improved by high-precision seismic layer velocity processing with generalized linear inversion. Based on the acoustic velocity-density intersection diagram and organic matter evolution characteristics and structural features, the paper explored the high pressure formation mechanisms of shale intervals in the Fuling area. It was concluded that the abnormal pressure in the Silurian shale formations in the Fuling area was the result of the combined effect of three mechanisms:undercompaction, hydrocarbon generation and tectonic compression.

Heterogeneity characteristics and controlling factors of black shale in Jiaoshiba, Fuling, Sichuan Basin

LIU Meng, LIU Chao, SHU Zhiheng, LU Yongchao, GU Qian, TAN Congwen, XU Xiang

2018, 40(1): 118-125. doi: 10.11781/sysydz201801118

Abstract(1105) PDF-CN(353)

Abstract:
The study of macroscopic and microscopic heterogeneity of shale is one of the core aspects of shale gas exploration and development. The black shale in Jiaoshiba area in Fuling of Sichuan Province can be divided into two third-level sequences and nine sub-layers. The macroscopic heterogeneity mainly shows as follows. Laminations decrease first and then increase from bottom to top, sandy bands first increase and then decrease, while pyrites gradually decrease. Graptolithina in the transgressive system tract is mainly diplograptus type, while those in the early and late high system tracts are mainly monograptus type. Graptolithina abundance gradually reduces from bottom to top. The microscopic heterogeneity mainly shows as follows. TOC content in the transgressive system tract is the highest, and then decreases upwards, while clay mineral content gradually increases from bottom to top. On the whole, three kinds of sedimentation, bio-current, isochronous flow and terrigenous source, jointly controlled the heterogeneity of black shale in the Jiaoshiba area.

Preservation mechanism of Fuling shale gas

FAN Ming, YU Lingjie, ZHANG Wentao, LIU Weixin, XU Ershe, YANG Zhenheng

2018, 40(1): 126-132. doi: 10.11781/sysydz201801126

Abstract(1553) PDF-CN(521)

Abstract:
The essential difference between conventional gas and shale gas in reservoir space is the difference in pore size or pore structure. The shale burial history, gas content, production data and isotope fractionation of desorbed gas in the Jiaoshiba area of Fuling, Sichuan Province indicate that shale gas was stored in the inter-connected pore units formed by single or multiple organic matter types, and its preservation mechanism was attributed to capillary pressure and static water pressure. Therefore, tectonic structure or trap shape has little impact on shale gas enrichment. The destruction of shale gas preservation conditions by tectonic activity was mainly determined by the decrease of static water pressure caused by tectonic movements, the destruction of lamination caused by geologic stress, and the decrease of capillary sealing ability caused by the opening of lamellae under horizontal compression conditions. Faults releasing tectonic force would not cause further destruction of lamination. On the contrary, they might be helpful for the preservation of a footwall which could be the optimum shale gas target. The recovery ratio of shale gas could be derived from the theory of capillary pressure, which would supply guidance for production.

2018, 40(1): 133-133.

Abstract(465) PDF-CN(193)

Abstract:

2018 Vol. 40, No. 1

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