石油实验地质

2023, 45(6): .

Abstract(153) PDF-CN(38)

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Development progress and outlook of deep and normal pressure shale gas of SINOPEC

CAI Xunyu, ZHOU Dehua, ZHAO Peirong, ZHANG Hua, QIAN Keran, WAN Chenxiang

2023, 45(6): 1039-1049. doi: 10.11781/sysydz2023061039

Abstract(966) HTML (319) PDF-CN(162)

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In the past decade, with the improvement of shale gas exploration and development theory and techno-logy, the commercial development of marine shale gas from Ordovician Wufeng to Silurian Longmaxi formations in southern China has been achieved, and the target of shale gas exploration and development is gradually shifting towards shale gas of deep and complex structural areas and new formations. In order to further promote efficient exploration and development of shale gas, a systematic review was conducted on the recent exploration and deve-lopment progress of SINOPEC shale gas and an analysis was conducted on the development trend of shale gas in China. The research results indicate that: ① The high-quality Fuling National Shale Gas Demonstration Zone has been built and a key technology system for three-dimensional development of marine shale gas has been innovatively formed. ② The large-scale and efficient development of atmospheric shale gas in Dongsheng and Baima blocks of Nanchuan has been realized, and four shale gas accumulation and dispersion models have been constructed: anticline, monocline, reverse fault blocking, and residual syncline. A fine zoning and differentiated development model and a low-cost technology system for atmospheric shale gas have been preliminarily formed. ③ The deep large-scale fields of trillions of square meters in southeastern Sichuan basin edge have been preliminarily implemented, an "overpressure rich gas" model of marine deep shale gas has been innovatively formed, and a fracturing technology system of deep shale gas in the deep range of 4 000-4 500 m has been preliminarily formed. ④ Major breakthroughs have been made successively in Jurassic of Yuanba and Puguang, Permian of Hongxing and Puguang, and Cambrian of Jingyan and Qianwei. ⑤ The future breakthrough and development of shale gas cannot be achieved without innovative research on exploration and development theory and technology. The integration of exploration and development, geological engineering, and technology and economy must be adhered to. The complexity of deep, normal-pressured, and geological characteristics of new shale gas formations should be fully understood. In addition, policy support is also required.

Beneficial development practice and countermeasures of Baima block in Fuling shale gas field, Sichuan Basin

LIU Chao, BAO Hanyong, WAN Yunqiang, GAN Yuqing

2023, 45(6): 1050-1056. doi: 10.11781/sysydz2023061050

Abstract(353) HTML (171) PDF-CN(62)

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In recent years, while actively promoting the development and adjustment of high-pressure shale gas reservoirs such as Jiaoshiba shale gas reservoir, Fuling shale gas field has steadily expanded its development targets to Baima block and other complex structural blocks in order to ensure continuous and stable production capacity. Based on the strong structural deformation, complex geological conditions, low single-well productivity, and great development difficulty of Baima block, this paper deeply studies the tectonic deformation stages, stress field distribution characteristics, favorable targets, and development technical countermeasures of Baima block by means of fracture zone calcite U-Pb dating, three-dimensional stress field modeling, geoengineering integration evaluation and other technical methods, and has made positive progress: it is suggested that the thrust nappe force is the main controlling factor of the deformation difference of marine normal pressure shale gas reservoirs in Fuling area; the evaluation parameter system of "two categories, six items" for development area selection is established, and the south of Baima syncline core is identified as the most favorable target for beneficial development; a differentiated development technology policy based on the development characteristics of natural fractures has been formed; the engineering process countermeasures based on different geological characteristics such as gas well buried depth, stress property and crack are formed. On the basis of the above understanding, and in accordance with the idea of "overall deployment, evaluation-construction integration, and platform replacement", 30 development well locations were deployed and implemented in 2021-2022, the average ROP was increased by 38%, the fracturing rate was increased by 2-3 times, the single stage fracturing cost was reduced to 850 000 yuan, the daily gas output was stable at 800 000 square meters, and the annual gas output reached 224 million square meters in 2022, basically realizing beneficial development.

Exploration and development practice of normal pressure shale gas in Dongsheng structural belt, Nanchuan area, southeast Chongqing

HE Xipeng, ZHANG Peixian, REN Jianhua, WANG Wei, LU Bi

2023, 45(6): 1057-1066. doi: 10.11781/sysydz2023061057

Abstract(329) HTML (174) PDF-CN(75)

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The Dongsheng structural belt in Nanchuan area, southeast Chongqing, is located in the transitional zone of the southeastern margin of Sichuan Basin. It has experienced multi-period tectonic reformation and has typical geological characteristics of complex structure, complex preservation conditions and complex in-situ stress field, which leads to a significant difference in single well production. In order to increase the single well production of normal pressure shale gas wells in Dongsheng complex structural belt and realize profitable development, through target processing of seismic data, analysis of structural characteristics, study of accumulation regularity and analysis of production dynamics, as well as the strengthening of basic research and exploration and development practice, four key technical countermeasures for realizing profitable development of normal pressure shale gas in Dongsheng complex structural belt are defined: (1) improve the accuracy of shallow velocity model and structure interpretation; (2) optimize well pattern deployment, increase well-controlled reserves; (3) integrate geology and engineering, and coordinate drilling, orientation and steering to improve the drilling rate of sweet spots; (4) establish a zonal differentiated fracturing scheme to improve fracture complexity. These four countermea-sures provide technical support for the profitable development of normal pressure shale gas in complex structural zones, and provide reference for the exploration and development of other similar areas along the basin margin.

Development practice and challenges of deep shale gas in southern Sichuan Basin

ZHAN Guowei, YANG Jian, ZHAO Yong, ZHANG Nanxi, WANG Baobao, LI Shuguang

2023, 45(6): 1067-1077. doi: 10.11781/sysydz2023061067

Abstract(480) HTML (230) PDF-CN(86)

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There is great potential for developing deep shale gas resources, but the engineering geological conditions are relatively poorer, making it difficult for benefit development. In order to support the benefit development of deep shale gas, taking the development practices of Weirong and Yongchuan gas fields in the southern region of Sichuan Basin as an example, focusing on the difficulties of complex deep shale gas structures, developed fractures, thin high-quality reservoirs, rapid production decline, and low EUR, with the goal of "good well placement, good well drilling, and good well management", a key development technology system is formed by use of the integrated method of geophysics, geological modeling, fracturing simulation, and numerical simulation based on the research on precise gas reservoir description and seepage experiments, which is characterized by geological sweet spot evaluation and prediction technology, well network optimization design technology in complex tectonic areas, "four in one" drilling tracking guarantee technology, and full life cycle production control technology. At the same time, based on the problems exposed during development process, the difficulties and challenges in the coupling mechanism of "structure-fault-stress field", characterization of small-scale and microscale fractures, optimization of development technology strategies were summarized, and the problems that need to be continuously studied were proposed. The conclusion is that: ① The geological parameters such as porosity and gas content of deep shale are basically equivalent to those of medium-deep strata, but the engineering parameters are more complex, characterized by high in-situ stress, high horizontal stress difference, and high fracture pressure, making it difficult to transform; ② Key supporting technologies in dessert evaluation and prediction, modeling-numerical simulation integration technology, and fine production management has been formed in deep shale gas, with good development results; ③ At present, deep shale gas is mainly faced with challenges such as casing deformation, pressure channeling, and EUR non-compliance. It is necessary to further advance technical research in geological fine evaluation, fluid migration patterns, and modeling-numerical simulation integration.

Progress and research direction of normal-pressure shale gas exploration and development in southeastern Chongqing

YUN Lu, GAO Yuqiao, GAO Quanfang

2023, 45(6): 1078-1088. doi: 10.11781/sysydz2023061078

Abstract(436) HTML (291) PDF-CN(84)

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There are high-pressure shale gas reservoirs and normal-pressure shale gas reservoirs in the Sichuan Basin and its periphery. In recent years, SINOPEC East China Oil & Gas Company takes technical research for normal-pressure shale gas in the complex tectonic regions of basin margin and the fold belt outside Sichuan Basin in southeastern Chongqing, makes significant progress in exploration and development of normal-pressure shale gas, and forms relatively perfect geological theory and technology series of normal-pressure shale gas after more than ten years of research. The normal-pressure shale gas has the characteristics of complex structure, very different preservation condition, and complex in-situ stress compared with high-pressure shale gas. The exploration and development progress and cognition of normal-pressure shale gas in southeastern Chongqing are systematically summarized from geological characteristics, enrichment laws and exploration and development efficiency: (1)The continental shelf facies in deep-water shelf controls the high-quality shale distribution of normal-pressure shale gas, the multistage tectonism controls the differential distribution of tectonic types, fractures and in-situ stress, and the preservation condition becomes better from east to west and from south to north; (2)Four accumulation-dispersion modes of normal-pressure shale gas were established to guide exploration deployment. In the basin margin area, three 100 billion cubic meters increasing reserves zones of Pingqiao, Dongsheng and Yangchungou were completed in the basin margin, and Nanchuan normal-pressure shale gas field was found. In the basin outside area, some favorable exploration targets were confirmed, such as Wulong Syncline, Daozhen Syncline, and Laochangping Anticline; (3)The development technology policy of normal-pressure shale gas was formulated, controlling factors of productivity were defined, and benefit development was realized.Through systematic summary of previous achievement understanding, exploration and development experience, the challenge was analyzed, and the research direction was cleared, to provide reference for normal-pressure shale gas benefit development in similar areas of South China.

Discussion on genesis and geological significance of "low resistivity and low gas content" of Longmaxi Formation shale in southeastern Sichuan

WEI Fubin, LIU Zhujiang, CHEN Feiran, YAN Wei, WANG Qiang

2023, 45(6): 1089-1096. doi: 10.11781/sysydz2023061089

Abstract(527) HTML (257) PDF-CN(85)

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In order to clarify the genesis of "low resistivity and low gas content" in the shale of Wufeng-Longmaxi formations and effectively guide the next step of shale gas exploration in Sichuan Basin, a detailed study on the problem based on a large number of drilling surveys, dissections, and analysis of laboratory test results in the entire area was carried out herein. Low-resistivity wells of Longmaxi Formation shale in this area can be divided into two types based on their electrical and geological characteristics, which are less than 1 Ω·m and 1-10 Ω·m. Shale gas wells with resistivity less than 1 Ω·m are basically gas-free and mostly dry wells with relatively concentrated distribution areas, mainly located in southwestern Sichuan and western Changning. The resistivity curve of the shale exhibits a "thin neck" characteristic, with a Raman reflectance generally above 3.70% and a high amplitude graphite peak. In addition, the variation range of resistance values in rock electrical experiments under different states is small, and they all exhibit extremely low to low resistance characteristics, indicating that the conductivity of the rock skeleton caused by graphitization is the main factor affecting this type of shale. The drilling distribution area of shale with resistivity in the range of 1-10 Ω·m is relatively wider, mainly with slight gas content, distributed both inside and outside the basin. The characteristics exhibited by its electrical properties, laser Raman, and rock electrical experiments are significantly different from those of shale less than 1 Ω·m. The resistance curve of this type of shale exhibits a "gradual" characteristic, with a measured Raman reflectance of around 3.50% by laser Raman spectroscopy. The laser Raman spectrum also does not show obvious graphite peak characteristics. This type of shale undergoes a wide range of changes in rock electrical experiments under two states: dry water and saturated water, with a change in shale resistivity of 7 to 20 times before and after drying, and exhibits medium to high electrical resistance characteristics, revealing a significant impact of shale water content on shale resistivity. Based on actual drilling data, it is believed that the deterioration of shale gas preservation conditions and the increase in water content are the main reasons for this type of low-resistivity well.

Potential and future exploration direction of marine shale gas resources in China

LI Min, LIU Yali, FENG Dongjun, SHEN Baojian, DU Wei, WANG Pengwei

2023, 45(6): 1097-1108. doi: 10.11781/sysydz2023061097

Abstract(750) HTML (259) PDF-CN(87)

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Marine shale gas, represented by the shale gas from Wufeng-Longmaxi formations in southern China, is the main field for shale gas exploration and development in China. In recent years, marine shale gas exploration and development have been constantly facing new problems and challenges. Expanding new fields of shale gas resources and increasing shale gas production are still top priorities. The distribution characteristics, resource potential, and favorable area prediction of shale gas in typical marine formations in China are sorted out, with the results as follows. The geological and recoverable resources of shale gas in Wufeng-Longmaxi formations in Sichuan Basin and its peripheral regions are (17.50-33.19)×10¹² m³ and (3.50-6.14)×10¹² m³, respectively, with deep shale gas resources accounting for over 50%, mainly distributed in the high and steep structural belt in eastern Sichuan and in the low steep structural belt in southern Sichuan. The geological and recoverable resources of shale gas in the Permian Wujiaping Formation are (8.7-24.6)×10¹² m³ and (1.3-3.7)×10¹² m³, respectively, with exploration potential in areas such as Kaijiang-Liangping, Longjuba, Jiannan, and Sanxing in eastern Sichuan. The geological and recoverable resources of shale gas in the Qiongzhusi Formation are (5.69-12.71)×10¹² m³ and (0.89-1.06) ×10¹² m³, respectively, with favorable areas mainly distributed in areas such as Jingyan-Jianwei-Weiyuan-Ziyang in southwestern Sichuan, Nanjiang in northern Sichuan, and Yichang in the middle Yangtze region. The ancient marine formations such as the Doushantuo Formation, Hongshuizhuang Formation, and Xiamaling Formation have certain potential of shale gas resources, which are potential continuation of shale gas resources. The favorable areas for shale gas in the Doushantuo Formation are mainly distributed in western Hunan and Hubei and southeast Chongqing, while the favorable areas for shale gas in the Hongshuizhuang Formation are mainly distributed in the Chengde-Kuancheng area of Hebei. The favorable areas for shale gas in the Xiamaling Formation are mainly distributed in the areas of Zhuozhou in Hebei, Fangshan, Mentougou, Changping in Beijing, and Lanqi-yingzi. Based on this, three suggestions are further proposed for the future exploration direction of marine shale gas: the first is to focus on deep to ultra-deep and normal pressure shale gas, move towards new layers, and expand the field of shale gas exploration; the second is to deepen and enrich the exploration theory of deep to ultra-deep shale gas, normal pressure shale gas, and shale gas of new layer in the new area; the third is to focus on the improvement and innovation of deep to ultra-deep shale gas drilling and production technology and supporting equipment, and reduce the drilling and production costs of single wells of normal pressure shale gas.

Typical difference analysis and benefit-oriented development countermeasures of normal and high pressure shale gas in southeastern Chongqing

ZHOU Dehua, HE Xipeng, ZHANG Peixian

2023, 45(6): 1109-1120. doi: 10.11781/sysydz2023061109

Abstract(382) HTML (202) PDF-CN(68)

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Southeastern Chongqing is located in the transition zone of the southeastern margin of Sichuan Basin. Shale gas reservoirs of normal and high pressure are developed in this area. In order to promote normal pressure shale gas development benefits, starting from the typical difference analysis of normal and high pressure shale gas, through the research of drilling, core observation, experimental analysis, accumulation conditions, and production dynamics, combined with shale gas exploration and development practices in southeastern Chongqing, it is clarified that the normal pressure shale gas has the typical geological characteristics of small thickness of high-quality shale, low porosity, poor preservation conditions, and medium gas content. The accumulation of normal pressure shale gas is controlled by sedimentary facies, preservation conditions, and in-situ stress field. Affected by multi-stage structural transformation and differential uplift, the mechanism of normal pressure shale gas generation is complex, which has the characteristics of low initial production, short stable production period, slow decline, and high flowback rate. There are obvious differences between normal and high pressure shale gas in geological characteristics, enrichment regularities, generation mechanism, and production law. Considering the poor grade of normal pressure shale gas resources in southeastern Chongqing, four key countermeasures for the benefit-based development of normal pressure shale gas are put forward: (1) The basic geological research is furthered and the enrichment regularities and sweet spots are clarified. (2) The development technology of variable well spacing, long horizontal section, small inclined angle, strong transformation, low height difference and controlled pressure difference is established to increase the production of single well. (3) The innovation of engineering technology such as low-cost drilling and efficient fracturing is increased to achieve speed acceleration, efficiency improvement, and cost reduction. (4) The institutional mechanism is innovated and an efficient organization and operation mode is created. The four key countermeasures effectively promote the transformation of normal pressure shale gas from resources to reserves and from reserves to benefits, facilitating the efficient development of normal pressure shale gas in southeastern Chongqing.

Differences in preservation conditions of deep shale gas in high-steep complex tectonic belt: taking Qijiang high-steep complex tectonic belt in southeast Sichuan as an example

ZHANG Xuliang, LIU Zhujiang, CHEN Chao, SU Kelu, ZHANG Yuying, CHEN Feiran, ZHANG Di

2023, 45(6): 1121-1131. doi: 10.11781/sysydz2023061121

Abstract(399) HTML (182) PDF-CN(83)

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The southeastern Sichuan Basin is one of the key targets for shale gas exploration in China. Currently, the exploration has gradually been delved into deep and ultra-deep formation fields. However, due to various constraint factors such as drilling and earthquakes, research on the tectonic characteristics and shale gas preservation conditions in this area is inadequate. In order to find out the tectonic deformation characteristics of Qijiang high-steep complex tectonic belt in southeast Sichuan and its impact on the enrichment law of deep shale gas, and to provide a basis for subsequent exploration deployment, a high-steep structural model is established based on the analysis of tectonic deformation characteristics and practice drilling data, and the quantitative evaluation of the main controlling factors of differences in preservation conditions is carried out on the basis of the model. The research results show that: (1) Qijiang high-steep structure has the layered deformation feature of "steep upper part and flat lower part + dominated by gypsolyte + steep front"; (2)There is a widely developed Cambrian gypsum salt layer in the Qijiang area, whose plastic deformation controls the uplift of the overlying structure; (3) The factors affecting the preservation conditions of shale gas in the study area include active deformation strength, fracture system, normal stress of fault plane, angle between structure and geostress, roof detachment layer and other factors. The interaction of multiple factors leads to obvious differences in the preservation conditions in the study area. According to the analysis results, the evaluation criteria for the preservation conditions of Qijiang high-steep structures are established, and it is defined that the Longsheng-Taozidang tectonic belt has single tectonic stress, low active deformation intensity and well-closed structure, which is the main favorable target for the next exploration.

Progress of normal-pressure shale gas engineering technology in southeast Chongqing and the research direction of next steps

YAO Hongsheng, FANG Qilong, YUAN Mingjin, ZHANG Zhuang

2023, 45(6): 1132-1142. doi: 10.11781/sysydz2023061132

Abstract(400) HTML (155) PDF-CN(64)

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The normal-pressure shale gas block in southeast Chongqing is located in the transitional zone of the basin margin and the extrabasinal fold area, which has the geological characteristics of complex structure, large stress difference and low pressure coefficient, which brings great challenges to improve the efficiency and production of engineering technology. Shallow surface fractures and caverns are developed in this area, with many thief zones, and long drilling and completion period. The structural stress changes quickly and the difference coefficient is large, so it is difficult to form complex fracture network. The lack of formation energy and low drainage efficiency affect the continuous and stable production of gas wells. Therefore, with the goal of "increasing quality, speed, efficiency and yield", key technologies are innovated and implemented, and the benefits of engineering processes are created constantly. With the aim to "speed up, improve efficiency and reduce cost" in drilling projects, the normal-pressure shale gas drilling and completion technology is formed, which focuses on well structure optimization and drilling with optimized parameters, and integrates equipment and tools. The mechanical drilling rate increases by 14.90% per year, the drilling and completion period decreases by 10.67%, and the drilling cost decreases by 7.64%, setting multiple new records in the same period. Focusing on increasing efficiency and reducing cost of fracturing projects, fracture complexity is improved through "moderately close cutting + temporary plugging and turning", effective multi-scale support of fracture network is promoted by "high-strength sand injection + sand-ceramic particle size combination", low-cost fracturing materials and cost-reduced equipment and tools are integrated and applied, forming the characteristic fracturing process and supporting facilities of "complex fracture network + economic materials + intelligent fracturing equipment". The final EUR of one kilometer per well was increased from 34 to 45 million cubic meters, and the cost decreased by 34.6%. With the goal of "fine management of the whole life cycle, delay of decline, and efficiency improvement by tapping the potential", the full-life cycle drainage and gas production technology system of mechanical drainage such as early selection of pipe string, mid-stage foam drainage + compressor depressurized mining, late-stage single pipe jet pump and heavy-duty pump + liner pipe has been established, and precise policies have been implemented in different areas, classification and stages, and the annual decline rate of old wells has been reduced by 2.1%. The production time rate of the whole field increased from 95.9% to 98.7%. Through the research on the whole process of engineering technology, it strongly supports the efficient development of normal-pressure shale gas in southeast Chongqing, and provides beneficial reference for the efficient exploitation of other normal-pressure shale gas.

Practice and understanding of fracturing in Weirong shale gas field

YANG Yonghua, SONG Yangao, WANG Xingwen, LIU Lin, CI Jianfa, LIN Lishi

2023, 45(6): 1143-1150. doi: 10.11781/sysydz2023061143

Abstract(366) HTML (164) PDF-CN(56)

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Compared to the middle and shallow strata, the engineering geological characteristics of Weirong deep shale gas are more complex, with the four characteristics of high ground stress, high horizontal stress difference, high plasticity, and high formation pressure. The complex engineering geological characteristics bring three major challenges: difficulty in forming complex fracture networks, difficulty in supporting and maintaining artificial fractures, and frequent occurrence of abnormal situations such as casing deformation. The specific performance result is the low single well EUR after gas well fracturing. Through unremitting exploration and practice, the fracturing technology has been continuously improved in the process of discovering and solving problems, and a series of measures of "fine optimization, real-time warning, operating pace control, and W-shaped well network" for preventing casing deformation and increasing post fracturing output has been formed based on the concept of balanced fracturing. The technology has been promoted and applied in 39 wells, and the fracturing effect has been continuously improved, with an average EUR increase of 500×10⁴ m³ per well, and a decrease of casing deformation rate from 42.4% in 2022 to 16.67% at present. Due to the impact of the production of adjacent old wells on the production of newly fractured production wells, the output of new wells after fracturing is lower than the previous stage. With the existing well spacing of 400 m (Phase Ⅰ)/300 m (Phase Ⅱ), there is room for reduction and optimization in fracturing scale. Subsequent new wells should be differentiated and optimized based on remaining reserves, and research on fracturing technology shall be carried out continuously, achieving the beneficial development of Weirong deep shale gas.

Progress and development suggestions of deep normal pressure shale gas engineering technology

ZHANG Wenping, LI Shuangming, ZHANG Jincheng, ZHANG Yanyi, MIN Wenxuan

2023, 45(6): 1151-1159. doi: 10.11781/sysydz2023061151

Abstract(461) HTML (200) PDF-CN(58)

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Compared with the exploration and development of medium-shallow shale gas, deep shale gas is deeply buried, with complex structures and variable pressure systems, making it difficult to increase drilling speed. The reservoirs are of poor compressibility and it is difficult to transform the volume. How to improve drilling and completion efficiency and reduce drilling and completion costs is the largest challenge in achieving the economic benefits of deep shale gas development. In order to clarify the current technical level and existing problems of deep normal pressure shale gas drilling and completion, the technical indicators and progress of deep shale gas in drilling and completion engineering at home and abroad are summarized and analyzed in this paper and it points out the existing problems and puts forward suggestions. SINOPEC has realized the economic benefit development of deep normal pressure shale gas in blocks such as Weirong and Yongchuan and has basically formed a high-efficiency drilling technology system for long horizontal wells with low-cost high-performance oil-based drilling fluid, enhanced drilling parameters, high-torque positive displacement motor, personalized drill bit, precise guidance and efficient control of long horizontal wells, real-time drilling monitoring and intelligent optimization technology as the core. The maximum horizontal section length and one-trip footage have been extended to 4 386 m and 4 225 m respectively. However, compared with the advanced records in North America, there is still a certain gap between the life of positive displacement motor, stability and reliability of rotary steering tools, super one-trip drilling technology and ratio, and near-bit push tools. Therefore, it is necessary to research and develop the core tools to further improve the drilling efficiency. Due to the limitation of economic development benefits, the deve-lopment of deep shale gas in North America is less than 4 200 m. In China, we have broken through the 4 700 m deep shale gas fracturing technology and formed an independent 4 700 m deep shale gas fracturing technology system with fracturing technology, segmented tools, main materials, and monitoring technology as the core. However, for deep and ultra-deep shale in complex structural areas, it is difficult to form complex fracture nets. It is extremely necessary to further improve the fracture propagation mechanism, develop a fracturing fluid system with better drag reduction and 175 MPa fracturing equipment to break through the bottleneck of efficient fracturing technology for 4 700-6 000 m shale gas.

Application evaluation and promotion effect of normal pressure shale gas demonstration well in Nanchuan area in southeastern Chongqing

WANG Yunhai, HE Qing, ZHU Zhichao, LONG Zhiping, PENG Xing, CAO Jianshan

2023, 45(6): 1160-1169. doi: 10.11781/sysydz2023061160

Abstract(346) HTML (171) PDF-CN(47)

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Nanchuan area in southeastern Chongqing is rich in normal pressure shale gas resources, which is an important area for SINOPEC's shale gas exploration and development. Due to the complex geological conditions and imperfect engineering technology, the overall efficiency of drilling acceleration and efficiency improvement in this area can not meet the requirements for large-scale benefit-based development of normal pressure shale gas. Therefore, Yangye 54-3HF well in Yangchungou block in this area is selected as the first normal pressure shale gas demonstration well of SINOPEC to research and form a regional optimal and fast drilling and completion demonstration technology series. On the basis of systematic analysis of regional drilling technology difficulties, combined with basic research on formation pressure resistance characteristics and formation pressure system, the demonstration well research systematically explores key drilling technologies such as shallow formation leakage technology, well structure optimization technology, accelerating tool optimization technology, trajectory control and orientation technology, low-density strong plugging oil-based drilling fluid technology, and optimal fast completion technology. A low-cost, optimal, and fast drilling demonstration technology system with the core of shallow formation prospecting, large-capacity clean water drilling, optimized well structure, domestic acceleration tools, low-density and strong plugging oil-based drilling fluid, integrated geological engineering orientation, and low-pressure wellbore fast cementing technology is formed. The drilling period of the demonstration well is 19.96 d, which is the shortest drilling period in 4 500 m well depth in China, and the ROP is 24.88 m/h, which is 141.79% higher than the fastest ROP of 10.29 m/h in the similar well depth in the same region. The rate of drilling in high-quality shale is 100%, and the cementing quality is excellent, which has played a good demonstration and leading role. After the promotion and application, various technical and economic indicators such as the regional ROP and drilling period have been significantly improved, speeding up the exploration and development process of normal pressure shale gas in Nanchuan area. The practice of normal pressure shale gas demonstration wells in Nanchuan area has shown that the efficient drilling and completion technology series formed by the demonstration well research can meet the requirements of drilling acceleration and efficiency improvement in horizontal wells of normal pressure shale gas, effectively promoting the four improvements in petroleum engineering to a new level, and laying a technical foundation for the construction of similar gas fields around the Sichuan Basin, and helping achieve greater progress in stabilizing oil and gas production, reducing costs, and improving efficiency in the upstream industry in China.

Progress in deep shale gas engineering technology in Weirong gas field in southern Sichuan

WANG Xingwen, MIAO Weijie, HE Xinxing, XU Jian

2023, 45(6): 1170-1177. doi: 10.11781/sysydz2023061170

Abstract(459) HTML (192) PDF-CN(53)

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Weirong gas field is the first deep shale gas field in China, with the characteristics of "deep burial depth, thin high-quality reservoirs, high ground stress, high horizontal stress difference, high plasticity and high formation pressure". The engineering technologies of drilling, completion, fracturing, and drainage face challenges such as long drilling cycles, small renovation volumes, low complexity, and complex wellbore flow laws. In response to complex geological challenges, we continuously enhance geological understanding, deeply integrate gas reservoir geology and engineering technology, and continue to research the drilling and production engineering technology with the goal of reducing costs and increasing efficiency and breaking through the benefits of deep shale gas. After three rounds of exploration and optimization of drilling technology, we strengthen and improve mechanical drilling speed, reduce downhole complexity, and shorten drilling cycles. The optimization of fracture configuration in fracturing technology has increased the breadth of complex fractures, and the integration of large displacement expansion and high sand carrying has achieved the increase and support of fracture control volume. The drainage process is based on gas-liquid two-phase flow research to identify wellbore flow patterns, forming a decision-making method for the entire lifecycle drainage process. Finally, an engineering technology sequence focusing on "fine trajectory control for optimal and fast drilling", "balanced expansion of fractures for strong support fracturing", and "full cycle effective drainage" was formed, continuously promoting the process of benefit deve-lopment. With the deep shale gas development engineering technology proposed herein, an accumulated new production capacity of 2.5 billion cubic meters in Weirong gas field has been completed, providing valuable experience for deep shale gas engineering technology at home and abroad, as well as a direction for further exploration and research in ultra-deep shale gas development.

Numerical modeling of in-situ stress and prediction of favorable area of shale gas layer in Wufeng to Longmaxi formations, Nanchuan region, southeastern Chongqing

LIU Ming, YANG Ruiqing, YANG Fengli, LIU Haojuan, ZHANG Zhiping, WANG Wei, HU Panpan

2023, 45(6): 1178-1188. doi: 10.11781/sysydz2023061178

Abstract(415) HTML (198) PDF-CN(89)

Abstract:
Upper Ordovician Wufeng to Lower Silurian Longmaxi formations in Nanchuan region, as an important shale gas productive layer, is characterized by large shale thickness, deep burial depth, and complex in-situ stress with rapid direction changes. Therefore, the study of in-situ stress field is of significance for effective deve-lopment of shale gas in the study area. In order to clarify the characteristics and distribution of the in-situ stress field, the SHELLS finite element stress field modeling method, with faults, topography, heat flow, petrophysical parameters and boundary conditions as constraints, was used in the study of the stress field in the Wufeng-Longmaxi formations in the Nanchuan region.The results indicate that the maximum compressive horizontal principal stress is in thrust regime and that there are four principal stress directions and regions in general: NW-SE, NE-SW, near EW and near SN. The strain rate is in thrust regime, with three regions of low strain rate (magnitude ≤ -18), medium strain rate (magnitude between -18 and -17.6) and high strain rate (magnitude ≥ -17.6) and their corresponding NE-SW, NW-SE, SN and EW spreading directions. The fault slip rate regime is in thrust, the fault slip rates range from 0 to 0.001 2 mm/a. The modeled results of the maximum compressive horizontal principal stress, the strain rate and fault slip rate were compared with the measured data respectively, including the maximum compressive horizontal principal stress directions measured in drilled wells, the regime and magnitude of strain rate in Guizhou and Chongqing, and the properties of regional faults. The modeled results showed high agreement with the measured data, indicating the accuracy of the predicted results. Finally, based on fracture openness and fracture development revealed by modeled results, favorable fractured reservoir development zones for shale gas was evaluated, and class Ⅰ and Ⅱ zones for further exploration and development were predicted.

Drilling practice of marine shale gas in Permian Wujiaping Formation in Hongxing area of eastern Sichuan

LI Jun, LU Heping, HU Xianghui, WANG Li, ZHOU Qing, PENG Meng

2023, 45(6): 1189-1195. doi: 10.11781/sysydz2023061189

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Abstract:
Permian Wujiaping Formation in Hongxing area of eastern Sichuan is rich in high-quality shale, and multiple wells have achieved high productivity of industrial gas. It is an important replacement block for the natural gas production capacity of the Jianghan Oilfield. However, due to the complex structure and lithology, deep burial depth of the target layer, and large fluctuations in the attitude of thin reservoirs, complex situations such as well leakage and collapse occuring frequently, low mechanical drilling speed, long drilling cycles, and difficulty in ensuring the drilling rate of high-quality reservoirs seriously restrict the benefit development. Based on the summary of previous data, the drilling difficulties were analyzed, the optimal design of drilling engineering was carried out, and some key rock breaking tools were selected to optimize the density and sealing performance of drilling fluid. The "three opening" wellbore structure with three different diameters, "irregular tooth PDC and mixed drill bits + high torque equal wall thickness screw + reinforced parameter drilling", simple pressure control by a rotary control head, and low density and strong sealing drilling fluid technology for "both leakage and collapse treatment" were formed. We have established a geological engineering integrated guidance technology based on "vertical depth prediction, segmented slope control, and five charts and one table", and proposed the direction for further improvement. The on-site application shows that: (1) the "three opening" wellbore structure with three different diameters meets the safety drilling requirements in Hongxing area, laying the foundation for drilling speed increase. The parameter drilling was enhanced by high-performance PDC, and the mechanical drilling speed of each opening is significantly improved. The drilling speed of the third opening section in the Permian formation increased by 15%, and the horizontal section increased by 22%; (2) The density reduction and nano sealing drilling fluid technology effectively reduced the number and time of complex treatments, and the time for complex treatments was reduced by 20.5% compared to the early implementation of wells; (3) The penetration rate of high-quality reservoirs significantly increased to 93.27%, an increase of 19.85% compared to the previous period.

Method for identification of fractures in shale gas horizontal wells in eastern Sichuan Basin and its application

PENG Yongmin, DONG Shixiong, BIAN Ruikang, DU Wei, QIAO Hui, LIU Zengqin

2023, 45(6): 1196-1203. doi: 10.11781/sysydz2023061196

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Abstract:

The relationship between fractures and gas logging in Nanchuan-Wulong area in eastern Sichuan Basin is utilized to study the identification of fractures in shale gas horizontal wells based on geological (core), imaging logging, logging evaluation, seismic prediction, and other data. First, to solve the problems of lack of core and imaging logging and difficulty in identifying natural fractures in shale gas horizontal wells, a core scale shale natural-fracture identification model is established through vertical wells from a geological perspective in this paper, and the development of high angle fractures in the core is consistent with the high values and peaks of total hydrocarbon anomalies. Second, in combination with the fracture identification mode, the fracture development section of non-coring vertical wells can be quickly and qualitatively identified at a low cost based on total hydrocarbon information. There will be a sudden increase in the total hydrocarbon value in the fracture development section, especially in the shale section with low total organic carbon (TOC). The sudden increase in the total hydrocarbon value also represents the existence of fractures. Finally, the plate method of TOC and normalized total hydrocarbon correlation is used to quantitatively identify vertical and horizontal well fracture sections without coring and imaging logging data. The area delineated by a normalized total hydrocarbon value ≥0.4 and TOC ≥0.5% are considered as the fracture development section of a horizontal well. Based on the identified horizontal well fracture section, from the perspective of geological engineering integration, it is possible to avoid or pay attention to these densely developed large or giant fractures in advance, thereby increasing the production of a single well.

Pore structure and free gas transport characteristics of deep shale: taking Longmaxi Formation shale in Sichuan Basin as an example

WAN Chengxiang, GUO Xusheng, SHEN Baojian, CHANG Jiaqi, XUE Zixin, DU Wei

2023, 45(6): 1204-1214. doi: 10.11781/sysydz2023061204

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Abstract:
Deep shale gas is an important research direction for increasing shale gas storage and production in the Longmaxi Formation of Sichuan Basin. But there are differences in reservoir and seepage characteristics between shallow and medium-buried shale gas, which to some extent limits the progress of exploration and development of deep shale gas. In order to clarify the pore structure characteristics of deep shale gas reservoirs and the transport characteristics of shale free gas, this paper takes the high-quality shale of Longmaxi Formation in southern Sichuan as an example to carry out experiments on observing and quantitatively characterizing the pore structure of shale reservoirs. In addition, based on the transport mechanism of bulk gas, the transport characteristics, critical conditions, and dynamic evolution laws of shale free gas were explored. The experimental and computational results indicate that: (1) The pore morphology characteristics of deep shale reservoirs are not significantly different from those of shallow and medium-buried shale, but the pore structure characteristics of medium pores are more obvious, with pore volume accounting for 62.5%-69.7%; (2) The transport modes of deep shale free gas are divided into three types: transitional flow, slippage flow, and Darcy flow. The critical pore sizes of the three modes in the Yongchuan area are 4.2 nm and 420 nm, respectively. On this basis, a transport chart for free gas in the entire basin has been established; (3) From shallow to deep shale, the critical pore size corresponding to different transport modes of free gas decreases accordingly. The main transport mode of free gas changes from the transitional flow (up to 63.0%) to the slippage flow (up to 67.3%) and the Darcy flow accounts for no more than 2%. The transport capacity of free gas rapidly decreases from shallow to medium-buried shale, while the transport capacity of medium to deep shale free gas remains basically stable with increasing burial depth. By analyzing and comparing the pore structure characteristics and free gas transport characteristics of deep and shallow shale reservoirs, this study can effectively support the deployment of efficient exploration and development plans for deep shale gas and even shallow shale gas in the next step.

Method of estimating the effective fracture volume of shale gas wells using flowback data and its application

WANG Yimin, LI Jiqing, WAN Yunqiang, LIU Li, ZHANG Qian, ZHU Chaoguang, TANG Yawan

2023, 45(6): 1215-1220. doi: 10.11781/sysydz2023061215

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The fracture network parameters of multiple-fractured horizontal wells in shale gas reservoirs are usually obtained by interpretation of gas production data. However, it is difficult to obtain the effective fracture volume. In order to quickly obtain the effective fracture volume of shale gas wells, a fracturing fluid flowback model for multiple-fractured horizontal wells in shale gas reservoirs was established. Combining the water phase material balance equation and seepage equation, the expression for the effective fracture volume of multiple-fractured horizontal wells in shale gas reservoirs was derived. Analyzing the model solution, it was found that when water flowing enters the boundary dominated flow stage, the curve of the rate-normalized pressure and material balance time is a unit slope line in the double logarithmic coordinate. By using the rate-normalized pressure and material balance time data at this stage, the effective fracture volume of shale gas wells can be estimated. Based on this, a method for estimating the effective fracture volume of shale gas wells using fracturing fluid flowback data was proposed. The application examples showed that: (1) the fracturing fluid flowback model for multiple-fractured horizontal wells in shale gas reservoirs can quickly and reliably estimate the effective fracture volume of shale gas wells, and the results are credible; (2) the fracturing fluid flowback data during the gas testing period should be considered when estimating the effective fracture volume of shale gas wells, otherwise the results would be smaller than the actual results; (3) the proposed method can also be a means of recognizing and quantifying the fracturing interference effect of adjacent wells on the effective fracture volume of shale gas wells. The research results provide a new method for estimating the effective fracture volume of shale gas wells, and also provide a new idea and method for recognizing the fracturing interference of adjacent wells in oilfields.

Application of measurement and control technology in deep and normal pressure shale gas exploration and development

GE Xiang, LIU Wei, SUN Xin, WANG Chunwei, MA Lin

2023, 45(6): 1221-1230. doi: 10.11781/sysydz2023061221

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Abstract:
Deep and normal-pressure shale gas is the key field of shale gas exploration and development of SINOPEC. At present, this type of shale gas is faced with difficulties in the beneficial development. In order to increase the productivity of single well and further reduce cost and increase efficiency, higher technical requirements are put forward for wellbore measurement and control technology. In order to accurately evaluate shale gas reservoirs, quantitative characterization of reservoir micro-characteristics, prediction of pore pressure coefficient, calculation of gas content, evaluation of low-resistivity shale, and compressibility evaluation of shale gas reservoirs have been carried out, forming a relatively mature shale gas "double sweet spots" fine evaluation technology. In order to improve the drilling rate of deep high-quality shale, a working model integrating directional drilling, mud logging, logging and steering is created. Based on multi-attribute geological modeling and well-to-seismic integration, the geosteering technology for horizontal wells in complex structural areas is formed. According to the difference of geological characteristics in different blocks, the application scopes of the two drilling speed improvement technologies, namely rotary steering and screw + MWD, are defined, thus realizing targeted measures for speed improvement. To meet the requirements of large-scale volumetric fracturing, a number of technologies such as multi-stage perforating bridge plug combined operation, equal aperture perforation, high temperature underground microseismic monitoring and "tractor + DAS fiber" fracturing monitoring have been developed and applied. The shale gas "double sweet spots" fine evaluation technology, the technology for improving reservoir drilling rate, and the technology for increasing drilling speed and fracturing performance have been widely used in deep and normal-pressure shale gas field, which well support the exploration and development of deep and normal-pressure shale gas. Next, SINOPEC will give full play to its advantages in the technology integrating directional drilling, mud logging, logging and steering, continue to promote measurement and control technology innovation, and continue to solve key problems in the interpretation and evaluation technology of new formations/new types of shale gas, the development of high-temperature measurement and control instruments and tools, and the acquisition of basic data, so as to fully guarantee the high-quality exploration and cost-effective development of deep and normal-pressure shale gas.

2023, 45(6): 1231-1231.

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2023, 45(6): 1232-1232.

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2023 Vol. 45, No. 6

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