深层页岩微观力学特征及控制机理——以涪陵地区平桥区块JYA井深层页岩为例

Micromechanical characteristics and controlling mechanism of deep shale: a case study of well JYA in Pingqiao block, Fuling area

孔令运 宋广朋 蒋恕 王子航 李继庆 时贤

KONG Lingyun SONG Guangpeng JIANG Shu WANG Zihang LI Jiqing SHI Xian

1. 中国地质大学(武汉) 油气勘探开发理论与技术湖北省重点实验室, 武汉 430074; 2. 中国地质大学(武汉) 构造与油气资源教育部重点实验室, 武汉 430074; 3. 中国石化 江汉油田分公司 勘探开发研究院, 武汉 430223; 4. 中国石油大学(华东) 石油工程学院, 山东 青岛 266580

1. Hubei Provincial Key Laboratory of Oil and Gas Exploration and Development Theory and Technology, China University of Geosciences (Wuhan), Wuhan, Hubei 430074, China; 2. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences (Wuhan), Wuhan, Hubei 430074, China; 3. Exploration and Development Research Institute, Jianghan Oilfield Company, SINOPEC, Wuhan, Hubei 430223, China; 4. College of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China

四川盆地涪陵地区深层页岩气具有构造复杂、地应力高、地应力差大、地层温度高、致密化程度高、低孔低渗、孔渗变化规律复杂等地质特征，不同井之间产量差异大，原因之一是对于深层页岩气储层的地质力学特征和控制机理认识不足，适合压裂的甜点区间识别不准确。因此，对涪陵地区五峰组—龙马溪组海相页岩进行研究，围绕深层页岩气储层的微观地质力学特征与控制机理这一关键科学问题，通过微观岩石力学实验、数字光斑实验、X射线衍射、总有机碳含量、SEM扫描电镜等5个系列实验设计，结合数字图像处理技术，精细刻画了龙马溪组页岩在加载条件下的应力场和位移场变化及微观裂纹扩展过程，分析了龙马溪组页岩的变形与破裂特征。实验测得深层页岩总有机碳含量约为4.2%，石英含量为55.4%，黏土矿物含量为26.9%，明确了深层页岩的微观损伤变化的5个过程，即压密、弹性、裂纹均匀扩展、裂纹扩展破坏及脆性破坏。在石英等脆性矿物及有机质等软组分的控制作用下，深层页岩微观破裂具有多种裂缝扩展模式。同时，计算了深层页岩样品的断裂韧性指数，其中Ⅰ型断裂韧性指数为18.279 MPa·√m,Ⅱ型断裂韧性指数为1.243 MPa·√m。实验得到的断裂韧性指数可应用于评价深层页岩的脆性，也可为深层页岩的压裂改造提供指导。

The deep shale gas in the Fuling area is characterized by complex structures, high crustal stress, significant stress differences, high formation temperatures, high compaction levels, low porosity, low permeability, and complex porosity-permeability variation patterns. One reason for the significant production differences between wells is the insufficient understanding of the geomechanical features and controlling mechanisms of deep shale gas reservoirs, and the inaccurate identification of sweet spots for hydraulic fracturing. This study focuses on the marine shale of the Wufeng-Longmaxi formations in the Fuling area, investigating the micromechanical characteristics and controlling mechanisms of deep shale gas reservoirs through five series of experiments: micro rock mechanics experiments, digital speckle experiments, X-ray diffraction, total organic carbon content measurement, and scanning electron microscopy (SEM). Coupled with digital image processing technology, the changes in stress field and displacement field, and microcrack propagation processes in the Longmaxi shale under loading conditions were meticulously depicted. The deformation and fracture characteristics of the Longmaxi shale were analyzed. Experimental results indicated that the total organic carbon content in the deep shale is approximately 4.2%, with quartz content at 55.4% and clay mineral at 26.9%. The study identified five stages of microdamage evolution in deep shale: compaction, elasticity, uniform crack propagation, crack propagation failure, and brittle failure. Under the influence of brittle minerals such as quartz, and soft components such as organic matter, the microcracks in deep shale exhibit various propagation modes, including transgranular, intergranular, and laminated layer cracks. Additionally, the fracture toughness indices of the deep shale samples were calculated, with Mode Ⅰ index being 8.279 MPa·√m and Mode Ⅱ index being 1.243 MPa·√m. These experimentally obtained fracture toughness indices can be applied to evaluate the brittleness of deep shale, providing guidance for deep shale fracturing modification.

国家自然科学基金(42130803)、国家自然科学基金面上项目(42072174)和湖北省自然科学基金(2023AFB110)联合资助。

https://doi.org/10.11781/sysydz202404683