原位注热开采下裂缝形态对油页岩层热解影响分析

Effect of fracture morphology on pyrolysis of oil shale layer under in-situ heat injection mining

摘要

针对油页岩原位注热开采过程中裂缝形态对储层热解的影响效果不明，无法准确判断实际热解效率的难题。以抚顺油页岩储层为研究对象，采用数值模拟方法，建立了热-流-固三场耦合的数值模型，验证了模型的可靠性，探究油页岩2种裂缝形态（水力压裂裂缝、平行层理裂缝）注热开采过程的差异性，得到储层温度、注汽压力、地层垂直位移及上下岩层温度随注热时间变化规律。结果表明:在平行层理裂缝中油页岩储层存在多条热解路径，而水力压裂裂缝中油页岩储层基于网状高温通道均匀热解；水力压裂裂缝相较于平行层理裂缝具有更好的连通性，仅需50 d油页岩层平均温度可以达到有机质热解所需温度；开采结束后，平行层理裂缝与水力压裂裂缝模型地层最大垂直位移分别为0.14、0.12 m，距离注热井越近的岩层垂直位移越大；上下岩层由于油页岩层热量逸散所形成的高温（＞100 ℃）区域面积分别为521.11、650.93 m²，水力压裂裂缝模型热量损耗更多。现场油页岩原位注热开采时需合理调节注热时长并使水力裂缝远离油页岩储层上下边界，避免高温高压蒸汽热量耗散。

Abstract

In view of the problem that the influence of fracture morphology on reservoir pyrolysis during in-situ thermal injection and exploitation of oil shale is unknown，and the actual pyrolysis efficiency cannot be accurately judged. Taking Fushun oil shale reservoir as the research object，a numerical simulation method was used to establish a numerical model of thermal-fluid-structure coupling，which compared with the previous results to verify the reliability of the model，explore the difference in the heat injection and exploitation process of the two fracture morphologies （hydraulic fracturing fracture and parallel stratum fracture） in oil shale，and obtain the variation law of reservoir temperature，steam injection pressure，vertical displacement of formation and upper and lower rock layer temperature with heat injection time. The results show that there are multiple pyrolysis paths in oil shale reservoirs in parallel fractures，while oil shale reservoirs in hydraulic fracturing fractures are uniformly pyrolyzed based on network high temperature channels. Compared with parallel fractures，hydraulic fracturing fractures have better connectivity，and the average temperature of oil shale layer can reach the temperature required for organic matter pyrolysis in only 50 days. After the end of mining，the maximum vertical displacement of parallel strata fracture and hydraulic fracturing fracture model strata was 0.14 m and 0.12 m，respectively，and the vertical displacement of the rock layer closer to the heat injection well was greater. The areas of high temperature （＞100 ℃） formed by the heat dissipation of oil shale layer in the upper and lower rock formations are 521.11 m² and 650.93 m²，respectively，and the heat loss in the hydraulic fracturing fracture model is more. During the in-situ heat injection exploitation of on-site oil shale，it is necessary to reasonably adjust the heat injection time and keep the hydraulic cracks away from the upper and lower boundaries of the oil shale reservoir to avoid high temperature and high pressure steam heat dissipation.

关键词

油页岩 / 原位注热开采 / 裂缝形态 / 平行层理裂缝 / 水力压裂裂缝

Key words

oil shale / in-situ heat injection mining / crack morphology / parallel bedding fractures / hydraulic fracturing crack

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基金资助

国家自然科学基金资助项目(51874165)

辽宁省兴辽英才计划资助项目(XLYC1902106)