基于二维裂缝网络数值模拟的干热岩储层热采效率评价  

Evaluation on the heat extraction efficiency of hot dry rock reservoirs based on two-dimensional fracture network numerical simulation

作　　者：唐宜家 马天寿[2] 陈力力 张玉婷 王锐 TANG Yijia;MA Tianshou;CHEN Lili;ZHANG Yuting;WANG Rui(Engineering Technology Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610052,China;State Key Laboratory of Oil&Gas Reservoir Geology and Exploitation//Southwest Petroleum University,Chengdu,Sichuan 610500,China;Engineering Technology Department,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610051,China)

机构地区：[1]中国石油西南油气田公司工程技术研究院 [2]“油气藏地质及开发工程”国家重点实验室·西南石油大学 [3]中国石油西南油气田公司工程技术处

出　　处：《天然气工业》2022年第4期94-106,共13页Natural Gas Industry

基　　金：四川省杰出青年科技人才项目“深层页岩水平井井壁稳定流固化热耦合弹塑性有限元模拟”(编号:2020JDJQ0055)。

摘　　要：增强型地热系统(EGS)的热采效率评价方法是实现干热岩储层热能效益开发的重要手段。为了评价干热岩储层热采效率,基于质量守恒和能量守恒定律,综合考虑复杂裂缝网络、水力裂缝、井筒效应等因素影响,建立了二维随机裂缝网络干热岩储层热采数值模型,并采用有限元方法对模型进行求解;通过对比单裂缝热采解析解和数值模拟结果,验证了模型准确性;并进一步分析了水力裂缝开度,天然裂缝开度、走向、长度、密度,以及裂缝网络连通漏失性断层对EGS热采效率的影响规律。研究结果表明:①与单裂缝热采解析模型相比,数值模拟得到的产出温度最大误差为7.54%,满足热采模拟要求;②水力裂缝开度越大、天然裂缝开度越小,热采效率越高;③天然裂缝长度、密度和走向均能导致缝网连通性增强,流体容易向裂缝网络漏失而无法产出,导致热采效率降低;④裂缝网络在连通漏失性断层的情况下,会造成流体向断层的恶性漏失,导致热采效率变差。结论认为,EGS设计和开发需要避开漏失性断层,采取有利于降低天然裂缝网络连通性的措施,该成果认识有助于指导干热岩储层井位部署、压裂设计与采热工艺措施优化。The evaluation method of heat extraction efficiency of enhanced geothermal system(EGS)is an important way to achieve the benefit development of geothermal energy from hot dry rock reservoirs.In order to evaluate the heat extraction efficiency of hot dry rock reservoirs,this paper establishes a numerical model of heat extraction from hot dry rock reservoirs with two-dimensional stochastic fracture networks based on the laws of conservation of mass and energy by considering the influence of complex fracture networks,hydraulic fractures,wellbore effect and other factors comprehensively,which is solved by means of the finite element method.Then,the accuracy of the model is verified by comparing the analytical solution of single-fracture heat extraction with the numerical simulation results.Finally,the influences of hydraulic fracture aperture,natural fracture aperture,strike,length and density,and leakage faults connected with fracture networks on the heat extraction efficiency of EGS are further analyzed.And the following research results are obtained.First,the maximum error of output temperature by numerical simulation is 7.54%compared with that by the single-fracture heat extraction analytical model,which meets the requirements of heat extraction simulation.Second,the larger the hydraulic fracture aperture and the smaller the natural fracture aperture,the higher the heat extraction efficiency.Third,natural fracture length,density and strike can all enhance the connectivity of fracture networks,so that the fluid easily leaks into the fracture network and cannot be produced,leading to the reduction of heat extraction efficiency.Fourth,when the fracture network is connected to the leakage fault,it will cause massive leakage of fluid to the fault,leading to the deterioration of heat extraction efficiency.In conclusion,in the design and development of EGS,leakage faults shall be avoided and measures should be taken conducive to reducing the connectivity of natural fracture networks.The research results provide guidance

关 键 词：干热岩 增强型地热系统 离散裂缝网络 随机裂缝 井筒传热 热采模拟 热采效率 断层 

分 类 号：P314[天文地球—固体地球物理学]