基于嵌入式离散裂缝模型的增强型地热系统热—流—力—化耦合分析  

Analysis of thermal-hydraulic-mechanical-chemical coupling for EGS based on embedded discrete fracture model

作　　者：韩东旭 张炜韬 焦开拓 宇波[1] 李庭宇 巩亮[2] 王树荣[5] HAN Dongxu;ZHANG Weitao;JIAO Kaituo;YU Bo;LI Tingyu;GONG Liang;WANG Shurong(School of Mechanical Engineering,Beijing University of Petrochemical Technology,Beijing 102617,China;School of New Energy,China University of Petroleum(East China),Qingdao,Shandong 266580,China;State Key Laboratory of Power Engineering Multiphase,Xi'an Jiaotong University,Xi'an,Shaanxi 710049,China;Low-Speed Aerodynamics Research Institute,China Aerodynamics Research and Development Center,Chengdu,Sichuan 621050,China;State Key Laboratory of Efficient and Clean Energy Utilization,Zhejiang University,Hangzhou,Zhejiang 310058,China)

机构地区：[1]北京石油化工学院机械工程学院 [2]中国石油大学(华东)新能源学院 [3]西安交通大学动力工程多相流国家重点实验室 [4]中国空气动力研究与发展中心低速空气动力研究所 [5]浙江大学能源高效清洁利用全国重点实验室

出　　处：《天然气工业》2023年第7期126-138,共13页Natural Gas Industry

基　　金：国家自然科学基金重点基金“增强型地热系统热—流—力—化四场耦合热质传输机理研究”(编号:51936001);能源高效清洁利用全国重点实验室开放基金课题(编号:ZJUCEU2022001)。

摘　　要：增强型地热系统(以下简称EGS)在长期取热过程中会受到流(Hydraulic)、热(Thermal)、力(Mechanical)、化(Chemical)等多种物理场的综合作用影响。虽然嵌入式离散裂缝模型(以下简称EDFM)能够有效模拟裂缝型储层中流场、温度场、力场和浓度场的变化,但目前基于EDFM的热—流—力—化(以下简称THMC)四场耦合的相关研究和认识还不足。在考虑储层非均质性、物性参数变化和水—岩反应的基础上,基于EDFM建立了裂缝型储层的THMC四场耦合模型,对EGS运行过程中的流场、温度场、位移场和浓度场的时空演化进行了模拟分析。研究结果表明:(1)当基岩渗透率较低时,开采温度下降缓慢,EGS可维持较长年限的较高开采温度,但渗透率较低时会造成开采井质量流率减小,进而影响净取热功率;(2)当裂缝渗透率或裂缝开度发生改变时,EGS均可维持一定年限的较高温度稳定输出,随后出现不同幅度的下降,但当裂缝渗透率增大到一定值或者裂缝开度减小到一定值时,改变裂缝参数对开采温度的影响减弱;(3)当EGS运行40年时,采用变物性流体比采用常物性流体计算的开采温度偏低22℃,而考虑水—岩反应的开采温度偏低了15℃,储层平均孔隙度值增大12.5%。结论认为:(1)在对长期运行的EGS进行研究时,应综合考虑储层岩石参数、注入流体物性以及水—岩反应等因素的影响;(2)未来应考虑储层其他矿物组分的化学反应、力学变形对流—热—化三场影响的双向耦合,以便为EGS储层的工程开发和利用提供更准确、可靠的预测。Enhanced geothermal system(EGS)is subject to the comprehensive effects of multiple physical fields during the long-term heat extraction process,including hydraulic(H),thermal(T),mechanical(M)and chemical(C)fields.The embedded discrete fracture model(EDFM)can effectively simulate the variations of flow,temperature,mechanical and concentration fields in fractured reservoirs.At present,however,the thermo-hydro-mechanical-chemical(THMC)coupling model is less researched.In this paper,the THMC coupling model of fractured reservoir is established based on EDFM by considering the changes in reservoir heterogeneity and physical properties as well as water-rock reactions.Then,the spatiotemporal evolution of flow,temperature,displacement and concentration fields in the operation process of EGS is simulated and analyzed.And the following research results are obtained.First,when matrix permeability is lower,the production temperature declines slowly,and EGS can maintain higher production temperature for a long time.On the other hand,lower permeability can lead to the decrease of mass flow rate of production well,so the heat extraction power is impacted.Second,when fracture permeability or fracture opening changes,EGS can output higher temperature stably for a certain period and then the temperature decreases at different amplitudes.When the fracture permeability increases to a certain value or the fracture opening decreases to a certain value,the influence of the change in fracture parameters on production temperature gets weak.Third,the calculated thermal production temperature using a variable physical fluid is 22℃lower than that using a constant physical fluid after EGS operates for 40 years.When water-rock reaction is taken into account,the thermal production temperature is 15℃ lower,and the average reservoir porosity is 12.5%higher.In conclusion,when researching a long-term operating EGS,it is necessary to comprehensively consider the influences of reservoir rock parameters,physical properties of injected fluid,water

关 键 词：增强型地热系统 嵌入式离散裂缝模型 热—流—力—化耦合模型 裂缝型储层 水—岩反应 热开采 影响因素 数值模拟 

分 类 号：P314[天文地球—固体地球物理学]