热冲击作用对干热岩起裂压力与裂隙扩展形态的影响  

Influence of thermal shock on fracture initiation pressure and fracture morphology in hot dry rock hydraulic fracturing

作　　者：刘帅[1] 柴军瑞[1] 薛熠 白雪[1] 张劲松 LIU Shuai;CHAI JunRui;XUE Yi;BAI Xue;ZHANG JingSong(State Key Laboratory of Eco-hydraulics in Northwest Arid Region,Xi'an University of Technology,Xi'an 710048,China)

机构地区：[1]西安理工大学省部共建西北旱区生态水利国家重点实验室,西安710048

出　　处：《地球物理学进展》2023年第4期1487-1496,共10页Progress in Geophysics

基　　金：国家自然科学基金(12002270);陕西省重点研发计划(2022ZDLSF07-06)联合资助。

摘　　要：在干热岩水力压裂中,低温水接触高温地热储层诱发热冲击会加速储层裂隙萌生与扩展,强化干热岩储层的压裂效果.本文提出了一种考虑热冲击效应的起裂压力预测公式,该模型将热应力作用和力学参数劣化作用耦合到起裂压力的计算中.建立了考虑热冲击效应的热-水-力-损伤耦合模型,开展Morris全局灵敏度分析,研究了不同岩石初始温度、弹性模量、均质性指数、初始渗透率对水压裂隙扩展形态的影响.结果表明,水压裂隙的起裂是热冲击导致的抗拉强度劣化、冷收缩产生的热应力和孔隙水压力三者的共同作用的结果.随着岩石初始温度的升高,热应力和抗拉强度劣化的贡献越大,表明热冲击效应随着温度的升高而变得更加强烈.弹性模量、泊松比、热膨胀系数和表面换热系数的增加会降低起裂压力.表面换热系数和热膨胀系数是干热岩水力压裂过程中起裂压力的灵敏参数,并且与其他参数的相互作用较强.在EGS项目选址时,选择初始温度较高、弹性模量较大、初始渗透率较大和均质性指数较小的干热岩储层,有利于构建更复杂的裂隙网络.During the hydraulic fracturing process of hot dry rock,thermal shock induced by low temperature water contacting high temperature geothermal reservoir will accelerate the initiation and expansion of reservoir fractures and enhance the fracturing effect of hot dry rock reservoir.A prediction formula of fracture initiation pressure considering thermal shock effect is proposed in this paper.The model couples the thermal stress and the degradation of mechanical parameters into the calculation of fracture initiation pressure.A thermal-hydro-mechanical-damage coupling model considering thermal shock effect is established,and Morris global sensitivity analysis is carried out to study the effects of different rock initial temperature,elastic modulus,homogeneity index and initial permeability on the expansion morphology of hydraulic fractures.The results show that the initiation of hydraulic fracture is the combined effect of tensile strength deterioration caused by thermal shock,thermal stress caused by cold shrinkage and pore water pressure.With the increase of initial rock temperature,the contribution of thermal stress and tensile strength deterioration is greater,indicating that the thermal shock effect becomes stronger with the increase of temperature.The increase of elastic modulus,Poisson's ratio,thermal expansion coefficient and surface heat transfer coefficient will reduce the initiation pressure.The surface heat transfer coefficient and thermal expansion coefficient are sensitive parameters of initiation pressure in the process of hydraulic fracturing of hot dry rock,and have strong interaction with other parameters.In the site selection of EGS project,the selection of hot dry rock reservoirs with higher initial temperature,larger elastic modulus,larger initial permeability and smaller homogeneity index is conducive to the construction of more complex fracture network.

关 键 词：干热岩 水力压裂 热冲击作用 起裂压力 裂隙扩展形态 Morris全局灵敏度分析 

分 类 号：P314[天文地球—固体地球物理学]