增强型地热系统储层低温诱导开裂机理与模型研究

Reservoir stimulation is the key technical problem to the enhanced geothermal systems, and many other significant underground energy engineerings. This project aims to reveal the mechanism of low temperature induced fracturing and to establish the corresponding model. On the base of large-scale indoor physical modeling tests and a variety of macro, mesoscopic testing technologies, combined with thermodynamic and rock mechanics theories, the rule and mechanism of hot rock fracturing induced by cold water stimulation will be investigated. The influences of different injection temperatures, injection rates and in-situ stress conditions on the crack shape, direction, density and type will be studied, and the fracture damage model considering the temperature stress of low temperature stimulation will be built; the program module will be developed to link the model with the coupled THM simulator, and the validation and optimization of model will conducted through the comparative analysis with typical field test data. The results of this project about mechanism on low temperature induced fracturing will provide theoretical foundation and scientific basis for a reasonable design of the underground reservoir stimulation by cold fluid injection, for the reduction of reservoir treatment costs and improvement of the mining efficiency as well as for the control of environment negative effects.

储层改造是EGS等诸多地下重大能源工程的关键技术问题。本项目以揭示热岩低温诱导开裂机理和建立强度模型为目标，通过室内大尺寸物理模型试验及多种宏、细观测试技术，结合热力学和岩石力学理论，探寻冷水刺激热岩诱导开裂规律和机理，研究不同注入温差、注入速率及地应力条件对裂纹形状、走向、密度、种类等特征的影响，并建立考虑温度应力的低温刺激岩石断裂损伤强度模型；开发程序模块实现其与热-流-固多场耦合平台的搭接，通过与典型场地监测数据的对比分析对模型进行验证与优化。本项目关于储层低温诱导开裂机理及影响规律的研究，旨在为合理设计地下热储层冷流体刺激开裂，降低储层改造成本并提高开采效率，以及控制环境负效应提供理论基础和科学依据。

在地热工程中，流体-温度-应力的耦合模拟计算是工程设计、运行中的重点及难点。在此背景下，依托国家自然科学基金项目“增强型地热系统储层低温诱导开裂机理与模型研究” (项目编号：41602243)，开展了单缝变温导流换热室内实验，分析了温度应力对干热岩导流能力的影响规律；通过现场热响应试验及室内实验，获取并分析了长春、哈尔滨以及加格达奇地区的导热系数和比热容等热物理参数的范围及变化规律，依据热响应试验结果计算了几个区域地埋管地源热泵工程的地热能可利用量；针对我国北方高纬度地区冬季供暖产生的热不均衡问题，提出了一种利用中层地热能供暖的新型的中低温干热岩-热泵系统，以沈阳地区为例通过数值模拟对其长期运行效率及成本进行了分析；针对华北地区，选取唐山某大型水源热泵实际工程进行数值模拟研究，提出多种优化方案解决系统冷堆积问题；研发程序对TOUGHREACT和FLAC3D进行搭接，通过建立相应算例，研究增强型地热系统对井抽灌引起的水-热-力耦合过程，分析渗流场及温度场的分布及演化趋势，揭示多场耦合强度规律及影响因素。