Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model
Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model
复制标题
基于3-D THM模型的增强型地热系统双水平井排热能力数值研究
DOI：
10.3390/en11020280
复制
发表时间：
2018
期刊：
影响因子：
3.2
通讯作者：
Chuanyin Jiang
中科院分区：
文献类型：
--
作者：
Zhixue Sun;Ying Xin;Jun Yao;Kai Zhang;Li Zhuang;Xuchen Zhu;Tong Wang;Chuanyin Jiang
增强型地热系统（EGS）是一种通过水力压裂，从热干岩中经济地提取热量的人工热储。作为EGS热回收过程的核心要素，工质传热主要发生在裂缝处。由于天然裂缝和诱导裂缝的方向通常垂直于地层中最小主应力方向，因此水平井生产作为一种有效的增产手段，可以显著增加与热储层的接触面积。本文采用双水平井体系开发热储层，将热储层视为由基质岩石和离散裂缝网络组成的裂缝性多孔介质。利用局部热不平衡理论，建立了EGS抽热过程的耦合THM数学模型和理想的三维数值模型。根据热回收寿命、平均出口温度、产热量、发电量、能源效率和热回收率来评估EGS的热提取能力。结果表明，在一定的储采参数下，产热、发电量和热采寿命可以达到双水平井系统的商业化目标，但能源效率和整体热采收率仍处于较低水平。最后，提出了提高采热能力的一系列优化措施，包括生产条件和热储建设设计。
The Enhanced Geothermal System (EGS) constructs an artificial thermal reservoir by hydraulic fracturing to extract heat economically from hot dry rock. As the core element of the EGS heat recovery process, mass and heat transfer of working fluid mainly occurs in fractures. Since the direction of the natural and induced fractures are generally perpendicular to the minimum principal stress in the formation, as an effective stimulation approach, horizontal well production could increase the contact area with the thermal reservoir significantly. In this paper, the thermal reservoir is developed by a dual horizontal well system and treated as a fractured porous medium composed of matrix rock and discrete fracture network. Using the local thermal non-equilibrium theory, a coupled THM mathematical model and an ideal 3D numerical model are established for the EGS heat extraction process. EGS heat extraction capacity is evaluated in the light of thermal recovery lifespan, average outlet temperature, heat production, electricity generation, energy efficiency and thermal recovery rate. The results show that with certain reservoir and production parameters, the heat production, electricity generation and thermal recovery lifespan can achieve the commercial goal of the dual horizontal well system, but the energy efficiency and overall thermal recovery rate are still at low levels. At last, this paper puts forward a series of optimizations to improve the heat extraction capacity, including production conditions and thermal reservoir construction design.