基于局部热非平衡的含裂缝网络干热岩采热性能模拟

Numerical simulation of heat mining performance of hot dry rocks with fracture network based on a local thermal non-equilibrium model

关键词:  干热岩  离散裂缝网络  温度-渗流-应力耦合  局部热非平衡  注采井网

Key words:  hot dry rocks  discrete fracture network  thermo-hydro-mechanical coupling  local thermal non-equilibrium  injection-production well pattern

摘要:

采用压裂技术在干热岩中构造裂缝网络,工作流体在裂缝内的循环携热使干热岩中高温资源得到有效提取。为真实模拟岩体与流体间能量传递,基于局部热非平衡理论,将储层视为由基质岩体与离散裂缝组成的双重介质模型,建立温度-渗流-应力全耦合模拟采热过程中流体流动、热量传递、岩体变形的相互作用,进而对不同注采井网和模型参数下采热性能进行研究。结果表明:干热岩资源开采过程的模拟有必要采用温度-渗流-应力 耦合,裂缝分布的非均匀性对采热性能有影响;注采井网的合理布局有利于地热能大规模动用与高效开发;基岩热膨胀系数影响温差引起的热应力作用从而影响采热性能;合理选择注采压差有利于开发,压差过大将缩短开发寿命,注入温度越高采热速率越高。

Abstract:

Heat carrying fluids can be injected and circulated in fractured networks formed in hot dry rocks for effective heat mining. In order to simulate the heat transfer process between the rock mass and the working fluid realistically, a local thermal non-equilibrium model was adopted, considering the reservoir as a dual-medium model composed of matrix rock and discrete fractures. The interactions of the fluid flow, heat transfer and rock mechanics during the heat mining process was simulated via a full thermo-hydro-mechanical(THM)coupling model, and the heat mining performance with different inject-product well patterns and operation parameters was investigated. The simulation results show that the adoption of the THM coupling model is necessary and adequate for the simulation of the heat resource mining process, and the heterogeneous distribution of the fractures has an significant influence on the performance of heat mining. Reasonable layout of the injection-production well patterns is conducive to the large-scale utilization and efficient exploitation of the geothermal energy. The thermal expansion coefficient of the rock matrix can affect the thermal stress induced by temperature difference, thus affecting the heat mining performance. Rational selection of injection-production pressure difference is beneficial heat extraction, but an excessive pressure difference can shorten the duration of the process.