地热开发中考虑堵塞效应的热-流-固耦合数值模拟

    NUMERICAL SIMULATION OF THERMO-HYDRO-MECHANICAL RESPONSE CONSIDERING CLOGGING EFFECT IN GEOTHERMAL EXPLOITATION

    • 摘要: 基于多孔热弹性和瞬态流场理论,并考虑储层孔隙内部细小颗粒迁移诱发的堵塞效应,建立横观各向同性介质的热-流-固-颗粒迁移耦合模型。该模型能够考虑颗粒迁移与孔隙水流动、热量传递和介质应力的耦合特性。采用Galerkin加权余量和隐式有限差分法得到有限元体系下的位移、孔隙水压、温度和颗粒含量控制方程,开发注抽水工况下考虑堵塞效应的储层热-流-固时空响应有限元模拟程序。通过对已有试验结果模拟验证了有限元程序的准确性与可靠性。为进一步获取堵塞的影响机制,对注抽水时孔隙表面附着大量细小颗粒的地热储层响应进行了有限元模拟。结果表明细小颗粒迁移诱发的堵塞效应会造成井周储层渗透系数明显降低,孔隙水压力大幅度升高。当地热储层温度较低时介质内部的堵塞效应可忽略,然而较高的储层温度将使更多颗粒发生迁移,增强堵塞效应,使井周孔隙水压力迅速升高并降低采热效率。通过对比不同附着颗粒含量下的储层注抽水响应模拟结果发现抽水时的渗透系数衰减值和范围较注水时更大,注入水不含固体颗粒悬浮物时将明显降低堵塞效应。本文研究成果将为地热能开发中的防堵设计提供理论指导。

       

      Abstract: Based on the porothermoelastic theory and transient flow field,and considering the clogging caused by fines migration in the fissures of formation,the thermo-poro-elasto-fines migration model of transversely isotropic medium is proposed to consider the coupling characteristics of fines migration,fissure fluid flow,heat transfer,and stress evolution. By using Galerkin weighted residuals and implicit finite difference method,the governing equations of displacement,pore pressure,temperature,and fines concentration are established based on the proposed model,and the finite element procedure is developed to simulate the thermo-hydro-mechanical response of formation under clogging effect during fluid injection/production operations. The existing test data is simulated,and results show the model has a good capacity for predicting the well impedance in the field. The spatiotemporal response of formation to water injection and production is simulated to obtain the influencing mechanism of clogging. Results show that the clogging phenomenon caused by fines migration leads to permeability decline and pore pressure rise surrounding the wellbore. When reservoir temperature is low,the clogging effect could be neglected; higher reservoir temperature makes more fines detach from their original location and enhances the clogging effect,which leads to larger pore pressure surrounding the wellbore and lower exploitation efficiency. By comparing numerical results of reservoir's response with different concentrations of fine particles,permeability decline is found to be more serious for water production,and the clogging effect is weakened when injected water does not contain suspended solids. The conclusions of this study provide theoretical guidance for anti-blocking design in geothermal exploitation.

       

    /

    返回文章
    返回