裂隙型多孔介质内非线性热对流及其失稳动力学研究

The heterogeneous fractured porous medium is a typical structure in addressing the underground fluid resource exploitation such as geothermal reservoir, petroleum reservoir, etc, and its impact on environmental evaluation. Using linear diffusion laws to solve the seepage and heat transfer problems in such complex and structural formations is no longer accurate. In this project，both the theoretical analysis and an experiment in lab-scale will be performed to investigate the heterogeneous characteristics of nonlinear seepage, coupled convective heat transfer and the dynamic characteristics of the instability in the fractured porous media from the micro- and macro-scaled perspectives. A packed particles porous media with fractures will be built and under that condition, the heterogeneous seepage flow in the fracture and its instability conditions and the nonlinear characteristics of coupled non-isothermal thermal convection will be discussed. The specific contents include: geometric parameters and space distribution of fractures, the effect of particle diameter distribution, the thermal properties of the seepage fluid, the control parameters of the macro-flow like pressure and temperature on the macroscopic anisotropic transport characterization parameters such as permeability coefficient, the convective heat transfer coefficient, etc. Combined the perturbation theory, lattice Boltzmann method and the spectral method, the seepage field and temperature field in a complicated channel will be simulated numerically by considering the nonlinear inertial effect, the jump of the momentum and energy at the interface, further determine the instability parameters, also the dynamic characteristics under variable instability conditions. The research results are expected to provide important theoretical guiding to know the seepage and the heat transfer in a complex structure of the petroleum reservoirs and geothermal reservoirs.

含裂隙非均质多孔介质是地热热储、石油储等地下流体资源开发、环境评价常遇到的典型结构，采用线性扩散定律研究此复杂结构地层中的渗流及换热等问题已不再准确。本课题拟从微观和宏观不同角度对裂隙型多孔介质内非线性渗流特性、耦合对流换热及失稳动力学特征进行理论和实验研究。探讨以颗粒堆积型多孔介质内存在裂隙情况下，其内渗流各向异性特征及失稳条件、耦合非等温场热对流情况下非线性特征，具体研究内容包括：裂隙几何参数及空间分布、堆积颗粒相粒度分布、渗流流体热物性与宏观流动压力与温度控制参数等对宏观各向异性输运表征参数如渗透系数、对流换热系数等的影响。结合扰动理论，格子-玻尔兹曼及谱方法数值模拟考虑非线性惯性效应和界面动量及能量跳跃时复杂通道内的渗流场及温度场分布，进而明确失稳参数及失稳情况下的动力学特征。研究结果对准确掌握复杂结构地热热储层、石油储层内的流体渗流与传热规律具有重要理论指导意义。

含裂隙非均质多孔介质是地热热储、石油储等地下流体资源开发、环境评价常遇到的典型结构，采用线性扩散定律研究此复杂结构地层中的渗流及换热等问题已不再准确。本课题从微观和宏观角度对裂隙型多孔介质内非线性渗流特性、耦合对流换热及失稳动力学特征进行了研究。考虑局部热非平衡效应以及界面应力、热流条件，获得了典型平行裂隙型多孔介质各区域渗流场，流固两相温度场，阻力系数、对流换热系数等精确解析解，探讨了裂隙几何参数及空间分布、渗透率、固流相热物性、内热源等对输运表征参数如阻力系数、对流换热系数等的影响，并对比得出了局部热平衡条件适用情况；另对多孔介质区流速较大时增加的非线性惯性效应情况给出了实验证明，获得了裂隙型多孔介质内惯性效应影响下的速度及流固两相温度分布数值解；此外，结合扰动理论及谱方法推导模拟了考虑复杂界面条件的失稳参数及失稳情况下的动力学特征。结果表明：不同热流界面条件下流动阻力及换热程度的变化都对较小裂隙高度更为敏感，而界面应力跳跃系数对复合通道内流体压降及换热影响都可以忽略，仅在高渗透率及较小界面应力跳跃系数下压降计算需考虑界面应力跳跃以及努赛尔数的预测结果与界面应力连续条件时的略有不同；各参数不同会导致努塞尔数随裂隙高度变化出现不同类型曲线，包括出现努塞尔数最大或最小值或单调变化；多孔介质固相或流相引入内热源对换热影响很大且程度相似，会使努塞尔数曲线加剧出现奇点且流固两相温差更大，此时局部热非平衡比局部热平衡条件更适合于预测热性能，而当达西数小于10-3时，无论是在局部热平衡还是热非平衡条件下考虑惯性效应对努塞尔数影响可以忽略；相较于不渗水的固体壁面，多孔介质壁面进一步增加了流动的不稳定性，且随着渗透率的增加，流体流经裂隙型多孔介质通道的稳定性变弱。研究结果对准确掌握复杂结构含裂隙储层内的流体渗流与传热规律具有重要理论指导意义。