非常规油气藏多场耦合渗流理论研究进展

Multiphysical field coupling in unconventional oil and gas reservoirs

非常规油气藏是目前世界油气开发的重点领域,由于非常规油气藏的储层条件差,渗流场与应力场、温度场耦合作用,流体的流动更为复杂,以往对多场耦合理论的运用存在简易化和适应性缺陷,工程中缺少理论指导下的更有效的开采工艺与开发方法,制约了这类油气藏的大规模高效开发,亟需对多场耦合渗流力学理论进行深入认识,以对工程问题提供有效指导.从实验认识、理论分析、仿真模拟三个方面阐述了我国非常规油气资源开发领域的多场耦合渗流力学理论的研究现状,重点围绕多尺度介质力学行为特性表征、岩体和流体的温度响应机制、耦合作用的概念及数学模型、多场耦合模拟仿真方法等关键问题的最新成果、认识展开论述.在此基础上对地下真实应力及温度环境的模拟、烃类吸附及置换的热量测试等问题进行分析,建议针对岩石的塑性应变、重复压裂后的应力环境变化、混合烃类的输运模型、以及流动条件随应力和温度变化的模型等科学问题进一步深化.旨在为进一步阐明我国非常规油气藏开发的动用机理、确定高效开发方法提供指导,同时希望能够促进渗流力学的学科发展.

Research in the field of oil and gas development has focused on the production of unconventional reservoirs all over the world.Unconventional oil and gas reservoirs have poor flow conditions,and the interaction of flow,stress,and temperature fields is very complex.Therefore,multiphysical field coupling is essential.The previous application of multiphysical field coupling theory has defects such as oversimplification and inadequate adaptability.Furthermore,the lack of adaptive production practices and effective development plans limits large-scale and efficient development,and there is an urgent necessity to investigate the adaptive multiphysical field coupling theory.Currently,the core rheology in fluid–solid coupling settings can often be measured by a triaxial test system under high temperature and pressure conditions combined with flow experiments.Moreover,the changes in pores and fractures can be tested by micro-CT and SEM.In addition,adsorption is considered an exothermic process,and desorption is deemed a heat-absorbing process,so the reservoir temperature decreases at the location where desorption occurs.Therefore,the production of unconventional oil and gas triggers a series of interactions.As the fluid flows into the wellbore through the fractures,the pressure drop increases the effective stress,decreasing the average pore radius and altering the inherent permeability.Moreover,the change of pressure causes a variation in the micro-flow effect,significantly impacting the apparent permeability,and the heat variation during desorption and adsorption also changes the flow condition as well as the physical properties of the fluid.As a result,these physical fields are closely related.A series of fully coupled partial differential equations are necessary to define the production process by modeling the dynamic porosity and permeability in various flow sectors to distinguish the interactions between different zones and physical fields.These complex interactions generally need to be solved by numerical methods.Thus,a simulator is needed that satisfies the accuracy requirements to match the actual situation.Moreover,adaptability to the decoupling process and acceptable speed requires research for high-performance computing solutions that can perform distributed or cloud computing for a large-scale unconventional reservoir simulation.Future research is necessary for laboratory measurements under realistic stress and temperature environmental conditions of the formation and hydrocarbon adsorption experiments.There should be further understanding of scientific issues such as the plastic strain of the porous rocks,changing stress environment after refracturing,and mixed hydrocarbon transport models with varying stress and temperature.This article further clarifies the dynamics and determines effective production methods of unconventional reservoirs in China to promote the development of flow mechanics.