基于声震效应的页岩储层多组分流体多场耦合流动机理

Due to the complexities of pore structure and seepage law in shale gas reservoirs, its fluid flowing mechanism is always the difficult point to restrict the efficient development of shale gas reservoirs, especially under the condition of massive fracturing where the multi-field coupled flow mechanism, including sound field, flow field, pressure filed and temperature field, is urgent to be researched deeply. Based on the mechanisms for improving the recovery of coal bed methane by ultrasonic vibrating effects, this paper introduces and studies the relevant acoustic attenuation law influenced by the pore structure and physical properties of shale formation, and combining with improved ultrasonic vibrating experiment to study the characteristic parameters of adsorption, desorption, diffusion and percolation occur in nano-scale pore and establish mathematical characterization model, at the same time, comprehensively employing acoustic streaming theory and multi-field coupled simulation experiment to probe multi-compenents fluid multi-field coupling mechanism of shale formation, analyze the sensitive extent of the field effects, innovatively establish the theory of multi-field coupling fluid flow under ultrasonic vibrating effects, and form the method of multi-field coupling multi-compenents fluid flow numerical simulation. This paper tries to innovatively apply the shale gas enhanced-production theory based on ultrasonic vibrating effects, lay the applied technology infrastructure of shale gas development using ultrasonic vibration, establish the new innovative mode of shale gas development and enrich the domestic shale gas development theory.

由于页岩储层孔隙结构与页岩渗流的复杂性，其流体流动机理一直是制约页岩储层高效开发的难点，特别是在大规模压裂条件下的声场、流场、压力场及温度场耦合流动机理急需深入研究。本项目基于声震法提高煤层气采收率机理，拟引入声震法对页岩孔隙结构与物性特征等影响声波衰减规律进行研究，结合改进的声震实验，研究声震效应作用下的页岩储层微纳米孔隙多组分流体渗流特征参数变化规律，构建声流耦合影响的吸附、解吸、扩散数学表征模型，同时采用多场耦合物理模拟实验，探究页岩储层耦合作用机理，分析场效应敏感性程度，创新建立声震效应下页岩储层多场耦合渗流理论，形成页岩储层多场耦合数值模拟方法。本项目试图创新完善声震效应的页岩储层增产理论，奠定声震法开发页岩气藏的应用技术基础，丰富我国页岩气开发理论。

页岩气资源作为一种非常规油气资源，地质储量巨大，对于维护我国能源战略安全具有重要意义。我国页岩气藏具有物性差、产能低、递减快的特征，因此研究提高页岩气采收率的方法至关重要。本课题受国家自然科学基金资助，依托中国石油大学（北京）科研平台，基于对声波衰减规律的研究，结合实验与理论分析方法，研究声震效应作用下的微纳米孔隙多组分流体渗流特征参数变化规律。通过构建声流耦合影响的吸附、解吸、扩散数学表征模型，阐明页岩储层多场耦合作用机理，分析场效应敏感性程度，创新完善声震效应下页岩储层耦合渗流理论，并形成页岩储层多场耦合数值模拟方法。声波作用下页岩等温吸附、解吸实验研究表明：页岩的等温解吸曲线相比等温吸附曲线存在滞后现象，解吸不彻底；由于声波作用的热效应和机械振动的综合作用，页岩对气体的吸附量减小，解吸量增大，页岩渗透率提高，声波功率越大，效果越明显。基于页岩等温吸附规律，建立一种声场作用下考虑过剩吸附量修正的页岩吸附甲烷模型，并与实验数据拟合较好。建立了声场作用下的页岩气藏耦合渗流模型，并且采用有限差分离散方程和牛顿—拉普森迭代法进行数值求解。对比分析有无声场作用页岩气产能递减曲线表明，在页岩气流动的后期阶段，有声场作用的页岩气藏产量递减慢，生产时间长，无声场作用的页岩气藏产量递减快，生产时间短；通过对不同超声波衰减系数的页岩气产能递减曲线的分析，超声波衰减系数越小，产量递减就越慢，生产时间越长。除此之外，超声波衰减系数存在一个阈值，当超声波衰减系数大于阈值时，超声波对于储层的作用几乎可以忽略不计。实例分析结果表明：声场作用下的页岩气藏在开发中后期递减较慢，声场作用对于促进页岩气的增产具有一定的效果。本项目创新丰富了我国页岩气开发理论,为声震法开发页岩气藏资源奠定了理论与应用基础。