考虑储气库裂隙储层分形特点的天然气渗流规律分析

考虑储气库裂隙介质分形特点以及临界运移饱和度的影响,根据两相不稳定渗流理论和分形理论,将裂隙储层介质分形参数引入到相对渗透率的预测,建立了储层相对渗透率与裂隙尺寸、典型单元体尺寸、毛管压力之间的关系;并分析了高含水衰竭油气藏裂隙储层改建储气库后的渗流规律及井底压力变化规律。采用计算模型与三维渗流模型所得计算结果进行了对比分析,并研究了分形维数、典型单元体尺寸、裂隙尺寸比、储层厚度、注气速率、排水速率对储气库井底压力的影响。计算结果表明:采用的计算模型考虑了裂隙储层的分形特点,具有较高的计算精度,可以满足实际工程计算需求;气相相对渗透率随着分形维数的增大而增大,水相相对渗透率随着分形维数的增大而减小;储气库井底压力随着裂隙介质分形维数、储层厚度、排水速率的增大而减小;随着典型单元体尺寸、裂隙尺寸比、注气速率的增大而增大。

Seepage law analysis of natural gas considering the fractal features of crack reservoir in underground gas storage

Considering the influence of fractal features and critical migration saturation, a new model is proposed to predict the relative permeability of crack reservoir based on two-phase non-stationary flow and fractal theory. And the seepage law and bottom hole pressure in depleted reservoir gas storage were analyzed. The results of depleted reservoir gas storage by the model were compared with the results by three-dimensional seepage mathematical model. In addition, parameters were studied to investigate the bottom hole pressure as a function of the fractal dimension, representative elementary volume, Lmin/Lmax, reservoir thickness, injection rate, drainage rate. The results show the fractal seepage model is precise and correct, and can meet the actual engineering demands. The relative permeability of gas is equidirectional with the increase of fractal dimension, and the relative permeability of water is reverse to the increase of fractal dimension. The bottom hole pressure is equidirectional with the increase of representative elementary volume, Lmin/Lmax, injection rate, and is reverse to the increase of fractal dimension, reservoir thickness and drainage rate.