考虑储层孔隙介质分形特点的衰竭气藏储气库储层压力分布预测

考虑储层孔隙介质分形特点以及储层压力变化对储层介质渗流参数的影响,根据气体不稳定渗流理论,建立了衰竭气藏储气库储层压力动态分布的分形渗流模型,并推导出了注气过程动态储层压力的预测公式。在对本文模型计算结果与三维渗流模型计算结果对比分析基础上,研究了分形维数、弯曲率、储层厚度、气体黏度、注气速率和注气时间对地下储气库储层压力分布的影响,并计算了国内某衰竭气藏储气库BN-4井注气后的储层压力分布。结果表明:本文所建立的模型具有较高的计算精度,可以满足实际工程计算需求;分形维数和渗透率随着孔隙度的增大而增大,储气库储层介质的应力敏感性受毛细管外壁的岩性影响较大;衰竭气藏储气库的储层压力随着储层介质弯曲率、气体黏度、注气速率、注气时间的增大而增大,随着分形维数和储层厚度的增大而减小;分形维数、储层厚度、注气速率、注气时间对储气库储层压力的影响比较显著,而介质弯曲率和气体黏度对其影响不明显。为充分利用储气库储层,实际工程中注气井的间距不宜过大及可适当延长注气时间。

Dynamic reservoir pressure prediction of depleted reservoir gas storage considering the fractal feature of porous medium

Considering the fractal feature of porous medium and the influence of reservoir pressure change on seepage parameters in depleted reservoir gas storage, the fractal seepage model was built up to calculate the reservoir pressure based on unstable gas seepage flow. The reservoir pressure of depleted reservoir gas storage by the new model was compared with the results by three-dimensional seepage mathematical model. In addition, the influence faceors of reservoir pressure were studied, such as increase fractal dimension, tortuosity, reservoir thickness, gas viscosity, injection rate and time. The results show the fractal seepage model is precise and correct, and can meet the actual engineering demands. The fractal dimension and permeability increase with the increase of porosity. The stress sensitivity of porous medium in depleted reservoir gas storage is strongly influenced by rock property of capillary wall. The reservoir pressure of depleted reservoir gas storage increase with the increase of tortuosity, gas viscosity, injection rate and time, but decrease with the increase of fractal dimension and reservoir thickness. The fractal dimension, reservoir thickness, injection rate and time have great effects on the reservoir pressure, whereas the tortuosity and gas viscosity have little influences on it.