页岩储层压裂水平井气-水两相产能分析

Gas-water two-phase productivity analysis for the fractured horizontal well in shale reservoirs

传统的页岩气产能模型忽略了压裂液返排期间气-水同流对产能的影响,针对该问题,建立综合考虑页岩气吸附解吸、扩散、滑脱效应、应力敏感、毛管渗吸效应的气-水两相渗流数学模型,并基于有限差分,采用SS方法求解得到页岩储层产气规律及地层流体饱和度分布。对比分析不同裂缝网络渗透率、人工主裂缝渗透率、人工主裂缝长度、页岩气吸附解吸、毛管力作用对页岩气产量的影响,结果表明:生产初期,受压裂液返排的影响,日产气量呈先升高后降低的趋势,出现产气峰值,初期产气量明显低于不考虑压裂液返排所预测的产气量,但后期产气量基本一致。裂缝网络渗透率越高、人工主裂缝渗透率越高,产气量峰值出现的时间越早且初期产气量越高。人工主裂缝越长,产气量峰值出现的时间越晚,初期产气量越高。页岩气吸附解吸对初期产气量的影响不明显。考虑毛管力作用,压裂液返排率越低,产气量越高。

Traditional shale gas productivity models do not consider the effect of gas-water two-phase flow on the productivity during the backflow of fracturing fluid.This study proposes a new shale gas productivity model that considers the ef.fect of gas-water two-phase flow as well as the effect of shale gas adsorption,desorption,diffusion,slippage,stress sensitivity,and capillary imbibition.The model calculates the productivity of shale gas and the distribution of formation fluid saturation using the SS method based on the finite difference theory.The model was applied to a real field case to analyze how shale gas productivity was affected by the permeability of fracture network,the permeability of artificial major fractures,the length of artificial major fractures,the adsorption and desorption of shale gas,and the capillary force on shale gas.The results were compared to field observations.In the early period of production,the daily shale gas production first raised,peaked,and then dropped due to the backflow of the fracturing fluid.Compared to the case considering no backflow of fracturing fluid,the case considering the backflow of fracturing fluid has significantly lower shale gas production at the early period but similar production at the later period.The shale gas production at the early period increased with increasing fracture network permeability,artificial major fracture permeability,and artificial major fracture length.The shale gas adsorption and desorption had little effect on the shale gas production at the early period.The capillary force,however,would lower the backflow rate of the fracturing fluid,thus increasing the shale gas production,which is consistent with field observations.