河道型低渗透储层有限导流垂直裂缝井动态特征

Performance of vertical fractured wells with finite conductivity in channel-type reservoirs with low permeability

低渗透储层内考虑启动压力梯度的流体渗流过程中,动边界的传播规律反映储层的动用范围,并影响井底压力动态.建立河道型低渗储层考虑启动压力梯度和存在动边界的有限导流垂直裂缝井双线性流渗流数学模型,通过Laplace变换,得到动边界传播方程和地层流体压力分布方程;在Laplace变换域中,运用牛顿迭代和Stehfest数值反演方法计算获得井底压力分布特征、动边界传播规律及产能动态曲线.结果表明:启动压力梯度越大,动边界传播越慢、压力损失越大、井产量下降越快;定产条件下,裂缝导流能力越大,压力损失越小;裂缝导流能力对动边界传播影响较小;定压条件下,动边界存在最大值.由压力分布特征和动边界范围确定单井最大动用面积,对实际生产具有指导意义.

In a reservoir with low permeability,there is a moving boundary in fluid transient flows in the presence of threshold pressure gradients(TPG),The transmission of the moving boundary may indicate the size of the drainage area as well as exert visible influences on the pressure behavior.Including TPGs and moving boundaries,the paper presents a bilinear flow mathematical model of finite-conductivity vertically fractured wells in a channel-type reservoir with low permeability.Both moving boundary equation and reservoir pressure distribution are obtained by means of Laplace transformation.Moving boundary pattern,wellface pressure distribution characteristics and rate decline behavior are analyzed by using Newton iteration in Laplace domain and Stehfest numerical inversion.It is shown that the higher the TPG is,the slower the moving boundary spreads,the larger pressure loss is,the faster well production declines.In the condition of constant flow rate,the greater the fracture conductivity is,the lower pressure loss is.Influences of the fracture conductivity on the moving boundary pattern may be little in the earlier stage and will disappear soon by time elapsed.However,we can employ a uniform-flux fracture model to evaluate the moving boundary pattern.In the condition of constant pressure,there is a maximum value for the moving boundary,so we can determine the maximum single production area,the results will provide practical reference for the actual production.