致密油藏直井体积压裂非稳态渗流问题

针对致密油藏直井体积压裂的非稳态渗流问题,建立了考虑启动压力梯度和压敏效应的两区复合模型,利用稳态逐次逼近非稳态的半解析方法进行求解,分析致密油藏直井体积压裂后压力传播规律,以及影响压力传播的主要因素.计算结果表明:当存在启动压力梯度和压敏效应时,流体渗流阻力增大,压力传播速度减缓,压力传播半径变小,最终导致井底流压降低,井口流量减少.对于两区复合模型,压裂改造区内渗流阻力小,压力传播速度快,体积压裂改造范围越大,压力传播速度越快,压力传播半径越大.对于定井底流压情形,改造区域半径越大,油井产能越高,但是当改造半径大于一定值后,改造半径的扩大对于提升油井产能的作用不再明显.

Study on non-steady flow characteristics of volume fracturing for vertical well in tight oil reservoir

For non-steady flow problem of fracture network reconstruction vertical well in tight oil reservoirs, a two-region composite seepage model considering the pressure gradient and pressure-sensitive is built, and the model is solved using a semi-analytical method of steady-state successive approach to unsteady-state solution. The results show that the existence of pressure gradient and pressure-sensitive effect slow down the well bottom pressure and pressure propagation speed for the reason that pressure gradient and pressure-sensitive increase the formation flow resistance. In two- region composite seepage model, pressure propagation speed in fracture reconstruction region is faster than pressure propagation speed in non-fracture reconstruction zone. The larger fracture reconstruction radius, the larger pressure propagation radius is. For constant-pressure production, with increase of fracture reconstruction region radius, well production rate increases, while its increasing rate is decreasing.