凝析气藏压裂返排参数优化

CONDENSATE GAS RESERVOIR FRACTURING BACKFLOW PARAMETER OPTIMIZATION

低渗透凝析气藏开采过程中,为保证气井有较高的产量和提高气藏产能,需要实施水力压裂的措施来改善地层渗流能力,而压裂后的返排过程影响到液锁对地层的伤害程度。建立压力返排模型和压裂后的产能模型,确定合理的返排速度,是保证压裂施工返排成功的基础。首先构建压裂返排物理模型,然后通过保角变换,将压裂后形成的椭圆形流动区域转化为圆形的渗流区域,利用平面径向流产能公式来确定压裂后气井的产能。利用返排模型可以确定出压裂返排过程中裂缝和地层内的压力分布,结合产能模型可以确定出不同返排速度时两种液锁现象对产能的影响。实例分析表明,凝析气藏压裂返排速度影响气井的产能,返排速度过快或过慢都会降低气井的产能,中原油田白庙断块沙三段以100m3/d左右的初始返排速度返排,压裂后将获得最佳的产能。

Hydraulic fracturing is a simulation measure usually taken during low-permeability condensate gas reservoir production to improve formation percolation capacity for higher rate and productivity. Fracturing fluid backflow influences the severity of formation damage due to liquid invading. It is the basis of successful fracturing backflow to establish the models of backflow and postfrac productivity and then determines proper backflow speed. The approach is to establish physical model of fracturing backflow and then to convert elliptical flowing zone formed after fracturing to spherical percolation zone by conformal transformation and to determine postfrac productivity using plane radial flow productivity equation. Backflow model can be used to determine the pressure distribution in the fracture and formation in fracturing process. In conjunction with use of productivity model, the impact of two different types of liquid invading on productivity with variant backflow speeds can be determined. Case study indicates that condensate gas reservoir fracturing backflow speed affects well productivity and selecting backflow speed either too high or too low would result in low well productivity. An initial backflow speed of 100 m^3/d has been applied on Formation Sha-3 of Baimiao Fault-Block in Zhongyuan Oilfield and the optimum postfrac productivity has been observed.