注采井网条件下水平井体积压裂重复改造优化设计

鄂尔多斯盆地超低渗透油藏具有低渗、低压、低丰度的特征,采用"五点水平井注采井网+分段压裂"开发,有效提高了初期单井产量。然而,受裂缝间距大、改造规模小、水平段中部能量补充困难及裂缝长期导流能力下降快等因素影响,水平井长期生产产量递减较大。基于典型水平井生产拟合数值模型的压力场和剩余油饱和度场分布,定义了储层改造体积指数、油藏接触面积指数、缝网导流能力指数及地层压力保持指数,并以此表征裂缝网络模型的增产指标。采用新型NF裂缝网络模型,系统对比评价了各指标的增产潜力及其与产量的敏感程度,最终提出了水平井"SRV+Ct+Cd+ps"的体积压裂重复改造优化设计方法。该方法在某区长6超低渗透油藏现场应用后取得较好的增产效果,4口试验井与常规重复压裂相比,单井产量提高50%~70%。

Re-fracturing optimization for horizontal wells on condition of flooding pattern

The ultra-low permeability reservoir in Ordos Basin has three typical characteristics such as low permeabihty,low pressure and low abundance.The initial oil production of single well has been improved effectively by horizontal wells and staged fracturing in recent years.The five injection-production well pattern has one horizontal oil producing well and four vertical water injecting wells.However,with long-term producing,the horizontal well production decrease greatly because of four key factors such as large fracture spacing,small stimulating scale,low reservoir pressure in the middle of the horizontal well without energy supplement and long term fracture conductivity decline.The pressure distribution and remaining oil saturation distribution were obtained from the production fitting between a typical horizontal well and a reservoir numerical model.Based on the results,four indices such as Stimulating Reservoir Volume Index,Reservoir Contact Area Index,Fracture Network Conductivity Index and Reservoir Pressure Index have been defined to characterize the new fracture network model (NF model).After that,the re-fracturing potential of each index and the sensitivity to production have been evaluated and contrasted systemlly.Finally,a volume refracturing optimization design method (SRV+Ct+Cd+ps) was put forward for horizontal wells.This re-fracturing design method is applied to four testing horizontal wells in ultra-low permeability Huaqing Oil field in Ordos Basin.The oil production increased about 50％ to 70％ compared with the production of other conventional re-fracturing horizontal wells.