安棚深层系裂缝特征重新认识与井网调整

Study on fracture characteristics and well pattern adjustment in the deep Anpeng reservoirs

安棚深层系是典型的低孔特低渗透砂砾岩油气藏,其天然裂缝发育,影响油藏的井网部署和注水开发效果。根据地表露头、岩心和薄片分析,安棚深层系主要为高角度构造剪切裂缝。根据定向取心和成像测井资料,研究区以近东西向裂缝最发育,其次是北东向和北西向裂缝,不同部位不同方向裂缝的发育程度存在一定的差异。根据水压致裂和校正后的井径崩落资料,研究区现今地应力优势方位为50°～60°。在北东—南西方向现今地应力影响下,研究区北东向裂缝的张开度大,连通性好,渗透率高,为主渗流方向。因此在研究区下一步的井网调整中,可将目前的五点法面积注采井网转化为沿北东向主渗流裂缝的行列式注水开发井网,油藏数值模拟预测结果表明,调整后第5a采出程度为11.7%,单井累积产油量为1.4×104t,在原油价格(不含税)为2640元/t时,评价期内的内部收益率(税后)为24.68%,具有较好的经济效益。

The deep Anpeng reservoir is a typical glutenite reservoir with low porosity and ultra-low permeability.Natural fractures developed well and impact the well pattern arrangement and flood development effect.According to the data of outcrops,cores and thin sections,tectonic shear fractures with high dip angle are the main type of origin in the deep Anpeng reservoir.Based on the analysis of orientated cores and imaging logging data,the tectonic fractures can be classified into three sets,with the fractures most developed in E-W orientation and secondly in NE-SW and NW-SE orientations.According to hydrofracturing and revised data of wellbore breakouts,the preferred orientation of in-situ stress is 50°-60°.Under the influence of in-situ stress of NE-SW orientation,the fractures of NE-SW orientation,having the biggest aperture,the best connectivity and the highest permeability,are the main permeable direction in the study area.Consequently,the current five-point well pattern of E-W well row should be transformed into row well pattern parallel to main permeable direction of NE-SW fractures.This well pattern will have good development effect from numerical reservoir simulation.