特低渗透油藏水驱规律及最佳驱替模式

Waterflooding and optimum displacement pattern for ultra-low permeability reservoirs

为了进一步改善特低渗透油藏开发效果,提高水驱采收率,通过大量特低渗透油藏水驱开采特征研究,揭示了特低渗透油藏的水驱规律:在注水开发过程中,特低渗透油藏会首先沿现今最大水平主应力方向注、采井间开启注水动态裂缝,随着注水压力的升高,或将开启与之成最小角度的注采井连线方向裂缝,导致注入水沿裂缝方向注采井无效循环,造成油藏水驱开发效果很差。等值渗流阻力法计算结果也证明了面积驱替径向渗流转为裂缝线性侧向驱替平行流后可大大降低渗流阻力。由此提出了"沿现今最大水平主应力方向注水动态裂缝线性注水、侧向基质驱替"的井网转换模式。井网模式的转换避免了注水动态裂缝导致的注入水无效循环,消除了动态裂缝对储层非均质性的影响,减小了渗流阻力,扩大了水驱波及程度。现场应用效果显著,单井产能增加了一倍,平面波及系数提高了43. 2%,水驱采收率提高了19. 3%。

This study reveals the waterflooding pattern of ultra-low permeability reservoir after the analysis of waterflooding recovery characters of plenty ultra-low permeability oil reservoirs,with a view to further bettering the development of ultra-low permeability oil reservoirs and enhancing oil recovery.It can be concluded that fractures induced by water injection will open along the injection-production line in the direction of in-situ maximum horizontal principal stress.In addition,as the angle between the in-situ maximum principle stress and the injection-production line becomes smaller with the increase of water injection pressure,the induced fracture is more likely to open,resulting in an invalid circulation of injected water to injection-production wells and poor waterflooding effect.Moreover,the seepage resistance of linear lateral displacement of the fracture is less than that of the radial displacement calculated by equivalent percolation resistance method.In turn a well pattern conversion mode of“linear injection into dynamic fractures along the direction of in-situ maximum horizontal principal stress with matrix displacement of lateral side”is proposed.The optimized well pattern can improve water sweep efficiency by mitigating the effect of dynamic fractures on reservoir heterogeneity and reducing seepage resistance.In application,the productivity of single wells has doubled,the plane sweep coefficient has increased by 43.8%,and the waterflooding recovery ratio has increased by 19.3%.