饶阳凹陷路27断块油水倒置成因分析

Cause analysis of oil-water inversion in Lu 27 fault block of Raoyang sag

针对饶阳凹陷路27断块高孔高渗储层内油水倒置问题,以NgⅡ1小层路27-18井区为例,从砂体组合与单一砂体2个层面入手,通过岩心观察、测井分析及高压压汞等手段对砂体内部结构进行解剖。研究表明:路27-18井区在NgⅡ1小层发育心滩与辫状河道2种微相,位于高部位的心滩砂体沉积界面充分发育,砂体上部覆盖泥质沉积,构成与低部位河道砂体间的渗流屏障;河道砂体内部泥质纹层频繁发育,且在砂体上段倾斜砂层分布,形成砂体内部侧向渗流屏障。低部位油气在向上运移过程中分别受砂体内及砂体间两重屏障封阻,未能在高部位成藏,导致井区内油水倒置。

Oil-water inversion is common in lithologic reservoirs or tight reservoirs,which is mostly caused by lithologic pinch-out or physical sealing.However,the cause of oil-water inversion in high porosity and permeability reservoirs has not been fully explained.Lu 27 fault block in Raoyang depression has high porosity and permeability,but oil-water inversion is prominent in the fault block.Taking Lu 27-18 well area of NgII1 as an example,the internal structure of the sand body is dissected through core observation,log analysis and high pressure mercury injection,starting from two layers of sand body combination and single sand body.The results show that there are two kinds of microfacies in the NgII1 layer in the well area of Lu 27-18,i.e.core beach and braided channel.The sedimentary interface of core beach sand body at high position is well developed.The upper part of the sand body is covered with argillaceous sediment,which constitutes a seepage barrier between the upper part of the sand body and the lower part of the channel sand body.The argillaceous ripple layer in the inner part of the channel sand body develops frequently and inclines the upper part of the sand body.Distribution forms lateral seepage barrier inside sand body.In the process of upward migration of oil and gas in low position,oil and gas are blocked by double barriers in sand body and between sand bodies respectively,which fails to form reservoirs in high position,resulting in oil and water inversion in well area.