红河油田长8裂缝性致密储层微观水驱油特征

Microscopic Waterflooding Characteristics of Chang-8 Fractured Tight Reservoir in Honghe Oilfield

红河油田长8储层基质物性差且普遍发育裂缝,注入水难以进入基质驱油并实现有效波及是当前面临的主要开发难题。为明确长8裂缝性致密储层的水驱油特征,改善水驱油效果,开展了恒速压汞及低速非达西渗流等试验研究,结果表明红河长8储层平均喉道半径仅0.82μm,孔喉组合以小孔—微细喉为主,且存在较明显的启动压力梯度,是导致长8储层吸水能力弱的主要因素;同时开展注入性评价和不同注入条件下的水驱油试验,结果表明长8储层有效注入并波及的压力条件为注入压力略低于裂缝重张压力,且远低于地层破裂压力;注水采油具有驱替—渗吸协同作用,等作用点储层渗透率为0.4mD;影响驱油效率的主要因素包括储层物性、不同储层组合方式、注入参数等。以此明确了长8储层以裂缝驱油+基质渗吸为主的驱油特征,并结合矿场注水开发试验,建立了适合红河长8裂缝性致密储层有效注水技术政策。

The matrix properties of Chang-8 reservoir in Honghe oilfield are poor,and the fractures are generally developed,so the water is difficult to enter the matrix with effectively displace and spread.In order to make clear the characteristics of water displacement and improve the effect of water flooding,the experiments of constant velocity mercury injection and low velocity non Darcy flow were studied.The results showed that the average throat radius of the Chang-8 reservoir is only about 0.82μm with small pore and micro fine throat assemblage and apparent start-up pressure gradient,which is the main factor that leads to weak water absorption capacity.The experiment of evaluation of injection and different injection conditions of water flooding showed that the conditions of effective injection and spread is the right injection pressure which is slightly lower than the fracture reopening pressure,and far lower than the formation fracture pressure.Water injection has a synergistic effect of displacement and imbibition,and the action point is 0.4 mD.The main influence factors of oil displacement efficiency include reservoir physical property,different reservoir combination,injection parameters,etc.The displacement characteristic of Chang-8 reservoir is fracture displacement&matrix imbibition.The suggestions which establish effective water injection technology policy is provided basing on the field water injection test in Chang-8 reservoir.