特低～超低渗透储层油水渗流效应分析及开发启示

摘要

以鄂尔多斯盆地志丹油田烟雾峁区块延长组长4+5,长6储层为例,基于岩心渗流实验的归一化处理、考虑启动压力梯度、引入有效驱动系数及油水粘度比,将渗流理论与室内实验及生产实践密切结合,综合分析特低～超低渗透储层油水渗流效应,探讨其注水开发启示.结果表明,特低～超低渗透储层渗流特征受启动压力影响,启动压力将导致油井提前见水;当含水饱和度大于某一临界值后,油层含水变化率逐渐减小,无因次采液指数与采油指数之间的分化逐渐加剧,其相对稳定的变化区间则是油层提液增产及调整挖潜的重要机遇期.依据无因次采液、采油指数变化规律及其相应的含水率变化区间,可将特低～超低渗透油层开采过程划分为初产、稳产、有效提液、低效循环等4个阶段;在中高含水期,较高的有效驱动系数有利于油层提液增产;在特高含水后期,较小的有效驱动系数及油水粘度比则有利于油层提高低效循环阶段的最终采收率.流体饱和度不仅对特低～超低渗透油层含水率及采液采油指数等变化具有重要的控制和影响,而且也是导致区块生产差异的主要因素.对于那些饱和度分布不同、平面及层间生产差异比较突出的井区,应依据其所处开采阶段分别采取不同的对策参数,以改善油田整体开发效果.%Taking the Chang 4 + 5 and Chang 6 reservoir of the Mesozoic's Yanchang Formation of YW block of Zhidan oiffield in Ordos basin as an example,based on the normalization processing of core seepage experiment data,considered starting pressure gradient,introduced effective driving coefficient and oil-water viscosity ratio,made the seepage theory closely combine with indoor experiment and production practice,synthetically analyzed oil-water percolation effect of extra-ultra low permeability reservoir,and discussed the water injection development enlightenment.The results showed that,the seepage characteristics of an extra-ultra low permeability reservoir influenced by the start-up pressure,start-up pressure would lead to water breakthrough in an oilwell ahead of time;when water saturation is greater than a certain critical value,rising rate of the reservoir water ratio would increase,the difference between dimensionless fluid and oil productivity index would gradually intensify,the relatively stable change interval between the two is an important time to adjust the exploit way for increasing oil production.Based on the change rule of dimensionless fluid and oil productivity index and the corresponding change range of moisture content,the development process of extra-ultra low permeable reservoirs can be divided into four stages:early production,stable production,effective increase production fluid,and low efficiency circulation;during medium and high water cut period,higher effective driving coefficient is helpful to increasing oil production;during ultra-high water cut stage,smaller effective driving coefficient and oiL/water viscosity ratio is beneficial to improve the ultimate recovery of low efficiency circulation stages.Fluid saturation has not only important control and influence on moisture content and fluid productivity index change for the extra-ultra low permeable reservoir,but also is a major factor that cause block production difference;For some well-block that has different saturation distribution and prominent production difference in plane and interlayer,its development process should take different countermeasures parameters to improve the oilfield overall development effect based on the mining stage.