低渗砂砾岩储层三元孔隙结构特征及其渗流机理与改善水驱对策

Enhanced Water-Drive Recovery Based on Microscopic Seepage Mechanism for Low Permeability Glutenite Reservoir with Ternary Pore-Throat Structure Characteristics of WS Field

针对低渗砂砾岩与砂岩储层产能测试结果差异大的问题,以北部湾盆地乌石凹陷流沙港组低渗砂砾岩储层为主要研究对象,通过设计室内岩心实验开展了微观孔隙结构、微观渗流能力、微观渗流特征和改善水驱提高采收率策略研究.研究发现,乌石凹陷流沙港组低渗砂砾岩储层具有三元孔隙结构特征,大孔喉和微小孔喉更加发育,导致“高气测渗透率、低液测渗透率、低驱油效率”的渗流特征和“大孔喉富含注入水、中吼喉富含剩余油、微小孔喉富含原始束缚水”的剩余油微观分布特征,提高微观波及系数、增加中孔喉动用率是提高采收率的关键,建议采用注低价高矿化水转变润湿性和不稳定注水发挥渗吸作用的策略改善水驱效果、提高最终采收率.

In view of the large difference in productivity test results between low-permeability glutenite pay zone and sandstone pay zones,taking the low-permeability glutenite reservoir of Liushagang Formation in Wushi Sag of Beibu Gulf Basin as the main research object,the research on microscopic pore structure,microscopic seepage capacity,microscopic seepage characteristics and strategies for improving water flooding effect to enhance oil recovery was carried out through the indoor core experiments.The results show that the low-permeability glutenite reservoir has the characteristics of ternary pore structure,and the large pore throat and micro pore throat are more developed,resulting in the seepage characteristics of "high gas permeability,low liquid permeability,and low oil displacement efficiency" and the post-displacement fluid microscopic distribution characteristics of "large pore throat is rich in injection water,medium throat is rich in remaining oil,and micro pore throat is rich in original bound water".The key to improve the recovery factor of low permeability glutenite reservoir is to improve the microscopic sweep coefficient to increase the utilization rate of medium pore throat crude oil.It is suggested to change wettability by injecting low valent and high salinity water and utilize imbibition role by unsteady water injection to improve water flooding effect and enhance oil recovery.