WHZ油田致密储层微观特征及介质变形敏感实验

Microscopic characteristics and sensitivity experiment of medium deformation in the tight reservoirs of WHZ oilfield

致密储层普遍存在应力敏感现象,会造成油井生产一段时间后产量大幅递减。针对WHZ油田致密储层开发过程中存在的问题,利用岩心核磁共振T2测试方法,得到孔喉半径及T2截止值等参数,分析了WHZ油田致密储层岩石组成、孔喉结构及孔渗分布等微观特征,基于岩心流动实验及统计分析方法,得到升、降围压过程中随围压变化的渗透率,研究了致密储层无因次渗透率与无因次围压之间的函数关系,分析了致密储层介质变形影响因素,并结合矿场实际分析不同开发方式下的油田生产情况。结果表明:WHZ油田致密储层多孔介质经过升、降围压后,渗透率将产生不可逆损失,且压力降低会影响孔喉结构的重新分布,即使补充能量也难以恢复至初始值,存在储层介质永久性伤害。WHZ油田实际资料表明,降压开采使产能受损,同期产能同步注水开发高于未注水开发。因此,在油田开发过程中应尽量保持合理的地层压力,避免因储层介质变形引起产量损失。

Common phenomenon of stress sensitivity in the tight reservoirs may result in great decline of production after producing for some time for the oil wells. According to the development problem of the tight reservoirs in WHZ oilfield,T2 testing method through core NMR was applied to obtain pore-throat radius and T2 cutoff value and other parameters. The microscopic characteristics of rock composition,the pore-throat structure and the distribution of porosity and permeability in the tight reservoirs of WHZ oilfield were analyzed. Based on the experiment of core flooding and the method of statistical analysis,the variation of core permeability with the confining pressure was understood,and the function relationship between dimensionless permeability and dimensionless confining pressure for the tight reservoirs was researched. Influencing factors on medium deformation for the tight reservoirs were analyzed and the oilfield production situation under various development modes was analyzed combined with the actual field situation. The result shows that the permeability damage of porous medium is irreversible under loading and unloading confining pressure for the tight reservoirs in WHZ oilfield,and the re-distribution of pore-throat structure may be affected in the process of pressure drop. It's hard to recover the initial value and permanent damage may form for the reservoir even if energy is supplemented. Actual data of the WHZ oilfield show that the productivity loss may occur under pressure drop and the productivity with synchronous water flooding may be higher than that with no water flooding. Therefore,a reasonable formation pressure is necessary in the process of oilfield development,which may avoid production loss resulted from medium deformation of the reservoirs.