安塞油田长6油层组长期注水后储层变化特征

在注水开发模拟实验及现场测试资料的基础上,以压汞实验、物性测试等方法对模拟实验前后岩芯进行分析,研究了安塞油田长6油层组长期注水开发后储层特征变化规律及成因。结果表明,随着注水量增加,渗透率总体明显降低,渗透率平均变化4.72%;水驱后孔隙度平均增加0.15%,而孔隙组合类型未发生明显变化;退汞效率平均降低4.39%;喉道中值半径变小但分布类型没变化;储层润湿性整体向亲水方向发展。低渗透储层特征发生变化的机理主要是:储层中颗粒和填隙物在注入水的冲刷作用下发生溶解、破碎和迁移,一部分被水冲出,一部分滞留在细喉道处形成堵塞,导致孔喉连通性变差,储层非均质性增强;注入水冲刷作用使储层岩石表面及孔喉表面性质发生变化,进而引起储层润湿性发生变化。

Characteristics of Chang-6 Oil-bearing Formation Changes After Long Term Waterflood Development in Ansai Oilfield

Based on waterflood development simulated experiment and field data analyses, core was analyzed by mercury injection experiment and physical-mechanical test, characteristics of Chang-6 Oil-bearing Formation changes after long term waterflood development in Ansai Oilfield was discussed. The result showed that permeability evidently decreased with the increase of water injection rate as a whole, the average rate of change was 4.72%; porosity increased by an average of 0.15% and there was no apparent change in the type of pore combination; efficiency of mercury withdraw decreased by an average of 4.39%; the median radius of throats diminished, however, there was no significant change of distribution characteristics; reservoir wettability transformed from lipophile to hydrophile on the whole. Characteristics of low-permeability reservoir varied after long term waterflood development. The mechanisms were that the clay particle and interstitial material in reservoir dissolved, crushed and moved by the action of injected water washing, one part was carried away by injected water, and the another part still stayed in thin pore-throat, caused the pore connectivity worse and the heterogeneity of reservoir was stronger; the variation of the properties of reservoir rock and pore-throat surfaces caused the change of reservoir wettability.