利用注聚合物泥浆伤害岩电实验参数变化评价特低渗透储层

Evaluation of ultra-low permeability reservoirs by electricparameter variation of damaging polymer mud in the petrophysical experiment

针对鄂尔多斯盆地陕北斜坡长6特低渗透储层受聚合物泥浆伤害,微电极电阻率曲线在渗透层上的正幅度差异不明显,直观指示油气层和水层的深、中、浅探测电阻率在常规储层的有序排列基本消失.通过注聚合物泥浆驱替前后岩石电阻率与孔隙度及含水饱和度实验关系分析,驱替后岩样电阻率显著增大,岩样电阻率随含水饱和度增大而减小的基本规律不复存在.归纳其岩性系数a、电阻率系数b比驱替前大得多,饱和度指数n由正变负,反映出注聚合物泥浆驱替破坏了储层孔隙结构及其基本特征,测井中造成了范围较小的高侵和特高侵地层电阻率带.从而提出在较为致密的低渗砂、致密砂聚合物泥浆伤害储层中,利用微电极负差异及其电阻率曲线不规则增高变化划分特低渗透油层有效厚度,并以实例阐明了利用岩电实验参数变化评价特低渗透储层的方法.

Ultra-low permeability reservoirs can be damaged by polymer mud in the Chang 6 reservoir of Shanbei Slope of Ordos Basin. It makes positive range separation of microelectrode resistivity curve of permeable beds not obvious, and the ordered arrangements of ME and DIL-MSFL which intuitively indicate hydrocarbon reservoir and water zone disappear. By experimental analysis on rock resistivity, porosity and water saturation before and after polymer flooding, core resistivity in the experiment was notably increased, and the phenomenon that core resistivity reduces as wa ter saturation increases disappears. The results showed that lithology factor A and resistivity factor B are much greater than that before displacement, and saturation exponent N is changed from positive to negative, reflecting that reservoir pore structure and its essential characteristics are destroyed after polymer flooding. And it results in a smaller range of high and ultra-high transgression formation resistivity zone in logging. Because reservoirs damaged by polymer mud include dense low permeability sad and competent sand, it is suggested that effective thickness of ultra-low permeability reservoirs can be determinedby irregular changes of micro-electrode negative separation and its resistivity curve. Finally, the method that evaluation of ultra-low permeability reservoirs is madeby parameter variation of electric petrophysical experiment is tested by example.