长期水驱对低渗储层物性与渗流特征影响实验研究

Experimental study on the influence of long-term waterflooding on physical properties and percolation characteristics of low permeability reservoir

针对长庆安塞油田长期水驱开发后,注水井近井地带储层孔隙度、渗透率变化规律认识不清的问题,开展了长期水驱前后的孔隙度、渗透率测试,结合X衍射全岩与黏土矿物分析、场发射扫描电镜、计算机断层扫描、恒速压汞等实验,分析了引起岩石物性参数变化的原因。结果表明:长期水驱后,黏土矿物矿物含量下降,水流通道壁上的黏土矿物颗粒被水流冲刷发生膨胀及运移,在喉道处形成堵塞,表现为喉道半径分布呈现出大喉道所占比例降低,中小喉道所占比例升高的趋势。长期水驱后的注水井近井地带储层孔隙度增大,渗透率降低,束缚水饱和度和前缘含水饱和度升高,残余油饱和度降低,驱油效率升高。由于近注水井地带储层渗透率降低,有可能起到类似堵水的效果,堵塞一部分优势水流通道,从一定程度上降低了注水井近井地带非均质性,使得注入水更多进入低渗透储层,从而提高注入水的波及系数。

After a long-term waterflooding development in Ansai Oilfield,Changqing Oilfield,the reservoir porosity and permeability changes in the area near the water injection well are not clearly understood.The porosity and permeability tests before and after a long-term waterflooding are carried out,and the changes of rock physical parameters caused by the changes are analyzed in combination with X-ray diffraction analysis of whole rock and clay minerals,field emission scanning electron microscopy,computer fault scanning,constant velocity mercury injection and other experiments reason.The results show that after long-term water flooding,the content of clay minerals decreases,the clay mineral particles on the wall of the water channel expand and migrate,and form blockage at the throat,which shows that the distribution of throat radius shows the trend of reducing the proportion of large throat and increasing the proportion of medium and small throat.After long-term water flooding,the reservoir porosity near the well increases,the permeability decreases,the irreducible water saturation and the front water saturation increase,the residual oil saturation decreases,and the displacement efficiency increases.Due to the decrease of reservoir permeability near the water injection well,it is possible to have the similar effect of water plugging,blocking some of the dominant water flow channels,reducing the heterogeneity of the near well area of the water injection well to a certain extent,making the injected water more into the low-permeability reservoir,so as to improve the sweep efficiency of the injected water.