An Advanced Approach to Study the Seepage Characteristics of Dynamic Remaining Oil in Porous Media at Pore Scale

摘要

The study of remaining oil microscopic percolation characteristics in porous media at pore scale plays an important role in enhanced oil recovery. Especially the dynamic remaining oil, which is different from the static remaining oil, makes a major contribution to production. The study of dynamic remaining oil percolation characteristics in pore scale plays an important role in both explaining the micro flow mechanisms from micro level and providing theoretical guidance to enhance oil recovery. In this paper, dynamic remaining oil is first defined by comparing to the static remaining oil and an advanced method combining the glass etching microscopic model experiments and computer image processing & recognition techniques that can identify and analyze the flow characteristics in pore scale is introduced. The method can automatically classify the microscopic remaining oil flowing patterns considering the flowing shape and the connect-relationship among the oil, water and rock. Compared to artificial identification results, the error range of this method is less than 5%. Meanwhile, it increases the processing speed greatly. And furthermore it provides an approach for the studying of dynamic remaining oil seepage characteristics in pore scale. Then the advanced approach is used to analyze the variable relationship of pore scale different flowing patterns micro dynamic remaining oil in high water cut period. Research result shows that all the remaining oil in ultrahigh water cut period can be classified into five categories that respectively are clustered stream, multi-porous stream, columnar stream, membranous stream and droplet stream. Among of the five categories, clustered stream possess the largest proportion and are also the main factor of relative permeability curves recurved. Meanwhile, with water saturation rising, clustered stream gradually transformed into other patterns like multi-porous stream, columnar stream, membranous stream and droplet stream. Also we find that the occurring occasion of clustered stream inflection point is positively correlated to the maximum water saturation. Meantime, the result indicates oil/water flowing regularity and the reason of oil-water relative permeability curves non-linearity during ultrahigh water cut period from the microscopic point of view. And it also provides a guidance to enhance recovery degree of remaining oil and the recovery efficiency. Overall, an open and flexible research method to study dynamic remaining oil about flowing characteristics in pore scale by combining microscopic etching glass modeling experiment and computer image recognition & processing technology is introduced in this paper. And according to different research purposes, the range of characteristic parameters is easy to be adjusted to meet various studying demands.