Study on the Mechanism of Reversing Oil Displacement for Increasing the Production of Crude Oil in Low Permeability and Ultra-Low Permeability Oil Field

Abstract

Conventional water flooding method becomes ineffective facing low and ultra-low permeability oilfields, and the recovery rate of the non water harvesting period is only about 20%. Most residual oil is trapped in the reservoir and cannot be recovered. The conversion of injection well into production ones is used on some scale at home and abroad as a technique of oilfield adjustment, stimulation and EOR. Yet, problems like the optimum converting time, microscopic stimulation mechanisms, etc., have not been clearly studied. The optimum time for reverse displacement can be acquired through forward and reverse displacement experiments of man-made cores with different permeability. Then, based on CT scanning technology an analysis is made of the processes of the forward displacement (till the converting time point) and the reverse displacement (till the end). According to the information of pores and water-oil distribution extracted from the CT graphs, water flooding characteristics and the change in residual oil distribution in different layers and at different displacement stages can be recognized. With the process of forward water injection, the residual oil in the core behave as types of discontinuous phases, including film flow, blob flow, slug flow, multi-pore flow, etc., the total volume fraction of which increases with the displacement continuing. During the reverse displacement, in contrast, the former dispersed residual oil gradually gathered in cluster that is comparatively more recognizable. Meanwhile, the amount of multi-pore flow ascend, which is most obvious. These factors made part of the residual oil better displaced. By above analysis, a reasonable microscopic explanation of the stimulation technology by converting injection wells into production ones. The article concisely and directly uncovered the microscopic mechanism of the reverse displacement to enhance oil recovery. Based on the study and taking other influential factors of development into account, instructions can be made on further EOR process of low and ultra-low permeability oilfield at lower costs and with higher efficiency, which is one of the top concerns for most low permeability oilfields.