基于孔隙尺度的碳酸盐岩油藏微观剩余油变化特征

Study on microscopic residual oil variation characteristics in carbonate reservoirs based on the pore-scale research

碳酸盐岩油藏储量丰富且产量可观,是目前油气勘探开发的重要领域。由于具有孔喉结构复杂、孔渗相关性差、非均质性强等特征,此类油藏经水驱开发后剩余油分布情况复杂,导致后续提高采收率措施应用效果不理想,调整方向不明确。为探究碳酸盐岩油藏水驱过程中剩余油分布及其变化特征,选取不同渗透率的碳酸盐岩岩样,利用原位CT扫描技术,在不同驱替速度条件下获取水驱开发结果;将差分成像法与分水岭算法相结合,通过图像处理操作进一步量化识别岩样孔隙结构,并形成孔隙组成对微观剩余油分布影响的综合认识。研究结果表明:随着水驱过程中注入速度增加,剩余油饱和度呈下降趋势,其中簇状剩余油占比降低,而膜状和滴状剩余油占比升高,且低渗储层的采收率提高程度优于高渗储层;储层孔喉尺寸越小,孔喉连通性越差,剩余油分布越零散,簇状剩余油体积越小,滴状剩余油滞留比例越高。此类油藏的后期开发应重点改善微观孔隙与孔隙边缘剩余油动用效果,并依据储层的渗透率条件使用不同的开发方式及适宜的生产参数。本文研究可为碳酸盐岩油藏提高采收率方法的选择提供依据。

Carbonate reservoirs are abundant in reserves and have considerable production potential,which is a crucial area for current oil and gas exploration,development.Due to their complex pore-throat structure,poor pore-permeability correlation,and strong heterogeneity,the distribution of remaining oil in such reservoirs after water flooding is complex.This complexity leads to ineffective application of subsequent enhanced oil recovery measures and unclear adjustment directions.In order to explore the distribution and variation characteristics of remaining oil during water flooding in carbonate reservoirs,carbonate rock samples with different permeabilities were selected and in-situ CT scanning technology was used to obtain the results of water flooding development under different displacement speeds.The differential imaging method was combined with the watershed algorithm to further quantify and identify the pore structure of rock samples through image processing operations,forming a comprehensive understanding of the impact of pore composition on the distribution of microscopic remaining oil.The results show that as the injection rate increases during water flooding,the remaining oil saturation shows a downward trend,in which the proportion of clustered remaining oil decreases,while the proportion of film and drop-shaped remaining oil increases.The degree of recovery improvement in low permeability reservoirs is better than that in high permeability reservoirs.The smaller the pore-throat size and the poorer the connectivity of pore-throats,the more scattered the distribution of remaining oil,the smaller the volume of clustered residual oil,and the higher the retention proportion of droplet residual oil.Consequently,the later-stage development of such reservoirs should focus on improving the mobilization effectiveness of micro-pore and pore-edge residual oil.Different development methods along with appropriate production parameters should be employed based on the reservoir's permeability conditions.This study provides a basis for selecting methods to improve oil recovery in carbonate reservoirs.