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