Characteristics of fluid distribution and synergistic enhancement mechanisms during CO2+viscosity-reducing agent injection in heavy oil reservoirs

doi:10.3969/j.issn.1006-6535.2025.06.014

Abstract

Abstract: Faced with the difficulties of thermal development and low recovery in mid-deep heavy oil reservoirs,and based on the CO₂ solubility in heavy oil and the operational principle of viscosity-reducing agents,micro-scale flow simulations were conducted involving synergistic viscosity reduction and enhanced production experiments.The study examined the mechanism by which CO₂ and CO₂+viscosity-reducing agent jointly improved heavy oil recovery.Experimental results showed that under reservoir conditions,CO₂ dissolved in heavy oil to form minute CO₂-in-oil bubbles(0.016-0.051 mm in diameter),significantly improving crude oil mobility;after displacement,the swept coefficient reached 56.4% and oil recovery degree 37.3%.The viscosity-reducing agent caused crude oil to form fine emulsion droplets,expanding the CO₂ sweep area;the viscosity reduction rate exceeded 99.0%,and the swept coefficient reached 65.3%,with recovery up to 46.2%.This indicated that CO₂ improved oil flowability via solution-induced expansion and viscosity reduction,and its synergistic action with the viscosity-reducing agent could substantially enhance displacement efficiency and sweep extent.The formation of foam oil and blockages by emulsified droplets were the key mechanisms improving sweep efficiency.This study provides practical guidance for enhancing recovery in mid-deep heavy oil reservoirs and for realizing CO₂ geological styorage.

Key words: heavy oil reservoir, CO₂, PVT experiment, visualization experiment, sweep efficiency, synergistic enhancement

CLC Number:

TE345

ZHANG Yang, WANG Xiaoyan, WANG Haifeng, ZHANG Zufeng, ZHANG Nan, BAO Lei, PANG Zhanxi. Characteristics of fluid distribution and synergistic enhancement mechanisms during CO₂+viscosity-reducing agent injection in heavy oil reservoirs[J]. Special Oil & Gas Reservoirs, 2025, 32(6): 116-123.

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Characteristics of fluid distribution and synergistic enhancement mechanisms during CO₂+viscosity-reducing agent injection in heavy oil reservoirs

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