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<p>Injecting CO<sub>2</sub> into an oil reservoir can enhance oil recovery and storage CO<sub>2</sub> at the same time. Initial oil saturation, wettability and CO<sub>2</sub> injection velocity will affect the flow characteristics of CO<sub>2</sub>, oil, and water in the rock matrix, thus affecting oil displacement efficiency and CO<sub>2</sub> sequestration rate. Combining the volume of the fluid method with image processing technology, a method for analyzing the three-phase displacement of porous media is composed to study the microscopic characteristics of CO<sub>2</sub>-oil–water displacement system under different conditions. The results show that the displacement phase diagram based on two-phase displacement is applicable to three-phase displacement as well. The inlet/outlet pressure difference increases sharply at the beginning of displacement, and then continuously decreases until it stabilizes. The average capillary pressures show a relatively stable trend overall. The final quantities of three-phase clusters show the following relationship: <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(N_{oil} &gt; N_{water} &gt; N_{{CO_{2} }}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mrow> <mi mathvariant="italic">oil</mi> </mrow> </msub> <mo>&gt;</mo> <msub> <mi>N</mi> <mrow> <mi mathvariant="italic">water</mi> </mrow> </msub> <mo>&gt;</mo> <msub> <mi>N</mi> <mrow> <mi>C</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation>. The relationship between the number and size of oil or water clusters obeys the power law <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(P(N)\sim S^{ - \tau }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mrow> <mo stretchy="false">(</mo> <mi>N</mi> <mo stretchy="false">)</mo> </mrow> <mo>∼</mo> <msup> <mi>S</mi> <mrow> <mo>-</mo> <mi>τ</mi> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>. Contact angle has the greatest impact on the displacement capability of CO<sub>2</sub> after breakthrough, followed by injection velocity. In addition, the effects of initial oil saturation, injection velocity, and wettability on sequestration rate and displacement efficiency are also discussed. The results show that initial oil saturation has little effect, while injection velocity and wettability have significant effects on sequestration rate and displacement efficiency. The research results can provide a theoretical basis for evaluating reservoir recovery and CO<sub>2</sub> sequestration rate. </p>

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Influence of Initial Oil Saturation, Injection Velocity and Wettability on Microscopic Characteristics in CO2-Oil–Water Displacement System

  • 期刊论文

  • 发表日期：

    2025年6月26日

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  • Xianxian Lyu,
  • Zhechao Wang,
  • Liping Qiao,
  • Fei Liang,
  • Zhu Han

摘要

Injecting CO2 into an oil reservoir can enhance oil recovery and storage CO2 at the same time. Initial oil saturation, wettability and CO2 injection velocity will affect the flow characteristics of CO2, oil, and water in the rock matrix, thus affecting oil displacement efficiency and CO2 sequestration rate. Combining the volume of the fluid method with image processing technology, a method for analyzing the three-phase displacement of porous media is composed to study the microscopic characteristics of CO2-oil–water displacement system under different conditions. The results show that the displacement phase diagram based on two-phase displacement is applicable to three-phase displacement as well. The inlet/outlet pressure difference increases sharply at the beginning of displacement, and then continuously decreases until it stabilizes. The average capillary pressures show a relatively stable trend overall. The final quantities of three-phase clusters show the following relationship: \(N_{oil} > N_{water} > N_{{CO_{2} }}\) N oil > N water > N C O 2 . The relationship between the number and size of oil or water clusters obeys the power law \(P(N)\sim S^{ - \tau }\) P ( N ) ∼ S - τ . Contact angle has the greatest impact on the displacement capability of CO2 after breakthrough, followed by injection velocity. In addition, the effects of initial oil saturation, injection velocity, and wettability on sequestration rate and displacement efficiency are also discussed. The results show that initial oil saturation has little effect, while injection velocity and wettability have significant effects on sequestration rate and displacement efficiency. The research results can provide a theoretical basis for evaluating reservoir recovery and CO2 sequestration rate.