Investigation of CO2 flooding considering the effect of confinement on phase behavior

doi:10.13745/j.esf.sf.2022.2.80

Abstract

Abstract:

CO₂ injection can effectively improve oil recovery in tight oil reservoirs. However, the micro-nano pores in tight formations lead to confinement, such as adsorption or fluid-pore wall interaction; whilst the conventional theory of phase equilibrium can not well describe the interaction between CO₂ and hydrocarbons. To address this problem, this paper first proposes a phase equilibrium model considering micro-nano confinement. The model modifies the Peng-Robinson Equation of State (PR-EOS) by introducing adsorption effect and fluid-pore wall interaction parameters. The relative deviations of dimensionless critical temperature and pressure of fluid components are evaluated respectively. The calculated results show good agreements with the experimental data, validating the proposed model. Then, fluid phase behavior under reservoir temperature and pressure is evaluated. Results show that micro-nano confinement reduces the bubble point pressure, increases the dissolved gas/oil ratio and formation volume factor, and reduces oil viscosity and interfacial tension. In addition, results of light hydrocarbon extraction and CO₂ diffusion indicate that the micro-nano confinement effect reduces the extraction coefficient of light hydrocarbon and enhances CO₂ diffusion, which facilitate CO₂-crude oil contacts and improve oil recovery. The proposed model can accurately predict the phase behavior of the CO₂-multicomponent mixture in tight formations, and provide strong theoretical support for the application of CO₂-EOR in tight oil reservoirs.

Key words: micro-nano pore confinement, phase equilibrium, CO₂ flooding, CO₂ diffusion, tight formations

CLC Number:

T348

ZHANG Yuan, ZHANG Min, LIU Renjing, CHEN Junjie. Investigation of CO₂ flooding considering the effect of confinement on phase behavior[J]. Earth Science Frontiers, 2023, 30(2): 306-315.

Figures/Tables 14

Fig.1 Rectangular pore cross section

Fig.2 Flow chart of phase equilibrium calculation considering adsorption effect and fluid molecule pore wall interaction

Fig.3 Critical temperature and pressure shift of different components

Table 1 Critical temperature and pressure of bulk fluid and confined fluid

限域效应参数	临界温度、压力及其单位	CO₂	N₂	C₁	C₂-C₅	C₆-C₁₀	C₁₁₊
bulk	T_c/K	304.200	126.200	190.600	274.740	438.680	740.290
bulk	P_c/MPa	7.353	3.384	4.585	3.687	2.533	1.773
β=1.5	T_cm1/K	291.548	120.951	182.673	263.313	420.432	709.502
η=0.4	P_cm1/MPa	7.047	3.243	4.395	3.533	2.428	1.699
β=1.5	T_cm2/K	289.529	120.453	182.237	260.869	412.167	709.330
η=0.7	P_cm2/MPa	6.9667	3.220	4.377	3.479	2.348	1.698
β=2.5	T_cm3/K	283.114	117.452	177.388	255.695	408.269	688.977
η=0.4	P_cm3/MPa	6.843	3.149	4.268	3.431	2.357	1.650

Fig.4 Pressure-Temperature phase diagram of Eagle Ford reservoir

Fig.5 RS, Bo and μo under different parameters η and β

Fig.6 The interfacial tension under different parameters β and η

Fig.7 The interfacial intension under different CO2 injection(β=0.7,η=1.5)

Fig.8 Extraction coefficient of methane under different parameters β and η

Fig.9 Extraction coefficient of methane under different CO2 injection(β=0.7,η=1.5)

Fig.10 CO2 diffusion coefficient in liquid phase under different parameters β and η

Fig.11 CO2 diffusion coefficient in gas phase under different parameters β and η

Fig.12 Diffusion coefficient of CO2 in liquid phase under different CO2 injection(β=0.7, η=1.5)

Fig.13 Diffusion coefficient of CO2 in vapor phase under different CO2 injection(β=0.7, η=1.5)

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Investigation of CO₂ flooding considering the effect of confinement on phase behavior

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