考虑微纳米限域效应对相平衡影响的CO2驱油机理研究

doi:10.13745/j.esf.sf.2022.2.80

摘要/Abstract

摘要：

注二氧化碳能够有效提高致密油藏采收率。然而,致密储层低孔、低渗,微纳米孔喉发育,孔隙中流体受到吸附、流体分子与孔壁相互作用等限域效应的影响,传统相态理论难以对微纳米孔隙中二氧化碳同烃类的相互作用进行准确描述。为此,本文首先提出一种考虑微纳米限域效应的相平衡理论模型。通过引入吸附效应和流体分子-孔壁相互作用参数,对Peng-Robinson状态方程(PR-EOS)进行修正。分别计算了流体组分的无因次临界温度和临界压力的相对偏差值,计算值同实验值符合良好,验证了算法的准确性。然后进行了储层温度压力下的流体相平衡计算。结果表明,微纳米限域效应使流体泡点压力降低,溶解气油比和地层油体积系数增大,原油黏度和界面张力降低。此外,对于CO₂驱油过程中轻烃抽提作用和CO₂扩散作用研究表明,微纳米限域效应使轻烃的抽提系数降低,CO₂扩散作用增强,有利于CO₂与原油充分接触,提高原油采收率。该模型能够准确预测致密储层CO₂-原油多组分混合物的相行为,为致密储层CO₂驱油提高采收率技术的应用提供理论支持。

关键词: 微纳米限域效应, 相平衡, CO₂驱油, CO₂扩散, 致密储层

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

中图分类号:

T348

张园, 张敏, 刘仁静, 陈俊杰. 考虑微纳米限域效应对相平衡影响的CO₂驱油机理研究[J]. 地学前缘, 2023, 30(2): 306-315.

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.

图/表 14

图1 矩形孔型结构

Fig.1 Rectangular pore cross section

图2 考虑吸附效应和流体分子-孔壁相互作用的相平衡理论计算流程图

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

图3 组分临界温度和临界压力相对偏差值 (a)临界温度相对偏差[19⇓-21];(b)临界压力相对偏差[22-23]。

Fig.3 Critical temperature and pressure shift of different components

表1 体相流体和受限流体的临界温度和临界压力值

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

图4 Eagle Ford储层流体的压力-温度相图

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

图5 不同参数η和β下的Rs,Bo和μo a—溶解气油比Rs;b—地层油体积系数Bo;c—原油黏度μo。

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

图6 不同参数β和η下的界面张力变化

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

图7 不同CO2注入下,界面张力的大小(β=0.7,η=1.5)

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

图8 不同参数β和η下,轻烃的抽提系数

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

图9 不同CO2注入下,轻烃的抽提系数(β=0.7,η=1.5)

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

图10 不同参数β和η下,CO2在液相中的扩散系数

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

图11 不同参数β和η下,CO2在气相中的扩散系数

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

图12 不同CO2注入下,CO2在液相中的扩散系数(β=0.7,η=1.5)

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

图13 不同CO2注入下,CO2在气相中的扩散系数(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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考虑微纳米限域效应对相平衡影响的CO₂驱油机理研究

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

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