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碳酸盐岩油藏注二氧化碳采收率及驱油效率影响因素实验研究

利用二氧化碳岩心注入实验，研究在有和没有流动水饱和的情况下，混相和近混相条件下影响二氧化碳注入驱替效率的参数。

EOR 是指提高采油率。首字母缩略词文本概念背景。霓虹灯闪耀的文字。3D 渲染
来源：Evgeny Gromov/Getty Images

混相气注入是轻质碳酸盐岩油藏中应用最广泛的提高采收率 (EOR) 方法，可作为三次和二次方法。混相气具有较高的驱替效率，通常会导致与气体接触的油藏部分的残余油饱和度 ( S orm ) 较低。准确测定S orm并了解影响驱替效率的参数对于混相气 EOR 项目的成功至关重要。

本文提出了一个全面的实验方案，旨在研究多个参数对混相和近混相二氧化碳 (CO 2 ) 注入的采油率、置换效率和S orm的影响。本研究调查的参数包括实验压力、注入的孔隙体积 (PV)、注入速率、岩石类型和初始水饱和度 ( S wi )。

岩心驱替实验使用新鲜原油，压力从低于最低混相压力 (MMP) 开始，到远高于 MMP，使用长达 1 英尺、直径达 2 英寸的储层岩心样品。所有二氧化碳注入实验均使用垂直岩心进行，从顶部注入气体以确保稳定置换。

实验结果表明：（1）原油采收率随压力降低而降低，当压力从4,250 psi 降至2,700 psi时， S orm增加超过20个饱和单位；（2）低压下CO 2突破发生得更早，从而导致更多的CO 2回收利用和潜在的CO 2封存量降低；（3）采收率受注入的PV 的影响很大，并且在低压下进行的实验中这种影响更为显著；（4）由于油和CO 2 之间的界面张力低，注入速率对混相或近混相CO 2 的原油采收率和S orm的影响不显著；（5）岩石非均质性对原油采收率和CO 2突破具有很强的影响，因此也影响CO 2回收利用和项目的经济性；（6）在注入CO 2之初存在流动水导致驱替效率降低和S orm升高。然而，这种水阻效应需要通过实验针对特定的储层岩石/流体系统来确定。本研究结果不能推广至其他储层。

本研究结果对所研究油藏中二氧化碳注入的设计和性能预测具有重要意义。建议在油藏压力下开始注入二氧化碳，在某些情况下，该压力比 MMP 高出 1,500 psi 以上，因为它具有出色的置换效率，并且由于后期突破而减少了二氧化碳的回收。但是，更高的压力可能会对所需的二氧化碳量、压缩成本和项目经济性产生负面影响。

本摘要摘自 SK Masalmeh（ADNOC）、SA Farzaneh 和 M. Sohrabi（赫瑞瓦特大学）以及 M. Alhammadi ADNOC 撰写的论文 SPE 218525。该论文已通过同行评审，可在 OnePetro 上的 SPE 期刊上以开放获取形式获取。

原文链接/JPT
Enhanced recovery

Experimental Investigation of Factors Affecting Oil Recovery and Displacement Efficiency of Carbon Dioxide Injection in Carbonate Reservoirs

Investigation into the parameters affecting the displacement efficiency of CO2 injection under miscible and near-miscible conditions in the presence and absence of mobile water saturation using carbon dioxide core injection experiments.

EOR mean Enhanced oil recovery. Acronym text concept background. Neon shine text. 3D render
Source: Evgeny Gromov/Getty Images

Miscible gas injection is the most widely applied enhanced oil recovery (EOR) method in light oil carbonate reservoirs as a tertiary and secondary method. Miscible gas has high displacement efficiency and usually results in a low residual oil saturation (Sorm) in the parts of the reservoirs that are in contact with the gas. Accurate determination of Sorm and understanding the parameters that affect displacement efficiency are crucial for successful miscible gas EOR projects.

In this paper, we present a comprehensive experimental program designed to investigate the effect of several parameters on oil recovery, displacement efficiency, and Sorm of miscible and near-miscible carbon dioxide (CO2) injection. The parameters investigated in this study are the experimental pressure, pore volume (PV) injected, injection rate, rock type, and initial water saturation (Swi).

The coreflood experiments were performed using live crude oil at pressures starting below the minimum miscibility pressure (MMP) to pressure well above the MMP, using reservoir core samples of up to 1 ft long and 2 in. in diameter. All CO2 injection experiments were performed using vertically oriented cores, with gas injection from the top to ensure stable displacement.

The experimental results show that (1) oil recovery decreases as pressure decreases with Sorm increasing by more than 20 saturation units as the pressure decreases from 4,250 psi to 2,700 psi; (2) CO2 breakthrough was much earlier at lower pressure, which leads to more CO2 recycling and potentially lower CO2 sequestration volume; (3) the recovery factor is strongly affected by the PV injected, and this effect is much more significant for the experiments performed at lower pressure; (4) the injection rate has an insignificant effect on oil recovery and Sorm for miscible or near-miscible CO2 because of the low interfacial tension between oil and CO2; (5) rock heterogeneity has a strong effect on oil recovery and CO2 breakthrough and, hence, on CO2 recycling and economy of the projects; and (6) the presence of mobile water at the beginning of CO2 injection resulted in lower displacement efficiency and increased Sorm. However, this water blocking effect should be determined experimentally for a given reservoir rock/fluid system. The results of this study cannot be generalized for other reservoirs.

The results of this study have important implications for the design and performance predictions of CO2 injection in the reservoirs under study. Starting CO2 injection at reservoir pressure, which, in some cases, is more than 1,500 psi above MMP, is recommended because of its superior displacement efficiency and less CO2 recycling because of later breakthrough. However, a higher pressure may negatively affect the required CO2 volume, the compression cost, and project economics.

This abstract is taken from paper SPE 218525 by S. K. Masalmeh, ADNOC; S. A. Farzaneh and M. Sohrabi, Heriot-Watt University; and M. Alhammadi ADNOC. The paper has been peer reviewed and is available as Open Access in SPE Journal on OnePetro.