Experimental Study of Pore-Scale Mechanisms of Carbonated Water Injection

Abstract

Carbon dioxide (CO 2 ) injection is a well-established method for increasing recovery from oil reservoirs. However, poor sweep efficiency has been reported in many CO 2 injection projects due to the high mobility contrast between CO 2 and oil and water. Various injection strategies including gravity stable, WAG and SWAG have been suggested and, to some extent, applied in the field to alleviate this problem. An alternative injection strategy is carbonated water injection (CWI). In CWI, CO 2 is delivered to a much larger part of the reservoir compared to direct CO 2 injection due to a much improved sweep efficiency. In CWI, CO 2 is used efficiently and much less CO 2 is required compared to conventional CO 2 flooding, and hence the process is particularly attractive for reservoirs with limited access to large quantities of CO 2 (offshore reservoirs or reservoirs far away from inexpensive natural CO 2 resources). This article describes the results of a pore-scale study of the process of CWI by performing high-pressure visualisation flow experiments. The experimental results show that CWI, compared to unadulterated (conventional) water injection, improves oil recovery as both a secondary (before water flooding) and a tertiary (after water flooding) recovery method. The mechanisms of oil recovery by CWI include oil swelling, coalescence of the isolated oil ganglia and flow diversion due to flow restriction in some of the pores as a result of oil swelling and the resultant fluid redistribution. In this article the potential benefit of a subsequent depressurisation period on oil recovery after the CWI period is also investigated.

The influence of spreading coefficient on carbonated water alternating gas injection in a heavy crude oil

“…This is likely due to dissolved CO 2 in both phase of crude oil and brine that increases with pressure. Oil swelling is one of the most important mechanisms that have also been observed at carbonated water injection prior to the CO 2 injection in the micromodel tests using the light and heavy oils [5]. Under the same pressure, increase in IFT is expected due to the lower solubility of carbon dioxide in the brine and oil phases at higher temperature.…”

“…Moreover, they observed that CO 2 flooding performances after WI and CWI are different. That was, the injection of carbon dioxide after CWI recovered more oil compared to that after WI [5,38]. The proposed mechanism for the higher performance of CO 2 I in the former process was due to the existence of a continuous oil film between the water and the displacing CO 2 phases.…”

“…To produce the trapped oil phase enhanced oil recovery (EOR) techniques are suggested and applied [1,2]. In this regard, extensive laboratory studies and field applications of water alternating gas injection (WAGI), cyclic injection of carbonated water (CW) and CO 2 , carbon dioxide-EOR processes to investigate the potential of carbonated water injection as an injection method for improved oil recovery and CO 2 storage have been performed [3][4][5][6][7][8]. Storing carbon dioxide underground is being considered as a promising sequestration technology for mitigating greenhouse gas emissions [9][10][11].…”

“…crude oil, reservoir brine and CO 2 ) distribution, and flow behavior within http reservoir at high pressure conditions [12,13]. Two main mechanisms of oil recovery that occur in the carbonated water injection (CWI) process include swelling and coalescence of trapped oil and the oil viscosity reduction as a result of diffusion and segregation of CO 2 from carbonated water into oil [5]. The interfacial tension reduction can also be the other positive effect of CWI compared to water injection (WI) process in the oil reservoir [14].…”

Experimental Investigation on CO2 Injection in Block M

“…e most commonly used methods for EOR by CO 2 injection are CO 2 -water alternate flooding, immiscible flooding, miscible flooding, and cyclic CO 2 injection [5,6]. e mechanism of EOR by injecting CO 2 primarily includes a reduction in the viscosity of crude oil and expansion, vaporization, extraction, and improvement in the oil removal efficiency [7,8].…”