Abstract
Many experimental investigations on carbonated water injection (CWI) have shown an increase in oil recovery which CWI is defined as the process of injecting CO2-saturated water in oil reservoirs as a displacing fluid. In every enhanced oil recovery method, the potential formation damage of the injected fluid is considered. This is due to the fact that the injection of incompatible fluids often causes clay swelling and fines migration and thus impairs the formation permeability. Permeability reduction by clay particles mostly depends on its distribution which can be pore lining, pore bridging, dispersed or combination of these causing pore blocking or pore-throat diameter reduction. Besides, fine migration is considered as an important mechanism of recovery improvement during injection of low-salinity water in sandstone oil reservoirs. The present paper investigates the impact of injection of carbonated water and brines with the different salt concentrations on oil recovery and formation damage focusing on permeability variation. The investigation has been done on 12 relatively homogeneous clay-containing sandstone cores, while the compositions of the injection water were varied from 40,000 to 1000 ppm, at 176° F and 2000 psi. The amount of recovery improvement and permeability drop recorded in all tests and the fine effluent of two experiments were analysed using XRD, one for CWI and one for WF (water flooding). In all salinities, CWI has shown more oil recovery improvement than conventional water. CWI of 40,000 ppm showed the minimum permeability reduction of 6 percent, while the highest permeability was obtained by injection of water with 1000 ppm. Maximum ultimate oil recoveries of 61.2% and 42% were achieved by 1000 ppm both for CWI and WF, respectively. In comparison with brine injection, CWI resulted in more permeability drop in salinity above critical salt concentration (CSC), while below CSC, WF has caused more formation damage than CWI. Experimental results also showed that fine migration was the main reason behind formation damage. It was also revealed that permeability was significantly reduced due to fine production in the effluent.
Highlights
In today’s world, inexpensive production of oil and gas is decreasing, and the side expenditures of operations are rising
We carried out several low-salinity water injections into the cores to evaluate the amount of ultimate oil recovery improvement in each salinity in the absence of dissolved carbon dioxide
This paper investigated the influence of carbonated water injection (CWI) and WF on oil recovery improvement and induced formation damage in various low salinities
Summary
In today’s world, inexpensive production of oil and gas is decreasing, and the side expenditures of operations are rising. Even after implementing these methods, a significant part of IOIP (initial oil in place) remains in the underground, in heavy oil reservoirs. In this regard, investigating an efficient EOR method is highly recommended. There is a heated controversy around potential concerns of global warming throughout the world This issue has made the utilisation of greenhouse gases globally viral in EOR projects. Among these greenhouse gases, CO2 has the advantages of the highest solubility in water which would increase water density and decrease the oil density. On the other hand, CO2 usually is placed in the critical state in the most reservoirs condition, which brings in advantages of chemical stability, high volume and density compared to noncritical state (Egermann et al 2005)
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