The effect of CO2 on carbonate rock during carbon dioxide flooding of petroleum reservoirs was investigated using dolomite cores. The studies were made at several pressure levels to determine the effects of pressure on the interaction of CO2 and dolomite.
Fifteen cylindrical dolomite cores with lengths varying from 3 in. to 9 in. and with diameters of 2.25 inches were chosen for the study. The cores were saturated with 0.1 N KCl solution which was displaced with liquid CO2. The tests were conducted at pressures varying from 1000 psig to 2500 psig. while the temperature of the system was maintained 80 °F.
The results of the laboratory study showed that CO2 would dissolve some of the rock aroundan injection well in a field application. The higher the injection pressure, the more pronounced would be this effect. Dissolved carbonate was found to be precipitated along the flow path as the pressure dropped in the laboratory experiments. The precipitate reduced the permeability of the rock. The amount of carbonate precipitated was dependent on the magnitude of the pressure drop. The larger the pressure drop. the more the carbonate precipitation and the reduction in the permeability of the rock.
The efficiency of a tertiary oil recovery process will be affected when the injected fluid(s) react chemically with the reservoir rock.l Chemical reaction between the rock and the injected fluid could be in form of fluid adsorption on to the rock surfaces or rock dissolution by the injected fluid. In microemulsion flooding, the efficiency of the process is affected by surfactant adsorption on to the rock surface.1 Holm2 reported a study in which the permeability of a dolomite core increased threefold after about nine pore volumes of carbon dioxid.e slug and carbonated water was injected through the core. This is a case of rock dissolution by the injected fluid. CrawEord et. al 3 reported a case history in which the use of carbonated water as postfracture treating fluid resulted in rapid and complete well cleanup.
Formation of stalactite and stalagmite in caverns show that. although carbon dioxide does dissolve carbonate rocks in the presence of water, the reaction is to some extent reversible in nature. This understanding can be extended to the reaction between CO2 and the rock in CO2 flooding of carbonate reservoirs. Since many carbonate reservoirs (mostly dolomite are potential candidates for CO2 flooding, there is a need, EOR an in-depth study of the reaction between CO2 and dolomite rock. The object of this study was to investigate the effect of CO2 on dolomite rocks and the effect of pressure on CO2-dolomite rock interaction.
The purpose of this paper is to present the result of the investigation to show that while CO2 can dissolve pore linings of carbonate rocks and increase the rock permeability near the injection well, calcite crystals are precipitated and are deposited in the flow path when the pressure is reduced.