Pore Level Visual Investigation of Oil Recovery by Solution Gas Drive and Gas Injection

Abstract

Abstract The mechanisms of oil recovery by solution gas drive and by gas injection have been studied. The flow visualization experiments were performed in a high pressure heterogeneous micromodel reproduced from real rock micrographs. The micromodel was also employed in series with a compatible glass head pack. Pressure depletion and displacement experiments by methane, propane and water flooding were conducted on a live North Sea crude. The video observations and the measurements made are reported. The pore level investigation of solution gas drive revealed the mechanisms of nucleation, and the growth of gas bubbles at different pressure levels. The spontaneous movements of large bubble-oil interfaces contribute to the oil recovery process during the early stages of production. The recovery mechanisms at the higher gas saturations were found to be similar to be immiscible gas drive behavior observed with experiments of methane injection at low capillary numbers. The asphaltenes flocculation under dynamic conditions of oil displacement was studied by propane slug injection. The miscible displacement of oil by propane did not induce any significant asphaltene precipitation within the pores. Introduction Microscopic mechanisms of multiphase flow in porous media determine the oil recovery behavior. Visual microscopic studies under conditions similar to the real recovery processes in the reservoir can provide a valuable insight into the complex fluid transport mechanisms within the pore space of an oil reservoir. The mechanisms of oil recovery by solution gas drive have not been fully studied. A microscopic investigation of the recovery mechanisms can lead to a better understanding of the gas bubble nucleation and displacement behavior. Further the vast amount of reservoir engineering information generated during this mode of recovery may be used more successfully for gas injection studies when the mechanics of the recovery methods are more clearly understood. In an undersaturated oil reservoir, when the oil is produced and the reservoir pressure drops to the saturation point, the evolvement of the gas phase should occur. However, some degree of supersaturation may occur, i.e., the gas can remain in solution. As the formation and growth of gas bubbles are the essential features of the solution gas-drive mechanism, the nucleation phenomena is of considerable interest. Kennedy and Olso studied the formation of bubbles in a supersaturated mixture of methane-kerosene in a window cell packed with quartz and calcite crystals. Supersaturations expressed as the differences between the prevailing pressures and the bubble point up to 5.30 MPa (770 psi) were observed when the saturated liquid pressure was rapidly reduced. At supersaturation below 0.21 MPa (30 psi), no gas bubbles were observed even after 138 hours. Wieland and Kennedy investigated the nucleation phenomena in cores of different rock materials and noticed some degree of supersaturation for live oil mixtures. Chatenever et al studied visually the solution gas-drive mechanism of a mineral oil saturated with butane at atmospheric pressure in packed porous media. A state of supersaturation was reached before gas nuclei were observed. P. 233^