The Displacement of Heavy Oil From Diatomite Using Hot Water and Steam

Abstract

Abstract Results of diatomite core displacement tests designed to study the effects of fluid system, rock type, stress and temperature are presented here. Two heavy oils (12.3 and 17.8°API) were evaluated using water varying in temperature from 91 to 550°F and steam at either 330 or 550°F. Three amorphous Opal-A and 1 crystalline Opal-CT rock types were tested at effective stress levels varying from 450 to 1100 psi. Measurements are provided for both dead and live-oil density and viscosity, live-oil thermal expansion, and remaining oil saturation as a function of temperature and fluid displacement type and phase. Hot-water flooding at about 200°F as compared to 100°F was shown to be capable of increasing oil displacement efficiency from about 30 to 60% of original oil-in-place. Hot-water flooding at either 330°F or 550°F was shown to be capable of further increasing displacement efficiency to about 70% of OOIP, with the higher temperature water providing only marginally improved recovery. Steamflooding at 550°F was shown to be capable of recovering more than 80% of OOIP and was much more efficient than the 330°F steamfloods. The lowest residual oil saturations and highest displacement efficiencies were consistently measured for rock type "C", a dirty Opal-A found in prior published research to be the most compressible of the various rock types. Counter-current imbibition (CCI) of water and oil is considered to be a key mechanism in the published research performed to understand the effects of hot fluid injection in diatomite, where core samples were purposely tested at low effective stress levels to minimize the effects of compaction. Laboratory-measured displacement efficiencies are presented here for stress and temperature levels typical of field conditions, where the primary diatomite pore structure is radically altered and the diatomite skeletal material is crushed by thermally-induced compaction. Under these field conditions, displacement efficiencies are surprisingly high for hot fluid injection processes in diatomite, particularly for hot-water flooding. The remaining oil saturation data are applicable in numerical modeling studies, and differences in oil displacement efficiency by rock type highlight the need to use different geological facies when building geo-cellular models of diatomite reservoirs.