Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Wettability change (or a relative permeability effect) has long been considered a mechanism for enhanced oil recovery. Reports show that adsorption of petroleum heavy ends, mainly asphaltenes and resins, onto a rock surface can alter its wettability. Reports also show that high concentrations of CO$\sb2$ will induce the formation of a solid phase in CO$\sb2$/crude mixtures. However, the propensity of a reservoir system for CO$\sb2$-induced hydrocarbon precipitation and how this deposition affects the rock wettability has not been yet investigated. Once variables such as oil composition, pressure, temperature, brine chemistry, and surface mineralogy are adequately defined it becomes possible to evaluate amenable mechanisms of improved oil recovery. This study employed a prototype, high pressure/temperature, variable volume circulating cell with porous media traps. Stainless steel filters were used to determine how (1) pressure, (2) temperature, and (3) oil composition influence CO$\sb2$-induced organic deposition. Short Berea sandstone consolidated cores were used to investigate the effects of (1) initial wettability, (2) water saturation, (3) brine chemistry, and (4) clay activity on deposition. The experimental results indicate that CO$\sb2$-induced organic deposition increases rapidly with pressure to a maximum near the minimum miscibility pressure, then declines slightly with further increases in pressure. The results also show that temperature is a variable only in that it determines the pressure required to develop miscibility. An empirical correlation using viscosity and compositional data predicts the tendency of a stock tank oil to exhibit CO$\sb2$-induced deposition. Furthermore, the experimental results demonstrate that initial wettability has a minimal effect on CO$\sb2$-induced deposition; however, water saturation, brine chemistry, and clay activity significantly influence the adsorption process. Finally, CO$\sb2$-induced deposition alters strongly water-wet cores to Salathiels' mixed-wettability state.

Pages

219

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