Displacement front stability of steam injection into high porosity diatomite rock

Abstract

Steamflood displacement in porous media is considered to be stable, as compared to other gas-flooding techniques. Stability on the microscopic and core scale lends stability to steam movement on the reservoir scale. Initial aspects of this work use analytical methods to examine frontal stability in high-porosity rocks. Analytical methods indicate stable steam fronts for typical reservoir properties, but they also predict unstable displacement in high-porosity rock. The second portion of this work uses pattern level thermal simulation to study the stability of steam drives in high-porosity rocks. Two different permeability models (an isotropic model and a thief model) are compared at three average porosities (25%, 50% and 70%). Small thermal conductivities are shown to induce the formation of the steam fingers. More importantly, the simulation results show that as the rock porosity increases, steamfront stability decreases. This is exemplified by earlier breakthrough times for models that have greater average porosity. While the stability of a steam front does decrease, analysis indicates that the difference is likely not significant, around a 20% reduction in breakthrough time, compared to other aspects. For example, reservoir heterogeneity has a much greater impact on breakthrough time than does the relatively unstable displacement front associated with high-porosity rock.