Investigation of Unexpectedly Low Field-Observed Fluid Mobilities During Some CO2 Tertiary Floods

Abstract

SummaryPhase behavior, inorganic precipitation, and wettability are investigated as possible reasons for the unexpectedly low field-observed mobilities during some CO2 floods, in particular, the Denver Unit, Wasson field CO2 pilot. The observed mobility was not a near-wellbore effect and probably played a major role in reservoir sweep: the low effective permeability offset the detrimentally low CO2 viscosity. Experimental and simulation studies, supplemented by literature data, lead to the conclusion that rock wettability could be the root cause of these low fluid mobilities. Phase behavior effects, though they may play a role, are not necessary to explain the injectivity behavior, and inorganic precipitates probably have little effect under the conditions investigated here. Thus, current simulator modeling of low fluid mobilities, which are based on arbitrary permeability reduction factors allegedly caused by phase behavior, appears unjustifiable even though overall simulator results may be acceptable.