An Investigation into Enhanced Recovery under Solution Gas Drive in Heavy Oil Reservoirs

Abstract

Abstract Some of the heavy oil reservoirs in Western Canada and Venezuela show anomalously high primary recovery under solution gas drive process. Pressure decline rate in these reservoirs is low compared to that expected under solution gas drive in conventional oil reservoirs. Several theories have been proposed for these anomalous behaviors. The objective of this study is to examine one of the proposed theories, which suggests that gas mobility in heavy oil is low. In this study, gas mobility under solution gas drive is measured by performing depletion experiments. The depletion was carried out at four different rates. The Eclipse-100 Black oil simulator was used to match the experimental data. The direct results from the experiments show that the critical gas saturation is not very high. Thus, critical gas saturation cannot explain high recovery. However, it was found that the gas mobility in heavy oil is quite low, when compared to that expected in conventional oil. Experimental results indicated that higher rates of pressure drop resulted in higher super-saturation, higher critical gas saturation and lower relative permeability to gas. Physical explanation of the observed behavior is offered in light of the anomalous behavior of heavy oil reservoirs. An empirical model was developed to predict gas mobility, critical gas saturation and supersaturation as a function of depletion rate for the system studied.