Experimental study of enhancement of injectivity and in-situ oil upgrading by steam-propane injection for the Hamaca heavy oil field

Abstract

Experiments were conducted to study the feasibility of using propane as a steam additive to accelerate oil production and improve steam injectivity in the Hamaca field, Venezuela. The experiments utilized a vertical injection cell into which a mixture of sand, oil and water was tamped. The Hamaca oil sample had an oil gravity of 8°API and a viscosity of 25,000 cp at 50°C. The injection cell was placed inside a vacuum jacket, set at the reservoir temperature of 50°C. Superheated steam at 170°C was injected at 3.5 ml/min (cold-water equivalent) simultaneously with propane at the top of the cell. The cell outlet pressure was maintained at 50 psig. Four propane:steam mass ratios were used, namely, 0:100 (pure steam), 2.5:100, 5:100, and 10:100. Produced liquid samples from the bottom of the cell were collected, treated to break emulsion, and analyzed to determine oil and water volumes, and density and viscosity of the oil. The oil was subjected to SARA analysis to determine the degree of in-situ oil upgrading. Composition of the produced gas was determined using a gas chromatograph. Each run lasted three hours. Experimental results indicated the following. First, with steam-propane injection, start of oil production was accelerated by 17% compared to that with pure steam injection. In the field, this could translate into significant gains in discounted revenues and reduction in steam injection costs. Second, steam injectivity with propane as an additive was up to three times higher than that for pure steam injection. Third, oil production acceleration and injectivity increase were practically the same for runs with propane as a steam additive (irrespective of the propane:steam mass ratios). Propane appears to be a viable steam additive at propane:steam mass ratios as low as 2.5:100.