Experimental studies of steam-propane and enriched gas injection for the Minas light crude oil

Abstract

Experimental studies were carried out to compare the benefits of propane as an additive in steam injection and in lean gas injection to enhance production for the Minas light crude oil (34⁰API). The studies on steam-propane were specifically conducted to better understand production mechanisms involved in steam-propane injection and to investigate effects of expected field pressure and temperature conditions on steam-propane injection for the light Minas crude oil. The steam-propane experiments involved injecting steam or a mixture of steam and propane into a cell in which was tamped a mixture of sand, oil and water. The cell was placed inside a vacuum jacket set at a reservoir temperature of 200⁰F. Superheated steam at 490⁰F was injected at 4.5 ml/min (cold-water equivalent) while the cell outlet pressure was maintained at 450 psig. A total of four runs were successfully performed with two different propane:steam mass ratios, namely, 0:100 (pure steam) and 5:100 (steam-propane). Produced liquids were collected from the bottom of the cell and analyzed to determined oil and water volumes as well as oil density and viscosity after being treated to break the emulsion. The gas injection experiments involved injecting reconstituted Minas field production gas or Minas gas enriched with propane into a cell saturated with live Minas oil. The live oil was prepared in an oil-gas recombination apparatus, and closely replicated oil properties at current reservoir conditions (solution GOR of 134 SCF/STB, bubble-point pressure of 280 psig.) Minas gas was injected at 500 ml/min into the cell set at reservoir temperature of 200⁰F. A total of four runs were successfully performed with two different propane:gas mass ratios, namely, 0:100 (pure lean gas) and 5:100 (enriched gas). The main results of the study are as follows. First, with steam-propane injection, no improvement on production acceleration time, oil recovery or steam injectivity was observed compared with pure steam injection. Second, with enriched gas injection, oil recovery increased from 61% OOIP with lean gas injection up to 74% OOIP with enriched gas (5:100 propane:gas mass ratio). Analysis of produced oil gravity and viscosity indicate little change in values compared to that of the original oil. Of the processes investigated (pure steam, steam-propane, lean gas, and enriched gas injection), enriched gas injection appears to be technically the most feasible EOR method for Minas field. It is recommended therefore to conduct research on possible application of water-alternating-gas (WAG) injection with propane-enriched Minas gas to enhance production from the Minas field.