A novel foam process with CO2 dissolved surfactant for improved sweep efficiency in EVGSAU field

A successful CO2-foam gas conformance enhancement technology pilot has operated at the East Vacuum Gray-burg San Andres Unit (EVGSAU) since Jan 2018 by ConocoPhillips in cooperation with Dow. In early 2020, the scope of the pilot was expanded from one pattern to three patterns. The expansion phase was implemented to evaluate scalability of this technology to patterns with diverse conformance issues and productivity in-efficiencies. Severe vertical and areal conformance issues were initially identified in these patterns, resulting in early gas breakthroughs and poor oil sweep efficiencies. Due to economic success of the first phase, the same surfactant with high foaming tendencies, high gas solubility, and low adsorption characteristics was implemented in the new patterns. The first phase of foam implementation on an inverted pattern showed a complete elimination of out-of-zone injection, redistribution of CO2 into previously un-swept flow intervals, and oil production uplift. In contrast to this first pattern, the gas injectivity was reduced by 20-50% after only two foam cycles in the new patterns. Based on injection profile logs (IPL), no out-of-zone injection was identified before the surfactant injection for the two new patterns, which can be the reason for such rapid injectivity responses. Similar to the first pattern, deep conformance corrections were confirmed as gas was redirected from highly connected producers to other producers within the new patterns. A lower surfactant dosage was applied to one of the new patterns to optimize chemical consumption, while sustaining the performance. The surfactant concentration was also reduced in the first pattern to study the effect of a lower dosage on a known performing pattern. During the foam implementation, the gas to water ratio (GWR) at the pattern injectors was increased to maintain the patterns at the baseline total fluid throughput. This adjustment resulted in more than a 50% reduction in water consumption and a 17% improvement in gas utilization. Overall, a sustainable increase in oil production rate (-35% over the baseline for the last two years) was achieved in the three foam patterns. This robust solution of gas conformance enhancement required-2 lbs. of foaming material per barrel of incremental oil produced, which confirms economic success and commercial viability of the foam technology for a full field-scale implementation. The application of this foam technology has potential to extend the life of a mature asset like EVGSAU by arresting the historical decline in the oil production rate. Reduction in energy and water consumption per barrel of oil produced make the CO2-EOR process more sustainable and strengthen its potential in carbon capture, utilization and sequestration (CCUS) application.