Unconventional Reservoir Hydrocarbon-Gas Foam Enhanced-Oil-Recovery Pilot: Design, Implementation, and Performance Analysis

Abstract

SummaryAn immiscible hydrocarbon-gas foam enhanced-oil-recovery (EOR) pilot has been designed and implemented in a hydraulically fractured tight reservoir in the Woodbine Field in Texas. Although gas injection is considered the main EOR technology for tight fractured unconventional reservoirs, gaseous foam has not previously been considered as an effective conformance solution in fractured formations. In this paper, we present experimental evaluation of the surfactant, field-pilot design, and implementation and performance analysis of the pilot toward developing an unconventional hydrocarbon-gas foam EOR conformance solution.Several surfactants were screened through a bulk-foam test for the harsh reservoir conditions (120°C, 3.23% salinity, and ∼27% clay). The selected surfactant was further evaluated for static adsorption on reservoir rocks at room temperature to ensure an economic field pilot. The surfactant was also evaluated for oil-brine emulsion tendency to mitigate any field-implementation issues. A single horizontal injector and two surrounding horizontal producer pads were developed for an improved oil recovery/EOR pilot implementation in the Woodbine Field. Water and produced hydrocarbon gases were injected alternately, as well as in coinjection mode; however, no consistent incremental oil was observed. Injected gas and water broke through on an order of hours and days, respectively. The injector showed more connectivity with one of the producers, suggesting a strong areal conformance problem. A steady baseline operation was established by coinjecting gas and water at a constant gas fraction and total constant rate that resulted in a steady production baseline. The baseline injection was continued with surfactant injection in brine for in-situ foam generation.During 5 weeks of surfactant injection, foam generation and mobility reduction were confirmed with the increase in the measured bottomhole pressure. Mobility control resulted in out-of-zone (OOZ) injection elimination for both gas and water and gas diversion to bypassed areas. With conformance corrected at the injector and deeper in the reservoir, oil-production rates more than doubled, gas utilization was improved, and a low gas/oil ratio (GOR) and improved volumetric sweep were confirmed. The increased oil production continued for at least 6 weeks after completing surfactant injection. More than 2,000 bbl of incremental oil was recovered in 11 weeks of pilot operation. This current work confirms the technical efficacy and potential of the gaseous foam conformance solution for incremental oil production with gas-EOR in unconventional plays.