Abstract
An immiscible hydrocarbon foam (HC-Foam) enhanced oil recovery (EOR) pilot has been designed and implemented in a hydraulically fractured tight reservoir in the Woodbine field, Texas. Although gas injection is being considered as the main EOR technology for unconventional tight fractured reservoirs, gaseous foams of this type have not been previously considered as an effective conformance solution. This paper presents experimental evaluation of the surfactant, field pilot design and implementation and performance analysis of the pilot towards developing an unconventional HC-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 producers pad was developed for an IOR/EOR pilot implementation in Woodbine field. Water and produced hydrocarbon gases were injected alternately as well as in co-injection mode, however no consistent incremental oil was observed. Injected gas and water broke through on the 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 co-injecting gas and water at a constant gas fraction and total constant rate that resulted in steady production baseline. The baseline injection was continued with surfactant injection in brine for in-situ foam generation. During five weeks of surfactant injection, foam generation and mobility reduction were confirmed with the increase in the measured bottom-hole pressure. Mobility control resulted in out of zone 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-to-oil ratio and improved volumetric sweep were confirmed. The increased oil production continued for at least 6 weeks after completing surfactant injection. More than 2000 bbl. of incremental oil was recovered in 11 weeks of pilot operation. Current work confirms the technical efficacy and potential of the gaseous foam conformance solution for incremental oil production in unconventional plays.
