Derisking Low-Tension-Gas Flooding in a Carbonate Field in North Oman: Results and Insights from a Successful Foam-Assisted WAG Injection Pilot

Abstract

Abstract Lekhwair is a medium-large low-permeability carbonate reservoir in Northern Oman in a mature waterflood stage. To address the challenges of EOR in this reservoir, Low-Tension-Gas (LTG) flooding has been identified as a promising technology. The LTG concept is to use surfactants to reduce the interfacial tension between water and oil to mobilize residual oil in combination with foam for conformance control. In practice, for each goal different surfactant types are required. The objectives of this paper are to present the results and insights gained from the first successful foam pilot of LTG flooding in Oman. This pilot focused on the first objective of improving gas conformance by demonstrating the in-situ foam generation through Surfactant Alternating Gas (SAG) injection. The injection plan consisted of 5 cycles of immiscible Water-Alternating-Gas (WAG) injection using N2 to establish a baseline, followed by 11 cycles of Surfactant Alternating Gas (SAG) injection for foam generation. A robust surveillance program was implemented for real-time monitoring of pressure responses, saturation profiles, and reservoir fluids dynamics, ensuring a detailed evaluation of the SAG flooding process. The pilot successfully achieved its objectives. Foam generation through SAG injection was confirmed. Bottom hole pressure data demonstrated increasing trends during SAG stages, providing evidence of foam generation within the reservoir. Logging data validated flow diversion from high-permeability to low-permeability zones. The integration of field data for history matching the reservoir dynamic model allowed for better understanding of the SAG process and to evaluate the feasibility of several development concepts. The single-well pilot demonstrated the successful generation of in-situ foam through SAG injection. This achievement has profound implications for maturing LTG technology in low-permeability carbonate reservoirs in Oman. The success of this pilot contributes novel insights into the application of Low-Tension-Gas (LTG) flooding in low-permeability carbonate reservoirs and opens exciting opportunities of chemical EOR in Northern Oman.