Dr. Yongan (Peter) Gu
Professor, Petroleum Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, Canada.

Speech title: Optimum Miscible CO₂-SWAG/WAG Injection in the Bakken Formation

Abstract: In the past two decades, the shale gas and oil attract the world’s petroleum industry and become the largest new hydrocarbon resources. For example, the Bakken formation in Western Canada and the adjacent states in USA has approximately 271-503 billion barrels of high-quality light oil in place and becomes a vast and vital light oil resource. This tight shale oil formation has permeabilities of 0.01 to 1 mD and the oil recovery factor of its primary production is estimated to be 1-3%. Water is very difficult to inject in large volumes into it, whereas CO₂ may breakthrough it more easily than water. Thus how to properly inject water and/or CO₂ and maximize the oil recovery in the Bakken formation becomes a key technical challenge.
In this paper, miscible CO₂ simultaneous water-and-gas (CO₂-SWAG) injection and CO2 water-alternating-gas (CO₂-WAG) injection in the Bakken formation are experimentally studied. A total of fifteen coreflood tests are conducted by applying waterflooding, miscible CO₂ flooding, miscible CO₂-WAG and CO₂-SWAG injection. The miscible CO₂-SWAG injection with an injected water‒gas ratio (WGR) of 1:3 in volume achieves the highest oil recovery factor and carbon utilization factor, which is followed by the miscible CO₂-WAG injection with the optimum slug ratio of approximately 1:1, miscible CO₂ flooding, and waterflooding. The WGR and the WAG slug size show strong effects on the fluid production trends in the miscible CO₂-SWAG and CO₂-WAG injection processes, respectively. In comparison with water or CO₂ alone, the water‒CO₂ mixture has a much lower mobility in the tight formation. Hence, the high oil recovery in the optimum CO₂-SWAG/WAG injection is attributed to a well-controlled water-CO₂ mobility and a substantially weakened waterblocking effect.
In summary, the optimum CO₂-SWAG/WAG injection presented in this study can become an effective CO₂-EOR technology in many tight shale oil formations, in conjunction with the advanced hydraulic fracturing and horizontal-well drilling technologies.