Volume 33: CCUS Technologies for the Carbon Neutrality: Part I

Novel Schemes for Improving Recovery Factor of Ultra-thin Low-permeable Sandstone Reservoir by CO2 Flooding, Case Study: CCUS project in V Reservoir, Canada Xuejun Hu

Abstract

The V reservoir is ultra-thin, low-permeable sandstone with net pay of less than 3m and air permeability of 5.1 mD. Its primary recovery is 10% of OOIP due to low permeability and high heterogeneity. CO2 miscible flooding has been implemented since 1998 to improve oil displacement and increase oil production. This paper discusses a case study on the field to show effect of a new CO2 EOR scheme. This paper presents a CO2 flooding development plan specifically tailored to ultra-thin sandstone reservoirs with strong heterogeneity. A line drive flood pattern was designed to make full use of the anticlinal structure of the reservoir. Moreover, the development plan minimized the adverse effects of gravity segregation by injecting CO2 at the structurally high part of the reservoir and producing oil at the low part. The injection-production well pattern is designed to overcome facility constraints by placing vertical producers in the thicker part of the reservoir sand body, while horizontal producers in the thinner part of the edge sand body. The method of water and gas alternating injection was adopted to improve the sweep efficiency and have a better conformance control in the late stage of CO2 flood. The actual production results of the oilfield show that with the new CO2 flooding development plan, the recovery rate has increased by 22%, and the daily oil production has also increased from approximately17 m3/d before the implementation of the plan to 140 m3/d approximately. After historical matches, the dynamic model statistical calculation results of the reservoir numerical simulation also show that the CO2 miscible sweeping volume reaches more than 82% of the total sand volume. It is predicted that the ultimate recovery factory can reach higher than 50%. The above good oil displacement effect comes from the effectiveness of the following methods. The anticline structure has a favorable dip angle creating a gravity overriding effect on CO2 flood. When CO2 is injected at the high structure and migrates to the low structure, it fully interacts with the crude oil, boosting oil recovery. Horizontal wells are used in thin sand formations to significantly maximize contact with the reservoir and enhance oil flow. The technique of alternating gas and water injection is used with dynamically adjusted pressure to create a “gas lock,” blocking high permeability areas and reducing gas channeling. This paper depicts the guidance to efficiently develop the ultra-thin, low-permeable reservoir. The new scheme includes methods such as injecting CO2 into the high part of the reservoir and producing oil at the low part, using horizontal wells to produce thin sand bodies at the edge, and dynamically adjusting the gas and water alternating injection pressure to reduce gas channeling.

Keywords CCUS, CO2 flooding, ultra-thin formation, low-permeable reservoir, water and gas alternating injection