CO2 sequestration-EOR in Yanchang oilfield, China: Estimation of CO2 storage capacity using a two-stage well test

Abstract

Depleted oil fields are often considered as the first target for carbon geo-sequestration. However, evaluation of an accurate CO2 dynamic storage capacity, ultimate recycled CO2 and enhanced oil recovery (EOR) are key elements for a successful project. The Yanchang Petroleum Company (YP)’s oil field is located at Ordos Basin and it is the second largest low permeability oil field in China with a very short and inefficient primary and secondary oil recovery. Thus, CO2 EOR was considered by YP to be an appropriate tertiary oil recovery approach. In this work, the Wuqi reservoir in the Yanchang field was selected to study the feasibility of full-field CO2 sequestration with EOR. The Wuqi reservoir has been in production for over a decade and has historical data that can be history matched. To acquire essential dynamic data for evaluation of CO2 injectivity/dynamic storage capacity, a specific two-stage well test design is proposed to inject first water and then CO2. It will provide accurate effective permeability estimates for water (test phase 1) and CO2 (test phase 2) at the injection well. The test will also inform the operator on the location water and CO2 fronts in the reservoir. Using two monitoring wells simultaneously, significantly increases the radius of investigation (ROI) that can be achieved for a given pumping scenario and will also describe the reservoir heterogeneity.