A new screening method of low permeability reservoirs suitable for CO2 flooding

Abstract

Since the existing gas flooding reservoir screening criteria lack economic indexes reflecting future dynamic production performances, indexes reflecting economic profits are added into the exiting criteria (related to well oil production rate) to form a new method of selecting low permeability reservoirs suitable for CO2 flooding. Reservoir engineering methods of average well peak oil production rate prediction for gas drive is given by employing the concept of “Oil production rate multiplier due to gas flooding”. Based on the principles of technical economics, the method calculating the economical limit well oil production rate of CO2 flooding is also presented. On this basis, a new screening criterion of reservoirs suitable for CO2 flooding is proposed: if the peak well oil production rate predicted by reservoir engineering method is higher than the economic limit well oil production rate, the target reservoir is suitable for CO2 flooding. Furthermore, a four-step reservoirs screening method is advanced: technical screening, economic screening, fine feasibility evaluation, recommendation of optimal gas flooding blocks. The new screening criteria were applied to evaluate the CO2 flooding potential of seventeen blocks in an oilfield, which ended up with only 32.4% of the original oil in place from conventional method suitable for CO2 flooding. It is recommended blocks suitable for CO2 flooding be selected according to the new procedure to ensure economic success. Key words: CO2 flooding, low permeability reservoirs, screening criterion, oil production rate multiplier due to gas flooding, reservoir engineering method, economic limit well oil production rate