Enhanced oil recovery in shale reservoirs by gas injection

Abstract

The current available technique to produce shale oil and gas condensate is through primary depletion using horizontal wells with multiple transverse fractures. The oil recovery factor is only a few percent. There is a big prize to be claimed in terms of enhanced oil recovery (EOR). Because gas price is low and oil price is high, maximizing liquid oil production from gas condensate reservoirs becomes shale producers' top interest. This paper provides the status of enhanced oil recovery (EOR) in shale oil and gas condensate reservoirs by gas injection. It starts with the discussion of possible EOR options in shale reservoirs. For the gas injection option, the huff and puff mode is compared with the gas flooding mode. Different modes of water injection in shale oil reservoirs are also compared. The discussion and comparison show that gas injection is more feasible in shale reservoirs than waterflooding and any other EOR methods. The rest of the paper focuses on review of gas injection in shale reservoirs, which covers the following. • Mechanisms of gas injection. • Experimental results on huff and puff gas injection. • Simulation results on huff and puff gas injection. • Gas injection in gas condensate reservoirs. This paper summarizes the EOR efforts which has been made in the industry and provides the direction for the industry future efforts to maximize liquid oil production.