Experimental Investigation of Recovery Performance of Different Gases in a Tight Lower-Cretaceous Danish North Sea Reservoir

Upper Cretaceous reservoirs have produced most of the Danish oil and gas until now but the increasing demand for hydrocarbons leads to extraction from less favourable formations in the Lower Cretaceous in the North Sea. These reservoirs are composed of chalk, which is a low permeable rock but with high storage capacity. As ultimate oil recovery by natural depletion is low and water based EOR methods are less practical due to low injectivity of the reservoir rock, gas injection is a proper scenario thanks to low viscosity and good miscibility effects of gas. Availability of gas, feasibility of operation and environmental issues limit options for injection. Therefore, a comparison between final recovery obtained by different gases can help us to a better selection, environmentally and economically. Produced gas is always a candidate because of availability at place and compatibility with reservoir content. Flue or exhaust gas and pure CO2 are other candidates that can also contribute to carbon sequestration and reduce CO2 emission. This study, through a series of core flooding experiments, evaluates the sweep efficiency of produced gas, flue gas and supercritical CO2 injection in a lower Cretaceous reservoir at pressures of 250 and 350 bar and reservoir temperature.