Laboratory Experiments of Tertiary CO2 Injection Into a Fractured Core

Abstract

Abstract The efficiency of tertiary CO2 injection at the reservoir conditions into fractured cores has been investigated experimentally. The experiment was designed to illustrate the process of water imbibition and CO2 injection into a North Sea chalk reservoir. The core and core holder assembly were designed to allow a 2 mm gap to surround the core simulating a fracture. Live reservoir oil was prepared and used to saturate the matrix system. Due to the large permeability contrast between the core (4 mD) and the fracture it is not feasible to saturate the core by simply flooding the system with live oil, since oil would flow through the fracture and only partially saturate the core. To overcome this problem a unique technique has been developed for saturating the matrix system with reservoir fluids. This method ensures a homogeneous fluid composition within the pore system before the fracture system is initialized by the injection fluids (water/CO2). During the experiment, the matrix system was first saturated with the live reservoir oil, during which the gap was blocked by a sealing material. In the next step the sealing material was removed and water was injected into the gap. Finally CO2 was injected at a low and constant rate into the gap. Oil and water production and fluid composition were monitored and the results show that injection of CO2 could significantly recover residual oil after water injection.