Laboratory investigation of Weyburn CO2 miscible flooding

Weyburn reservoir, located in southeast Saskatchewan and operated by PanCan adian Petroleum Ltd., has reached its economic limit of production by water flooding. The reservoir is a target for tertiary CO2 miscible flooding to e nhance oil recovery and extend its production life. A comprehensive study h as been conducted by the Saskatchewan Research Council and PanCanadian to a ssess the suitability of the process for Weyburn. This paper presents a technical evaluation of CO2 near-miscible for Weyburn reservoir. This is based on laboratory studies conducted with three Weybur n oils collected from different of the reservoir. These studies included: ( i) measurement of minimum miscibility pressure for the reconstituted reserv oir fluids for pure and impure CO2, (ii) determination of PVT properties fo r reservoir fluid-CO2 mixtures, and (iii) assessment of recovery behaviour from uniquely designed laboratory coreflood tests representing the permeabi lity contrast of the reservoir. The studies indicated that the CO2 minimum miscibility pressure for the Wey burn reservoir oils varied from about 11.5 to 14.5 MPa, indicating suitabil ity for CO2 miscible flooding. PVT data generated for the three Weyburn res ervoir fluid-CO2 mixtures showed that viscosity reduction and oil swelling by CO2 also contributed to oil recovery. A slight manipulation of the measu red PVT properties of the mixtures made it possible to obtain single proper ty curves for the three Weyburn oils. This feature can be used to estimate the PVT behaviour for any CO2 injected into the Vuggy zone could rise to th e upper Marly zone and help enhance oil recovery. A separate simulation and modelling study conducted by PanCanadian Petroleum Ltd. satisfactorily mat ched the experimental PVT properties, MMP values and recovery mechanism sug gested by the coreflood behaviour.