Abstract

This paper reviews the main results of the Norwegian RUTH (Reservoir Utilization through advanced Technological Help) research program on the Gas Flooding and the Combined Gas-Water (CGW) Injection.

Laboratory experiments have shown that gas injection in chalk cores lead to significant oil recovery that is dominated by phase behavior. Vertical core flooding experiments in high permeable sandstone and fluid systems exhibiting different wetting and spreading conditions, show continuous oil production lasting several months, leading to low oil saturations. Laboratory measurements of three-phase relative permeabilities by the steady state method and unsteady state displacement, under spreading and non-spreading conditions, have shown that oil relative permeability at low oil saturations take on different values. Gas relative permeability is lower in three-phase mode compared to two-phase mode and it is strongly dependent on the saturation history. WAG injection in a layered composite core with accompanied simulations, have shown that capillary forces dominate the flow process under low rate conditions, and that WAG injection can significantly increase the recovery factor compared to water flooding.

For reservoir simulation, a formulation for three phase relative permeability and capillary pressure has been developed that uses three sets of two-phase data, accounting for the six two-phase end point values, improving the modeling capability of oil recoveries and final three-phase saturation profiles from vertical core flooding experiments. A computer program has also been developed that transforms process history data from fine grid compositional simulation to coarse grid compositional simulation for the purpose to generate pseudo relative permeabilities and pseudo capillary pressures, and for scaling analysis.

Stochastically generated reservoir models of fluvial and shallow marine depositions have been used in simulation studies to analyze up-dip WAG injection processes. Results show that the mixed three-phase flow zone is greater than what may be derived from empirical models, and that heterogeneity contrasts extends the gas-water mixed zone. Simulation studies are also conducted to assist in analyzing field pilots such as in the Snorre (fluvial) and Brage (marine) fields.