Gas-Oil interaction and Gravity impact on high permeability WAG experiments.

This study evaluates the impact of the gas-oil interaction on miscible gas injection experiments,and also the gravity impact on these experiments. The program comprised 4 reservoir conditionsexperiments, conducted in multi-contact miscible conditions, with live oil and reservoir rock, and differentWAG slug sizes, starting either with water or with gas. More conventional 2-phase laboratory conditionexperiments were also conducted and available for comparison. The field of interest is a high-pressuresandstone green field, in deep offshore environment, with low dip and high permeabilities.Advanced monitoring allowed to visualize and quantify the thermodynamic phenomena of stripping andswelling for all experiments, as well as gas override and water underride for the horizontal experiments.The results compare recovery factors, the evolution of trapped gas, water saturation, and productivity indicesacross various injection cycles. The experimental design allowed efficient monitoring of effluent productionvolumes at respective reservoir pressure and temperature conditions, and at surface conditions with clearseparation of flashed oil, oil produced via gas, and gas, complemented by compositional analysis of gasesand liquids.The history match of 1D and 2D cases allowed to quantify the 2-phase petrophysical parameters like relativepermeabilities, and also the three-phase parameters specific to alternate injections of gas and water (GWGWand WGWG long slugs and GWGW short slugs).A specific focus was set on the gravity impact on a scenario with maximum gas-oil interaction (GWGW):varying the orientation from horizontal to vertical showed a substantial change in behavior: the mixing zonewas much reduced, changing the nature of the gas-oil interaction.Flow analysis and understanding were enhanced using a real time 2D X-ray imaging system to visualize 3-phase fluid distribution within the rock sample. The study's findings clearly demonstrate that alternating thephases of injection helps to stabilize and achieve better distribution of the gas, leading to enhanced recoverydue to the thermodynamic exchanges.Overall, these WAG injections illustrate the benefit of 3-phase flow even in high permeability horizontalfloods: the high recovery factors, which were expected for miscible conditions, were achieved much quickerwhen alternating gas and water as injected phases.