Carbonate reservoirs from Pre-salt layer are responsible for a significant volume of Brazils total oilproduction.Recovery mechanisms applied are mostly water injection,aiming for pressure maintenanceand oil recovery increase through macroscopic oil displacement,complemented by gas injection to disposeproduced CO2 rich gas stream into the reservoir.Production strategies were originally built using producerscombined with gas and water injectors.Later,based on a serious of technical studies,including the onesdescribed here,most injection wells were converted to water alternating gas(WAG).In the literature,WAGinjection is applied mostly to gas injection projects to increase oil recovery and provide mobility control;as a recovery mechanism the WAG process combines the increased microscopic sweep efficiency from thegas with the improved macroscopic sweep efficiency obtained from the water.In this work we performthe screening and evaluation of WAG injection as a recovery mechanism in a heterogeneous carbonatereservoir from the Brazilian pre-salt.For that purpose,we use both analytical and numerical methods,thelater using a commercial compositional simulator.The screening indicates that this reservoir is a candidatefor WAG injection.Lab data shows thermodynamic miscibility at initial pressure levels and phase behaviorobserved in experiments is matched to a Peng-Robinson equation of state(EoS).Results from numericalsimulation have a good qualitative agreement with analytical results and data from the literature,indicatinghigher oil recovery for greater gas injection.The increase in oil recovery estimated by numerical simulationis compared with actual data from the literature using dimensionless variables where we observe goodagreement of our expectations to previous field results.We conclude that the efficiency of WAG injection,in these reservoirs,relies on factors such as gas availability,miscibility development and flow pattern to bedeveloped due to reservoir heterogeneities(channeling versus dispersive flow).
展开▼
