Abstract

Carbon dioxide (CO₂) injection is the most promising technique to enhance the recovery of high gravity oil with the existing oil price situation. Even though, challenges still exist for thick and heterogeneous reservoirs at very high temperature. The problems faced in such reservoirs are low displacement efficiency and very high injection pressure requirement for a miscible displacement. The effort being done by researchers to overcome the situations is the use of silica nanoparticle as an agent to form CO₂-silica nanoparticle foam. Currently, the related literature shows that CO₂ miscible displacement is rarely performed at very high temperature and consequently no relevant effort has been made to investigate the stability of CO₂-silica nanoparticle foam, while there are many oil reservoirs with temperature of higher than 250 ^oF. Therefore, related studies on such situations are needed. The present work consists of two stages. First, slimtube and coreflood experiments of CO₂ injection are conducted at about 270 ^oF, respectively, to both determine the Minimum Miscibility Pressure (MMP) of the selected live oil system and the oil recovery. Secondly, CO₂-silica nanoparticle foam stability in various brine salinity at such high temperature will be investigated and effectiveness of the selected stable foam will be tested through an oil displacement using native cores.

In this paper, the results of both slimtube and coreflood experiments are first presented. A live paraffinic oil with 34 ^oAPI is used. The standard slimtube apparatus is employed. Stacked core composing of three native core plugs of different permeability ranging from 75 to 503 milidarcies are used to represent rock heterogeneity. At a temperature of 270 ^oF, MMP of the oil obtained from the slimtube experiment is 2960 psi, about 100 psi higher than that obtained from the coreflood experiment. The slimtube test gives oil recovery 94.2% and the coreflood as expected yields lower recovery, 84% of the initial oil in place. The importance of the tests is two folds that the MMP of the oil system is firmly known while the existing empirical correlations estimate the values ranging from 2718 to 5578 psi and a relatively low coreflood oil recovery suggests further investigation of stability of CO₂-silica nanoparticle foam at that temperature in an attempt for enhancing the oil recovery.

 

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