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Effect of Gas Enrichment and Numerical Dispersion on Enriched-Gas-Drive Predictions

1990; Volume: 5; Issue: 04 Linguagem: Inglês

10.2118/18060-pa

2469-9683

Fred I. Stalkup,

Hydraulic Fracturing and Reservoir Analysis

Summary This paper examines the effect of gas enrichment in reservoir-scale enriched-gas-drive displacements through predictions made with a compositional simulator and the Peng-Robinson equation of state (PREOS). The calculations examine behavior for a classical three-component condensing-gas drive and for a 12-component reservoir-fluid characterization that predicts condensing/vaporizing-gas-drive behavior. The predictions also illustrate behavior for two simplified reservoir analogues: a homogeneous cross section with a low vertical/horizontal permeability ratio and a stratified cross section. An important feature of this study is that the impact of numerical dispersion on the predictions is assessed through numerical sensitivity calculations. The simulations show that (1) numerical dispersion causes an abnormally large, erroneous, predicted increase in recovery with increasing gas enrichment and a predicted incremental recovery over waterflooding that could be too large by as much as a factor of two; (2) the most realistic predictions are obtained by extrapolating recoveries to a gridblock size of zero, even though the extrapolation may be imprecise and the degree of convergence to the correct answer is unknown; (3) numerical dispersion causes too large a predicted increase in recovery with gas enrichment beyond the critical enrichment; and (4) calculated oil recovery vs. gas enrichment for the 3- and 12-component fluid characterizations studied is qualitatively similar for injection gases that give displacements ranging from highly immiscible to essentially first-contact miscible (FCM), although absolute differences in incremental recovery are sometimes as large as 1 to 2% of original oil in place (OOIP).