A Case Study in Scaleup for Multicontact Miscible Hydrocarbon Gas Injection
Summary We describe the strategy and results of scaleup done to simulate a multicontact miscible hydrocarbon water alternating gas (WAG) injection process. To adequately model both oil recovery and solvent retention in WAG, one must model three-phase flow including gas trapping. Scaleup of the multicontact miscible gas process is particularly difficult because of the very fine-scale structure of the gas fingers and the miscible front. The case studied is a heterogeneous mixed wet reservoir with a transition zone down to an underlying aquifer. The objective was to develop pseudo relative permeability curves and other parameters that are suitable for running in a full-field limited compositional model with three hydrocarbon components. Both history-matching and systematic approaches were used to generate pseudo relative permeability curves that reproduced results of high-resolution, fully compositional (FC) reference simulations. Dynamic pseudoization techniques were used to derive first guesses at pseudos, but required further calibration to reproduce reference simulations successfully. In matching incremental miscible gas/oil recovery timing and solvent retention, varying three phase water relative permeability was much more effective than varying the mixing parameter. The predictive capability of pseudos was tested for changes with respect to slug size, WAG ratio, and solvent enrichment. Pseudos derived for one pattern or cross section were tested in other patterns or cross sections. Pseudos worked well with respect to changes in WAG ratio, fairly well with respect to changes in solvent enrichment, and moderately well for changes in slug size. They were less robust with respect to changes in description. Introduction Estimation of the incremental recovery and solvent utilization in a multicontact miscible hydrocarbon gas process is challenging. On one hand, important features of the process occur over small-length scales and cannot be estimated readily without very fine-grid, FC simulation. The condensing/vaporizing drive entails the concentration of enriching components into a narrow miscible front that is smeared by coarse areal gridding. High vertical grid refinement is needed to capture thin gas fingers that form within layers of high permeability. SPE 53006 was revised for publication from paper SPE 39626, first presented at the 1998 SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 19-22 April.