Drainage Three-Phase Flow Relative Permeability on Oil-Wet Carbonate Reservoir Rock Types: Experiments, Interpretation and Comparison with Standard Correlations

Abstract

Three-phase flow data play a major role in the design of various E&P applications (gas injection, WAG, SAGD) and also in the context of gas storage activity (additional oil related to the conversion of depleted oil fields). Intermediate to oil-wet carbonate reservoirs comprise huge global oil reserves, and hence it is very important to characterize three-phase flow data to reduce current uncertainties. This work is an experimental contribution to share new data sets of three-phase relative permeability (kr) obtained under drainage conditions (gas saturation increase) on different intermediate to oil-wet carbonate rock-types of two giant Middle East reservoirs. In each case, the ternary diagrams have been obtained through the numerical interpretation of displacement experiments conducted at various initial saturation conditions (from Swi to Sorw). Three-phase kr tables (functions of two saturations Sg and Sw) have been adjusted by trial-and-error method until a good history match was obtained for all the experiments (production data and pressure drop) with one unique set of tables. This process has led to very similar tables for each of the two rock-types in two different reservoirs. Key findings are as follows:  at a constant gas saturation, krg decreases with increasing amount of water  krw depends on two saturations, excepted at low Sw  kro depends on two saturations, excepted at low So, and the concavity of the isoperms is opposite, compared with the water-wet case. It leads globally to a reduced mobility of the oil phase under oil-wet context. The general shape of oil isoperms is in good agreement with published results by Oak (1991), Petersen et al. (2008), and Weifeng et al. (2012) obtained on intermediate-wet and oil-wet sandstone samples. The results also show that the Stone’s models fail in reproducing the experimental observations whatever the phase considered. Therefore, the current three-phase relative permeability models must be used with caution to simulate three-phase processes in oil-wet carbonate reservoirs. This is illustrated