Abstract
Universality, a desirable feature in any system. For decades, elusive measurements of three-phase flows have yielded countless permeability models that describe them. However, the equations governing the solution of water and gas co-injection has a robust structure. This universal structure stands for Riemann problems in green oil reservoirs. In the past we established a large class of three phase flow models including convex Corey permeability, Stone I and Brooks–Corey models. These models share the property that characteristic speeds become equal at a state somewhere in the interior of the saturation triangle. Here we construct a three-phase flow model with unequal characteristic speeds in the interior of the saturation triangle, equality occurring only at a point of the boundary of the saturation triangle. Yet the solution for this model still displays the same universal structure, which favors the two possible embedded two-phase flows of water-oil or gas-oil. We focus on showing this structure under the minimum conditions that a permeability model must meet. This finding is a guide to seeking a purely three-phase flow solution maximizing oil recovery.
Highlights
An effective Enhanced Oil Recovery method is the so-called WAG injection, which consists of injecting water and gas alternately
The equations governing the solution of water and gas co-injection has a robust structure. This universal structure stands for Riemann problems in green oil reservoirs
The solution has, generically, the following structure: it comprises a 1-wave group across which all saturations change preceded by a 2-wave group possessing states along one of the remaining edges of the saturation triangle; the latter wave is a two-phase solution; namely, the solution of a Riemann problem with right state given as a green reservoir and left state consisting of a mixture of either water and oil or gas and oil
Summary
An effective Enhanced Oil Recovery method is the so-called WAG injection, which consists of injecting water and gas alternately. We do not make a distinction in this study between WAG and sWAG injection For these problems, the solution has, generically, the following structure: it comprises a 1-wave group across which all saturations change preceded by a 2-wave group possessing states along one of the remaining edges (water-oil or gas-oil) of the saturation triangle; the latter wave is a two-phase solution (cf [9]); namely, the solution of a Riemann problem with right state given as a green reservoir and left state consisting of a mixture of either water and oil or gas and oil. We identify in a peculiar model, the minimal conditions for which the universality is preserved
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