Simulation of Residual oil Saturation in Near-miscible gas Flooding Through Saturation-dependent Tuning of the Equilibrium Constants

Abstract

Conventional miscible or near-miscible gas flooding simulation often overestimates oil recovery, mostly because it does not capture a series of physical effects tending to limit interphase compositional exchanges. Those can be for instance microscopic bypassing of oil situated in dead-end pores or blocked by water films, as well as macroscopic bypassing due to sub-grid size heterogeneities or fingering.We here present a new engineering solution to this problem in the near-miscible case, relying on our in-house research reservoir simulator (IHRRS). The principle is, while using a black-oil or an equation of state description, to dynamically decrease the K-value of heavy components and possibly increase the K-value of light components as the oil saturation reaches the desired residual limit; this enables changing the phase boundaries when needed while preserving the original fluid behavior during the initial production stages.The benefits of the proposed method are demonstrated on a reservoir conditions tertiary gas injection experiment, performed in our laboratories, for which residual saturations as well as oil phase and individual components production rate have easily and successfully been history matched. Results are then compared to matches obtained using saturation exclusion and ␣-factors methods. As a proof of concept, suitability of the method to simulate incomplete revaporization of condensate during gas cycling is also illustrated, on the third SPE comparative solution project case.

Non-Equilibrium Phase Behavior of Hydrocarbons in Compositional Simulations and Upscaling

“…Several industry-adopted approaches were proposed to simulate the effects of incomplete mixing and oil bypassing in gas-injection projects, with most focus on miscible and near-miscible displacements [4,5,9,11,25,27,29]. All of them are based on some tuning parameters used to correct input mixture composition or output equilibrium constants for flash calculations in a grid cell, or component flows in mass conservation equations, with no control over thermodynamic consistency of the model formulation.…”

“…In numerical simulations, this effect is associated with model grid cell sizes. In addition to upscaling methods based on tuning parameters, such as the well-known method of alpha-factors [4,5,29], two thermodynamically-consistent procedures were independently presented in [19,33]. Further progress was reported in [16,17].…”