First Contact Minimum Miscibility Pressure for Enhanced Oil Recovery: Tracing Pressure- Composition (P-x) Phase Envelopes and Analyzing Injection Fluid Effects.

FEDERICO E. BENELLI; PISONI, GERARDO O.; CISMONDI, MARTÌN

CAMPINAS

Conferencia; Iberoamerican Conference on Supercritical Fluids ? PROSCIBA; 2023

UNICAMP

Enhanced oil recovery (EOR) encopasses a set of techniques used during reservoir fluid extraction process, once the reservoir pressure has decreased and is not enough for moving the fluid to the surface. One important technology corresponds to the injection of a gas stream like the produced natural gas, nitrogen or CO2 into the reservoir. This injection of gas increases the pressure of the reservoir, displacing the oil from one or more injector wells to production wells. During the injection process, a phase equilibria phenomenon occurs, where part of the oil vaporizes into the injected gas, and part of the injected gas is condensed and diluted into the oil. This two-phase equilibrium exchange occurs until, eventually, complete miscibility is reached. Achieving full miscibility between both phases is of high importance since this assures that the displacement gas is fully used in the process and also no gas can break through. The minimum pressure at which the injected gas and the oil are fully miscible is known as minimum miscibility pressure (MMP). EOR by gas displacement is also of high interest from an environmental point of view when CO2 is used as a displacement gas, since it can be a way to store the gas generated during different processes in the wells, reducing the amount released into the atmosphere.This process is usually simulated as a series of discrete steps where on each step, one phase is in equilibrium with the next step phase, and the other phase is in equilibrium with the previous step phase. A simpler and more conservative way of estimating the required pressure for a gas injection EOR operation is considering the first contact minimum miscibility pressure (FC-MMP), which is the minimum pressure at which the original injection gas and the reservoir fluid are completely miscible. This value will be higher than the real MMP which develops through the counter-current multicontact process alluded above. Therefore, the determination of the FC-MMP already provides a good (and safe) initial guess for the pressure at which the EOR process should be done.In this work, we develop and implement an efficient algorithm to determine the FC-MPP by tracing the phase envelope at fixed temperature and with global composition as a function of a percentage of injected gas. The implementation is based on the continuation method, an efficient mathematical method to trace lines for a system of equations where one variable can be specified. The algorithm is tested on multiple characterized reservoir fluids from the literature, and can be used as examples of fluids containing asphaltenes, water and/or CO2. We also study the effect of different kinds of injection fluids (mostly CO2 and different mixtures of light alkanes), studying how these different fluids impact the FC-MMP.