Tie-Line Solutions for MMP Calculations By Equations-of-State

Abstract

Minimum miscibility pressure (MMP) is one of the most important parameters in the design of successful gas floods. One technique for calculation of MMP uses the analytical method based on the method of characteristics (MOC). Although MOC is the fastest MMP calculation method available today, it can suffer from robustness owing to complex phase behavior observed in some field displacements. The current MOC method implemented in commercial software assumes that the composition route is composed of a series of shocks from one key tie line to the next. For some displacements, however, these key tie lines do not control miscibility and significant errors in MMP can result. One way to eliminate the error lies in constructing the entire composition route, which is challenging for many complex multicomponent oil displacements.This paper examines how to determine the unique composition route for all conceivable phase behavior complexities, making the MOC method for MMP calculation significantly more robust. The approach relies on solving for all tie lines in the composition route directly, independent of fractional flow. MMP estimation is based solely on the tie-line route calculation in tie-line space, where both tie-line rarefactions and shocks may exist. MMPs that result from 1-D displacements of oil by gas are therefore decoupled from fractional flow, making the calculation significantly easier and more robust. Once tie lines in the composition route are determined, specific compositions for a given fractional flow can be mapped onto the tie-line solution, completing the composition route if desired. Compared to current methods, the formulation in tie-line space has a smaller rank, few or no umbilic points, and as stated is independent of fractional flow. Example solutions show that MMPs are easily calculated with this approach for complex displacements that were incorrectly or very difficult to solve before, including multicomponent gas injection with bifurcating phase behavior.Slim-tube experiments are widely accepted as the best experimental procedure to determine the MMP for miscible gas floods (Jarrell et al. 2002). Slim-tube experiments use real fluids that can capture the complex interactions between flow and phase behavior in porous media such as those that occur in condensing and vaporizing (CV) drives (Zick 1986, Stalkup 1987. Slim-tube experiments, however, take significant time to conduct, and are expensive. Thus, only a few MMPs can be obtained this way in practice. Other experimental methods like the rising-bubble apparatus (RBA) (Christiansen and Haines, 1987) and the vanishing-interfacial tension test (VIT) (Rao 1997) have been developed to limit slim-tube experiments for MMP calculation but these experiments fail to capture the interaction of phase behavior and flow that occurs in porous media (Zhou andOrr 1998, Orr andJessen 2007). The MMPs from RBA and VIT tests are accurate for simple binary displacements, but become less accurate as the number of components increase (Jessen and Orr 2008) and shoul...

Robust Flash Calculation Algorithm for Microemulsion Phase Behavior

“…is zero. Parameterization of the tie lines [45] is used to define a relationship for n D . The tie-line space parameter is defined based on overall composition so that no iteration is required in the flash calculations.…”

Enhanced Method-of-Characteristics Approach for Determination of Minimum Miscibility Pressure in Displacements with Bifurcated Phase Behavior

“…Khorsandi and Johns changed the system of equations and solved the displacement problem in the tie-line space for the case of bifurcated phase behavior. 12 Bifurcated phase behavior adversely affects the MOC shock-jump method in two different ways as described below.…”

“…The multiple mixing cell method predicts MMP based on multiple repeated contacts between oil and gas. Previous multiple mixing cell methods suffered from inability to estimate MMP for the condensing/vaporizing (CV) drive mechanism. − Ahmadi and Johns introduced a simple procedure to determine all key tie lines and tie lines in between and used the smallest of those as the MMP determining tie lines. However, it is relatively difficult to detect all tie lines for multiple component mixtures.…”

“…Their approach allows prediction of MMP for gas injection processes using any number of components for both oil and gas mixtures. Khorsandi and Johns changed the system of equations and solved the displacement problem in the tie-line space for the case of bifurcated phase behavior . Bifurcated phase behavior adversely affects the MOC shock-jump method in two different ways as described below.…”

A simulation approach to achieve the best miscible enrichment in gas flooding and chemical injection process for enhanced oil recovery

“…This experimental technique, however, is expensive and time‐consuming to perform. Slim tube compositional simulations are therefore becoming more common for MMP measurements and allow for a large number of cases to be investigated simultaneously at low costs . Slim tube simulation replicates the displacement process in physical slim tube experiment through one‐dimensional grid blocks.…”