Analytical Solutions for Gas Displacements with Bifurcating Phase Behavior

SPE Improved Oil Recovery Symposium

et al. 2014

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Low-temperature oil displacements by CO 2 involve complex phase behavior, where three hydrocarbon phases can coexist. Reliable design of miscible gas flooding requires knowledge of the minimum miscibility pressure (MMP), which is the pressure required for 100% recovery in the absence of dispersion or as defined by slim-tube experiments as the "knee" in the recovery curve with pressure where displacement efficiency is greater than 90%. There are currently no analytical methods to estimate the MMP for multicomponent mixtures exhibiting three hydrocarbon phases. Also, there are no reliable numerical methods to estimate the MMP using compositional simulation largely because of robustness issues of three-phase equilibrium calculations, inaccurate three-phase relative permeability models, and phase identification and labeling problems that can cause significant discontinuities and failures in the simulation results. How miscibility is developed, or not developed, for a three-phase displacement is not well known.We developed a new multiple three-phase mixing cell method that gives a relatively easy and robust way to determine the pressure for miscibility or more importantly the pressure for high displacement efficiency. The procedure that moves fluid from cell to cell is robust because it is independent of phase labeling (i.e. vapor or liquid), has a robust way to provide good initial guesses for three-phase flash calculations, and is also not dependent on three-phase relative permeability (fractional flow). These three aspects give the mixing cell approach significant advantages over using compositional simulation to estimate MMP or to understand miscibility development. The approach can be integrated with previously developed twophase multiple mixing cell models because it uses the tie-line lengths from the boundaries of tie triangles to recognize when the MMP or pressure for high displacement efficiency is obtained. Application of the mixing cell algorithm shows that unlike most two-phase displacements the dispersion-free MMP may not exist for three-phase displacements, but rather a pressure is reached where the dispersion-free displacement efficiency is maximized. This is the first paper to examine a multiple mixing cell model where two-and three-hydrocarbon phases occur and to calculate the MMP and/or pressure required for high displacement efficiency for such systems.

Section: Example Calculationsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Multiple Mixing Cell Method for Three-Hydrocarbon-Phase Displacements

SPE Improved Oil Recovery Symposium

et al. 2014

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“…However, heavy oil is typically depleted of the C 2 -C 5 hydrocarbons and the miscible mixture between any heavy oil and CO 2 may only be achieved at pressures in excess of safe reservoir operational conditions (i.e., above fracture pressure). Furthermore, minimum miscibility pressure (MMP) may not exist for some heavy oils (Khorsandi et al, 2014). The reservoir pressure should ideally be close to and preferably higher than MMP to have a high efficiency CO 2 flood, and ultimate storage efficiency.…”

Section: Physics Of Co 2 Floodsmentioning

confidence: 99%

Reduced-Order Model for CO2 Enhanced Oil Recovery and Storage Using a Gravity-Enhanced Process

SPE Annual Technical Conference and Exhibition

et al. 2014

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CO 2 flooding offers a means to recover significant amounts of oil while simultaneously sequestering CO 2 . Estimates of recovery and geologic storage by CO 2 enhanced oil recovery (EOR) are highly uncertain owing to reservoir heterogeneity and other reservoir design parameters. One way to optimize the design and characterize the uncertainty of such processes is to introduce a response surface model (RSM), which offers a simple-to-use and useful tool to forecast expected recoveries and storage potential for reservoirs with a broad range of reservoir and design parameters, with potential utility in development of high-level (i.e., regional and national scale) prospective resource assessments.Injectivity is important to economics of CO 2 flood enhanced oil recovery, and horizontal wells can greatly increase the injectivity and, when coupled with horizontal production wells, the sweep efficiency, recovery, and storage efficiency in many horizontal and dipping reservoirs. This paper develops a reduced-order model (ROM) for continuous CO 2 flooding in heterogeneous oil reservoirs when a horizontal injector and producer are used in a specific optimal pattern. The ROM aims to quickly estimate oil recovery and CO 2 storage efficiency based on values of key dimensionless scaling groups. The key scaling groups for first contact miscible (FCM) two-phase (hydrocarbon and water) flow are derived, and their impact on performance metrics of oil recovery and CO 2 storage potential are analyzed. First contact miscibility between the hydrocarbon phases is modeled based on the assumption that semi-gravity or gravity stable processes will offer sufficient time for CO 2 to contact oil. In this research, a response surface analysis using both a Box-Behnken (BB) experimental design and Latin hypercube sampling (LHS) was also made to predict recovery and storage, and results of that analysis were used to validate the important scaling groups. Monte Carlo simulation with these response surfaces was then used to predict the P10, P50, and P90 expected recoveries and storage efficiencies.The results show that the processes of CO 2 EOR and storage in heterogeneous oil reservoirs can be effectively scaled using 11 groups: effective aspect ratio, CO 2 -or water-oil mobility ratios, buoyancy ratio, normalized initial oil saturation, buoyancy number, residual hydrocarbon saturation, residual water saturation, Dykstra-Parsons coefficient, and correlation length coefficients in x-and z-directions. Furthermore, the results show that oil recovery and CO 2 storage efficiencies of 82 to 91% can be obtained in this process for continuous reservoirs with no water influx. This is the first paper that considers a gravity-enhanced process using all horizontal wells, where the process may not be completely gravity stable, to efficiently recovery incremental oil and store CO 2 . The approach represents a "next generation" CO 2 EOR scenario to yield a large volume of CO 2 stored per bulk volume of reservoir given unlimited CO 2 injection capability, little wa...

“…Li et al (2014b) extended mixing cell methods to three-phase displacements. The multiple mixing cell method of Ahmadi and Johns (2011) is accurate even for complicated phase behavior (Mogensen et al 2009, PennPVT toolkit manual 2013, Rezaveisi et al 2015, Khorsandi et al 2014. Nevertheless, it would still be useful to have other computational methods, such as those based on MOC, as another check of the MMP.…”

mentioning

confidence: 99%

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

SPE Annual Technical Conference and Exhibition

2015

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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...