Using a Multiple-Mixing-Cell Model to Study Minimum Miscibility Pressure Controlled by Thermodynamic Equilibrium Tie Lines

A simple and robust algorithm has been developed to calculate the minimum miscibility pressure (MMP), which is considered one of the crucial and essential design parameters of miscible gas injection projects for enhanced oil recovery (EOR). This algorithm is to track all tie-line lengths through the cell-cell calculation by the minimum distance function for the prediction of MMP. The MMP is the pressure at which any one of all key tie-line lengths becomes zero. To verify the accuracy of the revised MMC algorithm for determining MMP, several examples taken from the published literature have been examined. The calculation results of our revised MMC algorithm show excellent agreement with those estimated by MOC, MMC, and slim-tube experiments, which are found to be reliable within acceptable accuracy (4.53%-0.50%).

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Notice of Violation of IEEE Publication Principles - A new approach for calculation of minimum miscibility pressure based on a multiple-mixing-cell model

2010 Second International Conference on Computational Intelligence and Natural Computing ◽

10.1109/cinc.2010.5643807 ◽

2010 ◽

Author(s):

Li Jungang

Keyword(s):

Cell Model ◽

New Approach ◽

Minimum Miscibility Pressure ◽

Multiple Mixing

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Application of Multiple-Mixing-Cell Method To Improve Speed and Robustness of Compositional Simulation

SPE Journal ◽

10.2118/169063-pa ◽

2015 ◽

Vol 20 (03) ◽

pp. 565-578 ◽

Cited By ~ 2

Author(s):

Mohsen Rezaveisi ◽

Russell T. Johns ◽

Kamy Sepehrnoori

Keyword(s):

Phase Equilibrium ◽

Gas Injection ◽

Computational Time ◽

Simulation Methods ◽

K Value ◽

Acceptable Accuracy ◽

Multiple Mixing ◽

Tie Lines ◽

Tie Line ◽

Equilibrium Calculations

Summary Standard equation-of-state-based phase equilibrium modeling in reservoir simulators involves computationally intensive and time-consuming iterative calculations for stability analysis and flash calculations. Therefore, speeding up stability analysis and flash calculations and improving robustness of the calculations are of utmost importance in compositional reservoir simulation. Prior knowledge of the tie-lines traversed by the solution of a gas-injection problem translates into valuable information with significant implications for speed and robustness of reservoir simulators. The solution of actual-gas-injection processes follows a very complex route because of dispersion, pressure variations, and multidimensional flow. The multiple-mixing-cell (MMC) method, originally developed to calculate minimum miscibility pressure of a gas-injection process, accounts for various levels of mixing of the injected gas and initial oil. This observation suggests that the MMC tie-lines developed upon repeated contacts may represent a significant fraction of the actual simulation tie-lines encountered. We investigate this idea and use three tie-line-based K-value-simulation methods for application of MMC tie-lines in reservoir simulation. In two of the tie-line-based K-value-simulation methods, we examine tabulation and interpolation of MMC tie-lines in a framework similar to the compositional-space adaptive-tabulation (CSAT) method. In the third method, we perform K-value simulations based on inverse-distance interpolation of K-values from MMC tie-lines. We demonstrate that for the displacements examined, the MMC tie-lines are sufficiently close to the actual simulation tie-lines and provide excellent coverage of the simulation compositional route. The MMC-based methods are then compared with the computational time by use of other methods of phase-equilibrium calculations, including a modified application of CSAT (an adaptive tie-line-based K-value simulation), a method using only heuristic techniques, and the standard method in an implicit-pressure/explicit-concentration-type reservoir simulator. The results show that tabulation and interpolation of MMC tie-lines significantly improve phase equilibrium and computational time compared with the standard approach, with acceptable accuracy. The results also show that computational performance of the MMC-based methods with only prior tie-line tables is very close to that of CSAT, which requires flash calculations during simulation. The K-value simulations by use of MMC-based tie-line-interpolation methods improve the total computational time up to 51% in the cases studied, with acceptable accuracy. The results suggest that MMC tie-lines represent a significant fraction of the actual tie-lines during simulation and can be used to significantly improve speed and robustness of phase-equilibrium calculations in reservoir simulators.

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Effect of Gas/Oil Capillary Pressure on Minimum Miscibility Pressure for Tight Reservoirs

SPE Journal ◽

10.2118/199354-pa ◽

2019 ◽

Vol 25 (02) ◽

pp. 820-831 ◽

Cited By ~ 2

Author(s):

Kaiyi Zhang ◽

Bahareh Nojabaei ◽

Kaveh Ahmadi ◽

Russell T. Johns

Keyword(s):

Capillary Pressure ◽

Hyperbolic Equations ◽

Fluid Pressure ◽

Gas Oil ◽

Minimum Miscibility Pressure ◽

Tight Reservoir ◽

Tie Lines ◽

Tight Reservoirs ◽

Shale Reservoirs ◽

The Impact

Summary Shale and tight reservoir rocks have pore throats on the order of nanometers, and, subsequently, a large capillary pressure. When the permeability is ultralow (k < 200 nd), as in many shale reservoirs, diffusion might dominate over advection, so that the gas injection might no longer be controlled by the multicontact minimum miscibility pressure (MMP). For gasfloods in tight reservoirs, where k > 200 nd and capillary pressure is still large, however, advection likely dominates over diffusive transport, so that the MMP once again becomes important. This paper focuses on the latter case to demonstrate that the capillary pressure, which has an impact on the fluid pressure/volume/temperature (PVT) behavior, can also alter the MMP. The results show that the calculation of the MMP for reservoirs with nanopores is affected by the gas/oil capillary pressure, owing to alteration of the key tie lines in the displacement; however, the change in the MMP is not significant. The MMP is calculated using three methods: the method of characteristics (MOC); multiple mixing cells; and slimtube simulations. The MOC method relies on solving hyperbolic equations, so the gas/oil capillary pressure is assumed to be constant along all tie lines (saturation variations are not accounted for). Thus, the MOC method is not accurate away from the MMP but becomes accurate as the MMP is approached when one of the key tie lines first intersects a critical point (where the capillary pressure then becomes zero, making saturation variations immaterial there). Even though the capillary pressure is zero for this key tie line, its phase compositions (and, hence, the MMP) are impacted by the alteration of all other key tie lines in the composition space by the gas/oil capillary pressure. The reason for the change in the MMP is illustrated graphically for quaternary systems, in which the MMP values from the three methods agree well. The 1D simulations (typically slimtube simulations) show an agreement with these calculations as well. We also demonstrate the impact of capillary pressure on CO2-MMP for real reservoir fluids. The effect of large gas/oil capillary pressure on the characteristics of immiscible displacements, which occur at pressures well below the MMP, is discussed.

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Modified Multiple Mixing Cell Method for Determining Minimum Miscibility Pressure

Chemistry and Technology of Fuels and Oils ◽

10.1007/s10553-016-0745-7 ◽

2016 ◽

Vol 52 (5) ◽

pp. 574-582

Author(s):

Chenshuo Zhang ◽

Zifei Fan ◽

Anzhu Xu ◽

Lisha Zhao

Keyword(s):

Cell Method ◽

Minimum Miscibility Pressure ◽

Multiple Mixing

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Phase Behavior and Minimum Miscibility Pressure in Nanopores

SPE Reservoir Evaluation & Engineering ◽

10.2118/168865-pa ◽

2014 ◽

Vol 17 (03) ◽

pp. 396-403 ◽

Cited By ~ 101

Author(s):

Tadesse Weldu Teklu ◽

Najeeb Alharthy ◽

Hossein Kazemi ◽

Xiaolong Yin ◽

Ramona M. Graves ◽

...

Keyword(s):

Phase Behavior ◽

Electrostatic Interactions ◽

Structural Changes ◽

Unconventional Reservoirs ◽

Gas Oil ◽

Confined Space ◽

Liquid Equilibrium ◽

Minimum Miscibility Pressure ◽

Multiple Mixing ◽

Carbon Dioxide Co2

Summary Numerous studies indicate that the pressure/volume/temperature (PVT) phase behavior of fluids in large pores (designated “unconfined” space) deviates from phase behavior in nanopores (designated “confined” space). The deviation in confined space has been attributed to the increase in capillary force, electrostatic interactions, van der Waals forces, and fluid structural changes. In this paper, conventional vapor/liquid equilibrium (VLE) calculations are modified to account for the capillary pressure and the critical-pressure and -temperature shifts in nanopores. The modified VLE is used to study the phase behavior of reservoir fluids in unconventional reservoirs. The multiple-mixing-cell (MMC) algorithm and the modified VLE procedure were used to determine the minimal miscibility pressure (MMP) of a synthetic oil and Bakken oil with carbon dioxide (CO2) and mixtures of CO2 and methane gas. We show that the bubblepoint pressure, gas/oil interfacial tension (IFT), and MMP are decreased with confinement (nanopores), whereas the upper dewpoint pressure increases and the lower dewpoint pressure decreases.

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Multiple-Mixing-Cell Method for Three-Hydrocarbon-Phase Displacements

SPE Journal ◽

10.2118/169150-pa ◽

2015 ◽

Vol 20 (06) ◽

pp. 1339-1349 ◽

Cited By ~ 2

Author(s):

Liwei Li ◽

Saeid Khorsandi ◽

Russell T. Johns ◽

Kaveh Ahmadi

Keyword(s):

Relative Permeability ◽

Cell Model ◽

Phase Identification ◽

Displacement Efficiency ◽

Compositional Simulation ◽

Fractional Flow ◽

Two Phase ◽

Cell Method ◽

Multiple Mixing ◽

Three Phase

Summary Low-temperature oil displacements by carbon dioxide involve complex phase behavior, in which three hydrocarbon phases can coexist. Reliable design of miscible gasflooding 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 slimtube experiments as the “knee” in the recovery curve with pressure in which displacement efficiency is greater than 90%. There are currently no analytical methods to estimate the MMP for multicomponent mixtures exhibiting three hydrocarbon phases. Also, the use of compositional simulators to estimate MMP is not always reliable. These challenges include 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 three-phase multiple-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 the use of compositional simulation to estimate MMP or to understand miscibility development. One can integrate the approach with previously developed two-phase 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 in which the dispersion-free displacement efficiency is maximized. The authors believe that this is the first paper to examine a multiple-mixing-cell model in which two- and three-hydrocarbon phases occur and to calculate the MMP and/or pressure required for high displacement efficiency for such systems.

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Improving MMP by Co-Injection of Miscible CO2 With Abu Dhabi Crude Oil

Volume 6: Polar and Arctic Sciences and Technology; Offshore Geotechnics; Petroleum Technology Symposium ◽

10.1115/omae2013-10258 ◽

2013 ◽

Author(s):

Khalid Javid ◽

Hadil Abu Khalifeh ◽

Hadi Belhaj ◽

Mohammed Haroun

Keyword(s):

Carbon Dioxide ◽

Crude Oil ◽

Carbonate Reservoirs ◽

Abu Dhabi ◽

Co2 Injection ◽

Solvent Mixtures ◽

Minimum Miscibility Pressure ◽

Injection Process ◽

Tie Lines ◽

Simulation Cell

Miscible CO2 injection is a method to increase oil production. Combinations of Carbon dioxide with other gases as miscible solvents are emphasized in this paper to improve CO2 miscible injection process. Emphasis is on identifying CO2 solvent mixtures with reduced MMP to achieve miscibility at reasonable injection pressures in Abu Dhabi fields. Two targeted crude oils (Oil 1 and Oil 2) from Abu Dhabi carbonate reservoirs are utilized. The minimum miscibility pressure (MMP) of targeted oils with mixtures of N2, CH4, C2H6, and HC rich gas of varying composition with CO2 injection gas are evaluated through simulation. Cell to Cell and Semi-analytical (key tie lines) methods are applied using CMG simulator. Results show that miscibility is predicted to occur with multiple contact miscibility (MCM): vaporization and/or condensation mechanisms. The increase of C2H6 concentration in the CO2 injected gas reduced MMPs for targeted Oil 1 by 100 psi/10 mol%. However, N2, CH4 and HC rich gas increments in CO2 injected gas increased the MMPs for targeted Oil 1. MMP was observed to be 2300 psi for pure ethane with Oil 1. In addition, MMPs for targeted oils with N2/ C2H6 and N2/ CH4 injected gas mixtures are assessed. This study can open possibilities for future enriching of CO2 and N2 miscible injection to improve miscibility and recovery of oil.

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Improved Multiple-Mixing-Cell Method for Accelerating Minimum Miscibility Pressure Calculations

SPE Journal ◽

10.2118/199360-pa ◽

2019 ◽

Vol 25 (04) ◽

pp. 1681-1696 ◽

Cited By ~ 1

Author(s):

Haining Zhao ◽

Zhengbao Fang

Keyword(s):

Search Algorithm ◽

Mixing Ratio ◽

Gas Oil ◽

Two Phase ◽

Minimum Miscibility Pressure ◽

Multiple Mixing ◽

Calculation Process ◽

Successive Substitution ◽

Tie Line ◽

Pressure Estimate

Summary An improved algorithm for accelerating minimum miscibility pressure (MMP) computation using the multiple-mixing-cell (MMC) methods is presented. The MMC method is widely used to accurately calculate the MMP. In this study, we proposed an acceleration algorithm toward original MMC method to directly locate the shortest key tie-line (TL) after a certain amount of contacts through the adjustment of the gas/oil mixing ratio during the calculation process. The algorithm contains the following key components: (1) mixing cell cutoff strategy to avoid unnecessary flash calculations; (2) gas/oil mixing ratio adjustment to prevent lost information on the shortest key TL during the cell cutoff process; (3) a search algorithm for pressure to improve the next step pressure estimate; (4) the fast and reliable two-phase flash implementation by combining full Newton method with recently proposed iteration variables and conventional successive substitution method. The improved MMC model is shown to be faster than the original MMC method in computing MMP.

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Multiple-Mixing-Cell Method for MMP Calculations

SPE Journal ◽

10.2118/116823-pa ◽

2011 ◽

Vol 16 (04) ◽

pp. 733-742 ◽

Cited By ~ 44

Author(s):

Kaveh Ahmadi ◽

Russell T. Johns

Keyword(s):

Analytical Methods ◽

Oil And Gas ◽

Equilibrium Phase ◽

Variable Number ◽

Simulation Methods ◽

Displacement Efficiency ◽

Fractional Flow ◽

Cell Method ◽

Multiple Mixing ◽

Tie Lines

Summary The minimum miscibility pressure (MMP) is a key parameter governing the displacement efficiency of gasfloods. There are several methods to determine the MMP, but the most accurate methods are slim-tube experiments, analytical methods, and numerical-simulation/cell-to-cell methods. Slim-tube experiments are important to perform because they use actual crude oil, but they are costly and time consuming. Analytical methods that use the method of characteristics (MOC) are very fast and help to understand the structure of gasfloods. MOC, however, relies on finding the unique and correct set of key tie lines in the displacements, which can be difficult. Slim-tube simulation methods and their simplified cell-to-cell derivatives require tedious fluid and rock inputs, and their MMP estimates can be clouded by dispersion. This paper presents a simple and accurate multiple-mixing-cell method for MMP calculations that corrects for dispersion, and is faster and less cumbersome than 1D simulation methods. Unlike previous mixing-cell methods, our cell-to-cell mixing model uses a variable number of cells, and is independent of gas/oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method only relies on robust P/T flash calculations using any cubic equation-of-state (EOS). The calculations begin with only two cells and perform additional cell-to-cell contacts between resulting equilibrium-phase compositions based on equilibrium gas moving ahead of the equilibrium liquid phase. We show for a variety of oil and gas compositions that all key tie lines can be found to the desired accuracy, and that they are nearly identical to those found using analytical MOC methods. Our approach, however, is more accurate and robust than those from MOC because we do not make approximations regarding shocks along nontie-line paths, and the unique set of key tie lines converges automatically. The MMP using our mixing-cell method can be calculated in minutes using an Excel spreadsheet and is estimated from a novel bisection method of the minimum tie-line lengths observed in the cells at four or five pressures. Our multiple-mixing-cell method can calculate either the MMP or the minimum miscibility for enrichment (MME) independent of the number of components in the gas or oil. Our approach further supports the notion that the MMP is independent of fractional flow because we obtain the same key tie lines independent of how much fluid is moved from one cell to another.

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