Phase Behavior and Minimum Miscibility Pressure in Nanopores

Teklu, Tadesse Weldu; Alharthy, Najeeb; Kazemi, Hossein; Yin, Xiaolong; Graves, Ramona M.; AlSumaiti, Ali M.

doi:10.2118/168865-pa

Cited by 188 publications

(94 citation statements)

References 19 publications

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“…Fig. 3b illustrates an example of 3D molecular structure of kerogen (Vandenbroucke 2003). One can observe that one can model the kerogen pore in first approximation by a slit-graphite pore.…”

Section: Molecular-simulation Proceduresmentioning

confidence: 99%

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Effect of Confinement on Pressure/Volume/Temperature Properties of Hydrocarbons in Shale Reservoirs

et al. 2016

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Shale reservoirs play an important role as a future energy resource of the United States. Numerous studies were performed to describe the storage and transport of hydrocarbons through ultrasmall pores in the shale reservoirs. Most of these studies were developed by modifying techniques used for conventional reservoirs. The common pore-size distribution of the shale reservoirs is approximately 1 to 20 nm and in such confined spaces that the interactions between the wall of the container (i.e., the shale and kerogen) and the contained fluids (i.e., the hydrocarbon fluids and water) may exert significant influence on the localized phase behavior. We believe this is because the orientation and distribution of fluid molecules in the confined space are different from those of the bulk fluid, causing changes in the localized thermodynamic properties.This study provides a detailed account of the changes of pressure/volume/temperature properties and phase behavior (specifically, the phase diagrams) in a synthetic shale reservoir for pure hydrocarbons (methane and ethane) and a simple methane/ethane (binary) mixture. Grand canonical Monte Carlo (GCMC) simulations are performed to study the effect of confinement on the fluid properties. A graphite slab made of two layers is used to represent kerogen in the shale reservoirs. The separation between the two layers, representing a kerogen pore, is varied from 1 to 10 nm to observe the changes of the hydrocarbon-fluid properties. In this paper, the critical properties of methane and ethane as well as the methane/ethane mixture phase diagrams in different pore sizes are derived from the GCMC simulations. In addition, the GCMC simulations are used to investigate the deviations of the fluid densities in the confined space from those of the bulk fluids at reservoir conditions. Although not investigated in this work, such deviations may indicate that significant errors for production forecasting and reserves estimation in shale reservoirs may occur if the (typical) bulk densities are used in reservoir-engineering calculations.

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Section: Molecular-simulation Proceduresmentioning

confidence: 99%

“…. (a) STM image of Haynesville shale (Curtis et al 2010), (b) 3D molecular structure of kerogen(Vandenbroucke 2003), and (c) molecular model representing kerogen in shale reservoirs. Periodic boundary conditions used to extend the simulated system to represent kerogen pore network.…”

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confidence: 99%

Effect of Confinement on Pressure/Volume/Temperature Properties of Hydrocarbons in Shale Reservoirs

et al. 2016

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“…Overfitting problem also limits its capability of MMP prediction. In addition, both empirical correlation and data-driven model may not be suitable to unconventional reservoirs since in small pores, such as nanopores, phase behavior and MMP are significantly affected by confinement effect (Teklu et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Application of PC-SAFT Equation of State for CO2 Minimum Miscibility Pressure Prediction in Nanopores

Wang

Chen

2016

SPE Improved Oil Recovery Conference

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CO 2 miscible injection is generally one of the most efficient enhanced oil recovery (EOR) methods and widely used in the conventional oil reservoirs. The applicability of CO 2 EOR technology for unlocking the resources from unconventional tight and shale formations and the mechanisms of miscible flooding in these reservoirs still remain unclear. An important parameter used to evaluate the feasibility of CO 2 miscible flooding is the minimum miscibility pressure (MMP). Even though experimental approaches, empirical correlations and theoretical methods have performed well in measuring or predicting MMP between CO 2 and crude oil in conventional reservoirs, they may not be suitable for unconventional formations as phase behavior and MMP can be significantly affected by confinement effect in small pores (e.g., nanopores) in such formations.In this study, a new MMP prediction model based on the modified Parachor Model associated with the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) is developed to determine CO 2 MMP both in the bulk phase and nanopores. The Parachor Model is modified to account for the confinement effect of nanopore walls on the equilibrium interfacial tension (IFT). The Equilibrium IFT reduction in nanopores is related to a temperature-dependent and slit pore width-dependent modification term. The parameters of the new Parachor Model are determined by matching the vapor-liquid surface tension values for CH 4 , C 2 H 6 , C 3 H 8 , n-C 4 H 10 , and n-C 8 H 18 in nanopores, respectively. The prediction ability of the new model is verified by comparing the predicted MMP in the bulk phase with the results of other theoretical approaches and slim-tube experimental data. Finally, the new model is applied to estimate the MMP between Bakken oil and CO 2 stream. The effect of temperature, slit pore width, and impure components in the injected CO 2 on the MMP are also studied. The newly developed model successfully reproduces MMP in bulk phase as compared with both other methods and experimental data. The overall average absolute relative deviation (AARD) for MMP is within 8 %. The calculated equilibrium IFT for liquid-vapor phase has a good agreement with molecular simulation results. For Bakken oil-CO 2 system, if the slit pore width is larger than 10 nm, MMP is independent on pore width; otherwise, it decreases significantly with the decrease of the pore width. If pore width decreases to 3 nm, 67.5 % decrease in the IFT is observed and 23.5% reduction is achieved for MMP between Bakken oil and CO 2 stream, indicating that it is easier to reach miscibility in nanopores, and CO 2 miscible flooding might be a promising enhanced oil recovery (EOR) technology for tight oil and shale oil reservoirs. Furthermore, MMP increases with an increase of temperature in bulk phase, whereas IFT and MMP decrease with an increase of temperature in nanopores.

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“…The procedures to accommodate capillary pressure was mentioned in Brusilovsky (1992), Shapiro and Stenby (2001) as well as our previous publications (Wang et al, 2014;Teklu et al, 2014). The pressures of the gas and the liquid phases are different by the capillary pressure, which is calculated using the radii of cylindrical nanopores, an assumed contact angle , and an interfacial tension (IFT) that is estimated with the parachor correlation (Weinaug and Katz, 1943) (1)…”

Section: Vapor-liquid Equilibrium Calculation With Capillary Pressurementioning

confidence: 99%

“…Li et al, 2014) to approach the problem from molecular or molecular density function level. Others focused on modeling of the effect of nanoconfinements through modified equation of state (Travalloni et al, 2010a;2010b) or modified vapor-liquid equilibrium calculations that consider the capillary pressure and/or critical properties shifts (Du and Chu, 2012;Devegowda et al, 2012;Fathi et al, 2013;Nojabaei et al, 2013;Firincioglu et al, 2013;Wang et al, 2013;Jin et al, 2013;Alharthy et al, 2013;Wang et al, 2014;Teklu et al, 2014). Some studies went further and incorporated the effect of nanoconfinement into reservoir simulators (Firincioglu et al 2012;Du and Chu, 2012;Fathi et al, 2013;Firincioglu et al, 2013, Wang et al, 2013Nojabaei et al, 2013;Alharthy et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Experimental Study and Modeling of the Effect of Pore Size Distribution on Hydrocarbon Phase Behavior in Nanopores

Wang

Neeves

Yin

et al. 2014

SPE Annual Technical Conference and Exhibition

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Pore sizes of many shale and tight oil and gas reservoirs are in the range of nanometers. In these pores, the phase behavior of hydrocarbon mixture is affected by the capillary pressure and the surface forces and is different from that characterized in PVT cells. Many existing phase behavior models use a single pore size. This research investigates the effect of a pore size distribution on the phase behavior of hydrocarbon mixtures.Pure n-pentane and a ternary mixture of n-butane, i-butane, and n-octane were loaded into a nanofluidic device with microchannels and nano-channels to study phase transition due to evaporation. For n-pentane, evaporation in the nano-channels took place immediately after the liquid in the micro-channels completely evaporated. For the ternary mixture, however, evaporation in the micro-channels slowed down and did not progress into the nano-channels despite continuous heating, because evaporation in the micro-channels changed the composition of the remaining liquid.A vapor-liquid equilibrium calculation procedure that considers the effect of capillary pressure, the sequence of phase change due to pore size distribution and the associated compositional change was developed and used to simulate depressurization of light oil and retrograde gas inside nanoporous media. The pore size distributions were characteristic of tight reservoirs and the fluid compositions were representative of typical reservoir fluids. Predictions of the model show that phase transition in porous medium with pore size distribution is a process that cannot be described by a single phase boundary, because the initial phase change alters the composition of the remaining fluid, which in turn suppresses the next phase change. For the oil, capillary pressure due to nanoconfinement increased the level of supersaturation and the critical gas saturation had a strong influence on the properties of produced fluids; for the retrograde gas, the effect of capillary pressure was insignificant due to the low interfacial tension. Despite the choice of fluids, calculations indicate that the smallest pores are probably always occupied by hydrocarbon liquid during depressurization. Experiments and modeling presented in this research provide tools to investigate and understand the effect of nanoconfinement on phase behavior, which assist the development of shale oil and gas condensate reservoirs.

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Phase Behavior and Minimum Miscibility Pressure in Nanopores

Cited by 188 publications

References 19 publications

Effect of Confinement on Pressure/Volume/Temperature Properties of Hydrocarbons in Shale Reservoirs

Effect of Confinement on Pressure/Volume/Temperature Properties of Hydrocarbons in Shale Reservoirs

Application of PC-SAFT Equation of State for CO2 Minimum Miscibility Pressure Prediction in Nanopores

Experimental Study and Modeling of the Effect of Pore Size Distribution on Hydrocarbon Phase Behavior in Nanopores

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