Modeling the density profiles and adsorption of pure and mixture hydrocarbons in shales

Ma, Yixin; Jamili, Ahmad

doi:10.1016/j.juogr.2016.03.003

Cited by 35 publications

(13 citation statements)

References 38 publications

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“…DFT utilizes the minimization of the grand potential to obtain the equilibrium-density profile and does not require capillary pressure to relate the pressure difference between the bulk and confined phase. DFT in combination with the Peng–Robinson equation of state (PR-EOS) has been invoked to examine density profiles and phase equilibrium of hydrocarbons in nanoporous media. , However, DFT suffers from drawbacks such as difficulty in assigning proper pore–fluid potentials and expensive computational cost for the adsorption integral equation . Recently, Travalloni et al reported a pore-size-dependent equation of state (EOS) by extending the PR-EOS to nanosystems. , This EOS is formulated by introducing the interaction between fluid molecules and the pore wall as a square-well potential.…”

Section: Introductionmentioning

confidence: 99%

Confinement-Induced Supercriticality and Phase Equilibria of Hydrocarbons in Nanopores

2016

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For over a century, the phase behavior of bulk fluids has been described as PVT (pressure-volume-temperature) three-dimensional properties, but it has become increasingly clear that the liquid-vapor phase behavior in confined geometries is significantly altered from the bulk. Efforts have been devoted to accessing confined phase transitions using sorption, molecular simulations, and theoretical methods. However, a comprehensive picture of PVT relationships for confined hydrocarbons remains uncertain. Herein, we introduce d (confining pore diameter) as a fourth dimension, and we present PVT-d behavior of confined fluids in nanopores. For the first time, a T-d phase diagram is presented for n-hexane, n-octane, and n-decane under multiple confinement scales (37.9, 14.8, 9.8, 6.0, 4.1, 3.3, and 2.2 nm cylindrical pore diameter) using experimental differential scanning calorimetry and PVT-d equation of state theory at atmospheric pressure. As pore diameter decreases from 37.9 to 4.1 nm, the bubble point increases by as much as 15 K above bulk, until we observe behavior consistent with a supercritical state, pointing to confinement-induced supercriticality. Remarkably, experimental and theoretical findings overlap very well, showing that this approach effectively captures the phase boundaries between the liquid, vapor, and supercritical fluid regions. The model and completed EOS are additionally extended to calculation of isothermal capillary adsorption, and its validity is discussed.

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Section: Introductionmentioning

confidence: 99%

Confinement-Induced Supercriticality and Phase Equilibria of Hydrocarbons in Nanopores

2016

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“…The BET model was more suitable in their work. A simplified local density model was also successfully used to model the shale adsorption (Chareonsuppanimit et al 2012;Ma and Jamili 2016). Mostly the sorbed layer is considered immovable and static, but this is not correct.…”

Section: Introductionmentioning

confidence: 99%

Gas sorption and non-Darcy flow in shale reservoirs

Wang

Sheng

2017

Pet. Sci.

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Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry's law is used to describe dissolution. The K coefficient in Henry's law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. The surface diffusion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. Whenincreases, but the relationship is not linear as the Klinkenberg effect suggests. The effect of adsorption on the gas flow is significant in nanopores (r 2 nm). Adsorption increases apparent permeability in shales at low pressures and decreases it at high pressures.

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“…There have been some studies on the adsorption and transport of multi-component hydrocarbon mixtures in shale organic matter. Ma and Jamili (2016) used Simplified Local-Density theory coupled with Modified Peng-Robinson equation of state to predict the density of pure and mixture hydrocarbons in confined pores. They found that the compositions of the fluid mixtures are not uniformly distributed across the pore.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study of Transport and Storage of Methane in Kerogen

2016

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Studying kerogen structure and its interactions with fluids is important for understanding the mechanisms involved in storage and production of hydrocarbons from shale. In this study, adsorption and transport of methane in a three dimensional type II kerogen model are studied using molecular dynamics simulations. Grand Canonical Monte Carlo (GCMC) simulations are used to simulate the adsorption of methane and NonEquilibrium Molecular Dynamics (NEMD) simulations are employed to simulate transport of methane in the kerogen model. The kerogen model prepared by Ungerer et al. (2014) is used in this study. In order to build a representative solid state model of kerogen, eight kerogen molecules are placed in a periodic cubic cell. Once the initial configuration of kerogen molecules is prepared, constant-temperature constant-volume (NVT) simulations and then constant-temperature constant-pressure (NPT) simulations are performed to obtain the final structure. For the final structure, density values are calculated and compared with the reported density range for kerogen density. Adsorption isotherm, self and transport diffusion coefficients of methane in the final kerogen structure are also calculated. Simulation results for the adsorption isotherm are fairly close to experimental results reported for a Haynesville shale sample. Computed values for self and transport diffusivities decrease as pressure increases and transport diffusion coefficients approach the self-diffusion coefficients.

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Modeling the density profiles and adsorption of pure and mixture hydrocarbons in shales

Cited by 35 publications

References 38 publications

Confinement-Induced Supercriticality and Phase Equilibria of Hydrocarbons in Nanopores

Confinement-Induced Supercriticality and Phase Equilibria of Hydrocarbons in Nanopores

Gas sorption and non-Darcy flow in shale reservoirs

Molecular Dynamics Study of Transport and Storage of Methane in Kerogen

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