Modifying Van Der Waals Equation of State to Consider Influence of Confinement on Phase Behavior

Ma, Yixin; Jin, Luchao; Jamili, Ahmad

doi:10.2118/166476-ms

Cited by 27 publications

(27 citation statements)

References 22 publications

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“…These results are in general agreement with the findings from molecular simulation studies of Singh et al (2009). In previous work (Ma et al (2013)), the van der Waals equation of state was modified to model the phase behavior of hydrocarbon fluids for all ranges of pore sizes from bulk (very big pores) to nanopore scale sizes ( In their study, the model provided a priori predictions of the CO 2 adsorption data on the 27 coals with an average absolute percent deviation of 12%. Meanwhile, the generalized SLD-PR model appears to be sufficiently robust and should be extremely useful in reservoir simulators.…”

Section: Introductionsupporting

confidence: 82%

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Modeling the Effects of Porous Media in Dry Gas and Liquid Rich Shale on Phase Behavior

Jamili

2014

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Because of the confinement effects in shale formations, fluid flow is different compared to conventional reservoirs. The interactions between the fluid molecules and porous wall inside nanopores play such an important role that can change the phase behavior of the fluids. The fluids in shale reservoirs are usually stored in two forms, free fluids and adsorbed fluids. The region where free fluids are stored has negligible fluid-wall interactions while the region for adsorbed fluids is under strong pore wall influence. The current available equations of state cannot capture the phase behavior of the adsorbed phase in porous media due to the ignorance of the fluid-wall interactions. This paper discussed the effects of the fluid-wall interactions on fluid phase behavior from a modeling of of view.The production from shale reservoirs in the US has shifted from gas windows to condensate windows and oil windows recently due to low natural gas price. Liquid-rich shales, such as Barnett, Eagle Ford, and Marcellus are brought more attentions than ever before. Thus, it is critical to understand the fluid phase behavior and properties and their impacts on production in the condensate systems. Our work focuses on the predictions of fluid critical property change and fluid density change inside nanoporous media. Simplified Local-Density theory for single component coupled with modified Peng-Robinson Equation of State was used to predict the density profiles of dry gas (pure methane) in confined pores. The model was then extended to mixtures for the study of condensate systems.Our results showed that due to the fluid-wall interactions, the fluid density is not uniformly distributed across the pore. The fluid density is higher near the wall than that in the center region of the pore. It also showed that depending on fluid types, temperature, pressure and pore sizes, the fluid density profile would change. The pore size range we focused on was from 2 nm to 10 nm. In order to present the condensate system, a synthetic mixture of 75% methane and 25% n-butane is used. It is found that fluid composition is not uniform across the pore. Heavier component (n-butane) tends to accumulate near the wall while lighter component (methane) would like to stay in the center region of the pore. For a 10 nm wide pore, the composition of n-butane of the synthetic mixture can be as high as 66% close to the pore wall.

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Section: Introductionsupporting

confidence: 82%

“…• Equation of state Kuz (2002 and2004), Derouane (2007), Travalloni et al (2010a and2010b) and Ma et al (2013)). …”

Section: Introductionmentioning

confidence: 99%

Modeling the Effects of Porous Media in Dry Gas and Liquid Rich Shale on Phase Behavior

Jamili

2014

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“…These results are in general agreement with the findings from molecular simulation studies of Singh et al (2009). In previous work (Ma et al (2013)), the van der Waals equation of state was modified to model the phase behavior of hydrocarbon fluids for all ranges of pore sizes from bulk (very big pores) to nanopore scale sizes (in shale formations). Such an equation of state can describe the phase behavior and fluid properties of fluids as a function of pore size and molecule size.…”

Section: Introductionsupporting

confidence: 86%

Using Simplified Local Density/ Peng-Robinson Equation of State to Study the Effects of Confinement in Shale Formations on Phase Behavior

Jamili

2014

SPE Unconventional Resources Conference

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A large amount of hydrocarbon fluids in shale formations are stored within the organic matters where the pore sizes are in the order of nanometer scales. Inside these nanopores, the interactions between the fluid molecules and porous walls play such an important role that can change the phase behavior as well as transport mechanisms of the hydrocarbon fluids. For a shale gas reservoir, the natural gas in the reservoir is usually stored in two forms, free gas and adsorbed gas. The region where free gas is stored has negligible fluid-wall interactions while the region for adsorbed gas is under strong pore wall influence. The current available equations of state cannot capture the phase behavior of the adsorbed gas phase due to the ignorance of the fluid-wall interactions.This work focuses on modifying the Peng-Robinson equation of state (PR-EOS) using the Simplified Local-Density (SLD) theory. From the modified PR-EOS, the fluid density at any arbitrary position inside the pore can be calculated using the local density approximation. A density profile for any particular hydrocarbon fluids can be obtained by calculating the local densities of the fluids at each discretized interval along the pore. From the density profile one can distinguish the regions of adsorbed phase, transition phase and bulk phase of the fluids. The thickness and averaged fluid densities for each phase can also be obtained from the model. Once the thickness of the absorbed phase is known, it is possible to determine whether adsorption is a single layer or multilayer.Our preliminary results show that depending on fluid types, either a single layer or multilayer adsorption is presented in those nanometer pores near the pore wall. The pore size range we focused on was from 100 nm to 1 nm. Methane and n-Butane were considered as fluids. When the pore size gets smaller and smaller, the absorbed layers at opposite pore walls can be merged together and result in the absence of the bulk fluid phase in the center areas of the pores. In this case, all the fluids in the pore are under influence of the wall. Our results also indicate that the fluid-wall interactions can have a much larger impacts on light components (methane) rather than heavy components (n-butane). That is, the density of the adsorbed phase of methane is more than two times the free gas density of methane (bulk density), while the n-butane adsorbed density is only slightly higher than its bulk density. The model has also been validated with molecular simulations for accuracy approval. IntroductionAs more and more development and production activities are involved in shale plays, the shale gas transport in nanoscale porous media draws attention recently. It is well known that in typical shale formations especially inside the organic content, the pore throat diameter tends to be in the order of nanometers whereas the molecule sizes tend to vary from a minimum of 0.373 nm for methane to significantly larger values for higher carbon number hydrocarbons. In general, fluids under confinement e...

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“…In addition, Zarragoicoechea and Kuz (2004) showed that the shifts on the critical temperature are proportional to the size of the mesopore. Normally, as the pore size decreases, the critical temperature and freezing/melting point tend to decrease (Kanda et al 2004;Moore et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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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Modifying Van Der Waals Equation of State to Consider Influence of Confinement on Phase Behavior

Cited by 27 publications

References 22 publications

Modeling the Effects of Porous Media in Dry Gas and Liquid Rich Shale on Phase Behavior

Modeling the Effects of Porous Media in Dry Gas and Liquid Rich Shale on Phase Behavior

Using Simplified Local Density/ Peng-Robinson Equation of State to Study the Effects of Confinement in Shale Formations on Phase Behavior

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

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