The Unsteady-State Nature of Sorption and Diffusion Phenomena in the Micropore Structure of Coal: Part 2—Solution

Kolesar, J.E.; Ertekin, Turgay; Obut, Salih

doi:10.2118/19398-pa

Cited by 30 publications

(14 citation statements)

References 7 publications

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“…Diffusion is the process where flow occurs as a result of random molecular motion from a location of high concentration to a location of lower concentration (Kolesar et al, 1990a(Kolesar et al, , 1990bSmith and Williams, 1984;and Crank, 1975). Diffusion in coal is a combination of Knudsen, bulk, and surface diffusions, depending on the coal structure and pressure (Smith and Williams, 1984).…”

Section: Diffusionmentioning

confidence: 99%

Changes in properties of coal as a result of continued bioconversion

Pandey¹

2016

International Conference and Exhibition, Barcelona, Spain, 3-6 April 2016

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Microbial actions on coal have long been identified as a source of methane in coalbeds.Andrew Scott (1995) was the first to propose imitating the natural process of biogenic gasification, possibly leading to recharging coalbed methane (CBM) reservoirs, or setting up natural gas reservoirs in non-producing coalbeds. This study was aimed at identifying the changes in coal properties that affect gas deliverability in coal-gas reservoirs, when treated with microbial consortia to generate/enhance gas production. The experimental work tested the sorption and diffusion properties for the coal treated and, more importantly, the variation in the relevant parameters with continued bio-conversion since these are the first two phenomena in CBM production.During the first phase, single component sorption-diffusion experiments were carried out using pure methane and CO2 on virgin/baseline coals, retrieved from the Illinois basin. Coals were then treated with nutrient amended microbial consortia for different periods. Gas production was monitored at the end of thirty and sixty days of treatment, after which, sorption-diffusion experiments were repeated on treated coals, thus establishing a trend over the sixty-day period.The sorption data was characterized using Langmuir pressure and volume constants, obtained by fitting it over the Langmuir isotherm. The diffusion coefficient, D, was estimated by establishing ii the variation trend as a function of pore pressure. The pressure parameter was considered critical since, with continued production of methane, the produced gas diffuses into the coal matrix, where it gets adsorbed with increasing pressure. During production, the pressure decreases and the process is reversed, gas diffusing out of the coal matrix and arriving at the cleat system.The results indicated an increase in the sorption capacity of coal as a result of bioconversion. This was attributed to increased pore surface areas as a result of microbial actions. However, significant hysteresis was observed during desorption of methane and was attributed to preferential desorption from sorption sites in the pathways leading to pore cavities. This is corroborated by the increased rates of diffusion, especially for methane, which exhibited rates higher than that for CO2. This contradicted the results for untreated/baseline coal, which were in agreement with previous studies. Effort was made to explain this anomaly by the nonmonotonic dependence of effective diffusion coefficient on the size of the diffusing particles, where in coalbed environments, CO2 has smaller kinetic diameter than methane.iii ACKNOWLEDGMENTS I would like to express my sincere appreciation and gratitude to my academic advisor and Thesis Chair, Dr. Satya Harpalani, for his guidance, encouragement, constructive criticism and patience throughout my study. Without his help and advice, this study would not have been possible. I would also like to thank him for giving me the opportunity to come to Southern Illinois University and work under his supervision.

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Section: Diffusionmentioning

confidence: 99%

Changes in properties of coal as a result of continued bioconversion

Pandey¹

2016

International Conference and Exhibition, Barcelona, Spain, 3-6 April 2016

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“…This term is defined as follows: 144 a v rni qt = -Y---at (5) In Equation 5, V rni represents the volumetric methane concentration in the micropore which is a strong function of pressure. The constant y is a conversion factor with a numerical value of 5.615 and units of cubic feet per reservoir barrels 14 (7) At this point, we introduce the sorption functional group. This variable will play a critical role in combining the gas and water equations into a single relationship.…”

Section: Formulationmentioning

confidence: 99%

A Type-Curve Solution for Coal Seam Degasification Wells Producing Under Two-Phase Flow Conditions

Mohaghegh¹,

Ertekin²

1991

All Days

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In this paper a new series of type curves that can be used in the characterization of coal bed reservoirs are presented. The proposed type curves take into consideration the presence of water in the coal seam and its coproduction with gas. The developed type curves are capable of handling the presence of the non-linear desorption phenomenon which plays a major role in the flow dynamics of methane in coal seams.A previously developed numerical model has been instrumental in the construction of the new type curves. During the development phase, gas and water equations were collapsed into a single expression. This consolidated transport expression was then put into a dimensionless form and necessary dimensionless groups were identified. The terms which relate to desorption process were included within the total system compressibility. This was made possible through a newly developed sorption functional group.The proposed type curves assume radial flow geometry around a degasification well which fully penetrates the formation. These type curves are generated for constant pressure specifications at the inner boundary. Coal seam initially is assumed to be in saturated state.The proposed type curves were tested extensively using a wide range of coal properties including desorption characteristics, and were identified with unique characteristics. The uniqueness of the type curves are preserved throughout the different flow regimes.The proposed type curve solution for coal bed reservoirs undergoing two-phase flow can be instrumental in analyzing the constant pressure drawdown test data from a degasification well.

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“…Pseudo-statedy state sorption formulation is mathematically less rigorous than unsteady state formulation which requires more computational work and memory when implemented in the numerical models. Although long term forecasts of these two models do not differ significantly, 12 Spencer et aI. 13 concluded that the early time predictions obtained using pseudo-steady state approach may not be accurate.…”

Section: Introductionmentioning

confidence: 96%

A Comprehensive Study of Pressure Transient Analysis with Sorption Phenomena for Single-Phase Gas Flow in Coal Seams

Anbarci¹,

Ertekin²

1990

All Days

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This paper identifies the need for the development of specialized solutions for pressure transient analysis in coal seams and, subsequently, provides a comprehensive solution package for these reservoirs. The proposed solutions are applicable to radial systems with finite wellbore radius and with either an infinite outer boundary, a constant pressure outer boundary or a closed outer boundary. At the inner boundary constant pressure or constant terminal rate cases can be specified.The single-phase flow formulation for coalbed methane includes non-equilibrium sorption phenomena in the coal matrix and laminar gas transport in the natural fracture network (cleat system). The transport of methane in the coal matrix is described by using spherical elements. The mathematical models which account for unsteady state and pseudosteady state matrix/fissure methane transfer are incorporated to the transport equation.In order to obtain a closed form solution in real time domain and avoid the pitfalls of numerical inversion approximate inversions of the solutions from the Laplacian space are also developed. These closed form solutions are found to be in good agreement with the numerically inverted solutions. The effects of different models of matrix/fissure flow on the solution are also discussed. The validity of the proposed analytical solutions are checked against a numerical simulator and comparisons showing good agreements between the two are presented.The solution package describes forward solutions which have the potential to be used in an interpretation method for insitu characterization of coal seams and other gas reservoirs where adsorption and desorption phenomena are considered to be active.

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The Unsteady-State Nature of Sorption and Diffusion Phenomena in the Micropore Structure of Coal: Part 2—Solution

Cited by 30 publications

References 7 publications

Changes in properties of coal as a result of continued bioconversion

Changes in properties of coal as a result of continued bioconversion

A Type-Curve Solution for Coal Seam Degasification Wells Producing Under Two-Phase Flow Conditions

A Comprehensive Study of Pressure Transient Analysis with Sorption Phenomena for Single-Phase Gas Flow in Coal Seams

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