Gas Adsorption/Diffusion in Bidisperse Coal Particles: Investigation for an Effective Diffusion Coefficient in Coalbeds
Bibliographic record
Abstract
Abstract Pore structure of coalbeds exhibits multi-scale heterogeneity. It is common practice to characterize the coalbeds using two distinctive porosity systems: a well-defined and uniformly distributed network of natural fractures, and nearly impermeable and non-uniform coal matrix blocks. The blocks consist of microporous solids with large internal surface area and strong affinity for some naturally occurring chemical species such as methane and carbon dioxide. At high coalbed pressures, therefore, these species exist abundantly and/or could be stored in large quantities at a physically adsorbed liquidlike state. Much work has been carried out on adsorption capacity of various coals. Diffusive transport processes within the matrix blocks could be the rate limiting step for adsorption during gas injection and production operations. Identifying these processes and determining their contributions to overall (upscaled) mass transport is a complex and time consuming procedure. The paper presents numerical diffusion models in varying coal particles and investigates transport mechanisms. For this purpose, the coal particle is represented as a microporous solid penetrated by a network of larger interconnected macropores. The solid consists of pores of the order of a few molecular diameters and adsorbs the bulk of the gas. A simple relationship between the apparent and intrinsic (macropore and solid) Fickian diffusion coefficients is shown to exist in the case of single-component (methane) nonlinear Langmuir-type adsorption. Mass transport in the bidisperse coal particle is significantly influenced by the adsorption in microporous solid. The investigation is then extended to study concentration dependence of the microporous solid diffusion for binary (methane-CO2) mixtures. It is found that co-diffusion of the gas molecules enhances significantly, while counter-diffusion diminishes the mass transport in the solid in the presence of competitive sorption dynamics. The isotherm nonlinearity effects and the influence of lateral interactions among the adsorbed molecules in the solid phase are discussed. A sensitivity analysis is given to identify conditions that promote desorbed methane production from and adsorbed CO2 storage in the microporous solid. The work finds application in modeling CBM and ECBM processes. Introduction As an unconventional natural gas resource, coalbed methane receives worldwide attention. Deep coal seams that are not accessible for mining are suitable for in-situ gas production using conventional drilling, well completion and gas recovery technologies. Hence, a vast amount of natural gas is globally available. Unlike the conventional gas resources, however, the gas storage, flow and transport processes in coalbeds are quite complex mainly due to an intricate nature of the coalbeds. Coalbeds are porous media often characterized by a bimodal pore structure: a primary structure consisting of micro- and mesoscale pores, and a secondary structure with macropores and interconnected natural fractures. The microporous coal has extremely large internal surface area and strong affinity for certain naturally occurring chemical species such as methane, carbon dioxide, nitrogen and water. At high coalbed pressures, therefore, majority of the natural gas in-place, in particular methane, exists abundantly at an adsorbed liquid-like state in the microporous solid [1]. Depressurizing the coalbed yields a significant volume of methane.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".