Coal seams, particularly deep unmineable coal reservoirs, are the most important geological desirable formations to store CO 2 for mitigating the emissions of greenhouse gas. An advantage of this process is that a huge quantity of CO 2 can be sequestrated and stored at relatively low pressure, which will reduce the amount of storage cost required for creating additional platform to store it. The study on CO 2 storage in coal seam to enhance coal bed methane (ECBM) recovery has drawn a lot of attention for its worldwide suitability and acceptability and has been conducted since two decades in many coalmines. This article focuses on the coal seam properties related to CO 2 adsorption/desorption, coal swelling/shrinkage, diffusion, porosity and permeability changes, thermodynamic/thermochemical process, flue gas injection, etc. Here, the performance analysis of both CO 2 storage and ECBM recovery process in coal matrixes is investigated based on the numerical simulation. In this study, a one-dimensional mathematical model of defining mass balances is used to interpret the gas flow and the gas sorption and describe a geomechanical relationship for determining the porosity and the permeability alteration at the time of gas injection. Vital insights are inspected by considering the relevant gas flow dynamics during the displacement and the influences of coal swelling and shrinkage on the ECBM operation. In particular, pure CO 2 causes more displacement that is more efficient in terms of total CH 4 recovery, whereas the addition of N 2 to the mixture assists to make quicker way of the initial methane recovery. However, this study will support future research aspirants working on the same topic by providing a clear conception and limitation about this study. Keywords CBM recovery • Carbon dioxide storage • Gas flow dynamics • Gas adsorption • Coal swelling List of symbols t Overall porosity c Cleat porosity p Macroporosity n c Number of components n Adsorbed phase concentration (mol/m 3) c Actual gas phase concentration (mol/m 3) c 1 Effective pressure coefficient (1/Pa) c 2 Swelling coefficient u Superficial velocity of fluid (m/s)

Moisture adsorption in the coal seams affects the gas adsorption capacity and can alter the coal deformation and permeability criteria of the coal seam. The effect of dynamic loss of moisture content, both on moisture and gas sorption-induced coal swelling/shrinkage strains, during the coalbed methane (CBM) production, is crucial. This study investigates the interactions among coal matrix, absorbed gas, and moisture content, based on the coal swelling/shrinkage strains and gas adsorption decay criteria. Consequently, a mathematical model of the coal deformation is developed for the proper evaluation of the moisture effect. For developing the model, this paper considers the standard gas flow and moisture loss equations to assess the volumetric content, equilibrium pressure, and density of the moisture. Finally, it comprehensively analyzes the sensitive factors and effects of elemental parameters of moisture content on coal deformation and coal permeability. The results show that moisture content at adsorbed state significantly changes the coal swelling/shrinkage strain and that distorted swelling and shrinkage characteristics can promote the permeability alternation in wet coal reservoirs. Moreover, the intermolecular attraction between the coal structure and the moisture content has a significant effect on methane adsorption/desorptioninduced deformation in coal structure. This study also designs the coal deformation strains as a function of moisture content by the Langmuir type model and evaluates the hysteresis rate between the swelling and shrinkage characteristics. The findings of this paper can characterize a wet coal reserve for CBM production and anticipate future production under different operating conditions.

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Coalbed methane is extracted from the adsorbed state in coal seams with lower pressure and production rate. In previous studies, researchers only focused on the methods that were developed for making a relationship between the underground production rate and surface flow rate without any type of optimization procedure. In this study, the main purpose is to do a review on finding out of surface layout plan to optimize the maximum gas flow rate by developing an improved pipeline network. The more the optimization of the layout plan for designing pipeline network, the lower the amount of investment need to provide. Here, a mathematical model is proposed for the gas transportation based on the hydraulic and thermodynamic calculations of the pipeline network. Not only that, but also the filtration mechanism of depressurization and desorption for the gas flow through pipe section are evaluated here. After that, the pressure drop and pipeline efficiency are explored to find out the best design of pipeline network from the observed results. Finally, based on this study, many uncertainties can be reduced associated with the installation of pipeline network for gas transportation.

The extraction procedure of coalbed methane is usually different from conventional type of gas extraction. Generally, the CBM extraction procedure is completed within two approaches. First one is drilling on the surface for heading downward through the ground & second one is extracting through the existed underground coal mines. For making the CBM extraction an economic viable, well optimization development should be implemented with carefully. So, an evaluative technique called 'Unit Technical Cost' briefly known as UTC can be one of the better way to evaluate the well optimization development. This optimization technique is evaluated practically based on the two major coal basins of china, known as 'Qinshui basin & Ordos Eastern Margin basin'. The well completion & simulation process can be examined by the parameters that are used in this technique. This paper is tried to give a new research on CBM well development based on using the UTC method for making decision criteria to calculate the optimization level. The calculation is done using the detailed properties of UTC in the well development by establishing the process theory. In this research, the production profiles are evaluated for building up the engineering & geologic parameters where the product price, operating cost & project investment is evaluated for finding the economic parameters. This is found from the optimized results that a horizontal well should be optimized for its economic feasibility in the Qinshui Basin where directional well optimization is better for Ordos Eastern Margin Basin.