Coalbed gas is generated during coalification process and remain in the coal as an adsorbed form. This paper discusses the mechanism of generation of coalbed gas and identification of its origin. Two samples has been retrieved from exploratory borehole of Jharia Coalfield. Location of the study area was shown in figure 1. Gas content of these coal samples has been found and some gas is collected in glass bottle from desorption canister. After collection of this adsorbed gas, it was analyzed through gas chromatography and isotopic ratio mass spectrometer. Analyzed coalbed gas contains primarily CH4, ranges from 72.25% to 83.21% and CO2, ranges from 2.63% to 3.05%. Stable isotope geochemistry shows that isotopic fraction is between CH4, C2H6 and CO2. Stable isotopic fractionation and coalbed gas composition is shown in table 1. Isotope of δ13CO2 varies from -21.3% to -17.9%. CDMI and hydrocarbon index (CHC) was also calculated. CDMI index ranges from 3.51 to 3.54 which that coalbed gas might be of thermogenic origin. CHC index ranges from 68.77 to 95.07 % which shows generated CO2 is of organic in nature. Calculated dryness index ranges from 0.986 to 0.990 which shows that coalbed gas is dry to very dry in nature. Coal samples was characterized on the basis of petrochemical and petrographic for the coalbed methane recovery from Jharia Coalfield. Analyzed coalbed gas contains mainly thermogenic methane with substantial amount of biogenic methane. δ13CO2 for biogenic was assumed to be -20% to -15% for the samples. Biogenic proportion for the samples was observed 24.65% and 13.77% respectively while for thermogenic proportion, it was found around 75.35% and 86.23%.

Coalbed Methane is an attractive source of energy to mitigate the growing energy demand of India. It is often abbreviated as unconventional source of energy. In this paper two bore hole samples (J/01 & J/02) were collected and characterized for the isotherm studies to know the sorption capacity of the coal. Pure gas isotherm was constructed based on the manomateric method. Pure gas isotherm was constructed in indigenously fabricated setup. Langmuir model was used for the prediction of sorption capacity at particular pressure. Langmuir constants (PL & VL) were calculated using regression analysis. It was found that volume wise CO2 has 2.09 to 2.75 times more adsorption capacity than coal.Once pure gas isotherm was drawn and PL and VL was calculated. Langmuir constants were given as follows: CH4 -VL (scf/ton) of J/01 and J/02 are 227.27 and 454.55 respectively CH4 -PL (psi) of J/01 and J/02 are 128.54 and 173.68 CO2-VL (scf/ton) of J/01 and J/02 are 476.19 1250 respectively CO2-PL(psi) of J/01 and J/02 are 133.33 596.13 Binary mixture of CH4 and CO2 was modelled at different gas mixtures and at pressure of 2000 psi. Multicomponent iterative model (MIA) was proposed using Newton Raphson iteration to study the co adsorption isotherm of CH4 and CO2 at different binary mixtures. It was found that one CO2 mole fraction increases in gas phase. For sample J/01 Enhanced Coalbed Methane (ECBM) recovery will occur after 27.4 % of CO2 in gas phase while ECBM recovery will occur after 13.03% of CO2 in gas phase. Pure component isotherm and co adsorption isotherm is given in figure 1 & 2.