Executive Summary : | The pore-fracture system of coalbed methane (CBM) reservoirs affects gas adsorption and the gas transportation behaviors in coal seams. Fracture networks account for the permeability of the CBM reservoir and have a noteworthy effect on the success of exploiting and extracting methane from subsurface drilling. The aims of the project are to define the spatial orientation of the cleats presented in a coal seam and to estimate the cleat density, coalbed permeability, in-situ stress, rock mechanical properties, to perform geochemical analysis, to build geomechanical and wellbore stability models and sweet spot identification. The mechanical earth model will favor the hydraulic fracturing injection of fluids under in-situ stress to allow more gas production. Cleat orientation is observed locally to deviate from the settings resulting from the stress field during the time of cleat formation. Hence, cleat orientation mapping from coalfield and image log study in any basin will represent the spatial distribution current day stress field. The relation between coalbed permeability and confining pressure will be investigated through laboratory testing and modeling approaches. Geomechanical and wellbore stability modeling will be carried out in a few coalfields of central and eastern India. The model will be used to explore the sensitivity of CBM extraction behavior to several controlling factors, including initial fracture permeability, fracture spacing, desorption capacity, production pressure, and fracture and matrix porosities. The rock mechanical parameters namely; uniaxial compressive strength (UCS), tensile strength, cohesion (c), the angle of internal friction and the state of stress are controlling the stability of the wellbore. The coal petrography and geochemical properties affect the degree of methane sorption of coal. Methane gas is significantly adsorbed onto the internal surface of coal particles. The adsorbed gas volume is being described by the Langmuir isotherm for pure gas (e.g., Yang, 1987). The fractures or cleats in coals are stress-sensitive compared to the micropores in the coal matrix. Overall coal strength data is required to study and analyse the failure behavior of the coal in few CBM fields of eastern and central India. Complete knowledge of the broad stress profile would assist the wellbore stability including the stress-dependent permeability models. Moreover, it would serve the engineering development of geoscientists working in the area of fault activity analysis, geomechanical analysis, planning for horizontal well drilling, casing and coal primary/secondary hydraulic fracturing. |
