ISSN: 2578-4846
Authors: Jape N , Datchanamurthi and Ghosh S
Coal Bed methane is a vital energy resource and has been developing rapidly for the last two decades. Also, India's commitment to become a gas-based economy emphasizes more on increasing domestic gas production. Hence, there is a tremendous potential that can be exploited from coal bed gases. Wellbore stability is a critical factor throughout the life cycle of any well, particularly wherever coal formations are present in the subsurface, as coal beds possess several challenges mainly because of the low fracture gradient of coal and several natural fracture networks present in the coal beds. This review paper provides an overview of the factors influencing the wellbore stability of different types of wellbore modelling techniques, namely the analytical model, Poro-elastic model which is the most widely used technique and gives results with reasonable accuracy, Thermo-hydro-mechanical (THM) coupling model, and other numerical simulation techniques like finite element model used for calculating of and the stress distribution around the wellbore in the case of vertical and horizontal wells, as this is the crucial criterion for calculating fracture gradient. Amongst which, the THM coupling method is the most advanced modelling technique and is used when high thermal stresses are present. After this, it discusses the different drilling fluids used for drilling in the coal seams like oil based muds, degradable polymer based drilling fluids which have minimum formation damage and foam based drilling fluids which have efficient cuttings carrying capacity. Also, their limitations and advantages and the effects on permeability damage and tensile fractures caused by the drilling fluids. Thus, giving an overall review of the technological improvements in the CBM extraction processes.
Keywords: Wellbore Stability; Coal Bed Methane; Wellbore Modelling; Coal Seams
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