Method to Determine Permeability and Stresses in Fractured Porous Coal Seam by Gas Pressure Measurements in Shut-In Well
L. A. Nazarov, L. A. Nazarova
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Fractured porous coal seam, gas flow, gas, dual permeability, pressure in shut-in well, inverse problem
Abstract
The authors substantiate the method for the qualitative assessment of stresses and permeability parameters characterizing mass transfer in gas-saturated fractured porous coal mass, namely: mass transfer coefficient β, and permeability coefficients of fractured zone and matrix, k1 and k2, respectively. The method consists in formulation and solving of a mixed-type inverse problem within the framework of a dual porosity/dual permeability model to estimate the values of β, k1 and k2 by the measurement data of the pressure P(t) in a shut-in vertical well. The solvability of the inverse problem is demonstrated on the basis of the analysis of the introduced objective function, and an original algorithm is developed to find a minimum value of the function using additional information on the behavior of P(t). It is found that in the course of time, the function P(t) reaches a stationary value which is independent of the model parameters and is equal to the pressure of gas in an intact seam, which makes it possible to calculate the horizontal stresses outside the influence zone of the well. The proposed method can be used to provide parameters for geomechanical modeling in justification of technologies of pre-mine drainage and methane recovery.
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