Pressure transient analysis of coalbed reservoirs with vertically fractured wells and radial discontinuities

This study identifies the need for the development of specialized solutions for pressure transient analysis in coal seams and, subsequently, provides a comprehensive solution package for these reservoirs. The proposed solutions are applicable to radial systems with finite wellbore radius and with either an infinite outer boundary, a constant pressure outer boundary or a closed outer boundary. At the inner boundary constant pressure or constant terminal rate cases can be specified. Included in the provided solution package are the solutions representing the pressure transient behavior of composite coal reservoirs and a coal reservoir with a hydraulically stimulated well. Uniform-flux fracture model is used to model hydraulically induced fractures.; The single-phase flow formulation for coalbed methane includes non-equilibrium sorption phenomena in the coal matrix and laminar gas transport in the natural fracture network (cleat system). The transport of methane in the coal matrix is described by using spherical elements. The mathematical models which account for unsteady state and pseudosteady state matrix/fissure methane transfer are incorporated into the transport equation.; In order to obtain a closed form solution in real time domain and avoid the pitfalls of numerical inversions approximate inversions of the solutions from the Laplacian space are also developed. The effects of different models of matrix/fissure flow on the solution are also discussed. The validity of the proposed analytical solutions are checked against a numerical simulator and comparisons showing good agreements between the two are presented.; A simplified analysis technique to determine the desorption characteristics of coal seams using pressure transient analysis is also presented. The proposed technique is based on asymptotic representation of an approximate analytical solution. The versatility of the approximate analytical solution is demonstrated through a simple analysis procedure which does not require the use of computationally laborious functional groups.; Type curves, closed form solutions and analysis techniques which are presented in this study provide engineering tools to be used for the in situ characterization of coal seams and other unconventional gas reservoirs with sorption/diffusion phenomena.