Coalbed methane gas resources have become a significant part of the total United States gas reserves. Recently, many completions in coalbed reservoirs are horizontal. Coal is an anisotropic, naturally fractured medium, comprised of a low permeability matrix surrounded by a high permeability fracture "cleat" system. The anisotropy makes a coalbed reservoir a good candidate for horizontal completions in order to intercept more fracture areas. This paper addresses horizontal well testing in coalbed reservoirs.

The majority of the gas in coalbed reservoirs is stored in an adsorbed state on the coal grain surfaces. To mobilize this gas requires a pressure drawdown across the matrix boundary, which is created by the depletion of the cleat system.

The paper presents the drawdown and buildup solutions for a horizontal well in a coalbed methane gas reservoir. Pseudosteady state gas desorption and uniform pressure distribution along the well is assumed. A solution is obtained for anisotropic, semi-infinite reservoir with constant rate production at the well. Successive Laplace and Fourier integral transforms are applied with numerical Laplace inverse transform. The match of analytical solution with numerical simulation data is presented.

Investigations into the effects of the diffusion coefficient D, and sorption parameter θ, are presented.

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