Identification of potential locations for well placement in developed coalbed methane reservoirs

Abstract This study investigates well placement in developed coalbed methane (CBM) reservoirs. A workflow is developed to find potential locations for well placement within the reservoir. It consists of a reservoir simulator and statistical analysis. The application of this workflow is to reduce the need to perform computationally expensive simulations in large reservoirs to obtain potential locations for drilling an additional well. The workflow is also used to study the role of dominant reservoir properties in finding potential locations for well placement. The effects of permeability anisotropy, gas and water relative permeabilities, sorption time, and water content in well placement are discussed. Results demonstrate that permeability anisotropy results in the formation of elliptical drainage areas around the wells. When drainage patterns are orthogonal to the direction of placement of wells, the drainage area of the reservoir is large and penetrated into distant locations. This leads to a non-uniform drainage area and extends well placement options to distant locations. Comparison between well placement in two scenarios with different gas and water relative permeabilities shows that potential locations tend to be on a border region between existing wells and virgin area when water mobility is restricted by water relative permeabilities. This region has the advantage of having higher pressure and gas content compared to locations among existing wells. In this study, changing the sorption time does not affect the well placement within the reservoir. Except at very early times, gas production from presented reservoir models is mainly controlled by Darcy flow in cleat system (permeability-dominated) rather than diffusion process in coal matrix.

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