Large quantities of water are produced from coalbeds within the Ferron Sandstone as part of coalbed methane production. The groundwater flux, flow patterns, and water chemistry in the Ferron Sandstone and adjacent units respond to increased water drainage from the coals. Modeling can address the complex interaction between the regional groundwater flow system, the local flow system in the cleated (fractured) coal, and faults. Objectives are to describe the local groundwater flow system in a “typical” coalbed using a discrete fracture network (DFN) method, describe the regional groundwater flow system in the Ferron Sandstone and contiguous units utilizing GIS and MODFLOWP, quantify potential water yields of a “typical” coalbed, and identify the effects of dewatering the main coal as a result of gas production.

Preliminary DFN modeling shows that block-scale permeability calculations of the coal's cleat network can be used to determine a bulk permeability for a specific direction. This determination quantifies the degree of anisotropy of the network which will be included in the regional-scale flow model representing a coalbed layer.

A 3-D digital representation of the Ferron Sandstone and contiguous units has been developed for the regional groundwater flow system. This 3-D model describes the geometry and permeability patterns of units controlling groundwater flow. The digital model is used to assess potential water yields and the effects of dewatering through pumping simulations. Hydrochemical data are used to help identify the effects of dewatering. As a result, the study will help assess the effects of coalbed methane production on the groundwater flow system.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah