Colmenares, Lourdes B.¹, Mark D. Zoback¹
(1) Stanford University, Stanford, CA

ABSTRACT: Wellbore Completion Methods and Water Production of CBM Wells in the Powder River Basin

Accompanying the growth in Coal Bed Methane (CBM) production in the Powder River Basin (PRB) of Wyoming and Montana has been an increase in produced water due to the required dewatering of the coals to release the adsorbed methane. Our goal in this study has been to evaluate wellbore completion practices to determine if there are ways to produce less CBM water and still achieve adequate depressurization for methane production. Various lines of evidence suggest that a significant amount of water produced from CBM wells may come from the formations adjacent to the coal seams. One factor possibly exacerbating water production from adjacent strata is the vertical growth of hydraulic fractures during the drilling and completion of CBM wells. This can potentially result in both excess CBM water production and inefficient depressurization of coals. We have been analyzing water-enhancement data in coals to obtain the magnitude of the least principal stress in the coal seams in about 100 wells. The preliminary data indicates that the hydrofracs are horizontal in some areas because the least principal stress is the vertical stress. In such areas vertical fracture growth is obviously not a problem. In other areas, hydraulic fracture growth is vertical (the least principal stress is the least horizontal stress) and vertical fracture propagation is expected. We are now analyzing water production data to determine if there is significantly more water production in the areas where vertical fracture growth occurs.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.