Optimizing Hydraulic FracturingTreatments for CBM Production UsingData From Post-Frac Analysis

摘要

Commercial coal bed methane (CBM) development iscurrently in its infancy in Canada. Often the challenge tocommercial development of this unconventional resource is tolocate reservoir sweet spots and to economically optimizecompletion and stimulation design for coal gas extraction.Most CBM wells require hydraulic fracturing to produce atcommercial gas rates. It is important to understand thatfracturing of coals is very different from fracturingconventional sandstone reservoirs. Coal is a naturallyfractured material (cleat system) with very unique rockmechanical properties, and is inherently prone to complexand/or multiple fractures. This may include T-shaped, ‘railroadtrack’, or branched fractures.This paper will present data from a regional CBM project inAlberta to illustrate the complexity and the challenges ofdesigning fracture treatments in a tectonically active area.Regional differences in in-situ stress are shown to have a largeinfluence on the producibility of a particular coal zone. Thefrac gradient information derived from the post-frac analysiscan be used to locate sweet spots for piloting. Also, the sameinformation can be used for optimizing the hydraulic fracturedesign and placement in the pilot project.In multiple coal zones, the indirect vertical fractureconnectivity (IVFC) technique has been successfully used toreduce the probability of complex fracturing. Comparisons ofthis technique to the conventional completion technique will bediscussed in this paper. Other key technologies in the fracdesign include formulation of a special nitrogen foamsurfactant frac fluid that minimizes frac face damage,orientated perforations in deviated well bores that minimizecomplex frac geometry, and radioactive tracer logs that areused to verify and optimize frac design.