US EPA

8748845 

Meetings & Symposia 

The dry coal anomaly - The horseshoe canyon formation of alberta, Canada 

Hoch, O 

2005 

1745-1758 

English 

The Horseshoe Canyon coal formation in Alberta, Canada is an anomaly for coals. It is dry, for the most part producing no formation water. Therefore, no dewatering is required. In fact, it is severely damaged by water influx. Normal permeability injection tests and conventional hydraulic fracturing techniques, even foams, have been unsuccessful in this environment. The best part of this reservoir has an areal extent in excess of 12,000 square miles containing 1-2 BCF per square mile of recoverable gas. Commercial development of this resource is a very appealing prospect. Numbers of coal seams vary from 5 to 30 per well, spread out over 600 - 1,300 ft. Individual seam thicknesses vary from 1 to 13 ft. Most seams are discontinuous over a large area. The better part of the formation has permeability in the range of 1 - 100 md. This makes it difficult to avoid damaging the formation during drilling and cementing operations, hence some type of stimulation is required. Nitrogen hydraulic fracturing is the only stimulation process that has had any success in this formation to date. The treatments involve pumping nitrogen at high rates, without proppant, through coiled tubing (CT) and a selective cup-type packer (SCP), isolating each coal seam while treating it. Bottomhole treating gradients vary greatly with an average of approximately 2.2 psi/ft. Whether these nitrogen treatments are in fact fracturing the formation or just having the damage flushed out has been a matter for speculation. Over 1,600 wells have been treated in this way and more continue to be added on an everyday basis. This paper describes the formation characteristics and geology of the Horseshoe Canyon coal and presents case histories of hydraulic fracturing treatments performed including production results. Copyright 2005, Society of Petroleum Engineers.