The Dry Coal Anomaly-The Horseshoe Canyon Formation of Alberta, Canada

摘要

The Horseshoe Canyon coal formation in Alberta, Canada isrnan anomaly for coals. It is dry, for the most part producing nornformation water. Therefore, no dewatering is required. In fact,rnit is severely damaged by water influx. Normal permeabilityrninjection tests and conventional hydraulic fracturingrntechniques, even foams, have been unsuccessful in thisrnenvironment. The best part of this reservoir has an areal extentrnin excess of 12,000 square miles containing 1-2 BCF perrnsquare mile of recoverable gas. Commercial development ofrnthis resource is a very appealing prospect.rnNumbers of coal seams vary from 5 to 30 per well, spreadrnout over 600 – 1,300 ft. Individual seam thicknesses vary fromrn1 to 13 ft. Most seams are discontinuous over a large area. Thernbetter part of the formation has permeability in the range of 1rn– 100 md. This makes it difficult to avoid damaging thernformation during drilling and cementing operations, hencernsome type of stimulation is required.rnNitrogen hydraulic fracturing is the only stimulationrnprocess that has had any success in this formation to date. Therntreatments involve pumping nitrogen at high rates, withoutrnproppant, through coiled tubing (CT) and a selective cup-typernpacker (SCP), isolating each coal seam while treating it.rnBottomhole treating gradients vary greatly with an average ofrnapproximately 2.2 psi/ft.rnWhether these nitrogen treatments are in fact fracturing thernformation or just having the damage flushed out has been arnmatter for speculation. Over 1,600 wells have been treated inrnthis way and more continue to be added on an everyday basis.rnThis paper describes the formation characteristics andrngeology of the Horseshoe Canyon coal and presents casernhistories of hydraulic fracturing treatments performedrnincluding production results.