Maximizing Energy at Coalface for Coalbed Methane Fracturing Operations

Abstract

Abstract Nitrogen coiled tubing fracturing is the predominant method for completing and stimulating dry coalbed methane (CBM) formations, such as the Horseshoe Canyon in the Western Canadian Sedimentary basin. A typical well has an average of 20 pay zones that are stimulated individually. The coal cleats are fractured by pumping nitrogen at high rates through coiled tubing (CT) into perforations isolated by straddle assembly. Currently energy that can be delivered to the coalface of these dry CBM wells has been limited by the friction pressure through (CT). Efforts to increase the energy have involved increasing CT size and increasing surface horsepower. Economics and logistics practically limit the pipe size to 2 7/8 in. for deeper wells and 3¼ in. for shallow wells using CT fracturing technique. This paper discusses the development of a technique which initially eliminates the CT friction limits on transferring energy to coalface. A large-volume pressure pulse is released downhole during the fracturing process to create an order of magnitude change in available energy at the fracture face, compared to current dynamic fracturing processes. The additional energy is dissipated by increasing the surface cleat area exposed. The development of the technique and field tests results will be discussed. Introduction The Horseshoe canyon dry coal formations have been commercially exploited since late 2000. From the beginning it was clear the Horseshoe Canyon CBM play was a unique CBM play, it is set apart by consisting of a dry under pressured coal. The coal therefore does not require dewatering before production. The coal consists of multiple thin seams, ranging from 10 - 30 seams per well. The coal seam thickness ranges lies between 0.1 and 2.5 meters. (Fig 1 - Horseshoe Canyon CBM log) The production rates from these CBM wells dictates that a efficient drilling and completion model be adopted in order to be economic. The current model that is utilized is the wells are drilled with coiled tubing drilling rigs, cased and cemented. Wireline perforating crews are then dispatched to perforate the zones of interest in a rig less operation. The individual coal seams are then stimulated via the injection of dry nitrogen at high rates through a coiled tubing reel that is equipped with a fracturing isolation tool. The dry coal has not responded well to any other form of stimulation. The lack of success of more traditional stimulation methods is deemed to be damage to the dry under pressured coal seams.