Stimulation Technology in the Antrim Shale

Abstract

Abstract The Antrim Shale of the Michigan Basin has been one of the most active natural gas plays in the U.S., with 1992 drilling exceeding 1200 wells. Gas production from the Antrim, reported to contain 76 Tcf (2.1 × 10'2m') of in-place resource, reached 74 Bcf (2.1 × 10'm') in 1992 with 2,600 wells producing at year end. Much of the 1992 drilling activity can be attributed to the expiration of the Section 29 tax credit which was applicable to the Antrim Shale. The Gas Research Institute has targeted the Antrim Shale as a focus of stimulation research. Two field research projects addressing stimulation technology in the Antrim Shale were initiated during 1992 in cooperation with producing companies, one which is investigating methods to optimize hydraulic fracturing treatments and one which is investigating the potential application of alternative, low-cost stimulation methods. The first project, being performed in cooperation with Ward Lake Energy, is studying whether single-stage fracture treatments (one treatment for two shale horizons) are more cost-effective than individual treatments for each zone. Four offset study wells were selected for the project; two open-hole completions to evaluate single-stage treatments and two cased-hole completions to evaluate multiple-stage treatments. Pre- and post-stimulation pressure transient testing, mini-fracs, bottomhole treating pressure data, and post-frac borehole camera surveys have been incorporated into the research program. Preliminary results indicate that single-stage fracture treatments do contact both shales, however the stimulation achieved in each zone has not been clearly defined yet. The second project, being performed in cooperation with Terra Energy, is comparing the costs, stimulation effect and production performance of three offset wells stimulated by (a) an acid bailout treatment, (b) high-energy gas fracturing and (e) hydraulic fracturing. Post-stimulation pressure transient testing, production testing and stimulation diagnostics have been incorporated into the research program. preliminary results indicate that hydraulic fracturing provides superior production results. The lower costs of the alternative treatments, however, may still make them attractive under certain reservoir conditions. Introduction The Antrim Shale of the Michigan Basin contains a large resource of unconventional natural gas, currently estimated to be more than 76 Tcf (2.1 × 10'm'). It has been one of the most active natural gas plays in the U.S., accounting for over 1200 wells drilled during 1992. As of December 1992, 2,600 Antrim Shale wells were producing 230 MMcfd (6.5 × 10'm') of natural gas from the primary production trend (Figure 1). Despite the high level of development activity, current techniques for completing and stimulating Antrim Shale wells may still require improvement to maximize gas recovery from this unconventional gas reservoir. In response to the large opportunities that exist to expand the potential methane recovery from this resource through advanced stimulation technologies, the Exploration and Production Technology Department of the Gas Research Institute (GRI) has targeted the Antrim Shale as a focus of research. The Antrim Shale is a shallow, underpressured, naturally fractured, dual-porosity shale reservoir with characteristically low matrix permeability, and with adsorbed gas, free gas and mobile water coexisting in the reservoir. P. 659^