Applying Advanced Fracture Diagnostics to Optimize Fracture Stimulation in Coalbed Methane Reservoirs: Case History of Two Fields in the Rocky Mountains

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCoalbed methane development continues to increase accounting for 8% of U.S. gas production in 2002. Many coalbed methane wells must be stimulated by hydraulic fracturing in order to achieve economic production rates. However, optimizing hydraulic fracture treatments in coalbed methane is difficult and advanced diagnostics can aid in the process. This paper discusses completion optimization for two coalbed methane reservoirs in the Rocky Mountains. Hydraulic fracture mapping was performed with treatment well tiltmeters on several wells in each reservoir. Treatment well tiltmeter fracture mapping is an emerging technology to optimize development of low permeability reservoirs. The fracture height measured with the treatment well tools was used to calibrate a fracture model for each field. The fracture mapping, calibrated model and on-site diagnostics were used to modify completion and stimulation strategy in these fields.The completion strategy for both fields was fairly similar early on. Fracture mapping showed height growth through several coal stringers in both areas. There was some degree of containment in the laminated lithology bounding the pay packages but one field was more prone to height growth at higher pumping rates. Job size and injection rate were drastically reduced in this field because of the height growth tendencies and the presence of nearby water sands. This paper shows how the application of fracture diagnostics and engineering can reduce costs and help avoid costly errors. One example is shown with advanced diagnostics applied early in the development of a field and another example is shown with diagnostics applied after some development has already occurred. The differences in hydraulic fracture geometry that can occur between areas are also shown and how they create changes in completion strategy.

Effect of Formation Modulus Contrast on Hydraulic Fracture Height Containment

“…Layered materials have higher resistance to fracturing, and are considered to have a "composite layering effect" to hinder fracture growth (Warpinski et al 1998;Wolhart et al 2004). Some of the mechanisms contributing to a composite-layering effect require interfacial slippage or debonding.…”

“…It has been observed that sometimes the fracture is more contained in height than predicted by simulators. Some new mechanisms and explanations have been given, including the "composite layer effect," "shear dampening," and fracture behavior at layer interfaces, for the unexpected height containment (Warpinski et al 1998; Barree and Winterfeld 1998;Wolhart et al 2004).…”

Effect of Formation Modulus Contrast on Hydraulic Fracture Height Containment

“…6,11 Some of the mechanisms contributing to a composite layering effect require interfacial slippage or debonding. Layered materials have higher resistance to fracturing, and are considered to have a "composite layering effect" to hinder fracture growth.…”

“…6,10,11 On the other hand, more advanced numerical models have been developed for hydraulic fracture simulators, 1,12 and the combined effect of height containment mechanisms can now be studied with fewer approximations for hydraulic fracturing conditions. It has been observed that sometimes the fracture is more contained in height than is predicted by simulators.…”