The analyses of over 100 multi-point pressure transient tests by Reeves et al. demonstrated that non-Darcy flow effects can be substantial and minimization of these effects was determined to be key in deliverability improvement. TSO fracturing was attempted at three gas storage reservoirs in Nebraska, Michigan, and Ohio.
As a result of formation damage, individual US gas storage wells are prone to deliverability loss at a reported average rate of 5% per annum. To bypass this damage and sustain/enhance well deliverability, several new and novel fracture-stimulation technologies have been tested in gas storage fields across the U.S. as part of a joint U.S. Department of Energy and Gas Research Institute R&D program that began in 1994. These new technologies include tip-screenout fracturing, hydraulic fracturing with liquid CO2 and proppant, extreme overbalance fracturing, and high-energy gas fracturing. This paper presents, in summary form, the final results obtained from this multi-year R&D project, which concludes in 1999.
A total of nine field test sites have been involved in the project; fracturing operations at all sites is completed, and limited post-stimulation deliverability and pressure-transient testing remains for each. In total, over 30 new and novel fracture treatments have been performed, close to 100 deliverability and pressure transient tests performed, and about 45 pre and post-fracture diagnostic tests performed.
Significant accomplishments have been numerous. First, the potential application of the various new and novel fracture stimulation technologies to gas storage wells has been demonstrated. Secondly, a lack of analytical design tools has been identified for some of the fracture stimulation technologies investigated. In response, a dynamic fracture and wellbore simulator has been modified to model the extreme overbalance fracturing process, and for the first time EOB downhole pressure records have been collected for analysis. Similarly, for the first time, downhole pressure/temperature records have been collected for a liquid CO2 with proppant fracture treatment. Finally, a comprehensive data set of multi-point deliverability and pressure transient tests has been assembled. This has provided a unique insight into the impact of fracture stimulation on gas storage wells, particularly with respect to the reduction of important non-Darcy flow effects, deliverability profiles, post-frac cleanup effects and how these factors change over time.
Based on the results derived from the project, conclusions have been drawn concerning the applicability and utility of these technologies, storage well damage conditions and remediation candidate selection, and future technology needs.
Author(s): SPE, SPE, S.R. Reeves, L.J. Pekot, and G.J. Koperna, Advanced Resources International Inc., and James R. Ammer, U.S. Department of Energy
Paper Number: SPE 56728