Restimulation Technology for Tight Gas Sand Wells

Abstract

Abstract In 1996, the Gas Research Institute (GRI) performed a scoping study to investigate the potential for natural gas production enhancement via restimulation in the United States (lower-48 onshore). The results indicated that the potential was substantial (over a Tcf in five years), particularly in tight sand formations of the Rocky Mountain, Mid-Continent and South Texas regions. However, it was also determined that industry's current experience with restimulation is mixed, and that considerable effort is required in candidate selection, problem diagnosis, and treatment selection/design/ implementation for a restimulation program to be successful. Given a general lack of both specialized (restimulation) technology and "spare" engineering manpower to focus on restimulation, GRI initiated a subsequent R&D project in 1998 with several objectives. Those objectives are to 1) develop efficient, cost-effective, reliable methodologies to identify wells with high restimulation potential, 2) identify and classify various mechanisms leading to well underperformance, 3) develop and test non-fracturing restimulation techniques tailored to selected causes of well underperformance and, 4) demonstrate that, with improved technologies in these key areas, restimulation is a viable and attractive approach to improve well recoveries and economics. The approach adopted for the R&D program is a combination of candidate selection methodology development, conceptual well underperformance/problem classification, laboratory studies, and actual field experiments and demonstrations of restimulation treatments. At this time, a multi-process candidate selection methodology has been developed, consisting of production comparisons, engineering based performance assessments, and pattern recognition technology. Also incorporated into the overall methodology are individual well reviews, economic analysis, and a new short-term field test for candidate verification. Laboratory studies have also identified new procedures for effective clean-up of unbroken gel in propped and natural fractures. In total, twenty actual restimulation treatments are planned at four separate test sites. Currently active sites are in the Rocky Mountain and Mid-Continent regions. One site is located in the Big-Piney/LaBarge Producing Complex in the northern Moxa Arch area of the Green River Basin. As of this writing, three restimulation treatments have been performed at this location. The second site is the combined Rulison, Parachute and Grand Valley fields in the Piceance Basin. Candidate selection has been completed, and actual field-testing and restimulation activities are expected to begin in July 1999. The third site is the Carthage field in East Texas. Candidate selections are complete at this site also, with field activities also scheduled to begin in July. The fourth test site, not yet active, is in the Wilcox Lobo Trend of South Texas. This paper is the first comprehensive publication of results from this recent GRI initiative. It provides detailed descriptions of the candidate selection and restimulation methods employed, the results obtained, and should prove to be of value to operators seeking a production enhancement from tight gas sand wells throughout the United States and internationally.