Performance drivers in restimulation of gas-storage wells

To maintain or enhance deliverability of gas-storage wells in the Clinton sand in northeast Ohio, an annual restimulation program was established in the late 1960s. The program calls for as many as 20 hydraulic fractures and refractures per year. Several wells have been refractured three to four times, while there are still wells that have only been fractured once in the past 30 years. As the program continues, many wells will be stimulated a second. third, or fourth time. This paper summarizes an attempt to carefully study the response of the Clinton sand to hydraulic fractures and to identify the performance drivers in each series of fracture jobs. Are the performance drivers the same for the later fractures (second, third, and fourth fracture jobs) as they were for the first ones, or do they change'? This paper attempts to answer such questions. Identification of major performance drivers becomes important when new jobs are to be designed. They not only play an important role in enhancing the response of the wells to new stimulation jobs, but they also may prove to be an important economic factor in the design of new stimulation procedures. If, for instance. it is concluded that an increase in proppant volume does not influence the stimulation outcome after the second refracture. then fewer resources can be used for proppant volume and can be directed toward parameters that are more influential. This study employs a combined neural-network and fuzzy-logic tool to identify the performance drivers.