Current Use of Limited-Entry Hydraulic Fracturing in the Codell/Niobrara Formations-DJ Basin

Abstract

SPE Members Abstract In the last several years, limited-entry perforating has been used for hydraulically fracturing the Codell and Niobrara formations in the Denver-Julesburg (DJ) Basin. Limited-entry perforating reduces stimulation costs with no apparent effect on production. Several papers have presented guidelines for designing a limited-entry treatment. A primary concern for treating multiple intervals is to ensure that both zones receive the necessary treatment. Currently, some operators simply ratio the number of perforations in each interval to the volume of treatment required for each interval. To ensure that both zones are being treated, a minimum pressure drop of 700 to 1,000 psi is usually used for limited-entry design. Changes in the perforation discharge coefficient and diameter during the treatment, combined with changes in the net treating pressure, affect the perforation pressure drop calculation. To determine the actual pressure drop across the perforations, designers use a real-time spreadsheet calculation. This paper reviews limited-entry treatments pumped in 34 wells that verify spreadsheet calculations. Changes in the perforation discharge coefficient and diameter will be presented, as well as the effect of proppant concentration and velocity through the perforation. The current spreadsheet calculation used on location to calculate the pressure drop across the perforations is also discussed. Introduction The Niobrara and Codell formations are the two primary production intervals for most of the wells being completed in the DJ Basin. The Niobrara is a micritic limestone consisting of three benches. At a depth of approximately 6,800 ft, the overall interval is generally between 150 and 250 ft thick. The Ft. Hays formation, the lower member of the Niobrara group, separates the Niobrara and Codell. There is a transition at the top of the Codell from a carbonate to a calcareous sandstone to a fine-grained sandstone with a high clay content. At a depth of approximately 7,000 ft, the Codell is typically 8 to 14 ft thick. Both the Codell and Niobrara are overpressured gas reservoirs with a low permeability ranging from 0.01 to 0.1 md. In the past, the Codell and Niobrara intervals were fractured separately. P. 107