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.

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