Abstract
Completions in the Weber formation have historically been perforated over balanced and then acid stimulated. Flow rates before acidizing were virtually 0 Mcf/D. Acid was an important step in the completion process. The Weber gas reservoir has low permeability (0.5 - 1.5 mD) and is now low pressure (2800 to 2300 psi at 14,000 ft). Typical flowing rates for these wells range from 1 to 5 MMcf/D. A new perforating technique utilizing the dynamic under balanced method was implemented in two wells, Brady 38W and Brady 56W. The wells were perforated with tubing-conveyed guns with initial over balances of 3250 and 3750 psi. The dynamic under balanced method creates an instantaneous under balance even though the annular space between the gun and the casing is initially over balanced. This perforating method also leaves significantly less perforation "skin." The proof is in the success of the two wells, which have rates equal to or in excess of the existing wells and yet required no acid stimulation. From historical comparisons of 18 prior completions, these wells should have had nearly zero flow without acid when perforating using an initial over balance of up to 3750 psi in the annulus. This paper discusses the new dynamic under balanced perforating design and its application to low-permeability, under-pressured reservoirs.
