Four wells in the U.S. Gulf of Mexico were worked over in reservoirs with bottomhole pressures (BHPs) ranging from 0.17- to 0.23-psi/ft gradients using the frac-pack technique. The purpose of the paper is to detail the chronology and expose the learning curve which led to the successful completions. Treatment tools, tubulars, design, rate, and fluid selection are discussed as they were applied in the implementation of each successive treatment.
The wells in the workover program were located in the U.S. Gulf of Mexico, in the Vermilion 255 field, from the Vermilion 267 "C" and "F" platforms. Work was completed on three wells, in the fourth quarter of 1992, and a fourth in July 1993. None had a gravel-pack (GP) completion prior to work and production had been ceased in each due to formation sand produced into the wellbore. The BHPs were expected to range from 1,700 to 4,000 psi, at vertical intervals from 9,400 to 11,082 ft. Well parameters could not be determined until new completions were installed; therefore, valuable design information had to be estimated prior to treatments. In the fourth well, BHP memory gauges were run to obtain accurate downhole treatment data for future jobs.
The planned completion technique was a frac-pack which was designed to place a maximum amount of sand into the reservoir and accomplish a low drawdown completion due to the expected low BHP. This technique, as well as variations, has been used for nearly two years in Gulf of Mexico reservoirs and is well documented. In each application, the GP screen and liner were in place throughout the frac-pack, again to minimize damaging the completion after gravel placement. The four treatments were pumped with the implementation process modified and improved each time to place more sand/gravel in the reservoir.
The Vermilion 255 primary field development occurred between 1975 and 1978. The completions were conventional, nongravel packed, predominantly dual completions with alternates common. Sand production became a problem in almost all wells at varying stages of depletion resulting in insufficient reservoir drainage.