Abstract

The industry has been designing casing and tubing for wells for many years by using the expected operational loads to calculate the triaxial stresses on the tubular walls. Part of the triaxial stresses is the radial component. In most cases pressures less than 15,000 psi, the radial triaxial component is not a major factor in the stress on the tubing wall. However, on higher pressure wells (above 15,000 psi) this radial component becomes significant in the design of the tubing and casing. During the conceptual design of ChevronTexaco’s deepwater Tahiti project, several wells were projected to depths of anywhere from 26,000’ to over 30,000’ TVD. Under certain operational loads (such as fracturing or perforating), the pressures at the deeper horizons can exceed more than 25,000 psi (both inside and outside the tubing). We then asked ourselves a question, “If the radial load becomes significant on the actual tubing wall, what would the same radial load do to our connections”? It is very important to point out that you can have no differential pressure across a connection and still have intense radial loads.

Introduction - Overview of Tahiti Field

The Tahiti field is a subsalt discovery of oil located in approximately 4,000 ft of water in the Gulf of Mexico. In March 2002, ChevronTexaco drilled the Tahiti #1 well in over 4,000 ft of water to a total depth of 28,411 ft. The well was approximately 190 miles southwest of New Orleans. Two additional wells were drilled to delineate the field. They verified the aerial extent of the reservoir. The appraisal wells confirmed a reservoir extent of over 3 miles with over 1,000 feet of net pay in high-quality sandstones. These wells indicated an estimate of 400 to 500 million barrels of ultimate recoverable oil reserves. This reservoir is one of the most significant net pay accumulations in the Gulf of Mexico.