A two-year comprehensive effort to design, test, manufacture, and deploy a new high-pressure completion tubular for Chevron's deep-water Gulf of Mexico operations is presented. The completion application expected harsh, aggressive loading modes and high pressures to be encountered. The major challenge was to design, test and manufacture a subsea completion string that would provide efficient hydraulics during the fracturing operations while ensuring mechanical and pressure integrity.
Results from comprehensive finite element modeling designed to evaluate the application loads are presented. An extensive physical test program to evaluate the structural integrity and sealability performance was conducted. The test included a series of combined load conditions which included axial loads (maximum 1,100,000 lb. tension, 215,000 lb. compression), internal (maximum 29,920 psi), external (maximum 25,279 psi) pressures, and bending loads (3°/100 ft. curvature). Multiple-step load cycles were conducted at both room and elevated temperatures.
Compared to earlier designs, the new 5-7/8 in. tubular design has double-start thread form which provides cost savings by reducing the make-up time from stab to shoulder by approximately 11 seconds saving trip time. The design's unique dual-radius thread root offers a step-change improvement in fatigue resistance. The new design also provides significant reduction in repair cost in comparison to earlier designs. The initial deployment of the new design is planned for wells in the Chevron-operated Jack and St. Malo oilfields which are located 40 km from each other (Figure 1). The Jack field lies in Walker Ridge blocks 758 and 759 at a water depth of 7,000 ft. The St. Malo field lies in Walker Ridge Block 678 at a water depth of 7,000 ft. The Jack and St. Malo field reservoirs are located in the lower tertiary trend about 20,000 ft. below the seabed. Details of the initial field deployment of the completion tubular are presented including evaluation of the running characteristics, connection damage, and repair cost.
As deep-water drilling continues to expand, high-performance completion tubulars must evolve to meet mechanical requirements and provide cost saving, efficiency, and safety.