The Thunder Horse challenge: Optimize perforating performance in an HP/HT deepwater well
L. Sabbagh - Schlumberger
D. Blalock, H. Leung - BP
J. Melvan - Orbis Engineering
The Thunder Horse field in 6,000 ft (1,829 m) of water in the Gulf of Mexico, has stacked consolidated sandstone reservoirs at 20,000 to 30,000 ft (6,096-9,144 m) subsea with pressures of 14,000 to 18,000 psi (96.5-124 MPa), temperatures of 190 to 270° F (88-132° C), and mean rock strengths of 4,000 psi. The wells normally are completed with a 7-in. (17.8-cm) liner and perforated with 3 3⁄8-in. (8.6-cm), high-shot-density (HSD) wireline guns with deep penetrating charges. However, as a result of drilling problems in one well, a 4 ½-in. (11.4-cm) production liner was cemented in the 8 ½-in. (21.6-cm) hole. The tight tolerance between the fired guns and the pipe ID created an additional challenge. After extensive analysis, design, and yard testing showed the well could be perforated safely using 2 7⁄8-in. (7.3-cm) HSD guns with new enhanced deep penetrating charges that could deliver better perforation performance than the original gun system. The results from the well’s cleanup program indicated an even better perforation efficiency than observed earlier.
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The Thunder Horse deepwater project, one of the largest in the Gulf of Mexico, will be produced from the Thunder Horse> production, drilling, and quarters facility. Transocean’s Discoverer Enterprise is in the background.
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This BP-operated deepwater development with partner ExxonMobil is in Mississippi Canyon blocks 776, 777, 778, and 822. The field contains hydrocarbons in two main structures: Thunder Horse North (THN) and Thunder Horse South (THS). In 1999, THS was discovered by the MC778-1 well, and THN was discovered in 2000 by the MC776-1 well. Both structures consist of dip closures near a salt wall.
Well history
The well was drilled originally in 2001 and later sidetracked in the 13 3⁄8-in. (34-cm) casing to maximize reservoir access. The sidetrack and completion were from Transocean’s Discoverer Enterprise, a fifth-generation dynamically positioned drillship.
The well had to be sidetracked again during deeper drilling because of stuck drillstrings. Drilling also was delayed by weather problems such as loop currents, tropical storms, and hurricanes, all common in the GoM. While running the 7-in. (17.8-cm) production liner, it became stuck and was set high above the top of the reservoir. The best available option was to case the 8 ½-in. (21.6-cm) hole across the reservoir with a 4 ½-in. (11.4-cm) contingency liner. After successful placement of the 4 ½-in. liner, the well was released to the completion team. The completion team, who had already prepared for a 7-in. liner completion, had to redesign and prepare equipment for the new 4 ½-in. liner size within a relatively short time. Once under way, the actual completion operations went essentially as planned.
Original perforation plan
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Volume 68 Issue 9
September 2008
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