Abstract

Thunder Horse field, a new subsea development in 6,000 ft of water in the Gulf of Mexico (GOM) has stacked consolidated sandstone reservoirs that occur at 20,000 to 30,000 ft subsea with pressures of 14,000 to 18,000 psi, temperatures of 190 to 270°F, and mean rock strengths of 4,000 psi. The reservoirs do not require sand control and are completed with perforated casing. Four wells have been completed, perforated, and cleaned up since 2004 using drillship Discover Enterprise and a completion workover riser. The 2004 flowtest in Thunder Horse was the first time the industry produced hydrocarbons to surface from the GOM HPHT environment. The wells are normally completed with a 7-in. liner and perforated with 3 ?-in. HSD wireline guns with deep penetrating charges. In 2006, as a result of drilling problems, a 4 ½-in. production liner was cemented in the 8 ½-in. hole. To achieve a productivity index and skin factor close to the original design, it was necessary to perforate using 2 ?-in. HSD guns. The tight tolerance between the fired guns and the pipe ID created an additional challenge. Extensive analysis, design, and yard testing revealed that the well could be safely perforated using 2 ?-in. HSD guns with the new enhanced deep penetrating charges and that this 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. Downhole permanent gauges were essential to minimize underbalance conditions during perforating to prevent gun and line damage. Perforating was done between cleanup flow stages. Bullheading partial wellbore volume reduced surface pressure during perforating. The gauges monitored wellbore pressure at the reservoir during the bullheading operations for signs of perforation plugging.

Introduction

Thunder Horse is a deepwater Gulf of Mexico development project. BP owns 75% working interest and ExxonMobil owns 25%. The project is located in the Mississippi Canyon Blocks 776, 777, 778, and 822 in the Gulf of Mexico (GOM), approximately 100 miles off the Louisiana coast (Fig. 1), in water depths of 6,000 ft. The field contains hydrocarbons in two main structures: Thunder Horse North (THN) and Thunder Horse South (THS) (Fig. 1). 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.

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