Back to What's New

May 2005

ChevronTexaco Tahiti Site Investigation

During June 2004, TDI-Brooks was contracted by ChevronTexaco Exploration and Production Company to conduct a geotechnical coring site investigation in their Tahiti Development Project in the Gulf of Mexico. Locations of interest within Blocks 596, 640, and 641 of the Green Canyon Area were examined. TDI-Brooks collected several jumbo piston, standard piston and box cores as a part of a Final Site-Specific Investigation. The water depth at the sampling locations ranges from 1,200 to 1,300 m. The objective of the investigation was to determine the engineering properties of the shallow soils for the purpose of future manifolds, PLETS, SCR touchdown points, and MODU anchors. Cores were collected close to seafloor wellheads and also nearby a drill ship.

Figure 1. Recovery of the 65-ft, 6,000-lb, 4-inch Jumbo Piston Corer onboard
the R/V JW POWELL.

TDI-Brooks was responsible for the planning and execution of the coring program using the R/V JW Powell, and completed the following field operations:

• Jumbo Piston Cores (JPCs) up to 60-ft penetration (Figures 1 and 3)
• box cores to 21-in. penetration (Figure 2)
• USBL corer positioning, survey services and water depth measurement.

Figure 2. Shear strength measurements being conducted with a motorized miniature
vane (MV) at 3-cm intervals down a 50-cm x 50-m stainless steel box corer.

Navigation specifications were highly rigorous. Positioning accuracy was achieved by use of an Ultra-Short Baseline (USBL) position-monitoring system with an acoustic beacon mounted to the coring rig and a transducer mounted in the vessel's moon pool. The coring navigation included monitoring the coring rig in three dimensions and guiding it to within the desired radius by vessel movement while countering the effects of currents, wind, and wave action. Field and laboratory tests included an array of standard and specialized geotechnical measurements.

Figure 3. Extraction of the 4-inch core liner for the 65-ft Jumbo Piston Corer.

TDI-Brooks returned to the Tahiti survey area and obtained cores and data in March 2005, when more Jumbo Piston Cores were collected using the R/V JW Powell. The primary purpose of the job was to determine if grout from drilling activities had extruded into the surrounding strata at a depth of about 30 ft. The length of the cores recovered exceeded 50 feet for all cores. TDI-Brooks contracted the engineering analysis component of the programs to Geoscience, Earth and Marine Sciences, Inc. (GEMS) in Houston.