During January and February 2005, TDI-Brooks was contracted by Shell International Exploration and Production, Inc. to undertake a geotechnical site investigation in the south-central portion of the Alaminos Canyon Area in the Gulf of Mexico. Locations of interest within Block 857 and 813 were examined. The water depth at these locations ranges from 7,700 to 9,200 ft. The overall objectives of the investigation were to ground-truth geologic features identified by AUV data, develop a stratigraphic framework and determine the engineering properties of the shallow soils at the area of interest.
The site investigation comprised four stages, including two separate field operations: � Seafloor Verification with the Shell-supplied vessel Ocean Service:
- Coring Program using the TDI-Brooks’ vessel R/V JW Powell
- Geotechnical and geochemical laboratory testing; and
- Reporting.
The Seafloor Verification cruise included a ROV video survey of potential development locations, along a pre-determined circuitious route of about eleven (11) nautical miles distance. The ROV video survey verified various geologic features identified by AUV data, including Perdido Canyon walls and slump debris along axis, notches, fluid expulsion craters, grooves, and furrows. The primary objectives were to aid in determining the origin and extent of fluid expulsion features and erosional processes (see Figures 1 and 2). In addition to the video survey, the ROV extracted push cores of the seafloor sediment at select locations, and obtained samples of the water column near the seafloor. TDI-Brooks was responsible for the successful extraction and analysis of the core material from this cruise.
Figure 1. Still photograph taken by ROV of a mound covered by chemosynthetic bacteria (i.e., the white fluffy material on the gray sediment background).
Figure 2. Still photograph taken by ROV of a mound inhabited by chemosynthetic bivalves and white chemosynthetic bacteria. This is one of a few indications of chemo communities along the survey track of possible fluid expulsion features.
TDI-Brooks was also responsible for the planning and execution of the Coring Program, which comprised the following field operations:
- Long cores, up to 60-ft. Long cores included Jumbo Piston Cores and conventional piston cores depending on specific conditions
- 50-cm x 50-cm box cores to generally 24-inch of penetration
- USBL corer positioning, survey services and water depth measurement
Field and Laboratory tests included an array of standard and specialized geotechnical and geochemical measurements. Dramatic evidence of natural seepage of oil and gas was documented, as illustrated by these photos of bacterial mats, chemosynthetic seep communities and “live” seeping oil and gas (Figure 3).
Additional details on the R/V JW POWELL or TDI-Brooks Int’l Inc. can be found at www.tdi-bi.com.
Figure 3. Photograph of an oil-stained core recovered in the Great White development area.
