Bottom Current Measurements at GoM Furrows for the Cascade and Chinook Fields Development

Abstract

This paper presents near-bottom current profile measurements in furrows located east of the Sigsbee Escarpment in the Cascade-Chinook field development flowline route from the facilites to the Chinook manifold in the Walker Ridge region of the Gulf of Mexico in water depths greater than 2500 meters. These furrows are deep channels aligned with the southwestward direction and in a variety of configurations with typical dimensions of 5 to 10 meters depth and 15 to 50 meters width. The measurement systems were custom designed bottom frames with acoustic current profilers and turbidity sensors deployed by Remotely Operated Vehicle (ROV) to accurately position the frames in predetermined positions inside the furrows. An innovative approach was developed to address cost effectively the technical challenge of the scheduled regular 4-month data recovery. To reduce costs, it was elected to deploy an acoustic modem from a vessel to download data from the subsea frames in lieu of recovering and redeploying the frames with the use of an ROV. In general the Sigsbee Escarpment region experiences a complex deep water flow regime not completely evaluated or understood as yet. The steep gradients of the continental slope act as a wave guide for many flows associated with conservation of potential vorticity such as the Topographic Rossby Waves (TRW). The propogation of these waves and their flow affects the bottom currents in the furrows and on the sea floor. Spectral analysis of the bottom current measurements indicated a 12-day coherence peak that may be associated with TRWs. Speed values above 0.30 m/s were measured at the first bottom bin and the direction of the flow was most frequently aligned with the furrow's main axis. Introduction The production facilites of Petrobras America Inc. (PAI) Cascade and Chinook fields in Walker Ridge Block 249 and adjacent blocks are close to the base of the Sigsbee Escarpment. There is limited knowledge of the currents at the site in this complex bed form. PAI launched a rigourous current measurement program at the site which included measurement of current in the furrows, to develop an appropriate current profile design criteria for the project. This paper provides the preliminary data analysis of measurements taken over a 12 month period by PAI Contracor, the Woods Hole Group (WHG). Figure 1 provides a general view of the eastern Sigsbee Escarpment and furrows fields on the vicinity of Cascade and Chinook fields, located on Walker Ridge area.