Gumusut-Kakap Project: Geohazard Characterization and Effect on Field Development

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 12554, "Gumusut-Kakap Project: Geohazard Characterisation and Impact on Field- Development Plans," by C. Hadley, D. Peters, and A. Vaughan, SPE, Shell International E&P, and D. Bean, Sarawak Shell Sdn. Bhd., originally prepared for the 2008 International Petroleum Technology Conference, Kuala Lumpur, 3-5 December. The paper has not been peer reviewed. Shell and venture partners encountered numerous seafloor and near-seafloor geohazards at the deepwater Gumusut-Kakap field on the continental slope offshore Malaysia. Early identification of the geohazards, by interpretation of exploration 3D-seismic data and evaluation of discovery and appraisal-well logs, provided the impetus necessary to undertake an extensive data-acquisition program to determine the extent of the hazards and the mitigation needed for a successful development. Introduction The Gumusut-Kakap field in the Malaysian deepwater province offshore northwest Borneo was discovered in 2003 with the drilling of the Gumusut-1B well. The field is 120 km offshore, in the southern portion of Sabah Block J and Block K. Four appraisal wells, Gumusut-2 and Gumusut-3 in Block J and Kakap-1 and Kakap-2 in Block K, were drilled during 2004–05. The seafloor slopes regionally to the southwest, with a gradient of approximately 5°, and water depths within the development area vary from 900 to 1200 m. Seafloor and near-seafloor sediments are hemipelagic, interbedded with turbidites and mass-transport deposits (MTDs). Exploration 3D-seismic data and data from the discovery and appraisal wells were interpreted in 2005 to identify geohazards that could influence field-development plans and to screen potential surface well locations. The seafloor extraction from the 3D-seismic data set revealed a variable seafloor topography. The most prominent topographic features are a series of upper-slope canyons, which are interpreted to be the seafloor expression of buried mass-transport complexes and a steep-sided seafloor bulge. The bulge rises 120 to 150 m above the surrounding seafloor and is approximately 8 km wide. The bulge is the surface expression of one of a series of deep-seated anticlines, which are common in the region. Both flanks of the bulge have been eroded by downslope mass failures. Appraisal wells Gumusut-2, Kakap-1, and Kakap-2 were drilled on the bulge. Anomalies in the subsurface data included a bottom-simulating reflector (BSR) between 150 and 180 m below the seafloor, which underlies the downdip portion of the bulge and coincides with an extensive seismic wipeout zone.