Reliable prediction of conductor axial capacity is essential to the successful construction and operation of offshore hydrocarbon wells. The process of jetting to install conductors introduces uncertainty in evaluating capacity, which is made more challenging due to the nature of carbonate sediments. Furthermore, limited information exists in relation to time dependent increases in axial capacity, as the sediment ‘recovers’ from the installation process. A study of axial capacity of jetted conductors in carbonate sediment was undertaken via physical centrifuge modelling at the National Geotechnical Centrifuge Facility (NGCF) at The University of Western Australia (UWA). The testing programme included the investigation of varying installation parameters such as bit space-out position, extent of vertical reciprocating motion, and jetting flow rate; while the influence of broaching and conductor casing joints were also studied. Model jetted conductor installations were completed in both reconstituted and undisturbed carbonate sediments retrieved from the North West Shelf (NWS) of Australia, allowing a study of sediment fabric effects. The axial capacity of the model conductor was analysed at prototype set-up times ranging from 5 days to over 5 years, thereby documenting the changing capacity over time. This paper presents selected results from the testing programme, and provides discussion to inform full-scale jetted conductor installations in deepwater regions where carbonate sediments are present.
Alex Osuchowski, Phil Watson, Conleth O'Loughlin, Yuxia Hu, Rose Zhang, Meysam Banimahd, Ben Holland and Matthew Kuo
Keywords: offshore, jetted conductors, jetting, centrifuge modelling, carbonate
Publisher: DFI