Tullow Oil has installed jetted well conductors at deepwater sites offshore Ghana. Variability in axial loadcarrying performance was observed. A study was initiated to understand the various influences on conductor performance, distinguishing between those that were non-controllable (e.g. geology, soil conditions) and those that were controllable (e.g. installation practice, well design). Influence metrics were developed and systematically examined against conductor performance to search for trends and relationships. An understanding of the expected regional soil variability over the development area was reached through an engineering geological review. The study defined future best practice recommendations for conductor jetting, which now constitute established installation practice for ongoing operations in the area. This paper describes the study and its findings, and emphasises how its success hinged on Tullow Oil's ability to make available geophysical and geotechnical data, together with comprehensive jetting and drilling operations records.
Tullow Oil and its development partners are developing the Jubilee field, which spans the Deepwater Tano and West Cape Three Points blocks in deepwater offshore Ghana (Figure 1). During the period from November 2008 to February 2010, conductors were installed by jetting at 17 locations within the development area. Water depths ranged from ~1080–1560m. At three of the locations, the conductors slumped several metres into the seabed when the weight of the surface casing was transferred from the drill string.
The database of 17 jetted installations was considered to have a useful and meaningful amount to base attempts to understand the various influences on conductor performance. Table 1 summarises the dataset, including selected key parameters. The conductor diameter was 36 inches throughout. These parameters represent a subset of the overall set of potential influences investigated during the study (as described in section 2.2).
