Exploration and appraisal of a 120 km2 four-way dip closure: what could possibly go wrong?
K. D. Fielding, D. Burnett, N. J. Crabtree, H. Ladegaard, L. C. Lawton, 2014. "Exploration and appraisal of a 120 km2 four-way dip closure: what could possibly go wrong?", Hydrocarbon Exploration to Exploitation West of Shetlands, S. J. C. Cannon, D. Ellis
Download citation file:
Large four-way dip closures were obvious on multi-client 3D seismic data acquired during 1996–1998 over the unlicenced ‘White Zone’ between the Faroe and Shetland Islands. Cambo, located at the junction between the Westray and Corona ridges, is the largest of these features and covers an area of between 50 and 150 km2. As of October 2011, Hess and its co-venturers had drilled four wells on the Cambo structure. This paper represents a brief summary of the results of these wells as an Exploration Case study. Key conclusions from this case study include: (1) it is the subsurface setting and not the drilling environment that controls uncertainty level in recoverable oil and requirement for appraisal; drilling in an environment where wells are expensive does not imply you will need fewer of them prior to making a development decision; (2) a volumetrically small oil field requires at least as much delineation as a large one of equal complexity and lateral extent; indeed, more data may be required in order to mitigate risk of commercial failure; and (3) crestal locations for wildcat exploration wells are often not optimal; this is especially the case if reservoir presence or column retention is the key risk of the play type being tested. Efforts at Cambo now focus on constraining the remaining subsurface uncertainties to an acceptable level and moving the project forward towards development sanction. Despite the knowledge acquired from the extensive exploration and appraisal campaign completed to date by the Cambo co-venturers, at the time of writing the timing of development and preferred development solution at Cambo remains unclear.
Figures & Tables
This volume addresses the challenges facing explorers and developers alike in a region that is becoming a major focus of the petroleum industry in the United Kingdom, Faroes and North Norway. Several West of Shetland fields are still in the appraisal phase almost a decade after discovery. Sub-volcanic exploration risks remain high: sub-volcanic structural traps are imaged poorly, and so the geophysical community is responding with the application of latest technology. The more simple reservoirs might not be large enough to prompt informed and speedy development decisions; larger fields might have a combination of complexities, requiring a phased approach to the development. Infrastructure has been slow to arrive and planned developments have been subject to dramatic swings in fiscal regime ranging from special allowances to unexpected tax increases.
Environmental challenges are significant when moving into more remote, deeper water. The perception of these challenges by the third parties has become much more acute. To sustain its right to operate, the industry has to demonstrate safe drilling operations and appropriate response capability with government agencies.