Abstract The UK Oil & Gas Authority carried out post-well failure analyses of exploration and appraisal wells in the Moray Firth and the UK Central North Sea to fully understand the basis for drilling the prospects and the reasons why the prospects failed. The data consisted of Tertiary, Mesozoic and Palaeozoic targets/segments associated with 97 wells drilled from 2003 to 2013. Seal was the primary reason for failure followed by trap, reservoir and charge. Root causes for failure were a lack of lateral seal, the absence of the target reservoir and the lack of a trap. The main pre-drill risk was not accurately predicted in over one-third of the cases and a third of the segments were targeted on the basis of perceived Direct Hydrocarbon Indicators. This study identified a number of interpretation gaps and pitfalls that ultimately contributed to the well failures. These included poor integration, improper application of geophysics, lack of regional play context, and absent or ineffective peer review. Addressing these gaps in a comprehensive and systematic way is fundamental to improving exploration success rates.

Abstract The Goldeneye gas–condensate field lies in the Moray Firth Basin of the North Sea and illustrates the potential for further field life after the normal end of production. It was discovered in 1996 in a three-way dip-closed structure in the Lower Cretaceous Captain Sandstone. Five development wells were drilled from a single production platform and first gas was produced in 2004. The field pressure decline indicated partial aquifer support and no compartmentalization. Approaching the end of production, the opportunity arose to propose Goldeneye as a store for CO 2 . The cap-rock seal was capable of containing gas and the removed hydrocarbons left a significant volume that could be refilled without raising pressures above original conditions. The field's good reservoir properties were favourable for injection, the wellstock and infrastructure were modern, and CO 2 sources were available close by. The different requirements of a storage project called for a detailed understanding of the overburden to guard against possible leak paths and to identify secondary containment. Furthermore, greater understanding of the aquifer was needed as it limits storage volumes through its impact on reservoir pressures. Updated interpretation, analysis and modelling demonstrated that Goldeneye is an excellent potential CO 2 storage site, which gives it a possible second span of life helping to offset UK CO 2 emissions.

Abstract Chevron North Sea Limited operates Alba and Captain, two large, mature, heavy oil fields in blocks 16/26 and 13/22a of the UK sector of the North Sea, respectively. Although the fields are structurally and stratigraphically different, their development schemes have been similar. Common components to both fields are that they are marine sandstone reservoirs; have one steel jacket, plus subsea templates; are under water injection for pressure support; utilize long horizontal development wells; use pilot holes and logging while drilling (LWD) geosteering tools to optimize well locations; and have seismic resolution issues. New technologies and techniques have been developed and adopted to maximize production and reserves from the fields. The benefits to both Alba and Captain of previous and new technologies are reviewed below.

Abstract The Scott Field, located in the UK Central North Sea, is in a mature stage of development. The Scott platform has been on production since 1993, when the Scott Field came on stream, followed in 1993 by the subsea tie-back of the Telford Field development, located to the south of Scott. By 2005 the Scott Field had produced 400×10 6 boe cumulative production. However, the field was producing at water cuts approaching 90% and the previously completed 2002–2004 infill drilling campaign had not met expectations. A change in strategy was undertaken in the subsequent 2005–2007 Scott drilling campaign, which yielded positive results, adding reserves and significantly increasing platform export rates. The focus moved from peripheral targets towards the edge of the field to lower risk targets closer to existing well control. Success was also attributed to focusing on the seismic interpretation of block bounding faults in poorly imaged areas of the field, allowing identification of small fault-bound targets. The recent drilling has demonstrated that significant value can be found in small and often complex accumulations within an extensively drilled mature field.