Geochemical models of CO 2 injection into reservoir sandstones often predict the growth of minerals that will permanently store the CO 2 in solid form, and injection experiments record significant fluctuations in porewater chemistry on a short time scale. Yet the proportion of CO 2 reaction may be small, even over geological time scales. A southern North Sea (UK) gas accumulation with a high natural CO 2 content (c. 50 %) forms a natural analogue to engineered storage, and provides a calibration point for

The deep-water metasedimentary rocks of the late Dalradian Macduff Slate Formation preserve a record of distal glaciomarine sedimentation in the form of ice-rafted dropstones and related bedding-deformation structures, glaciogenic debris-flow diamictites and an allochthonous slump unit. The input of ice-rafted debris was cyclical and probably related to periodic disintegration of the marine margin of an ice sheet. Downslope resedimentation processes, typical of glaciated continental margins, were responsible for the diamictites and slump deposits which were probably derived from the adjacent outer shelf and upper slope, in common with Pleistocene analogues off NW Britain. The uppermost diamictite bed is an integral part of the deep-marine succession, in contrast to the previously proposed lodgement-till hypothesis.

Up to the present, exploration of the UK Lower Cretaceous deep-water sandstone play has been confined largely to the Moray Firth basins. The Lower Cretaceous of the Central Graben area has been modelled previously as predominantly shale-prone, and hence unattractive to exploration. There is a growing realization that this may not be the case. Since seismic imaging of Lower Cretaceous sandstones is known to be poor whether hydrocarbon-bearing or water-wet, a robust depositional model must be constructed from well and regional geological data in order to predict sandstone distribution and geometry, and hence to aid identification of potential hydrocarbon traps. Of the hundreds of wells drilled in the Central Graben area that targeted deeper Jurassic-Triassic reservoirs, virtually all have been located on the flanks of the graben, or on intra-graben highs. However, 71 of these wells have proved sandstones or traces of sandstone within the Lower Cretaceous, giving grounds for optimism that more substantial deep-water sandstone developments may be present within the graben depocentres. Twenty-six leads have been identified within these depocentres; most of these are located within stratigraphic traps in interpreted detached basin floor fans.

This paper analyses the statistics of existing United Kingdom Continental Shelf (UKCS) fields and discoveries as a means of assessing which plays are likely to contain the greatest untapped potential for stratigraphic traps. Current Department of Trade and Industry (DTI) estimates put the maximum discovered ultimate recovery of the UK at 50 billion (× 109) barrels of oil equivalent (BBOE); estimated technically recoverable undiscovered resources are between 4.1 to 21.3 BBOE, based on a prospect mapping approach.As of end 2003, 82% of the oil and gas fields and discoveries on the UKCS have been found in structural traps; 12% have been found in combination structural/stratigraphic traps and only 6% in stratigraphic traps. The majority of stratigraphic traps and combination traps occur in association with syn-rift (Upper Jurassic) and post-rift deep-water plays. There has been relatively little direct exploration for stratigraphic traps until recently, and a number of the major discoveries in stratigraphic traps were found by chance. Few substantial untested structural traps remain in the UK North Sea except at considerable depth with associated risks. We estimate that perhaps 50% of the UKCS undiscovered resources are located in stratigraphic or combination traps, principally within syn- and post-rift deep-water sandstone plays.

The United Kingdom Continental Shelf (UKCS) has been a very successful exploration province in the last 38 years, with an average technical success rate of 31% from its 2150 exploration wells. Though the peak of exploration activity on the UKCS occurred during the 1980s and 1990s, there have been 41 successes from 82 wells in the last four years, representing an improved recent success rate of 50%.