No abstract

A Middle Oxfordian to Volgian sequence stratigraphic model for the Greater Shearwater area is presented. This model builds on the genetic stratigraphic sequences of Partington et al. (19936), refining the position of key stratigraphic surfaces with an additional emphasis on sequence boundary description. Most stratigraphic surfaces are believed to be related to tectonic events superimposed on a gradual rise in relative sea-level from the Middle Oxfordian to Volgian. Biostratigraphic information drawn from throughout the UK Central Graben allied with regional log correlation and seismic data has allowed a robust sequence stratigraphic framework to be developed which is applicable to the Greater Shearwater area.

The 40-yearhistory ofthe pre-Cretaceous high-pressure-high-temperature(HPHT)plays ofthe UK CNS isdescribed.The exploration andexploitation ofthisbasinhasbeenachieved byremarkabledevelopments inseismic, drillinganddevelopment technologies. Theseadvanceshaveprovided predictivegeologicalmodels to address significant multipleriske lements,a ndthe ability to drill andd evelop reservoirs safely inHPHT conditions withtemperaturesinexcess of3008 F, reservoirp ressuresexceeding10 000 psia ndsurface to reservoirpressuregradients inexcess of0.8psi/ft. UK ContinentalShelfexploration acreage wasfirst awarded in 1964inthe First Licence Round.Atthistimeseismic datadid not image the BaseCretaceous surface andearly drillingactivity focused on the Tertiary andon obvioussalt supported anticlinesormajor basement ridges. The subsequent periodfrom 1968-1972 sawthe discovery ofthe first hydrocarbons inthe pre-Cretaceous ingraben margins tructureso ro nm id-grabenhighs,b ut the deeperHPHT realm remained untested.Int he 1970s the discovery ofthe Auk, Argyll andFulmarFieldsestablished potentially significant plays aroundthe fringesofthe basin. However,e xploration for pre-Cretaceous reservoirs int he deeperp arts ofthe basinw hereH PHT conditions occurred faced significant operationalobstacles. Asthesewereovercomethe 1980s sawthe extension ofpre-Cretaceous plays into the HPHT realm,withdeep,high-quality reservoirs occurringatdepthsinexcess of 15000 feet. Thisexploration phaseresulted int he discovery ofsignificant reservesatt he Elgin,F ranklin, Shearwater,Jade andETAP fields. Throughoutthe exploration history ofthe CNS, the accurateprediction ofdeep reservoirdistribution andquality andtop sealintegrity haveb eencrucialt os uccess. Innovativeseismic technologieswill playakeypart inreducingthe remaininguncertaintiesintheseplayelements.

A review is given of the development of the understanding of the structure and stratigraphy of a classic petroleum province through 35 years of NW European Petroleum Geology Conferences, using new examples to illustrate the interplay between tectonics and sedimentation in the development of some of the major hydrocarbon plays. Cimmerian tectonics is discussed, with regard to the evidence for regional-scale truncation beneath the Mid Cimmerian unconformity, and the stratal motifs characteristic of rifting associated with the Early and Late Cimmerian events. New data revealing the structural geometries associated with polyphase rifting in the East Shetland Basin are presented. The seismic and sequence stratigraphy of Jurassic and Cenozoic sequences are reviewed and new data presented, with a discussion of generic play controls in North Sea Jurassic deepwater reservoirs. The development of integrated hydrocarbon system studies is reviewed, and the remaining challenges to predictive capabilities discussed. The impact of advances in geoscience and technology on North Sea creaming curves is discussed.

Identifying or ruling out groundwater discharges into sediment and surface waters is often critical for evaluating impacts and for planning remedial actions. Information about subsurface structure and groundwater can be helpful, but imperfect information, heterogeneous materials, and the likelihood of preferential pathways make it difficult to locate seeps without direct seep monitoring. We present the practical application of a method that uses fiber optic temperature measurement to provide high-resolution, sensitive, and dynamic monitoring of seepage from sediments over large areas: distributed temperature sensing to identify groundwater discharge (DTSID). First, we introduce a stochastic Monte Carlo method for designing DTSID installation based on site characteristics and the required probability of detecting particular size seeps. We then present practical methods for analysing DTSID results to prioritize locations for further investigation used at three industrial locations. Summer conditions generally presented greater difficulty in the method due to stronger environmentally-driven temperature fluctuations and thermal stratification of surface water. Tidal fluctuations were shown to be helpful in seepage detection at some locations by creating a dynamic temperature pattern that likely reflects changing seepage with varying water levels. At locations with suitable conditions for the application of DTSID, it can provide unique information regarding likely seep locations, enhancing an integrated site investigation.