Abstract An improved understanding of the controls on reservoir quality is key to ongoing and future exploration of the Central North Sea Triassic play. This paper presents a regional integrated study of 50 000 ft of wireline log data, 10 000 ft of core, 4431 routine core analyses measurements and 377 thin sections from 86 cored wells. Triassic Skagerrak Formation sandstones represent thin-bedded heterogeneous reservoirs deposited in a dryland fluvial–lacustrine setting. Fluvial-channel facies are typically fine–medium grained and characterized by a low clay content, whilst lake-margin terminal splay facies are finer grained, more argillaceous and micaceous. Lacustrine intervals are mud-dominated. Primary depositional textures retain a primary control on porosity evolution through burial. Optimal reservoir quality occurs in aerially and stratigraphically restricted fluvial-channel tracts on the Drake, Greater Marnock, Puffin and Gannet terraces, and the J-Ridge area. These primary textural and compositional controls are overprinted by mechanical compaction, the development of early overpressure and diagenesis. Anomalously high porosities are retained at depth in fluvial sandstones that have a low degree of compaction and cementation, including chlorite. Forward modelling of reservoir quality using Touchstone™ software has been validated using well UK 30/8-3 where reservoir depths are >16 000 ft TVDSS (true vertical depth subsea).

Abstract Recent exploration in portions of the Mississippi Salt Basin indicates that some models used in the interpretation of surface and subsurface data may be inadequate to explain several salt features. Models are important in interpretation because of the depth of the objectives and the complexity of the salt ridges. Significant oil and gas reserves trapped by the salt and related faults in Upper Jurassic reservoirs were discovered from the late 1960s to the early 1980s. Early models show concordant overburden on the flanks of a simple, symmetrical salt anticline. However, with further drilling, Upper Jurassic formations and the underlying salt were not encountered where predicted by the anticlinal model, suggesting that many of the salt ridges in the basin are more complex. Well-log data indicate that the flanks of such salt features may dip at rates greater than those proposed by the symmetrical anticline model. A study using an integrated approach to test the viability of a more complex salt-ridge model was conducted to aid in the interpretation of surface and subsurface data in the Mississippi Salt Basin. Gravity data in conjunction with seismic reflection data and well-log information form the database from which salt models were created. Seismic reflection data and well control provide a reasonable estimate of the depth of the sources of the gravity anomalies. The gravity data, on the other hand, have been used to help constrain the interpretation of the seismic data by providing a better geometric framework for the salt bodies observed on the seismic data. Eucutta Field and Diamond Field were selected as test areas for the salt models, based on the availability of data. The two fields are located along different types of parallel salt ridges. Eucutta is located deeper in the basin, in an area of large salt features, and Diamond is located closer to the rim of the basin, where smaller salt features are more common. Results of the study indicate that an asymmetrical pattern exists in which the flanks of the ridges may dip at different rates. Both the Eucutta and Diamond salt ridges exhibit a steeply dipping flank on the basinward side of the salt ridge and a more gently dipping landward flank. The salt ridges also appear to have a complex variation along strike in the structure of the salt. The variations of the salt features in both the strike and dip directions appear to reflect the variations in the way the overlying sediments were deposited.