Fault Seal Analysis in the North Sea

ABSTRACT: The majority of North Sea structural traps requires that at least one fault be a sealing fault. Over 400 faults from 101 exploration targets and 25 oil and gas fields were analyzed in a regional study of the North Sea. The faults cut clastic successions from a variety of depositional environments (marine, paralic, and nonmarine). The emphasis of the study was on fault-related seals that act as pressure or migration barriers over geologic time. Parameters such as fault strike and throw, reservoir thickness, depth, net-to-gross ratio, porosity, and net sand connectivity were plotted against seal performance to define trends and correlations to predict fault seal characteristics. A correlation appears to exist between fault orientation and sealing, although this is not statistically significant. Sealing is proportional to fault throw normalized as a fraction of the reservoir thickness. The great majority of faults with throw greater than the thickness of the reservoir interval were sealing faults. The most useful parameters in fault seal prediction are fault displacement, net-to-gross ratio, and net sand connectivity. The conclusions of this study have general applicability to fault seal prediction in exploration, development, and production of hydrocarbons in clastic successions in the North Sea and perhaps other areas as well.