Integrated Characterization of Fault and Top Seal at Velocette: Understanding Trap Fill, Breach and Depletion Mechanisms

Exploration well 6607/3-1S (Velocette) marks the first significant penetration of sandy intervals within the Cretaceous Nise Formation on the eastern flank of the Utgard High. A 9-meter gas column was encountered in the upper section of the reservoir, with a total confirmed trap column of approximately 66 meters. Post-well studies focused on understanding the reason for reduction in column height from a pre-drill estimate of 240 meters to a post-drill column of 66 meters.

Laboratory analyses showed that the top seal could support a gas column of over 3700 meters, and mechanical seal strength indicated a headspace of more than 58 bar before failure. Therefore, the top seal is not the limiting factor for the trapped column. Fault membrane seal analysis revealed that while most of the Velocette relies on sand-shale juxtaposition, the areas relying on the membrane fault seal can accommodate a column larger than 140 meters. Thus, the fault membrane seal is not the limiting factor for the observed column. A fault reactivation study showed that the bounding faults are critically stressed under current pore pressure conditions, suggesting that any increase in pore pressure could induce fault reactivation.