AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Regional Approach to Solve Structural Complexity and Cataclastic Fault Seal, Southern North Sea
(1) Shell E&P, Assen, Netherlands.
The southern part of the North Sea is a very mature basin, with exploration and production for ca. 40-50 years. Many fields have reached their end-of-field-life and new hydrocarbon discoveries are needed to extend the life of existing infra-structure. The remaining prospectivity is small in volume, difficult to drill and/or at relatively high exploration risk. The volumes in structures could be larger in case a longer hydrocarbon column is kept in place by fault seal.
Predicting fault seal in this area is not straightforward: 1) the region has a long and complex tectonic history with several phases of extension and compression under different main stress orientation; 2) the region has structural complexity due to the interaction of four different fault systems; 3) the Permian Rotliegend reservoir has high N/G and requires sand-on-sand (cataclastic) sealing faults, being difficult to determine its seal strength. However, proven cataclastic fault seal exists in places, with across-fault pressure difference up to 200 bar.
Especially burial depth, temperature, fault movement, palaeo-stress directions and orientation of faults are critical elements for cataclastic fault seal. Integration with basin modeling and geochemistry, field data, accurate fault interpretation, a regional approach to understand the regional context and interaction of different fault systems, and incorporation of the structural evolution in fault seal analysis are therefore required. This approach highlights weak fault sections that form potential spill points, and highlights which fault segments are sealing or leaking.
The extensive fault seal study led to renewed insights in the fault seal mechanism in the area, and resulted in several successful new discoveries with additional hydrocarbon column related to cataclastic fault seal. The results have extended the production of hydrocarbons in the area for a number of years. It illustrates that a new and structured approach with full integration of disciplines can open new opportunities in a very mature basin.