Factors controlling fracture characteristics in Chalk Formations in the Dutch Offshore

Abstract

Faults can both improve producibility and fluid flow in hydrocarbon reservoirs, and cause leakage and instabilities in sealing layers. For this reason it is of importance to create a multiscale understanding of the drivers behind deformation, and how deformation is accommodated. Carbonates have always been of interest to the oil and gas industry as carbonates house some of the world’s largest oil and gas reserves. Understanding, and maybe predicting the geometries and fracture types could therefore be of integral importance to the E&P industry. For that reason two seismic datasets were provided for analysis on both a Fault Network Scale (faults over >1km in length) and a Small Seismic Scale (faults <1km in length). For the Fault Network Scale Petrel was used for seismic interpretation of the faults, as only the largest faults were interpreted in both seismic datasets. For the Small Seismic Scale OpendTect was used for enhanced seismic interpretation. OpendTect’s fracture enhancing attributes and filters provide seismic images with a high level of detail. These attributes were applied to 5 generated steering-cubes, to display even the smallest faults. The results on
the Fault Network Scale show that most faults are caused by regional tectonics. However in areas where salt is underlying the chalks of the Chalk Group, halokinesis is the main driver of deformation. On the Small Seismic Scale drivers behind deformation differ more, fluid expulsion drives polygonal faulting patterns in areas where salt tectonics or far field extensional tectonics are absent. Towards halokinesis structures salt tectonics will be the main driver behind deformation. In areas where salt is absent, far field tectonics can still influence chalks forming fractures either parallel or perpendicular to the major surrounding
faults.