UK

BP Amoco ABAL have carried out an investigation into possible causes of poor performance of a Southern North Sea well for BP Amoco. It was concluded that proximity to fault damage zones where granulation seams inhibit reservoir permeability was a probable cause of poor performance (see R&D Programme). BP Amoco are incorporating the results into their well planning programme.

Schematic diagram of a fault damage zone showing width, orientation, and density of small scale structures relative to a main fault.

Typical appearance and scale of fault related reservoir damage in cross section. Granulation seam clusters tend to form two distinct sets, one parallel to the main strike of faulting, and one that is conjugate.

Left - typical appearance and scale of fault related reservoir damage. Right - sketch map schematically shows the orientation of granulation seams in the crestal area between two faults. Clearly the area between the two faults is highly compartmentalised, and the preferred well orientation to breach most compartments would be normal to the faults.

 

Photomicrograph of a granulation seam in thin section.

Key features of granulation seams: Quasitabular seams of crushed rock Characterised by intense grain size reduction, compaction and porosity loss Commonly less than 1cm in thickness Accommodate shear offsets which are typically less than a few millimetres Return to experience