Ofori Pearson¹, Robert Krantz², Richard Fox³
(1) University of Arizona, Tucson, AZ
(2) Arco Alaska Inc, Anchorage, AK
(3) BP Amoco, Anchorage, AK

Abstract: Predicting fault-fluid behavior at Prudhoe Bay: quantifying risk with a new shale gouge ratio tool

Detailed analysis of fault zone properties and fluid flow risks requires integration of fault geometry with local stratigraphy. The character of the fault zone results in part from the proportion of clay included, which varies along strike and with depth. The shale gouge ratio is proving an effective parameter for predicting fault zone character, and, when integrated with other structural and reservoir information, can be used to predict sealing and conductive potential. Conductivity is critical for well planning, especially where wells must cross faults. Wells at Prudhoe Bay often target specific locations on faults to minimize lost circulation risk.

A simple new tool has been developed which enables geologists to make a quick analysis of shale gouge ratio over an entire fault. Unlike existing software, this tool requires only a single faulted horizon plus a column of Vshale data, and provides a more intuitive output than popular triangle diagrams. The tool is a Microsoft Excel workbook and can be used in any setting where detailed stratigraphic and fault geometry information is available.

Areas on a fault surface with high shale gouge ratios are less likely to act as fluid conduits than areas with low shale gouge ratios. The tool creates an image of the fault surface (projected onto the footwall) that shows how shale gouge ratio varies as a function of stratigraphy and fault throw. The fault surface image allows well planners to target a specific location on the fault surface through which to drill.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana