Tim Needham, Graham Yielding, Brett Freeman
Hydrocarbon reservoirs are often separated into compartments by sealing faults. Faults act as seals either by juxtaposition of reservoir intervals with sealing lithologies or by the sealing properties of the fault surface itself. It is possible to analyse juxtaposition sealing by the construction of 'Allan' fault-plane diagrams. Refined versions of these diagrams can be produced by optimising the fault interpretation. The extent of the fault surface can be determined by displacement analysis and the position of tips and splays identified. Horizon cut-offs can be accurately positioned by the use of an algorithm which 'snaps' the horizons on to the fault surface. The fault surface can also be modelled so that topographic variations in the surface are incorporated into the f nal diagram. Detailed reservoir stratigraphy can be added between seismic markers so that areas of cross-fault communication can be identified.
The ability of the fault surface itself to act as a seal is a function of the displacement at any point on the fault surface and the lithology of the units displaced past that point. Using the displacement mapped on the fault surface, in conjunction with lithological information it is possible to calculate the potential for sealing by clay smear at any point. By careful calibration using well test and production data it is possible to use the clay smear estimates to predict the likely behaviour of faults bounding undrilled compartments.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995