Fault-Seal Analysis Methods
Successful fault-seal analysis methods integrate fundamental information on the fault-zone architecture,fault-rock properties and pressure data.An important tool for evaluating the flow potential across a fault is a strike view,or map of the fault plane with the hanging wall and footwall intersections superimposed on the modeled fault surface.18 Allan diagrams use this technique to show possible fluid-migration pathways, leak points or sealing areas across the fault, and have also helped explain the location of hydrocarbon/water contacts in various fields worldwide.Allan diagrams typically use the seismically interpreted horizons to define the hanging wall and footwall offset across the fault and lithology interpreted from well logs to identify the stratigraphic changes between the seismic horizons.Sophisticated mapping tools allow the development of Allan diagrams as 3D models.(left)These models require significant amounts of data and can be time-consuming to develop,although new software tools,such as the Petrel workflow tools application,have reduced the processing time significantly.
An alternative to the complicated evaluation of the distribution of the stratigraphy across the fault plane,as used in Allan diagrams,is a simplified juxtaposition triangle diagram,which enables a quick initial examination and prediction of fault-seal capacity.This technique images the hanging wall and juxtapositions for varying throws and allows an evaluation of the juxtaposed stratigraphic intervals for a given throw (below left).These diagrams simplify the analysis of juxtaposition for a single fault plane.The effects of multiple small-throw faults may also be quickly evaluated using these diagrams.The juxtaposition is simply evaluated at the smaller throws for each fault.