Integrating 3-D seismic data, field analogs, and mechanical models in the analysis of segmented normal faults in the Wytch Farm oil field, southern England, United Kingdom

Abstract

We propose a methodology for the analysis of normal fault geometries in three-dimensional (3-D) seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault-controlled oil fields. Limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization. Detailed seismic data analyses that incorporate principles of normal fault mechanics, however, can reveal evidence of fault segmentation. We integrate seismic attribute analyses, outcrop analog observations, and numerical models of fault slip and displacement fields to augment the use of 3-D seismic data for fault interpretation. We applied these techniques to the Wytch Farm oil field in southern England, resulting in the recognition of significant lateral and, to a lesser extent, vertical segmentation of reservoir-scale faults. Slip maxima on fault surfaces indicate two unambiguous segment nucleation depths, controlled by the lithological heterogeneity of the faulted section. Faults initiated preferentially in brittle sandstone and limestone units. Subsequent growth and linkage of segments, predominantly in the lateral direction, resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima. Reservoir compartmentalization is greatest at the level of prevalent segment linkages, which corresponds at Wytch Farm with the predominant hydrocarbon-producing unit, the Sherwood Sandstone. At relatively shallower depths, fault segments are younger and less evolved, resulting in a greater degree of segmentation with intact relay zones.