NURMI, ROY D.
Schlumberger, Houston, TX

Abstract: Analysis of Structure and Faulting Encountered by Exploration or Development Wells

Significant advances in borehole technology and techniques have been developed to improve upon the interpretation of complex subsurface structures. However, accurate interpretation of the structural complexities encountered by either exploration or development wells, but not defined by seismic, still requires an geological understanding of the structural possibilities in addition to the technology and techniques being used. Reliance on dipmeter surveys is slowly being replaced by borehole imagery of a variety types, including resistivity, nuclear, and acoustic measurements and, thus, it is possible to determine the structural variation even when intervals become near vertical or overturned. New sonic imaging developments are allowing for the imaging of structure, faults and fractures tens of feet away from a wellbore. In addition, other borehole measurements can be used to define the vertical and lateral variations of the stress field as well as the geological characteristics of fault and fracture populations.

Many recent studies confirm that there are more faults than defined by seismic and that faults can be conduits in one part of a structure while behaving as barriers in still another. 3D seismic, geochemical fluid studies and borehole technology are all aiding in fault characterization in developed fields, however, fault evaluation is particularly improved by assessment efforts undertaken using horizontal wells. Reactivation of faults and subsurface dissolution along faults are important factors in creating fault conduits within reservoirs around the world, and although these apertures are small they can be detected by borehole imagery, confirmed by Stoneley acoustic waves and/or calibrated by wireline pressure sensors.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California