Experimental and Numerical Models of Basement-Detached Normal Faults

ISLAM, QUAZI T., and PAUL R. LAPOINTE, ARCO Oil and Gas Company, Plano, TX, and MARTHA O. WITHJACK, Mobil Research and Development Corporation, Dallas, TX

The ability to infer more accurately the type, timing, and location of folds and faults that develop during the evolution of large-scale geologic structures can help explorationists to interpret subsurface structures and generate new prospects to better assess their risk factors. One type of structural setting that is of importance in many exploration plays is that of the basement-detached normal fault. Key questions regarding such structures are (1) what structures form, (2) where do the structures form, (3) when do the structures form, and (4) why do the structures form? Clay and finite element models were used to examine the influence of fault shape on the development of folds and faults in the hanging wall of basement-detached normal faults. The use of two, independent methods hel s to overcome each method's inherent limitations, providing additional corroboration for conclusions drawn from the modeling. Three fault geometries were modeled: a fault plane dipping uniformly at 45 degrees; a fault plane that steepens from 30 degrees to 45 degrees; and a fault plane that shallows with depth from 45 degrees to 30 degrees. Results from both modeling approaches show that (1) antithetic faults form at fault bends where fault dip increases, (2) faults become progressively younger towards the footwall, (3) the zone(s) of high stress and faulting are stationary relative to the footwall, (4) anticlines with no closure form below faults shallow, and (5) closed anticlines form only above the point where faults steepen.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)