Kagan Tuncay¹, Ashraf Khalil¹, Gonca Ozkan¹, Peter J. Ortoleva¹
(1) Lab. for Computational Geodynamics, Indiana University, Bloomington, IN

Abstract: The Salt-Fault-Fracture Connection

Salt withdrawal, diapirism and other tectonics induces stress changes in the neighboring less ductile strata that can cause them to fault or fracture. A new comprehensive rock rheologic model is used to predict the effect of salt tectonics on faulting and fracturing in the surrounding more brittle lithologies. We show how the salt tectonic-induced changes can affect the expulsion, migration and trapping in salt tectonic regimes.

A model of shear failure and rock competency, fracturing and gouge coupled to fluid flow is used to demonstrate the complex (chaotic) hydrologic nature of faults. It is shown that an active fault can fluctuate dramatically in its flow and other properties due to its seismic (vs. creeping) behavior. Along a fault, there can be seismic and creeping sections. As the fault system is nonlinear, the average effect over many seismic events can be dramatically different than for a creeping section. Thus, the role of a fault as a seal or conduit in the exploration context of the overall flow over the 10-100 million year time frame can be dramatically affected by its history of rock failure, fractures, gouge and diagenesis.

The role of fluid flow and deformation in the salt, fault, fracture system arises through the dependence of the failure of rocks on fluid pressure through effective stress. Thus, overpressured brittle lithologies are more vulnerable to salt tectonic-induced faulting and fracturing. In turn, the latter foster petroleum expulsion and migration, making the relocation of petroleum from source rock to reservoir a very complex dynamic phenomenon. Our 3-D reaction-transport-mechanical basin model is shown to capture these complex phenomena and thereby serve as a valuable E&P analysis tool for salt tectonic regimes.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana