Скачать или смотреть AAPG PSGD Webinar/Q&A: David Ferrill presents Faulting and Fracturing in the Austin Chalk

Webinar is the first 55 min followed Q&A for 40 min.

Abstract:

Outcrops of Late Cretaceous Austin Chalk in south-central and southwest Texas were investigated to assess fault and fracture networks, failure modes, relationships to mechanical stratigraphy and regional structural position, and role in fluid movement. The outcrops are along the updip edge of the Gulf of Mexico marginal fault system and represent the nearest outcrop exposures to active drilling and production from Austin Chalk in south Texas. In the study area, the fault system consists of northeast-striking normal faults, and intervening relay structures. Similar extensional fault patterns exist in the subsurface Austin Chalk in the exploration and production area. Field investigations document significant variability in failure modes (extension versus shear failure), fracture orientations, and fracture intensity.

Opening-mode (extension) fractures reflect the strong influence of mechanical layering on nucleation, spacing, vertical penetration, and lateral extent of fractures. Systematic extension fracture networks are best developed in chalk and limestone beds – these fractures tend to be bed-restricted, terminating in adjacent mudrock or ash beds. Incompetent beds within the Austin Chalk not only localize fracture terminations, but frequently have caused fault (shear fracture) dip change (refraction). Fault and fracture orientations and timing relationships reflect stress rotation and structural overprinting controlled by regional and local structural position (e.g., in the San Antonio relay ramp).

Faults in Austin Chalk outcrops exemplify deformation and fluid histories of subseismic-scale faults in mechanically layered chalk-dominated strata. Exposures of near-horizontal Austin Chalk in southwest Texas contain northwest- and southeast-dipping normal faults with exposed heights of meters to 10’s of meters, and displacements of centimeters to decimeters. Local fault dips are steep to vertical through chalk and limestone beds, and moderate through marl, mudrock, and clay-rich ash beds, producing refracted fault profiles. Fault surface characteristics reflect various failure modes – tensile, hybrid, shear, and (locally) compactive shear behavior depending on host lithology. Dilational zones associated with steep fault segments host calcite veins. Crack-seal textures in fault-zone veins record repeated reactivation of refracted fault profiles. Fluid inclusion and stable isotope geochemistry analyses indicate formation at depths of 1.4 to 4.2 km (4,593 to 13,780 ft). Fluids include locally sourced saline waters and externally sourced (migrated) waters and oil in rocks that did not reach oil maturation conditions.

Failure mode and deformation behavior (dilation versus slip) in the Austin Chalk relate in predictable ways to the mechanical stratigraphy and stress state. Dilation tendency versus slip tendency patterns on faults and other fractures – analyzed using detailed orientation or structural geometry data and stress information – allow prediction of deformation modes, volume change, and fluid conduit versus barrier behavior of structures.

Bio:

David A. Ferrill is an Institute Scientist at Southwest Research Institute in San Antonio, Texas. He received his B.S. degree in geology from Georgia State University in 1984, his M.S. degree in geology from West Virginia University in 1987, and his Ph.D. in geology from the University of Alabama in 1991, and he is a licensed professional geoscientist (geology) in the state of Texas. Before joining Southwest Research Institute in 1993, he was an exploration geologist at Shell Offshore Incorporated, and an assistant professor at Georgia Southern University. David is a structural geologist with international research experience in contractional, extensional, and strike-slip tectonic regimes, and international oil and gas exploration and production experience. He led SwRI’s Eagle Ford joint industry project, and currently leads SwRI’s Permian Basin Consortium, and performs analyses of faulting, fracturing and reservoir deformation, and provides structural geological training and contract consulting for the oil and gas industry. David is a founding member of the AAPG Petroleum Structure & Geomechanics Division and served as past President.