Cratering Reservoir Potential by Impact Cratering

Peter H. Schultz

Impact craters are gaining increasing acceptance and value as sites for potential hydrocarbon reservoirs. Nevertheless, such structures are often difficult to interpret and assess because their physical expressions from geophysical data have few exposed terrestrial analogs for comparison. Observational, theoretical, and experimental studies directed toward understanding the nature of well-preserved craters on other planets, however, establish a two-dimensional template for understanding and interpreting the three-dimensional view, critical for assessing hydrocarbon potentials. But terminology often used in describing an impact structure needs to be placed in a process context. Impact craters are not produced instantaneously but evolve through time. The process occurs in t ree different stages of formation corresponding to the transfer of kinetic energy: compression, excavation, and modification. The compression stage roughly corresponds to the time required for transfer of energy from impactor to target and is reflected in the formation of a central penetration zone in smaller craters and the central uplift in larger craters (often called the "central plug, diapir, brecciated core, or disturbed zone"). The excavation stage occurs as the cratering flow field draws material downward near the center and outward from the cavity. In craters that are not heavily modified by collapse (such as Meteor Crater), this stage produces a truncated-cone profile prior to erosion. In larger craters (depending on substrate), the excavation stage is transient. The uplifted r m collapses and produces the distinctive floor ("ring syncline, central basin, annular structural low"), wall ("megablock or ring-graben" zones), and rim ("ring anticline, faults, or megaterrace"). Traps are created stratigraphically inside (shock-disrupted rock and depositional capping) or outside (inverted stratigraphy, fractured/faulted target, porous ejecta) as well as structurally inside (uplift, wall terraces) or outside (concentric listric faults or seismically triggered failure). Larger complex craters create greater potential for hydrocarbon traps. Consequently, potential reservoirs can be created during each stage but the most important criteria remains the realtors' motto: location, location, location!

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California