ABSTRACT: Seismic Identification of Potential Source/Reservoir Rocks in a Rift Setting

Teh-An George Chou, Tai-Chang Shih

The kinematics of the complex interplay between extensional (listric) faulting and synrift sedimentation within a rifted half-graben control the formation of structural traps, as well as the development of potential source/reservoir rocks in such a geologic setting. Recent studies on listric faulting based on sand-box experiments show that the stratal geometric patterns of prerift sediments and synrift sediments are significantly different. We simulated the observation of Ellis and McClay on the computer (with programs developed by T. G. Chou), and further studied the synrift (i.e., syndeformation) sedimentation. The modeling results reveal that the stratal pattern resulting from a high sedimentation rate (relative to subsidence rate) is distinctly different from that res lting from a low synrift sedimentation rate. In areas with very low synrift sedimentation rates, a characteristic stratal pattern of downstepping toplaps is observed, whereas for areas with high sedimentation rates simple toplap commonly is the result. This is a breakthrough in seismic identification of areas having low sedimentation rates vs. those having high sedimentation rates. If an area experienced a prolonged period of low sedimentation rate, potentially it would provide favorable conditions for the development of source rocks. An area with high sedimentation rates, however, would likely be more favorable for the development of reservoir rocks within the half-graben system. A systematic analysis of the synrift stratal geometry allows better interpretation of depositional environme ts and permits improved evaluation of the source/reservoir potential of rift basins.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990