Evolution of Structures above a Salt Diapir - Case Study from the Arabian Gulf Region

Al-Fahmi, Mohammed M.; Plesch, Andreas; Shaw, John; Cole, John

We employ volumetric, geomechanically-based structural restoration methods to obtain insights into the development of structures within the sedimentary cover above an interpreted salt body in the Arabian Gulf region. The study area is a hydrocarbon-bearing dome that owes its structural uplift to a combination of salt and regional tectonics. We investigate the stratigraphic section from Permian to Tertiary and concentrate on: 1) the evolution of the dome structure, 2) the patterns and displacement history of faults in the dome, and 3) strain patterns from both folding and faulting at reservoirs through geological time. The study utilizes 3-D seismic reflection and well data to model subsurface horizons and associated structures. The 3-D model was divided into several mechanical units obtained from an existing 1D geomechanical model developed for the area. The restoration technique allows us to simultaneously restore each mechanical unit to a pre-deformation (unfolded and unfaulted) configuration with limited boundary conditions. Analysis of the dome and fault growth suggests two stages of faulting, and a stage of folding that produced a gentle dome structure. Normal faulting was developed within the Paleozoic section, followed by fault reactivations and development of new normal faults within the overlying Jurassic and Cretaceous strata. Analysis of the structure indicates a slow uplift we associate with salt movement in Early Jurassic with increasing rates of uplift in the Late Cretaceous and Early Tertiary concomitant with the Zagros orogeny. The non-radial patterns of the faults and graben systems, and the relative timing of faulting and folding, suggest that the structure is a reactive diapir. Within the Jurassic reservoirs, the strain patterns calculated for pre Tertiary structural growth indicate larger strains around faults, and relatively lesser strains in areas only flexed by dome development. However, we find that the uplift during Late Cretaceous and Early Tertiary results in increased flexure/fold related strains within the Jurassic reservoirs. This provides a model to predict a relative timeframe for fault and flexure-associated fractures, as well as the locations of these fracture systems. The information from the restoration model improves our understanding about the structural history and strain patterns within the reservoirs, and can be integrated with further subsurface data for reservoir development.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013