Distribution and mechanisms of overpressure generation and deflation in the late Neoproterozoic to early Cambrian South Oman Salt Basin

摘要

Late Neoproterozoic to early Cambrian intra-salt Ara reservoirs of the South Oman Salt Basin represents a uniquenself-charging petroleum play with respect to hydrocarbon and overpressure generation and dissipation. Reservoirnbodies (termed ‘stringers’) are isolated in salt and frequently contain low-permeable dolomites that are characterizednby high initial production rates because of hard overpressures. A database of more than 30 wells has beennutilized to understand the distribution and generation of overpressures in intra-salt reservoirs that can be separatednby up to 350 m of salt. A temporal relationship of increasingly overpressured reservoirs within stratigraphicallynyounger units is observed, and two distinctly independent trends emerge from the Oman dataset; one hydrostaticnto slightly above hydrostatic and one overpressured from 17 to 22 kPa m)1, almost at lithostatic pressures. Structural,npetrophysical and seismic data analysis suggests that overpressure generation is driven by fast burial of thenstringers in salt, with a significant contribution by thermal fluid effects and kerogen conversion. Structural and geometricninformation indicates that present-day hydrostatic stringers have been overpressured in their earlier geologicnevolution. Evidence for these initial overpressures in currently hydrostatic reservoirs is provided by hydrocarbonveinedncores from halite overlying the reservoirs. A proposed pressure deflation mechanism can be related to thencomplex interplay of salt tectonics and fast deposition of early Cambrian to Ordovician age clastics.