Abstract: Optimal Oil Recovery Strategies in Miocene Transgressive-Barrier, Coastal-Plain, and Mixed-Load Fluvial Systems in the Mioceno Norte Area, Lake Maracaibo, Venezuela

W. A. Ambrose, F. P. Wang, M. S. Akhter, Jirapa Skolnakorn, Milton Mendez, Regulo Alvarez

Miocene oil reservoirs in the 30-km² Mioceno Norte area are estimated to have a recovery efficiency of only 27 percent at the end of primary recovery operations at the current 40-acre well spacing. Although this area has produced oil since the 1930s, appreciable volumes of oil remain in multiple, poorly contacted reservoir compartments. Strategic development of these compartments could improve ultimate recovery up to an additional 15 to 20 percent of the original oil in place.

Multiple Miocene regressive-transgressive episodes in the Maracaibo Basin resulted in a complex reservoir architecture. Basal Miocene fluvial deposits, deposited during a forced regression, are overlain by shelf and transgressive barrier-island deposits of a highstand systems tract. Episodes of upper Miocene fluvial and lacustrine-fill deposits, bounded by continuous paleosol marker beds, record climate changes or intermittent tectonic activity resulting in reorganization of dip-dispersal systems.

We used an integrated reservoir-characterization program incorporating structural, stratigraphic, seismic, palynological, petrophysical, petrographic, petroleum-engineering, and volumetric analyses to target areas for strategic oil recovery. Remaining oil is inferred to occur mainly in narrow (less than 2000 m wide), uncontacted or poorly contacted fluvial- and distributary-channel sandstones commonly projected between existing well spacing. Additional remaining oil exists in tidal-channel and backbarrier areas where washover-fan sandstones pinch out into muddy lagoonal-fill deposits.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela