Geological controls on remaining oil in Miocene fluvial and shoreface reservoirs in the Mioceno Norte area, Lake Maracaibo, Venezuela

Facies architecture and structure are the primary controls on reservoir geo metry, fluid-flow pathways, and distribution of remaining oil in fluvial an d shoreface reservoirs of Miocene age in the 46.7 km(2) Mioceno Norte area in northern Lake Maracaibo. This mature field is undergoing depletion and n earing the final stages of primary recovery. Although the area has produced oil since the 1940s, appreciable volumes of oil (commonly 400 to 1200 x 10 (3) STB (stock tank barrels)/20-acre drainage area) remain in multiple, pea rly contacted reservoir sandstones at the current 984 ft (300 m) well spaci ng. Detailed lithofacies maps document the control of sandstone architectur e on hydrocarbon distribution and demonstrate that the current well spacing on a grid pattern is too large to recover efficiently the remaining oil. M oreover, the facies architecture influences water-cut patterns and the irre gular advancement of inferred oil-water contacts on the western margin of t he field. A wide variety of infill wells, recompletions, redrilled wells, h orizontal wells, and water-injection wells is proposed. Approximately 80 x 10(6) STB of remaining oil will be produced by maintaining the current 984 ft (300 m) well spacing. However, an additional 46.5 x 10(6) STB can be pro duced with geologically targeted infill wells, recompletions and horizontal wells. In addition, new water-injection wells can appreciably increase oil recovery by enhancing sweep efficiency and providing pressure support.