Structurally complex, heterogeneous, tide-dominated deltaic reservoirs in the Lower Misoa Formation (lower Eocene C members) in the LL-652 area of Lagunillas field in the Maracaibo Basin, Venezuela, have produced 166 million stock-tank barrels (MMSTB) of oil but have a low recovery efficiency of 22 percent. These reservoirs will contain more than 900 MMSTB of unrecovered mobile oil when primary recovery operations at the current 80-acre well spacing end. In this study we characterized lower Eocene reservoirs in the LL-652 area, Lake Maracaibo, to improve estimates of hydrocarbon reserves, to identify potential areas for secondary-recovery projects, and to establish a field-depletion plan to evaluate advanced recovery opportunities and extended development.A significant remaining oil resource lies in poorly drained or undrained reservoir compartments confined by a combination of complex structure and depositional heterogeneity. Sealing and partly sealing faults, including northwest-trending normal faults and younger north-northeast-trending reverse faults, bound large-scale structural compartments. Stratigraphic heterogeneity is controlled by dip-elongate, distributary-channel, and tidal-ridge sandstones that commonly pinch out over distances of less than 2,000 ft (>610 m). Because these two facies compose most of the reservoir sandstones, they contain most of the remaining oil.The main control on porosity and permeability distribution in the C members in the LL-652 area is depth. Volume of quartz cement in particular influences reservoir quality, and because volume of quartz cement increases significantly with depth, reservoir quality decreases with depth. Within each reservoir interval, however, depositional architecture controls porosity and permeability distribution. For example, significant permeability contrasts (as much as three orders of magnitude) exist locally between distributary-channel and tidal-flat, fluvial-estuarine channel and distal deltafront, and distributary-channel and delta-front facies, where clay clasts at the base of the distributarychannel facies may retard vertical fluid flow.Cumulative production varies greatly in each reservoir interval as a result of differences in ages of producing wells, greater-than-average production in areas of repeat section and inferred increased fracture permeability in zones of reverse faults, and differences in net thickness of perforated intervals. The tide-dominated deltaic depositional fabric, however, controls net sandstone and net pay thickness of each reservoir interval and therefore must affect cumulative production.We made maps of hydrocarbon pore volume (SoPhiH) and remaining oil on the basis of improved petrophysical characterization and production apportioning to specific reservoir horizons by permeability feet (kh). These maps indicate that most remaining oil lies in the poorly developed and structurally complicated north part of the field and where narrow (less than 2,000 ft [
Ambrose, W. A., Ferrer, E. R., Dutton, S. P., and others, 1995, Production Optimization of Tide-Dominated Deltaic Reservoirs of the Lower Misoa Formation (Lower Eocene) LL-652 Area, Lagunillas Field, Lake Maracaibo, Venezuela: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 226, 46 p.