Abstract T he Bureau of Economic Geology and Corpoven S.A. (now Petróleos de Venezuela) jointly undertook a detailed reservoir characterization study of the Merecure and Oficina Formations in the Arecuna field of the Faja region, Eastern Venezuela Basin. The primary objective of the study was to delineate the volumes and residency of remaining oil saturation and to develop appropriate advanced recovery strategies for maximizing recovery efficiency of the heavy oil in the Faja region. Initial completions in the field were all from vertical wells, and production rates were subeconomic. The field-development strategy was to accelerate production rates by taking advantage of increased drainage efficiencies of horizontal wells. A horizontal-well drilling program, however, requires a very accurate reservoir model, particularly in the Faja, where the reservoirs were highly compartmented because of complex faulting and lateral and vertical facies heterogeneity of the fluvial reservoirs. Moreover, hydrocarbon- and water-bearing reservoirs are strongly interlayered in the field, requiring the trajectory of the horizontal wells to be targeted accurately. A 46-well drilling program, implemented after the reservoir characterization, validated the geologic model (in some cases confirming geologic predictions as much as 1050 m [3500 ft] from the nearest well data). Although the overall drilling program was highly successful, eight wells experienced water-production problems and were deemed uneconomic. A postmortem analysis of the unsuccessful wells indicates that most of the water problems were mechanical in nature, but coning of the aquifer and uncertainty in defining pay-resistivity cutoffs (as a result of variable water resistivities) also contributed to failure of some wells.