Reservoir characterization of the upper Merecure and lower Oficina Formations sands in the Leona Este Field, Eastern Venezuela Basin

Abstract

The "S5", "T" and "U1" sands, traditionally described as part of the lower section of the "Oficina" Formation, and the "U2" sand, as part of the upper interval of the "Merecure" Formation, contain the largest oil remaining reserves of the Leona Este Field, which is located in the southern portion of the Eastern Venezuela Basin. Two or more of these reservoir sands, which are interbedded with shales, have been simultaneously produced pursuing an increase in the oil production rate, but an unexpected production performance was obtained: the accelerated and early increase of the water volume associated to the produced oil has caused the shut down of some wells in the Leona Este Field. In order to understand this productive performance and to re-evaluate the hydrocarbon potential of the study interval, it is important to describe these reservoirs in terms of their depositional origin and trap formation. An integrated reservoir model was constructed using all the available geological, geophysical and production data. The hydrocarbon trapping mechanism of each studied stratigraphic interval, traditionally known as the "S5", "TU", "TL", "U1U", "U1L", "U2U", "U2MA", "U2MB" and "U2L" sands, includes two components: ʺ Stratigraphic component: each stratigraphic interval presents one or more reservoir zones composed by sandy deposits that fill belts of stacked tidal-fluvial channels in a SSE-NNW trending tide-dominated estuarine system. In most intervals, these contemporaneous-in-deposition reservoir zones are not connected due to the lateral variation of facies present in the tide-dominated estuary. ʺ Structural component: northward dipping strata have been offset by a W-E trending major normal fault and secondary normal faults striking parallel to the major one. The major fault is the southern seal of the hydrocarbon traps. The most important prospects of the study interval are the reservoir zones 1 and 2 of the "U1L" sand, the reservoir zone 3 of the "U2MB" sand, and the "U1U" sand, which show more than 15 feet of average net sand thickness, and contain the largest volume of recoverable oil per reservoir zone in the Leona Este Field.