Sedimentology, Sequence Stratigraphy, and Reservoir Architecture of the Eocene Mirador Formation, Cupiagua Field, Llanos Foothills, Colombia
Juan Carlos Ramon, Andres Fajardo, 2006. "Sedimentology, Sequence Stratigraphy, and Reservoir Architecture of the Eocene Mirador Formation, Cupiagua Field, Llanos Foothills, Colombia", Giant Hydrocarbon Reservoirs of the World: From Rocks to Reservoir Characterization and Modeling, P. M. (Mitch) Harris, L. J. (Jim) Weber
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The stratigraphic architecture and facies distributions in a high-resolution time-space framework define the three-dimensional (3-D) reservoir zonation of the Mirador Formation in the Cupiagua field. A high-resolution genetic sequence stratigraphy study, using more than 731m (2400 ft) of core and 40 well logs, is integrated with petrophysical information to populate a static structural model based on the interpretation of a 312-km2 (120-mi2) 3-D seismic volume. Dynamic data (pressure, gas tracers, gas-oil ratio behavior) are integrated with the geological model to better define sandstone bodies' lateral continuity. Production logs (production logging tools) complement petrophysical data in the definition of fluid-flow units.
Three scales of stratigraphic cycles are recognized in the Mirador Formation. Short-term (high-frequency) cycles correspond to progradational-aggradational units. Six intermediate-term cycles are identified by the stacking patterns of their component short-term cycles and by the general trend of facies successions, indicating increasing or decreasing accommodation-to-sediment supply (A/S) ratios. Two long-term cycles are defined from the stacking pattern of the intermediate-term cycles and by the general trend of facies successions.
The lower half of the Mirador Formation consists of coastal-plain facies tracts and is composed of channel, crevasse splay, and swamp and flood-plain facies successions. A bay facies tract occurs in the upper half of the Mirador Formation and is composed of bay-fill, bay-head delta, and channel facies successions.
The lower Mirador Unit was deposited over a wide flood-plain sequence. Each intermediate-term cycle is composed of aggradational channel deposits, pro-gradational and aggradational crevasse splay bodies, and aggradational swamp and flood-plain facies successions. The first two intermediate-scale cycles (I, II) show a seaward-stepping pattern, and then the next cycle (III) shows a landward-stepping stacking pattern. The fall-to-rise turnaround is located at the base of cycle II. The upper Mirador shows the continuous landward-stepping pattern and places prograding bay-head delta and bay-fill facies successions over the alluvial-plain setting of the Lower Mirador. This upper unit consists of three onlapping cycles composed of a succession of aggradational channel deposits, prograda-tional bay-head delta, and bay-fill deposits with a landward-stepping stacking pattern. During this cycle, deepening-up bay-fill facies successions were deposited in the area as a consequence of the increasing accommodation conditions that prevailed in the area. Finally, the Mirador is capped by restricted-marine shales of the Carbonera Formation.
The Cupiagua structure is a large, east-verging, asymmetric anticlinal fold that trends north-northeast in the hanging wall of the frontal fault. Average length and width of the Cupiagua structure are 25 and 3 km (15 and 1.8 mi), respectively. The original oil in place in the Cupiagua field is estimated between 1000 and 1100 MMSTB of oil and 3000 to 4500 mmcf of gas. The Mirador Formation accounts for approximately 51% of the recoverable oil in the Cupiagua field.