Sedimentology, Sequence Stratigraphy and Reservoir Architecture of the Eocene Mirador Formation, Cupiagua field, Llanos Foothills, Colombia

Juan Carlos Ramon¹ and Andres Fajardo-Diaz^2
1 BP, Bogota, Colombia
² Chevron-Texaco, Bogota, Colombia

This paper describes the stratigraphic architecture and facies distributions within a high resolution time-space framework and defines the 3-D reservoir zonation of the Mirador Formation in the Cupiagua Field. A high-resolution genetic sequence stratigraphy study using more than 2400 feet of cores and 40 well logs was integrated with petrophysical information to accomplish these objectives. The structural model is based on the interpretation of a 312 km2 3D volume. 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 were 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 were 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 tract and is composed of channel, crevasse splay and swamp/floodplain 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 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. Finally, the Mirador is capped by restricted marine shales of the Carbonera Formation.