ICE 2022


Chichimene Akacias and Lorito fields (ChiAkLo) have a complex structural and sedimentary evolution changing through geological history associated to different regional stresses that have generated the current reservoir configuration. The target of this study is the main producing unit, T2, which consists of 300 ft of clean sandstones deposited in a transition environment during 3 different periods: Maestrichtian, Paleocene and Eocene. In this paper, we present a methodology that integrates geosciences to production data, to explain the current fluid distribution that supports an unusual prospective model and development plan. The workflow starts with a detailed structural and stratigraphic regional seismic interpretation to help understand the control of the different deformation stages on the deposition and charge of T2 unit. Then a petrophysical review tries to explain the original fluids distribution of the reservoirs; and finally, we integrate some production data to validate the whole model. The structural mapping showed that at Lower Oligocene there was a regional SW-dipping homoclinal charged trap, then inverted during Miocene. This inversion resulted in the current reservoir geometry where fluids reaccommodation is still incipient due to the heavy oil high viscosity. The T2 sedimentary model defined by a stratigraphic seismic interpretation shows East-to-West variations, as well as changes in reservoir quality, from fluvial systems in Castilla Field to braided deltas and delta fronts in ChiAkLo, variations controlled by a fault system at Lower Paleocene that represented the limit of an asymmetrical hemigraben generated during Cretaceous. The petrophysical model suggests 3 different FWL’s, one for each geological period, meaning that the geological trap for ChiAkLo is not in equilibrium since the structural inversion occurred recently. On the other hand, the increase of Sw from NE to SW, observed by wells drilled at almost the same depth, suggests that the fluid distribution is not responding to the current inverted structure, but to a previous paleostructure. This prospective model, validated by the production and logging of more than 300 wells, can explain the low production in the attic of Lorito, the transition zone in the flank of Akacias, and the high oil saturation in the footwall of Chichiemene. Thus, this model has become an accurate tool to give technical support to the development plans for the ChiAkLo trend.