Tertiary Depositional Environments And Reservoir Properties In The Sinu Accretionary Prism (Offshore -Colombia)

The Sinu accretionary prism is located in the northwestern corner of South America (Colombia) . This area has been submitted to major tectonic events related with the convergence of South America, Nazca, Caribbean and Cocos plates. The sedimentary clastic input influence of the Magdalena River delta since the Miocene (figure 1) was another key point for the evolution of this area. Overlying the oceanic crust, an Upper Cretaceous and Tertiary sedimentary sequence that could reach about 8000 m of thickness was deposited in the Sinu area. An integrated sedimentary and seismic stratigraphic study was carried out to predict the depositional environments and the reservoir properties in the study area. To attain these objectives the available well and outcrop data were integrated, a seismic facies interpretation of the available 2D information was performed in the Upper Miocene-Lower Pliocene interval and five paleogeographic maps from the Upper Paleocene to the Pleistocene were elaborated. During the Upper Paleocene to Lower Oligocene ages there was a low sedimentary clastic input in the Sinu area, improving the risk of reservoir presence. Later on, during the regional marine regressive phase of Late Oligocene, the development of turbiditic deposits is very probable and expected in the area. From the Middle Miocene, the major uplift of the Andean Cordilleras increased drastically the sedimentation rates of the paleo Magdalena and the paleo Sinu rivers. These fluvio- deltaic deposits passed to upper and lower fan environments towards the basin. The paleogeography model indicates that lower fan deposits were extensively developed in the Northern sector of the Sinu accretionary prism during the Upper Miocene - Early Pliocene. Additionally, the seismic facies observed (chaotic and continuous to discontinuous) are interpreted as sheet sands and distributary channels, considered as good to excellent potential reservoirs. In conclusion, good reservoir properties are expected for the Upper Miocene - Lower Pliocene lower fan turbiditic deposits related with the Paleo-Magdalena Delta.