ICE 2022


More than 1.4 Bbls of heavy oil (11-15° API) have been discovered to date in hydrodynamic traps in the southeastern Llanos Basin of Colombia. The largest is the Rubiales Field, but other important accumulations such as Quifa, Caño Sur and Pendare are present in this area. The common element of these fields is that they are stratigraphic traps defined by the intersection of the top seal (the Miocene Carbonera C6 Unit) with an inclined oil-water contact (OWC) (dipping 0.3° towards the NW). The overall tilt of the OWC is fairly small (about 3.5 to 6 m/km), a value that is in the lower range of cases with documented tilted OWC due to hydrodynamics. In most cases the accumulations occur where there are minor inflections in the top seal formed by differential subsidence controlled by the underlying paleo-relief of the Paleozoic. The area of stratigraphic traps coincides with the forebulge of the Llanos Basin as well as with a major gravity high. A striking feature is that the area of the stratigraphic traps, which is found south east of the Meta River, is being actively uplifted. This is evidenced in the different levels of terraces that are present south of the Meta River. These terraces have a concentration of iron concretions at the surface, probably indicating paleo-phreatic zones. The highest present-day terrace has an elevation of 287 m, (vs. approx. 140 m of the Meta River). This is evidence that this zone is actively being uplifted (at least 200 m) and eroded in contrast to the rest of the basin that is a zone of deposition. All these stratigraphic accumulations have a very strong aquifer, and it has been proposed that the tilted OWC is related to hydrodynamic flow from the margin of the basin, or from areas with a higher hydraulic head. However, the orientation of the tilted OWC trend (NE-SW) is almost perpendicular to the hydraulic head contours for the basin but coincides with the orientation of the Llanos Basin forebulge. The OWC trend also coincides with the present-day strike and dip of the Carbonera Formation, which in turn is controlled by the deposition of the overlying thick Mio-Pliocene molasse sediments of the Guayabo Group. It is proposed that the tilting of the OWC is related to recent uplift in areas where the oil is biodegraded due bacterial activity and did not have time yet to equilibrate. This model could be applied to the exploration of other areas of the basin.