Seismic and structural analysis of the San Francisco oil field (Colombia). Structural controls on a complex hydrocarbon charge history

In this work, we use key seismic lines, surface geology, and well data to document the structural style and evolution of the San Francisco Anticline. The seismic data from the area displays a unique expression of different unconformities that helped to reconstruct the evolution of the San Francisco Anticline. The San Francisco Anticline can be defined as an inversion structure that started its evolution during the late Oligocene-early Miocene as an anticline in the hanging-wall of the Dina footwall shortcut. This initial growth occurred before the out-of-sequence Miocene activation of the San Jacinto inversion fault which is the modern boundary of the anticline. However, the earliest structure to grow in the study area appears to have been the Natagaima Basement High which began to grow in the Oligocene, but remained inactive from the Miocene to Recent. The current oil-water contact in the San Francisco oil field is much higher than the spill point. As a result, we hypothesize that the reservoirs in the anticline received early charge which postdated the initial late Oligocene-early Miocene growth of the structure, since some Miocene overburden would have been required for hydrocarbons to have been expelled. However, that early charge presumably occurred at some point during the Miocene, since the higher oil-water contact when compared to the spill point of the modern San Francisco Anticline probably implies that the final geometry of the San Francisco Anticline had not yet been reached. We summarize this evolution in a sequential kinematic restoration.