General Geology and Oil Occurrences of Middle Magdalena Valley, Colombia1
The Middle Magdalena Valley is a depressed area of some 12,500 square miles lying between the Central and Eastern Ranges of the Colombian Andes. Its sedimentary fill ranges in age from Paleozoic to Recent. In Cretaceous time this area formed only a small central part of a much more extensive basin area, the Colombian geosyncline, whereas, of the basin which developed in Eo-Oligocene time, it formed a western shallow margin, deepening rapidly eastward.
Commercial production of heavier asphaltic- and naphthenic-base oils is being obtained from Tertiary reservoirs at La Cira-Infantas, Casabe, Velasquez, and Cantagallo. Some lighter paraffinic crudes have been found in Cretaceous reservoirs at Buturama and Totumal. The location of these areas with respect to their position in the Tertiary and Cretaceous basins supports the hypothesis that heavy oils form first and migrate to the margins or shelf areas, and the lighter oils are confined to traps located in a more central part of the depositional basin.