Maturation mapping in the Tertiary La Vela basin, based on bottom-hole temperatures of 12 wells, indicates that only the Paleogene Guarabal Formation and the lowermost part of the Miocene Agua Clara Formation reached temperatures adequate for the generation of oil.

Plotting of temperature contours on cross sections of the basin and on isopach maps delimited the extent of the potential oil-forming units. Flows of oil in drill-stem tests came from wells on a basement horst adjacent to a deeply buried "pod" of Guarabal Formation, which was suggested as the local source rock.

Later geochemical analyses of samples from three wells confirmed this model by showing that the Miocene Agua Clara Formation was immature and contained insufficient amounts of organic matter to be an oil source. Furthermore, it was confirmed that the "pod" of Paleogene Guarabal Formation was mature, and contained up to 6% total organic carbon as well as predominantly oil-prone kerogen.

Accurate location of the oil-generating beds in the La Vela basin was thus made possible by geochemical mapping, and should help focus exploratory drilling on those traps most likely to contain oil accumulations.

End_of_Article - Last_Page 533------------