Unconventional Gas Shale Assessment of La Luna Formation, in the Central and South areas of the Middle Magdalena Valley Basin, Colombia

Emilio J. Torres-Parada
University of Oklahoma, ConocoPhillips School of Geology and Geophysics Norman, Oklahoma. U.S.A.
[email protected]

La Luna formation, South American upper cretaceous sequence, has been recognized as one of the most important hydrocarbon source rocks in Colombia. This formation is described as calcareous shales and limestones, black in color, high foraminifera content and calcareous concretions. Outcrop studies are under analysis in the southern and central part of the Middle Magdalena Valley basin Colombia, to assess its gas shale potential. La Luna has been sub-divided into three members by previous authors: the upper, middle and lower, named respectively as Galembo (calcareous shales with limestone layers and nodules), Pujamana (claystone, mudstone, gray shale and cherts) and Salada (black shales, black mudstones, black calcareous claystone, black limestone layers and concretions with pyrite). Stratigraphic sections were measured, for the Galembo, Pujamana and Salada members in the central and south areas of the basin with a formation average thickness of ~1000 ft. The principal recognized lithologies were black siliceous and calcareous shales, in planar and thin strata with foraminifera lamina and calcareous concretions; also limestone is prominent in these members, principally black mudstone and pyritized calcareous concretions. The average thickness for Galembo member is 730ft and the Salada member is 500ft. The observed facies association indicates a shallow marine, middle shelf in a transgressing sea environment. A primary assessment for la Luna formation indicates a good potential for a shale gas system, where good organic matter content is present, the formation has reached maturity levels for hydrocarbons generation and has relatively high clay floccule porosity for oil and/or gas storage.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects