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

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

La Luna Formation, part of the South American upper Cretaceous sequence, is described as calcareous shales and limestones, black in color, with high foraminifera (Globigerina) content, with calcareous and phosphate concretions. The member’s sub-division is: 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).

The total organic carbon (TOC) values for Galembo are from 1.09% to 11.90% and for Salada from 2.15% to 11.90 with Type IIS kerogen. Liquid hydrocarbons would be present in the northern and central part of MMVB, and condensates and dry/wet gases are related to the southern MMVB areas. Biomarker analyses reveal variations in redox conditions and a predominant marine organic matter input with anoxic and high salinity conditions. The identified SEM total porosity for Galembo is 8.5% and 8.11% for Salada. The depositional environment is shallow marine, middle shelf. Four major third order stratigraphic cycles corresponding to the three La Luna Formation members deposition events are proposed during a sea level rise towards the La Luna Formation top.

This primary assessment of the La Luna Formation indicates a good potential for a shale gas system, where good organic matter content is present, the formation reached maturity levels for hydrocarbon generation and has relatively high porosity for oil and/or gas storage. The thicknesses in outcrop vary from 180-720 ft. for Galembo and 300-400 ft. for Salada and 500 ft. for the transitional Pujamana member.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects