Detailed Organic Geochemical Characterization from Cretaceous Sequence: Potential Unconventional Reservoirs - Shale Gas/Shale Oil, In the Middle Magdalena Valley Basin (MMV), Colombia
Juliao, Tatiana M.1; Márquez, Robert; Zamora, Wilson H.; and Perez Carrillo, Edgar R.
A detailed geochemical study from the cretaceous sequence in the La Luna-1 well, first well drilled by Ecopetrol for unconventional reservoirs - Shale Gas/Shale Oil in Colombia, was carried out in more than 1000 samples (core and cuttings), separated about three feet, in order to identify the better intervals, which can be considered prospective for this type of deposits.
The upper Cretaceous La Luna Formation has been divided in three members: Salada, Pujamana and Galembo, each present geochemical characteristics distinctive than others, associated with different depositional paleoenvironmental conditions. In the Salada and Galembo members consist predominantly of marine organic matter (kerogen type II, oil prone) associated to Mid-external platform environments, with most TOC values higher than 2% (between 2 and 8%). The Pujamana member consists of marine organic matter (kerogen II, oil prone) with important input of terrestrial organic matter (kerogen III, gas prone) indicating paleoenvironmental conditions more proximal in the marine shelf with TOC values, in general lower than 2%. Tablazo formation consist of marine organic matter (kerogen type II) associated with a half platform environment, significantly variable organic contents between 0.3% to 26% TOC (average of 5.1%); however the high TOC values (> 6%), can be related to presence of bitumens and pyrobitumens recognized, even in the lower part was found a foot formed by almost fully impsonita (solid bitumen) with high carbon content (about 70%).
The thermal maturity data indicate, for upper part La Luna formation, reached the early to middle stage in the oil window (Tmax 432-440°C and Ro 0.6-0.8% ) while the middle and lower part reached middle to late stage in the oil window (Tmax 440-448°C and Ro 0.8-1.0%). Tablazo formation reached the gas window (Tmax 450-500 ° C and Ro 1.4 and 1.6%).
The interpretation from the geochemical data (TOC-LECO, Rock Eval Pyrolysis VI, Organic Petrography, Palynofacies and Gas Content) allowed the identification of seven intervals with good geochemical characteristics, in order to be considered prospective for unconventional reservoirs in the La Luna formation, ranging from 50 to 419 feet, with total gas content between 70 and 100 scf/ton and/or relative high liquid hydrocarbon content in the rock (S1: 2-10 mg HC/g rock). In the Tablazo formation was recognized a 423 feet interval with total gas content between 90 and 200 scf/ton.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013