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Evaluation of Source Rock Distribution and Quality of the Cenomanian-Coniacian La Luna Fm. in the Middle Magdalena Valley, Colombia, by Applying Organic Facies Modelling (OF-Mod)

Mann, Ute1; Blanco-Velandia, Vladimir O.; Majewska-Bill, Monika; Juliao, Tatiana; and Felix, Maarten
1[email protected]

The Middle Magdalena Valley (MMV) is a semi-mature exploration area with medium-to small-scale discoveries. Active petroleum systems consist of Cretaceous source rocks and Cretaceous or Tertiary reservoirs. The Late Cretaceous La Luna Fm. has been considered to be the main hydrocarbon source rock in the MMV, and has also been discussed in terms of shale gas potential recently.

Several authors report facies changes in the La Luna Fm. Based on crude oil analyses and rock extracts a more terrestrial-influenced facies type is reported in the eastern part of the MMV while more marine type organic matter deposited under anoxic conditions is observed in the sediments in northern and north-western parts. Several authors state that the existing knowledge about the depositional processes controlling the La Luna Fm. in the MMV is limited and only few integrated stratigraphic and geochemical studies exist.

In the present study our objective was to investigate the depositional controlling factors and to provide a volumetric and qualitative description of the source rock potential of the La Luna Fm. of the MMV by means of the process-based organic facies modelling software OF-Mod 3D. OF-Mod 3D is a computer application for simulating source-rock potential distribution and quality variations in basin kitchen areas during basin analysis studies. The study area covers a 67 km x 242 km portion of the MMV and the modelling interval ranges from the top of the Simitiacute; Fm. (103 Ma) to the top of the La Luna Fm. (98 Ma). Seismic depth maps were used in addition to well tops, gamma ray logs and organic geochemical data for a number of wells for calibration. Three main work steps were performed: (1) Palaeowater depth reconstruction for the top and the base of the la Luna Fm. (2) Stratigraphy modelling and subsequently (3) organic sedimentation modelling. Several modelling scenarios have been accomplished and a good match between measured and modelled data was achieved. A relatively high amount of terrestrial organic matter indicating a mixed type (II-III/III-II) to almost entirely terrestrial type of kerogen was modelled in the middle part of the study area, which is supported by the geochemical data from the wells. Temporally variable anoxia was introduced to account for variations in TOC and HI data particularly in one well. The thickest accumulations of very good source rock potential with the highest TOC and HI values were modelled in the northern part of the study area.


AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013