Microbial and Thermogenic Petroleum Systems in the Colombian offshore Caribbean — New Geochemical Insights in an Emerging Basin
Colombian offshore Caribbean has been historically considered an exclusively dry natural gas petroleum province in which gas was originated predominantly from microbial activity. Chuchupa and Ballenas fields discovered in the 1970´s as well as recent (2014-2017) discoveries Orca, Kronos, Gorgon and Purple Angel confirm the presence of an emerging methane-dominated basin. However, interpretation of new natural gas analysis suggests that these dry gas accumulations contain a mixture of microbial and thermogenic gases. We systematically analyzed and interpreted major gas compounds (C1-C5) and methane isotopes (δ13C1) in recent wells. Natural gases have methane relatively depleted in 13C (δ13C1 values from -77‰ to -70‰) in all samples collected at temperatures below 50°C. This observation supports the presence of an active primary microbial petroleum system related to a high sedimentation rate and low geothermal gradients in the last 7 My. As the temperature increases above 50°C, δ13C1 values progressively increase and reach values around -45‰ at temperatures 90°C, which suggest an increasing contribution of thermogenic methane at greater depths. Although none of the gas-bearing reservoir are located deep enough to contain a dominant contribution of charge from an active thermogenic system, these geochemical observations indicate the presence of thermogenic plays in the area. This presentation discusses the key geochemical evidence and models supporting an active thermogenic system within the Colombian offshore Caribbean, and highlights new exploration opportunities within this emerging basin.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019