Geochemical Methods Required to Determine the Sources of Oils from Latin American Basins

Abstract

Abstract

We have conducted extensive geochemical studies on oil samples from many of the major producing and prospective regions in Latin America, including the Mexican Gulf of Mexico (MGOM), the Brazilian margin, many basins of Colombia, and Eastern Venezuela. In every case, without exception, we have discovered and characterized the contributions of deep sources that had previously escaped recognition, determined many oil accumulations to be co-sourced mixtures, and characterized new sources that had not been previously proven.

In every case these aspects of the petroleum systems had been previously missed because preceding geochemical studies only relied upon biomarker GC-MS and isotope ratios of oil fractions. These analyses conducted repeatedly over three decades arrive at virtually the same results each time without achieving significant advances in understanding the petroleum system architecture. They can be relegated to screening status in preparation for the advanced analyses required. The following examples from case studies will be presented to illustrate these advances:

1. All onshore MGOM basins show areas where oil cracking has occurred and in many such cases the deeply sourced (cracked) oil has a different source from the shallow sourced black oil. Cracking analysis by quantitative diamondoid analysis, and source determination by diamondoid isotope analysis (CSIA-D) and fingerprinting of large diamondoids (QEDA) have proven to be the key to understanding deep sources and their mixtures in co-sourced oil accumulations.
2. Source delineation in Colombia is complex due to a plethora of complications, including charges from deep, extensive oil biodegradation and co-sourced oilfields. A combination of diamondoid maturity and source correlation methods, gas chromatography-mass spectrometry-mass spectrometry (GC-MS-MS) for age-related biomarkers, and CSIA of biomarkers (CSIA-B) is required to see past this challenging complexity.
3. Turonian, Cenomanian, Albian and Barremian-Aptian sources in the Brazilian margin are distinguished by CSIA-B and QEDA. Other methods provide only ambiguous or partial information.
4. Eastern Venezuela has been shown to have four active sources, one in the Early Cretaceous, one in the Late Cretaceous, and two in the Tertiary. A deep source(s) in the Espino Grabin, possibly Jurassic or older, might generate light hydrocarbons, a reserve that remains essentially untapped.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016