--> Applied Petroleum Source Rock Evaluation and High-Resolution Sequence Stratigraphy for Unconventional Reservoirs in La Luna Formation (Cenomanian – Santonian) Northwest Maracaibo Basin, Venezuela

AAPG ACE 2018

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Applied Petroleum Source Rock Evaluation and High-Resolution Sequence Stratigraphy for Unconventional Reservoirs in La Luna Formation (Cenomanian – Santonian) Northwest Maracaibo Basin, Venezuela

Abstract

Since the early 2000s, the exploration of unconventional reservoirs has become very important around the world for their high source of energy and for their high economic value. Venezuela's oil wealth has a world class hydrocarbon source rock that symbolizes one of the most prolific places for oil accumulation in Venezuela and around the world. This source rock is the so-called La Luna Formation (Cretaceous in Age) located in eastern Venezuela, Maracaibo Basin.

One of the theories that make it one of the best source rocks in the world is its relationship with an extensive transgression and dysaerobic water column that created the best conditions for the preservation and the productivity of this high organic matter source rock. One the worldwide oceanic anoxic events (OAE2) developed in the Cretaceous at the same time as deposition of the La Luna Formation in northern South America. However, local variations in depositional and diagenetic conditions have manifestly affected the preservation and dilution of the organic source material to some degree. This generates small-scale variability in the depositional environments creating a better-quality source rock variation within the sequence that can be more prospective than others. To understand the variability of the depositional conditions, variations in organic matter source, thermal maturity, and depositional environments the use of biomarkers was critical in this study.

The methodology was based on the integration of elemental proxies, source rock evaluation and biomarker analysis using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and a high-resolution sequence stratigraphic characterization to unravel the stratigraphic origin and migration pathways of presently existing petroleum systems.

La Luna Formation was characterized with TOC values ranging from 3.85-9.13 wt%, showing a Type II kerogen, a “Good-to-Excellent” oil generation potential and a thermal maturity of 0.78% Ro on average. Biomarker analyses revealed variations in redox conditions and a predominance of marine organic matter deposited under anoxic and high-water salinity conditions. The observed facies association and biomarker analyses identified the depositional environment as shallow marine, middle carbonate shelf, in a transgressing sea. These assessments indicate a good potential for an unconventional resource, where good organic matter content generated high prospectivity towards the Maracaibo basin.