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Understanding a Non-Conventional Petroleum System - Neuquen Basin (Argentina): Deep Volcanic Sills Analysis Through a 2d Basin Modeling Approach

N. Crépieux1, F. Reverdy1, R. H. Gonzales2, and G. Baudot2
1Total, Pau, France
2Total Austral Exploration, Buenos Aires, Argentina

The main objective of this paper was to access a better understanding of non conventional petroleum system: volcanic sills intruding a thick and buried clastic serie. This analysis focused on the determination of hydrocarbons generative system using a 2D modeling approach and the impact of sill intrusion on the host rock behaviour. This technical approach allows testing different geological scenarii and all necessary adequate parameters.

Methodology:

The workflow used for this study is described as follows:
- Review of all available geochemical data ( Source Rock Potential and maturity)
- Input data of sedimentary and structural elements relatively to the intrusive bodies versus host rocks in the 2D application
- Definition of the boundary conditions
- Building of 2D model
- Run the base case with the 2D model and sensitivity tests

The “sill” petroleum system efficiency was supported by some assumptions linked to source rock properties, the timing of HC generation, the remaining potential for HC production at the intrusive time, a clastic Jurassic reservoir holding tank and the preservation of the first gas accumulations.

Main Conclusions:

- HC Generation :
The best documented base case scenario assigning a Type II/III O.M. for the Los Molles interval (Jurrassic SR) identified the timing of HC generation as a critical factor by comparison to the intrusive time.

- HC Migration :
The Lajas (Jurassic) holding tank scenario is not documented by the 2D modelling. But the source tracking tool of 2D Petromod indicates that a lateral migration and a very near vertical migration limited to the source rock affected by the volcanic thermal effect could contribute to the sill charging process.

As a consequence, a quantitative evaluation concluded that the volume of hydrocarbon generated and mobilized by the thermal effect of the intrusion, could be significant and at least could explain partly, the sill gas accumulation.

- Preservation
In case of no structural components, a high risk of gas leakage occurs in the sill accumulation

Sensitivities:
The sill petroleum system efficiency was supported by some strong assumptions linked to some unreliable parameters as for example the original source rock potential and source rock kinetics
That why some sensitivity tests have been run in order to evaluate the impact of these uncertainties on timing and HC migration.

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AAPG Search and Discovery Article #90091©2009 AAPG Hedberg Research Conference, May 3-7, 2009 - Napa, California, U.S.A.