--> ABSTRACT: Predicting Petroleum Composition by Modeling: Case Studies from Brazilian Marginal Basins, by Penteado, Henrique B.; Araújo, Laury; Trindade, Luiz A.; #90135 (2011)

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Predicting Petroleum Composition by Modeling: Case Studies from Brazilian Marginal Basins

Penteado, Henrique B.1; Araújo, Laury 1; Trindade, Luiz A.2
(1)Petrobras, Rio de Janeiro, Brazil. (2) Petrobras Energía S.A., Buenos Aires, Argentina.

Petroleum exploration is moving towards ever deeper and complex prospects. Considering the huge costs involved in offshore operations and the economic dependence of discoveries on petroleum type, it is of utmost importance to be able to predict fluid composition and properties. A compositional kinetic model for petroleum primary and secondary cracking using classes for PVT modeling has been developed for Brazilian lacustrine and marine source-rock sequences. This kinetic scheme has been widely applied in 3D petroleum systems modeling in Brazilian marginal basins to assess the timing of oil and gas generation, and for the prediction of petroleum composition and PVT properties.

A total of more than 70 non-biodegraded oils from both lacustrine and marine source rocks, with API gravities ranging from 27 to 55, was characterized by quantitative gas chromatographic analyses. Mass percentages of oil fractions based on boiling point and molecular weight ranges (C6 to C60+) were estimated. With these results, a PVT-type description of compound classes was adopted for the expelled oils. Combining results for the oils with those for the gas phase, an enhanced PVT description was achieved for the whole petroleum (C1 to C60+).

The kinetics for primary cracking of lacustrine and marine source rocks were derived from Rock-Eval data, with corrections introduced for the actual petroleum expulsion efficiency because most of the heavy components (resins and asphaltenes) of early-generated oil remain adsorbed within the source rock. As kerogen cracking proceeds, heavier and less stable compound classes can undergo secondary cracking, thus producing lighter and more gas-rich petroleum. The kinetics and stoichiometry of secondary cracking of each compound class were derived from experiments of artificial cracking of oils using several pyrolysis techniques. By coupling the primary and secondary compositional kinetic schemes, petroleum composition and its PVT properties (density, API gravity, GOR, saturation pressure) can be continuously assessed throughout source-rock maturation.

Petroleum compositions provided by this new PVT-type kinetic scheme reproduce well those of real accumulations in Brazilian marginal basins, thus allowing its application as a powerful predictive tool in exploration prospects in frontier areas. Additionally, the modeled temperature history of reservoirs was used to estimate the extent of petroleum alteration by biodegradation.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.