Print this pageIdentification of High-Resolution Features on Formation Pressure Gradients: A Case Study in a Heavy Oil Accumulation of the Campos Basin, Offshore Brazil
Artur, Paulo C.1; Beneduzi, Carlos F.2; De
Andre, Carlos A.1; Roberto, Silas A.1
(1)UO-BC/EXP/AAG,
PETROBRAS S.A., Macaé, Brazil. (2) E&P-EXP/AFOE/AFP, PETROBRAS S.A., Rio de
Janeiro, Brazil.
Important features in hydrocarbon reservoirs can be identified from the analysis and interpretation of formation pressure data. When the original pressures are still preserved, one can identify changes of fluid gradients, fluid contacts, discontinuities related to vertical permeability barriers, or even the reservoir structural compartmentalization. This analysis can become more complex due to capillary, wettability and compositional variation effects of the hydrocarbons.
The interpretation technique most commonly used is the conventional pressure-depth plots, which sometimes becomes a very complicated task due the difficult to express small pressure variations and when there is no enough density contrast between fluids, especially in the presence of reservoirs containing heavy oil.
For over 10 years, Petrobras has been developing special techniques to highlight small and subtle pressure differences caused by variations in oil composition and permeability barriers. The ratio of static pressures to their true vertical depths plotted against the vertical depth helps to distinguish fluid pressure gradients, thus making it easier the reservoir fluid typing and their contacts definition. This technique is also used in regional studies. The analysis should be preceded by careful planning and quality control of data. The pressure data analysis in combination with other data sources should be evaluated qualitatively and relevant information should be treated statistically in order to provide a sensitivity analysis.
Cretaceous sandstones were investigated regarding the facies description and petrophysical-structural aspects aiming to provide expertise to the analysis and understanding of some anomalies observed in the pressure gradient analysis. Some considerations were made about the oil column composition variations, the presence of effective barriers to vertical flow and connectivity between the reservoirs, and their structural and hydraulic compartmentalization. Different types of aquifers associated with accumulations were also identified.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.