| dc.description | The determination of producing intervals and oil quality
in a reservoir requires the study of different geochemical
parameters. In particular, oil quality reflects the
compositional characteristics of hydrocarbons that
impact the economic viability of an exploration,
development, or production opportunity. In general, oil
quality may affect the direct economic value of the crude
oil. Typical oil-quality properties include API gravity,
viscosity, sulfur, asphaltene, and metals (e.g., vanadium,
nickel) contents, and acidity. Biodegradation can
significantly impact essentially all oil-quality properties of
crude oils in producing zones. More specifically, oil
biodegradation typically (a) decreases API gravity, (b)
reduces the content of saturated and aromatic
hydrocarbons relative to polar compounds (c) increases
oil viscosity, (d) increases oil acidity and (e) increases
the sulfur content and the concentration of certain metals
(e.g., V and Ni). As a consequence, the residual oil
resulting from biodegradation becomes enriched in NSO
compounds (resin and asphaltene fractions), sulfur and
metals (Connan, 1984; Wenger et al., 2002; Larter et al.,
2006). Knowledge of the lateral and vertical variations in
the oil-quality properties as a consequence of
biodegradation is an important key to the development
and implementation of enhanced oil recovery methods.
Venezuela has one of the world’s largest reserves of
heavy and extra heavy biodegraded crude oils in the
Eastern Venezuelan Basin, which includes the widely
studied Orinoco Oil Belt and the Socororo Major Area in
the Maturin sub-basin. The Socororo field, and in
particular the ES-SOC oil well, in the Socororo Major
Area is the subject of this study. Here, we describe the
vertical variability in the extractable organic matter
(EOM) of sidewall core samples and oil composition.
The latter was correlated to the characteristics of the
source rock (e.g., lithology, organic-matter input, redox
depositional conditions, and thermal maturity) in order to
establish oil quality as a consequence of biodegradation. | |
