ABSTRACT: Structural
Interpretation
in the Upstream Petroleum Industry: Application of Global
Experience and Key Technologies
ANDO, CLIFFORD J. , ExxonMobil Exploration Company, Houston, Texas
The
fundamental goal of structural
analysis in the petroleum industry is to develop
a 3-D geometrically and kinematically consistent
interpretation
honoring all
data, which can be used to evaluate all aspects of the hydrocarbon system that
have been influenced by
structural
history. Those aspects can include trap,
seal, source rock distribution, maturation, secondary migration, and reservoir
distribution.
Structural
interpretation
is conducted at a wide range of scales
between regional and prospect, with large variations in data quality and
availability. Where seismic data quality is high, advanced volume and surface
interpretation
technologies can provide detailed, confident
structural
interpretations. However, where data are sparse or of lower quality, the
interpretations will be more model-based. In all cases, the
interpretation
process must be underpinned by the sound application of fundamental geological
and physical principles.
Two decades ago,
traditional, descriptive, analog-based structural
styles analysis began to give
way to a more quantitative approach using cross section balancing and kinematic
modeling. These techniques are used to validate interpretations and test the
range of admissable alternatives, and remain an important part of the toolkit.
More recent advancements in subsurface technology, including high quality 3-D
seismic data, and tools such as discontinuity volumes, horizon slices, and
surface visualization techniques allow us to address technical uncertainties and
risk with
structural
analysis in ways not done before. In areas with
high-quality seismic data, the tasks of identifying
structural
style and
defining the gross trap container are made easier than ever before, with
emphasis shifting from mapping the trap container toward evaluating trap
integrity by mapping fault networks and their interaction with the
stratigraphic
framework. Mapping the fault network and understanding
stratigraphic
variations
in faulted traps is essential for predicting reservoir and seal juxtaposition
relationships, and the likelihood of compartmentalization. In areas with complex
traps and poor seismic imaging, it is especially important that all available
data are incorporated to support the
structural
interpretation
. Many diverse
data types must be integrated to address the inherent risks associated with
structural
complexity. In these cases, the non-unique nature of
structural
interpretations necessitates special consideration of the full range of
admissable alternatives.
The structural
interpretation
, at global, regional, and trap scales, impacts a wide range of
derivative analyses, and must be accurate and consistent enough to meet the
business need at hand. Studies of sedimentation patterns, heat flow, fluid flow,
and seal integrity depend upon a rigorous
structural
interpretation
. In
addition, a consistent fault framework should be carried through the various
technical stages of hydrocarbon column prediction, prospect assessment, geologic
modeling, and reservoir simulation. Despite advances in seismic imaging,
complexities and imageability of faults at the trap scale continue to dominate
uncertainty in maps, and complicate predictions of reservoir performance during
planning for development and production. Key learnings in those areas, for
example improved understanding of how fault architecture controls reservoir
segmentation, are leading to more rigorous, realistic treatment of faults in
geologic models and reservoir simulations. In regional analysis, experience in
complex basins, such as those with linked
structural
/depositional histories and
mobile salt or shale substrates, has led to a clearer understanding of controls
on hydrocarbon play elements. In these types of basins, the interplay between
structural
evolution and sediment dispersal has a profound effect on trap
formation, reservoir distribution, and hydrocarbon migration. Regional
structural
analysis, when integrated with other core technical pursuits,
provides a powerful means to identify and pursue viable hydrocarbon plays.
Effective structural
interpretation
on a global basis requires considerable effort. A potential
strength for companies with worldwide activities is the utilization of
cumulative learning from basins with similar
structural
styles; this also
represents a substantial challenge. In an effort to optimize the use of global
experience and application of core technologies, ExxonMobil has created and
disseminated best practices for certain key technical areas. Such an approach
for
structural
interpretation
integrates workflows for
structural
trap and seal
analysis, spanning the business cycle from regional/play analysis to mature
field production. Thorough execution of basics, application of global
experience, and attention to the range of alternative interpretations can
support confident business decisions in areas with significant technical
hurdles.
AAPG Search and Discovery Article #90916@2001-2002 AAPG Distinguished Lectures