Exploration Insights November 2019 | Page 36

Exploration Handbook | 37
the impact of these uncertainties is considerable. Without prior
knowledge, a range of appropriate or inappropriate models can
be derived from equivocal data. The impact of such conceptual
uncertainties has the potential to be as great as those associated
with the positioning of features in the seismic data, itself.
PRACTICALITIES AND FUTURE TRENDS
© 2019 Halliburton
Figure 6> Interpreted seismic line showing the varied seismic facies and systems tracts in syn and post-rift parts of the section. Image
derived from Richardson (2017).
The continuity of reflectors can also be affected by seismic data quality and it is a skill of the interpreter to
differentiate real signals from noise. During interpretation of a grid of seismic data, care also needs to be taken
to ensure selected reflectors tie at their point of intersection. Furthermore, during analysis, the interpreter
needs to be self-critical and aware of the uncertainties and assumptions used in the processing of seismic data.
The detail required during seismic interpretation reflects the position in the lifecycle of the asset. In the
early stages of exploration, it is normally sufficient to identify the main faults, prominent reflections, and
unconformities in a 2D section to help to delimit the basin-filling packages (Bertram and Milton, 1996).
These data provide insights into the tectonostratigraphic evolution of a basin and factors that may influence
subsidence and deposition. They also provide input into models for trap densities to be used in yet-to-find
calculations. Initial depth models constructed from the seismic are then used to map the effective limit of
reservoirs and migration directions from mature source rocks when combined within burial models. Seal
risk may also be recognized where leaking hydrocarbons are noted in the form of gas chimneys. Other
seismically derived indicators of hydrocarbons include flat-spots in potential traps. These can represent oil-
water contacts. Once a prospect has been ranked and selected, 3D seismic facilitate more detailed mapping
of reservoirs and structures, and an assessment of the volume of hydrocarbon-filled rock to be carried out.
SEISMIC STRATIGRAPHY
The main principle of seismic stratigraphy is that seismic reflectors follow bedding and represent time lines
(Bertram and Milton, 1996). When seismic data have sufficient resolution, seismic facies interpretation is
possible. Seismic facies are characterized by the configuration of reflectors, their continuity, amplitude,
frequency, internal velocity, and form (Mitchum et al., 1977). The configuration of reflections also allows
penecontemporaneous deformation to be recognized. Due to the form of some seismic facies, the
geomorphology of depositional systems can be assessed (Pummard et al., 2019). In long regional transects,
groups of seismic facies are arranged into sets bounded by unconformities or their correlative conformities.
These seismic sequences incorporate a range of depositional environments that define a systems tract
(Figure 6). The identification of these sequences is the basis for sequence stratigraphic interpretation,
discussed in the June edition of the Exploration Handbook (Davies, 2019).
INTERPRETATIVE UNCERTAINTY AND MODEL BIAS
Conceptual uncertainties are common in seismic interpretation and result from the scale, extent, and
resolution of data, and the range of experiences of the interpreter (Bond et al., 2007). During interpretation,
Due to the importance of seismic, the development of seismic
technologies continues at pace. These developments impact
acquisition through to the interpretation and visualization of data.
For example, drones can be used to deploy geophones to create
cost efficiencies. During interpretation, data science and machine
learning techniques can be used to enhance interpretation by
automating the population of faults, picking all of the reflectors in
the data, identifying seismic facies, and/or interpreting rock or fluid
properties. These developments will maximize our utilization of
seismic data.
REFERENCES
Ashcroft, W. 2011. A Petroleum Geologist’s Guide to Seismic Reflection. Wiley, 1-157
p. (XURBB_469891).
Bertram, G.T. and N.J. Milton 1996. Seismic Stratigraphy. In Emery, D. and K. Myers
(Eds.), Sequence Stratigraphy, p. 45-60. (XURBB_642014).
Bond, C.E., A.D. Gibbs, Z.K. Shipton and S. Jones 2007. What do you think this is?
“Conceptual uncertainty” in geoscience interpretation. GSA Today, v. 17, no. 11, p.
4-10. (XURBB_627560).
Davies, A. 2019. Sequence Stratigraphy in Exploration. Exploration Insights Magazine.
Exploration Insights Magazine no. June, p. 22-28. (XURBB_641393).
Gluyas, J. and R. Swarbrick 2004. Petroleum Geoscience. Blackwell Publishing Ltd
(Wiley-Blackwell), 1-359 p. (GURBB_234804).
McQuillin, R., M. Bacon and W. Barclay 1984. An Introduction to Seismic
interpretation: Reflection Seismics in Petroleum Exploration. Graham & Trotman, 1-287
p. (GURBB_156843).
Mitchum, R.M., P.R. Vail and J.B. Sangree 1977. Seismic stratigraphy and global
changes of sea level, part 6: stratigraphic interpretation of seismic reflection patterns
in depositional sequences. In C.E. Payton (Eds.), Seismic stratigraphy - applications to
hydrocarbon exploration. AAPG Memoir no. 26, p. 117-133. (MEBIB18645).
Paumard, V., J. Bourget, T. Payenberg, A.D. George, R.B. Ainsworth and S. Lang
2019. From quantitative 3D seismic stratigraphy to sequence stratigraphy: Insights
into the vertical and lateral variability of shelf-margin depositional systems at
different stratigraphic orders. Marine and Petroleum Geology, v. 110, p. 797-831.
(XURBB_642015).
Richardson, P. 2017. The Roebuck Basin — Searching for a Potential Viable Petroleum
System in an Underachieving Basin. In Neftex Exploration Insights Magazine.
Exploration Insights Magazine no. August. Exploration Insights. (XURBB_634459).
Sutcliffe, O.E. 2019. Well Data: Interpretation and Correlation in Exploration.
Exploration Insights Magazine, v. July, p. 24-32. (XURBB_642016).
AUTHOR
Dr. Owen E. Sutcliffe, Head of Global Geology and Geophysical Practices,
Halliburton Landmark.
Owen started his career as a postdoctoral research assistant with the
University of Wales, Aberystwyth, and LASMO. In 2000, he joined
Badley Ashton and Associates before his employment began at Neftex
Petroleum Consultants in 2003. Since the acquisition of Neftex by Halliburton in 2014,
he has held roles as Head of Stratigraphy and as Manager of Neftex Insights. Owen is
a member of The Geological Society, London and the PESGB.
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