Chapter 18
Explorational Rock Physics: The Link between Geological
Processes and Geophysical Observables
Per Avseth
The field of rock physics represents the link between
qualitative geological parameters and quantitative
geophysical measurements. Increasingly over the last
decade, rock physics has become an integral part of
quantitative seismic interpretation and stands out as a
key technology in petroleum geophysics. Ultimately,
the application of rock physics tools can reduce exploration risk and improve reservoir forecasting in the
petroleum industry.
This chapter covers basic rock physics principles and
practical recipes that can be applied in the field. The
importance and benefit of linking rock physics to geological processes, including depositional and compactional trends, is demonstrated. It is further documented
that lithology substitution can be of equal importance to
fluid substitution during seismic reservoir prediction. It
is essential in exploration and appraisal to be able to
extrapolate away from existing wells, taking into
account how the depositional environment changes,
together with burial depth trends. In this way rock
physics can better constrain the geophysical inversion
and classification problem in underexplored marginal
fields, surrounding satellite areas, or in new frontiers.
Finally, practical examples and case studies are presented to demonstrate a best-practice workflow and
associated limitations and pitfalls. Rock physics models
are combined with well log and pre-stack seismic data,
sedimentological information, inputs from basin modelling and statistical techniques, to predict reservoir
geology and fluids from seismic amplitudes.
18.1 Quantitative Seismic Interpretation
Using Rock Physics
The main goal of conventional, qualitative seismic
interpretation is to recognise and map geological elements and/or stratigraphic patterns from seismic reflection data. Often hydrocarbon prospects have been
defined and drilled entirely on the basis of this qualitative information. Today, however, quantitative seismic
interpretation techniques have become common oil
industry tools for prospect evaluation and reservoir
characterisation. The most important of these techniques include post-stack amplitude analysis (bright-spot
and dim-spot analysis), offset-dependent amplitude
analysis (AVO analysis), acoustic and elastic impedance inversion, and forward seismic modelling. These
techniques seek to extract additional information about
the subsurface rocks and their pore fluids from the
reflection amplitudes and, if used properly, they open
up new doors for the seismic interpreter. Seismic amplitudes primarily represent contrasts in elastic properties
between individual layers and contain information
about lithology, porosity, pore fluid type and saturation,
as well as pore pressure – information that cannot be
gained from conventional seismic interpretation. Seismic amplitude maps are increasingly important in prospect evaluation and reservoir delineation. As shown in
Fig. 18.1, the amplitude patterns often provide a good
insight into depositional patterns. Seismic amplitude
maps can be very useful in the delineation of subtle
traps that are not easily revealed from conventional (i.e.
stratigraphic and structural) seismic interpretation.
However, to make sure we understand the meaning
of the seismic amplitudes, a quantitative link is needed
between the geological parameters and the rock
Per Avseth (*)
Tullow Oil Norge, Oslo, Norway
NTNU, Trondheim, Norway
e-mail: per.avseth@tullowoil.com
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_18, # Springer-Verlag Berlin Heidelberg 2015
455
Explorational Rock Physics: The Link between Geological
Processes and Geophysical Observables
Per Avseth
The field of rock physics represents the link between
qualitative geological parameters and quantitative
geophysical measurements. Increasingly over the last
decade, rock physics has become an integral part of
quantitative seismic interpretation and stands out as a
key technology in petroleum geophysics. Ultimately,
the application of rock physics tools can reduce exploration risk and improve reservoir forecasting in the
petroleum industry.
This chapter covers basic rock physics principles and
practical recipes that can be applied in the field. The
importance and benefit of linking rock physics to geological processes, including depositional and compactional trends, is demonstrated. It is further documented
that lithology substitution can be of equal importance to
fluid substitution during seismic reservoir prediction. It
is essential in exploration and appraisal to be able to
extrapolate away from existing wells, taking into
account how the depositional environment changes,
together with burial depth trends. In this way rock
physics can better constrain the geophysical inversion
and classification problem in underexplored marginal
fields, surrounding satellite areas, or in new frontiers.
Finally, practical examples and case studies are presented to demonstrate a best-practice workflow and
associated limitations and pitfalls. Rock physics models
are combined with well log and pre-stack seismic data,
sedimentological information, inputs from basin modelling and statistical techniques, to predict reservoir
geology and fluids from seismic amplitudes.
18.1 Quantitative Seismic Interpretation
Using Rock Physics
The main goal of conventional, qualitative seismic
interpretation is to recognise and map geological elements and/or stratigraphic patterns from seismic reflection data. Often hydrocarbon prospects have been
defined and drilled entirely on the basis of this qualitative information. Today, however, quantitative seismic
interpretation techniques have become common oil
industry tools for prospect evaluation and reservoir
characterisation. The most important of these techniques include post-stack amplitude analysis (bright-spot
and dim-spot analysis), offset-dependent amplitude
analysis (AVO analysis), acoustic and elastic impedance inversion, and forward seismic modelling. These
techniques seek to extract additional information about
the subsurface rocks and their pore fluids from the
reflection amplitudes and, if used properly, they open
up new doors for the seismic interpreter. Seismic amplitudes primarily represent contrasts in elastic properties
between individual layers and contain information
about lithology, porosity, pore fluid type and saturation,
as well as pore pressure – information that cannot be
gained from conventional seismic interpretation. Seismic amplitude maps are increasingly important in prospect evaluation and reservoir delineation. As shown in
Fig. 18.1, the amplitude patterns often provide a good
insight into depositional patterns. Seismic amplitude
maps can be very useful in the delineation of subtle
traps that are not easily revealed from conventional (i.e.
stratigraphic and structural) seismic interpretation.
However, to make sure we understand the meaning
of the seismic amplitudes, a quantitative link is needed
between the geological parameters and the rock
Per Avseth (*)
Tullow Oil Norge, Oslo, Norway
NTNU, Trondheim, Norway
e-mail: per.avseth@tullowoil.com
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_18, # Springer-Verlag Berlin Heidelberg 2015
455