Geology Reference
In-Depth Information
Overview
Chapter
1
1.1 Introduction
This topic is about the physical interpretation of
seismic amplitude principally for the purpose of
finding and exploiting hydrocarbons. In appropriate
geological scenarios, interpretations of seismic ampli-
tude can have a significant impact on the
petrophysics and reservoir engineering. The core
aspect of the data integration is rock physics, which
can be defined as the study of
the relationships
between measurements of elastic parameters (made
from surface, well, and laboratory equipment), the
intrinsic properties of rocks (such as mineralogy, por-
osity, pore shapes, pore fluids, pore pressures, permea-
bility, viscosity, and stress sensitivity) and overall rock
architecture (such as laminations and fractures)
'
bottom
'
line
. At all stages in the upstream oil and gas business
techniques based on the analysis of seismic amplitude
are a fundamental component of technical evaluation
and decision making. For example, an understanding
of seismic amplitude signatures can be critical to the
recognition of direct hydrocarbon indicators (DHIs)
in the exploration phase as well as the evaluation of
reservoir connectivity or flood front monitoring in
the field development phase. Given the importance of
seismic amplitude information in prospect evaluation
and risking, all technical disciplines and exploration/
asset managers need to have a familiarity with the
subject.
'
(Sayers
and Chopra,
2009
). Rock physics effectively provides
the rock and fluid parameters for seismic models.
Pennington (
1997
) describes
'
the careful and
purposeful use of rock physics data and theory in the
interpretation of seismic observations
'
and calls this
'
approach
Seismic Petrophysics
. Others commonly
'
'
refer to it simply as
Rock Physics
(sensu lato),
Seismic
'
'
'
Rock Physics
(Wang,
2001
) or Quantitative Interpret-
ation (QI). The mind-set which drives the approach is
not new of course but modern data has provided a new
context. More than ever before there is an opportunity,
paraphrasing Sheriff (
1980
), to
'
reveal the meaning of
'
1.2 Philosophy, definitions and scope
The central philosophy is that the seismic interpreter
working in exploration and appraisal needs to make
physical models to aid the perception of what to look
for and what to expect from seismic amplitude
responses in specific geological settings. This usually
involves the creation of synthetic seismic models for
various rock and fluid scenarios based on available
well log data. In rank exploration areas the uncertain-
ties are generally such that only broad concepts,
assumptions and analogies can be used. By contrast,
in field development settings where data are readily
available, physical modelling can lead to a quantifica-
tion of reservoir properties from seismic (with associ-
ated error bars!).
Fundamental to this process of applying models in
seismic interpretation is the integration of data from a
variety of disciplines including geology, geophysics,
the wiggles
. There are numerous workers, past and
present, to whom the authors are indebted and whose
names occur frequently in the following pages.
The topic describes the theory of seismic reflectiv-
ity (
Chapter 2
) and addresses the key issues that
underpin a seismic interpretation such as phase,
polarity and seismic to well ties (
Chapters 3
and
4
).
On these foundations are built a view of how contrasts
in rock properties give rise to variations in seismic
reflectivity (
Chapter 5
). Seismic data quality is an all
important issue, controlling to a large extent the con-
fidence in an interpretation, and this is addressed,
from an interpreter
'
s perspective, in
Chapter 6
.
Examples of fluid and rock interpretations using
Amplitude Versus Offset (AVO) techniques are pre-
sented in
Chapter 7
for a variety of geological contexts.
The key rock physics components that drive seismic
models are documented in
Chapter 8
, whilst
'
1
the
