Geoscience Reference
In-Depth Information
Fig. 1.4
Example planned well trajectory with an expected fault, base reservoir surface and well path targets
Having designed the well path it can be useful
to monitor the actual well path (real-time
updates) by incrementally reading in the well
deviation file to follow the progress of the
'actual' well vs. the 'planned' well, including
uncertainty ranges. Using visualisation, it is eas-
ier to understand surprises as they occur, particu-
larly during geosteering (e.g. Fig.
1.4
).
model varies according to the QI process being
followed - this needs to be discussed with the
geophysicist.
In the example shown here (Fig.
1.6
), a reser-
voir model (top) has been passed through to the
simulation stage to predict the acoustic imped-
ance change to be expected on a 4D seismic
survey (middle). The actual time-lapse (4D)
image from seismic (bottom) is then compared
to the synthetic acoustic impedance change, and
the simulation is history matched to achieve a fit.
If input to geophysical analysis is the key
issue, the focus of the model design shifts to the
properties relevant to geophysical modelling,
notably models of velocity and density changes.
There is, in this case, no need to pursue the
intricacies of high resolution permeability archi-
tecture, and simpler (coarser) model designs may
therefore be appropriate.
1.6
Models for Seismic Modelling
Over the last few decades, geophysical imaging
has led to great improvements in reservoir
characterisation - better seismic imaging allows
us to 'see' progressively more of the subsurface.
However, an image based on sonic wave
reflections is never 'the real thing' and requires
translation into rock and fluid properties. Geo-
logical reservoir models are therefore vital as
a
priori
input to quantitative interpretation (QI)
seismic studies.
This may be as simple as providing the
layering framework for routine seismic inver-
sion, or as complex as using Bayesian probabi-
listic rock and fluid prediction to merge seismic
and well data. The nature of the required input
1.7
Models for IOR
Efforts to extract maximum possible volumes
from oil and gas reservoirs usually fall under
the banner of Improved Oil Recovery (IOR) or
Enhanced Oil recovery (EOR). IOR tends to
