Geoscience Reference
In-Depth Information
Fig. 6.54
Two joint sets abutting in a sandstone layer (view
down
on to the layer
top
)
A typical uncertainty list
for handling
structural model? Better to test the well
placement strategy against a range of models
to ensure some degree of robustness.
fault-related factors would be:
1.
How many faults
? Scenarios might include (a)
all seismically-mapped faults, (b) uncertain
faults evident from seismic coherence
analysis, edge-detection or curvature analysis,
(c) sub-seismic faults generated from struc-
tural deformation models.
2.
Fault displacement uncertainty
. Using maxi-
mum fault displacements observed from seis-
mic data with a range of
6.7.2 High Density Fractured
Reservoirs (Joint-Dominated)
6.7.2.1 Terminology
Joints are extensional fractures, formed when
rocks enter tensile space (the left-hand side of
the Mohr diagram) under a deviatoric stress in
excess of the tensile rock strength. They tend to
form regularly-spaced fractures (Fig.
6.54
) often
in more than one set, with sets mutually abutting.
Lateral displacement on joints is minimal,
although not necessarily zero as once a tensile
fracture has formed there may be millions of
years of isostatic activity to follow during
which some movement on any open fracture is
inevitable.
The properties of joint sets are influenced
strongly by the mechanical properties of the
5to
10 m to
reflect interpretation uncertainties.
3.
Fault seal uncertainty
. Testing fully-sealed
versus open fault scenarios, using a shale
gouge ratio (SGR) method linked to displace-
ment uncertainties, or using a range of
measured fault-seal values.
4.
Development scenario uncertainty
. Well
placement strategy is usually closely linked
to the overall structural model (bounding
faults and internal fault compartments). Why
allow the whole field development strategy to
depend entirely on an uncertain base-case
