Geoscience Reference
In-Depth Information
1000
100
10
1
0.1
0.01
0.000001
0.0001
0.01
1
100
10000
Permeability (mD)
Fig. 6.49 Capillary threshold pressure
versus permeability from a compiled dataset of fault-rock
samples ( solid symbols ) and unfaulted rock samples
( crosses and open symbols ) from Manzocchi et al. ( 2002 )
and T. Manzocchi (pers. comm.). The two lines are
published model relationships for unfaulted rocks ( black
line , Ringrose et al. 1993) and faulted rocks ( red line ,
Harper and Lundin 1997 ). For sources of datasets see
Manzocchi et al. ( 2002 ). Data have been normalized for a
moderately water-wet oil-water system (Redrawn from
Manzocchi et al. 2002 , Petroleum Geoscience, v. 8 #
Geological Society of London [2002])
Wherever faults are important in reservoir
modelling studies, considerable efforts are
needed to measure fault rock properties (e.g.
Sperrevik et al. 2002 ). Figure 6.49 shows a com-
piled set of measured values for P CT as a function
of permeability. Despite some spread in the data,
general empirical transforms between permeabil-
ity and capillary threshold pressure can be
established. The trends for faulted and un-faulted
rock samples are broadly similar, although low-
permeability clay-rich fault rocks tend to have
significantly higher P CT .
In order to represent the effects of faults in
reservoir flow simulation models, there are sev-
eral options:
1. Represent the fault as a transmissibility multi-
plier on the simulation cell boundary which
coincides with the fault plane (no multi-phase
effects included);
2. Represent the fault as a two-phase flow trans-
missibility multiplier on the simulation cell
boundary which coincides with the fault plane;
3. Represent the fault explicitly as a volume,
using grid cells within the fault zone and
adjacent to the fault zone or damage zone
(with multi-phase effects included).
The third option allows detailed analysis of
the effects of faults on flow, but is rarely used
because it may be computationally demanding.
The use of simple transmissibility multipliers
allows for more efficient reservoir simulations,
but neglects potentially important multi-phase
flow effects. Manzocchi et al. ( 2002 ) proposed
a versatile approach for inclusion of two-phase
transmissibility multipliers to represent faults
in reservoir simulation studies, allowing more
structural geological detail to be included in
reservoir models (e.g. Brandsæter et al. 2001b ;
Manzocchi et al. 2008a , b ).
6.7.1.6 Open Damage Zones
The discussion above concerns situations in
which low density fracture systems tend to seal
or at least reduce permeability across the fault
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