The Role of 4-D
Seismic
Interpretation
and Dynamic
Modeling in the Successful Drilling of a Late Stage Development Well in the
West Brae Field, North Sea, UK
Bacciotti, Florence 1; D'Amore, Karine 1;
Seguin, Julien 1
(1)Subsurface, Marathon Oil UK Ltd, Aberdeen,
United Kingdom.
West Brae is a Paleocene turbidite field composed of two
reservoirs: the Balder and the Flugga sandstones. Production started in 1997. A
4D seismic
volume was generated over the field (using 1993 baseline and 2007
monitor surveys) to aid the identification of potential late stage development
targets.
In the Flugga reservoir, the main 4D response is due to a water
rise caused by the producing wells. In the northwest area of the field, the 4D seismic
did not exhibit a water response despite the presence of a production well
since 2005. A water cone developed at the heel of the well but not at the toe,
although the reservoir properties remain equally good along the well path. To
the west of this area, a linear 4D water response feature is present along the
edge of the reservoir. These observations indicate the potential presence of a
compartment that is inefficiently swept or un-drained. A pilot hole drilled in
2005 in the northwest also showed that the oil-water contact had not risen
here, despite 8 years of production.
The integration of all the data
into the dynamic model during the
history matching process implied that extensive, but sub-
seismic
barriers
(faults, shales or both) are necessary to produce an effective baffle to fluid
flow and pressure transmission. Numerous iterations were carried out to
determine which geometries best reproduced the observed 4D signal while also
honoring the production and pressure
data
. The base case model incorporates a
shale barrier in the form of an anticline. In this model, all Flugga producers
are located above the anticline whereas the 2005 pilot penetrates the
compartment below the barrier. The barrier therefore protects the area without
a 4D water response from being swept by the producers. The linear feature
results from an edge drive mechanism induced by the producing wells as water
overrides the shale barrier.
Integration of 4D seismic
interpretation
and multiple alternative
history-matched dynamic models led to the definition of an economic infill
target in the compartment shown to be un-swept. A pilot well and an oil
producer were successfully drilled at the end of 2010. Both wells confirmed the
model of water overriding a shale barrier and the presence of an un-swept
compartment underneath.
The 4D seismic
has been a key tool for West Brae reservoir
management. Integration of the 4D
data
changed how the reservoir was viewed and
aided identification of a target that would not have been drilled otherwise.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.