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Using gilsonite as a fluid loss control additive
10 August 2005
We are drilling Forties reservoir in the Montrose field using oil
base mud and are reviewing the pro's and con's of using gilsonite as
a fluid loss control additive. A liner will be cemented and
perforated after drilling is competed. Our understanding is that a
number of operators in the North Sea are specifying gilsonite-free
mud for drilling reservoir intervals and we would like to gain an
understanding of the reasons behind such requirements to help inform
our decision making. Any input from SPREAD members would be
greatfully received.
2 answer(s)
Managing Director (
Relentless Pursuit Of Perfection Ltd.
Total Posts: 413
Join Date: 10/01/05
Bill Gilsonites are very cost effective fluid loss control agents
for OBM compared to the alternatives. They have one undesirable
characteristic however, which is that they soften at temperature.
This turns them into something similar to an asphaltene which has
obvious implications for permeability to oil when it´s an open hole
completion. Core tests at temperature (>250degF) have confirmed this
behavior and as a result a few operators have been keen to stay away
from them, considering them ”œformation damaging” in nature and
effectively banning them. In the case of cemented liners this is not
justified however as the mud removal of the cement and the
perforation tunnels effectively bypass any damage. But as you might
be aware the difference between cemented and open hole completions
is not well understood by a lot of people (sometimes you might be
telling them their job) and we just supply what´s asked for. In M-I
we generally use the amine treated lignite (trade name is VENCHEM)
and rubber based polymer alternatives (MI trade name ECOTROL). Most
of our mud stock is used by customers who specify no gilsonite at
all so it would not make sense to mix. Numerous core flood tests
have confirmed that neither are damaging as long as the bridging
solids do not form an internal filter cake. Another weird spin on
this debate is that one ”œmajor” operator has misinterpreted core
tests and come to the conclusion that the polymer based agent is
damaging when in fact they have already used it 10 years ago in an
open hole completion on their best producing HTHP well! For BP we
have been using the polymer agent almost exclusively, on the plus
side it is effective at small doses and dissolves in crude
containing aromatics (potentially neutral or better return open hole
perm). On the negative side however it increases the rheology. I
introduced the lignite agent on A17 when they were getting
differential sticking, as a means of tightening the fluid loss
without affecting the rheology and the mud engineers recommended to
continue with it. The mud designed for the LCD project and tested in
Sunbury contained both lignite and polymer product and we used both
agents on the 2 wells. Based on the production of the first well I
don´t think there is any mud related skin issue. In summary I would
not use Gilsonite in a mud to drill an open hole completion and
depending on the views of your completion / production department
not in the reservoir at all. Just to give you the opposite side of
the tracks, we use Gilsonite for Apache as it produces a cost
effective, stable formulation which requires minimal treatment while
drilling. They drill their open hole reservoir sections with water
based mud. Regards Bob
Managing Director -Relentless Pursuit of Perfection Ltd.
Relentless Pursuit Of Perfection Ltd.
Total Posts: 25
Join Date: 10/01/05
Bill, I personally don't have any experience in this area but have
forwarded your email to colleagues at BP and Apache. Will let you
know if anything crops up. Best wishes Dave Taylor
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