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Paper Number 74541-MS DOI What's this?10.2118/74541-MS
TitleDrilling HT/HP WellsUsing a Cesium Formate Based Drilling
Fluid AuthorsArild Saasen, Ole Henrik Jordal,
Statoil ASA; David Burkhead, Conoco Inc.; Per Cato Berg, Geir
Lklingholm, Erik SandtorvPedersen, Statoil ASA; Jim Turner, Michael
J. Harris, Cabot Speciality Fluids Source
IADC/SPE Drilling Conference, 26-28 February 2002, Dallas,
Texas
CopyrightCopyright 2002, IADC/SPE Drilling Conference
LanguageEnglish Preview
Abstract
During the drilling and completion of the Huldra field in the
North Sea, high temperature andhigh pressure conditions were
expected and encountered in the reservoir section. Thedifference
between the pore pressure and the fracturing pressure is small.
Cesium formate had
been evaluated as a potential drilling and completion fluid, but
technical hurdles could not becompletely addressed in time for the
first well. As a result of well control problems occurringin the
first well, with barite sag in the oil based drilling fluid as a
contributing factor, it wasnecessary to use a drilling fluid with
insignificant potential for sag. For the first time
worldwide the cesium formate brine was chosen as a drilling
fluid. This fluid could bedelivered solids free with densities up
to 2.2 s.g. The required down hole density in the wellwas 1.91 s.g.
At the same time it was necessary to have as little contribution to
the equivalentcirculating density (ECD) from the flow as
possible.
The paper describes how the cesium formate brine was used
successfully as a drilling andcompletion fluid. The effect of the
fluid on well control, hole cleaning, rate of penetration(ROP),
torque/friction, ECD, formation damage, casing wear and hole
stability are covered.The paper also describes actions required to
minimize losses of this very expensive fluid. Thechallenges
acquiring adequate formations logs while drilling are also
described. Finally, theuse of cesium formate brine during the
completing of the wells with open hole sand screens is
outlined.
Introduction
Huldra is a gas condensate field stretching from block 30/2 into
block 30/3 in the Norwegiansector of the North Sea, operated by
Statoil ASA. High temperature and high pressureconditions were
expected and encountered in the reservoir sections in this field.
Threeexploration wells were drilled on the field from 1979 to 1991,
which proved gas andcondensate.
A jackup rig in cantilever mode over a well head platform is
being used to drill and completethe planned wells. The production
platform will become unmanned after the last well is
drilled. The water depth is 125 m.
A severe well kick was experienced during the completion of the
first well. Barite sag in theoil based drilling fluid combined with
well geometry were significant factors contributing tothe well
kick. Additionally, the barite sagging problems increased the level
of concern withregards to screen plugging. For these reasons, the
ongoing qualification work on the formate
brines intensified.
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Based on prior industry experience with formate drilling and
completion fluids, and withvarious tests, it was then concluded
that cesium/potassium formate was the preferred drilling
and completion fluid.
Experience with formate brines
Use of potassium formate based fluids for drilling and
completion operations were introducedin the very early 1990's
1,2. These fluids were considered to have insignificant impact
on the
environment if discharged3. The maximum density for solids free
potassium formate isapproximately 1.59 s.g. Barite cannot be used
for further densification because it dissolvesslightly in
formates4.
Potassium formate was used both as a reservoir drilling and as a
completion fluid in the
Gullfaks field in Norway in the early 1990's5. Because it was
necessary to use a drill-in fluid
with a higher density than 1.59, manganese oxide was added as a
densifying agent. During
the completion the density was reduced to 1,57 s.g. No addition
of solids was necessary. Thewhole drilling and completion operation
is considered as a success.
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