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Oilfield Technology
August
2015
which helps reduce spikes throughout drilling and improves
ECD management.
These systems have been enhanced over the years with new
chemistries and alternate weighting agents. Micronised barite has
also been used in the industry for the most technically challenging
wells. The small particle size of the weighting agent allows for even
lower ECD values necessary for deepwater and HPHT applications.
Though effective at achieving low ECD values, micronised solutions
are not without their drawbacks. Past micronised barite systems
have struggled at times with inefficient hole cleaning and risk
of formation damage, and often were not suitable for use in
the reservoir. This forced some operators to avoid micronised
systems for the reservoir and instead use limited and expensive
options such as cesium formate brines for the completions stage.
Caesium formate excels in narrow margin completions due to its
inherent density and temperature stability.
Halliburton Baroid has taken on the challenge of delivering
a drilling fluid system for narrow margin applications that
provides all the performance benefits of an organophilic
clay-free invert emulsion system, yet has the versatility to handle
HPHT environments and is safe for use in the reservoir. The newly
formulated and globally available BaraECD® fluid system has now
proven its effectiveness in wells in the North Sea, functioning
effectively as a dual-purpose drilling and completion fluid.
NorthSeaapplication
A major operator was drilling an offshore well with a planned
4239 m total vertical depth (TVD) and 4850 m measured depth (MD).
Bottom hole temperatures were estimated at 135˚C (275˚F), and
the operator had experienced sag issues with its previous fluid
solution. The risk of formation damage was a significant concern.
The operator was looking for a fluid with a target of 1.96 sg density
with minimal sag (< 0.15 delta sg, 160˚C, 5-day static sag test) to
drill the 8 ½ in. reservoir section of the well without incurring the
significant cost of utilising caesium formate. Additional operational
issues including wellbore instability were also anticipated with a
caesium formate based fluid.
Halliburton Baroid leveraged the BaraECD fluid system that
has been proven in multiple deepwater and narrow margin wells
in the Gulf of Mexico. However, since the North Sea project had
higher bottomhole temperatures and even tighter ECD windows
than previous Gulf of Mexico projects, the fluid system needed to
be adjusted to accommodate new requirements. A combination of
new emulsifiers, suspension agents, and small particle sized barite
were added to the solution, and an extensive lab-testing phase was
conducted prior to application.
Test procedures were outlined to verify sag stability,
low rheology/low ECD profiles, and completion compatibility.
Both static and dynamic sag properties were tested. Static sag was
within the 0.15 delta sg requirement, and dynamic sag performed
significantly better than the 0.07 sg viscometer sag shoe test (VSST)
and 3 mm/hr dynamic high angle sag test (DHAST) targets. Low
rheology profiles were tested with a FANN 35 rheometer and were
required to fall below a dial reading of 30 at 100 rpm after 16 hours
of hot rolling at 150˚C (302˚F). Testing indicated that the fluid
performed well within the baseline requirements, consistently
demonstrating rheology values below a 24 dial reading at 100 rpm
on the FANN 35 unit. The goal for return permeability was to
Figure 1.
HalliburtonBaroid technicians conductmultiple tests on fluid systems before finalising solutions.
