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Oilfield Technology
August
2015
exceed 60%, and tests were conducted for both low (20 mD) and
medium (600 mD) permeability at 500 psi pressures and 150˚C
(302˚F) temperatures. The Baroid team utilised a core sample from
the formation, and the testing indicated the new fluid formulation
should exceed both low and medium permeability targets, with
potential return permeability ranges between 65% (20 mD) and
94% (600 mD).
With the solution verified in the lab, Halliburton personnel
formulated volumes necessary for field application and
preconditioned the mud using Halliburton’s Hydraulic Shearing
unit. The shearing unit is a critical piece of the BaraECD
fluid system, as it helps simulate rig site drilling conditions and
further stabilises the formulation. Preconditioning with the
shearing unit helps ensure that the fluid is ready to drill on arrival
and maintains proper yield points and low shear rheology.
Hydraulic simulations for the new fluid were conducted
with Baroid’s Drilling Fluids Graphics (DFG™) software. The
software allows modelling of multiple operational factors,
including downhole rheology, flow rates, temperatures, rate of
penetration (ROP), and RPM. Using the DrillAhead® Hydraulics
function, the team was able to simulate cuttings loads and ECDs to
identify proper guidelines to reduce risk and keep pressures within
the tight operating window.
With fluid formulation and hydraulic simulations complete,
the operator then applied the BaraECD fluid to drill the 8 ½ in.
reservoir section of the well. The system proved to be extremely
stable and demonstrated efficient hole cleaning, with no signs of
pack off. Pressure‑while‑drilling (PWD) tools were used throughout
the drilling process to verify downhole pressures, and values were
very similar to those predicted in the hydraulic simulations. The
operator was able to drill the reservoir without incurring sag issues
or fluid losses, and reached total depth ahead of schedule. To date,
the operator has extended use of the BaraECD system to at least
three additional wells.
Reducerigtime
In addition to the successful drilling of the reservoir section,
that ‘set the standard’ for this HPHT field, substantial rig time
was saved through being able to run the sand control screens
in the same fluid; at total depth, the fluid was circulated
over 270/325 mesh shaker screens and readily passed the
production screen test (PST). The screens were run to bottom
in the BaraECD fluid without issue. Production rates were at,
or above expectations, despite the BaraECD fluid being left
downhole for up to 30 days. The need to carry out a displacement
to a different screen running fluid (normally an expensive
caesium formate based fluid) was removed, thereby minimising
fluid handling and logistics and saving rig time. Fluid cost savings
alone amounted to around US$5 million per well. The successful
application of this technology has resulted in additional uses with
the same operator and with other operators in other countries in
the North Sea market.
Optimisedrillingperformance
New chemistries and a unique approach to building fluids allow
the BaraECD system to help optimise drilling performance and
provide minimal non‑productive time (NPT). Polymers, surfactants,
and a strict selection of colloidal solids enable low ECD values
with efficient hole cleaning and quickly forming, yet fragile gels.
The reduced rheology of the fluid may allow for increased flow
rates in suitable scenarios. Additionally, every BaraECD system
is pre‑conditioned with the hydraulic shearing unit to provide
consistent and predictable fluid rheology.
Improvesafety
Consistent rheology and sag resistance are critical factors to safe
and effective operations. With inferior fluids, barite settles to the
bottom of the fluid column and essentially creates a gradient of
mud weights downhole. Circulating the lighter fluid at the top
and then the heavier fluid at the bottom can cause dramatic
pressure variations. These events raise the risks of fractures
to the formation, significant fluid losses, hole collapse or even
kicks. High performance fluids with consistent rheology and high
resistance to barite sag are key components for all narrow margin
projects, including offshore, deepwater, and HPHT applications.
The BaraECD system is designed to gel quickly to suspend barite
and other particulates, yet return to target viscosities with very low
shear rates. This helps reduce the risk of pressure spikes, even in
wells with advanced temperature and pressure conditions.
Increaseaccess toreserves
Requirements for narrow margin projects vary significantly across
different regions and fields. A single fluid formulation may not be
suitable for every scenario. The BaraECD fluid system was designed
with a focus on versatility for narrow margin applications. Every
system is customised for each specific well. Base oils, chemical
concentrations, and even weighting agent particle size can be
adjusted. Standard API barite can be used in many instances and
has proven particularly effective in Gulf of Mexico operations. Small
particle size barite can be used in the most technically demanding
situations, as seen in the higher temperature, higher density
North Sea applications. Additionally, the multi‑purpose nature of
the fluid provides an effective substitution for operators that have
historically considered expensive options such as caesium formate
for completions. This versatility allows operators to drill in areas
that have not been historically economical due to NPT, sag, or
downhole losses.
Figure 2.
HalliburtonBaroid’s Hydraulic Shear Unit preconditions the
fluidprior to application.
