CASE STUDY
Integrated Drilling Fluid System Helps Complete
3,000-ft Shale Interval 9 Days Ahead of Plan
High-performance fluid system, sealing additive, and simulation software enable
meeting objectives with no fluid-related NPT, stuck pipe, or bit balling, UAE
CHALLENGE
Drill long interval through troublesome shale sections
Drill through heterogeneous, highly laminated
shale sections in the Laffan and Nahr Umr
Formations in a field offshore Abu Dhabi.
An operator planned to drill the 17½-in interval of its directional well through the Laffan and Nahr Umr
Formations offshore Abu Dhabi. The formations include challenging shale sections that exhibit high
heterogeneity and lamination, which pose the risks of wellbore breakout and instability. Because of rig
limitations and zero-discharge regulations, the use of nonaqueous fluid was not an option.
SOLUTION
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Customize a mix of field-proven
ULTRADRIL* high-performance water-base
drilling fluid system and POROSEAL*
copolymeric filtration-control
sealing additive.
Optimize drilling parameters and improve hole
cleaning efficiency by running simulations
in VIRTUAL HYDRAULICS* drilling fluid
simulation software during the planning
and execution phase.
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The ULTRADRIL system was selected because of its previously demonstrated success in the field.
The system comprises three primary components designed to deliver excellent inhibition.
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ULTRAHIB* shale inhibitor is a polyamine that inhibits swelling and migration by reducing the
tendency of clay to bond with water within an aqueous environment. The inhibitor works by
chemically bonding to reactive sites within clay structures, then drawing them tightly together so
that water molecules cannot penetrate the spaces between the clay particles.
ULTRAFREE* ROP-enhancing surfactant coats cuttings and metal surfaces, effectively reducing
the sticking tendencies of hydrated solids. This surfactant heads off costly gumbo buildup on bits,
BHAs, drillpipe, and casing, minimizing the risk of bit balling as well as helping to increase ROP.
Successfully drilled the 17½-in interval and
ran the 13⅜-in casing to bottom without
any issues related to drilling fluid.
ULTRACAP PLUS* advanced encapsulating shale inhibitor is a low-molecular-weight, dry acrylic
acid copolymer designed to provide cuttings encapsulation and clay dispersion inhibition. The
inhibitor adsorbs onto the clay surfaces and forms a protective film that prevents cuttings from
sticking to each other or to a shaker screen.
Required 1,000 bbl less of the ULTRADRIL
system with POROSEAL additive compared
with conventional water-base mud (WBM).
The POROSEAL additive was recommended for its ability to seal microfractures and reduce the risk of
shale destabilization. Extensive VIRTUAL HYDRAULICS software simulations were run during planning
and execution to optimize drilling parameters and improve hole cleaning efficiency.
RESULTS
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Integrate fluid, additive, and simulation for customized solution
Encountered no sloughing shale problems,
cavings, or mud losses during drilling.
Incurred no NPT related to drilling
fluid issues.
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For additional wellbore strengthening material, G-SEAL PLUS* industrial carbon and graphite bridging
agent was also included in the formulation at 6 lbm/bbl. In addition, 15-lbm/bbl calcium carbonate was
included to combat potential losses across the suspected faults.
Eliminated the need for backreaming while
tripping out of hole and experienced no
stuck pipe or bit balling.
Completed section in 17 days versus
26 planned days.
A core plug (left) and thin section (right) from the reservoir were sent to a laboratory, where extensive
VIRTUAL HYDRAULICS software simulations were run to optimize drilling parameters and to improve hole
cleaning efficiency.
Drilling Fluid Systems
CASE STUDY: Integrated drilling solution helps complete long shale interval 9 days ahead of plan, UAE
Meet objectives 9 days ahead of plan and without fluid-related NPT
The 17½-in interval was drilled and 13⅜-in casing was successfully run to bottom without issue.
The section was completed in 17 days, which was 9 days sooner than planned. No shale sloughing,
cavings, or mud losses were encountered during drilling, and no NPT related to drilling fluid was
incurred. Further, backreaming was not required while tripping out of hole, and the casing was run to
bottom without stuck pipe, bit balling, or other issues.
Mud weight at TD was 1.32 relative density—less than the planned 1.35 relative density. Additionally,
the volume of ULTRADRIL system with POROSEAL additive was 1,000 bbl less than would have been
required using conventional WBM. As a result of deploying the G-SEAL PLUS agent and calcium
carbonate, no losses were observed across any faults.
Mud Properties
Relative density
Yield point, lbm/100 ft2
Densitometer reading at 6 rpm
API fluid loss, mL/30 min
pH
Methylene blue test, lbm/bbl
ULTRAHIB inhibitor, % by volume
POROSEAL additive, % by volume
ULTRAFREE surfactant, % by volume
ULTRACAP PLUS inhibitor, lbm/bbl
Planned
1.22–1.35
45–55
16–20
<3
9.5–9.8
<5
3–3.5
3
3
2–2.5
Minimum
1.22
30
12
2.4
9.5
0
2.9
2.5
2.9
2
Maximum
1.32
48
19
3
9.8
5
3
3
3
2.7
The mud properties of the ULTRADRIL system with POROSEAL additive were customized to overcome wellbore breakout
and instability, enabling the successful drilling and casing of the 17½-in interval drilled through the challenging shale.
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