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TAMU - Pemex
Well Control
Lesson 17
Special Well ControlApplications
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Special Well Control
Applications
Underbalanced Drilling
Well Control in Unconventional Hole
Programs
Casing and Cementing Operations
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Underbalanced Drilling
These are wells where the ECD is
intentionally kept below theformation pore pressure.
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Reasons for UBD
Minimize formation damage
Faster penetration rates
Longer bit life and fewer trips
Eliminate one or more casing strings
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Reasons for UBD
Reduced risk of lost circulation
Reduced risk of differential sticking
Lower mud costs
Earlier oil sales
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Underbalanced Drilling
Air and Natural Gas Drilling
Mist and Foam Drilling
Underbalanced Drilling w/Mud
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Simplified Air
Drilling System
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Using the
Choke to
Control
Pressures inWell Control
and in UBD
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Well Control
Equipmentfor Air or
Natural Gas
Drilling
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RotatingHead used
in Air
Drilling
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Air and Natural
Gas Drilling
Compressor at
surface
Drillpipe Float
Gas in drillstring
Friction
These make DP
gauge unreliable
for BHP
determination
Casing gauge
is used topredict BHP
zT
D
csp
g
epp3.53
K
!
How do you
determineBHP?
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zTD
csp
g
epp 3.53K
!
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zT3.53
D
cssh
g
epp
K
!
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Mist and Foam Drilling
Mist drilling may be used when small
water flows would cause mud rings
with air or natural gas drilling.
Water is injected downstream of the
compressors until the air is nearly
saturated with water vapor.
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Mist and Foam Drilling
Foam drilling can tolerate still more
water than mist.
Foams are generated by shearing
water and gas together with a
foaming surfactant and bentonite or
polymers added for betterhole
cleaning.
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Underbalanced Drilling with Mud
Air can be injected into the mud stream
to lighten the mud column.
One way is to inject at the standpipe
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Air Injection
Options
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Used to determine volume of air to inject:Reduce 9.0 lb/gal mud to 5.0 lb/gal effective density at TD
9.0 5.0 = 4.0
Vm
VeVm Ve lb/gal
Ve lb/gal
5.0
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Mud
Simulator
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Tz77.2
pK!
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UBD with Weighted Mud
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Annulus isfilled with
heavy mud
as DP is
being
pulled outof hole
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Unconventional Wellbores
and Drilling Practices
Horizontal and ERD Wells
Slim-Hole Applications
Coil-Tubing Operations
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Horizontal and ERD Wells
For Horizontal and ERD Wells the window for
acceptable mud weights narrows.
The high angle reduces frac pressure,lowering the maximum mud weight allowed
Hole collapse increases the minimum mud
weight.
Mud weight may limit the length of the lateral
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NOTE Same TVD, but ERD well has smaller
MW window, and higher ECD.
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9,642
KOP10,000
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Heel
Terminus
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Additional Pressure Concerns
in Horizontal Wells
Cuttings beds require high annularvelocity
Surge and Swab pressures higher
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Lessoverbalance
during trip
(pSWAB = 10.3 * 3
= 31 psi
Circulating while
POH can offset
swab pressure
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Additional Pressure
Concerns
ERD wells more prone to kicks and lost
circulation (smallerMW window)
SICP lower for ERD
Gas migration less of a problem
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Fig. 6.15Surface
Pressure
Relationship
for a
Horizontal
Well closed in
on a kick
SIDPP = SICP
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Gas trappedin washouts
reduces
migration
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Vertical height remains
constant in lateral section
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Slim-Hole Applications
High annular friction during circulation
Small pit gains yield long vertical heightof kick fluid resulting in high SICP
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Coil-Tubing Operations
Continuous, non-jointed pipe which is
stored on a reel and transported to awellsite to perform a specific
operation
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Fig 6.19
Coiled Tubing
stuffing box
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Coiled Tubing
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CT growth with time
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Casing and Cementing
Operations
Running the Casing
Cementing the Casing
The Annular Flow Problem
LinerTop Tests
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Running the Casing Operator should replace upper DP
rams with casing rams.
SIP could result in large upward forces
on the large diameter casing.
Large diameter casing results in highsurge and swab pressures.
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Comparison of surge/swab
pressures for casing vs. DP
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Cementing the Casing
pbh = pch + ph +(pf+- (pss +(pa
pbh = BHP
pch
= choke backpressure
ph = HSP
(pf = circulating friction pressure
(pss = surge or swab pressures
(pa = pressure resulting from fluid
acceleration
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Fig. 6.34
Downhole
Pressures
associatedwith a
Cement Job
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Cementing Consideration Spacer density and volume
High viscosities
U-tubing of cement slurries
Freefall of cement
Flash setting of cement
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Effect of bridged
annulus on wellbore
pressures whilecementing
Cement
Cement
may
flash-
set
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Fig. 6.36
Effect ofCement
Channeling
on
Hydrostatic
PressuresHigher
Cement
Hydrostatic
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The Annular Flow Problem
The transition period between
development of gel strength and
setting sometimes allows flow
High gel strength cement can
support the HSP of mud column
above and allow flow into the cement
Gas may then percolate upward
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Fig. 6.37 Cement
Gel Strength
Development andHSP Reduction
with TimeFormation Pressure
No gas migration if
gel strength exceeds500 lbf/100 sq/ft
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