PETE 661 Drilling Engineering

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PETE 661Drilling Engineering

• Lesson 21
• Well Control Complications

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Well Control Complications

• Volumetric Well Control
• Lubrication
• Complications During Conventional Kill
• Techniques to Reduce Annular Friction

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HW 12 - due Dec 02, 2002

• Review

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Gas Kick Migration

• While a well is shut in the casing pressure
  increase by 1,040 psi in 2 hours.
• Mud Weight 10 lb/gal
• How fast is the kick migrating?

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Gas Kick Migration
p p 1,040
0.052 10 X 1,040 psi
X 2,000 ft (in 2 hrs.)
Migration rate 1,000 ft/hr
X ft ?

• How fast is the kick migrating?

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Volumetric Well Control

• Non-Circulating method of well control.
• Allows a gas bubble to migrate to the surface
  while systematically allowing the bubble to
  expand. It also maintains the BHP at or above
  formation pressure
• Used whenever circulation cannot be used to kill
  the well.

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Two situations can be present

• Drillpipe can be used to monitor pressure
• Drillpipe cannot be used

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Drillpipe can be used

• When
• Bit is on bottom
• Bit is not plugged
• No float in drillstring

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Drillpipe can be used

• Procedure
• Determine a safety margin for the casing pressure
  (usually 50 - 100 psi above initial stabilized
  SICP and SIDPP)
• Determine working margin (50 - 100 psi above
  safety margin)
• As bubble migrates, casing pressure will
  eventually reach the safety margin

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Drillpipe can be used

• Procedure
• Allow the casing pressure to reach the upper
  limit of the working margin
• Very slowly bleed a small volume of mud from the
  annulus (approximately 1/4 bbl) into a calibrated
  tank. Then close the choke.
• Let Drillpipe pressure stabilize

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Drillpipe can be used

• Procedure, contd
• If new SIDPP gt Initial SIDPP Safety margin,
  repeat bleeding procedure.
• If SIDPP Initial SIDPP Safety margin, stop
  bleeding and allow casing pressure to increase
  again.
• Repeat until circulation can be restored or
  bubble has reached the surface

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Drillpipe Pressure, psi
Working Margin
Safety Margin
SIDPP
Volume of Mud Bled, bbl
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Drillpipe cannot be used

• Plugged bit
• Migrating fluid is below the bit (bit is off
  bottom)
• Drillpipe has parted or has a hole that is
  above the influx

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Drillpipe cannot be used

• Well closed in on the blind rams
• Pumps are inoperable and the drillstring is not
  full of mud
• Gas has entered the drillstring
• If drillpipe pressure cannot be used, what can we
  do?

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Volumetric Procedure

• 1. Record the initial SICP
• 2. Allow the casing pressure to increase by the
  predetermined safety margin.
• 3. Allow the casing pressure to further increase
  by the predetermined working margin.

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Volumetric Procedure

• 4. Bleed mud from the choke manifold into a
  measuring tank while maintaining a relatively
  stable casing pressure.
• Continue to bleed mud until the volume in the
  measuring tank is equivalent to the muds HSP of
  the working margin buildup.
• The HSP is based on the hole dimensions at the
  depth of the rising influx.

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Volumetric Procedure

• 6. Repeat steps 3 through 5 until choke
  pressures stabilize, secondary control can be
  regained, or the influx surfaces.
• 7. Stop the bleed process if gas exits the
  choke. Monitor annulus pressures for further
  buildup.

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Volumetric Procedure

• Allowable increase in surface casing pressure
• 0.052 MW h

h

• Volume of mud bled from casing
• A h

BHP constant
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Example 6.1
pipe on the bank means pipe is out of hole
DATA D10,000ft MW8.7ppg Pit Gain20bbl
Blind Rams Closed ISICP100psi
increasing w/ time 9 5/8in
36lb/ft casing set at 2500ft Open hole diam8
3/4in where fracg0.70psi/ft Tempg70F0.009F/ft
. Write vol proc.
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Example 6.1
0.0528.7 ppg 0.452 psi/ft
(MAASP)
MAASP Max Allow Annulus Surf. P.
(8.7 lb/gal brine)
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Example 6.1
(max BHP)
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Example 6.1
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Example 6.1
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Example 6.1
DVMUD is due to being in the casing (17.10 bbl
instead of 16.46 bbl.)
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Example 6.1
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Casing Pressure, psig
Working Margin
200
Safety Margin
100
Pit Gain, bbl
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16.46 bbl of mud
Casing Pressure, psi
Volumetric Drillers Method
Time, min
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Casing Pressure
Time
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Lubrication

• Process of replacing gas at the surface of a
  wellbore with mud.
• Pump mud into the wellbore
• Let mud fall
• Bleed gas
• Repeat

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Lubrication
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Lubrication Procedure
h

• Desired decrease in surface casing pressure
• 0.052 MW h

h

• Volume of mud added to casing
• A h

BHP constant
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Example 6.2

• Consider the final condition in Example 6.1 where
  all the gas has migrated to the surface.
• Write a lubrication procedure for replacing the
  gas with mud.

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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Example 6.2
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Off Bottom Well Control

• Volumetric
• Use same procedure as before
• Staging in the Hole
• Entails circulating mud of sufficient density to
  control BHP at the current position of the bit
  (off bottom)
• Tripping in the hole some distance
• Repeat

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Off Bottom Well Control
Note changes in pressure as the kick migrates
past the bit
(no float in drillstring)
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Off Bottom Well Control
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Complication During Conventional Kill
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Techniques to Reduce Annular Friction

• Low choke procedure
• Overkill Mud Weights
• Spotting a Balanced Heavy-Weight Pill
• Reverse Circulation
• Bullheading
• Dispersing or Segmenting a Gas Kick

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Low choke procedure

• Operator intentionally opens the choke to reduce
  the surface casing pressure.
• I do not recommend this although some operators
  choose to use this procedure

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Overkill Mud Weights
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Overkill Mud Weights
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Example 6.6

• Estimate the maximum shoe pressure if a 10 ppg
  mud were used to kill the well and prepare a
  drillpipe pressure schedule
• Calculate the pressure at the shoe if the well
  had to be shut-in at the instant the string was
  filled with the new mud.

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Example 6.6
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Example 6.6
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Example 6.6
The shut-in results in a shoe pressure 181 psi
higher than fracture pressure
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Spotting a Heavy-Weight Pill
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Spotting a Heavy-Weight Pill
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Spotting a Heavy-Weight Pill
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Spotting a Heavy-Weight Pill
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Reverse Circulation
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Bullheading

• Pump into a shut-in well and attempt to place the
  influx back into the formation.
• Reasons
• H2S kicks
• Inability to circulate on bottom
• Loss zone below the kick disallows adequate
  circulation rates for a kill
• To buy time
• Inability to withstand the maximum surface
  pressures during conventional kill

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Example 6.8
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