Quartz School for Well Site Supervisors
Section – 5
Well Control Procedures I
Schlumberger Private
Module – 11
Drilling Problems
& Solutions
Contents
•
Summary of Well Control Methods – Bottom Hole Pressure Constant
•
Conventional Well Control Methods
– Pipe on bottom, circulation is possible
Driller’s Method
•
Wait and Weight Method
– Changes in annular pressure while circulating the influx out
– Comparison of the two conventional well control methods
– Surface indications of down hole problems during well control
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•
Maximum Allowable Annular Surface Pressure, MAASP
•
Meaning of MAASP during well control – Exercise and discussion
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Secondary Well Control
Summary of well conditions and WC Methods
A. Pipe is on bottom; Circulation is possible:
•
Driller’s Method (“two circulations”) – BHP CONSTANT
•
Wait and Weight (“one circulation”) – BHP CONSTANTE
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•
Volumetric Method (Static) – string stationary – Controlled
expansion of influx while ascending to surface or above the bit
where can be circulated out, while keeping BHP CONSTANT
•
Lubricate and Bleed – String stationary / gas at top of annulus –
Controlled evacuation of gas following three consecutive steps:
•
a) injection of mud into the annulus via kill line
•
b) waiting time to allow phase segregation
•
c) bleeding gas from the annulus via choke line
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B. Pipe is off bottom or out of hole; gas influx is migrating :
Secondary Well Control
Summary of well conditions and WC Methods
C. Pipe is off bottom or out of hole – no circulation
Stripping Procedure – conventional: no migration (or the gas kick was
already evacuated of well bore by following methods in B.) The drill string
is forced back to bottom through the closed BOP by its own weight, while
keeping BHP CONSTANT. Then, a circulation method applied (W&W)
•
Combined Stripping & Volumetric – pipe is off bottom & gas is migrating:
Simultaneous stripping and controlled expansion of gas influx as it ascends
to surface in the annulus, while keeping BHP CONSTANT
¾
Standard Procedure recommended by Schlumberger – IPM
Common steps for all Secondary Well Control Methods:
1. Evacuation of influx out of well bore
2. Restore or Create Overbalance (when it is required)
Both steps (1. & 2.) are done while keeping BHP CONSTANT at all times
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Secondary Well Control
Summary of well conditions and WC Methods
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D. Well Control in Cased Holes (For Well Completion & Work Over Operations)
• “Bullheading” – Reversing the influx into the formation: in low pressure or
depleted zones and lost circulation; no fracturing of permeable formation
• Reverse Circulation – pumping kill fluid in the annulus and returns taken from
tubing, BHP = Constant
• Direct Circulation – Similar to W&W Method, BHP = constant
• Stripping Procedure – conventional: Pipe forced back to bottom through
closed BOP by its own weight while keeping BHP CONSTANTE. Then, a
circulation method is applied (W&W)
• Combined Stripping & Volumetric – pipe is off bottom & gas is migrating:
Simultaneous stripping and controlled expansion of gas influx ascending to
surface in the annulus, while keeping BHP CONSTANTE
• Mechanical Well Control: Installation of mechanical barriers in the tubing
string or casing to stop well flowing (Back Pressure Valve, Bridge Plug, etc.)
• Kill fluid (packer fluid): fluid left in the annulus for WC purposes (use of S.S.)
• Concentric Well Control: Injection of coiled tubing or snubbing pipe into the
hole to circulate control fluids from the bottom of the hole
Conventional WC Methods – Circulation Methods
A. Pipe is on bottom; Circulation is Possible
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For all Methods, measure and calculate in advance:
• Slow Circulation Pressure = Pressure Reduced,
– Determine the friction losses through out the system
– Measured at pump speed planned to use during well control
– Common slow pump rates are 20, 30, 40 SPM
– Measure Slow Pump Pressures with all mud pumps on the rig
• Pre-calculate:
– Pipe volume and / or pump strokes to displace it
– Annulus volume and / or pump strokes to displace it
• Have ready to use a kill sheet for the W&W method or for the
second circulation of the Driller’s method, if preferred
The Driller’s Method
Step 1 – Circulate with mud in the hole to evacuate the influx :
•
Mud pump is started first; then the choke is gradually open
•
While pump is accelerated to reach its reduced speed,
circulating for a short period of time (1 – 3 minutes)
- Due to the circulation, the dynamic BHP is higher than the static BHP as
the annular pressure losses are reflected on bottom
- For this reason no additional influx of formation fluids is permitted due to
the this safety factor on BHP which is the ECD
•
When the kill speed is reached, the circulating pressure (CP) on Drill
Pipe side is kept constant, by operating the choke, until all the influx is
evacuated from the annuls to the surface. Annular pressure will not
remains constant any more; only the CP will.
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-The Shut In Casing Pressure (SICP) is kept constant with the choke, while
The Driller’s Method
How to estimate the Circulating Pressure on Drill Pipe side, CP
•
If both the Shut In Drill Pipe Pressure (SIDPP) and the Slow Circulation Rate
(SCR) are known, the Circulating Pressure CP is calculated as follows:
CP
=
(1) 1225 psi
(2)
500 psi
(2) SIDPP: Shut In Drill Pipe Pressure
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(1) CP: Pump Circulating Pressure once
the slow pump rate (SCR) or kill rate is
reached
(3) 725 psi
(3) SCR: Reduced Pressure, recorded at
slow circulation rate (SCR) before the influx
was taken = Friction losses in the system
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Example:
SIDPP + SCR
The Driller’s Method
How to estimate the Circulating Pressure on Drill Pipe side, CP
b.
If Shut In Drill Pipe Pressure (SIDPP) and / or the Slow Pump Rate (SCR) are
NOT KNOWN, as may happen in one of the following conditions:
The ACTUAL Circulating Pressure, CP is established as follows:
•
•
•
•
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Select ANY SLOW PUMP RATE appropriated for well control operations
Start the pump and while speeding it to the selected SCR keep the recorded
Shut In Casing Pressure, SICP for a short period of time (1 to 3 minutes)
When reached the desired SCR, check the Circulating Pressure on Drill Pipe
side as the ACTUAL Circulating Pressure, CP
The measured or ACTUAL CP contains the unknown terms SIDPP and SCR
and will be KEPT CONSTANT until all kick is evacuated out of the well bore
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SIDPP = 0 (due to a solid back pressure valve in the drill string)
SCR = ?? (it could be taken in very different conditions of depth, well
geometry, mud properties, its value is not reliable or it not taken at all)
The Driller’s Method
Step 1: Circulate with mud in the hole to evacuate the influx :
How dynamic BHP is kept constant when the influx is circulated out of well
BHP = HPDs + CP – ΔPDS
SCR = ΔPDS + ΔPA Æ BHP = HPDP + SIDPP + (ΔPDS + ΔPA) – ΔPDS
BHP = HPDS + SIDPP + ΔPA Æ BHP in dynamic conditions (circulating BHP)
Each term component of the dynamic BHP is kept constant as follows:
Hydrostatic Pressure inside DP (HPDs)
By keeping constant the original MW
before the kick is taken
Shut In Drill Pipe Pressure (SIDPP)
By keeping constant the CP read in the
DP side which contains the SIDPP
Annular Friction Losses (ΔPA)
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By keeping constant the selected Slow
Circulating Rate that defines the ECD
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CP = SIDPP + SCR Æ BHP = HPDS + (SIDPP + SCR) – ΔPDS
The Driller’s Method
Step 1 – Circulate with original mud to evacuate the influx :
How to turn the pump off, while keeping constant BHP?
Start closing the choke and gradually reduce pump speed until turn it off.
Close the choke only when the pump is completely stop
•
While turning the pump off:
– Hold casing pressure constant at shut-in value by adjusting the choke
– Annular pressure losses are removed when the pump is stopped
– BHP returns to its shut- in value
•
When the well is shut in there are two options:
– New SICP is zero Æ well is static with overbalance. End of process
– New SICP is not zero Æ well can flow due to underbalanced condition.
– In this case New SICP = original SIDPP (if the influx was properly
evacuated, as per the previous procedure). Circulate with heavy mud
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•
The Driller’s Method
Step 2 – Circulate with weighted mud, MW2, only if over balance is required:
•
Mud pump is started first; then choke is gradually open
•
Having reached the selected SCR, continue pumping heavy mud and
– Keep the New Shut-In Casing Pressure (SICP2) constant, by operating
•
Annular pressure losses will increase the static BHP
•
No additional influx of formation fluids is permitted with this safety
factor on BHP due to the ECD
•
Count barrels, strokes or minutes required from surface to the bit, to verify
when the drill string is filled with heavy mud
•
Record the Final Circulating Pressure (FCP) when heavy mud is at the bit
•
Keep the FCP constant until heavy mud returns to the surface. This can be
checked with annular volume, strokes and confirmed by weighting the mud
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coming out of hole.
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the choke, until the heavy mud reaches de bit
The Driller’s Method
Step 2 – Circulate with weighted mud if over balance is required:
•
Circulate to fill the annulus with heavy mud from bit to surface:
– Read the Final Circulating Pressure on the drill pipe side (FCP) when the
heavy mud (MW2) reaches the bit.
•
Turning the Pump Off & Checking for Flow:
– Start closing the choke while slowing the pump down
– Turn the pump off and then shut the well in.
– Verify that SICP is ZERO. (SIDPP should also be zero.)
– Open the well (via choke manifold) and check for flow
– Open BOP and verify static conditions
– Resume well operations
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– Continue circulating with heavy mud keeping constant the recorded
(FCP) until the heavy mud returns to surface.
The Driller’s Method - Summary
Step 1: Circulate with original mud in hole, keeping Circulating Pressure (CP)
on Drill Pipe side constant until all the influx is evacuated out to the surface
(BHP is kept constant as CP is kept constant)
Keep CP = Constant
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SICP
¾Select one slow pump rate, SCR.
¾Start circulation with original MW1
¾Keep SICP constant while the pump
reaches the selected SCR, (1-3 min.)
¾Check Circulating Pressure, CP, on
DP side, when pump reaches the SCR
¾Count strokes, or time required to
pump bottoms up = annular volume
¾Verify kick is evacuated out of
well by measuring (MW)out = MW1
¾Keep this CP constant until all influx
is circulated out of the well
P1 > P2
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The Driller’s Method - Summary
Step 2 – Circulate with weighted mud, MW2 to displace original mud in hole, MW1
while keeping BHP constant and above the formation pressure
(This step is required ONLY when an Overbalance on the formation is needed)
2º Keep FCP = Constant
Once the influx is evacuated with Step 1, shut the well in.
If, SICP2 = 0 Æ No Undebalance. Influx was swabbed in.
Step 2 is required: Circulate the well with MW2
Calculations:
SICP = SIDPP
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If, SICP2 = 0 Æ Well is Underbalanced; SICP2 = SIDPP1
1º Keep SICP2
= Constant
MW2 = MW1 + SIDPP/(factor x TVD) + OBÆ SIDPP = SICP2
Nº pump strokes or volume to fill Drill Pipe with heavy mud
¾Step 2 – Circulate with MW2
¾1º) Keep SICP2 constant until heavy mud reaches the bit.
(check strokes, volume or time from surface to bottom )
¾Record Final Circulation Pressure, FCP, when heavy mud
MW2 is at the bit
¾2º) Keep FCP constant until heavy mud returns to surface
(Count Strokes& time for bottoms up, check MWout = MW2)
¾Close
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the well in and verify, SICP = 0 & no flow.
P1 > P2
The Wait and Weight Method
One Step: Circulate with heavy mud (MW2) to evacuate influx and
simultaneously displace original mud to establish the over balance required,
while keeping BHP constant
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While the drill string is being filled with heavy mud:
• Follow the Pumping Schedule prepared in the kill sheet, by adjusting the
choke to reduce circulating pressure from the calculated initial circulating
Pressure (ICP) to the Final Circulating Pressure (FCP)
To Fill the annulus with heavy mud:
• Keep constant the FCP (circulating pressure just when the drill string is full
with heavy mud) until heavy mud returns to surface by manipulating the
choke. Verify that MWin = MWout = MW2 before stop pumping
To turn the pump off and check the well:
• Start closing the choke while slowing the pump down
• Shut the pump off and close the well in
• Verify that SICP = 0. (SIDPP should also be zero)
• Open the well and check for flow
The Wait and Weight Method - Summary
Circulate with heavy mud to evacuate the influx and simultaneously establish the
overbalance required, while keeping BHP constant
Calculations:
Æ Requirements: both “SIDPP” & “SCR” are known
ICP Æ FCP
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MW2 = MW1 + SIDPP/(factor) x (TVD) + OB: Kill Mud Weight
ICP = SIDPP + SCR: Initial Circulating Pressure
FCP = SCR x (MW2 / MW1): Final Circulating Pressure
Prepare “Kill Sheet” with “Pumping Schedule” & volumes
OB: Over Balance
Circulation with heavy mud, MW2:
•While pumping heavy mud to fill the drill string, follow
the “pumping schedule” in the kill sheet to reduce the
circulating pressure from ICP to FCP
•Continue pumping and keep FCP constant, until heavy
mud returns to surface. Check: MWin = MW out = MW2
•Shut the well in and verify that SICP = SIDPP = 0
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P1 > P2
Changes in Surface Casing Pressure
While circulating the influx out
Three things cause surface casing pressure to change:
Loss of hydrostatic pressure between the bottom of the hole and the surface
– Caused by gas expanding and displacing mud
– Compensated by a continue increment in annular pressure at surface
(with the choke) until gas reaches the surface
2.
Gain in hydrostatic pressure between the bottom of the hole and the surface
– Caused by gas leaving the well (venting) which is being replaced with
mud entering into the annulus from the drill pipe
– Compensated by a reduction in annular pressure at surface (with the
choke)
3.
Gain in hydrostatic pressure between bottom and surface
–
–
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Caused by light (original) mud being displaced in the annulus with
heavier (kill) mud from the drill pipe
Compensated by an additional reduction in annular pressure at surface
when kill mud is inside the annulus (with the choke)
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1.
Pressure Changes in Annulus
Case 1
Case 3
Wait and Weight
(No gas migration)
Wait and Weight
(Gas migration)
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Case 2
Driller’s Method
First circulation
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W&W vs Driller’s Method
Theoretical vs Actual
860
1) Theoretical Driller’s
2) Theoretical W&W
Casing Pressure, psi
4) Actual Driller’s
Time
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3) Actual W&W
680
Pressure Changes at Casing Shoe
Case 1
Case 2
Case 3a
Case 3b
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Driller’s Method
First circulation
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Wait and Weight
(No gas migration)
Wait and Weight
(Gas migration)
W&W vs Driller’s Method
Driller’s
Theoretical
W&W Actual
W&W Theoretical
Strokes
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Casing shoe pressure, psi
Casing Shoe at 4000 ft
Hole Geometry Vs Top of Gas Bubble
Gas kick taken at TD
Hole geometry: 8-1/2” Hole, 5” DP
8000’
10,000’
15,000’
16,000’
24,000’
In each case the gas will reach the shoe before the kill weight
mud reaches the bit, even if the gas migration rate is ZERO
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5000’
Hole Geometry Vs Top of Gas Bubble
Hole size range
Top of gas when
kill mud reaches bit
17-1/2” – 20”
17-1/2” – 20”
3,000’
5,000’
SURFACE
510’
12-1/4” – 13-3/8”
5,000’
135’
12-1/4” – 13-3/8”
12-1/4” – 13-3/8”
7,500’
10,000’
1,753’
3,614’
12-1/4” – 13-3/8”
12,500’
5,450’
8-1/2” – 9-5/8”
7,500’
SURFACE
8-1/2” – 9-5/8”
10,000’
SURFACE
8-1/2” – 9-5/8”
8-1/2” – 9-5/8”
12,500’
15,000’
900’
2,300’
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Total depth
Conventional (Circulation) WC Methods – Summary
A. Pipe is on bottom; Circulation is Possible
•
The Driller’s Method:
- Step 1: Circulate with mud in the hole for influx evacuation
¾ This step is required ONLY if the influx is caused by under balance
(BHP < Formation Pressure)
•
Wait and Weight Method
- One Step: Circulate with weighted mud to displace original mud and
simultaneously evacuate the influx and restore the over balance
¾ It is not necessary if the influx was mechanically induced
(swabbed-in) and there was enough overbalance before tripping.
Once the influx is evacuated, the overbalanced condition is
restored
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- Step 2: Circulate with control mud to restore or create over balance
The Driller’s Method - Conclusions
Advantages:
Simplicity – Less calculations are required than Wait and Weight method.
•
Circulation can start immediately – Effect of gas migration reduced
•
Removes the influx and stabilizes wellbore pressure at earliest possible
period of time.
•
Viable option if limited barite is available or is inexistent at the rig site
•
If the influx was mechanically induced (swabbed in), the second circulation
is not required. This is only done when the influx is due to under balance
(Formation Pressure > BHP)
Disadvantages:
•
As mentioned above, it may require more than one circulation
•
Under certain conditions will cause the highest pressure on the casing shoe
•
More circulation time may cause damage to well control equipment
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The Wait and Weight Method - Conclusions
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Advantages:
• In some circumstances, it generates the lowest pressure on the formation
near casing seat
• In a long open hole section, it is the least likely method to induce lost
circulation
• Requires just one circulation and therefore less chance to damage Well
Control Equipment (plugging, erosion, etc)
• It is ‘De facto’ or “Standard” Well Control Method for many Of oil & Gas
Operators
Disadvantages:
• Requires a longest waiting period prior to start circulation (stuck pipe?)
• In a case where a significant amount of hole is drilled prior to taking the
kick, the cuttings may settle out and pack off the annulus
• Gas migration is a problem while the mud system is being weighted up
• Could be an inadequate procedure if the influx was swabbed: no over
balance is required..!
Surface Indicators of events & problems
During well control operations
Choke washout
Drillpipe
pressure
Casing
pressure
⇓
⇓
Gas at surface
⇓
Hole in the drillstring
⇓
Pipe parted
⇓
Bit nozzle lost
⇓
Pump volume drops
⇓
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Pump
SPM
⇑
⇑
⇓
⇓
⇓
⇓
⇑
⇓
⇑
⇑
⇓
⇑
⇑
⇓
⇑
Gas feeding in
Pit level
⇑
⇑
⇑
⇑
Choke plugged
⇑
Bit nozzle plugged
⇑
⇓
Hole caves in
⇑
⇓
⇓
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Lost circulation
Drillstring
weight