Petroleum Engineering 406
Lesson 6
Well Control
Unusual Operations
• Well Control Manual
– Chapter 13
• Homework 4
– Due Feb. 17, 1999
• Pipe off bottom or out
of hole
– Stripping
– Snubbing
• Excessive casing
• Lost circulation
• Hole in casing string
• Plugged drillpipe or
• Hole in drillpipe
• H2S kicks
• Trapped pressure
• Gas kicks in OB mud
• Gas cut mud
• Determine SPP after
Pipe off bottom or out of hole
• Kick is below bit
– Cannot circulate kick
out with bit at this
– Must get to bottom
• Stripping
• Snubbing
Pipe off bottom or out of hole
• Stripping - tripping
• Snubbing - tripping
into or out of the well
into or out of the well
under pressure through
under pressure through
closed preventers
closed preventers
• Buoyed weight of the
• Buoyed weight of the
drillstring > force
drillstring < force
exerted by the
exerted by the
wellbore pressure
wellbore pressure
Forces acting on drillstring
• Down
– weight of drillstring
– downward forces from
pressure on upsets
• Up
– buoyancy effects
– upward forces from
pressure on upsets
Forces acting on drillstring
• Net effect
– down
• buoyed weight of
– up
• force from pressure
acting on cross
sectional area of pipe
inside the BOP
• =Pressure x area
Stripping through annular
• Install safety valve in
top of drillstring
(inside BOP)
Stripping through annular
Stripping through annular
Stripping through rams
Stripping through rams
Stripping through rams
Stripping through rams
Snubbing calculations
• F=PxA
• Example: A well has 450 psi pressure.
• 2-7/8”, 6.5 lb/ftpipe in well with BOP
closed. What is the upward force on the
• F=450x.07854x2.875^2=2919 lbf
• =449 ft of pipe if suspended in air
Snubbing calculations
• What is the buoyed weight of 279’ of
2.875”, 6.5 lb/ft pipe (pipe empty)
suspended in 13.2 ppg mud?
• W=Lx[Pipe wt.-{(OD)2x.0408xMWo}]
• W=572 lbf
Snubbing calculations
• What is the increase in buoyed weight if the
tubing is filled with 13.2 ppg mud?
• Wi=Lx(ID)2x.0408xMWi
• 894 lbf
Snubbing calculations
• General form of buoyed weight of pipe in
the wellbore
• W=Lx [Pipe wt.-{(OD)2x.0408xMWo}+
Excessive casing pressure
• Casing pressure exceeds:
– Rated pressure of BOP
– Rated pressure of casing
Lost circulation during kick
• Partial loss
• Total loss
• Pump LCM keep
• ?
Lost circulation during kick
• Circulating out kick
• Casing seat fractures
– Underground blowout
• Determine where thief
zone is
• Pump heavy mud on
bottom, light on top
• Spot barite plug
Lost circulation during kick
• Drilling into thief zone
• Upper zone kicks
• Gunk squeeze on
• Kill upper zone
Hole in casing string
• Treat similar to lost circulation
• Can set casing patch
• Cement
Plugged drillpipe or bit
• If you can continue to
• adjust kill sheet to
reflect the increase in
pressure loss
• If you cannot continue
to circulate
• May have to “blow”
the jets out, or
Hole in drillpipe
• Must plug the hole
– strokes to bet incorrect
– SPP incorrect
– wash DP in two
• Pump softline or panty
• Set plugs, strip out,
replace leaky joint,
strip back in
H2S kicks
• Hydrogen Sulfide
– very poisonous,
– explosive
– accumulates in low areas
• Some people bullhead
Trapped pressure
Record SIDPP and SICP
Bleed small amounts of mud from annulus
Close choke, record SIDPP and SICP
If both pressures are lower than before,
repeat bleeding.
• If SIDPP is the same and SICP is slightly
higher, stop bleeding.
Gas kicks in OB mud
• Solubility of gas in OB mud can mask the
kick indicators.
• Look for small pit gains, and small flow
• Gas remains in solution until near the
surface, where it comes out of solution
(sometimes violently) and expands rapidly
Gas Cut Mud
• What is it?
• Where does it come from?
• How dangerous is it?
• Are we loosing much HSP?
Gas Cut Mud
• Determine where gas came from by:
– circulating BU
– If gas goes away with circulation
• probably drilled gas
– If gas does not go away with circulatio
• raise MW
• Causes very little loss of HSP
– almost all expansion near the surface
Gas Cut Mud
Gas Cut Mud
Gas Cut Mud
Gas Cut Mud
Gas Cut Mud
Gas Cut Mud
Gas Cut Mud
Determine SPP after kick
• Slowly increase pump speed to kill speed
– maintaining casing pressure = SICP
• When pumps are up and stable at kill speed
– record circulating DPP
• SPP=Circulating DPP - SIDPP