Petroleum Engineering 406 Lesson 6 Well Control Unusual Operations.
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Transcript of Petroleum Engineering 406 Lesson 6 Well Control Unusual Operations.
Contents
• Pipe off bottom or out of hole– Stripping
– Snubbing
• Excessive casing pressure
• Lost circulation• Hole in casing string
• Plugged drillpipe or bit• Hole in drillpipe
• H2S kicks
• Trapped pressure• Gas kicks in OB mud• Gas cut mud• Determine SPP after
kick
Pipe off bottom or out of hole
• Kick is below bit– Cannot circulate kick
out with bit at this point.
– Must get to bottom• Stripping
• Snubbing
Pipe off bottom or out of hole
• Stripping - tripping into or out of the well under pressure through closed preventers
• Buoyed weight of the drillstring > force exerted by the wellbore pressure
• Snubbing - tripping into or out of the well under pressure through closed preventers
• Buoyed weight of the drillstring < force exerted by the 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 drillstring
– up• force from pressure
acting on cross sectional area of pipe inside the BOP
• =Pressure x area
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 pipe.
• 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}+ {(ID)2x.0408xMWi}]
Excessive casing pressure
• Casing pressure exceeds:– MASP– Rated pressure of BOP– Rated pressure of casing
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 bottom
• Kill upper zone
Plugged drillpipe or bit
• If you can continue to circulate
• adjust kill sheet to reflect the increase in pressure loss
• If you cannot continue to circulate
• May have to “blow” the jets out, or perforate
Hole in drillpipe
• Must plug the hole– strokes to bet incorrect
– SPP incorrect
– wash DP in two
• Pump softline or panty hose
• 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 increases
• 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