Petroleum Engineering 406

Lesson 6

Well Control

Unusual Operations

Read

• Well Control Manual– Chapter 13

• Homework 4– Due Feb. 17, 1999

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

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

SnubbingSnubbing

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

• Partial loss

• Total loss

• Pump LCM keep circulating.

• ?

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

Hole in casing string

• Treat similar to lost circulation

• Can set casing patch

• Cement

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

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 while– maintaining casing pressure = SICP

• When pumps are up and stable at kill speed– record circulating DPP

• SPP=Circulating DPP - SIDPP