03 hole problems
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HOLE PROBLEMS
Avoid hole problems and
stuck pipe if at all possibleto reduce costs
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Lost Circulation
Lost circulationLost circulation occurs when the
effective hydrostatic (mud weight,
friction losses and cuttingsconcentration) becomes greater than
the formation pore pressure plus the
resistance to flow of the fluid throughthe formation
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Hole Problems
Lost circulation
While drilling all
the fluid pumpedinto the drill
string returns to
the mud tank atthe surface
It is a closed
system
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Hole Problems
Lost circulation
Lost circulation
is when all or aportion of the
circulating fluid is
lost to theformation
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Lost Circulation
Can loosecirculation intoprimary orsecondaryporosity
Generally,primary porosity
will range from 8to 30% forreservoirs
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Lost Circulation
Secondary porosity is porositygenerated by altering the rocks
such as the dolomitization of
limestone or fracturing
Fractures
Vugs
Oolite
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Lost Circulation
Permeability is a measure of theresistance to flow of a fluid
through a rock
Measured in Darcys or millidarcys
Most reservoirs have less than one
Darcy of permeability and will not
accept whole mud (with solids)
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Lost Circulation
Lost circulationShallow formations with high porosity
and permeability that will accept
whole mudShallow sands
Increase viscosity and/or add LCM
LCM - Lost Circulation Material -anything that is cheap and readily
available
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Lost Circulation
Can often use LCM sweeps wherethe LCM is removed from the system
using the shale shaker after one to
two circulationsCan loose circulation due to excess
penetration rate
Increased solids content of the mudwill increase the circulating density
(ECD) contributing to lost circulation
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Lost Circulation
Lost circulation due to secondaryporosity (deep or shallow)
Usually use LCM
Adding LCM requires bypassing the shaleshaker unless just pumping a sweep
Bypassing the shale shaker increases mud
density which will increase the possibility of
lost circulation LCM can seal natural fractures but does not
prevent fracturing if the fracture gradient is
exceeded
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Lost Circulation
Lost circulation due to secondaryporosity (deep or shallow)
Usually use LCM
Pick up off bottom while mixing the LCM toprevent stuck pipe
Keep the pipe moving
Can drill ahead while spotting LCM to open
up the entire loss zone (short distance) Drilling ahead may be necessary prior to
trying other methods to control lost
circulation
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Lost Circulation
Lost circulation due to secondaryporosity (deep or shallow)
Drill without returns (blind drilling)
Drilling with no fluid returns to the surface Cuttings go into the lost circulation zone
Uses large quantities of fluid
250 gpm (0.94m3/min) equivalent to 7,000
bbls (1,113m3) in a 20 hour drilling day Mixing that quantity of mud would be difficult
Usually use water
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Lost Circulation
Lost circulation due to secondaryporosity (deep or shallow)
Drill without returns
Must still have enough annular velocity toclean the hole, water requires even more
annular velocity than mud
Sloughing can be a problem
Well control can be a problem Usually not done in exploratory wells
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Lost Circulation
Lost circulation due to secondaryporosity
Pump cement plugs
Can be expensive and time consuming Entire lost circulation zone should be open
Dont want to drill two feet and loose
circulation again
Set back BHA and run drill pipe open endedat loss zone
Must know the location of the loss zone
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Lost Circulation
Lost circulation due to secondaryporosity
Pump cement plugs If the loss zone is not on bottom, you may
have to run a temperature survey todetermine the location of the loss zone
Spot a balanced plug and trip out of hole topick up BHA
Trip in hole with bit and WOC Try to fill hole
Drill out cement plug and repeat ifnecessary
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Lost Circulation
Lost circulation due to secondary
porosity
Gunk squeeze
Pumping diesel and bentonite
Bentonite does not yield in diesel When the bentonite contacts the formation
fluids, it will hydrate and block the loss zone
Works better in fresh water zones
In salt water zones, pump fresh water downannulus while pumping gunk down drill pipe
Cement can be added to the mixture
May be environmentally unacceptable
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Lost Circulation
Lost circulation due to secondaryporosity
Diacel squeeze Diacel is a clay which has very high gel
strengths and may help plug loss circulationzone
May use proprietary products from mudcompanies or cementing service
companies Many are polymers with delayed cross
linking
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Lost Circulation
Lost circulation due to secondary
porosity
Underbalanced drilling
Reduce the mud weight by adding air or
nitrogen to the mud Air or mist drilling
Foam drilling
Aerated fluid drilling
Formations must be stable and potentialproduction rates (oil, gas and water) must
be lower
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Lost Circulation
Lost circulation by exceeding thefracture gradient
If the hydrostatic of the drilling fluid
exceeds the fracture gradient, lostcirculation will occur
LCM may help a little and is more
effective at shallower depths
If you cannot lower the mud weight, you
will have to run casing
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Lost Circulation
Lost circulation by exceeding thefracture gradient
Service companies are working on
products to increase the fracturegradient
Have had mixed success so far
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Stuck Pipe
Stuck pipe is a big problem inthe drilling industry
In the Netherlands, the stuck pipe
incidents resulted in 5% of the drillingcapital expenditure in 1993
Shell reported stuck pipe in 70% of its
wells causing 80% of the lost timewhile drilling in Nigeria
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Stuck Pipe
Stuck pipe incidents cost over onebillion dollars per year through lossesin rig time, production and drillingoperations, tools and equipment, andthrough expenses for fishing or side-tracking operations
The cost is ever increasing as more
and more deviated and horizontalwells are drilled with more expensiveequipment
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Stuck Pipe
It is estimated that more than 65% ofstuck pipe occurrences can be
avoided with better planning and
drilling crew trainingThere is a need for better awareness
of the problem and continued
emphasis on prevention measures toachieve minimal stuck pipe incidents
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Differential Pressure Sticking
PfAF fs
, k, P
PheDrill CollarHole
Filter Cake
Drill CollarHole
Filter Cake
Thin Filter Cake
Af
Af
Thick Filter Cake
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Differential Pressure Sticking
Differential Pressure StickingAcross from a permeable formation
Stuck while the pipe was not moving
Can occur anywhere in the hole
Can circulate without a problem
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Getting unstuckPull or slack off (jar) the maximum
immediately
Spot oil or a proprietary productReduce pressure by U-Tube
Reduce pressure by pumping
nitrogenWashover stuck pipe
Sidetrack
Differential Pressure Sticking
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Differential Pressure Sticking
PreventionDont let the pipe sit without moving
Use spiral drill collars
Stabilize drill collarsReplace drill collars with HWDP
Reduce pressure differential
Thin filter cakeAdd oil to mud (reduce friction coefficient)
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KeyseatOccurs high in the hole
Got stuck while pipe was moving
If not stuck, may go down but not up
past a point
Can still circulate without difficulty
Can occur in any formation
Keyseating
K i
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Keyseating
KEYSEAT FORMATION
K ti
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Getting out of the holeWork pipe through the keyseat area
back ream
If stuck, back off two or three jointsabove the stuck point
Run jars and jar down
Sidetrack
If in acid soluble formation, spot acid
Keyseating
K ti
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Keyseating
Can use a keyseat
wiper at the top ofthe drill collars to aid
in back reaming
through the keyseatinterval
K ti
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Prevent keyseatMinimize dogleg severityBHA
design
Reducing the number of drill collarsadding HWDP
Drill with a downhole motor and
minimize rotation of the drill string
String ream potential keyseat
Keyseating
B ld
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BouldersRiver beds
Volcanics
Glacial fill
Many times they are a problem in the
surface hole
Can also be a problem deeper where
the formation is highly fractured
Boulders
B ld
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Boulders
Indications
Severe torque while drilling, sometimes the
drill string rotation is stopped and the string
stuck
Difficulty in pulling off bottom or pulling thefirst few stands
No difficulty in circulating
Free movement down with difficulty moving
up
The tight spot is not in the same place but
rather moves around
B ld
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Boulders
The only choice is to break up theboulder with movement of the drill
string
Cant get the mud viscosity highenough to circulate large rocks out of
the hole
S i F ti
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Squeezing formationsSalt can cause problems while drilling
Salt causes casing collapse during
production
Design casing for 1 psi/ft (22.6
kPa/m) collapse
Drill with salt saturated mud or oil
based mud
Squeezing Formations
S i F ti
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Marl Increase mud weight
Shale
More likely it is the buildup of gumbo onwalls of hole
There is no conclusive evidence that the
hole size in a shale section is reduced
due to the shale moving
Should see a smaller hole on caliper log
Squeezing Formations
S i F ti
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Squeezing Formations
Reactive formationswill absorb water and
swell
The sticky formation
can then stick to the
walls of the hole and
the drill string
Shale does notactually move into the
wellbore
Shale Slo ghing
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Sloughing shaleFour causes of sloughing shale
Water sensitive
Tectonically stressed
Over pressured
Combination of above
Shale Sloughing
Shale Sloughing
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Water sensitiveShale has highly reactive clays
Usually associated with younger and
softer shale
Absorbs water
Use a more inhibited mud
depending upon how long the
formation will be open
Shale Sloughing
Shale Sloughing
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Water sensitive
Salt can be added to the mudsodium,
potassium, magnesium, calcium
(potassium is most effective)
Some polymers will help to inhibit shalesLignosulfonate muds used to tolerate
higher solids content
Oil or synthetic based muds are the onlymuds that will truly inhibit the shales
Reduce API fluid loss?
Shale Sloughing
Shale Sloughing
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Shale Sloughing
Tectonically
stressed
Large differences
in horizontal
stresses willcause sloughing
Forms an elliptical
hole when it
sloughs
Shale Sloughing
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Tectonically stressed
Usually associated with heavy
faulting near mountains and thrust
faults
Increasing mud weight will stop it
depending upon the stress imbalance
and degree of water sensitivity
Formations are less stable when
drilling at higher angles or horizontally
Shale Sloughing
Shale Sloughing
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Shale Sloughing
Open hole logshowing stress
related
sloughing withelliptical hole
Caliper 1
Caliper 2
Shale Sloughing
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Over pressured shaleMud weight in wellbore is too low
Pressure differential exceeds the
tensile strength of the shale
Fails in long, thin pieces
Increase mud weight
Shale Sloughing
Hole Problems
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Hole Problems
Sloughing causedby over pressured
shale
The shale has
sloughed in long
thin pieces
Shale Sloughing
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Shale Sloughing
Unconsolidatedformation
While drilling across
an unconsolidatedzone, loose sand and
gravel may collapse
and pack-off the
wellbore
Shale Sloughing
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Shale Sloughing
Form a filter cake on theunconsolidated formation
Increase the viscosity of the drilling
fluid to do a better job of cleaning thehole
Shale Sloughing
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Shale Sloughing
Fractured and faultedzones
Similar to boulders
If the fractured materialsloughs fast enough, it
may stick the drill string
Increase mud viscosity
to clean the hole
Shale Sloughing
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Shale Sloughing
Under gauge holeForcing the bit into an
under gauge hole can
cause the pipe to get
stuck and/or damage thebit
If an under gauge hole is
encountered, ream thebit to bottom with lower
bit weight
Shale Sloughing
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Shale Sloughing
Collapsed casingCan be caused by under
designed casing or
casing wear while drilling
Need to change the
casing design
Shale Sloughing
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Shale Sloughing
Poor hole
cleaning
If the hole is not
cleaned
efficiently, abuildup of
cuttings can
pack off and
cause the drillstring to get
stuck
Shale Sloughing
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Shale Sloughing
Poor hole cleaningMust do a better job of cleaning the
hole which will be discussed in a
separate chapter on Lifting Capacity
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