.CH 3 Drilling Problems
.CH 3 Drilling Problems
.CH 3 Drilling Problems
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Assoc. Prof. Abdul Razak Ismail, UTM
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Assoc. Prof. Abdul Razak Ismail, UTM
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Contents
1. Stuck pipe/pipe sticking
2. Lost circulation
3. Shale problem/borehole instability
4. Mobile formations
5. Undergauge hole
6. Kick and blowout (will cover in Chapter 6)
7. Other problems
Shallow hydrocarbon zones
High bottomhole temperature
Corrosion
Assoc. Prof. Abdul Razak Ismail, UTM
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(b) (c)
Assoc. Prof. Abdul Razak Ismail, UTM
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a. Differential/wall sticking
Definition: A pressure differential
around the circumference of drill
collars or pipe
Wall sticking is caused by:
pipe is held by suction force
resultant from overbalance
hydrostatic pressure forcing
filtrate into a permeable zone
which leaves a thick mud cake
on the wall of the hole Stuck drill pipe results when it
porous and permeable formation becomes motionless against a
permeable bed. After cake
motionless drill string buildup, hole pressure presses
pipe against wall
Assoc. Prof. Abdul Razak Ismail, UTM
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b. Mechanical sticking
A drill pipe can be stuck mechanically when:
Cuttings and sloughing formations pack off the
annular space around the drill string (especially
during a pump shutdown period)
Drill through several layers of formation of
different hardness
Junk dropped from surface
The drill string is run too fast until it hits a bridge,
a tight spot or the hole bottom
c. Key seating
Definition: a phenomenon happens at the dogleg where a
new hole is created by drill string until the drill pipe is
stuck to the wall
When it passes through a dogleg, it tries to straighten and
thus, creating a lateral force which causes the drill pipe
joint to dig into the formation at the dogleg bow
A key-seat can only be formed if the formation is really
soft and the hanging weight below the dogleg is big
enough to create a substantial lateral force
This problem can be identified when the drill string can be
moved downwards but not upwards
2. Lost Circulation
One of the major problems in drilling operation
Occurred in almost every formation and at virtually
all depths
Occurs when hydrostatic pressure of mud exceeds
the breaking strength of the formation
Definition: Partial or complete loss of drilling
fluid during drilling, circulating or running casing
Loss zones
Horizontal Vertical
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Assoc. Prof. Abdul Razak Ismail, UTM
Underground blowout
Natural causes
Unconsolidated shallow formations
Porous and permeable formations
Natural Fractures and voids
Easily Fractured Formations
Types of
loss zones
Fracture
Increase with
depth
Assoc. Prof. Abdul Razak Ismail, UTM
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Pumping time
Assoc. Prof. Abdul Razak Ismail, UTM
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Treatment
Identify the source of mud loss
Determine the appropriate treatment
Amount loss
(% of the
Type Action/Remarks
circulating
rate)
Usually treated as a routine problem
Seepage loss < 10% without interfering with any part of the
operation
Treated immediately but the current
Slight loss 10 - 25% operation may continue if geopressured
zones are not present in the well
Hazadous 25 - 50% Stop all operations (excluding well
control) until remedial action has
Severe > 50% resolved the problem
Assoc. Prof. Abdul Razak Ismail, UTM
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To Combat LC
Raised the bit into the cased part of the hole & wait
Reduce mud weight
Spot LCM of proper size
Prevention of LC
Control downhole pressure
minimize hydrostatic pressure
maintain minimum annular velocity
avoid restriction in the annulus
Setting the intermediate casing into the transition zone
Raised weight of mud gradually when combating high
pressure zones
Start pumps only after rotating pipe
Run & pull drill pipe in the hole slowly
Never spud pipe
In areas of known LC pretreat with LCM
Assoc. Prof. Abdul Razak Ismail, UTM
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Prevention of LC (ctd)
Break circulation slowly
circulate at a slow rate and low pressure until good returns are
obtained without loss of mud, then increase the circulation rate
Selecting a mud system
maintain a minimum mud viscosity and gel strength to prevent
setting of the weighing material
mud system should be able to resist contamination
maintain minimum mud density
use filler materials (loss circulation materials) to prevent severe
loss of mud to the formation to restore circulation
Prevention of LC (ctd)
Use a simple drilling programme and have a good
drilling practice
drill the lost-circulation zone with a maximum-clearance drilling
assembly
lower the drill pipe slowly
Observation of well hole and precautionary steps
extra mud-storage capacity
make sure supply of mud-mixing and lost circulation material is
ample
observe the mud level
Remedial actions
Reduction of mud weight
Correction of lost returns by waiting periods
Placement of soft plugs - LCM
Placement of mud containing a high concentration of bridging
particles
Adoption of special drilling methods such as blind drilling,
drilling under pressure, drilling with air, or aerated mud
Drill ahead-cuttings circulating in the mud system can act as
lost-circulation material
Pull the bit up at least 50 ft from the bottom
Dry drill - minimize the effects of lost circulation or regaining
circulation in minimal time
Assoc. Prof. Abdul Razak Ismail, UTM
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LCM
Fibrous material - sawdust, cotton seed hulls, hay,
leather, bark
Lamellated (flat, flacky) material - mica, cellophane
Granular material - nut shell, perlite, volcanic ash
Combination of two or more of the above materials
Hydration of shale
Mechanical fissuring of shale
sections due to pressure
surges
Restricted hole gauge
(balling, etc.)
Borehole instability
An unstable borehole poses several problems for
the drilling operation:
fill on trips increasing the drilling time & decreasing bit
life
hole washout
swelling formations producing tight hole
Mechanical Hydration
factors factors
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Assoc. Prof. Abdul Razak Ismail, UTM
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Mechanical factors
Erosion effect
annular flow of mud
depend on degree of turbulence in the annulus and
mud viscosity
Impaction by drill string cause the breakage of
shale
Caving due to horizontal movement of the shale
section
Hydration factors
Shale hydration force
the drilling of shale section relieves the compaction
force on the borehole
Osmotic hydration
the difference in salinity between the mud and
formation water of the shale
adsorption force when formation water of the shale is
more saline than the mud
desorption force when the mud is more saline than the
formation water
Other factors
Dipping shale
shale expansion in a direction perpendicular to its
bedding planes
more shale heaving when the section is highly dipping
Abnormal pressured shale
water content of the rock is much higher compared to
the normal pressure shale
plasticity of the shale is high due to the overburden load
shale will be squeezed into the hole because the
difference between formation pore pressure and mud
hydrostatic pressure
Assoc. Prof. Abdul Razak Ismail, UTM
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Planning...
Examine the geology of the area for the
presence of water sensitive clays
Check the past case histories of geopressure
formation
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Assoc. Prof. Abdul Razak Ismail, UTM
Rig site identification
Pulled bit or stabilisers are undergauge
Occurs only when RIH
Sudden setdown weight
Circulation is unrestricted or slightly restricted
Bit stuck near the bottom of the hole or at the top of a cored section
Preventative Action
Use suitably gauge-protected bits and stabilisers
Consider the use of roller reamers
Always gauge all BHA components both when running in and
pulling out of the hole
Ream suspected undergauge sections
Slow the trip speed down before the BHA enters an undergauge
zone
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Assoc. Prof. Abdul Razak Ismail, UTM
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Causes of Kick/Blowout
Drilling into high pressure zones (abnormal pressure)
Swabbing when coming out of the hole
Improper hole fill-up on trips
Lost circulation during drilling or cementing
Detection of Kick/Blowout
Rise in pit level
Hole fails to take right
amount of fluid after
trips
Gas cutting or decrease
in mud weight
Increase in pump speed
or decrease in pump
pressure
Assoc. Prof. Abdul Razak Ismail, UTM
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Prevention of Kick/Blowout
Use high mud weight
Use right type of mud and keep in good
condition
Check mud weight frequently
Check fluid level frequently
Add weight material evenly
Do not add excessive weight reducing
materials such as oil or water
Trip slowly
Keep hole clean to prevent swabbing
Observe surface gas Assoc. Prof. Abdul Razak Ismail, UTM