03 Hole Problems

5/20/2018 03 Hole Problems

1/53

2005 PetroSkills LLC, All Rights Reserved

HOLE PROBLEMS

Avoid hole problems and

stuck pipe if at all possibleto reduce costs


2/53

2005 PetroSkills LLC, All Rights Reserved2

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


3/53


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


4/53


Hole Problems

Lost circulation

Lost circulation

is when all or aportion of the

circulating fluid is

lost to theformation


5/53


Lost Circulation

Can loosecirculation intoprimary orsecondaryporosity

Generally,primary porosity

will range from 8to 30% forreservoirs


6/53


Lost Circulation

Secondary porosity is porositygenerated by altering the rocks

such as the dolomitization of

limestone or fracturing

Fractures

Vugs

Oolite


7/53


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)


8/53 2005 PetroSkills LLC, All Rights Reserved8

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



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



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



Lost Circulation


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



Lost Circulation


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



Lost Circulation


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



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



Lost Circulation


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



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



Lost Circulation


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



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



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



Lost Circulation

Lost circulation by exceeding thefracture gradient

Service companies are working on

products to increase the fracturegradient

Have had mixed success so far



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



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



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



Differential Pressure Sticking

PfAF fs

, k, P

PheDrill CollarHole

Filter Cake

Drill CollarHole

Filter Cake

Thin Filter Cake

Af

Af

Thick Filter Cake




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


26/53


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



27/53



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)


28/53


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


29/53


Keyseating

KEYSEAT FORMATION

K ti


30/53


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


31/53


Keyseating

Can use a keyseat

wiper at the top ofthe drill collars to aid

in back reaming

through the keyseatinterval

K ti


32/53


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


33/53


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


34/53


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


35/53


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


36/53


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


37/53


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


S i F ti


38/53



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


39/53


Sloughing shaleFour causes of sloughing shale

Water sensitive

Tectonically stressed

Over pressured

Combination of above

Shale Sloughing

Shale Sloughing


40/53


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


41/53


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


42/53


Shale Sloughing

Tectonically

stressed

Large differences

in horizontal

stresses willcause sloughing

Forms an elliptical

hole when it

sloughs

Shale Sloughing


43/53


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


44/53


Shale Sloughing

Open hole logshowing stress

related

sloughing withelliptical hole

Caliper 1

Caliper 2

Shale Sloughing


45/53


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


46/53


Hole Problems

Sloughing causedby over pressured

shale

The shale has

sloughed in long

thin pieces

Shale Sloughing


47/53


Shale Sloughing

Unconsolidatedformation

While drilling across

an unconsolidatedzone, loose sand and

gravel may collapse

and pack-off the

wellbore

Shale Sloughing


48/53


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


49/53


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


50/53


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


51/53


Shale Sloughing

Collapsed casingCan be caused by under

designed casing or

casing wear while drilling

Need to change the

casing design

Shale Sloughing


52/53


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


53/53

Shale Sloughing

Poor hole cleaningMust do a better job of cleaning the

hole which will be discussed in a

separate chapter on Lifting Capacity

Date post:	10-Oct-2015
Category:	Documents
Upload:	brahim-letaief
View:	27 times
Download:	0 times

03 Hole Problems

Documents