Cleanout and Debris Removal

Debris Management and Cleanout

Debris Categorization

Solids

Gunk (sludges, emulsions, viscous liquids, PIPE DOPE!)

Junk introduced into the hole

Source: Wellcert www.GEKEngineering.com 1

Photograph (from Colombia) of cutter run.

www.GEKEngineering.com 2

Solids generated during the well

construction process typified by:

barite due to mud settlement

cuttings (cement and formation) due to poor hole cleaning

swarf from milling operations

mill scale rust and other solids from poorly prepared tubulars


Gunk from fluids used in the well

pipe dope tremendously damaging!

viscous muds (milling fluids and synthetic muds at low temperature)

gelled oil based mud after mixing with water


Junk introduced to the well:

seals/elastomeric materials from BOP and

seal stacks

cement plugs and float equipment after drill out

perforation debris

materials accidentally introduced e.g.: wood from pallets

dropped objects

hoses

tools


Junk introduced to the well:

Paint

During lab test in Germany,

(University of Hannover) we found

out that 1 ft2 of paint could plug

1 ft2 of screens.

Sandro Sanchez Adrialpetro Ltd.


RISKS AND ISSUES

Solids and junk result in inability to run the

completion (early setting of packers)

Solids and gunk have both caused problems functioning CIV/FIV type valves requiring bailer runs or coiled tubing intervention

Gunk may produce serious formation damage

Junk and solids can both prevent future well intervention activity or stick perforating guns

Debris on top of wireline plugs can prevent their recovery


The Well Patroller one type of cleanup device designed to remove

debris from the well.


Learning

Functioning the BOP with a clean fluid in the well can introduce junk

Mixing water, brines, and particularly acid with OBM without suitable

surfactants/solvents creates

insoluble gunk (very viscous sludge) that prevented packers being set


Best Practices pt. 1

Proper preparation of tubulars to eliminate rust and mill scale polish prior to use.

Careful fluid and hydraulic design to ensure effective hole cleaning and fluid compatibility

The cleanliness of the wellbore should be confirmed by a gauge ring or drift sub using the clean up/workover string.

Where there is concern about tubular condition (rust/mill scale/excessive doping/cement) pipe pickling should be considered.


TUBULAR: Size

Weight

Grade

3 1/2"

7.7#

L 80

4 1/2"

12.6#

L 80

5 1/2"

17#

L 80

7"

29#

L80

9 5/8"

47#

L80

Total Average Scale In Pounds

Per 1000ft.

81.31 38.98 165.31 147.17 194.88

Millscale Deposition In Pounds

Per Square Inch

0.00031 0.00011 0.0004 0.0002

8

0.00027

Source: Ramco, together with Robert Gordon's Institute of Technology, Wellcert


Mill Scale

The formation of mill scale occurs on steel products in the manufacturing process.

When steel is heated to temperatures above approximately 600C and its surface comes into contact with an uncontrolled atmosphere,

oxidization takes place. When the steel is cooled down, the oxidization

appears as scale.

Oxidization takes place on any surface in contact with air during the manufacturing process. For tubular goods this means that both

internal and external surfaces are affected. The action of rolling the

pipe can force the scale to tightly adhere to the parent metal.

Subsequent heat treatment to tubulars carried out in a furnace, without a controlled atmosphere, will add further deposits of mill

scale.


Removal of Mill Scale in Pounds (of weight loss) PER 1000FT.

TUBULAR: Size

Weight

Grade

3 1/2"

7.7#

L 80

4 1/2"

12.6#

L 80

5 1/2"

17#

L 80

7"

29#

L80

9 5/8"

47#

L80

TREATMENT

Internal Blast Cleaning (1) 40.32 15.46 84.00 19.49 83.33

External Wire Brush (2) 17.47 10.08 24.19 30.24 23.52

External Blast Cleaning (3) 40.99 23.52 81.31 127.68 111.55

Difference Between External

Blast and Wire Brush (3-2)

23.52 13.44 57.12 97.44 88.03

Total Millscale/Corrosion (1+3) 81.31 38.98 165.31 147.17 194.88 www.GEKEngineering.com 14

Scale Density

1 cubic inch of scale in air weighs 0.0614lbs.

1 cubic inch of scale in water weighs 0.0567lbs.


Volume of Scale, in3 per 1000 ft of pipe

(1728 in3 = 1 ft3)

TUBULAR: Size

Weight

Grade

3 1/2"

7.7#

L 80

4 1/2"

12.6#

L 80

5 1/2"

17#

L 80

7"

29#

L80

9 5/8"

47#

L80

Internal 711.1 272.7 1481.5 343.7 1469.7

External 722.9 414.8 1434.0 2251.9 1967.4

Total 1434.0 687.5 2915.5 2595.6 3437.1


Best Practices pt 2.

Use optimum dope (manufacturers recommendation) and torque to spec.

Dope the pin, not the box.

Function test BOP before placing on the well

Keep the hole covered when not in use


Tools for Cleanup

casing scrapers to remove cement and casing burs

brushes to remove gunk and cement

circulating subs to enable high circulating rates to be used

junk subs to remove solids and junk

jetting assemblies


Circulating Spacers and

Displacement Pills Displacement pills designed to ensure effective

mud displacement and water wetting of the casing in the event oil based muds are in use. Key roles:

disperse and thin the drilling fluid (need compatibility with drilling fluids)

lift out debris and junk

water wet pipe

remove pipe dope

effectively displace the mud


Issues

Well control is key in pill sequence (only possible to get thin, light fluids in turbulence

Pumping fluids to displace OBM without suitable surfactant packages may result in insoluble sludge

Low temps can affect surfactant effectiveness

Pills in turbulence lose carrying capacity if annular velocity drops below that required for turbulence


Issues

In high mud weight, risk of inducing barite sag needs to be considered (displacement pills thin

the mud to the point it can no longer support

barite)

HSE needs to be considered for all chemicals used, mixtures of displacement pills and mud

have to be separated from the active mud and

packer fluid for disposal (zero discharge issues)


Learnings

Conventional casing scrapers with spring actuated blocks have failed leaving junk in the hole or even a stuck tool. Conventional scrapers are not built for extended rotation or drilling. Scrapers work in reciprocation.

Failure rate of multifunction ball opening circulating subs has been high in some regions.

Weight actuated tools rely on maintaining weight set down on the tool to maintain the circulation path, all circulation is at one point. These tools should be run with the clutch option allowing drillpipe to be rotated independently of the pipe inside the liner.


Best Practices

A casing scraper should create maximum contact with internal diameter of casing, (match strength of tools to string needs).

Casing scrapers should enable rotation at rates up to 50 rpm. Scraper elements should be be capable of being lost in the hole.

Circulating sub should be of weight set down type (clutch option).

For a clean out strings in high angle cased and perforated well a debris recovery system is best.

Casing brushes are not considered necessary if an effective scraper is selected. If a brush is used it should

be redressed after each application. www.GEKEngineering.com 23

Filtration

Filtration removes solids to prevent build up of solids and helps prevent plugging in

the formation.

Two basic filtration systems are employed:

cartridges (nominal or absolute)

filter presses (Plate and Frame or Pressure Leaf)


Gel sample as pumped

After Centrifuge

Suspended fines in

gravel pack or frac

gel a problem?

Washouts in washpipe

(and screen) during

packing www.GEKEngineering.com 25

Risks and Issues

Filtration can impact pump rate of completion fluids

Filtration may be unnecessary cost in some wells, but should be assessed on a well-by-well basis (from potential damage mechanisms

Filter presses have the advantage of high solids tolerance and throughput - units are large but cheap to operate.

Cartridges used for small volumes of relatively clean material - smaller throughputs and less tolerance to dirty fluids, generally cartridges are more expensive

Can be health and environmental risks associated with operating and disposing of filtration medium.


Learnings

1. Cartridge units are not usually appropriate for dirty or viscosified fluids

2. DE press materials require good HSE control

3. Tendency is to over-specify filtration requirements.

4. Dont filter oil with a DE press.

5. Filtration less required when underbalance perforating(?)

6. Kill pills are usually not filtered

7. Absolute cartridge filters are 2-5 times cost of nominal and usually worth it, but check bed filtration first.


Best Practices

For general applications, coarse filtration to 80 microns is all that should be considered when fluids do not penetrate the formation

When a fluid penetrates the formation, filtration is more likely to be required. Filtration should be tailored to the pore throat size of the

formation. A simple guide to setting a specification is 14% (1/7th) of

the average pore throat diameter

Filtration below 2 microns is usually impractical

Always use a guard filter downstream of a DE press

For a DE press filtration, rate is approximately 1 bpm per 100 sqft for sea water and 0.5 bpm per 100 sqft for a brine


Determination of Well

Cleanliness The determination of how clean the well is usually based on the

cleanliness of fluids returning from the wellbore. The most

common measures are normal turbidity units (NTU) and solids

content, neither relate to what is left in the well.

Junk baskets, gauge rings and the SPS WellPatroller do give some positive indication of solids removal.

Other indicators of a clean well are torque and drag (related to the friction coefficient of fluid coating the casing walls) and

cleanliness of the clean up string when pulled.


Risks and Issues

NTU (a light transmission test) measurements rely solely on the cloudiness of the fluids, corrosion products in return fluids give high values, NTU and solids content are not directly related. Solids content will only assess materials collected at the bottom of the test tube during centrifuging.

Coloured water will give higher NTU values.

Using sample sizes of a few mls, it is difficult to draw conclusions about a well with an annular volume of 500 bbl, 0.1% vol/vol solids equates to +/- 1 cuft of solids

deposited for tubing contents of 200 bbl.


Measurement Learnings

To deal with rust color (or precipitation) interference with NTU readings, add a

small amount of HCl after the first reading

and re-measure.

If the junk basket is full, rerun.


Cleanup Best Practices and

Design Criteria, Pt 1 A solids content of about 0.05% determined by an electric centrifuge

is acceptable for most operations. For gravel packing this should be

reduced to 0.02%.

To determine solids content the standard tubes for sand content for the centrifuge are not usually appropriate, centrifuge tubes with

more accurate calibrations should be obtained.

NTU values should be used to track clean up with regular samples taken for analysis of solids content at a later date.

A target value of 50 NTU above surface pits should be used.

For critical wells e.g. high angle wells/where milling has occurred/previous problems with debris, a circulating junk basket

(e.g., the SPS WellPatroller is recommended).


Cleanup Best Practices and

Design Criteria, Pt 2 Where the string is rotated during clean up the increase

in torque can be used as an indicator, the coefficient of friction in sea water/brine is more than twice that of OBM.

Visual inspection of the clean up string, if it is mud free and water wet mud displacement has been successful, if the string is mud coated run a gauge ring/junk basket or SPS WellPatroller.

For critical application (e.g. gravel pack) use particle size analysers on location, laser particle size systems are recommended.


Debris Removal Equipment

Example tools:

casing scrapers to remove dried mud, pipe dope, cement and casing burs

brushes to remove pipe dope, bacteria colonies and cement

circulating subs to enable high circulating rates to be used

junk subs to trap and remove solids


Equipment Risks and Issues

Equipment failure may result in additional junk or a stuck clean up string, (not a common problem.

There have been instances with casing scrapers and brushes where the clean out tool has introduced junk to the hole when these are not of a single piece construction or have retaining mechanisms for blocks.

Circulating subs (particularly hydraulically operated) carry some risk associated with failing to close thus losing the ability to circulate to the bottom of the well.

Some of the equipment is only available from niche / specialist suppliers which carries risks around QA/QC and tool availability.

There is concern with running well clean up tools with minimum by pass area pushing large pieces of junk ahead and into CIV/FIV tools


Equipment Learnings

Conventional casing scrapers with spring actuated blocks have failed leaving junk in the hole or even a

stuck tool.

Conventional scrapers are not built for extended rotation or drilling. Scrapers work in reciprocation.

Failure rate of multifunction ball opening circulating subs has been high in some regions.


Equipment Learnings

Weight actuated tools rely on maintaining weight set down on the tool to maintain the circulation path (all circulation is at one point). These tools should be run with the clutch option allowing drillpipe to be rotated independently of the pipe inside the liner. (Rotation assists cleanout)

Recent experience with the SPS WellPatroller highlighted it is very effective at removing gunk and solids debris, this tool provides a level of assurance not available with any of the other tools (including conventional junk subs).


Best Practices and Design

Casing scrapers should create maximum contact with ID of casing, be a one piece design with full drill pipe strength and no weak internal connections.

Casing scrapers should enable rotation at rates up to 50 rpm, these should be of a design so that blocks are either retained in the body of the scraper. (UWG/Global) or are an integral design (SPS Razorback).

The preferred circulating sub should be of the type utilising weight set down to function, with a clutch mechanism. If a reliable hydraulic tool is developed this may become preferable as it allows reciprocation with circulation.

For clean out strings in high angle cased well a WellPatroller should be run (or if concern about debris or junk in the well).

Casing brushes are not considered necessary if an effective scraper is selected. If a brush is used it should be redressed after each application.


Performance Best Practices

A brine returns with an NTU < 30 above value of fluid in pits is excellent

performance

Clean returns after circulating < 150% of hole volume is good performance

Interface volumes between pills of

Information Capture

fluid designs and properties

flow rates

pill volumes and volumes circulated

equipment used

materials used and costs

interface volumes

pipe movement during displacement

time breakdown

fluids cleanliness v time during circulation

surface clean up

target vs actual

pipe movement and torque


Will Circulating a Well Really Clean

It Out?

Not necessarily. Clean-out efficiency depends on:

Ability to remove the solids from returning fluids; Fluid hydraulics - the flow rates in every section; Ability to disperse, then lift solids out of the well; Ability to effectively remove the dope, mud cake,

residues, etc., from the pipe walls.

Often, mechanical assistance is required! Pipe movement friction can increase as pipe

becomes water wet.


Circulation Options

Normal Circulation vs. Reverse Circulation

Annular Velocity (AV) w/ rotation vs. AV w/no rotation

Coiled Tubing vs. Drill Pipe

Mud vs. Brine

Ungelled vs. Gelled Brines

Liquids vs. Foam

N2 assistance vs. production gas lift

Mechanical assistance (pumps)


First Considerations

All liquids or solids? Type, size and density of solids? Casing and tubing sizes bottom to top? Well trajectory, restrictions, deviation, depth,

pressure limits?

Reservoir fluids and pressure? Reservoir leakoff potential at cleanout rates? Location access limits, size and weight limit? Equipment availability? Experience availability?


Photograph (from Colombia) of cutter run dope,

rust, mud, etc.


Scrapers and Brushes Physically Cleaning the Well

Available tools

Damage potential


Effect of Scraping or Milling Adjacent to Open

Perforations

-60

-50

-40

-30

-20

-10

0

10

20

1 2

% C

ha

ng

e in

PI

Short Term PI Change

Long Term PI Change

Perfs not protected by

LCM prior to scraping

Perfs protected by

LCM

SPE 26042

One very detrimental action was running a scraper prior to packer

setting. The scraping and surging drives debris into unprotected

perfs.


Casing Scraper Designed to

knock off perforation burrs,

lips in tubing pins, cement

and mud sheaths, scale, etc.

It cleans the pipe before

setting a packer or plug.

The debris it turns loose from

the pipe may damage the

formation unless the pay is

protected by a LCM or plug.


Iron accumulation on a

trench magnet.


Cleanout and Debris Removal

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