dop 205 - rev 6

7/28/2019 DOP 205 - Rev 6

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Drilling FluidsPage : 1 of 21Rev No : 6Date : 28.01.00Doc No : DOP 205

Document No. Document Title

DOP 205 Drilling Fluids

TABLE OF CONTENTS

1.0 PURPOSE...................................................................................................... 22.0 SCOPE........................................................................................................... 23.0 RESPONSIBILITIES...................................................................................... 24.0 DEFINITIONS.............................................................................................. 2 5.0 PROCEDURE................................................................................................ 2

5.0 Drilling Fluids.......................................................................................................... 25.1 Drilling Fluids Classification.................................................................................... 55.2 Drilling Fluid Field Tests....................................................................................... 115.3 Solids Control....................................................................................................... 135.4 Corrosion Control................................................................................................ 15

6.0 REFERENCES........................................................................................... 16 7.0 ENCLOSURES........................................................................................... 16

RevNo

Date Preparedby:

Verified by: Approved by:QA and Safety

Managers

Reason for Revision

4 21.01.98 KJO WVE / ICO AJE As per Revision Request001/96

5 12.03.99 IMI / LVA ICO AJE / BNO As per Procedural ReviewScheme

6 28.01.00 IMI / LVA ICO AJE / BNO Re-issued for im lementation

G:\Management Library\Drilling Operations Manual\DOP 200\DOP 205

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1.0 PURPOSE

The purpose of this procedure is to describe and give guidance on drilling fluidsand solids control.

2.0 SCOPE

This procedure applies to all Stena Drilling’s Units.

3.0 RESPONSIBILITIES

3.1 Senior Toolpusher

The Senior Toolpusher is responsible for the implementation of this procedure.

4.0 DEFINITIONS

N/A.

5.0 PROCEDURE

5.1 Drilling Fluids

Drilling Fluids are a large subject in themselves and it is beyond the scope of this procedure to consider them in extensive detail. The nature of drilling fluidsand procedures required to handle and treat them are changing. This is due tofurther research being carried out to find effective and economical fluids.There is the need to develop drilling fluids which will withstand the extremes of temperature and pressure in deep, hot holes. There is the need to limit andeventually prevent damage to the environment. This section is an attempt togive information that will aid understanding of drilling fluids and consider procedures that will be required to obtain environmentally friendly andeconomical solutions.

• Drilling muds consist mainly of three parts :-

1. The liquid phase (water or oil).

2. The reactive part (colloidal portion)-chemicals, clays etc..

3. The inert part - sand, weighting material etc..

Treatment of drilling muds is aimed at the colloidal portion as this is where themud can be improved by chemical treatment, or is damaged by contamination.


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• The drilling fluid has at least ten important functions :-

1. Removal of cuttings from the bottom of the hole to surface.

2. Cooling and lubrication of the bit and drill string.

3. Coating the hole with impermeable cake.

4. Controlling downhole pressures.

5. Suspending cuttings and weight material when circulation is stopped.

6. Releasing sand and cuttings at surface.

7. Supporting part of drill pipe and casing weights.

8. Reduce to minimum any adverse effects on formation adjacent to thehole.

9. Assist in obtaining information about the formations drilled.

10. Transmitting hydraulic horsepower to the bit.

Samples

A sample must be taken from the bulk manifold sampling cock during theloading of all drilling fluids.

Samples to be retained until the end of the well.

5.1.1 Cuttings Removal

The face of the hole and edge of the Bit are cleaned by the jetting action of fluidflowing from the Bit nozzles. The fluid being circulated up the well carries thecuttings towards the surface. The cuttings tend to sink through the fluid under the influence of gravity. The speed of this “sinking” is known as the SlipVelocity. As long as sufficient mud is circulated fast enough to overcome thiseffect, the cuttings are brought to surface. Hole Cleaning depends on severalfactors:

Velocity

The annular velocity is an important factor in getting cuttings to the surface.This is dependent on pump capacity, pump speed, hole size and drill pipe/drillcollar size. It is necessary to balance several factors when determiningcirculation rates. Too high a circulating rate will lead to annular velocities aroundthe Drill Collars being greater than the critical velocity. This will then lead to holeerosion (washing out). The Critical Velocity is dependent on mud properties.Too low a circulating rate will lead to the hole not being cleaned. It is importantto consider the effects of larger annuluses (e.g. drill pipe in marine riser). It canbe seen that when drilling small diameter hole (8½" & 6") that it may be

necessary to boost the riser to ensure that cuttings are lifted.Density


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This will have a buoyant effect upon the particles. Increasing mud densityincreases carrying capacity both by buoyancy and solids interference.

Viscosity

This depends on the concentration, quality and dispersal of the suspendedsolids in the mud.

5.1.2 Cooling And Lubrication

Heat is generated by friction in the bit and by contact between the drill string andthe hole sides. This heat is absorbed by the circulating fluid and released atsurface.

Lubrication is improved by use of emulsifying agents and lubricants.

5.1.3 Wall Building

A good drilling fluid will deposit filter cake on the side of the hole to strengthenthe formation and reduce fluid passing into the formation. This is achieved bytreating the mud to improve solids distribution and fluid loss reduction.

5.1.4 Control Of Downhole Pressures

This is achieved by use of mud density. Normally, the weight of water plus thesolids picked up from drilling is sufficient to balance normal formation pressures. Abnormal formation pressures require the addition of mud weighting materials

such as barite to increase the hydrostatic head of the mud column. This isdiscussed in greater detail in the Ref: Well Control Manual WCO 200.

5.1.5 Cuttings Suspension/Release

Cuttings being carried to surface are held in suspension by gelling or thixotropywhich develop well after circulation has stopped. When circulation resumes, themud returns to its fluid condition and the cuttings are carried to surface.Cuttings are then broken out using solids control equipment.

5.1.6 Weight Support

The weight supported by surface equipment becomes increasingly importantwith increasing hole depths. Since the drill pipe and casing are buoyed up by thedrilling fluid, then an increase in mud density will result in a reduction in the totalweight that the surface equipment must support.


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5.1.7 Hole Information

It may be necessary to adjust mud properties to improve data gathering.For example, addition of oils to lubricate the hole may be forbidden as it

interferes with the work of the Well site Geologist. Treating mud resistivityproperties to improve the interpretation of electric open hole logs are another area.

5.1.8 Transmit Hydraulic Horsepower To The Bit

The drilling fluid is the medium for transmitting available power at surface to thebit. Flow properties of the mud, plastic viscosity and yield point exert aconsiderable influence on hydraulics and need to be controlled at proper values. All the factors need to be balanced to ensure that the optimum power isavailable at the bit to clean the face of the hole.

5.2 Drilling Fluids Classification

There are many types of drilling fluid in use and new types are constantly beingdeveloped. They can be classified into groups as follows:

5.2.1 Water Base Fluids

Fresh Water Muds - Little Or No Chemical Treatment Required

• Spud Muds - bentonite or clay mix, sometimes mix water must be treated

with soda ash or lime. Generally used offshore to sweep hole as a pillwhilst drilling with sea water and dumping returns.

• Natural Muds - result from formations containing good mud making clays.

In most cases, the natural mud will be chemically treated and become oneof the treated muds discussed below.

Chemically Treated Muds - No Calcium Compounds Added

• Phosphate Muds - usually limited to areas with soft fresh water and good

mud-making formations. These would generally be used in relativelyshallow wells (7500ft or less) as phosphates cannot withstand temperaturesabove 180ºF, and are not effective when contaminated by salt or calcium.

• Organic Treated Muds:

1. Quebracho and other extracts - these are more resistant tocontamination and higher temperatures than phosphate muds.However they have been largely replaced by other types of organictreated muds.

2. Chrome Lignosulphonate - have been successful in wells with 400°Fbottom-hole temperatures and have low reactivity with formation clays.

• Calcium Treated Muds - the use of lime, gypsum or calcium chloride is no

longer so common as these muds have been replaced with lignosulphonatemuds due to their better reaction to high temperatures etc.


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• Salt Water Muds - these will be the most common types of water base

drilling fluid in use offshore :-

1. Sea Water Muds - combined with polymers.

2. Saturated Saltwater Muds - combined with polymers and used for drilling massive salt beds or domes to prevent hole enlargement due tosalt being dissolved in a non-saturated mud.

• Oil-Emulsion Muds (oil-in water) - these are a water base mud with oil mixed

so that the oil is suspended as individual droplets in the water phase of themud. These muds are effective in improving hole conditions,reducing torque and improving bit life as they offer better lubrication thanwater base muds.

5.2.2 Oil Base Fluids

These Have Many Applications And Have Many Advantages

• Good protection and reduced damage to producing formations.

• Good for drilling deep, hot holes as mud is more stable.

• Reduce problems associated with differential sticking.

• Reducing severe drill string corrosion problems.

• Drilling troublesome shale formations.

• Reducing Friction i.e. Torque and Drag particularly in directional wells.

The main disadvantage of using oil base fluids is containing them to preventenvironmental damage and the need to clean and treat drilled cuttings beforedisposing of them. They also present additional problems for Well Control asgases are more readily absorbed into solution and then break out higher up thehole. Ref. Well Control Manual WCO 200.

Procedures For Use Of Oil Base Muds (OBM)

It is essential that the loss of OBM to the hole and the environment is kept to aminimum. The following priorities should be observed :-

• Safety.

• Environmental Protection.

• Operational Progress.

Safety

• Safety clothing should be worn to minimise contact with OBM/Base Oilproducts. This should include the use of barrier creams to protect areas


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such as hands/arms which will be most at risk. Refer to Product DataSheets for detailed information on the products in use. This informationshould be available from the Service Mud Engineer or the Medic.

• Ensure that personnel designated to use equipment with OBM such asMud-Vac Units, High Pressure Wash Down Guns using Base Oil areproperly instructed in their use and that relevant precautions are observed.

• Spillage of OBM in working areas is to be minimised. The use of a

Mud Saver Valve is recommended to avoid spillage during connections. Any spillage’s should be dealt with immediately using Mud-Vac etc.

Environmental Protection

It is essential that procedures are developed to manage the use of OBM/BaseOil on the installation. These procedures must address several areas :-

• Prevent spillage of OBM/Base Oil from the unit.

• Monitor volumes of OBM/Base Oil onboard and account for all parts of the

system. Any discrepancies must be investigated immediately and correctedbefore continuing with operations. These must be reported to OIM,Senior Toolpusher and Operators Representative.

• Oil entrained with drilled cuttings must be monitored as required to ensure

compliance with guidelines/legislation. The use of cuttings cleaningequipment may be required for certain types of OBM’s.

The following are guideline procedures to assist in developing InstallationSpecific Procedures for Oil Base Muds and Base Oils:

Preparations For OBM

• Loading or Backloading of Oil Base Mud must be carried out under Permit

to Work.

• No OBM should be off loaded from the supply boat until all pits have been

cleaned and pit dump valves and main dump valve closed and Tie wraps or plastic chain installed on valve handles, also no OBM should be held in the

sand traps until the water base mud section of the hole is completed.

• Check the integrity of all dump valves, mud mixing system valves, loading

system valves and hoses.

• Check out mud saver/containment systems on the unit. Ensure that valves

are properly set up to route OBM to the recovery tank and not to dump.Test any pumps and alarms which may be part of this system.

• Check seals on the mud bucket in case it is necessary to pull a wet drill

string.

•Close and lock-off all dump valves etc. to prevent inadvertent dumping andloss of OBM.


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It is recommended that heavy duty tie wraps or plastic chain is used for this.In the event of an emergency such as a fire, when the mud pits might have to bedumped in a hurry, then the tie wraps or plastic chain can be broken. Keys to

the padlocks should be kept by both the S.T.P. and OIM. It is recommendedthat dump valves are only unlocked and operated under the permit system whenthe OIM and S.T.P. are satisfied that the tank contents to be dumped will notcreate a pollution hazard.

• To avoid water contamination of the oil base mud, it is recommended that

all water lines in pump room, shaker house above pits and flowlines areisolated/plugged as required. Any mixing pump packings lubricated bywater should be converted to grease lubrication or alternatively fitted with amechanical seal.

• Ensure that adequate supplies of protective equipment are available for

personnel who will come into contact with OBM/Base Oil.

• Ensure that Mud-Vacs, Washdown Guns etc. are set up, tested and

personnel receive proper instruction in their use.

• Order and fit any mud saver valves required to the DDM to minimise spillage

during drilling operations.

• Areas around mixing pumps, main mud pumps, possum belly tank shaker

house and rig floor to be bunded and sealed to ensure that OBM returns tocentral collection tank. Mousehole drain to return to system.

Loading/Backloading OBM/Base Oil

• Establish the quantity of Oil Base Mud and Base Oil to be loaded and

ensure that all personnel involved in the operation are fully briefed. Confirmwith the Supply Boat Master regarding the sequence of operations, thevolumes of base oil and oil base muds that he is carrying and an estimationof the volumes left on the boat after the operation is completed.

• It is customary for Oil Base Mud to be loaded direct to the Mud Pits and for

Base Oil to be loaded direct to its designated storage tank. It isrecommended that the Base Oil is loaded first to avoid any chance of oil

base mud being loaded into the tank. This will avoid the chances of solidssettling out and the tank having to be cleaned.


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• Consideration should be taken when operating within Areas of

Environmental Sensitivity with a view to this operation being carried outduring daylight hours only. At all other times, if it is required to carry out theoperation at night, an assessment should be made of the overside rig

lighting and it should be established that there is sufficient artificial lightingat the manifold and the area between the rig and the supply vessel toensure that any leaks are readily identified.

• Flotation jackets should be fitted to all bulk hoses used for the transfer of

OBM and any other oil cargoes.

• Prior to commencement, ensure that proper communications are

established between the parties involved in carrying out the operation.Recommended personnel :-

1. Master/Barge Engineer (in charge).

2. Control Room Operator.

3. Assistant Driller/Derrickman.

4. Service Mud Engineer.

5. Mud Loggers.

Ensure that there is always a watcher at the side of the installation observing theboat and hoses to raise the alarm in the event of a leak. The Master/Barge

Engineer may perform this task himself if necessary.

• Inform personnel before pumping starts and seek confirmation from the

supply boat master when pumping actually starts.

The Service Mud Engineer should take samples to ensure that there has beenno contamination on the supply boat and to ensure that the correct fluid isbeing pumped (i.e. base oil to the storage tank, oil base mud to the pits).

The Assistant Driller/Derrickman/CRO/Mud Loggers should monitor and recordquantities as required.

• Upon completion of the loading operation, the Assistant Driller/Derrickman,CRO, Mud Engineer and Supply Boat Master should tally up quantitiestransferred and identify/explain any discrepancies. Loading Valves andLines should be secured and valves chained and locked as required.

Transfer Of Base Oil To Mud Pits

• Assistant Driller/Derrickman should check that required valves are open,

dump valves are closed etc. before starting transfer operations.

• CRO/Barge Engineer should dip the storage tank before and after the

operation to check volumes.


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• Assistant Driller/Derrickman should monitor the transfer and ensure that

good communications are maintained during the operation. Mud Loggersmay assist in monitoring quantities.

• Upon completion of the operation, Volumes should be tallied up by

Assistant Driller/Derrickman and CRO and compared for discrepancies. (It isessential to determine volume contained in the transfer system and tank“dead” volumes when carrying out comparisons.) Transfer Volumes shouldbe recorded on both :-

1. Daily Marine Log.

2. Active Mud System Record.

3. Pit Room Mud Tank Volumes.

OBM Management During Well Circulation

• It may be necessary to run one shale shaker with larger mesh screens at

the start of OBM circulation until the mud warms up and the gels breakdown.

• Ensure that Shaker House and Pump Room are manned at all times

(Ref: Section 5.3.2 in DOP 202). Driller must be informed immediately andcirculation rate reduced if any OBM is lost over the screens.

• A high pressure washdown gun fed with base oil should always available to

wash shaker screens which might be blinding off.

• If losses at the shakers start to occur then the following procedure is

recommended :-

1. Shaker Hand advise Driller to cut back on circulating rate.

2. Assistant Driller to go to the Shaker House (advise Mud Engineer of theproblem).

3. Wash Screens/Carry out Screen Changes as required to preventlosses.

4. Advise Driller when it is possible to increase pump rate to optimum for hole cleaning.

• Keep decks clean and clear of OBM using Mud-Vacs to minimise slippery

conditions and to avoid OBM being carried to non-working areas.


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OBM Management During Tripping

• Maintain good trip records. Investigate any discrepancies thoroughly.

• Slug pipe to ensure pipe is as dry as possible. To reduce the build-up of

OBM on the setback area, it is good practice to pour one or two bucketcontents of base oil down the string to clean the pipe.

• If it is necessary to pull pipe wet, then a mud bucket must be used.

Ensure that this is well drained before removing same.

• Assistant Driller should carry out a visual inspection of the Trip Tank

Recirculating system to identify/isolate any leaks.

Clean Up When Finished With OBM

• Flush Surface Manifolds, mixing manifolds, mud transfer lines to mud pits.

• Wash down all Shakers, gratings on top of pits etc. with high pressure gun

(& detergent if necessary).

• Allow pits to settle and separate off water. Clean up water with detergent

and dump same when clean enough.

• Transfer dirty sludge to a slug pit. This will be transferred to a boat or

collection tank. Use Mud-Vacs to clean pits. If pits are still not clean,wash down again with detergent, transfer sludge and again use Mud-Vac to

remove the last of the sludge.

• Once pit is clear of OBM, wash out with sea water.

5.2.2.1 Pseudo Oil Based Mud

These fluids have all the advantages and applications associated with Oil BasedMuds and the same procedures outlined for the use of OBM must be followed.

POBM’s have zero toxicity and are biodegradable and thus in theory can bedischarged. This has been achieved by replacing the mineral oil content phaseof the drilling fluid with Ester, an organic derived “oil”. POBM is an expensive

mud system in terms of unit cost per barrel, however it is extremely costeffective when compared with the overall well cost of using water based mud or other mineral based muds. The cuttings can also be sent ashore for disposal or re-injected. Minimising surface losses is the key to POBM cost effectivenessand it is crucial that all practices relating to mud handling referred to in thissection are adhered to.

NOTE: Due to the high wax content in POBM, the system is highlysusceptible to low temperature gellation. Upon resumption of circulation after a period of the well being static all shale shakersshould be fitted with coarse screens to minimise surface losses andcirculation rates reduced to allow the mud to shear.

5.3 Drilling Fluid Field Tests


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It is necessary to perform certain tests to ensure that the mud is in proper condition to perform its various functions. More detailed information is availablein Drilling Fluid Manuals and Textbooks. The API has recommended standardmethods of testing in API 13B "Standard Field Procedure for Testing Drilling

Fluids".

Tests 5.3.1 and 5.3.2 will generally be carried out by the Derrickman/Shaker Hand and the results noted on the Daily Mud Weight Record (see Enclosure 1)and three results for the shift will be recorded on the IADC Report. The other tests will be carried out by the specialist Mud Engineer and will be recorded onthe Contract Mud Report as per the Operators Requirements. Reserve pitvolumes should also be recorded (see Enclosure 2).

5.3.1 Mud Weight

This may be reported as: Ib/gal, Ib/cu.ft, psi/1000ft or s.g. This is measured

using a Mud Balance. It is important that this is checked for proper calibrationdaily. Fresh water density = 8.33 PPG or 1.0 s.g.

5.3.2 Viscosity

This is measured using the Marsh Funnel and is reported in seconds per quart.It is important that calibration is checked regularly. The calibration is carried outwith water at 70ºF (plus or minus 5ºF.). This should be 26 seconds per quart(to within ½ sec each side). Supplementary information is obtained with theFann V-G meter, particularly with regard to the gel properties of the mud.This supplies Apparent Viscosity, plastic viscosity, yield point and gel strength.

5.3.3 Filtration

This is a measure of the wall-building property of the mud. This is determinedusing a filter press. The test determines the rate at which fluid is forced from afilter press containing the mud sample under specified conditions of time,temperature and pressure and measuring the thickness of the solid film left onthe filter paper.

5.3.4 Sand Content

The sand content of mud is determined using a sand-screen set. This measuressand content as a percentage by volume. It is important to monitor this closely

as high sand contents will lead to abrasion in lines and mud pumps.Pump problems can be minimised by maintaining low sand contents.

5.3.5 Liquids And Solids Content

Mud properties such as density, viscosity, gel strength and filtration rate dependto a considerable degree upon the solid content of the mud.

Solids content is determined by evaporating a weighed portion of mud andweighing the residue. Fluid content can be found by distilling the mud,condensing and measuring the liquid. The volume of liquid; oil and/or water ismeasured directly as a percentage. In Salt Water Muds, it is necessary to applya correction for the salt content as found by filtrate analysis.


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5.3.6 PH Concentration

The pH of a drilling fluid indicates its relative acidity or alkalinity. Double distilledwater is neutral, it is neither acid or alkaline. This is represented by a pH of 7.

Acids are represented by PH’s 1 - less than 7, a strong acid is seen with a pH of less than 1. Alkaline solutions range from just above pH 7 to a pH of 14 for strong alkaline solutions. Two main methods are used for determining the pH of drilling fluids. One is based on the colour changes seen for different PH’s whenusing phydrion paper. These colours are compared with a standard colour chartto read pH. The other method uses a Glass-Electrode pH meter which gives adirect measurement of pH. The control of the drilling fluid pH is important for several reasons; minimising steel corrosion, treating chemicals will not reactcorrectly if the pH range is wrong and their action may become inhibited.

5.3.7 Filtrate Analysis

These are chemical procedures which are used on mud filtrates to the presenceof contaminants, such as salt or anhydrite (Calcium Sulphate),or to assist in thecontrol of mud properties. These tests are applied to mud make-up waters asthey may contain salts which affect mud treatment.

Tests can be done to estimate properties such as :-

Alkalinity determination: High pH muds, Lime Content estimation -controlling properties of lime muds SaltConcentration (Chloride) - significant in areaswhere salt can contaminate the drilling fluid.Preservative Concentration - where a preservativeis being used to prevent deterioration of a treatingchemical e.g. fermentation destroying starch.

Hardness Tests: Measuring calcium and magnesium saltconcentrations. A hard water will require morebentonite to make a good gel mud as drilling clayshave low yields when mixed in hard water.

Resistivity: Control of this may be desirable for better formation evaluation from electric logs. This isdetermined by measuring the resistance toelectrical flow through a sample.


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Methylene Blue Test: this supplies information about the natureand type of clays present in the mud. The sameinformation is also required about the clays andshales that are being drilled, since they become

part of the mud system.

5.4 Solids Control

Mud solids control is one of the most important aspects of mud management.Drilled solids have adverse effects such as :-

• Increased drilling fluid maintenance costs.

• Difficulty in maintaining proper mud rheological properties.

•

Reduced Penetration rates.

• Decreased Bit Life and increased wear on pump parts.

• Increased frequency of differential sticking.

• Increased circulation pressure losses.

5.4.1 Solids Control Equipment

Mechanical removal of drilled solids is accomplished by three techniques :-

• Screening.

• Centrifugal force.

• Combinations of 1 and 2.

It is essential to properly set up and sequence solids control equipment toachieve successful solids removal of an upstream unit will result in overloadingon downstream equipment and a corresponding decrease in efficiency.

Proper Sequencing of Equipment - order of flow from well.

For Unweighted Muds For Weighted Muds

(i) Shale Shakers (i) Shale Shakers

(ii) Degasser (if used) (ii) Degasser

(iii) Desander (iii) Desander (use with caution)

(iv) Desilter (iv) Centrifuge

(v) Centrifuge

Shale Shakers


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The minimum size of screen mesh to be fitted will be determined by circulatingrates, solids loading (dependent on penetration rate, screen area and mudviscosity).

Allowances will have to be made when commencing circulation when muds arecold and until gels break down. Larger mesh screens may have to be carried onone shaker to allow for this. Once the mud has warmed up and become slicker then flow can be diverted to finer screens.

Centrifugal Equipment

These rely upon particle separation by size and specific gravity.

• Desanders/Desilters - These use hydroclones which are constructed in such

a way that as the mud is fed into them, a whirling motion of the fluid isinduced. Larger/heavier particles are thrown outward and tend to falltowards the tip of the cone. The fluid and lighter particles rise towards thetop of the cone and are returned to the mud system.

• Desander cones are usually 6" - 12" I.D. A common set up has enough

cones to process 150% of the mudflow.

• Desilter cones are usually 4" I.D. and again enough are fitted to process

150% of the mudflow.

• Mud Cleaners - These are a combination unit with a desilter mounted above

a fine screen shaker. Sufficient cones are used to process 100% of themud flow. The overflow from the desilter is returned to the mud system.The underflow is processed by the screen. This separates the barite fromthe solids not separated by the cone.

• Centrifuges - There are two basic types of centrifuge used to recover barite

and remove viscosity producing fine solids.

These are the decanting centrifuge and the concentric cylinder centrifuge.

5.5 Corrosion Control

Corrosion is a severe and costly problem in drilling. As the tubular goods aremostly iron based and drilling fluids are mainly water based then corrosion isalmost inevitable. This is minimised by the use of internal plastic coatings ondrill string components but it is still to be considered, particularly in wells whichhave greater concentrations of corrosive agents.


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Corrosive agents within the mud are :-

Oxygen

From the atmosphere, reacts with the iron to form oxides. This is shown bypitting of the steel, can be either localised (deep pits) or general(evenly distributed shallow pits). This is treated and removed from the mud withScavengers injected directly into the pump suction. Maintaining high pH willhelp control corrosion rates. Use of film forming chemicals may be consideredwhere necessary.

Carbon Dioxide

From formations and the bacterial degradation of mud chemicals. This is shownby severe pitting (worm eaten appearance). This is treated by maintaining pH of 9.5 or higher using caustic soda or lime where the intrusion is not too severe.

More severe cases may require treatment with film forming chemicals.

Hydrogen Sulphide

Formations are the primary source, but minor amounts may be produced bybacterial and thermal degradation of mud chemicals. This is shown by severepitting, embrittlement and stress cracking. Some generalised pitting and blacksulphide coating may be seen. This is treated by maintaining an alkaline mudwith caustic soda/and or lime and scavenging the sulphides formed.

The corrosivity of a drilling fluid may be estimated using preweighted ringcoupons. These rings are sized to fit into the relief groove in the tool joint box.The rings are placed in the drill string and exposed to the fluid for a period of time. during the drilling operation. Detailed procedures and testing times will beproduced if and when it is decided to carry out a corrosivity check.

Safety When Working With Mud Chemicals

It is essential when transporting, storing, mixing and testing Drilling Muds andTreating Chemicals that all safety precautions are observed as notedRef: Chemical Data Sheets and Safety Manual SAF 200.

6.0 REFERENCES Chemical Data Sheets

SAF 200 Safety Manual

WCO 200 Well Control Manual


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7.0 ENCLOSURES

Enclosure 1 Active System Mud Record (QA Documented

Form 036)

Enclosure 2 Pit Room Mud Tank Volumes (QA DocumentedForm 037)


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Drilling FluidsPage : 18 of 21Rev No : 6Date : 28.01.00Doc No : DOP 205 Enc 1

Enclosure 1

ACTIVE SYSTEM MUD RECORD


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Active System Mud Record

RIG ………… WELL No ............. DATE ............ TOUR FROM .......... TO ...........

MUD IN ACTIVE PIT MUD OUT

TIME WEIGHT VISCOSITY LEVEL WEIGHT VISCOSITY REMARKS

Previous Tour End of Tour Pit Levels

CHEMICALS USED IN ACTIVE SYSTEM

TYPE QUANTITY TYPE QUANTITY

Signature of Derrickman.........................................

G:\Management Library\Forms\Offshore\QA Documented Forms\036 – Active System Mud Record.doc - Rev 1 Page 1 of 1

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Enclosure 2

PIT ROOM MUD TANK VOLUMES


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Pit Room Mud Tank Volumes

RIG……….. WELL No................... DATE .................. TOUR FROM .........TO....... TIME PIT 1 PIT 2 PIT 3 PIT 4 PREMIX SLUG REMARKS

VOLUME VOLUME VOLUME VOLUME VOLUME VOLUME

Wt Vis Wt Vis Wt Vis Wt Vis Wt Vis Wt Vis

CHEMICALS USED

TYPE QUANTITY TYPE QUANTITY

Signature of Derrickman...........................................

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