Intro to Drilling Fluids New

7/21/2019 Intro to Drilling Fluids New

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Introduction to rilling Fluids

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Introduction to Drilling FluidsIntroduction to Drilling Fluids –– WBM/OBMWBM/OBM

• Course Contents:

• Course Objectives,

• Basic Functions,

• Basic Properties,

• Water based and oil based muds,

• Performance Testing.



• Course Objectives:

• At the end of this course,YOU will be able to:

• List functions & properties of drilling fluids,

• Understand the formation damage

• Describe different mud systems,

• Understand the performance testing of drilling muds




IntroductionIntroduction

• The drilling fluid is a liquid or gas that is circulated downthe drillpipe through the bit and up to the surface. Untiltoday an oil or gas well cannot be drilled without thisbasic concept of circulation.

• A cycle is referred to as the time required for the pump tomove drilling fluid down to the hole and back to thesurface,

• The drilling fluid is a key part of the drilling process, andthe success of a drilling program depends on its design.

• A drilling fluid for a specific area must be individually

designed to meet specific requirements.

• In general drilling fluids will have many properties that arebeneficial to the operation, but also have some propertiesthat are not desirable. There is always a compromise.



IntroductionIntroduction

• A service company provides mud engineering services on

rigs.

• Drilling fluid technology is dominated by three factors :

• Performance

• Economics

• Environmental concerns.



HistoryHistory

• 1900 Water and Clays

No control of properties

• Weighting Agent (‘40’s) Water base muds

• Controlled Filtrate(‘50/’60’s) Cellulose polymers

• Polymers ( 70 ’s) PHPA systems

• Mineral oils(‘80’s) Formation compatibilty

• Synthetics (‘90’s) Environmental




Section 1

Functions of Drilling Fluids



FunctionsFunctions ofof DrillingDrilling FluidsFluids

• Basic functions;• There are at least ten important drilling-fluid functions :

• Remove cuttings from the bottom of the hole, transport them to the surface andrelease them.

• To cool and lubricate the bit and drillstring,• Coat the hole with a low permeability wall cake (filter cake),

• Control subsurface pressures,

• Hold cuttings and weight material in suspension when circulation is stopped,

• Support part of the weight of drill pipe and casing,

• Prevent or reduce to a minimum any damage to the surrounding formations,

• Allows information to be obtained about the formations penetrated,

• Transmit hydraulic horsepower to the bit,

• Control corrosion,




• Remove cuttings from the bottom of the hole, transport them to thesurface and release them.

• Annular velocity is the key parameter to overcome the effect of gravity,

• Annular velocities between 100 and 200 ft/min are frequently used,• Annular velocity can be obtained from:

• AV=Pump rate (bbls /min) / Annular capacity (bbls / ft).

• Density and Viscosity also contribute to improving the carrying capacity of

a fluid,

• The cuttings and solids should be removed at the surface to obtain a

clean fluid to be pumped down the hole.

• Sand is very abrasive and if it is not removed it will damage mudpumps, lines, and tubulars.

• If the cuttings are not removed they will break down and fill the mud

with colloids which will deteriorate the properties of the mud.




• Cool and lubricate the bit and drillstring:

• As the bit and drillstring rotate against the formation, a tremendous amount of

heat is generated,

• The drilling fluid absorbs the heat generated and carries it to the surface,

where it is released to the atmosphere,

• The drilling fluid should have some lubrication properties which will help

reduce the torque and drag.

• The lubrication occurs between the hole and the surface of the bit or

drillstring

• Drilling fluid can also lubricate the bearings of the bit, of the mud motor etc…




• Deposit a low permeability/impermeable wall cake :

• A good drilling fluid should deposit a thin, low permeability filter cake on

the wall of the hole in front of permeable formations to consolidate the

formation and to retard the passage of fluid from the wellbore into theformation.

• The differential pressure will result in fluid invasion, which in absence of

a filter cake would force mud or filtrate into the formation,

• The loss of mud or high filtrate volume is likely to cause formation

damage,




• Control subsurface pressure :

• Mud hydrostatic pressure must be sufficient to prevent an influx ,

• The mud density ( mud weight) is the controlling factor:• Hydrostatic pressure exerted by the mud column:

Hydrostatic pressure (psi ) = (Vertical depth ft. )(mud weight lb/gal )(0.052)The mud gradient in (psi/ft) = (mud weight lb/gal )(0.052)




• Hold cuttings and weight material in suspension when circulation is

stopped:

• This is achieved with good thixotropic properties of the fluid.

• Thixotropy is the ability of a fluid to develop gel strength with time when it isallowed to stop at rest, but will also allow it to return to its fluid state by applying

mechanical agitation to it.

• Support part of the weight of drill pipe and casing:

• As a well is drilled deeper, the weight of the drill string and casing string

becomes a critical factor.

• The mud helps reduce the weight of the drill string and casing string as these

are buoyed up by a force equal to the weight of mud displaced.

• Increasing the mud weight increases the force of buoyancy.




• Avoid damage to productive zone :

• The fluid used to drill the production zone will have an important impact onwell productivity ,

• Loss of production results from:

- Swelling clays

- Reservoir pores blocked with solids and/or micro-emulsion droplets.

• Allows information to be obtained of the formations penetrated

• The properties of the fluid should not interfere with the logging program, theyshould facilitate obtaining the desired information.

• For example, the mud should have a defined/known resistivity so that whenlogs are run the resistivity of the formation can be derived.




• Transmit hydraulic horsepower to the bit :

• The drilling fluid is the medium to transmit hydraulic horsepower to the bit,

• The flow properties of the mud exert a considerable influence on hydraulics.

They should be optimized to obtain good hydraulics.• Optimum hydraulics will promote high penetration rates.

• Protect the drill pipe against corrosion :

• The drilling fluid should be non corrosive,

• Corrosion rates will increase as pH decreases.

• Corrosion can lead to :

- premature Wash out

- premature pump failure

- premature surface leaks.




Section 2

Properties of Drilling Fluids

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• Density

• The primary performance requirement for a drilling fluid is

pressure control

• The density of any mud is directly related to the amount andaverage specific gravity of the solids in the system,

• The control of density is important in that the hydrostatic

pressure exerted by the column of fluid is required to contain

formation pressure and to aid in keeping the hole open,

• The density of drilling fluids should be dictated by

formation pressures,

• The pressure exerted by the fluid column should behigher than the formation pressure.

PropertiesProperties ofof DrillingDrilling FluidsFluids

P tiProperties fof D illiDrilling Fl idFluids




• Density

• The control of density is important,

• The density will need adjustment during well operations,

• Weighting material such as Barite will be used due to its high

specific gravity ( 4.2 sg),

• Under circulating conditions the effective pressure is increased

by the circulating pressure,• The Equivalent Circulating Density

ECD = (depth x 0.052 x mud density(ppg)) +Pann

depth x 0.052





• Viscosity

• Viscosity is defined as the resistance of a fluid to flow.

• It is routinely measured in the field using the Marsh funnel and it is

the timed rate measured in seconds of what it takes one quart offluid to flow through the funnel. (water = 27s)

• As penetration increases, inert solids and contaminants enter the

mud system and can cause the viscosity to increase.

• The Marsh Funnel can be used to determine if the viscosity is in

the proper range.




• Rheology

• Rheology is the science of the deformation of materials ( if they are

solid ) or of their flow ( if they are liquid ) under applied stress.• In the case of drilling fluids Rheology is the study of the

characteristics that define the flow and gelation properties of a drilling

fluid.


P tiProperties fof D illi gDrilling Fl idFluids




Rheology-Characterisation of Fluids;

A

2 Platelets

F

-The resistance or drag force is the shear stress

v

v + dv

-The difference in the velocities divided by the

distance is called the shear rate





• Shear Stress – the force required to overcome a fluid’s resistance toflow, divided by the area that the force is acting on:

Force causing the shearing Unit : lb / 100 ft2

Surface area of the platelet

• Shear rate – the relative velocity of the fluid layers divided by theirnormal separation distance

Difference of velocity between 2 platelets Unit : sec-1

Distance between 2 platelets

P i f D illi Fl id




• Rheology Models ;

Shear rate

Shear

stress

Newtonian

BinghamPower Law/Non Newtonian

P iP i ff D illiD illi Fl idFl id




• Newtonian Fluids – no particles larger than a molecule – water. Shear Stress

is directly proportional to shear rate.

• Shear Stress = coefficient of viscosity * shear rate

τ = μγ

• Coefficient of Viscosity = Shear Stress / Shear Rate

The units of the coefficient of viscosity are : Centipoise, cP





Non-Newtonian Fluids (anything other than a Newtonian fluid) - Bingham

Plastic Model

• A model which has been used often to characterize the flow properties of

drilling mud is the Bingham plastic model.

• τ = τy + μpγ

( The shear stress is equal to the shear stress at zero shear rate + the

rate of increase of shear stress with increasing shear rate * shearrate.)

•The

τy ( shear stress at zero shear rate ) is called the yield point andthe μp ( rate of increase of the shear stress with increasing shear rate )

is called the plastic viscosity.





• Plastic Viscosity and Yield Point

• Measurements of the plastic viscosity and yield point areessential in determining the cause of abnormal viscosities indrilling fluids.

• Plastic viscosity is the part of flow resistance caused bymechanical friction (interaction of solid particles).

• High concentration of solids leads to friction which will in turnincrease the plastic viscosity. Decreasing the size of solids at

constant volume also increases the plastic viscosity becausethere is an increase in surface area which increases friction.

• The yield point, the second component of resistance to flow ofa drilling fluid, is the measurement of the electro-chemical or

attractive forces in a mud. These forces are a result ofnegative and positive charges located near the surface of theparticles.

P tiProperties fof D illiDrilling Fl idFluids




• Measuring Viscosity with the Fann V-G Meter

•The commonly used Fann V-G (viscosity-gel),or direct indicator

viscometer, is specially designed to measure the rheological

properties of the drilling fluid in the field.

• The instrument has a torsion spring-loaded bob which gives a

dial reading proportionnal to torque and analogous to the shear

stress.

•The speed of rotation rpm,is analogous to the shear rate.

•Instrument constants have been built in so that plastic viscosity

and yield point readings are obtained from dial readings for two

rotor speeds, 300 and 600 rpm.







• Gel Strength ( lb/100 ft2);• Gel strength measurements denote the thixotropic properties of the

mud. They are the measure of the attractive forces under static or

non flow conditions.

• Yield point, on the other hand is the measure of attractive forces

under flowing conditions.

• Gel strengths are classified as progressive ( strong ) or fragile (

weak ) type gels. A progressive gel starts low, but increases

consistently with time; whereas, a fragile gel, may start high initially

but only increase slightly with time.

• Progressive gels are undesirable because they may create

problems such as excessive pump rates to break circulation, lost

circulation, hole swabbing, etc.





• Gel Strength ( lb/100 ft2

)





• Non-Newtonian Fluids – Power Law Model

• The Power Law Model is a more versatile approach to describe the flowproperties of a non-Newtonian fluid.

• The equation for the power law model is: τ = Κγn

Where: τ = Shear stress

Κ = Consistency Index

γ = Shear rate (sec-1)

n = Power Law index

• The K and the n are constants representing characteristics of a particularfluid.

• K is a consistency index indicative of the pumpability of the fluid

• n is the Power Law Index indicating the the degree of non-Newtonian behavior over a given shear rate range.

• As a fluid becomes more viscous, K increases; as a fluid becomesmore shear thinning, n decreases.





• Rheology and flow regimes;

• In 1833, Osborne Reynolds conducted experiments with

various liquids flowing through a glass tube.• The type of flow in which all the fluid motion is in the

direction of flow, is now called laminar flow,

• A rapid, chaotic motion in all directions in the fluid is

called turbulent flow,

• A fluid’s flow at extremely low flow rates is plug flow,

• The flow can alternate back and forth between laminar

and turbulent, it is a transitional flow.





Velocity Profile ( Sliding motion )Velocity is maximum at the center

• Rheology - Laminar flow;





• Rheology - Turbulent flow;

Velocity Profile ( Swirling motion )Average particle velocity is uniform





• Rheology - Reynolds number

• Reynolds number takes into consideration the basic factors

of pipe flow :• Pipe, diameter, average velocity, fluid density and fluid

viscosity,

• Re= Velocity* pipe diameter* density / fluid viscosity

• Laminar < 2000- Transition - 3000 <Turbulent

The particular flow regime of a drilling fluid duringdrilling operations can have a dramatic effect on parameters

such as pressure losses, hole cleaning and hole stability.





• Filtration ;• There are two types of filtration - dynamic and static.

• In dynamic filtration, the flow tends to erode away the filter cake as

it is deposited; while in the static case, the cake continues to

become thicker with time.

• There is no way to measure dynamic filtration in the field, so

measurements done by the mud engineer are confined to tests

done under static conditions.

• For filtration to occur, the permeability of the formation has to be

such that it will allow passage of fluid between the pore openings.

• As the fluid is lost, a build up of the mud solids is formed on the wall

face. ( Wall Cake ). The solids that form the mud cake are both

native solids found in the formations drilled and different kinds of

solids added at the surface (fluid loss control additives).

• In order to obtain the best possible filter cake, careful consideration

should be given not only to the base materials used, but on the

particle size distribution.




• Filtration ;• The following problems occur from improper filtration control :

• Tight spots in hole causing excessive drag.

• Greatly increased pressure surges when moving pipe due todecreased hole diameter – further exacerbated by poor

rheology.

• Differential pressure sticking of the drill string due to increased

area of contact of pipe in a thick filter cake and rapid build-up ofsticking force in high permeability cake.

• Primary cementing problems due to poor displacement of

dehydrated mud and excessively thick filter cakes.

• Formation evaluation problems from excessive filtrate invasionand thick filter cakes.

• Excessive formation damage from mud filtrate.





• Filtration;• Drilling fluids used to drill the production zone have an impact

on well productivity due to the compositions and properties of

drilling and completion fluids,

• Filtration control, bridging and filtrate chemistry are the mostimportant properties for minimizing formation damage.

• How easy it is to remove the filter cake prior to production

ope t esp o gg u ds




• Filtration schematic;

Pore Throat

Fluid phase

Pore Blocking

Agent

Filter

Cake

pp gg




• Filtration control;• The formation of a thin tight filter cake will protect against high

drilling fluid filtrate invasion into the formation.

• Filtration control is achieved in drilling fluids by the addition ofbentonite clay, fluid-loss control polymers, lignite, resins, calcium

carbonate,etc.

• A common practice is to further reduce the filtration rate of the

drilling fluid before the reservoir formation is drilled.

• In many cases the reservoir formation is drilled with special clean (

clay free ) Drill-In fluids to prevent emulsions from forming and

plugging the formation. These fluids are formulated by polymers

and properly sized blocking inert solids such as Calcium

Carbonate.

pp gg



SolidsSolids ContentContent



SolidsSolids ContentContent

TheThe effecteffect ofof densitydensity onon PVPV -- YPYP



TheThe effecteffect ofof densitydensity onon PVPV YPYP

SolidsSolids controlcontrol











Section 3

Types of Drilling Fluids

Introduction to Drilling Fluidsg WBM/OBM/

TypesTypes ofof DrillingDrilling FluidsFluids



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• Water-based muds;

• The majority of drilling fluids are water based.

• The base liquid can be :

• Fresh water,

• Sea water,

• A specific brine base (NaCl, KCl, formate based)

• Special additives are used to build a water based mud in orderto achieve the rheological and filtration control parametersrequired to drill each individual hole section.




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• Water- based muds and additives ;

• Clay materials,

• Viscosity control additives,• Viscosifiers,

• Thinners,

• Filtration control additives,• Density control additives .




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• Clay materials ;

• Bentonite is used in drilling fluids for viscosity and fluid

loss control,

• Different grades of bentonite :

• Wyoming bentonite, pure sodium montmorillonite,

• API Bentonite, montmorillonite treated with polymers,

• OCMA Bentonite, calcium bentonite treated with soda

ash to replace the calcium with sodium,

• Commercial clays are graded according to their yield.

(Yield is defined as the number of barrels of 15 centipoisemud that can be obtained from one ton of dry material )




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• Clay materials ;,

• The yield of a clay will be affected by the saltconcentrations of water. Clay is hydrated in fresh water or

drill water. The higher the salt content the lower the yield.

• Hydration is reduced by the presence of Calcium andMagnesium ions, therefore a chemical treatment (Soda

Ash) of the base water will be necessary prior to hydration,

• Salt water gel (attapulgite) or prehydrated gel will be usedwith salt concentration. This product is rarely – if ever – used.







• Viscosity control additives ;,

• Organic Polymers such as Xanthan, PAC or CMC areviscosifiers with long chains molecules :

• Poly-anionic Cellulose polymer,

• Carboxyl Methyl Cellulose polymer,

• Chemicals thinners (dispersants) will reduce the viscosity

of drilling fluids:• Phosphates, lignites, lignosulfonates, tannins or

synthetic thinners may be used.




• Filtration control additives ;,

• Clays such as Bentonite support filtration building a cake,

• Organic Polymers such as starch will swell and is a veryeffective fluid loss control additive.

• Temperature stability is limited to 250 ° F,

• Low viscosity CMC and PAC are also good for forming a

filter cake,• PACs work with salinity( max 60,000ppm) and

temperature stability is limited 350 ° F.




• Density control additives ;,

• Limestone: Mud weight equivalent ( 12ppg)

• Calcium Carbonate, CaCo3 , Specific Gravity: 2.7• Barite: Mud weight equivalent ( 20ppg)

• Barium Sulfate, BaSo4, Specific Gravity : 4.2

• Hematite: Mud weight equivalent ( 25ppg)• Ferrous Oxide, Fe2O3, Specific Gravity: 5.0

• Galena: Mud weight equivalent (32ppg)

• Lead Sulfide, PbS, Specific gravity : 7.4




• Water- based muds;

• The diverse class of water- based mud needs to beclassified :

• Non inhibitive muds

• Where no inhibition is required to control hydratable ordispersible formations

• Inhibitive muds:• Where inhibition is required to control hydratable or

dispersible formations




• Non inhibit ive muds;

• The simplest water based muds, are usually inexpensive.

• Non inhibitive muds , lightly treated are used for :

• Top hole sections,

• Non reactive formations.

• The main components of these fluids are :

• Native formation clays, commercial bentonite,polymers

• Organic thinners - lignites.




• Inhibitive muds;

• Inhibitive muds reduce the chemical interaction betweenthe mud and the formation,

• The use of inhibitors in water based drilling fluidsminimize the swelling (hydration) of clays and reactive(dispersible) shales,

• The diverse inhibitors used are :

• Polymers,

• Cations (such as potassium from KCl)

• Glycols.




• Polymer muds;

• Polymers, naturals,synthetics are routinely used for:

•Viscosity

• Filtration control,

• Shale inhibition.

Water

Shale

Polymers




• High cation concentrations fluids;

• A cation is a mud inhibitor, such a salt, added to a drillingmud to minimize the hydration of formations.

• Cations exchange occurs.

• Inhibitor Cations :

• Sodium

• Calcium• Potassium




• Inhibition;

Ion ExchangeLimit Hydration

Na+

Na+

Na +

Na+

Water

Water + KCl

K+

K+

K+

Na+

Na+




• Water-based muds;

• Spud muds,

• Polymer muds,

• Lignosulfonates muds,

• Lime and calcium mud,

• KCl muds,

• Salt saturated muds,

• Glycol muds.




• Oil base mud;

• Oil-based drilling fluids are :

• Highly inhibitive,• Resistant to contaminations,

• Stable at high temperatures and pressures,

• Highly lubricious,• Non corrosive.




• Invert Emulsion;

• The basic components of an oil base mud include :

• Oil,

• Water / Brine,

• Emulsifier,

• Oil wetting agents,

• Fitration control agents

• Viscosifiers

• Weighting agent

A chemical emulsifier must be addedto prevent the water droplets tosettle out of the emulsion. Theemulsifier also permits water

originally present in the rockdestroyed by the bit to emulsifyeasily

A chemical wettability reversal agent isadded to make the solids in themud preferentially wet by oil ratherthan by water. Otherwise the solids

will be absorbed by the waterdroplets and cause high viscositiesand eventual settling of barite

• The volume percentage of oil and water are expressed as anoil / water ratio .




• Invert Emulsion;

Emulsifier

Water droplets

Oil External phase




Section 4

Performance Testing

PerformancePerformance TestingTesting



• API drilling fluids tests;

• Drilling fluids are continually measured and adjusted at

the wellsite.

• Basic physical and chemical tests serve to monitor the

drilling fluid conditions.

• American Petroleum Institute issues recommended

practices for testing procedures and equipments,

• API RP 13B -1 water based

• API RP 13B -2 oil based drilling fluids




• Standard API tests;

• Tests common to water and oil based muds:

• Mud weight – mud balance• Filtration – API filter press, HTHP Filter press

• Water ,Oil and Solids – API retort

• Viscosity and Gel strength• Marsh Funnel

• Viscometer – Fann 6 speed VG meter




• Formulas and units;

• Density : the primary performance requirement for a drilling

fluid is pressure control,

• The mud weight is the measure of the density of the

drilling fluid expressed as :

• pounds per gallon (lb/gal, ppg)

• pounds per cubic foot (pcf)

• kilograms per cubic meter.(kg/m3)





• Filtration : API Filter Press,

• Darcy law application,• Time 30 min,

• Atmospheric temperature,

• Pressure 100 psi,• Volume of filtrate,

• Cake analysis.





• Liquid and Solid content :

• A carefully measured sample of mud is heated in a 50 mlretort kit until the liquid components are vaporised,

• The vapors are then condensed and collected in a

measuring glass,

• The volume of liquid ( oil and/or water is directly read asa percentage,

• The volume of solids (suspended and dissolved) is

calculated by substraction of 100%.





• Rheology is tested with the Fann V-G meter .

• The commonly used V-G(viscosity-gel),or direct indicator

viscometer, are specially designed to facilitate the use of the

Bingham plastic Model in conjunction with drilling fluids in the

field.

• The instrument has a torsion spring-loaded bob which givesa dial reading proportionnal to torque and analogous to the

shear stress.

• The speed of rotation, rpm,is analogous to the shear rate.





• The determination of viscosities are obtained from the dial

readings at 600 rpm and 300 rpm .

• The datas are used to calculated:

• Apparent viscosity : Fann 600/2 ( cp )

• Plastic viscosity : Fann 600- Fann 300 ( cp )

• Yield Point: Fann 300 – Plastic Viscosity ( lbs /100ft2)

• Gel Strength - 10 Sec and 10 min





• Sand control:

• The percentage of sand in the mud is measured by using

a 200 mesh sieve and a graduate tube,

• The glass measuring tube is filled with mud to the scribe

line, water is then added up to the next scribe line,

• The fluid is filtered through the sieve,

• The sand % retained on the sieve is calculated washing

the sieve with a funnel and allowing the sand to settle.

Documents

Intro to Drilling Fluids New