4 3 drilling fluids

• Course Objectives:• List functions & properties of drilling and completion fluis, • Understand the formation damage • Describe different fluids systems, • Understand the solid control

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Drilling Fluids

Technology

• Course Objectives:

• List functions & properties of drilling and completion

fluis,

• Understand the formation damage

• Describe different fluids systems,

• Understand the solid control equipments

• Identify the environmental impact with drilling fluids

Drilling Fluids Technology

• 1900 Water and Clays

No control of properties

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

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

• Polymers ( 70 ’s) PHPA systems

• Mineral oils(‘80’s) Formation compatibilty

• Synthétics (‘90’s) Environmental

HISTORY & TECHNOLOGY

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Section 1

Functions and Properties of Drilling fluid

Functions & Properties

Functions & Properties

additives in a liquid phase,

rigs

Functions & Properties

• Cool and lubricate the bit,

• Transport drilled cuttings to the surface,

• Control subsurface pressures,

• Deposit an impermeable wall cake,

• Avoid damage to productive zone,

Functions & Properties

• The differential pressure will result an hydraulic invasion ,

• The mud or filtrate will enter into the formation ,

• The loss of mud into the wellbore will be expensive and

damaging,

• The loss of filtrate will cause formation damage,

• The cake will isolate the fluids from the formations.

Functions & Properties

• The fluid used to drill the production zone will have an

important impact on well productivity ,

• Loss of production results from:

- Swelling clays,

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

Functions & Properties

• Help obtain information on subsurface formations,

• Protect the drill pipe against corrosion,

• Promote penetration rates,

• Allow interpretable logs.

Properties

pressure control

average specific gravity of the solids of the system,

pressure exerted by the colum of fluid is required to contain formation pressure and to aid in keeping the open hole,

• The density of any drilling fluids should be didacted by

formation pressures,

• The pressure exerted by the fluid comum should be equal to or

slightly higher than the formation

Properties

• The weight will need adjustment during a well operation,

• Weighting material as Barite will be used due to its specific

gravity ( 4.2 minimum),

• Under circulating conditions the effective pressure is increased

by the pumping pressure,

• The Equivalent Circulating Density

ECD = Density( ppg) + Annular pressure loss

Depth * 0.052

Properties

hydraulics relate directly the borehole cleaning ,and hole stability,

matter and measures the internal resistance of a fluid to flow,

plates separated by some distance is known as the shear stress

-The resistance or drag force is the shear stress

-The difference in the velocities divided by the

distance is called the shear rate

v

v + dv

Properties

Surface of the platelet

Difference of velocity between 2 platelets

Distance between 2 platelets

Properties

• SHEAR STRESS

SHEAR RATE

Unit :Centi poise

-Newtonian fluid: the relationship is linear ( water,oil)

-Non Newtonian fluids :the shear stress does not increase in

direct proportion to the shear rate fluids

Properties

Shear rate

Shear stress

Newtonian Bingham Ostwald

Properties

•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.

Properties

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

Properties

Velocity Profile ( Swirling motion ) Average particle velocity is uniform

Properties

•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 during drilling operations can have a dramatic effect on parameters such as pressure losses, hole cleaning and hole stability.

Properties

• Rheology - Critical Velocity ;

Turbulent Flow Laminar Flow

Critical velocity Transition period

Shear rate Shear stress

Properties

static conditions( zero shearing),

and the ability of a colloid to form a gel,

• The common gel-strength measurements are initial and the

10 -min gels

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Section 2

Types of Drilling fluids

Types of fluids

•Water-based muds ;

– The majority of drilling fluids are water- based.

– The base liquid can be :

• Fresh water,

• Sea water,

• Salt water,

• Saturated salt water.

– Special additives are used to build a water based-mud

– Filtration control additives,

– Density control additives

Types of fluids

•Clay materials ;

– Bentonite is used in drilling fluids for viscosity and fluid loss control,

– Different grades of bentonites :

• Wyoming bentonite, pure sodium bentonite,

• 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.

Types of fluids

•Viscosity control additives ;,

– Organic Polymers as Pac or Cmc are viscosifiers with long chains molecules :

• Poly-anionic Cellulose polymer,

• Carboxyl Methyl Cellulose polymer, – Chemicals thinners (dispersants) will reduce the viscosity of drilling fluids:

• These chemicals produce negative charged anions in solution and reduce the positive charge on the edge of the clays plates,

• Phosphates, lignites, lignosulfonates, tannins may be used.

Types of fluids

•Filtration control additives ;,

– Clays as Bentonite as support filtration building a cake,

– Organic Polymers as Starch will swell and seal off the permeable zones effectivily,

• Temperature stability is limited to 250 ° F,

– CMC and PAC will be polymerized into a low viscosity grade ,

• Pacs work with salinity( max 60,000ppm) and temperature stability is limited 350 ° F.

Types of fluids

•Density control additives ;

– Limestone: Mud weight ( 12ppg)

• Calcium Carbonate, Ca Co3 , Specific Gravity: 2.7

– Barite: Mud weight ( 20ppg)

• Barium Sulfate, BaSo4, Specific Gravity : 4.2

– Hemathite: Mud weight ( 25ppg)

• Fer Oxyde, Fe2O3, Specific Gravity: 5.0

– Galena: Mud weight (32ppg)

• Lead Sulfide, PbS, Specific gravity : 7.4

Types of fluids

•Water- based muds ;

– The diverse class of water- based mud needs to be classified :

• Non inhibitive muds

– Commercial clays or hydratable clays from the formation,

– These solids will react with water,

• Inhibitive muds:

– Drilled solids as limestone, sand or commercial additive as Barite,

– No reaction with water.

Types of fluids

•Non inhibitive muds ;

– The simplest water based muds are usually inexpensive with a very low toxicity

– Non inhibitive muds , lightly treated are used for :

• Top hole sections,

• Non reactive formations.

– The main components of these fluids are :

• Native formation clays or commercial bentonite,

• Organics thinners.

Types of fluids

•Inhibitive muds ;

– Inhibitive muds reduce the chemical interaction between the mud and water-sensitive formations,

– The use of inhibitors in water drilling fluids minimize hydration and the swelling of clays and reactive shales,

– The diverse inhibitors :

• Polymers,

• Cations concentrations in fluids,

• Glycols.

Types of fluids

•High concentrations cationics fluids ;

– A cation is a mud inhibitor as a substance, such a salt, added to a drilling mud to minimize the hydration of formations.

– Cations exchange occurs.

Types of fluids

• Inhibition ;

Ion Exchange Limit Hydration

Types of fluids

•Glycols fluid system ;

– The Clouding process :

• The Glycol micelles in solution are stabilized by hydrogen bonding between water molecules and oxygen atoms present in the glycol molecule,

• The stabilization process is hydration,

– The clouding process is reversible with temperature.

Glycol in solution Glycol becomes unsoluble Separation

Types of fluids

Mud pits Glycol in solution

Downhole Glycol forms droplets

Temperature decreasing

Types of fluids

•Oil base mud ;

– Oil-based drilling fluids are :

• Oil wetting agents,

• Fitration control agents and viscosifiers,

• Weighting agent,

– The volume percentage of oil and water are expressed as an oil / water ratio

Types of fluids

Emulsifier Water Droplets Oil External phase

Types of fluids

•Invert Emulsion ;

– A wide variety of refined minerals oils has been developed for us in low-toxicity oil based-muds to reduce environmental problems.

– Petroleum oils are used for the continuous phase :

• High flash point > 120°C

• Anilin point > 65 °C

• Aromatics < 5 %

Types of fluids

Osmosis

Brine droplets ( Cl- H20- Ca ++ )

Cutting

Wellbore Oil mud

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Section 3

Performance Testing

Testing

•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.

– Americian Petroleum Institute issues recommended practises for testing procedures and equipments,

• API RP 13B -1 water based

• API RP 13B -2 oil based drilling fluids

Testing

•Sandart API tests ;

– Tests common to water and oil based muds:

• Mud weight,

• Filtration

• Water ,Oil and Solids

• Viscosity and Gel strength

– Marsh Funnel

– Viscometer.

Testing

•Sandart API tests ;

– Water - based (RP 13B-1)

• Sand

• Methylene blue capacity (clay reactivity)

• Drill pipe corrosion (salinity and rate)

• Viscosity;

– Viscosity measurement:

• Marsh Funnel.

Field Test

Testing

• Viscosity ;

viscometer, are specially designed to facilitate the use of the Bingham plastic Model in conjonction with drilling fluids in the field.

a dial reading proportionnal to torque and analogous to the shear stress.

• Viscosity;

– Viscosity measurement:

• Rotational Viscometer.

Field Test

Testing

• The datas are used to calculated:

– Apparent viscosity : Fann 600/2 ( cp )– Plastic viscosity : Fann 600- fann 300 ( cp )– Yield value: 2 ( Av-Pv ) lbs /100ft2

– Rheological index n:3.32 log 600/300 (flow profile)– Consistency index k : Fann 600/1020

• Viscosity;

– Viscosity measurement:

• Typical flow curve for drilling fluid.

Field Test

• Mud Properties & Measurements;

– Gel Strength:

• The Gel strengths refers to the increase in viscosity at zero shear rate,

• It is the measure of the attractive forces under static conditions,

Flat gel strengths

Time at zero shear rate

Testing

• Filtration;

• Darcy law application,

• API Filter Press.

Field Test

• Mud Properties & Measurements;

– Filtration:

Testing

•Chemical analysis ;

– Mud and filtrate titrations

• A method, or the process of using a standart solution for the determination of the amount of some substance in another solution.

• Indicator : Substances in acid-base titrations, change col or at the end of the reaction

• We used a pH meter or pH paper,

• The pH paper will turn to different colors depending on the

concentrations of hydrogens ions,

• pH paper can read off to the nearest 0.5 of a unit,

• pH meter gives a more accurate result to 0.1 of a unit.

• Mud Properties & Measurements;

– pH Determination:

• pHydrion paper.

Field Test

Testing

•Chemical analysis ; – Chloride content

• The amont of chloride in the mud is a measure of the salt contamination from the formation,

• The procedure involves using a filtrate sample , potassiumchromate indicator and silver nitrate solution,

• The titration is the Morh method,

• The chloride contend is calculated from:

– Cl = ml of Silver Nitrate *1000/ml of filtrate sample sample

g / l of solution

Testing

• A carefully measured sample of mud is heated in a retort kit

until the liqid components are vaporised,

• The vapors are then condensed and collected in a measuring

– Whole mud alkalinity

– Whole mud chlorides

– Whole mud calcium

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Section 4

Formation damage

Formation damage

impact on well productivity due to :

• The compositions and properties of drilling and completion

fluids,

• Filtration control , bridging and filtrate chemistry are the

most important properties for minimizing formation damage

Formation damage

• Filtrate invasion;

forced into the formation

• Rock and fluid properties,

• Drilling parameters,

• Drilling fluid filtration characteristics, compositions and

properties of drilling and completion fluids

Formation damage

• Filtration schematic;

Pore Throat Fluid phase

Pore Blocking Agent

Filter Cake

Formation damage

• Filtration control;

permeability.

• Bridging of pore openings,

• Building a Filter cake.

Formation damage

• Filtration

addition of bentonite clay, fluid-loss control polymers, lignite, resins,

• A thin and low-permeability filter cake is builded,

drilling fluid before the reservoir formation is drilled.

drilling the production interval.

Formation damage

often impaired by water mud filtrate invasion,

block oil and gas flow,

rates ( less damage) , the invading filtrate is oil rather than water

Formation damage

• Wells completed with slotted liners will be completed with

a special drill-in fluid,

• This fluid is only used to drill the resevoir interval and will

have many of the characteristics of a completion fluid,

• These special drill-in reservoir fluids contain brines,

polymerics additives, and size-salt or calcium carbonate for filter cake solids

• A drill-in fluid must act as both a drilling fluid and as a

completion fluid protecting the reservoir from damage

Formation damage

– Open hole and liner completions:

• Drill-in fluid definition:

– A fluid that possesses the desirable properties of a good drilling fluid but

will also provide the necessary attributes of a completion fluid,

– Its primary attribute is the development of a filter cake which

prevents formation damage and is easily removed

Formation damage

– Size salt fluids :

– A synergistic polymer blend of Xanthan gum and a crosslinked, hydroxypropylated starch derivate used for suspension and fluid loss control

– Sized salt is added to the system in order to provide bridging particles that initiate a readly removable filter cake

Formation damage

– Bridging fluids :

easily and effectively removed by the produced fluid.

particles on pore throat openings

wide range of permeability, from a few millidarcys to over 10 darcys

Formation damage

– The median particle size (in microns ) or D50 of the

calcium carbonate should be one half the median formation pore throat diameter

– Example : If the formation has a permeability of 400

millidarcys , the median particle size should be about