Petroleum Engineer''s Guide to Oil Field Chemicals and Fluids, Second Edition

Cẩm Nang dành cho Kỹ Sư Dầu Khí về : Hóa chất và Chất Lỏng Dầu Mỏ , Tái bản lần 2

Guide to Oil Field Chemicals and Fluids

Second Edition

Guide to Oil Field Chemicals and Fluids

Second Edition

Johannes Fink

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ISBN: 978-0-12-803734-8

This manuscript is an extension and update from Petroleum Engineer’s Guide to Oil

Field Chemicals and Fluids, which appeared in 2010.

The most recent literature including articles as well as mostly US patents that

appeared since 2010 are collected and introduced in the new text

Last but not the least, I want to thank the publisher for kind support, in particular,

Katie Hammon and Kiruthika Govindaraju

J.K.F.

March 9, 2015

v

This manuscript is an extension and update from Oil Field Chemicals, which

appeared in 2003 The text focuses mainly on the organic chemistry of oil field

chemicals As indicated by the title, preferably engineers with less background in

organic chemistry will use this text Therefore, various sketches of the chemicals and

additional explanations and comments are included in the text to those an educated

organic chemist is certainly familiar

The material presented here is a compilation from the literature, including patents

The text is arranged in the order as needed by a typical job It starts with drilling fluids

and related applications, such as fluid loss, bit lubricants, etc Then it crosses over to

the next major topics, cementing, fracturing, enhanced recovery, and it ends with

pipelines and spill

Some of the chemicals are used in more than one main field For example,

surfactants are used in nearly all of the applications The last three chapters

are devoted to these chemicals As environmental aspects are gaining increasing

importance, this issue is also dealt carefully

HOW TO USE THIS BOOK

INDEX

There are three indices: an index of acronyms, an index of chemicals, and a general

index

In a chapter, if an acronym is occurring the first time, it is expanded to long form

and to short form, for example, acrylic acid (AA) and placed in the index If it occurs

afterwards it is given in the short form only, i.e., AA If the term occurs only once in

a specific chapter, it is given exclusively in the long form

In the chemical index, bold face page numbers refer to the sketches of structural

formulas or to equations which refer reactions

BIBLIOGRAPHY

The bibliography is given per chapter and is sorted in the order of occurrence After

the bibliography, a list of tradenames that are found in the references and which

chemicals are behind these names, as far as laid open is added

ACKNOWLEDGMENTS

The continuous interest and the promotion by Professor Wolfgang Kern, the head of the

department is highly appreciated I am indebted to our university librarians, Dr Christian

Hasenhüttl, Dr Johann Delanoy, Franz Jurek, Margit Keshmiri, Dolores Knabl, Friedrich

vii

Scheer, Christian Slamenik, and Renate Tschabuschnig for their support in the acquisition ofliterature This book could not have been otherwise compiled Thanks are given to Professor

I Lakatos, University of Miskolc who directed my interest to this topic

J.K.F.

1 Drilling muds

According to American Petroleum Institute (API), a drilling fluid is defined as a

circulating fluid used in rotary drilling to perform any or all of the various functions

required in drilling operations

Drilling fluids are mixtures of natural and synthetic chemical compounds used to

cool and lubricate the drill bit, clean the hole bottom, carry cuttings to the surface,

control formation pressures, and improve the function of the drill string and tools in

the hole They are divided into two general types: water-based drilling muds (WBMs)

and oil-based drilling muds (OBMs) The type of fluid base used depends on drilling

and formation needs, as well as the requirements for disposition of the fluid after it

is no longer needed Drilling muds are a special class of drilling fluids used to drill

most deep wells Mud refers to the thick consistency of the formulation.

Drilling fluids serve several fundamental functions [1,2]:

• control of downhole formation pressures,

• overcoming the fluid pressure of the formation,

• avoiding damage of the producing formation,

• removal of cuttings generated by the drill bit from the borehole, and

• cooling and lubricating of the drill bit

In addition to these fundamental functions of drilling fluids, drilling fluids

preferably possess several desirable characteristics which can greatly enhance the

efficiency of the drilling operation

To perform these functions, an efficient drilling fluid must exhibit numerous

characteristics, such as desired rheological properties (plastic viscosity, yield value,

low-end rheology, and gel strengths), fluid loss prevention, stability under various

temperature and pressure operating conditions, stability against contaminating fluids,

such as salt water, calcium sulfate, cement, and potassium contaminated fluids [1]

Preferably, the drilling fluid exhibits penetration enhancement characteristics, by

having physical properties, which wet the drill string and keep the cutting surfaces of

the drill bit (whether of the roller cone or other configuration) clean

The wetting attribute is at least in part a function of the surface tension of the

fluid The drilling fluid also preferably has a high degree of lubricity, to minimize

friction between the drill string and the wall of the borehole, an extremely valuable

result being the minimizing of differential sticking In this situation, the hydrostatic

Petroleum Engineer’s Guide to Oil Field Chemicals and Fluids http://dx.doi.org/10.1016/B978-0-12-803734-8.00001-1 1

pressure of the drilling fluid column is sufficiently higher than the formation pressure

so that the drill string is forced against the wall of the borehole and stuck

Yet another desirable characteristic is the prevention from swelling of the solids

of the formation, that is, primarily clays and shales, which further reduces incidents

of drill string sticking, undergauge holes, etc Inhibition of clay swelling, in general,results from preventing the clays from adsorbing water

1.1 CLASSIFICATION OF MUDS

The classification of drilling muds is based on their fluid phase alkalinity, dispersion,and the type of chemicals used The classification according to Lyons [3] isreproduced inTable 1.1

Drilling muds are usually classified as either WBMs or OBMs, depending uponthe character of the continuous phase of the mud However, WBMs may contain oiland OBMs may contain water [4]

OBMs generally use hydrocarbon oil as the main liquid component with othermaterials such as clays or colloidal asphalts added to provide the desired viscositytogether with emulsifiers, polymers, and other additives including weighting agents.Water may also be present, but in an amount not usually greater than 50 volumepercent of the entire composition If more than about 5% of water is present, the mud

is often referred to as an invert emulsion, that is, water-in-oil emulsion

WBMs conventionally contain viscosifiers, fluid loss control agents, weightingagents, lubricants, emulsifiers, corrosion inhibitors, salts, and pH control agents Thewater makes up the continuous phase of the mud and is usually present in any amount

of at least 50 volume percent of the entire composition Oil is also usually present inminor amounts but will typically not exceed the amount of the water so that the mudwill retain its character as a water-continuous phase material

Potassium muds are the most widely accepted water mud system for drillingwater sensitive shales K+ ions attach to clay surfaces and lend stability to shale

Table 1.1 Classification of Drilling Muds

muds, gypsum muds, sea water muds, saturated salt water muds) Low-solids mudsb Contain less than 3-6% of solids Most contain an organic polymer Emulsions Oil in water and water in oil (reversed phase, with more than 5%

water) OBMs Contain less than 5% water; mixture of diesel fuel and asphalt

a Dispersed systems.

b

exposed to drilling fluids by the bit The ions also help hold the cuttings together,minimizing dispersion into finer particles Potassium chloride, KCl, is the mostwidely used potassium source Others are potassium acetate, potassium carbonate,potassium lignite, potassium hydroxide, and potassium salt of partially hydrolyzedpoly(acrylamide) (PHPA) For rheology control, different types of polymers are used,for example, xanthan gum and PHPA For fluid loss control, mixtures of starch andpolyanionic cellulose (PAC) are often used Carboxymethyl starch, hydroxypropylstarch, carboxymethyl cellulose (CMC), and sodium poly(acrylate) are also used.PHPA is widely used for shale encapsulation.

Salt water muds contain varying amounts of dissolved sodium chloride (NaCl) as

a major component Undissolved salt may also be present in saturated salt muds toincrease density or to act as a bridging agent over permeable zones Starch and starchderivatives for fluid loss control and xanthan gums for hole cleaning are among thefew highly effective additives for salt water muds

Sea water mud is a WBM designed for offshore drilling whose make-up water

is taken from the ocean Sea water has a relatively low salinity, containing about3-4% of NaCl, but has a high hardness because of Mg+2and Ca+2ions Hardness

is removed from sea water by adding NaOH, which precipitates Mg+2as Mg(OH)2and by adding Na2CO3, which removes Ca+2as CaCO3 Mud additives are the same

as those used in fresh water muds [4]:

by addition of NaOH (or KOH) and the appropriate silicate solution Silicate anionsand colloidal silica gel combine to stabilize the wellbore by sealing microfractures,forming a silica layer on shales and possibly acting as an osmotic membrane, whichcan produce in-gauge holes through troublesome shale sections that otherwise mightrequire an oil mud

Lime mud is a type of WBM that is saturated with lime, Ca(OH)2, and has excess,undissolved lime solids maintained in reserve Fluid loss additives include starch,hydroxypropyl starch, CMC, or PAC [4]

Drilling fluids used in the upper hole sections are referred to as dispersed

noninhib-ited systems They are formulated from fresh water and may contain bentonite The

Table 1.2 Classification of Bentonite Fluid Systems

Solid-Solid

Interactions

Inhibition

Dispersed Noninhibited Fresh water clay NaCl<1%, CaCl2 ,<120 ppm

Dispersed Inhibited Saline fluids, Na +, Ca2 +salt, saturated salt, gypsum,

lime Nondispersed Noninhibited Fresh water low-solids muds

Nondispersed Inhibited Salt and polymer fluids

classification of bentonite-based muds is shown inTable 1.2 The flow properties arecontrolled by a flocculant or thinner, and the fluid loss is controlled with bentoniteand CMC

Phosphates are effective only in small concentrations The mud temperature must beless than 55◦C The salt contamination must be less than 500 ppm sodium chloride.The concentration of calcium ions should be kept as low as possible The pH should

be between 8 and 9.5 Some phosphates may decrease the pH, so adding more NaOH

Quebracho-treated fresh water muds were used in shallow depths It is also

referred to as red mud because of the deep red color Quebracho acts as a thinner.

Poly(phosphate)s are also added when quebracho is used Quebracho is active at lowconcentrations and consists of tannates

1.1.5 LIGNOSULFONATE MUDS

Lignosulfonate fresh water muds contain ferrochrome lignosulfonate for viscosityand gel strength control These muds are resistant to most types of drilling contami-nation because of the thinning efficiency of the lignosulfonate in the presence of largeamounts of salt and extreme hardness

Lime muds contain caustic soda, an organic thinner, hydrated lime, and a colloidfor filtrate loss From this a pH of 11.8 can result, with 3-20 ppm calcium ions inthe filtrate Lime muds exhibit low viscosity, low gel strength, and good suspension

of weighting agents They can carry a larger concentration of clay solids at lowerviscosities than other types of mud At high temperatures, lime muds present a danger

of gelation

The average composition of sea water is shown inTable 1.3 Sea water muds havesodium chloride concentrations above 10,000 ppm Most of the hardness in seawater is caused by magnesium Sea water muds are composed of bentonite, thinner(lignosulfonate or lignosulfonate with lignite), and an organic filtration control agent

In nondispersed systems no special agents are added to deflocculate the solids in thefluid The main advantages of these systems are the higher viscosities and the higheryield point-to-plastics viscosity ratio These alterated flow properties provide a bettercleaning of the borehole, allow a lower annular circulating rate, and minimize thewashout of the borehole

Clear fresh water is the best drilling fluid in terms of penetration rate Therefore,

it is desirable to achieve a maximal drilling rate using a minimal amount of solid

Table 1.3 Composition of Sea Water

additives Originally, low-solids mud formulations were used in hard formations, butthey now also tend to find use in other formations Several types of flocculants areused to promote the settling of drilled solids by flocculation.

1.1.10 VARIABLE DENSITY FLUIDS

Variable density fluids are those that having a density that varies as a function ofpressure into the subterranean formation Such a fluid comprises a base fluid and aportion of elastic particles

The presence of the elastic particles in a variable density fluid allows the density

of the variable density fluid to vary as a function of pressure For instance, asthe elastic particles encounter higher downhole pressures, they compress, therebylowering their volume The reduction in the volume of the elastic particles in turnincreases the density of the variable density fluid

When the elastic particles are fully compressed, the density increases erably The increase in volume of the elastic particles in turn reduces the overalldensity of the variable density drilling fluid The resulting change in density may besufficient to permit the return of the variable density fluid through the riser to thesurface without any additional pumps or subsurface additives [6]

consid-The elastic particles can be a copolymer of styrene and divinylbenzene, acopolymer of styrene and acrylonitrile, or a terpolymer of styrene, vinylidenechloride, and acrylonitrile [6]

1.1.12 DRILL-IN FLUIDS

After drilling a well to the total depth, it is a normal practice to replace the drillingmud with a completion fluid This fluid is a clean, solids-free, or acid soluble,non-damaging formulation, intended to minimize reductions in permeability of theproducing zone Prior to producing from the formation, it is usually necessary tocleanup what is left by the original mud and the completion fluid, by breaking anddegrading the filter cake with an oxidizer, enzyme, or an acid solution

Nowadays, many wells exploit the pay-zone formations horizontally and forlong distances It is no longer practical in these wells to drill the pay-zone with

conventional solids-laden muds as the extended cleanup process afterwards ismuch more difficult Consequently, the modern generation of drill-in fluids weredeveloped.

Heavy brine completion fluids

Drill-in fluids are drilling fluids used in drilling through a hydrocarbon producingzone, also addressed as a pay-zone [7] Completion fluids are fluids used in com-pleting or working over a well Completion operations normally include perforatingthe casing and setting the tubing and pumps prior to, and to facilitate, initiation ofproduction in hydrocarbon recovery operations

As the pay-zone is penetrated horizontally, these fluids must provide the functional requirements of drilling fluids in addition to the non-damaging attributes

multi-of completion fluids In practice, the normal drilling mud is replaced with a drill-influid just before the pay-zone is penetrated, and used until the end of the operations.Choosing the right completion fluid is important because inappropriate fluids canhave a significant impact on a project, not only during completion operations andwell production startup, but also throughout the well’s productive life Experiencehas shown that some completion practices that work well in one location, but maynot work well in a different location

The importance of using clear completion and workover fluids to minimizeformation damage is well recognized and the use of clear heavy brines as completionfluids is now widespread [7]

Most heavy brines used by the oil and gas industry are calcium halide brines,particularly calcium chloride or calcium bromide brines, or formate brines How-ever, halide brines can cause structural failure in corrosion resistant alloys, andchloride and bromide brines in particular are known to cause pitting corrosionand stress corrosion cracking of corrosion resistant alloys if oxygen or carbondioxide is present In contrast, formate brines do not cause such corrosion andcracking but are more costly to purchase and have some solubility problems at highdensity

A phosphate based heavy brine drill-in or completion fluid has been described[7] The fluid is prepared with a phosphate brine, preferably consisting essentially ofwater with phosphates dissolved therein, preferably in a quantity ranging from about1.2-2.4 kg l−1.

Such a phosphate solution may be economically obtained from waste productfrom a sewage treatment plant, for example This phosphate solution in turn isblended with water, preferably fresh water although sea water might alternatively

be used, in a quantity such that the phosphate solution comprises more or less of theblend or even approximately half of the blend

Also, corrosion inhibitors and clay inhibitors may be added to the blend, althoughthe fluid is less corrosive without inhibitors than calcium halide brines Non-aminebased corrosion inhibitors designed to prevent oxygen corrosion in monovalent brinesare most effective [7]

1.2 MUD COMPOSITIONS

Commercial products are listed in the literature These include bactericides, corrosioninhibitors, defoamers, emulsifiers, fluid loss and viscosity control agents, and shalecontrol additives [8 12]

Minimizing the environmental impact of the drilling process is a highly importantpart of drilling operations to comply with environmental regulations that havebecome stricter throughout the world In fact, this is a mandatory requirement forthe North Sea sector The drilling fluids industry has made significant progress

in developing new drilling fluids and ancillary additives that fulfill the increasingtechnical demands for drilling oil wells These additives have very little or no adverseeffects on the environment or on drilling economics

New drilling fluid technologies have been developed to allow the continuation

of oil-based performance with regard to formation damage, lubricity and wellborestability aspects and thus penetration rates These aspects were greatly improved byincorporating polyols or silicates as shale inhibitors in the fluid systems

Polyols based fluids contain a glycol or glycerol as a shale inhibitor These polyolsare commonly used in conjunction with conventional anionic and cationic fluids toprovide additional inhibition of swelling and dispersing of shales They also providesome lubrication properties

Sodium silicates or potassium silicates are known to provide levels of shaleinhibition comparable to that of OBMs This type of fluids is characterized by ahigh pH (>12) for optimum stability of the mud system The inhibition properties of

such fluids are achieved by the precipitation or gelation of silicates on contact withdivalent ions and lower pH in the formulation, providing an effective water barrierthat prevents hydration and dispersion of the shales

These muds have water as the continuous phase Water may contain several solved substances These include alkalies, salts and surfactants, organic polymers incolloidal state, droplets of emulsified oil, and various insoluble substances, such asbarite, clay, and cuttings in suspension

dis-The mud composition selected for use often depends on the dissolved substances

in the most economically available make-up water or on the soluble or dispersivematerials in the formations to be drilled Several mud types or systems are recognizedand described in the literature such as:

• spud muds,

• dispersed/deflocculated muds,

• lime muds,

• gypsum muds,

• salt water muds,

• nondispersed polymer muds,

• inhibitive potassium muds,

• cationic muds, and

• mixed metal hydroxide muds

Despite their environmental acceptance, conventional WBMs exhibit majordeficiencies relative to OBMs/pseudo oil-based drilling muds (POBMs) with regard

to their relatively poor shale inhibition, lubricity, and thermal stability characteristics

To overcome those deficiencies, specific additives may, however, be added into theWBM compositions to deliver properties close to OBMs/POBMs, performance whileminimizing the environmental impact

Consequently, to meet the new environmental regulations while extending thetechnical performance of water-based drilling fluids, a new generation of water-basedfluids, also called inhibitive drilling fluids was developed to compete against OBMs.Also, to minimize the formation damage, new types of non-damaging drilling fluids,called drill-in fluid, have been developed to drill the pay-zone formations

Components for WBMs are shown in Table 1.4 Various methods for themodification of lignosulfonates have been described, for example, by condensationwith formaldehyde [19] or modification with iron salts [20] It has been foundthat chromium-modified lignosulfonates, as well as mixed metal lignosulfonates ofchromium and iron, are highly effective as dispersants and therefore are useful incontrolling the viscosity of drilling fluids and in reducing the yield point and gelstrength of the drilling fluids Because chromium is potentially toxic, its release intothe natural environment and the thereof is continuously being reviewed by variousgovernment agencies around the world

Therefore, less toxic substitutes are desirable Less toxic lignosulfonates areprepared by combining tin or cerium sulfate and an aqueous solution of calciumlignosulfonate, thereby producing a solution of tin or cerium sulfonate and a calciumsulfate precipitate [21]

Compositions with improved thermal stability

To avoid the problems associated with viscosity reduction in polymer-based aqueousfluids, formates, such as potassium formate and sodium formate are commonly added

Table 1.4 Water-Based Drilling Muds

Poly(acrylamide), carboxymethyl cellulose [ 16 ]

Carboxymethyl cellulose, zinc oxide [ 17 ]

Acrylamide copolymer, poly(propylene

glycol) (PPG) (water-based mud)

[ 18 ]

Table 1.5 Apparent Viscosity Before and

The stability of a wellbore treatment fluid may be maintained at temperatures

up to 135-160◦C (275-325◦F) Various poly(saccharide)s may be included inthe fluid The apparent viscosities of drilling fluids containing xanthan gum andpoly(acrylamide) (PAM) before and after rolling at 120◦C are shown inTable 1.5.

Shale encapsulator

A shale encapsulator is added to a WBM in order to reduce the swelling of thesubterranean formation in the presence of water A shale encapsulator should be atleast partially soluble in the aqueous continuous phase in order to be effective

A conventional encapsulator is a quaternary PAM, which is preferably a ernized poly(vinyl alcohol) Suitable examples of anions that are useful includehalogen, sulfate, nitrate, formate, etc [23]

quat-By varying the molecular weight and the degree of amination, a wide variety ofproducts can be tailored It is possible to create shale encapsulators for the use inlow salinity, including fresh water [23] The repeating units of quaternized etherifiedpoly(vinyl alcohol) and quaternized PAM are shown inFigure 1.1

Membrane formation

In order to increase the wellbore stability, it is possible to provide formulations forwater-based drilling fluids, which can form a semi-permeable osmotic membraneover a specific shale formation [24] This membrane allows a comparatively freemovement of water through the shale, but it significantly restricts the movement ofions across the membrane and thus into the shale

C C H

Quaternized etherified poly(vinyl alcohol) and quaternized poly(acrylamide) [23]

The method of membrane formation involves the application of two reactants to

form in situ a relatively insoluble Schiff base, which deposits at the shale as a polymer

film This Schiff base coats the clay surfaces to build a polymer membrane

The first reactant is a soluble monomer, oligomer, or polymer with ketone

or aldehyde or aldol functionalities or precursors to those Examples are carbon

hydrates, such as dextrin, linear of branched starch The second reactant is a primary

amine These compounds are reacting by a condensation reaction to form an insoluble

crosslinked polymerized product The formation of a Schiff base is shown in

Figure 1.2

Figure 1.2illustrates the reaction of a dextrine with a diamine, but other primary

amines and poly(amine)s will of course react in the same way Long chain amines,

diamines, or poly(amine)s with a relatively low amine ratio may require supplemental

pH adjustment using materials such as sodium hydroxide, potassium hydroxide,

sodium carbonate, potassium carbonate, or calcium hydroxide [24] The Schiff base

formed in this way must be essentially insoluble in the carrier brine in order to deposit

a sealing membrane on the shale during drilling of a well

By carefully selecting the primary polymer and the crosslinking amine, the

relative concentrations of these components, together with the adjustment of pH,

crosslinking and polymerization and precipitation of components occurs which

effectively forms an osmotically effective membrane on or within the face of the

exposed rock

The polymerization and precipitation of the osmotic membrane on the face of the

exposed rock significantly retards water or ions from moving into or out of the rock

formation, typically shale or clay The ability to form an osmotic barrier results in an

increased stability in the clays or minerals, which combine to make the rock through

which the borehole is being drilled [24]

They have oil as the continuous phase The oil most often selected is diesel oil,

mineral oil, and low toxicity mineral oil Because some water will always be present,

the OBM must contain water-emulsifying agents If water is purposely added (for

economical reasons), the OBM is called an invert emulsion mud Various thickening

OH OH OH HO

HO

HO HO

HO OH

FIGURE 1.2

Formation of a Schiff base [24]

and suspending agents as well as barite are added The emulsified water may containalkalies and salts

Due to their continuous phase, OBMs are known to provide unequaled mance attributes with respect to the rate of penetration, shale inhibition, wellborestability, high lubricity, high thermal stability, and high salt tolerance However,they are subjected to strict environmental regulation regarding their discharge andrecycling

perfor-OBMs are being replaced now by synthetic muds Diesel oil is harmful to theenvironment, particularly to the marine environment in offshore applications Theuse of palm oil derivatives could be considered as an alternative oil-based fluid that

is harmless to the environment [25] Hydrated castor oil can be used as a viscositypromoter instead of organophilic quaternized clays [26]

An OBM can be viscosified with maleated ethylene-propylene elastomers [27].The elastomers are ethylene-propylene copolymers or ethylene-propylene-dieneterpolymers The maleated elastomers are far more effective oil mud viscosifiersthan the organophilic clays used On the other hand, specific organophilic clays canprovide a drilling fluid composition less sensitive to high temperatures [28]

Poly-α-olefins (PAOs) are biodegradable and nontoxic to marine organisms They

also meet viscosity and pour point specifications for the formulation into OBMs [29]

The hydrogenated dimer of 1-decene [30] can be used instead of conventional organic

fluids, as can n-1-octene [31]

Poly(ether)cyclicpolyols

Poly(ether)cyclicpolyols possess enhanced molecular properties and characteristics

and permit the preparation of enhanced drilling fluids that inhibit the formation of

gas hydrates; prevent shale dispersion; and reduce the swelling of the formation to

enhance wellbore stability, reduce fluid loss, and reduce the filter cake thickness

Drilling muds incorporating the poly(ether)cyclicpolyols are substitutes for

OBMs in many applications [32–36] Poly(ether)cyclicpolyols are prepared by

thermally condensing a polyol, for example, glycerol to oligomers and cyclic ethers

Emulsifier for deep drilling

Two major problems are encountered when using OBMs for drilling very deep wells

[37] The first is a problem with the stability of the emulsions with temperature The

emulsifying agents that are stabilizing the emulsions must maintain water droplets in

an emulsion up to temperatures of 200◦C.

If the emulsion separates by coalescence of the water droplets, the fluid loses its

rheological properties The second is an environmental problem The emulsification

agents must not only be effective, but also as nontoxic as possible

Fatty acid amides consisting of N-alkylated poly(ether) chains are used as

emulsifiers For those the term polyalkoxylated superamides has been coined [38]

As a cosurfactant, tall oil fatty acids or their salts can be used

Biodegradable composition

In compositions of oil-based biodegradable drilling fluids biodegradability can be

imparted There, the main oil phase component is a mixture of methyl esters from

biodegradable fatty acids A typical formulation of a biodegradable drilling fluid is

shown inTable 1.6

Electric conductive nonaqueous mud

A wellbore fluid has been developed that has a nonaqueous continuous liquid phase

that exhibits an electrical conductivity increased by a factor of 104to 107compared

with conventional invert emulsion 0.2-10% by volume of carbon black particles and

emulsifying surfactants are used as additives Information from electrical logging

tools, including measurements while drilling can be obtained [40]

Water removal

Water can be removed from OBMs by the action of magnesium sulfate [41]

Table 1.6 Biodegradable Drilling Fluid [39]

D-Limonene 1 to 5 Pour point depressant

2,6-Di-tert-butyl-p-cresol 0.1 to 0.5 Antioxidant Hydrogenated castor oil 0.3 to 1 Oil component

Succinimide copolymer 0.1 to 0 0.5 fluid loss agent Sodium poly(acrylate) 0.1 to 0 0.5 fluid loss agent

Synthetic muds are expensive Two factors influence the direct cost: the costs perbarrel and mud losses Synthetic muds are the technical equivalent of OBMs whendrilling intermediate hole sections They are technically superior to all water-basedsystems when drilling reactive shales in directional wells However, with efficientsolids-control equipment, optimized drilling, and good housekeeping practices, thecost of the synthetic mud can be brought to a level comparable with OBM [42].POBMs or synthetic OBMs are made on the same principle as OBMs Theyhave been developed to maintain the performance characteristics of OBMs whilereducing their environmental impact The objective behind the design of these drillingfluids is to exchange the diesel oil or mineral oil base with an organic fluid whichexhibits a lower environmental impact The organic fluids used are esters, polyolefins,acetal, ether, and linear alkyl benzenes As with OBMs, POBMs may contain variousingredients, such as thickening and suspending agents, emulsifying agents as well asweighting agents

POBMs were developed to technically maintain the performance characteristics

of OBMs while reducing their environmental impact They are, however, not as stable

as OBMs depending upon the continuous phase From environmental perspective, thecurrent legislation is becoming as strict for POBMs as for OBMs The mud selectionprocess is based on the mud’s technical performance, environmental impact, andfinancial impact

Skeletally isomerized linear olefins exhibited a better high-temperature stability

in comparison with a drilling fluid prepared from a conventional PAO The fluid lossproperties are good, even in the absence of a fluid loss additive [43–46] Althoughnormal α-olefins are not generally useful in synthetic hydrocarbon-based drillingfluids, mixtures of mostly linear olefins are minimally toxic and highly effective asthe continuous phase of drilling fluids [44,47]

Acetals as mineral oil substitutes exhibit good biodegradability and are less toxic

than mineral oils [48,49] Acrylic acid (AA) salts are formed by the neutralization

reaction of AA in aqueous solution [50]

Alginates are hydrocolloids, which are extracted from brown marine microalgae

Water-soluble alginates are prepared as highly concentrated, pumpable suspensions

in mixtures of propylene glycol and water by using hydroxypropylated guar gum

in combination with carboxymethylated cellulose, which is used as a suspending

agent [51]

Inverted emulsion muds are used in 10-20% of all drilling jobs Historically, first

crude oils, then diesel oils and mineral oils, have been used in formulating invert

drilling fluids Considerable environmentally damaging effects may occur when the

mud gets into the sea Drilling sludge and the heavy mud sink to the seabed and partly

flow with the tides and sea currents to the coasts All of these hydrocarbons contain

no oxygen and are not readily degraded [52]

Because of problems of toxicity and persistence, which are associated with these

oils, in particular for offshore use, alternative drilling oils have been developed

Examples of such oils are fatty acid esters and branched chain synthetic hydrocarbons

such as PAOs Fatty acid ester-based oils have excellent environmental properties, but

drilling fluids made with these esters tend to have lower densities and are prone to

hydrolytic instability

PAO-based drilling fluids can be formulated to high densities and have good

hydrolytic stability and low toxicity They are, however, somewhat less biodegradable

than esters Further, they are expensive The fully weighted, high-density fluids tend

to be overly viscous [31]

Esters

Esters of C6 to C11 monocarboxylic acids [53–57], acid-methyl esters [58], and

polycarboxylic acid esters [59], as well as oleophilic monomeric and oligomeric

diesters [60], have been proposed as basic materials for inverted emulsion muds

Natural oils are triglyceride ester oils [61] and are similar to synthetic esters Diesters

also have been proposed [60,62–65]

Acetals

Acetals and oleophilic alcohols or oleophilic esters are suitable for the preparation

of inverted emulsion drilling muds and emulsion drilling muds They may replace

the base oils, diesel oil, purified diesel oil, white oil, olefins, and alkyl benzenes [52,

66] Examples are isobutyraldehyde, di-2-ethylhexyl acetal, dihexyl formal Also

mixtures with coconut alcohol, soya oil, and α-methyldecanol are suitable Some

aldehydes are shown inFigure 1.3

Inverted emulsion muds are more advantageous in stable, water sensitive

for-mations and in inclined boreholes They are stable up to very high temperatures and

O H

The high setting point of linear alcohols and the poor biologic degradability ofbranched alcohols limit their use as an environment-friendly mineral oil substitute.Higher alcohols, which are still just somewhat water-soluble, are eliminated for use

in offshore muds because of their high toxicity to fish Esters and acetals can bedegraded anaerobically on the seabed

This possibility minimizes the environmentally damaging effect on the seabed.When such products are used, rapid recovery of the ecology of the seabed takesplace after the end of drilling Acetals, which have a relatively low viscosity and

in particular a relatively low setting point, can be prepared by combining variousaldehydes and alcohols [52,67]

Anti-settling properties

Ethylene-AA copolymer neutralized with amines such as triethanolamine or

N-methyl diethanolamine enhances anti-settling properties [68,69]

Glycosides

The advantage of using glycosides in the internal phase is that much of the concernfor the ionic character of the internal phase is no longer required If water is limited

in the system, the hydration of the shales is greatly reduced

The reduced water activity of the internal phase of the mud and the improvedefficiency of the shale is an osmotic barrier if the glycoside interacts directly withthe shale This helps to lower the water content of the shale, thus increasing rockstrength, lowering effective mean stress, and stabilizing the wellbore [70]

Methyl glucosides also could find applications in water-based drilling fluids andhave the potential to replace OBMs [71] The use of such a drilling fluid could

Table 1.7 Other Materials for Inverted Emulsion Drilling Fluids

Hydrophobic side chain poly(amide)s from N,N-didodecylamine

and sodium poly(acrylate) or poly(acrylic acid)

[ 80 ]

reduce the disposal of oil-contaminated drilling cuttings, minimize health and safety

concerns, and minimize environmental effects

Miscellaneous

Other base materials proposed are listed inTable 1.7 Quaternary oleophilic esters

of alkylolamines and carboxylic acids improve the wettability of clay [83, 84]

Nitrates and nitrites can replace calcium chloride in inverted emulsion drilling

muds [85]

Reversible phase inversion

Invert emulsion fluids have been developed in which the emulsion can be readily

and reversibly converted from a water-in-oil type emulsion to an oil-in-water type

emulsion The essential ingredient is an amine based surfactant as additive The

amine surfactant may be diethoxylated tallow amine, diethoxylated soya amine, or

N-tallow-1,3-diaminopropane [86]

The invert emulsion is admixed with an acid that is functionally able to protonate

the amine surfactant When sufficient quantities of the acid are utilized, the invert

emulsion is converted so that the oleaginous fluid becomes the discontinuous phase

and the non-oleaginous fluid becomes the continuous phase

The conversion of the phases is reversible so that upon addition of a base capable

of deprotonating the protonated amine surfactant, a stable invert emulsion in which

the oleaginous liquid becomes the continuous phase and the non-oleaginous fluid

become the discontinuous phase can be formed [86]

In other words, when the drilling fluid is converted into an oil-in-water type

emulsion, solids, now substantially water-wet, may now be separated from the fluid

by gravity or mechanical means for further processing or disposal The fluid may then

be mixed with a base, the base being functionally able to deprotonate the protonated

amine surfactant

The base should be in sufficient quantities so as to convert the oil-in-water typeemulsion formed upon the addition of acid, back to a water-in-oil emulsion Theresulting water-in-oil emulsion may then be used as it is or reformulated into adrilling fluid suitable for the drilling conditions in another well [86].

1.2.6 FOAM DRILLING

While drilling low-pressure reservoirs with nonconventional methods, it is common

to use low-density dispersed systems, such as foam, to achieve underbalanced tions To choose an adequate foam formulation, not only the reservoir characteristicsbut also the foam properties need to be taken into account

condi-Parameters such as stability of foam and interactions between rock-fluid anddrilling fluid-formation fluid are among the properties to evaluate while designingthe drilling fluid [87]

A foaming composition having a specific pH and containing an ionic surfactantand a polyampholytic polymer whose charge depends on the pH is circulated in awell By varying the pH, it is possible to destabilize the foam in such a way as tomore easily break the foam back at the surface and possibly to recycle the foamingsolution [88]

Chemically enhanced drilling offers substantial advantages over conventional ods in carbonate reservoirs Coiled tubing provides the perfect conduit for chemicalfluids that can accelerate the drilling process and provide stimulation while drilling[89] The nature of the chemical fluids is mainly acid that dissolves or disintegratesthe carbonate rock

meth-Temperature and salinity effects

Coiled tubing applications include drilling operations, hydraulic fracturing, wellcompletions, removing sand or fill from wellbore, and other applications that involvepumping fluids at high temperatures and high salinity Because of curvature effects incoiled tubing, huge pressure losses occur, limiting the maximum flow rate achieved

By adding specific chemicals known as friction reducers or drag reducers to thefluids, these pressure losses can be minimized to a great extent

Only a few number of studies have been reported that relate to temperature andsalinity effects on drag reduction in fluids flowing through coiled tubing [90]

An experimental study of two commonly used drag reducers (700 and 820) flowing through coiled tubing with different salinities and temperatures hasbeen presented [90] Both small-scale and large-scale flow loops have been used Thesmall-scale flow loop includes a 0.5 in outside-diameter smooth coiled tubing, whilethe large-scale flow loop includes 2 3/8 in rough coiled tubings Elevated temperaturetests and salinity tests were conducted using optimum concentrations of drag reducers

ASP-in fresh water, 2% KCl, and synthetic seawater

Correlations were developed that can predict the drag reduction at different

salinities and temperatures The developed correlations show a reasonable agreement

with the experimental data [90]

The efficiency of drilling operations can be increased using a drilling fluid material

that exists as supercritical fluid or a dense gas at temperature and pressure conditions

occurring in the drill site, such as carbon dioxide

A supercritical fluid exhibits physical-chemical properties intermediate between

those of liquids and gases Mass transfer is rapid with supercritical fluids Their

dynamic viscosities are nearer to those in normal gaseous states

In the vicinity of the critical point the diffusion coefficient is more than 10 times

that of a liquid Carbon dioxide can be compressed readily to form a liquid Under

typical borehole conditions, carbon dioxide is a supercritical fluid

The viscosity of carbon dioxide at the critical point is only 0.02 c P, increasing

with pressure to about 0.1 c P at 70 MPa (about 10,000 psi) Because the diffusivity

of carbon dioxide is so high, and the rock associated with petroleum-containing

formations is generally porous, the carbon dioxide is quite effective in penetrating

the formation

This penetration is beneficial Carbon dioxide is commonly used to stimulate

the production of oil wells, because it tends to dissolve in the oil, reducing the oil

viscosity while providing a pressure gradient that drives the oil from the formation

Carbon dioxide can be used to reduce mechanical drilling forces, to remove

cuttings, or to jet erode a substrate Supercritical carbon dioxide is preferably

used with coiled-tube drilling equipment The very low viscosity of supercritical

carbon dioxide provides efficient cooling of the drill head and efficient cuttings

removal

Furthermore, the diffusivity of supercritical carbon dioxide within the pores of

petroleum formations is significantly higher than that of water, making jet erosion

using supercritical carbon dioxide much more effective than jet erosion using water

Supercritical carbon dioxide jets can be used to assist mechanical drilling, for

erosion drilling, or for scale removal Spent carbon dioxide can be vented to the

atmosphere, collected for reuse, or directed into the formation to aid in the recovery

of petroleum [91]

1.3 ADDITIVES

A variety of compounds useful as thickeners is shown inTable 1.8 Subsequently, the

individual compounds are explained in detail

Table 1.8 Thickeners

A water-soluble copolymer of hydrophilic and hydrophobic

monomers, acrylamide (AAm)-acrylate of silane or siloxane

[ 92 ] Carboxymethyl cellulose, poly(ethylene glycol) [ 93 , 94 ]

Amide-modified carboxyl-containing poly(saccharide) [ 96 ]

Thermally stable hydroxyethyl cellulose (HEC) 30% ammonium or

sodium thiosulfate and 20% HEC

[ 98 ]

AA copolymer and oxyalkylene with hydrophobic group [ 99 ]

Copolymers acrylamide-acrylate and vinylsulfonate-vinylamide [ 100 ]

Cationic poly(galactomannan)s and anionic xanthan gum [ 101 ]

Copolymer from vinyl urethanes and AA or alkyl acrylates [ 102 ]

Ferrochrome lignosulfonate and carboxymethyl cellulose [ 105 ]

a Stable up to temperatures of about 180◦C.

b Solubilized in acidic solution.

a pH of 5.5 to 10.5 or higher [111,112]

Mixed metal hydroxides

By addition of mixed metal hydroxides, typical bentonite muds are transformed to anextremely shear thinning fluid [113] At rest these fluids exhibit a very high viscositybut are thinned to an almost water like consistency when shear stress is applied

In theory, the shear thinning rheology of mixed metal hydroxides and bentonitefluids is explained by the formation of a three dimensional, fragile network of mixedmetal hydroxides and bentonite

The positively charged mixed metal hydroxide particles attach themselves to the

surface of negatively charged bentonite platelets Typically, magnesium aluminum

hydroxide salts are used as mixed metal hydroxides

Mixed metal hydroxides demonstrate the following advantages in drilling [114]:

• high cuttings removal,

• suspension of solids during shutdown,

• lower pump resistance,

• stabilization of the borehole,

• high drilling rates, and

• protection of the producing formation

Mixed metal hydroxide drilling muds have been successfully used in horizontal

wells, in tunneling under rivers, roads, and bays, for drilling in fluids, for drilling

large-diameter holes, with coiled tubing, and to ream out cemented pipe

Mixed metal hydroxides can be prepared from the corresponding chlorides treated

with ammonium [115] Experiments done with various drilling fluids showed that

the mixed metal hydroxides system, coupled with propylene glycol [116], caused the

least skin damage of the drilling fluids tested

Thermally activated mixed metal hydroxides, made from naturally occurring

minerals, especially hydrotalcites, may contain small or trace amounts of metal

impurities besides the magnesium and aluminum components, which are particularly

useful for activation [117]

Mixed hydroxides of bivalent and trivalent metals with a three dimensional

spaced-lattice structure of the garnet type (Ca3Al2[OH]12) have been described

[118,119]

Bit lubricants are dealt with in chapter 4 in detail During drilling, the drill string may

develop an unacceptable rotational torque or, in the worst case, become stuck When

this happens, the drill string cannot be raised, lowered, or rotated Common factors

leading to this situation include:

• cuttings or slough buildup in the borehole,

• an undergauge borehole,

• irregular borehole development embedding a section of the drill pipe into the

drilling mud wall cake, and

• unexpected differential formation pressure

Differential pressure sticking occurs when the drill pipe becomes imbedded in the

mud wall cake opposite a permeable zone

The difference between the hydrostatic pressure in the drill pipe and the formation

pressure holds the pipe in place, resulting in a sticking pipe Differential sticking may

be prevented, and a stuck drill bit may be freed, using an OBM or an oil-based or

water-based surfactant composition

Such a composition reduces friction, permeates drilling mud wall cake, destroysbinding wall cake, and reduces differential pressure Unfortunately, many of suchcompositions are toxic to marine life.

Hagfish slime

Hagfish are marine craniates of the class Agnatha or Myxini are also known asHyperotreti Some researchers regard Myxini as not belonging to the subphylumVertebrata, because they are the only living animals that have a skull but not avertebral column [120]

Despite their name, there is some debate about whether they are strictly fish, sincethey belong to a much more primitive lineage than any other group that is placed

in the category of fish (Chondrichthyes and Osteichthyes) The earliest fossil recorddates back approximately 550 million years, or earlier to the Lower Cambrian period.Their unusual feeding habits and slime-producing capabilities have led members ofthe scientific community and popular media to dub the hagfish as the most disgusting

of all sea creatures Although hagfish are sometimes called slime eels, they are noteels at all

Hagfish are long and vermiform, and can excrete copious quantities of a slime

or mucus of unusual composition When captured and held, for example, by thetail, they secrete the slime, which expands into a gelatinous and sticky goo whencombined with water If they remain captured, they can tie themselves in an overhandknot which works its way from the head to the tail of the animal, scraping off theslime as it goes and freeing them from their captor, as well as the slime

Recently it has been reported that the slime entrains water in its microfilaments,creating a slow-to-dissipate viscoelastic substance, rather than a simple gel, and it hasbeen proposed that the primary protective effect of the slime is related to impairment

of the function of a predator fish’s gills [121] It has been observed that most of theknown predators of hagfish are varieties of birds or mammals It has been proposedthat the lack of marine predators can be explained by a gill-clogging hypothesis,wherein one purpose of the slime is to impair the gill function of marine animals thatattempt to prey on the hagfish If true, it could be regarded as a highly successfulevolutionary strategy against predatory fish

Free-swimming hagfish also excrete slime when agitated and will later clear themucus off by way of the same traveling-knot behavior

The reported gill-clogging effect suggests that the traveling-knot behavior isuseful or even necessary to restore the hagfish’s own gill function after sliming Anadult hagfish can secrete enough slime to turn a 20 l bucket of water into slime in amatter of minutes Research is ongoing regarding the properties of the components

of hagfish slime filament protein

Drilling formations below the bottom of a body of water have beendescribed [122]

Hagfish may be caused to generate bodily slime in a container at the surface One

or more hagfish may be deployed in the container and agitated to cause secretion ofthe slime The slime may be lowered in a separate container along with the drilling

system when it is deployed on the water bottom The slime may be mixed with sea

water for use as a drilling fluid during the drilling operations Effective mixtures

may range from about one part hagfish slime to 10 parts of water to about one part

hagfish slime to about 20 parts of water Drilling operations may be performed as

known in the art of sea floor drilling using the above described hagfish slime-water

mixture [123]

Bacterial contamination of drilling fluids contributes to a number of problems Many

of the muds contain sugar-based polymers in their formulation that provide an

effective food source to bacterial populations This can lead to direct degradation

of the mud In addition, the bacterial metabolism can generate deleterious products

Most notable among these is hydrogen sulfide, which can lead to decomposition

of mud polymers, formation of problematic solids such as iron sulfide, and corrosive

action on drilling tubes and drilling hardware [124] Moreover, hydrogen sulfide is a

toxic gas

Many polymers are used in drilling fluids as fluid loss control agents or

viscosifiers Because of the degradation of the polymers by bacteria in drilling fluids,

an increase in fluid loss can occur All naturally occurring polymers are capable of

being degraded by bacterial action However, some polymers are more susceptible

to bacterial degradation than others One solution, besides using bactericides, is

replacing the starch with low viscosity PAC, polyanionic lignin, or other

enzyme-resistant polymers [125]

Certain additives are protected from biodegradation while drilling deep wells by

quaternary ammonium salts [126] This results in a considerably reduced

consump-tion of the additives needed

Bacteria control is important not only in drilling fluids, but also for other oil and

gas operations The topic is treated more extensively in Chapter 5 Some bactericides

especially recommended for drilling fluids are summarized inTable 1.9and sketched

out inFigure 1.4

Corrosion inhibitors are the subject of several topics in petroleum industries, such as

transport and completion They are detailed in Chapter 6

Bentonites are highly colloidal and swell in water to form thixotropic gels This

property results from their micaceous sheet structure Because of these

viscosity-building characteristics, bentonites find major use as viscosity enhancers or builders

in such areas as drilling muds and fluids, concrete and mortar additives, foundry and

Table 1.9 Bactericides for Drilling Fluids

Bis[tetrakis(hydroxymethyl)phosphonium] sulfatea [ 124 ] Dimethyl-tetrahydro-thiadiazine-thione [ 127 ]

a Absorbed on solid.

b Synergistically effective with organic acids.

c Synergistically effective with organic acids.

d Fungicide.

e Algicide.

4,5-Dichloro-2-N-octyl-isothiazolin-3-one

S N

O Cl

Cl (CH2 )7CH3

N N

Pyrazol

O N

Isooxazol

S N

Isothiazol 1,2-Benzoisothiazolin-3-one

N S O

FIGURE 1.4

Components for biozides

molding sands, and compacting agents for gravel and sand, as well as cosmetics.Most bentonites that are found in nature are in sodium or calcium form

The performance of a calcium bentonite as a viscosity builder often can beenhanced by its conversion to the sodium form Crude bentonite can be upgraded

to prepare a variety of solutions that have unusually high aqueous viscosities [136].The crude material is sheared and dried Sodium carbonate is then dry blended with

Table 1.10 Clay Stabilizers for Drilling Fluids

Sodium capryloamphohydroxypropyl sulfonate [ 142 ]

Partially hydrolyzed poly(acrylamide) and PPG, or a betaine [ 143 ]

a Water sensitive smectite or illite shale formations.

the material and pulverized These bentonite clays are self-suspending, self-swelling,

and self-gelatinizing when mixed with water

The modification of bentonite with alkylsilanes improves the dispersing

proper-ties [137] Incorporation of phosphonate-type compounds in bentonites for drilling

mud permits the blockage of free calcium ions in the form of soluble and stable

complexes and the preservation or restoration of the initial fluidity of the mud [138]

The phosphonates also have dispersing and fluidizing effects on the mud

1.3.6 CLAY STABILIZATION

Selected clay stabilizers are shown inTable 1.10 Thermally treated carbohydrates

are suitable as shale stabilizers [145–147] They may be formed by heating an

alkaline solution of the carbohydrate, and the reaction product may be reacted with a

cationic base The inversion of nonreducing sugars may be first effected on selected

carbohydrates, with the inversion catalyzing the browning reaction

Poly(acrylate)s are often added to drilling fluids to increase the viscosity and limit

formation damage The filter cake is critical in preventing reservoir invasion by mud

filtrate Polymer invasion of the reservoir has been shown to have a great impact on

permeability reduction [148] The invasion of filtrate and solids in drilling in fluidcan cause serious reservoir damage.

1.3.8 SHALE STABILIZER

Swelling due to shale hydration is one of the most important causes for boreholeinstability Three processes contributing to shale instability are considered [149]:

1 Movement of fluid between the wellbore and shale, which is limited to flow

from the wellbore into the shale

2 Changes in stress and strain, which occur during the interaction of shale and

filtrate

3 Softening and erosion, caused by invasion of mud filtrate and consequent

chemical changes in the shale

Adding a shale stabilizer to drilling fluids is an effective way to control clayswelling [150] A copolymer of AAm and acrylonitrile has been found to beeffective as a shale hydration swelling retarder Experimental results showed thatthe inhibitors developed have good properties to inhibit shale hydration swelling,especially their quaternized product 2-Hydroxybutyl ether and polyalkyl ethermodified poly(galactomannan)s have been described as useful shale inhibitors [151]

A copolymer of styrene and maleic anhydride (MA) with alkylene oxide basedside chains is effective as a shale stabilizer [152] A variety of poly(oxyalkyleneamine)s may serve as shale inhibition agents It was found that poly(oxypropylene)diamine H2N−CH(CH3)CH2[−OCH2CH(CH3)]x−NH2 [153] is the best, with

x < 15 Surfactants are used to change the interfacial properties Suitable surfactants

are given inTable 1.11

1.3.9 FLUID LOSS ADDITIVES

Filtration control is an important property of a drilling fluid, particularly whendrilling through permeable formations where the hydrostatic pressure exceeds theformation pressure It is important for a drilling fluid to quickly form a filter cakewhich effectively minimizes fluid loss, but which also is thin and erodible enough to

Table 1.11 Surface Active Agents for Drilling Muds

Table 1.12 Lost Circulation Additives

Partially hydrolyzed poly(acrylamide) 30%

hydrolyzed, crosslinked with Cr3+ [166]

Table 1.13 Lost Circulation Additives

Rice products [ 170 , 171 ] Waste olive pulp [ 172 ]

Pulp residue waste [ 175 ] Petroleum coke [ 176 ] Shredded cellophane [ 177 ]

allow product to flow into the wellbore during production [167] Fluid loss additives

are detailed in Chapter 2 Subsequently, a few fluid loss additives for drilling fluids

are summarized for quick reference (Table 1.12)

There are a number of methods that have been proposed to help to preventing

the loss of a circulation fluid [168] Some of these methods use fibrous, flaky, or

granular materials to plug the pores as the particulate material settles out of the slurry

Examples are given inTable 1.13

Other methods propose to use materials that interact in the fissures of the

formation to form a plug of increased strength Lost circulation additives are

summarized inTable 1.12

Water swellable polymers

Certain organic polymers absorb comparatively large quantities of water, for

ex-ample, alkali metal poly(acrylate) or crosslinked poly(acrylate)s [178] Such

water-absorbent polymers, insoluble in water and in hydrocarbons, can be injected into

the well with the objective of encountering naturally occurring or added water at

the entrance to and within an opening in the formation The resulting swelling of the

polymer forms a barrier to the continued passage of the circulation fluid through that

opening into the formation

The hydrocarbon carrier fluid initially prevents water from contacting the absorbent polymer until such water contact is desired Once the hydrocarbon slugcontaining the polymer is properly placed at the lost circulation zone, water is mixedwith the hydrocarbon slug so that the polymer will expand with the absorbed waterand substantially increase in size to close off the lost circulation zone [162,179–181].The situation is similar to an oil-based cement The opposite mechanism is used by ahydrocarbon-swellable elastomer [182].

water-Shear degradation of lost circulation materials

Lost circulation materials (LCMs) are widely used to mitigate fluid loss when drillingpermeable zones Their effectiveness, however, generally declines with circulationtime, and this decline is linked to the reduction in the average size of the solidscomponents, or shear degradation

Dimensional analysis and first-principle physics have been used to frame thosemechanisms into a scientific definition that directly connects the progressive LCMsize reduction to operational parameters such as the densities of particles andsuspending fluid, the size of particles, and the fluid viscosity

The introduction of large-sized materials in the drilling mud circulation systemhas become a common practice during the past decades for the mitigation of lostcirculation while drilling in permeable intervals [183] Solids with comparativelylarge diameters are carried with the drilling mud and, when fractures occur, theydeposit in the fractures or at the opening of the fractures, successfully blockingthe discharge of fluid out of the wellbore The effectiveness of such material wasobserved, however, to decline over time as the drilling mud circulates through themud pumps, the drill string, the bit nozzles, the wellbore annulus, and the mudrecycling system

The decline over time in the effectiveness of the LCMs and loss-preventionmaterials during drilling is widely linked to the degradation of these componentsthat have an average size that drops with circulation time [183]

Numerous experimental studies have attempted to quantify the LCM degradation

by reproducing the root phenomena in the laboratory The concept of shear dation has thus become a synonym for such studies, and it is widely used for theselection of materials to be used in drilling operations

degra-The concept of shear degradation and its effectiveness in capturing the progressivesize reduction of LCM during circulation has been examined [183] Using dimen-sional analysis, the tendency of a material to degrade can be determined in advance,whereby the density of the particles and suspending fluid, the size of particles,and the fluid viscosity are examined as the governing parameters Understandingthe underlying physics enables the selection of a more-shear-resistant engineered-particle drilling fluid, regardless of its application

Anionic association polymer

Another type of lost circulation agent is the combination of an organic phosphateester and an aluminum compound, for example, aluminum isopropoxide The action

of this system as a fluid loss agent seems to be that the alkyl phosphate ester becomes

crosslinked by the aluminum compound to form an anionic association polymer,

which serves as the gelling agent [184]

Fragile gels

A fragile gel is a gel that can be easily disrupted or thinned under shear stress, etc

But it can quickly return to a gel when the stress is alleviated or removed,

for example, as when the circulation of the fluid is stopped Fragile gels may be

disrupted by a mere pressure wave or a compression wave during drilling They break

instantaneously when disturbed, reversing from a gel back into a liquid form with

minimum pressure, force, and time

Metal crosslinked phosphate esters impart a fragile progressive gel structure to a

variety of oil and invert emulsion based drilling fluids, both at neutral or acidic pH

The amount of phosphate ester and metal crosslinker used in a drilling fluid

depends on the oil type and the desired viscosity of the drilling fluid Generally,

however, more phosphate ester and metal crosslinker is used for gelling or enhancing

the viscosity of the fluid for transport than is used for imparting fragile progressive

gel structure to the drilling fluid

Thus, metal crosslinked phosphate ester compositions enhance the fluid viscosity

for suspending weighting materials in drilling fluids during transport of the

flu-ids [185]

Aphrons

Other lost circulation additives can be encapsulated The encapsulation is dissolved

and the material swells to close fissures Microbubbles in a drilling fluid can be

generated by certain surfactants, and polymers known as aphrons are a different

approach to reduce the fluid loss [186]

An aphron drilling fluid is similar to a conventional drilling fluid, but the drilling

fluid system is converted to an energized air bubble mud system before drilling [187]

Permanent grouting

Lost circulation also can be suppressed by grouting permanently, either with cement

[188,189] or with organic polymers that cure in situ

Oxygen scavenger

Oxygen corrosion is often underestimated Studies have shown that the corrosion

can be limited when proper oxygen scavengers are used Hydrazine leads the group

of chemicals that are available for oxygen removal Because of its special properties,

it is used for corrosion control in heating systems and in drilling operations, well

workover, and cementing [190]

Hydrogen sulfide removal

It is sometimes necessary to remove hydrogen sulfide from a drilling mud niques using iron compounds that form sparingly soluble sulfides have been devel-oped, for example, with iron (II) oxalate [191] and iron sulfate [192] The sulfur isprecipitated out as FeS Ferrous gluconate is an organic iron chelating agent, stable

Tech-at pH levels as high as 11.5 [193]

Zinc compounds have a high reactivity with regard to H2S and therefore aresuitable for the quantitative removal of even small amounts of hydrogen sulfide [194].However, at high temperatures they may negatively affect the rheology of drillingfluids

Surfactant in hydrocarbon solvent

Methyl-diethyl-alkoxymethyl ammonium methyl sulfate has high foam ing properties [195]

extinguish-Biodegradable surfactants

Alkylpoly(glucoside)s (APGs) are highly biodegradable surfactants [196] The dition of APGs, even at very low concentrations, to a polymer mud can drasticallyreduce the fluid loss even at high temperatures Moreover, both fluid rheology andtemperature resistance are improved

ad-Deflocculants and dispersants

Deflocculants have a relatively low molecular weight Complexes of tetravalentzirconium with organic acids, such as citric, tartaric, malic, and lactic acids, and acomplex of aluminum and citric acid have been claimed to be active as dispersants.Polymers composed of sodium styrene sulfonate, MA, and a zwitterionic func-tionalized MA [197–200] are suitable The dispersant is especially useful in dispers-ing bentonite suspensions [201]

Polymers with amine sulfide terminal moieties are synthesized by using ols as chain transfer agents in aqueous addition polymerization reactions Thepolymers are useful as mineral dispersants [202]

aminethi-Shale stabilizing surfactants

There are special shale stabilizing surfactants consisting of non-ionic alkanolamides[203], for example, acetamide monoethanolamines and diethanolamines Acetoneand ethanolamine are shown inFigure 1.5

Toxicity

Alkyl phenol ethoxylates are a class of surfactants that have been used widely inthe drilling fluid industry The popularity of these surfactants is based on their costeffectiveness, availability, and range of obtainable hydrophilic-lipophilic balance

values [204] Studies have shown that alkyl phenol ethoxylates exhibit oestrogenic

effects and can cause sterility in some male aquatic species

This may have subsequent human consequences, and such problems have led

to a banning of their use in some countries and agreements to phase out their use

Alternatives to products containing alkyl phenol ethoxylates are available, and in

some cases they show an even better technical performance

There are many weighting materials, including barite and iron oxides, to increase the

specific weight of a slurry Conversely, the specific weight can be reduced by foaming

or by the addition of hollow glass particles

Barite

Barite has been used as a weighting agent in drilling fluids since the 1920s It is

preferred over other materials because of its high density, low production costs, low

abrasiveness, and ease of handling Other weighting materials have been used, but

they are problematic or costly Finished barite producers sometimes blend ores from

different sources to obtain the desired average density to meet API specifications

Some barite ores contain alkaline-soluble carbonate minerals that can be

detri-mental to a drilling fluid, such as iron carbonate (siderite), lead carbonate (cerussite),

and zinc carbonate (smithsonite) [205] Details of how to characterize barite have

been worked out [206] Barite can be modified to become oleophilic [207,208]

To recover barite from drilling muds, a direct flotation without prior dewatering

and washing of the drilling muds has been described [209] An alkyl phosphate is

used as a collecting and frothing reagent

A novel barite-inhibition assay based on the nucleation and inhibition model

has been proposed and used to evaluate the thermal stability of phosphonates

and polymeric scale inhibitors with regard to their potential application in high

temperature wells [210] Systematic experiments have been conducted to investigatethe time (minutes to days) and temperature (up to 200◦C) dependence of the thermaldegradation of the inhibitor, the impact of stainless steel and iron on the degradation

of inhibitors at high temperatures, and the difference between aging tests withinhibitors in solution and with those inhibitors adsorbed on core materials

The results not only enable a more accurate understanding of the thermaldegradation of scale inhibitors but also facilitate the selection and placement of scaleinhibitors for high-temperature oil and gas production [210]

The commonly used dynamic-tube-blocking methodology was modified Anapparatus was built to study the nucleation kinetics of barite-scale formation at hightemperatures in the presence and absence of scale inhibitors [211]

Barite formation was detected by monitoring the pressure change over amicrometer-sized in-line filter This has been proved to be an easy and accuratemethod to study mineral-scale-nucleation kinetics at high temperatures

Additionally, the nucleation kinetics of barite at 0-25◦C with and withoutthermodynamic hydrate inhibitors was investigated By using this modified dynamic-tube-blocking technique the nucleation kinetics of barite in 1 M NaCl solutions over

a temperature range from 25◦C to 200◦C and at various supersaturation conditionswas successfully measured A relationship of the precipitation kinetics of barite as afunction of temperature and the saturation index could established [211]

In particular, the inhibition efficiency of the phosphonate inhibitor hexamethylenetriamine-penta (methylene phosphonic) acid on the barite precipi-tation has been evaluated The effect of Ca2+ on the inhibition efficiency of thisinhibitor at a low temperature of 4◦C and at high temperatures of 175-200◦C wasinvestigated [211]

bis-Ilmenite

Environmental aspects suggest replacing barite with ilmenite However, the use ofilmenite as weighting material can cause severe erosion problems Using ilmenitewith a narrow particle-size distribution around 10μm can reduce the erosion to alevel experienced with barite [212]

Carbonate

It is reasonable to replace barite and iron-based weighting material with carbonate

if a high degree of weighting the muds is not required by the drilling conditions.Besides being cheaper than barite, a carbonate weighting material is less abrasive,which is especially important when drilling is performed in producing formations,and it is readily soluble in hydrochloric acid The main shortcomings of carbonatepowders are due to the presence of a coarsely divided fraction and noncarbonateimpurities [213]

Zinc oxide, zirconium oxide, and manganese tetroxide

Zinc oxide (ZnO), is a particularly suitable material for weighting because, it has ahigh density, 5.6 g ml−1versus 4.5 g ml−1for barite It is soluble in acids (e.g., HCl);and its particle size can be designed so that it does not invade the formation Acid

solubility is particularly desirable because dissolved ZnO can be produced through a

production screen without plugging it A high density means less weighting material

is needed per unit mud volume to achieve a desired density

The particle size, around 10μm, is such that the ZnO particles do not invade the

formation core with the filtrate On the other hand, the particle size it is not large

enough to settle out of suspension Zirconium oxide possesses similar properties as

ZnO It has a density of 5.7 g ml−1and is soluble in nitric acid and hot concentrated

hydrochloric, hydrofluoric, and sulfuric acids Therefore, a filter cake formed from

zinc oxide or zirconium oxide then can be dissolved The high acid solubility of

ZnO makes it particularly suitable as weighting material [214] On the other hand,

manganese tetroxide (Mn3O4) is so fine that it invades the formation with the filtrate

Hollow glass microspheres

Initially, glass microspheres were used in the 1970s to overcome severe lost

circulation problems in the Ural Mountains The technology has been used in other

sites [215] Hollow glass beads reduce the density of a drilling fluid and can be used

for underbalanced drilling [216–218] Field applications have been reported [219]

It has long been known that organophilic clays can be used to thicken a variety of

organic compositions Such organophilic clays are prepared by the reaction of an

organic cation with a clay If the organic cation contains at least one alkyl group

containing at least 8-10 carbon atoms, then such organoclays have the property of

in-creasing viscosity in organic liquids and thus providing rheologic properties to a wide

variety of such liquids including paints, coatings, adhesives, and similar products

It is also well known that such organoclays may function to thicken polar or

nonpolar solvents, depending on the substituents on the organic salt The efficiency of

organophilic clays in nonaqueous systems can be further improved by adding a polar

organic material with low molecular weight to the composition Such polar organic

materials have been called dispersants, dispersion aids, and solvating agents The

most efficient polar materials have been found to be low molecular weight alcohols

and ketones, particularly methanol and acetone

Organophilic clays are generally prepared by reacting a hydrophilic clay with an

organic cation, usually a quaternary ammonium salt compound produced from a fatty

nitrile Examples of hydrophilic clays include bentonite, attapulgite, and hectorite

Native clay surfaces have negatively charged sites and cationic counter ions

such as sodium and calcium cations Thus, the clay may be treated with a cationic

surfactant to displace the cations that are naturally present at the clay surfaces The

cationic surfactant becomes tightly held to the surfaces through electrostatic charges

In this manner, the hydrophilic nature of the clay is reversed, making it more soluble

in oil Bentonite that primarily contains sodium cations is known as sodium bentonite

Those monovalent sodium cations may be easily displaced from the clay, making a

large number of anionic sites available [220]

Quaternary ammonium compounds contain nitrogen moieties in which one ormore of the hydrogen atoms attached to the nitrogen are substituted by organicradicals One of the most popular quaternary ammonium compounds for organophilicclays is dimethyl dihydrogenated tallow ammonium chloride Tallow is composedfrom unsaturated and saturated fatty acids, including mainly oleic acid, palmitic acid,stearic acid, and other minor fatty acids.

The oil solubility of this compound is enhanced by its almost complete carbon structure and its two long chain alkyl groups Further, its two methyl groups

hydro-do not sterically interfere with close packing of the ammonium cation to the claysurface

The dimethyl dihydrogenated tallow ammonium chloride surfactant, however,cannot be efficiently activated at relatively low temperatures Improved cationicsurfactants have been developed in which the ammonium compounds have greaternumbers of alkyl groups One such surfactant includes a benzyl group that greatlyenhances the performance of organophilic clays at cold temperatures [220]

There is a synergistic action of two or more types of organic salts in the presence

of an organic anion The combination of hydrophobic and hydrophilic organic saltsand an organic anion provides an organophilic clay gellant, which exhibits improvedgelling properties in nonaqueous systems [221]

Examples are dimethyl dihydrogenated tallow quaternary ammonium chlorideand methyl bis-poly(oxyethylene) (15 units) cocoalkyl quaternary ammonium chlo-ride and the salts from stearic acid, succinic acid, and tartaric acid [222–225]

Biodegradable organophilic clay

Organophilic clays are treated with a quaternary ammonium surfactant having anamide linkage Quaternary ammonium surfactants are shown inFigure 1.6

The surfactants are based on stearamides The benzyl group greatly enhances theperformance of organophilic clays at cold temperatures near 7◦C.