Chapter 2

Boring fluid or clay is a fluid that is circulated through the drillstring and up the ring back to surface under normal boring operation. It is really of import in the boring procedure after the debut of rotary boring. The earlier utilizations were for good completions, but broadened with clip to include coring, stuck pipe release/prevention, annulus battalions, wellbore stabilisation, HPHT applications, caustic environments and directional boring.

2.1.1 Functions of Drilling Fluid

Assortment of additives was added into boring fluid to transport out the undermentioned maps:

Antagonizing formation force per unit area. The column of boring clay in the drill pipe and ring provides a hydraulic caput that counteracts the force per unit area in the formation forestalling runaway.

Protecting permeable zones from amendss. Particular boring clay additives build a filter bar on the walls of the well, forestalling boring mud loss into permeable formation.

Removing film editings from borehole. Jets of boring clay go outing from drill spot carry drill film editings off from the spot.

Cooling and lubricating the drill twine and spot. Clash of revolving drill biting heats the drill pipe and the spot. Circulating of boring clay cools the drill twine and lubricates it where contact is made with the formation.

Suspending solids. The boring clay has sufficient viscousness to suspend film editings and burdening agents when boring stops, as during add-on of drill pipe.

Supporting parts of the weight of drill twine. The steel rivulet pipe is supported in the hole in proportion to the volume and denseness of boring clay displaced by the pipe in ring.

Protecting, back uping, and stabilising borehole wall.

Aid in rating and reading of good logs.

2.1.2 Types of Drilling Fluids

There are three chief types of boring fluid which are ( 1 ) Water based clay ; ( 2 ) Oil based clay and ( 3 ) Gases fluid Water Base Mud

The term of H2O based clay is mentioning to any boring fluid that the uninterrupted stage is H2O. Several of additives can be besides present in this clay. Water based clay contain of H2O stage, inert solids, a reactive solids stage and chemical additive. All of these parts affect the overall clay belongingss.

There are several types of water-based clay systems consist of:

Clean H2O and native clay, used to bore compact formations which are usually force per unit area ( formation force per unit area peers hydrostatic force per unit area caused by formation fluids ) .

Dispersed muds – Lignosulphonate claies, used when the clay has to hold following such features such as comparative high clay weight, used at reasonably high formation temperature, low filtration loss required and high tolerance for taint by boring solids.

Nondispersed muds – KCl/ Polymer clay, used to bore H2O sensitive and sheding shales as productive sand which are prone to formation harm, fresh H2O nondispersed claies are applied.

Flocculation claies, used to increase dynamically in filtration, viscousness and gel strength.

Salt-saturated clay, used to bore through salt domes and salt subdivisions. Oil Based Mud

Opposite to H2O based clay, oil based clay is a boring fluid which contains petroleum or diesel oil as its uninterrupted stage with merely a little sum of H2O dispersed as droplets. This clay can hold every bit small as 3 % to 5 % or every bit much as 20 % to 40 % ( invert emulsions ) H2O content. Oil based clay systems are applied when:

Boring sensitive production zones or job shales.

Boring salt subdivisions and formations that contain hydrogen sulphide.

Danger of stuck pipe jobs

Boring at bottom hole temperature that are allowable by water-based clay. Gass Fluid

Gass boring unstable consist of air, natural gases, mist, aerated clay and froth. This type of boring fluid is used because it has lowest denseness that can forestall from formation harm and lost circulation. The usage of gases fluid as go arounding medium can be categorized into four boring operation:

Air or dust boring, which the circulating medium is air merely, maintains the lowest possible downhole force per unit area.

Mist boring, which H2O, incorporating a foaming agent ( soap ) , is injected into the air watercourse at the surface and discharged as a wet mist.

Foam boring, is frequently subdivided into stable- and stiff-foam boring, used to better hole-cleaning belongingss and boring large-diameter holes.

Aerated clay, which both air and clay flow at the same time in the ring as air bubbles dispersed in a liquid to cut down ECD below that of H2O.

2.1.3 Mud Properties

Mud belongingss are really of import to be measuring to guarantee the boring fluid meets necessary standards needed. These include clay weight, fictile viscousness, output point, gel strength, filtrate and mud bar. All these rheological belongingss can be controlled by adding suited additive. Plastic Viscosity, Apparent Viscosity and Yield Point

Viscosity is a belongings of fluids and slurries that indicate their opposition to flux, defined as the ratio of shear emphasis to shear rate. The viscousness of fluids varies with force per unit area and temperature. The viscousness of most fluids is instead sensitive to alterations in temperature, but comparatively to coerce fluctuations until they are exposed to high force per unit areas. The consequence of molecular weight on the viscousness of liquid is the liquid viscousness addition with increasing molecular weight.

Plastic Viscosity ( PV ) in centipoise ( cP ) or milliPascal seconds ( mPa•s ) is calculated from clay viscosimeter informations as:

PV ( cP ) = ?600 – ?300

Plastic viscousness is normally described as that portion of opposition to flux caused by mechanical clash. Chiefly, it is affected by:

Solids concentration

Size and form of solids

Viscosity of the fluid stage

The presence of some long concatenation polymer

The Oil-to-Water ( O/W ) or Synthetic-to-Water ( S/W ) ratio in invert-emulsion fluids

Type of emulsifiers in invert emulsion fluids.

An addition in fictile viscousness can intend an addition in the per centum by volume of solids, a decrease in the size of the solid atoms, a alteration in the form of the atoms or a combination of these. Any addition in the entire surface country of solids exposed will be reflected in an increased plastic viscousness.

The effectual viscousness is sometimes referred to as the Apparent Viscosity ( AV ) . The evident viscousness is reported as either the clay viscosimeter reading at 300 RPM ( ?300 ) or one-half of the metre reading at 600 RPM ( ?600 ) .

Output Point ( YP ) in lbs per 100 square pess ( lb/100 ft2 ) is calculated from Fann VG metre informations as:

YP ( lb/100 ft2 ) = 2 ten ?300 – ?600 or YP ( lb/100 ft2 ) = ?300 – PV

or in Pascals:

YP ( Pa ) = 0.4788 x ( 2 ten ?300 – ?600 )


YP ( Pa ) = 0.4788 x ( ?300 – PV )

Output point, the 2nd constituent of opposition to flux in a boring fluid, is a measuring of the electrochemical or attractive forces in a fluid. These forces are a consequence of negative and positive charges located on or near the atom surfaces. Output point is a step of these forces under flow conditions and is dependent upon:

Surface belongingss of the fluid solids ;

Volume concentration of the solids ; and

Electrical environment of these solids ( concentration and types of ions in the unstable stage of the fluid ) .

Output point is that portion of opposition to flux that may be controlled by proper chemical intervention. The output point will diminish as the attractive forces are reduced by chemical intervention. Decrease of output point will besides diminish the evident viscousness. Gel Strength

Gel strength is the belongings exhibited by some fluids which form a gel construction while inactive and so go fluid once more when shear is applied. Most water-base boring fluids exhibit this belongings due to the presence of electrically charged atoms or particular polymers that link together to organize a stiff matrix. Gel strength readings taken at 10-sec and 10-min intervals, and in critical state of affairss at 30-min intervals, on the Fann VG metre provide a step of the grade of gel strength nowadays in the fluid. The strength of the gel formed is a map of the sum and type of solids in suspension, clip, temperature, and chemical intervention. In other words, anything promoting or forestalling the linking of atoms will increase or diminish the gelation inclination of a fluid.

The magnitude of gelation, every bit good as the type of gel strength, is of import in the suspension of film editings and weight stuff. Gelation should non be allowed to go any higher than necessary to execute these maps. Excessive gel strengths can do complications, such as the followers:

Entrapment of air or gas in the fluid ;

Excessive force per unit areas when interrupting circulation after a trip ;

Decrease in the efficiency of solids-removal equipment ;

Excessive swobing while stumbling out of the hole ;

Excessive force per unit area surges while stumbling in the hole ;

Inability to acquire logging tools to the underside. Fluid Loss

A basic boring fluid map is to seal permeable formations and control filtration ( unstable loss ) . Potential jobs related to thick filter bars and inordinate filtration include tight hole, increased torsion and retarding force, stuck pipe, lost circulation, hapless log quality, and formation harm. Adequate filtration control and the deposition of a thin, low-permeability filter bar are frequently necessary to forestall boring and production jobs. Potential jobs from inordinate filter bar thickness:

Tight musca volitanss in the hole that cause inordinate retarding force ;

Increased rushs and swobing due to cut down annulate clearance ;

Differential sticking of the drillstring due to increased contact country and rapid development of lodging forces caused by higher filtration rate ;

Primary cementing troubles due to inadequate supplanting of filter bar ;

Increased trouble running shell.

Potential jobs from inordinate filtrate invasion:

Formation harm due to filter and solids invasion. Damaged zone excessively deep to be remedied by perforation or acidization. Damage may be precipitation of indissoluble compounds, alterations in wettability, and alterations in comparative permeableness to oil or gas, formation stop uping with mulcts or solids, and swelling of unmoved clays.

Invalid formation-fluid trying trial. Formation-fluid flow trials may give consequences for the filtrate instead than for the reservoir fluids.

Formation-evaluation troubles caused by inordinate filtrate invasion, hapless transmittal of electrical belongingss through midst bars, and possible mechanical jobs running and recovering logging tools.

Loging tools ( mensurating filtrate altered belongingss instead than reservoir unstable belongingss ) .

Oil and gas zones may be overlooked because the filtrate is blushing hydrocarbons off from the wellbore, doing sensing more hard.

Figure 2.1 Filter bar in a formation

Drilling fluids are slurries composed of a liquid stage and solid atoms. Filtration refers to the liquid stage of the boring clay being forced into a permeable formation by differential force per unit area. During this procedure, the solid atoms are filtered out, organizing a filter bar ( see Figure 2.1 ) . If the liquid stage besides contains an non-miscible liquid such as seawater in an oil-base clay so the non-miscible liquid droplets will besides be deposited in the filter bar and will help in filtration control. Permeability refers to the ability of fluid to flux through porous formations. Mud systems should be designed to seal permeable zones every bit rapidly as possible with thin, slick filter bars. In extremely permeable formations with big pore pharynxs, whole clay may occupy the formation ( depending on the size of the clay solids ) . In such state of affairss, bridging agents must be used to barricade the gaps so the clay solids can organize a seal. Bridging agents should be at least one-half the size of the largest gaps. Such bridging agents include calcium carbonate, land cellulose and a broad assortment of other lost-circulation stuffs.

2.2 Nanomaterial

Nanotechnology is a generic term for application that works with affair that is so little that it exist in the atomic and molecular kingdom. This term refer to application of utilizing nano-scale stuffs in technology or ability to engineer stuff in nanometer graduated table. Therefore, nanotechnology can be defined as the design and fiction of stuffs, devices and systems with control at nanometer dimension. At the nucleus of any procedure affecting nanotechnology is nanometer ( nanometer ) , which is one billionth of a metre and 10,000 times smaller than anything that the human oculus can see. At this size, the substance ‘s physical, chemical and biological belongingss are different from what they were at micron and larger graduated tables. Nanomaterials can be nanoscale in one dimension ( eg. surface movies ) , two dimensions ( eg. strands or fibers ) , or three dimensions ( eg. atoms ) . They can be in individual, amalgamate, aggregated or agglomerated signifiers with spherical, cannular, and irregular forms. Common types of nanomaterials include nanotubes, dendrimers, quantum points and fullerenes.

Nanotechnology offers the transmutation of oil and gas geographic expedition and production. It could supply radical solutions to jobs related to upstream and downstream operation. For illustration, nanotechnology can take to better understanding and control of rock/ fluid interactions and their effects on wellbore stableness, unstable loss and formation harm, thereby taking to improved boring efficiency. In oil and gas industry application, nanotechnology could be used to increase oppurtunities to develop geothermic resources by heightening thermic conduction, bettering downhole separation, and helping in the development of caustic stuffs that could be used for geothermal-energy production. Nanotechnology besides could assist better oil and gas production by doing it easier to divide oil and gas in the reservoir, heighten the possibilities of developing unconventional and stranded gas resources. The oil and gas industry relies on the strength and stableness of its stuff in all of its procedure. By constructing up such substaces on a nanoscale, it could bring forth equipment that is stronger, lighter and more immune. Nano stuff can be made as light and elastic as silk yet every bit strong as steel.

In boring industry, nanomaterial have great potency for a wide scope in the boring industry. Nanotechnology is non new, but its application in the oil industry is surely in its babyhood, including boring application. Adding nano stuff into boring clay can modify its belongingss and their suspension can supply many advantages. They can leave sedimentary, thermic, optical, mechanical, electrical, rheological and magnetic belongingss to a base fluid that can better its public presentation. For record, oil geographic expedition has used nanotechnology in boring clay for the past 50 old ages. The nanoparticles in boring claies are made of clays and are of course happening 1-nm-thick phonograph record of aluminosilicates. These nanoparticles exhibit extraordinary rheological belongingss in H2O and oil. Recent surveies indicates that successful applications of nanotechnology in boring are likely to happen with man-made nanoparticles, where size, form and chemical interactions are carefully controlled to accomplish the coveted fluid belongingss and boring public presentation.

Nanomaterial have alone belongingss due to their little size and high surface country per unit volume. As a consequence, they are found utile in many applications including oil and gas geographic expedition and production. Nanomaterial appear to be stronger and more reactive than non-nanomaterials. The passage from micro- to nanoparticles leads to alterations in physical every bit good as chemical belongingss of a stuff. Two of the major factors are the addition in the ratio of the surface country to volume, and the size of the atom. The addition in surface area-to-volume ratio, which addition as the atoms get smaller, leads to an increasing laterality of the behaviour of atoms on the surface country of atoms over those in the inside of the atom: this affects the belongingss of the atoms when they interact with other atoms. Because of the higher surface country of the nanoparticles, the interaction with other atoms within the mixture is greater, potentially taking to increased strength of the stuff, heat opposition and other belongingss of the mixture. Properties of nanomaterials depend extremely on the form, orientation and construction of single nanoparticles.

Recent research which related to application of nanomaterial in boring fluid is utilizing nanoparticles to diminish differential pipe sticking and its feasibleness in Persian oil Fieldss. These nanoparticles are carbon black atoms in which added to boring claies to execute some fuctions. This advantage of C black which has nanometer size atoms causes to do a clay bar which is more continues and integrated ( it means that clay bar has low permeableness ) . So, by holding integrated and low permeableness clay bar, it has less volume of filtrate and hence mud bar thickness is less than usual instances. Besides that, there are scientists at China ‘s Shandong University that are researching ways in which nanotechnology can be used to better boring procedure. In their specialized crude oil research lab, they have developed an advanced fluid assorted with nanosized atoms and superfine pulverization that significantly better boring velocity.