Introduction - International Association Of Drilling .
DRILLING FLUIDSIntroductionFL-1The principal functions of drilling fluid are to:Drilling fluids are fluids that are used during the drilling ofsubterranean wells. They provide primary well control ofsubsurface pressures by a combination of density and anyadditional pressure acting on the fluid column (annular orsurface imposed). They are most often circulated down thedrill string, out the bit and back up the annulus to the surfaceso that drill cuttings are removed from the wellbore. Control subsurface pressures, maintaining well control;Remove drill cuttings from beneath the bit and circulatethem to the surface; Maintain wellbore stability, mechanically and chemically; Transmit hydraulic energy to the drill bit and downholetools;Drilling fluids have a number of alternative names, acronyms Cool and lubricate the drill string and bit;and slang terms used within Allow adequate forthe industry. The most widelymation evaluation;used name is “mud” or “drill Provide a completeding mud” and both these termswellbore that will produce hywill be used interchangeablydrocarbons;throughout this chapter. Oth Suspend or minimizeer drilling fluid names andthe settling of drill cuttings oracronyms are: water-basedweight material when circulamud (WBM), oil-based mudtion is stopped, yet allow the(OBM), synthetic-based mud Figure FL-1: Drilling fluids are major factors in a successful drilling removal of drill cuttings in the(SBM), non-aqueous fluidsurface fluids processing sysprogram. Courtesy MI-SWACO, a Schlumberger company.(NAF), invert emulsion fluidtem; and(IEF), high performance water-based mud (HPWBM), drill-in Form a low permeability, thin and tough filter cakefluid (DIF) and reservoir drilling fluid (RDF). Similar to drillingacross permeable formations.fluids are so-called completion fluids that are used to finishthe well after drilling is completed. The fluids used duringThe performance of these functions depends upon the typecompletions are often referred to as workover and compleof formation being drilled and the various properties of thetion (WOC) fluids, clear brines and/or packer fluids.drilling fluid. Often, compromises are necessary due to a variety of factors. The selection and design of a particular drillDrilling fluid is a major factor in the success of the drillinging fluid and its properties depends on the complexity of theprogram and deserves careful study. Discussion in this manwell being drilled, subsurface pressures and temperatures,ual, however, is limited to its general features. A comprelogistics, cost and local experience. Drilling fluid perforhensive and more academic text on drilling fluids is “Commance is also affected by the drilling equipment being used.position and Properties of Drilling and Completion Fluids” byCaenn, Darley and Gray. The suppliers of drilling fluid mateThe properties of the drilling fluid should be adjusted to therials also offer a wide range of publications and numeroushydraulics available for the drilling operation and the well dearticles can be located in the technical literature of the oilsign. Rate of penetration (ROP) and bit life can be improvedand gas industry.by optimizing the hydraulic horsepower at the bit, especiallyfor roller cone bits. The ROP and bit life for polycrystallinediamond compact (PDC) cutter bits is improved when anadequate flowrate is used with minimal overbalance. Drillingfluid properties and circulation rates determine the parasiticDrilling fluids range from simply water or oil to compressedpressure losses in the drill string and the available pressure atair and pneumatic fluids to more complex water-based orthe bit for optimized drilling performance. The ROP is also afoil-based systems. Drilling fluid additives include weightfected by the density of the mud and nature of the suspendeding materials; viscosifiers; filtration control additives; pH/solids. Regular and complete tests are essential to the controlalkalinity control chemicals; dispersants/deflocculants/of mud properties. The interpretation of the results of thesethinners; surfactants and emulsifiers; shale inhibitors; corrotests and treatments to maintain appropriate fluid propertiession inhibitors/oxygen scavengers/hydrogen sulfide (H2S)is vital to the success of the drilling program.scavengers; lubricants; and bridging agents/lost circulationmaterials (LCMs). A brief description of these categories isincluded later in this section.Drilling fluid function and performanceIADC Drilling ManualCopyright 2014
DRILLING FLUIDSFL-2Testing drilling fluid propertiesRotary HoseStandpipeTop DriveMud PumpPump Discharge LineMud CleaningEquipment /Shale ShakerKelly or Drill Pipe,if Top Drive usedDrill PipeMud ReturnLineMud Tank/PitBoreholeDrill BitFigure FL-2: Basic land rig circulating system.Physical operating principlesThe three main functions of drilling fluids are to: Purpose of testingRoutine testing is carried out on drilling fluidsto determine the following: the density or mudweight; viscosity; gel strengths, filtration rate(also called fluid loss); sand content; solids, oiland water content; and chemical properties.Annulus Various properties of drilling fluid are monitoredand adjusted to achieve desired performance.Procedures for measuring fluid properties canbe found in API Recommended Practice 13B-1for water-based drilling fluids and Recommended Practice 13B-2 for oil-based drilling fluids.These procedures are revised and extended periodically as improvements are made and newtests are developed.Control subsurface pressures: These pressures arecontrolled by the hydrostatic pressure of the drillingfluid plus any surface-imposed pressure on the annulus.While circulating, annular pressure losses also imposeadditional pressure on the wellbore. Hydrostaticpressure is increased by increasing the density of thedrilling fluid. This is normally carried out by addingbarite (BaSO4), a high-density inert powder.Circulate drill cuttings from the well: This is dependenton a combination of fluid velocity, fluid viscosity, fluiddensity and drill string rotation.Maintain wellbore stability: This is dependent on thestrength of the rocks being drilled, local subsurfacestresses, differential pressure at the wellbore, drillingfluid chemistry, formation composition, filtrationcontrol, filter cake quality and bridging solids.Density or mud weightDensity or mud weight is the mass per unitvolume. In the field, it is measured with a mudbalance and is most often reported in poundsper gallon (lb/gal or ppg); specific gravity orSG (g/ml); kilograms per cubic meter (kg/cum); or pounds per cubic foot (lb/cu ft). Densityis used to determine the hydrostatic pressureof the mud column and can also be measuredand expressed as a gradient such as pounds persquare inch per thousand feet (psi/1,000 ft).This allows for easy calculation of the hydrostatic pressure at any depth.The mud scale is calibrated with water (freshwater weighs8.34 lb/gal and seawater weighs 8.55 lb/gal). The mudscale has four units scales graduated on the beam: lb/galor ppg, g/cc, lb/cu ft and psi/1,000 ft. Please refer to thesection entitled Calculations and Tables for the appropriatecalculations and unit conversions.ViscosityViscosity is a measure of the drilling fluids internal resistance to flow, or how thick or thin it is. Drilling fluids arenon-Newtonian, meaning that their viscosity is not constantfor all shear rates. These non-Newtonian fluids behave verydifferently than liquids like water or oil which are Newtonianwith a constant viscosity regardless of shear rate. Non-Newtonian drilling fluids are shear thinning such that they havelower viscosity at high-shear rates and higher viscosity atlow-shear rates. This is desirable for drilling where minimumpressure losses are wanted for the high-shear conditions inside the narrow bore of the drill string. Higher viscosity iswanted in the low-shear conditions of the larger annulus.Viscosity depends on the viscosity of the base liquid and theIADC Drilling ManualCopyright 2014
DRILLING FLUIDSFL-3type and concentration of solids in the drilling fluid. Viscosity is usually higher for higher density fluids due to the increased concentration of weight material such as barite. Asa general rule, thicker fluids are needed for larger diameterhole sizes and thinner fluids are needed for smaller hole sizes which have smaller annular flow areas.Viscosity is measured with two primary tools; a) the Marshfunnel (Figure FL-3) which is used to frequently measurerelative changes in viscosity, and b) a direct reading viscometer (Figure FL-4), which is used to measure the viscosity,gel strengths, and non-Newtonian characteristics precisely.The Marsh funnel is used to monitor relative changes in viscosity and is commonly reported as “funnel viscosity”. TheMarsh funnel viscosity is reported as the number of secondsrequired for a given fluid to flow a volume of 1 qt into a graduated mud cup. Its design and calibration can be verified using water. One quart of fresh water should be collected in 26( 0.5) sec at a temperature of 70 ( 5) F.Figure FL-3: Drilling fluid balance and Marshfunnel are used to measure fluid viscosity.A direct indicating rotational viscometer is used to measurethe viscosity at different shear rates to determine the rheology model coefficients. For field operations, the Binghamplastic rheology model coefficients of plastic viscosity (PV)and yield point (YP) are monitored. These two coefficientsare used to monitor the non-Newtonian properties of thedrilling fluid. These viscometers indicate the shear stress asa “dial unit” or “degree” (Ɵ) at a given shear rate (one dialunit equals about 1 lb/100 sq ft). The dimensions of the direct indicating viscometer are selected so that the PV andYP can be quickly calculated from the shear stress valuesmeasured at shear rates of 600 and 300 rpm. The PV incentipoise (cps) is calculated from the 600-rpm dial reading (Ɵ600) minus the 300-rpm dial reading (Ɵ300). The YP inlb/100 sq ft is then calculated from the 300-rpm dial reading minus the PV.PV (cps) Ɵ600 – Ɵ300YP (lb/100 sq ft) Ɵ300 – PVEq 1Eq 2Viscosity should be measured and reported at standard temperatures which are usually 120 F for most wells or 150 F forhigh-temperature wells. Shear stress values should also bemeasured at other shear rates for improved accuracy whencalculating pressure losses and when cleaning the hole. Typical six speed shear rates are taken at 600, 300, 200, 100,6 and 3 rpm. The Bingham plastic YP overestimates the realYP for most drilling fluids as well as the shear stress valuesat lower shear rates. For this reason, using better rheologymodels such as the Herschel Bulkley model is recommended for improved accuracy.IADC Drilling ManualFigure FL-4: Direct indicating viscometer (6 speed).The PV depends mainly on the concentration of solids andthe viscosity of the base liquid. It is representative of highshear rate viscosity such as is present inside the bore of thedrill string. The YP is a measure of the degree of non-Newtonian shear thinning behavior (increased thickening at lowshear rates is implied from higher YPs). The YP is a result ofthe attractive forces between particles in the fluid at lowershear rate conditions. It is also a measure of the hole cleaning capabilities of a fluid in vertical intervals. Often, a low-Copyright 2014
FL-4DRILLING FLUIDSan indication if the fluid is continuing to gel with longer periods of time (called progressive gels) or if it has reached arelatively constant value (called flat gels).Filtration or fluid lossFiltration or fluid loss is a relative measure of the liquid thatcould invade a permeable formation through deposited mudsolids. This liquid is called filtrate and the deposited solidsare called filter cake or mud cake. There are two standardfiltration tests that measure the volume of filtrate collectedafter a 30-min period of time using filter paper. These testsare the low-temperature/low-pressure fluid loss test, oftencalled the American Petroleum Institute (API) test, and thehigh-temperature high-pressure (HTHP) test. Results arereported as the milliliters (ml) which flow through a 7.1-sqin. area. The HTHP filtration test unit is a half-area (3.5-sqin.) press; therefore, the measured filtrate value is doubledfor reporting. Filter cake thickness is measured and reportedin units of 1/32 in. (or millimeters where SI units are used). Afilter cake thickness of 3 means 3/32 in.Figure FL-5: API low-temperature, low-pressure filter press.shear-rate yield point (LSRYP) is calculated using the shearstress values at 6 rpm and 3 rpm to better evaluate the realYP, the hole cleaning potential and the propensity for havingbarite sag.LSRYP (2 x Ɵ3) - Ɵ6Eq 3Gel strengthsGel strengths refer to the shear stress required to initiateflow after static periods of time. They are a measure of thedegree of gelation that occurs due to the attractive forcesbetween particles over time. Higher gel strengths are reported in the same units as YP (lb/100 sq ft). Sufficientgel strength will suspend drill cuttings and weighting materials during connections and other static conditions. Gelstrengths directly affect surge and swabbing pressureswhen making connections, tripping pipe or running casing.They also affect the pressure required to “break circulation”and the ease of releasing entrained gas or air. Gels are determined using the same direct indicating rotational viscometer as is used for viscosity. They are measured by observingthe maximum shear stress value while slowly turning the rotor or by using the 3-rpm setting after being static for someperiod of time. Standard values for gel strength are taken after 10 sec, 10 min and sometimes after 30 min. The changein gel strength values between these time periods also giveIADC Drilling ManualThe basic filtration test is called the low-temperature/low-pressure or API fluid loss test and is performed at ambient temperatures and 100 psi. The more advanced test isthe HTHP filtration test that is performed at a temperaturecloser to the bottomhole temperature and at a 500-psi differential pressure. While there is no standard temperaturefor the HTHP test, temperatures between 275 F and 325 Fare often set as the standard. This, of course, is dependenton the area and operator. The HTHP test should preferablybe run at the actual bottomhole temperatures and differential pressures existing in the wellbore, if possible.Filtration rate and filter cake thickness are both monitoredand reported properties. High fluid loss and thick filter cakessignificantly increase the possibility of having differentiallystuck pipe. A desirable filter cake is one that has ultralowpermeability and is thin, tough, compressible and slick (lubricious). These desirable properties cannot be determinedfrom the fluid loss values alone and many low fluid loss drilling fluids do not have a good quality filter cake. A desirablefilter cake is achieved by minimizing the drill solids content(colloidal-sized solids) of the drilling fluid and maintainingthe proper concentration of filtration control additives. Formost WBMs, the best quality filter cake is achieved by usingan adequate quantity of high-quality bentonite.There are many factors affecting filtration control including:thermal stability of the system; concentration, size, and typeof solids; the type and concentration of filtration control additives being used; and the presence of any contaminants inthe mud. Filtration control comes with increased cost. Localexperience and the frequency of stuck pipe should be usedto establish the target values for fluid loss and filter cake forthe formation and hole interval.Copyright 2014
DRILLING FLUIDSSand contentSand content refers to the volume percent of whole mud thatare “sand sized” particles, meaning they are larger than 74microns and do not pass through a 200 mesh screen. Thesemay be actual quartz sand or may be the coarse-sized barite particles, sized bridging solids, LCM, drilled solids or anyother particles larger than 74 microns. Sand content is measured using a sand content graduated glass tube, funnel and200 mesh sieve. It is monitored to gauge the effectivenessof solids control equipment, the shale shaker screen condition and the potential for increased abrasion to mud pumpsand other equipment in the circulating system including drillstring and downhole equipment.Solids, oil and water contentSolids, oil and water content are measured using a distillation report. With this information and other data from thechemical analysis, a complete breakdown of the composition of the drilling fluid can be made, often called a solidsanalysis. This will include oil content, water or brine content,low-gravity solids (mainly drill solids) and high-gravity solids (normally barite). Solids content affects drilling rate, flowproperties, gel strengths and the overall stability of the mud.Often, the frequency of dilution and chemical treatmentsare based on the results from this analysis. Optimum solidscontent and good solids control is essential for overall superior mud performance.Chemical contentChemical tests are carried out on the whole mud and filtrateto monitor specifications and to identify contamination. Depending on the type of drilling fluid being used, these testsmay include: pH, various measures of alkalinity (PM, PF, andMF for WBM and POM for NAF), lime content, chloride (orsalt), calcium (or total hardness), carbonate/bicarbonate,sulfate, methylene blue test (MBT), H2S, electrical stability,water activity and others. A description of these chemicaltests is outside the scope of this document, although the significance of some of these tests is shown in the section entitled System Maintenance and Contamination Treatments.Importance of the drilling fluidThe performance of the drilling fluid is critical to everyoneinvolved with the operation and to all aspects of the drilling operation. The drilling fluid is the primary means to keepthe well from blowing out and it is responsible for keepingthe hole in good condition such that drilling operations cancontinue to the desired depth. Drilling and completion fluidsare one of the most important parts of the well constructionprocess and ultimately the performance of the fluid will determine the success or failure of the operation. The responsibility of the proper selection and application of the drillingIADC Drilling ManualFL-5fluid is held jointly between the fluids supplier, the drillingcontractor and the operator.General rig personnel involvedThe general rig personnel involved with monitoring, operating and maintaining the drilling fluid are the drilling fluidstechnician (called the mud engineer) and one or more of thedrilling crew. The drilling fluids technician is normally employed by the drilling fluids supplier or may be a consultantworking for the operator or drilling contractor. The mud engineer performs periodic testing of the drilling fluid properties and recommends the treatments to be made. The derrickman is most often the rigsite worker who monitors mudweight and funnel viscosity, adds chemicals and controls thefluid processing equipment. The driller controls flow of thedrilling fluid to the wellbore with the mud pumps. On morecomplicated operations such as deepwater and offshore operations, the drilling fluid responsibilities described abovefor the derrickman may be performed by additional rig crew.This is usually someone assigned to monitor the shale shakers, mud pits and/or mixing operations.Categories of drilling fluidsThere are three broad categories of drilling fluids: Pneumatic fluids, which use compressed air or gas,foam and aerated muds; WBMs, which use water or brine as the base fluids; and NAFs, which use oil or other non-aqueous base fluidscalled OBMs or SBMs.Within each of these three broad categories, there are numerous variations in fluid properties and products that maybe used depen
well being drilled, subsurface pressures and temperatures, logistics, cost and local experience. Drilling fluid perfor-mance is also affected by the drilling equipment being used. The properties of the drilling fluid should be adjusted to the hydraulics available for the drilling operation and the well de-sign.
Fundamentals of drilling operations; the drilling rig equipment and their functions; drilling terminologies; drilling processes; planning of drilling operations; logistics, role and responsibilities of service companies including drilling contractor; the functions of drilling fluid, casing, cementing and components of a drill string; the different
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Lifting Capacity of Drilling Fluids, Pressure losses in the Circulating System and ECD Functions of the Drilling Fluids, Impact of Hydraulic on the Drilling Optimization Parameters affecting on the Drilling Penetrations Drilling Fluid Properties, Functions of Drilling Fluid Mud Properties and Problems related to Mud Properties
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This study investigated microRNA and mRNA expression and protein function associated with DNA repair in human oocytes and embryos. MicroRNAs have been shown to down-regulate and in some cases to stabilise the expression of several genes including repair genes. The first aim of this study was to analyse the differences in the expression of microRNAs and their target mRNAs involved in repair .
