I. Introduction to Drill String Design:Overview II. Drill String Components Drill Collars - Drill Pipe - HWDP III. Drill String Design Bottom Hole Assembly Selection Drill Pipe Selection Buckling and max WOBDrill String Design & BHADesignObjectives At the end of this lecture YOU will be able todescribe: Functions of Drill Pipe , Drill Collars and BHAselection Grades of Drill Pipe and strength properties Thread types and tool-joints Drill collar weight and neutral point Bending Stress Ratios and Stiffness Ratios Margin Of Overpull Basic design calculations based on depth to bedrilled. Functions of stabilizers and roller reamers.Agenda I. Definitions Mechanical properties ofsteel II. Introduction to Drill String Design:Overview III. Drill String Components Drill Collars - Drill Pipe - HWDP IV. Drill String Design Bottom Hole Assembly Design Drill Pipe Selection Buckling and max WOBDefinitions Mechanical Properties of Steel Young ModulusE = Stress divided by Strain = 30,000,000 Stress & StrengthStress = Strength divided by CrossSection Area Strain & stretchStrain = Stretch divided by original lengthDefinitions Mechanical Properties of Steel Elastic LimitLimit of stress beyond which, when the stress isremoved, the steel will have acquired a permanentstretch. Minimum Yield StressThe stress which gives a stretch of 0.5% . Whenthe stress is removed, the steel will have acquired0.2% of permanent deformation. Ultimate Tensile StressThe stress which will break the steelStress and strain curveFunctions of the Drill String The drill string is themechanical linkageconnecting the drill bit onbottom to the rotary drivesystem on the surface. The drill string serves thethree main followingfunctions :1. Transmit and support axialloads - WOB2. Transmit and supporttorsional loads - rpm3. Transmit hydraulics to cleanthe hole and cool the bit.Drill String Components The Drill String includesall tubular equipmentbetween the Kelly Swiveland the bitKellySurface Safety ValvesDrill PipeHeavy Walled Drill PipeDrill CollarJars Shock Subs BumperSubs Junk Baskets AcceleratorsetcThe Kelly/Top Drive Strictly speaking, Kelly/Top drive are notcomponents of the drillstring; however, theyprovide the essentialrequirements for drilling awell:1) Transmit rotation to thedrill string.2) Provide access to thedrilling fluid into the drillstring.3) Support the weight of thestring.The Kelly The Kelly is the rotating link between the rotarytable and the drill string. Transmits rotation and weight-on-bit to the drillbit Supports the weight of the drillstring Connects to the swivel and allow circulation thru pipe. The Kelly comes in lengths ranging from 40 to 54ft with cross sections such as hexagonal (mostcommon), square or triangular. Connected to a Kelly Saver SubKelly Cock The Kelly is usuallyprovided with two safetyvalves, one at the top andone at the bottom, calledKelly cock. The Kelly cock is used toclose the inside of thedrillstring in the event of akick. The upper & lower Kellycocks operate manually. IBOP / DPSV are not run inthe drill string but kepthandy on the rig floorTop Drive The top drive is basically a combined rotarytable and kelly. It is powered by a separate motor and transmitsrotation to the drill string directly without theneed for a rotary table.Advantages over the kelly system:1. Efficient reaming and back reaming.2. Circulating while running in hole or pulling out of holein stands3. The kelly system can only do this in singles; ie 30 ft.Drill Pipe FunctionTo serve as a conduit or conductor for drillingfluid To transmit the rotation from surface tothe bit on bottom ComponentsA pierced, seamless tube of forged steel orextruded Aluminum Tool joints attached toeach end of the seamless tube Tool JointsProvide connections for the drill stringSeparate pieces of metal welded to theseamless tube Thick enough to have pin or boxcut into themDrill Pipe Classification1. Size 2 3/8 to 6 5/8 refers to OD of pipe body2. Length Range 1 18 to 22 ft, Range 2 27 to 30ft,Range 3 38 to 45 ft3. Grade E - 75, X 95, G 105, S 135 the numbersdenote 1000s of psi minimum yield strength4. Weight Depending upon the size of pipe differentweight ranges5. Class API classification for used pipeFor example a drill pipe could be - 5, Range 2, G-105,19.5ppf, NewDrill Pipe Grades There are four grades of pipe commonly usedtoday.Used Drill Pipe Classification Unlike casing and tubing, which are normally runnew, drill pipe is normally used in a worncondition. It therefore has Classes:New: No wear, has never been usedPremium: Remaining wall not less than 80%.Class 2: Remaining wall not less than 70%.Class 3: Remaining wall less than 70%.Other details such as, dents and mashing, slip areamechanical damage, stress induced diametervariations, corrosion cuts and gouges, specified onTable 24 ( Classification of Used Drill Pipe ) of API RP7G.Drillpipe Upsets Where the pipe joins the tooljoint, the pipe wall thickness isincreased or upset. This increased thickness is used to decrease the frequency ofpipe failure at the point where the pipe meets the tool-joint. The drill-pipe can have Internal upsets (IU), ( OD stays the same ) External upsets (EU), ( ID stays the same ) Internal and External Upsets (IEU).Drill Pipe WeightsWhen referring to Drill Pipe Weights, there are four importantones:Plain end Weight Refers to the weight per foot of the pipebody.Nominal Weight - Refers to an obsolete standard. ( Weight ofRange I pipe with connections ) Is used today to refer aclass of Drill pipe.Adjusted Weight Refers to the weight per foot of pipeincluding the upset but excluding the tool joint based on alength of 29.4 ftApproximate Weight The average weight per foot of pipeand tool joints of Range II pipe. This approximate weight isthe number to use in Design calculations.Calculating Approximate WeightsCalculating Approximate WeightsDP Data from Table 7 Spec 7API RP 7G Table 1-3 New Pipe Data Table 4-5 Premium Pipe Data Table 6-7 Class Two Pipe Data Table 8-9 Tool-joint Data Table 10 Make-up Torque Data Table 12 Connection interchangeability Table 24 Classification of used DPTool Joints All API tool joints have a minimum yield strength of 120,000psi regardless of the grade of the drill pipe they are used on(E, X, G, S) API sets tool joint torsional strength at minimum 80% of thetube torsional strength. Make up torque is determined by pin ID or box OD. Themake up torque is 60% of the tool joint torsional capacity.The equation for determining make up can be obtainedfrom the appendix of API RPG7. ( Numeral A.8.2 ). Thisequation is rather complex, so the API developed a series ofcharts to find the recommended make up torque to anyconnection given the tool jt OD of box and ID of pin. Thesecharts can be found in API RP 7G ( Figures 1 to 25 )Make-Up Torque ChartsDrill string Connections The most common thread style in drill pipe is NC The thread has a V-shaped form and is identified by the pitchdiameter, measured at a point 5/8 inches from the shoulder Connection Number is Pitch dia*10 truncated to two digitsIf the pitch diameter is 5.0417 in This is an NC50 connectionMultiply 5.0417 by 10 50.417Choose rst two digits 50Hence NC 50NC Drill string Connections There are 17 NCs in use : NC-10 (1 1/16)through NC-77 (7 3/4) Typical sizes: NC 50 for tool joints with 6 1/2 ODfor 5 pipe and NC 38 for 4 3/4 tool joints and 31/2 pipe. Seal is provided by shoulder not threads. Aclearance exists between the crest of one threadand the root of the mating thread Use of Lead based dope vs Copper based dopefor DCs. Not for sealing but for lubrication, tohelp make-up and prevent gallingDrill Collars Functions To put weight on bit (WOB) To keep the drill string from buckling Types Typically 4 to 9 OD Most commonly in lengths of 30-31 feet Square collars where the holes tend to becrooked Spiral collars where there is chance ofgetting stuck (differentially, etc..) Collars with elevator and slip recessesMore functions of Drill Collars1. Protect the Drill string from Bending and Torsion2. Help to control direction and inclination of wells3. Drill straighter holes or vertical holes4. Provide Pendulum effect at low WOB5. Reduce dog legs, key seats and ledges6. Improve the probabilities of getting casing in thehole.7. Increase bit performance8. Reduce rough drilling, sticking and jumping9. As a tool in fishing, testing, completingMore Types of Drill CollarsIn areas where differentialsticking is a possibility spiraldrill collars and spiral HWDPshould be used in order tominimize contact area withthe formation.Slick Drill CollarSpiral Drill CollarDrill Collars StrappingAPI Drill Collar SizesDrill Collar ConnectionsCharacteristics DC connections are rotary shouldered connections andcan mate the various DP connections The shoulder provide the only positive seal againstfluid leakage The lubricant is Copper based dope The connection is the weakest part of the entire BHA The DC connections go through cycles of tension-compression and are subject to bending stresses Improper M/U torque, improper or insufficientlubricant, galling can all lead to connection failureDrill Collar Connections Stress Relief Features Stresses in DC connections are concentrated at thebase of the pin and in the bottom of the box(stronger) DP body bends easily and takes up the majority of theapplied bending stress, DP connections are thereforesubjected to less bending than the DP body. DCs and other BHA components are however muchstiffer than the DPs and much of the bending stressesare transferred to the connections. These bending stresses can cause fatigue failure at theconnections Stress Relief Groove / Bore BackStress Relief Pin FeatureStress Relief Pin & Box FeaturesDrill Collar Connections The stress relief groove is to mitigate the fatigue crackswhere the face and threads would have otherwise joined The Bore Back serves the same purpose at the bottom ofthe box Stress relief features should be specified on all BHAconnections NC-38 or larger. Pin stress relief grooves are not recommended onconnections smaller than NC-38 because they may weakenthe connections tensile and torsional strength. Bore Back boxes could be used on smaller connections. The Low-Torque face is to increase the compressive stressat normal M/U torque above that of a regular faceLo- Torq FeatureThe low torque featureconsists in removing partof the shoulder area ofthe pin and box.This allows for lowermake up torquemaintaining adequateshoulder loading.It is a common feature inlarge OD connections.Torsion limits for DCTorque is rarely limited by the DC connectionbecause rotary torque is usually higher in the DP atsurface and lower in the DC at deeper depths. If DC make-up torque >Dp make-up torque youhave no routine problems. BH Torque at any point should not exceed 80% ofmakeup torque for the connections in the hole toavoid over tightening connections which can leadto damage of seals.Torque Limits for DC API recommendedmakeup torque forconnections is apercentage of the totaltorsional yield of theconnectionMake Up Torque Tables for DCsHeavy Weight Drill Pipe Design Heavier wall and longer tool joints Center wall pad Also available in spiral design Function Used in transition zones between DC and DPThis prevents the DP from buckling Can be used in compression (?) Used for directional drilling Used in place of DC sometimes (?) To keep Drill Pipe in tension Not to be used for Weight on Bit in normalcircumstancesHeavy Weight Drill PipeCharacteristics Has the same OD as a standard drill pipe butwith much reduced inside diameter (usually3 for 5 DP) and has an integral wear padupset in the middle. It is used between standard Drill Pipe andDrill Collars to provide a smooth transitionbetween the different sections of thedrillstring components. Tool-Joint and Rotary shoulderedconnection just like DP HWDP, although stiffer than DP, can alsobuckleHeavy Weight Drill PipeHWDP in Compression? HWDP can be run both in tension and in compressionBUT!!! Manufacturers recommend not to run HWDP incompression in hole sizes larger than 12 Experience shows that they should not be run incompression in Vertical Holes If run in compression, rules of thumb are: TJOD + 6 > OH diameter 2 x TJOD > OH diameterStabilizersStabilizers Reasons for Using Stabilizers:1. They are used as a fundamental method of controllingthe directional behavior of most BHAs.2. Help concentrate the weight of the BHA on the bit.3. Minimize bending and vibrations which cause tooljoint wear and damage to BHA components such asMWDs.4. Reduce drilling torque by preventing collar contactwith the side of the hole and by keeping themconcentric in the hole. (FG!!)5. Help preventing differential sticking and key seating.More functions of Stabilisers- Drill straighter or vertical holes with packedassembly at suitable WOB- Improve the probabilities of getting casing inthe hole.- Increase bit stability and so bit performanceRoller Reamers I. Introduction to Drill String Design:Overview II. Drill String Components Drill Collars - Drill Pipe - HWDP III. Drill String Design Bottom Hole Assembly Selection Drill Pipe Selection Buckling and max WOBDrill Collar Selection Principles Drill Collar selection is governed by two major factors:Weight and Stiffness --- Size! Usually the largest OD collar that can be safely run isthe best selection More weight available for WOB Greatest stiffness to resist buckling and smooth directionaltendencies Cyclical movement is restricted due to tighter Clearances Usually Shortest BHA possible to Reduce handling time at surface Minimize # of Connections in the hole Minimize total DC in contact with the wall for differential stickingexposureWeight BHA Weight must be sufficient for the plannedWOB BHA Weight must be sufficient to account forBuoyancy BHA Weight must be sufficient to account forhole inclination BHA Weight must be sufficient so that theneutral point of axial loads is within the BHA with a safety factor of 15%BHA Design DF for excess BHA=1.15 Neutral Point (NP) totension should be indrill collarsDrill Collar Weight & Neutral PointBHA Design Procedure For Selecting Drill Collars: 1. Determine the buoyancy factor for the mudweight in use using the formula below: where BF =Buoyancy Factor, dimensionless MW =Mud weight in use, ppg 65.5 =Weight of a gallon of steel, ppgBHA Design 2. Calculate the required collar length to achieve thedesired weight on bit:DC Length = 1.15* WOB / (BF*Wdc) where: WOB=Desired weight on bit , lbf (x 1000) BF =Buoyancy Factor, dimensionless W dc =Drill collar weight in air, lb/ft 1.15 =15% safety factor. The 15% safety factor ensures that the neutral pointremains within the collars when unforeseen forces(bounce, minor deviation and hole friction) are present.BHA Design 3. For directional wells:DC Length = DC Length Vertical / Cos I where: I= Well inclinationNote: that for horizontal wells drill collarsare not normally used and BHA selection isbased entirely on the prevention of bucklingStiffness The BHA must have sufficient Stiffness tostabilize the BHA, optimize ROP and preventthe formation of Key Seats, ledges and doglegs The larger the DC, the stiffer the BHA Stiffness Coefficient := Moment of Inertia x Youngs Modulus of Elasticity= (OD4 ID4) / 64 x 30.000.000Bending Strength Ratio BSR is the relative stiffness of the box to the pin of a givenconnection. Describes the Balance between two members of a connection andhow they are likely to behave in a rotational cyclical environmentWhere:Zbox = box section modulusZpin = pin section modulusD = Outside diameter of pin and boxb = thread root diameter of boxthreads at end of pin.R = Thread root diameter of pinthreads of an inch from shoulderof pin.d= inside diameter or bore.Section Modulus for ConnectionsBSR in DC Connections A Connection is said to bebalanced if the BSR is 2.5 When BSR is higher tend tosee pin failures When BSR is lower tend tosee more box failures However, field experiencehas shown that: 8 Dc having BSRs of 2.5usually fail in the box 4-3/4 DC having BSR aslow as 1.8 very rarely fail inthe box.BSR in ConnectionsAdditional BSR Guidelines High RPM, Soft Formation Small DC (8 in in12.25 hole or 6 in in 8.25 hole) 2.25-2.75 Low RPM Hard Formations Large DC (10 in in12-1/4 hole 2.5-3.2 (3.4 if using lo-torqconnection) Abrasive formations 2.5-3.0 New DCs 2.75 more wear resistantAPI BSR Charts Fortunately for you APIhave worked theproblem!!! Pages 39-44 of Spec 7Glist the BSR ofConnections by OD andID of the collarT.H.Hill BSR TablesStiffness Ratio The SR measures the stiffness of a connection in a transition between 2types of pipe Based on field experience, in atransition from one collar or pipe toanother the SR should not exceed 5.5 for routine drilling 3.5 for severe or rough drillingNote: Stiffness ratios are calculated using tube ODs & IDs,not connections.BHA Design Process Design the Collars Max OD DC which can be handled, fished and drilledwith Excess BHA wt WOB Buoyancy Safety factor Connection Selection BSR SR Torque capability Stabilization and other directional requirementsExercise DP-05On a land rig we find the following collars:9 OD x 3 ID 6 5/8 FH connection8 OD x 3 ID 6 5/8 REG connection6 OD x 2 ID NC46 connectionGiven that we will drill a vertical 12 hole, with 9.5 ppg mud and 65000 pounds in arelatively hard formations, what API collar would you recommend?What would your recommendation on BSR be for the connection chosen?Check your recommended DCs with your recommended BSR.What would be the SR between the DC and 5 DP be?Is it acceptable?If not what would you do?What would be your final BHA? Length? Buoyed Weight? I. Introduction to Drill String Design:Overview II. Drill String Components Drill Collars - Drill Pipe - HWDP III. Drill String Design Bottom Hole Assembly Selection Drill Pipe Selection Buckling and max WOBDrill Pipe Selection Principles Drill Pipe selection is governed by two major factors:Size+Weight and Strength Usually the Drill Pipe with largest OD and ID is preferred Less pressure loss in the string More hydraulics available at the bit The Drill Pipe selection must address the following: Drill Pipe must allow to drill to TD Drill Pipe must support all weight below it (BHA+DP) Drill Pipe must provide Over pull capacity Drill Pipe must withstand slip crushing force Drill Pipe must resist burst and collapse loads Drill Pipe might have to work in H2S environmentAxial Loads Tension Design The greatest tension(working load Pw) onthe drill string occurs atthe top joint at themaximum drilled depthDrill Pipe Selection Parameters Tension Design Total weight, Tsurf, carriedby the top joint of drill pipewhen the drill bit is just offbottom Ldp = length of Drill Pipe Wdp = weight of Drill Pipeper unit length Ldc = weight of Drill Collars Wdc = weight of Drill Collarsper unit lengthDrill Pipe Selection Parameters Tension Design The drill string is not designed according to the minimum yield strength!!! If Drill Pipereaches yield: Drill Pipe can have permanent deformation. To prevent deformation damage to drill pipe, API recommends the use of maximumallowable design load ( Pa) Tmax = 0.9 x Tyield .(2) Tmax = Max. allowable design load in tension , lb Tyield = theoretical yield strength from API tables , lb 0.9 = a constant relating proportional limit to yield strength IPM Defines a tension Design factor of 1.1 be applied todesign loads. These accomplish the same thing. Do not double dip!Margin of Over Pull Margin of over pull is nominally 50Klb-100Klb,or in the limit of the difference between themaximum allowable load less the actual load Choice of MOP should consider Overall drilling conditions Hole drag Likelihood of getting stuck Slip crushing Dynamic loadingDrill Pipe Selection Parameters Margin of Overpull1. Determine max design load (Tmax) : (maximum loadthat drillstring should be designed for)Tmax = 0.9 x Minimum Yield Strength lbClass of pipe must be consideredDrill Pipe Selection Parameters Margin of Overpull 2. Calculate total load at surface using 3. Margin Of Overpull : Minimum tensionforce above expected working load to accountfor any drag or stuck pipe.Drill Pipe Selection Parameters Margin of Overpull 4. The maximum length of Drill Pipe that canbe used is obtained by combining equations 1and 3 and solving for the length of Drill PipeTHINK OF STUCK PIPE!!! When the Drill String is stuck, (and it mostcertainly is if there is Overpull !) the buoyancyis lost! When the Drill String is stuck, (and it mostcertainly is if there is Overpull !) the buoyancyis lost!Slip Crushing Force Slips because of the taper try to crush the DrillPipe. This hoop stress is resisted by the tube,and this increases the overall stress in thesteelSlip Crushing Force Generally expressed as a FactorDrill Pipe Selection Parameters You can only drill as far as you can set pipe inthe slips. Different than over pull, this is based onworking loadsMixed String Design Step 1 If we use different drill pipe, the weaker pipe goes onbottom and stronger on top Apply equation to bottom drill pipe first Step 2 Drill collars and bottomdrillpipe act as the weightcarried by top sectioneffectively the drill collar Apply the equation for top drill pipe lastOther Loads Collapse under Tension Burst Other loads not covered here Shock Loads Bending Loads Buckling Loads Torsion Torsion with Simultaneous TensionBiaxial Collapse The DP will collapse if:External Pressure Load > Collapse pressure rating A Design factor of 1.15 is used:External Pressure Load < Collapse rating / 1.15 When the string is in tension, the Collapse rating isfurther de-rated:Biaxial Collapse Collapse load is worst when For dry test workwhere pipe is run in empty Note the use of the Average Yield Point notminimumBiaxial Collapse For nominal Collapse Use D/t and correct formula Spec 7G Appendix A 3 Use the results found in Table 3-6 RP-7G For OD and ID, use Table 1 RP-7G For Avg Yp Use Table in section 12.8 RP 7GBurst Barlows formula applies Results are found in Spec 7G Table 3,5 & 7 Burst will occur if internal pressure load >burst ratingDrill String Design Process-2After the BHA Design is performed: Slip Crushing forces on DP Overpull tensile design at surface Lengths of DP Sections Burst Design Check Collapse under tension Design checkDrill String Design Factors Tension DFt Governs Max allowable tensionon the systemDFt is 1.1 Margin of OverPull MOP Desired excesstensile capacity over an above the hangingweight of the string at Surface. MOP 50-100K Excess BHA Wt Dfbha Amount of BHA interms of Wt in excess of that used to drill toassure all Compressive and torsional loads arekept in the Collars, Dfbha is 1.15Drill String Design Factors Torsion No Design Factor Required. Tool Joints aremade up to 60% of Torsional Capacity, and Tool jointsare designed to 80% of the tube Torsion Capacity. Thusif the design limits to tool joint make-up there is anadequate design factor built into the system Collapse DFc Tube is de-rated to account for BiaxialTensile reduction and a design factor of is used SLB DFcis 1.1-1.15 Burst DFb Simple burst is used with no allowance foraxial effects DFB is 1.0 Buckling DFB In Highly deviated wells it is possible touse DP in compression, provided it is not buckled.Buoyancy Buoyancy is the weight of the displaced fluid Buoyancy is usually accounted for via BF Buoyancy is creating a hydrostatic effect: thePressure-Area Force The forces acting on a drillstring are the self-weight and the hydrostatic pressure of the drillingfluid Buoyancy is creating a force acting at the bottomof the drill string and placing the lower portion ofthe drill string in compression and reducing thehook load by HP x CSABending & Buckling A tube subjected to a load willbend Bent is a condition in which thebending increases proportionallywith load When a little increase in load willresult in large displacements, thetube is said to be buckling The tube may not necessarily beyielded as buckling does notnecessarily occurs plastically The load which produces bucklingis called the Critical Buckling LoadNeutral Points Neutral Point of Tension & Compression: The point within a tube where the sum of theaxial forces are equal to zero Neutral Point of Bending: The point within a tube where the sum ofmoments are equal to zero The point within a tube where the average ofthe radial and tangential stress in the tubeequals the axial stress The point within a tube where the buoyedweight of the tube hanging below that pointis equal to an applied force at its bottom endForces in the Drill StringNeutral Point of Bending occurs where the effective hydrostatic forceequals the compressive force in the drillstring.BucklingNeutral point of bending is H = WOB / buoyed weight per foot ofstring In vertical wells, buckling will occur only below the neutralpoint of bending, hence the necessity to keep the buoyedweight of the BHA exceeding the WOB. In deviated wells, buckling will not only occur below theneutral point of bending but also above the neutral point ofbending when the compressive force in the drillstring exceedsa critical load.Drill string Design Now you should be able to describe: Functions of Drill Pipe , Drill Collars and BHA selection Grades of Drill Pipe and strength properties Thread types and tool joints Drill collar weight and neutral point Bending Stress Ratios and Stiffness Ratios Margin of overpull Slip crushing force Basic design calculations based on depth to be drilled. Functions of stabilizers and roller reamers Critical Buckling force and Neutral Point of BendingReferences API RP 7G Drill Stem Design and Op Limits API SPEC 7 Specifications for Rotary DrillingElements API SPEC 5D Specifications for Drill Pipe SLB Drill String Design manual TH Hill DS-1 Drill String Design