Introduction to Drillstring

DRILL STRINGIntroduction to Drill stringDrill string is defined as the drill pipe, with attached tool joints, that is used to transmit the fluid and rotational power from Kelly to the drill collars and bit.The Drill string primarily consists of Kelly, Drill pipe and the bottom-hole assembly (BHA). The Drill pipe section contains conventional Drill pipes, heavy weight Drill pipes. The BHA contains the following itemsDrill collarsStabilizersJarsReamersBit subBit

The drill string serves the following purpose:Provides a fluid conduit from the Rig to Bit

Impart rotary motion to the drill Bit

Allow weight to be set on the Bit

Lower and raised the Bit in the Well

Provides some stability to the Bottom - hole assembly to minimize vibration

Permits through-pipe formation evaluation when logging tools cannot be run in the open hole.Drill CollarDrill collars are heavy, thick walled steel pipes with threaded connections cut on both ends.

Mechanical PropertiesSpecified By : Example 8 x 3 , 6-5/8 Reg, Spiral

StandardSquareSpiral6It provides weight to the bit for drilling.It keeps the drill pipe in tension.It maintains weight to keep the drill string from being subjected to buckling.It helps provide the pendulum effect. It stabilizes the bit. Spiral drill collars are used to reduce differential pressure sticking in the hole. FUNCTION OF DRILL COLLARSDrill Collar

SPECIAL / OPTIONAL FEATURESStress relief features

Cold working of threads roots and stress relief groove

Low torque faceDrill CollarSPECIAL / OPTIONAL FEATURESGall resistance coatingElevator and slip recessesSpiral

SELECTION OF DRILL COLLARSizeWeightTapered string

Drill CollarThread protectors should be used and screwed fully on both pin and box ends when handling drill collars. Use cast steel protectors on pin and box end of drill collars while picking up from catwalk to derrick floor. Check that slips and elevator for handling the drill collars are of proper size.A safety clamp should be invariably used while making up or breaking drill collars. HANDLING OF DRILL COLLARSDrill CollarBefore make up clean the threads thoroughly, check for any burrs or damage and lubricate properly.Always use a good thread compound .Thread compound should contain 60% finely powdered metallic lead or 40-60%finely powdered zinc. If lift subs are used, its pin threads should be cleaned, checked and lubricated on each trip.A new joint should be carefully lubricated, made up, break out, re-lubricated and made up again on initial make up.

HANDLING OF DRILL COLLARSDrill CollarAlways use chain tong for initial tightening of drill collars.A torque gauge should be used on tong line to measure the make up torque.Always make up drill collars to appropriate recommended torque.On each trip rotate top two stands of drill collars to work in drill collar string below so that null point may not remain on the same joint.HANDLING OF DRILL COLLARSDrill CollarMake close visual inspection of every non-working joint while pulling out. Do not use rotary for making up or breaking out of drill collar connection.Do not over torque or under torque a drill collar connection during make up. Insufficient torque or too much torque both may cause problems.Do not jerk the line for applying pull for make up; give a long steady pull to the tong line.

HANDLING OF DRILL COLLARSDrill Collar14A Heavy Weight Drill Pipe (HWDP) looks like a normal drill pipe except for an upset centered along the tube

Heavy Weight Drill Pipe15Its wall thickness is up to 3 times that of a similar-sized normal drill pipe to add additional weight to the bit.

APPLICATIONS OF HWDPActs as an effective weight-on-bit member in extended-reach, horizontal, and conventional directional wellImproves directional control by reducing torque and drag reduce the risk of differential stickingActs as an active weight on bit member Reduces the risk of drillpipe fatigue failure Remedial operationsJar placementHydraulic improvementDrilling StablizerIt is composed of a hollow cylindrical body and stabilizing blades, both made of high-strength steel

It mechanically stabilizes the BHA in the borehole in order to avoid unintentional sidetracking, vibrations, and ensure the quality of the hole being drilled

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Drill pipe gradeLongest section of the drill string. Steel tube to transmit torque and hydraulic horsepower at the bit

Sizes (API): 2-3/8" to 6-5/8". Range Length (ft)

1 18-22 2 27-30 3 38-45

Classes of drill pipeClassColour code Identification Class I (New) 1 white band No notchesPremium (80% wall thickness) 2 white bands 1 Notch Class II (65% wall thickness, wear on one side) 1 yellow band2 NotchesClass III (55% wall thickness, wear on one side)1 Orange band 3 Notches

Common grades of drill pipe and their strengthGRADEMINIMUM YIELDpsiMAXIMUM YIELDpsiTENSILE STRENGTHpsiE7500010500085000X95000125000105000G105000135000115000S135000165000145000Nomenclature of drill pipeDrill pipe is designated by outer diametere.g..5

Drill pipe is designated by its nominal weighte.g..19.5ppf

General connection of 5 drill pipe mostly used. NC-505XH4 IFIdentification marking

KellyHeavy hexagonal or square steel pipeNormally used 37-54 in length and 5 1/4 size and 3 IDBox End- Left hand threads (6 5/8 REG), Pin End- Right hand threads(4 IF)Better hook load and tensile strength in hexagonal typeTransmits weight and torque through kelly bushingUsed along with Kelly Saver sub and pressure safety valve- upper kelly cock and lower kelly cockRegular lubrication of drive surfacesRegular inspection of drive bushing and kelly corners for wearCheck for crook and bendTransport with scabbard , no weldingDrill String FailureStressTension- Overpull exceeding tensile strength Cyclic stress/Fatigue - Compression and tension simultaneously Torque- Poor hole condition exerts twisting force on joints

Wash out Improper metal to metal sealing and uneven tightening

Twist off Excess torque, Tong & slip Marks, excessive unequal rotational moment of combinational string, Wear and thinning of pipe body, ageing , abrasive formation624Slip crushing Non uniform griping leading to crushing

CorrosionOxygen- Rusting and pitting leading to washouts and twist offCarbon Dioxide- Carbonic acid formation causing corrosionDissolved Salts- Increased conduction increases corrosion Hydrogen SulphideOrganic Acids- Lowers pH and removes protective layerTHANK U