Drilling Engineerning(英国钻井工程研究.pdf

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1、C O N T E N T S1.INTRODUCTION2.DRILLPIPE2.1Drillpipe Stress and Failure2.3Drillpipe Inspection3.TOOL JOINTS4.HEAVY WALL DRILLPIPE(HWDP)5.DRILL COLLARS5.1 Special Types of Collar6.OTHER DRILLSTRING COMPONENTS6.1.Stabilisers6.2Roller Reamer.6.3Shock sub (vibration dampener)6.4.Subs(substitutes)6.5.Dri

2、lling Jars7.DRILL STRING DESIGN7.1.Design of a Stabilised String7.2Bending Moments in String Design7.3Length of Drillcollars7.4Drill Pipe Selection7.4Design Procedure3 3The Drillstring2LEARNING OBJECTIVESHaving worked through this chapter the student will be able to:General:Describe the basic compon

3、ents and the function of each component in thedrillstring.Drillpipe:Describe the components parts of a joint of drillpipe.Describe the way in which drillpipe is classified in terms of size,weight and grade Describe the stresses and wear mechanisms to which the drillstring is exposed.Describe the tec

4、hniques used to inspect drillpipe and the worn pipe classificationsystem.Tooljoints:Describe a tooljoint and identify the major characteristics of a tooljoint HWDP:Describe HWDP Describe the reasons for running HWDP.Drillcollars:Describe the reasons for using Drillcollars.Describe the loads to which

5、 Drillcollars are subjected.Describe the function of:conventional;Spiral;Square and Monel Drillcollars.BHA Components:Describe the function of:Stabilisers;Roller Reamers;Shock Subs;Subs;andDrilling Jars.Describe the ways in which the above are configured in the BHA.Drillstring Design:Calculate the d

6、ry weight and buoyant weight of the drillstring.Calculate the length of drillcollar required for a drilling operation.Calculate the Section Modulus of component parts of the drillstring.Institute of Petroleum Engineering,Heriot-Watt University33 3The Drillstring1.INTRODUCTIONThe term drillstring is

7、used to describe the tubulars and accessories on which thedrillbit is run to the bottom of the borehole.The drillstring consists of drillpipe,drillcollars,the kelly and various other pieces of equipment such as stabilisers andreamers,which are included in the drillstring just above the drillbit (Fig

8、ure 1).Allof these components will be described in detail below.The drillcollars and the otherequipment which is made up just above the bit are collectively called the Bottom HoleAssembly(BHA).The dimensions of a typical 10,000 ft drillstring would be:ComponentOutside Diameter(in.)Length(ft)Drillbit

9、12 1/4”Drillcollars9 1/2”600Drillpipe5”9400The functions of the drillstring are:to suspend the bit to transmit rotary torque from the kelly to the bit to provide a conduit for circulating drilling fluid to the bitIt must be remembered that in deep wells the drillstring may be 5-6 miles long.KellyDri

10、ll PipeBottom Hole AssemblyCollars,Reamers,Stabilisers,JarsBitDrill StringFigure 1Components of thedrillstring42.DRILL PIPEDrillpipe is the major component of the drillstring It generally constitutes 90-95%of the entire length of the drillstring.Drillpipe is a seamless pipe with threadedconnections,

11、known as tooljoints(Figure 2).At one end of the pipe there is the box,which has the female end of the connection.At the other end of each length ofdrillpipe is the male end of the connection known as the pin.The wall thickness andtherefore the outer diameter of the tooljoint must be larger than the

12、wall thickness ofthe main body of the drillpipe in order to accommodate the threads of the connection.Hence the tooljoints are clearly visible in the drillstring.Tooljoints will be discussedin greater depth below.PinBoxTong areaBox counterboreMake and breakshoulderTong areaHardfacing(optional)Tapere

13、d elevatorshoulderEach length of drillpipe is known as a joint or a single.The standard dimensions fordrillpipe are specified by the American Petroleum Institute.Singles are available inthree API length“ranges”(see Table 1)with range 2 being the most common.Theexact length of each single must be mea

14、sured on the rigsite since the process used tomanufacture the drillpipe means that singles are not of uniform length.Since the onlyway in which the driller knows the depth of the drillbit is by knowing the length of thedrillstring the length of each length of drillpipe(and all other drillstring comp

15、onents)made up into the drillstring must be measured and recorded on a drillpipe tally.Thedrillpipe is also manufactured in a variety of outside diameters,and weights(Table2)which assuming a specific gravity for steel of 490 lb/cuft,is a reflection of the wallthickness of the drillpipe.The drillpipe

16、 is also manufactured in a variety of materialgrades(Table 3).The specification for a particular string of drillpipe could thereforeappear as:5”19.5 lb/ft Grade S Range 2Figure 2Tooljoint Institute of Petroleum Engineering,Heriot-Watt University53 3The Drillstring API RangeLength(ft)118-22227-30338-

17、45)Size(OD)(inches)23/827/831/231/255551/251/251/2 Weight (lb/ft)6.6510.409.5013.3015.5016.2519.5025.6021.9024.70 ID(inches1.8152.1512.9922.7644.6024.4084.2764.0004.7764.670APIGradeMinimum YieldStress(psi)Minimum TensileStress(psi)Yield Stress ratioTensile StressDEXGS55,00075,00095,000105,000135,000

18、95,000100,000105,000115,000145,0000.580.750.700.910.93All of these specifications will influence the burst,collapse,tensile and torsionalstrength of the drillpipe and this allows the drilling engineer to select the pipe whichwill meet the specific requirements of the particular drilling operation.Ta

19、ble 1Drillpipe LengthsTable 2Dimensions of DrillpipeTable 3Drillpipe Material Grades6Care must be taken when using the specifications given in Table 2 since although theseare these are the normally quoted specifications for drillpipe,the weights anddimensions are nominal values and do not reflect th

20、e true weight of the drillpipe orthe minimum internal diameter of the pipe.The weight per foot of the pipe is a function of the connection type and grade of thedrillpipe and the weight per foot that should be used when calculating the true weightof a string of pipe is given in Table 13.The weight of

21、 the pipe calculated in the manner described above will reflect the weightof the drillpipe when suspended in air(Weight in air).When the pipe is suspendedin the borehole it will be immersed in drilling fluid of a particular density and willtherefore be subjected to a buoyant force.This buoyant force

22、 will be directlyproportional to the density of the drilling fluid.The weight of drillpipe whensuspended in a fluid(Wet Weight)can be calculated from the following:Buoyant Weight(Wet Weight)of Drillpipe=Weight of pipe in Air x Buoyancy FactorThe buoyancy factor for a particular density of drilling f

23、luid can be found from Table15.Ex.1 Dimensions and weight of drillpipea.What is the weight in air of a joint(30ft)of 5”19.5 lb/ft Grade G drillpipe with 41/2”IF connections:?b.What is the wet weight of this joint of drillpipe when immersed in a drilling fluidwith a density of 12 ppg?2.1 Drillpipe St

24、ress and FailureIt is not uncommon for the drillpipe to undergo tensile failure(twistoff)whilst drilling.When this happens,drilling has to stop and the drillstring must be pulled from theborehole.The part of the string below the point of failure will of course be left in theborehole when the upper p

25、art of the string is retrieved.The retrieval of the lower partof the string is a very difficult and time consuming operation.The failure of a drillstring can be due to excessively high stresses and/or corrosion.Drillpipe is exposed to the following stresses:Tension-the weight of the suspended drills

26、tring exposes each joint of drillpipe toseveral thousand pounds of tensile load.Extra tension may be exerted due to overpull(drag caused by difficult hole conditions e.g.dog legs)when pulling out of hole.Institute of Petroleum Engineering,Heriot-Watt University73 3The Drillstring Torque-during drill

27、ing,rotation is transmitted down the string.Again,poor holeconditions can increase the amount of torque or twisting force on each joint.Cyclic Stress Fatigue-in deviated holes,the wall of the pipe is exposed tocompressive and tensile forces at points of bending in the hole.As the string is rotatedea

28、ch joint sustains a cycle of compressive and tensile forces(Figure 3).This can resultin fatigue in the wall of the pipe.Stresses are also induced by vibration,abrasive friction and bouncing the bit offbottom.CompressionTensionClosed DefectOpen DefectCompressionTensionCorrosion of a drillstring in a

29、water based mud is primarily due to dissolved gases,dissolved salts and acids in the wellbore,such as:Oxygen-present in all drilling fluids.It causes rusting and pitting.This may leadto washouts(small eroded hole in the pipe)and twist offs(parting of the drillstring).Oxygen can be removed from drill

30、ing fluids using a scavenger,such as sodiumsulphate.Even small concentrations of oxygen(1 ppm)can be very damaging.Carbon dioxide-can be introduced into the wellbore with the drilling fluid(makeupwater,organic drilling fluid additives or bacterial action on additives in the drillingfluid)or from the

31、 formation.It forms carbonic acid which corrodes steel.Dissolved Salts-increase the rates of corrosion due to the increased conductivitydue to the presence of dissolved salts.Dissolved salts in drilling fluids may come fromthe makeup water,formation fluid inflow,drilled formations,or drilling fluida

32、dditives.Figure 3Cyclic loading8 Hydrogen sulphide-may be present in the formations being drilled.It causes“hydrogen embrittlement”or“sulphide stress cracking”.Hydrogen is absorbed onto the surface of a steel in the presence of sulphide.If the local concentration ofhydrogen is sufficient,cracks can

33、be formed,leading rapidly to a brittle failure.Hydrogen embrittlement in itself does not cause a failure,but will accelerate failureof the pipe if it is already under stress or notched.Only small amounts of H2S needbe present to induce fatigue(13 ppm).Special scavengers can be circulated in themud t

34、o remove the H2S(e.g.filming amines).Organic acids-These produce corrosion by lowering the pH,remove protectivefilms and provide hydrogen to increase hydrogen embrittlement.Although added chemicals can build up a layer of protection against corrosion,thefatigue stresses easily break this layer down,

35、allowing corrosion to re-occur.It is thisinteraction of fatigue and corrosion which is difficult to combat.2.3 Drillpipe InspectionWhen manufactured,new pipe will be subjected by the manufacturer to a series ofmechanical,tensile and hydrostatic pressure tests in accordance with API Specifica-tion 5A

36、 and 5AX.This will ensure that the pipe can withstand specified loads.A jointof drillpipe will however be used in a number of wells.When it has been used it willundergo some degree of wear and will not be able to withstand the same loads as whenit is new.It is extremely difficult to predict the serv

37、ice life of a drillstring since no two boreholesexperience the same drilling conditions.However,as a rough guide,the length of holedrilled by a piece of drillpipe,when part of a drillstring will be:soft drilling areas:220000-250000 fthard or deviated drilling areas:180000-210000 ftThis means that a

38、piece of drillpipe may be used on up to 25 wells which are 10,000ft deepDuring the working life of the drillpipe it will therefore be necessary to determine thedegree of damage or wear that the pipe has already been subjected to and therefore itscapacity to withstand the loads to which it will be ex

39、posed in the future.Various non-destructive tests are periodically applied to used drillpipe,to assess the wear andtherefore strength of the pipe,and to inspect for any defects,e.g.cracks.The strengthof the pipe is gauged on the basis of the remaining wall thickness,or if worneccentrically,the avera

40、ge minimum wall thickness of the pipe.The methods used toinspect drillpipe are summarised in Table 4.Following inspection,the drillpipe is classified in terms of the degree of wear ordamage which is measured on the pipe.The criteria used for classifying the drillpipeon the basis of the degree of wea

41、r or damage is shown in Table 6.The Grade 1 orPremium drillpipe classification applies to new pipe,or used pipe with at least 80%of the original wall thickness still remaining.A classification of Grade 2 and aboveindicates that the pipe has sustained significant wear or damage and that its strength

42、Institute of Petroleum Engineering,Heriot-Watt University93 3The Drillstringhas been significantly reduced.The strength of some typical drillpipe sizes whennew,and when worn,is shown in tables 11 and 12.Drillpipe will generally be inspected and classified before a new drilling contract isstarted.The

43、 operating company would require that the drilling contractor provideproof of inspection and classification of the drillstring as part of the drilling contract.In general,only new or premium drillpipe would be acceptable for drilling in the NorthSea.METHODDESCRIPTIONCOMMENTSOpticalVisual inspectionS

44、low and can be in error if pipe internals notproperly cleanedMagnetic ParticleMagnetise pipe endsand observe attraction of ferrous particles to cracks detected by UV lightSimple and efficient.No information on wall thicknessUltra SonicPulse echo techniqueNo information oncracks.Very effective on det

45、ermination of wall thicknessGamma RayMagnetic InductionDetect disturbances inmagnetic flux field by pits,notches and cracksNo information on wall thickness.Internal cracks have to be verified using magnetic particle technique3.TOOL JOINTSTooljoints are located at each end of a length of drillpipe an

46、d provide the screw threadfor connecting the joints of pipe together(Figure 4).Notice that the only seal in theconnection is the shoulder/shoulder connection between the box and pin.Initially tooljoints were screwed on to the end of drillpipe,and then reinforced by welding.A laterdevelopment was to

47、have shrunk-on tool joints.This process involved heating thetool joint,then screwing it on to the pipe.As the joint cooled it contracted and formeda very tight,close seal.One advantage of this method was that a worn joint could beheated,removed and replaced by a new joint.The modern method is to fla

48、sh-weldthe tooljoints onto the pipe.A hard material is often welded onto the surface of thetooljoint to protect it from abrasive wear as the drillstring is rotated in the borehole.This material can then be replaced at some stage if it becomes depleted due toexcessive wear.When two joints of pipe are

49、 being connected the rig tongs must beengaged around the tool joints(and not around the main body of the drillpipe),whosegreater wall thickness can sustain the torque required to make-up the connection.TheTable 4Summary of inspectiontechniques10strength of a tool joint depends on the cross sectional

50、 area of the box and pin.Withcontinual use the threads of the pin and box become worn,and there is a decrease inthe tensile strength.The size of the tooljoint depends on the size of the drillpipe butvarious sizes of tool joint are available.The tooljoints that are commonly used for 41/2 drillpipe ar