Managing torque and drag

MANAGING TORQUE AND DRAG Schlumberger Sedco Forex SFM-TD-96 This presentation has been prepared to give you a better understanding of the different parameters involved in managing torque and drag Recommendations presented here should be applied within operational needs We want to disseminate this knowledge because great amounts of money and time are spent, every year, combating torque and drag problems One of them, stuck pipe, is an expensive, time-consuming and always undesirable event You will see how torque and drag levels can be monitored and measures implemented to effectively control them We will go through this process beginning with the design of the well, followed by the monitoring of torque and drag and their management By the end of this presentation you should have a good idea about how to effectively predict, monitor and control torque and drag NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page What is Friction? Motion Friction W Schlumberger Sedco Forex SFM-TD-96 During the first part of this presentation, we will concentrate on understanding torque and drag losses Let's look at what causes torque and drag and how they can be explained with simple physics Friction is the resistance to motion that exists when a solid object is moved tangentially with respect to the surface of another which it touches, or when an attempt is made to produce such motion NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page Laws of Friction I Frictional force is proportional to the normal force FD = µ.FN tan Ø = µ FD FN Ø W SFM-TD-96 Schlumberger Sedco Forex There are three (Newtonian) laws that provide the quantitative framework to understand friction: The first law states that the frictional drag force, FD, is proportional to the normal force, FN FD = µ FN The proportionality constant, µ, is the apparent friction coefficient However, when applied to drilling, µ is not a true sliding friction coefficient Instead, it acts as a correlation coefficient that lumps together the friction caused by various effects, including friction, plowing or gouging of the borehole wall and differential-pressure sticking forces This law is often expressed in terms of a constant angle of repose, or a frictional angle Ø , defined by: tan Ø = µ Ø is the angle of an inclined plane such that any object, whatever its weight, placed on the plane will remain stationary, but if the angle is increased by a small amount the object will slide down NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page Laws of Friction (cont.) II A friction coefficient is independent of the apparent area of contact III Frictional force is independent of sliding velocity Schlumberger Sedco Forex SFM-TD-96 The second law states that a material’s friction coefficient is independent of the apparent area of contact Therefore, large and small objects —made of the same material— have the same coefficient of friction The third law states that the frictional drag force is independent of the sliding velocity This implies that the force required to initiate sliding will be the same as the force required to maintain sliding at any specified velocity In practice the first two laws of friction are generally well obeyed In the case of the third law, experiments have shown that the friction coefficient decreases slightly with sliding velocity but for drilling applications this effect is negligible NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page Torque and Drag Torque Losses Drag Losses Schlumberger Sedco Forex SFM-TD-96 When drilling a well, there are two types of friction losses that cause us special concern: Torque losses, which are defined as the difference between the torque applied at the rig floor and the torque available at the bit Drag losses, which are measured as the difference between the static weight of the drillstring and the tripping weight Torque losses are referred to as rotating friction and drag losses as sliding friction In theory these types of friction are supposed to be identical, but in practice the uncertainties on surface torque and hookload measurements not allow a definitive conclusion Even though the concept of sliding friction has been extended to rotating pipe, sliding friction is always very low as vibration causes the pipe to bounce off the borehole walls, partially eliminating friction NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page What Causes Torque and Drag? Lateral Forces Drillstring Weight Borehole Inclination Directional Change Schlumberger Sedco Forex SFM-TD-96 Both torque and drag losses are caused by the lateral forces and the friction between the borehole wall and the drillstring These lateral forces depend on: • Drillstring Weight • Borehole Inclination • Directional Changes (dogleg severity) The last two parameters are closely related to the wellbore’s path NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page What Causes Torque and Drag? (cont.) Tension Side Force Side Forces Tension Schlumberger Sedco Forex SFM-TD-96 The diagram illustrates the effects of well profile on the distribution of contact forces between the drillstring and the wellbore NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page What Causes Torque and Drag? (cont.) Wellbore Path is influenced by: BHA Design Weight on Bit and Rotary Speed Formation Dip Borehole Diameter Formation Drillability Borehole Stability Schlumberger Sedco Forex SFM-TD-96 The path of a borehole is the result of complex interactions between the behavior of the rock and different drilling parameters like: • Bottomhole Assembly Design • Weight on Bit and Rotary Speed • Formation Dip • Borehole Diameter • Formation Drillability (perpendicular and/or parallel to the bedding plane) • Borehole Stability NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page What Causes Torque and Drag? (cont.) Drillstring Dynamics Torsional Waves Slip-Stick Motion Vibration Dampening Schlumberger Sedco Forex SFM-TD-96 Let's now look at the effects of drillstring dynamics on torque: When the downhole friction torque changes, a torsional wave is generated and propagates upwards towards the kelly (the drillpipe acts as a transmission line for torsional waves) A rotary table that has a completely constant speed, independent of the load, represents a fixed end for such a torsional wave As a result, torsional waves are reflected back down the drillstring with 100% efficiency Once vibrational energy is trapped in the drillstring, severe torsional oscillation can build up, leading to slip-stick motion and other problems4,5 The rotary table will respond to these large torque variations with significant speed variations The problem of severe oscillations associated with slip/stick motion of the bit can be reduced, even removed, by reducing the downhole static friction or controlling the rotary-table speed, in a way that dampens torsional oscillations by inducing a motion proportional to the torque variations This concept is called torque feedback and represents a sort of compromise between two contradictory requirements: maintaining the desired speed and holding constant torque NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page Other Considerations Drilling Equipment Integrity Dogleg Severity Casing String Integrity Bending Strength Side Forces Casing Wear Schlumberger Sedco Forex SFM-TD-96 10 As mentioned before, dogleg severity has an important influence on the magnitude of lateral forces For this reason, dogleg-severity values have to be kept below a certain critical level in order not to exceed the mechanical strength of the drillpipe and other rotary equipment This becomes more important with increasing inclination of the borehole Similar to a drillstring, the casing makes certain demands on acceptable values of inclination and direction of the borehole These values are related to: • Bending Strength • Side Forces (while running) • Casing Wear NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 10 Predicting Torque & Drag (cont.) Bit Torque from Mathematical Models Bit Design Weight on Bit Bit Wear Rotary Speed Bit Hydraulics Formation Hardness Schlumberger Sedco Forex SFM-TD-96 19 Predominantly based on lab measurements, mathematical models have been developed for predicting bit torque using various bit types However, actual bit torque varies substantially during drilling and is influenced by many factors, including: • Bit Design • Weight on Bit • Bit Wear • Rotary Speed • Bit Hydraulics • Formation Hardness Considering the complex nature of the influence of these factors on bit torque, mathematical models should be used carefully NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 19 Predicting Torque & Drag (cont.) Casing Considerations Running Casing Reciprocation/Rotation Other Considerations Hole Cleaning Schlumberger Sedco Forex SFM-TD-96 20 Simulated curves for weight and torque are helpful to the driller when running and cementing casing and liners, because deviations from the simulations may give early warnings of hole problems The ability to run and cement casings and liners depends heavily on torque and drag levels in a well Casing is sometimes not reciprocated or rotated for fear of sticking it off bottom, leaving a casing collar in the well head, or exceeding makeup-torque levels1 Simulations of up-, downweight and torque, caused by casing rotation during cementing, should be performed in the planning phase of a well to determine the feasibility of casing movement during the primary cement job Finally, when extended-reach wells are drilled, the same torque- and drag-simulation curves may also be used to monitor hole cleaning, where deviations from properly modeled torque and drag simulations may indicate problems like the presence of excessive cuttings beds or deficient hole cleaning NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 20 (cont.) 35 40 Predicting Torque & Drag µ = 0.3 20 10 15 Drag (klbf) 25 30 Mud Sweep DRAG CHART Schlumberger Sedco Forex 12000 11500 11000 10500 9500 10000 9000 8500 8000 7500 7000 6500 5500 (ft) 6000 5000 4500 4000 3500 3000 2500 2000 1500 500 1000 0 µ = 0.2 Predicted Actual SFM-TD-96 21 Example of a drag chart reflecting the increase of drag due to poor hole cleaning NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 21 Measuring Torque & Drag (cont.) Bit Torque from Field Measurements MWD Surface Measurement Offset Data Schlumberger Sedco Forex SFM-TD-96 22 In order to obtain an accurate measurement, bit torque should be monitored using a drilling-mechanics sub in the MWD tool This is of particular importance in extended-reach wells where torque and drag levels must be constantly optimized Alternately, crude bit-torque measurements can be taken by monitoring off-bottom and on-bottom surface torque, although this is only approximate since weight on bit causes variations in the drillstring tension/compression profile, affecting wall forces and string-torque magnitude A more empirical approach, to determine bit torque, is the use of a conservative upper limit from existing field data NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 22 Measuring Torque & Drag (cont.) Measuring Drag Pick-up Weight Slack-off Weight Schlumberger Sedco Forex SFM-TD-96 23 In order to monitor the levels of drag in the wellbore, two field measurements are routinely taken: Pick-up weight is the force necessary to lift the drillstring It includes the weight of the string, as well as the force necessary to overcome existing drag to come out of the hole Slack-off weight is the force necessary to lower the drillstring It includes the weight of the string, as well as the force necessary to overcome existing drag to go into the hole The latter manifests itself as a 'reduction' in the wight of the string NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 23 Measuring Torque & Drag (cont.) Determining Friction Coefficients Mud Lubricity Cased Hole Formation Type Schlumberger Sedco Forex SFM-TD-96 24 A good mud-system design is always important and should be aimed at reducing wellbore friction, specially in extended-reach applications Furthermore, mud lubricity should be distinctly defined for cased and open-hole intervals of each well section, as it will vary according to the respective friction coefficient Cased-hole friction should be based on correlating torque measured at the shoe prior to drilling out and during subsequent bit runs Open-hole friction factors should be independently determined based on the rate of torque increase with measured depth, in the open-hole section Distinct friction levels may also be imposed by different formations and significant torque changes can be seen when abrasive formations are encountered Also, cased-hole friction factors may increase during drilling once cuttings are brought back into the casing, resulting in higher pickup drag and/or torque NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 24 Controlling Torque Torque Reduction Well Trajectory Cased Hole Open Hole Mud Lubricity Lubricating Beads Use of LCM Schlumberger Sedco Forex SFM-TD-96 25 Several measures may be implemented to reduce torque: Optimization of the well trajectory, in terms of general design and execution, is critical to torque reduction Reduction of cased-hole torque can be achieved using non-rotating drillpipe protectors6 These protectors are ideally run over long intervals where drillstring/casing contact loads are high Reduction of open-hole torque can be achieved with subs which involve a non-rotating metal sleeve mounted on bearings6,7 Increased mud lubricity, through the use of additive lubricants, is another torque reduction option While in oil-base muds, increasing the oil-water ratio may improve lubricity Lubricating beads can reduce torque, but generally have to be continually added due to difficulty in recovering them at the surface As reference, dramatic torque reductions have been observed after the use of high concentrations of fibrous lost-circulation materials, which appear to form a low-side 'bed' with much reduced friction6 NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 25 Controlling Torque (cont.) Wellpath Considerations Trajectory Bottomhole Assemblies Optimum Profile Schlumberger Sedco Forex SFM-TD-96 26 In the case of extended-reach wells, it is even more important for the trajectory to be as smooth as possible and with minimum doglegs Thus, the ability to achieve directional control in the specific geology involved must be an integral part of the design process To the fullest extent possible, bottomhole assemblies should be designed to achieve the desired build/turn tendencies with the maximum amount of rotary drilling (as opposed to 'sliding') This tends to minimize doglegs as well as promote better hole cleaning and rate of penetration Intermittent sliding as a means of ongoing course correction is recommended over more dramatic, single-event course corrections As a result, oriented BHAs are preferred over rotary BHAs for extendedreach wells, but their optimum use is in rotary drilling to the fullest extent possible Steerable rotary drilling systems, some already available, will have a major impact on future extended-reach wells, because they provide ideal drilling systems in terms of smooth wellbore curvatures, via continuous reaction to changes in directional tendencies while drilling 2,3 With regard to torque and drag, the optimum profile depends on both local friction factors and the specific operation being considered; therefore, due to variations in friction factors between operating areas (even between different sections in a single well) there is no single “optimum” profile NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 26 Controlling Torque (cont.) Dynamic Torque Torsional Dynamics Torque Feedback BHA Design Schlumberger Sedco Forex SFM-TD-96 27 As mentioned before, besides the basic torque encountered in a wellbore during drilling, downhole vibrations generate an additional level known as dynamic torque The potential for torsional dynamics must be recognized when assessing torque-reduction measures To this, it is recommended that measurements be taken to examine the presence and magnitude of dynamic torque If torsional dynamics are present, the use of a torque-feedback system should be considered This system has shown to be successful in reducing torsional dynamics and thereby increasing available torque Bit selection and BHA design (particularly stabilization) also affect the propensity for torsional dynamics The key is to be aware of the impact of torsional dynamics, examine its presence via measurements and take appropriate remedial actions In the end, drilling limits will be determined by both mean and dynamic torque behaviors NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 27 Controlling Torque (cont.) Drillstring Optimization Tool Joints and Pipe Materials TJ Balancing and Thread Compounds Tandem Drilling Motors Other Schlumberger Sedco Forex SFM-TD-96 28 If the torsional limitation is related to the drillstring, as opposed to the rig, several means exist to optimize the strength of an existing drillstring or to design an enhanced drillstring Where options exist for specific drillstring design, consideration should be given to the use of high-torque tool joints and high-strength material grades Substantial increases in nominal torsional capacity, of existing drillstrings, can be obtained through tool-joint stress-balancing and the use of high-friction thread compounds Alternately, some operators have reported that significant de-coupling of bit and drillstring dynamics has been provided by double or extended power-section drilling motors Proprietary drillpipe is also available with integral blades to enhance hole cleaning and thereby reduce mechanically induced torque from cuttings beds In addition, some novel-design bit subs have proved effective in de-coupling bit and drillstring dynamics, under field conditions De-coupling is the action of adding a mechanical isolation, between two elements, in order to prevent the transmission of vibrations This can be achieved with elastic components that absorb vibrations and limit their transfer up the drillstring NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 28 Controlling Drag Well Profile Mud Lubricity Drillpipe Protectors Buckling Effects Schlumberger Sedco Forex SFM-TD-96 29 Measures exist to both reduce drag and develop improved or alternative means of achieving the desired operation, particularly in extended-reach wells As with torque reduction, the use of an optimized well profile, optimization of mud lubricity and the use of low-friction drillpipe protectors can reduce drag If drillstring buckling is a concern, as a result of high drag levels, consideration should be given to optimizing the drillstring design in order to minimize buckling severity This includes the use of a tapered drillstring configuration NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 29 Controlling Drag (cont.) Weight Distribution Hole Cleaning Thrusters Downhole Motors Traveling Equipment Schlumberger Sedco Forex SFM-TD-96 30 Distinct from drag reduction, techniques are also available to simply overcome existing drag, specially in extended-reach applications Running drill collars and/or heavy-weight drillpipe, in the near-vertical well section, can provide increased string weight and facilitate oriented drilling Extensive hole cleaning and pipe working, to remove cuttings, can temporarily improve the ability to slide in directional wells In some operating areas, thrusters or bumper subs are used to improve weight-on-bit delivery while sliding The use of extended or double power-section motors to increase stalling resistance has also been reported as a successful measure to improve the ability to drill oriented Even though traveling-equipment weight can be used to push the drillstring down and enable sliding, this action should be pursued using proper safety measures and after careful analysis of the operation, to ensure that the pipe is not being buckled in the process NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 30 Controlling Drag (cont.) Rotation Steerable Rotary Systems Stuck Pipe Schlumberger Sedco Forex SFM-TD-96 31 In terms of drag reduction, rotation is a virtual 'cure all’ and consideration should be given to qualifying any string for rotation This clearly includes liners, but can also include perforating, testing and completion strings As casing drag can be a critical limiting factor in extended-reach wells, optimized float shoes, casing-circulation tools, casing-flotation and casing-rotation schemes need to be considered The use of rotary drilling systems, which enable inclination control without oriented drilling, will increase drilling efficiency in directional wells The highly-variable gauge stabilizer2 is a major advance in this area, together with fully-steerable rotary drilling systems being developed Finally, in order to deal effectively with stuck-pipe situations, the driller needs to know how his actions at the surface will change the forces both in the drillstring and at the stuck point The influence of drag on the force available at the jar can be significant in directional wells8; therefore, the drag effect should be considered when a well is planned The use of a torque and drag simulator will enable calculations of hook load for a given tension or compression on the jar With such calculations, it is possible to estimate the force available at the jar if the string should stick, allowing the driller to set and fire the jars in the most efficient way NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 31 Summary Torque and Drag are caused by lateral forces and friction in the wellbore Optimization of well trajectory is critical T&D levels can be minimized through modeling BHAs should be designed for rotary drilling Schlumberger Sedco Forex SFM-TD-96 32 Let’s summarize the key points from this presentation: Torque and drag are caused by the lateral forces and the friction between the borehole wall and the drillstring (dogleg severity has an important influence on the magnitude of such forces) Optimization of the well trajectory, in terms of general design and execution, are critical to torque and drag reduction The optimum well profile depends on both local friction factors and the specific operation being considered Torque and drag modeling should be used to find the build rates, inclinations and drop rates to connect the upper hole section of a well to the target, with the least torque and drag As much as possible, bottomhole assemblies should be designed to achieve the desired build/turn tendencies with the maximum amount of rotary drilling NEXT SLIDE Technology Transfer “Managing Torque & Drag” Page 32 Summary (cont.) Bit torque should be monitored using an MWD tool Simulation curves should be used to monitor hole cleaning String design can help overcome existing drag Schlumberger Sedco Forex SFM-TD-96 33 In order to obtain an accurate measurement, bit torque should be monitored using an MWD tool Torque- and drag-simulation curves should be used to monitor hole cleaning Deviations from properly modeled torque and drag simulations may indicate problems like the presence of cuttings beds and poor hole cleaning Running drill collars and/or heavy-weight drillpipe, in the near-vertical well section, can provide increased string weight and facilitate oriented drilling in extended-reach applications THIS IS THE LAST SLIDE Technology Transfer “Managing Torque & Drag” Page 33 [...]... causing increased torque and drag levels NEXT SLIDE Technology Transfer Managing Torque & Drag Page 13 Downhole Effects Surface Torque Bit Torque Frictional String Torque Mechanical Torque Dynamic Torque Schlumberger Sedco Forex SFM-TD-96 14 Even though measures can be taken to minimize the causes of torque and drag, they must first be recognized Total surface torque is comprised of: • Bit Torque (influenced... instabilities and reduce torque and drag Identification of excessive stabilizer torque can lead to better equipment selection such as under-gauge stabilizers, reamers, etc Also, higher flow rates, careful rheology control and drillstring rotation can improve hole cleaning, minimizing the occurrence of cuttings beds NEXT SLIDE Technology Transfer Managing Torque & Drag Page 14 Managing Torque and Drag Predict... 15 Torque and drag losses will always be present during drilling; therefore, we should learn how to best manage them, specially in applications like extended-reach and horizontal drilling An approach called PMC ( Predict, Monitor, Control ) is suggested for this purpose NEXT SLIDE Technology Transfer Managing Torque & Drag Page 15 Predicting Torque & Drag Trajectory/Drillstring Design Rotary Torque. .. to monitor hole cleaning, where deviations from properly modeled torque and drag simulations may indicate problems like the presence of excessive cuttings beds or deficient hole cleaning NEXT SLIDE Technology Transfer Managing Torque & Drag Page 20 (cont.) 35 40 Predicting Torque & Drag µ = 0.3 20 10 15 Drag (klbf) 25 30 Mud Sweep DRAG CHART Schlumberger Sedco Forex 12000 11500 11000 10500 9500 10000... dynamics, examine its presence via measurements and take appropriate remedial actions In the end, drilling limits will be determined by both mean and dynamic torque behaviors NEXT SLIDE Technology Transfer Managing Torque & Drag Page 27 Controlling Torque (cont.) Drillstring Optimization Tool Joints and Pipe Materials TJ Balancing and Thread Compounds Tandem Drilling Motors Other Schlumberger Sedco... presentation: Torque and drag are caused by the lateral forces and the friction between the borehole wall and the drillstring (dogleg severity has an important influence on the magnitude of such forces) Optimization of the well trajectory, in terms of general design and execution, are critical to torque and drag reduction The optimum well profile depends on both local friction factors and the specific... considered Torque and drag modeling should be used to find the build rates, inclinations and drop rates to connect the upper hole section of a well to the target, with the least torque and drag As much as possible, bottomhole assemblies should be designed to achieve the desired build/turn tendencies with the maximum amount of rotary drilling NEXT SLIDE Technology Transfer Managing Torque & Drag Page... Predicted Actual SFM-TD-96 21 Example of a drag chart reflecting the increase of drag due to poor hole cleaning NEXT SLIDE Technology Transfer Managing Torque & Drag Page 21 Measuring Torque & Drag (cont.) Bit Torque from Field Measurements MWD Surface Measurement Offset Data Schlumberger Sedco Forex SFM-TD-96 22 In order to obtain an accurate measurement, bit torque should be monitored using a drilling-mechanics... wells where torque and drag levels must be constantly optimized Alternately, crude bit -torque measurements can be taken by monitoring off-bottom and on-bottom surface torque, although this is only approximate since weight on bit causes variations in the drillstring tension/compression profile, affecting wall forces and string -torque magnitude A more empirical approach, to determine bit torque, is the... Technology Transfer Managing Torque & Drag Page 24 Controlling Torque Torque Reduction Well Trajectory Cased Hole Open Hole Mud Lubricity Lubricating Beads Use of LCM Schlumberger Sedco Forex SFM-TD-96 25 Several measures may be implemented to reduce torque: Optimization of the well trajectory, in terms of general design and execution, is critical to torque reduction Reduction of cased-hole torque can be