Moyno ERT Power Sections Operational Guidelines
Moyno ERT Power Section Operational Guidelines Index 1. Introduction... 3 2. ERT Performance Graph Interpretation... 3 3. Elastomer Compression (Fit) Recommendations... 5 4. Relationship Between ERT Loading and Stator Durability... 9 5. Adjusting ERT Loading for Operational Temperature... 10 The designs and specifications for the tools described in this instruction manual were in effect at the time this manual was approved for printing. National Oilwell Varco, whose policy is one of continuous improvement, reserves the right to discontinue models at any time, or to change designs and specifications without notice or without incurring obligation.
1. Introduction Moyno ERT power sections dramatically improve motor ROP by providing up to twice the power to the drill bit than conventional power sections of the same length. High power outputs are achieved by applying an even thickness of rubber to an internally machined, one-piece stator contour. However, ERT power sections are not indestructible and just like conventional power sections, are more likely to suffer more damage the harder they are run. This document provides information that will allow the user to make informed decisions as to how to adjust ERT loading conditions to ensure ROP and service life objectives are achieved. Specific recommendations for differential pressure, flow rate and fit are provided, as well as the means to adjust loading conditions for different operational temperatures. 2. ERT Performance Graph Interpretation Compared to the performance graphs of conventional power sections, ERT power sections graphs incorporate additional information to help users identify the appropriate loading level to optimize drilling performance and reliability. ERT performance graphs also differ from those of conventional power sections in that they are based on actual dynamometer test data. The torque and speed of an ERT power section is determined in the same manner as a conventional power section: To Read Torque: Select a differential pressure on the x-axis and move vertically to the torque line. Then move horizontally to the secondary y-axis on the right of the graph and read the torque output. To Read Speed: Select the differential pressure on the x-axis and move vertically to the speed line corresponding to the flow rate being used. Then move horizontally to the primary y-axis on the left and read the rotor s speed at that pressure and flow. 150 45,000 (61,000) Speed (rpm) 125 100 75 50 25 1200 gpm (4540 lpm) Speed 900 gpm at 750 psi and 1200 gpm = 110 rpm (3400 lpm) 600 gpm (2270 lpm) Torque 115 hp 335 hp 195 hp 518 hp Torque at 750 psi = 20,000 ft-lbs 37,500 (50,840) 30,000 (40,675) 22,500 (30,500) 15,000 (20,335) 7,500 (10,170) Torque - ft-lbs (Nm) 0 0 0 250 500 750 1,000 1,250 1,500 1,750 (1,725) (3,450) (5,170) (6,900) (8,620) (10,350) (12,065) Differential Pressure - psi (kpa ) 3 www.nov.com downhole@nov.com
Moyno ERT Power Section Operational Guidelines The following graph demonstrates how to interpret and use the additional information provided in ERT performance graphs. 150 ERT Performance Graph Example 45,000 (61,000) Speed (rpm) 125 100 75 50 25 1200 gpm (4540 lpm) 900 gpm (3400 lpm) 600 gpm (2270 lpm) Torque 115 hp 1 335 hp A B 195 hp 3 2 518 hp 37,500 (50,840) 30,000 (40,675) 22,500 (30,500) 15,000 (20,335) 7,500 (10,170) Torque - ft-lbs (Nm) 0 0 0 250 500 750 1,000 1,250 1,500 1,750 (1,725) (3,450) (5,170) (6,900) (8,620) (10,350) (12,065) Differential Pressure - psi (kpa ) Red shading is used to highlight loading conditions that elevate elastomer stress levels and may reduce stator run life. Higher differential pressures and flow rates reduce stator life. Green shading is used to highlight less demanding loading conditions that will reduce elastomer stress levels and may increase stator run life. 1 The Max Efficiency line identifies the pressures and flow rates at which the power section makes the most efficient use of the available hydraulic energy. Typically, the power output at max efficiency is greater than 65% of an ERT s maximum power output, but it is achieved at less than 50% of the differential pressure required to produce the maximum power output possible. 2 The Max Power line identifies the differential pressure that maximizes power output for any given flow rate. 3 The lines listed as identify ranges in which 95% of both maximum horsepower and maximum efficiency are achieved, and indicate the sensitivity of both parameters to varying differential pressures. These ranges are typically quite wide, highlighting that significantly lower differential pressure loading can still provide over 95% of the maximum power output. Because of this and the fact that higher differential pressures increase elastomer stress and reduce power section life, the minimum differential pressure required to obtain this 95% of maximum power output should be considered the maximum loading level. B Operation in the area between the 95% max efficiency and 95% max power lines is the optimal range in which ERTs should be run. Both power and efficiency are near maximum values, but elastomer stress levels are lower than those created at maximum power due to much lower differential pressures. A Elastomer stresses in ERTs run at the flows and differential pressures described by this box will be lower than those incurred in the power sweet spot. The operational life of ERTs run in his zone should be longer than ERTs run at higher differential pressures and flows. 4
3. Elastomer Compression (Fit) Recommendations Although the steel support of the ERT stator lobe serves to strengthen the lobe during operation, the elastomer used in ERT stators is still subject to weakening and thermal expansion as operational temperatures increase. Additionally, the elastomer may also change shape or weaken due to exposure to oil-based drilling fluids. To ensure optimal field performance, it is therefore necessary to size ERT power sections and to reduce power section loading as operational temperatures increase. Sizing the power section entails reducing the power section s fit to compensate for the elastomer s expected thermal growth during operation, thereby reducing the stress created due to elastomer compression. Fit Calculation The fit of an ERT power section represents the amount that the stator s elastomer is compressed across its diameter by its mating rotor. An ERT s fit is determined in the same manner as with a conventional power section by subtracting the stator s minor diameter from the average rotor diameter: Even Lobe Rotors: Fit = Rotor Major Diameter + Rotor Minor Diameter - Stator Minor Diameter 2 Odd Lobe Rotors: Fit = (Rotor Valley to Crest Diameter) - Stator Minor Diameter Available Fits Three fits are available to cover the operational temperature ranges in which ERTs can be used: Power fits provide maximum power output, and while typically recommended for use at temperatures of up to 175 F, but can be used at up to 200 F for shorter runs. Endurance fits are sized to provide a zero compression, line on line fit at shop temperatures. High Temperature fits are recommended when operational temperatures exceed 250 F. Depending upon the ERT model, Endurance and High Temperature Fits can be obtained through the use of undersized (US) rotors, oversized (OS) stators or a combination of both. Recommended ERT Operational Temperature Range Example 0.025 0.020 0.015 Power Fit 0.64 0.51 0.38 Shop Fit (in) 0.010 0.005-0.005 Endurance Fit 0.25 0.13 0.00-0.13 Shop Fit (mm) -0.010-0.25-0.015-0.020 High Temp Fit -0.38-0.51-0.025-0.64 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) 5 www.nov.com downhole@nov.com
Moyno ERT Power Section Operational Guidelines Chart Interpretation Color coded areas are used to highlight acceptable temperature ranges for the obtained shop fit. Green zones represent the recommended temperature ranges for each fit. ERTs can be run in the yellow zones, but at the risk of shorter run times and decreased power output at lower compression levels. Example An ERT user intends to run their ERT at 175 F (79 C). What range of fits would be recommended for this application? Green Zone - Moving upward from 175 F to the green zone and then to the left axis indicates that the green zone shop fit for this application will be between -0.005 and 0.016 (-0.13 and 0.41 mm). Yellow Zones - Run life when operated at tighter fits of between 0.016 and 0.020 (0.41 and 0.51mm) may be less than that obtained from reduced fits, but power output will be higher. Power output will be reduced when operated at looser fits of between -0.005 and -0.014 (-0.13 and -0.036 mm). This may decrease drilling rates and contribute to greater fluctuations in torque output and therefore bit speed. The power section may see higher dynamic loading. 0.025 0.020 0.016 0.015 Power Fit 0.64 0.51 0.38 Shop Fit (in) 0.010 0.005-0.005 Endurance Fit 0.25 0.13 0.00-0.13 Shop Fit (mm) -0.010-0.014-0.015-0.020 High Temp Fit -0.25-0.38-0.51-0.025-0.64 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) Consideration of volume swell due to fluid exposure Due to the small elastomer volume of ERT stators the minor diameter of ERT stators will seldom grow by more than 0.005 (0.13 mm) when exposed to oil-based muds (OBMs). Should the user expect the elastomer to swell during use, subtract this expected swell from the measured shop fit to correct for the expansion. The recommended temperature ranges for the ERT will then be a function of this corrected fit. Example Continuing the above example, if the user expects the drilling fluid to swell the elastomer by about 0.005 (0.13 mm), what shop fit is recommended for an operation at 175 F (79 C)? Recommended fit with no elastomer swell = -0.005 to 0.016 (-0.13 to 0.41 mm) Expected minor diameter swell = 0.005 (0.13 mm) Recommended fit with elastomer swell = -0.010 to 0.011 (-0.25 to 0.28 mm) 6
Graphs describing the recommended shop compression levels for various operational temperatures are presented for each ERT model below. Recommended 2d" ERT Operational Temperature Range 0.010 0.25 0.005 0.13 Shop Fit (in) Endurance Fit 0.00 Shop Fit (mm) -0.005 High Temp Fit -0.13-0.010-0.25 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) Recommended 4w" ERT Operational Temperature Range 0.015 0.38 0.010 Power Fit 0.25 Shop Fit (in) 0.005-0.005 Endurance Fit 0.13 0.00-0.13 Shop Fit (mm) -0.010 High Temp Fit -0.25-0.015-0.38 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) 7 www.nov.com downhole@nov.com
Moyno ERT Power Section Operational Guidelines Recommended 62" and 6w" ERT Operational Temperature Range 0.025 0.64 0.020 0.51 0.015 Power Fit 0.38 0.010 0.25 Shop Fit (in) 0.005-0.005 Endurance Fit 0.13 0.00-0.13 Shop Fit (mm) -0.010-0.25-0.015 High Temp Fit -0.38-0.020-0.51-0.025-0.64 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) Recommended 8" and 9s" ERT Operational Temperature Range 0.025 0.64 0.020 0.51 0.015 Power Fit 0.38 0.010 0.25 Shop Fit (in) 0.005-0.005 Endurance Fit 0.13 0.00-0.13 Shop Fit (mm) -0.010-0.25-0.015-0.020 High Temp Fit -0.38-0.51-0.025-0.64 75 100 125 150 175 200 225 250 275 300 325 350 375 (24) (38) (52) (66) (79) (93) (107) (121) (135) (149) (163) (177) (191) 8
Adjustment of Shop Fit Measurement for Different Shop Temperatures The above graphs assume that the shop fit has been normalized to reflect the fit at 75 F (24 C). If the stator temperature when measured is dramatically above or below this temperature, the measured fit should be corrected according to the following table: Stator Temperature Correction Values - in (mm) Stator Elastomer Temperature ( F) 35 45 55 65 75 85 95 105 115 ( C) 2 7 13 18 24 29 35 41 46 2d 4w 62 & 6w 8 & 9s 0.002 (0.05 mm) 0.003 (0.08 mm) 0.005 (0.13 mm) 0.002 (0.04 mm) 0.002 (0.06 mm) 0.004 (0.10 mm) 0.001 (0.03 mm) 0.002 (0.04 mm) 0.002 (0.06 mm) 0.003 (0.07 mm) 0.001 (0.03 mm) -0.001 (-0.03 mm) -0.001 (-0.03 mm) -0.002 (-0.04 mm) -0.002 (-0.04 mm) -0.002 (-0.06 mm) -0.002 (-0.06 mm) -0.004-0.003 (-0.10 mm) (-0.07 mm) -0.002 (-0.05 mm) -0.003 (-0.08 mm) -0.005 (-0.13 mm) To use the table, simply add the numbers in the table to the shop fit based on the temperature of the stator s elastomer when its minor diameter was measured. This sum will replace the shop fit referenced in the table, which is then used as previously described. It should be noted that depending upon the storage conditions of the stator, the shop temperature may not be the same as the stator s temperature. This can occur when storing the stator outside at extreme temperatures and then measuring the stator inside without allowing the stator temperature to normalize. In situations like this, a direct measurement of stator elastomer temperature taken or the stator temperature should be allowed to reach an equilibrium with the shop temperature before the stator s minor diameter is measured. 4. Relationship Between ERT Loading and Stator Durability The reliability and durability of an ERT power section will be a function of the stress applied to the elastomer during operation, the rate at which the stress is applied and the strength of the stator s elastomer. Elastomer stress will be a function of static stress components such as power section fit as well as dynamic components such as centrifugal loading, which is a function of flow rate, differential pressure and the dynamic nature of the torque loading generated by the drill bit. The strength of an elastomer will decrease as operational temperatures increase and due to exposure to oil and synthetic based muds. Given the multitude of factors that affect power section loading and elastomer strength, it is not possible to provide a universal differential pressure recommendation that will be suitable for all applications. In addition, an ERT that is run reliably at a specific flow rate and differential pressure will not last as long at a higher flow rate unless the differential pressure loading is reduced. For example, the differential pressure loading level that may be appropriate for 175 F (79 C) will have to be reduced to obtain the same stator run life at 275 F (135 C). The method to do this is explained in section 5 below. It is possible, however, to provide a baseline loading level that the ERT user can adjust based on their experience and the specific operational conditions to which the ERT will be exposed. Customer feedback has indicated that a baseline loading level of 150 psi/ stage at 200 F (93 C) is generally optimal, and the ERT s mid flow point has typically produced an acceptable combination of high ROP and stator longevity. This loading level should be reduced at higher temperatures and at higher flow rates, or when running in fluids that tend to weaken the elastomer. Conversely, higher loading levels may be possible at lower temperatures, lower flow rates or benign drilling fluids. The following table provides the recommended baseline differential pressures for each ERT power section: Recommended Maximum Baseline Differential Pressure 287E7836 475E4536 475E4554 475E6725 650E6722 650E6727 675E6729 675E6731 675E6748 800E5652 962E6735 psi 540 540 810 375 330 405 435 465 720 780 525 Kpa 3720 3720 5580 2585 2275 2790 2997 3200 4960 5375 3615 9 www.nov.com downhole@nov.com
Moyno ERT Power Section Operational Guidelines 5. Adjusting ERT Loading for Operational Temperature In addition to adjusting ERT fit to compensate for the thermal expansion of the elastomer at elevated temperatures, it is also recommended that ERT loading be decreased as operational temperatures increase. This reduction in loading will offset the natural reduction in elastomer strength that occurs as temperatures increase, and in doing so extend run life. The recommended operational loading for an ERT at a specific temperature is expressed relative to baseline loading conditions that the user has associated with successful runs. The graph below allows the user to adjust their loading conditions in this manner for any temperature between 150 F and 375 F (65 C and 191 C). This graph applies to all ERT models. ERT Loading Adjustment for Temperature Loading Factor 1.0 1.0 0.9 0.9 0.8 0.8 0.7 ERT Loading Curve 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.1 Loading Factor = Differential Factor x Flow Factor 0.1 0.0 0.0 150 175 200 225 250 275 300 325 350 375 (65) (79) (93) (107) (121) (135) (149) (163) (177) (191) Loading Factor The example below explains how to adjust flow rate and differential pressures for different operational temperatures. Example An ERT user has obtained excellent runs with their 675ERT6748 at 250 F (121 C) and would like to know how they should adjust the loading conditions used at 250 F to obtain similar reliability at both 200 F (93 C) and 300 F (149 C). The fit has already been adjusted for operation at these temperatures. Referencing the figure below, the ERT Load Factors are 0.6 at 250 F and about 0.78 at 200 F. Ratioing these factors suggests that the ERT can safely handle a 30% greater load at 200 F than at 250 F. This calculation is depicted below: ERT Loading Adjustment for Temperature Loading Factor 1.0 1.0 0.9 0.9 0.78/0.6 = 1.3 (30% higher) 0.8 0.8 0.78 ERT Loading Curve 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.1 Loading Factor = Differential Factor x Flow Factor 0.1 0.0 0.0 150 175 200 225 250 275 300 325 350 375 (65) (79) (93) (107) (121) (135) (149) (163) (177) (191) Loading Factor 10
How to Translate Loading Factors to Pressures and Flows But how does the user translate this potential 30% increase in loading conditions to a specific differential pressure and flow rate? It would be simple to leave the flow rate unchanged and only adjust the differential pressure consumed. For this example, the user above could simply multiply the differential pressure used at 250 F by 1.3 (30% higher) to obtain the recommended pressure at 200 F. To ensure optimal power section life, it is best to also adjust flow rate, and therefore power section speed. Speed affects elastomer loading by changing the rate at which stress is applied to the elastomer, and affects the magnitude of the stress applied due to centrifugal loading, which increases as flow rates rise. Large reductions in elastomer stress can be achieved at lower flow rates since centrifugal loading increases exponentially with increased flow. Typically, only modest changes in flow rate are possible due to the need to ensure adequate hole cleaning and a sufficient supply of hydraulic energy to the power section. This is especially true with ERT power sections due to their typically exceptional ROPs. A 1% increase in speed is recommended for every 10 F decrease in operational temperature, and a 2% decrease in speed for every 10 F increase in temperature. Consequently, most of the change in power section loading will be provided by changes in differential pressure. The following describes in detail the steps necessary to determine recommended differential pressures and flow rates. For this example, the baseline loading conditions at 250 F are: 400 psi and 550 gpm. For clarity, only English units are used. 1. Determine change in loading factor from 250 F to 200 F A. Loading factors = 60% at 250 F, 78% at 200 F B. Change in Loading factor = 0.78/0.60 = 1.30 (30% higher) This indicates that the ERT can be loaded approximately 30% higher at 200 F than at 250 F. 2. Adjust the flow rate up by 1% (for lower operational temperatures) or down 2% (for higher operational temperatures) for every 10 F of temperature change from the flow rate that formed the baseline operational condition. A. Baseline operational temperature = 250 F B. Target temperature = 200 F C. Temperature difference = -50 F D. Flow rate factor = 1.05 (1% change for every 10 F decrease in temperature) E. Flow at 200 F = 578 gpm (Flow rate factor x 550 gpm = 1.05 x 550) 3. Adjust the Differential Pressure A. Differential Pressure Factor = Loading Factor / Flow Rate Factor B. Differential Pressure Factor = 1.30/1.05 = 1.24 C. Differential Pressure at 200 F = 495 psi (1.24 x 400 psi) Repeating the exercise for 300 F operation produces the following numbers: A. Loading at 250 F = 400 psi and 550 gpm B. Loading factor at 300 F = 0.44/0.6 = 0.73 C. Flow at 300 F = 495 gpm = 550 x 0.9 D. Pressure at 300 F = 324 psi = (400 x 0.73/0.9) 11 www.nov.com downhole@nov.com
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