New Technologies for BOP Shearing20 August 2013
Covey HallGlobal Manager for Consulting ServicesLloyd’s Register Energy – Drilling
Agenda
• History• Observations as 3rd party verifier• GTC Shear Study • Use of fiber-optic strain gauges• Acknowledgements • References
History
2003 and 2004 Shear StudiesPerformed by WEST Engineering for the MMS
Understanding the Shear FunctionUnderstanding the Shear Function
Last resort is to shear pipe Last resort is to shear pipe and secure the well with and secure the well with the sealing shear ram. the sealing shear ram.
Failure to shear could Failure to shear could result in a major safety result in a major safety and/or environmental and/or environmental event. event.
Improved strength, larger Improved strength, larger and heavier drill pipe and heavier drill pipe adversely affects the adversely affects the ability to successfully ability to successfully shear and seal. shear and seal.
Actual Shearing or Breaking ActionActual Shearing or Breaking Action
Lower Shear Blade
Upper Shear Blade Drill Pipe being
collapsed during the shearing process
Shear Blade Rake Angles that apply tension to the pipe during the separation process
Tension
Tension
Upper and Lower Upper and Lower Shear Blades Shear Blades crushing the drill crushing the drill pipe and pipe and beginning the beginning the shearing (or shearing (or breaking) breaking) operatiooperation.n.
Increased Shear Pressure due to Increased Shear Pressure due to Wellbore Pressure and Hydrostatic HeadWellbore Pressure and Hydrostatic Head
Closing RatioClosing Ratio
The areas where mud, seawater and BOP The areas where mud, seawater and BOP fluid pressures effect a BOP’s operation:fluid pressures effect a BOP’s operation:
1 – Mud Pressure1 – Mud Pressure2 – Seawater Pressure or 2 – Seawater Pressure or hydrostatic headhydrostatic head3 – BOP Fluid Pressure plus 3 – BOP Fluid Pressure plus hydrostatic headhydrostatic head4 – Seawater Pressure or 4 – Seawater Pressure or hydrostatic headhydrostatic head
Area 4 and its pressure effects do not exist Area 4 and its pressure effects do not exist on BOPs without tailrods.on BOPs without tailrods.
Hydrostatic Head
Wellbore Pressure
Observations AS 3RD PARTY Verifier
Observations
• There is a small but significant percentage of shear tests where the actual test exceeds the OEM calculation method.
• Deviation between actual shear pressure tests and theoretical calculations varies between OEMs
• Data input requirements vary between OEMs• Some use nominal yield, some use measured
stress from tensile test
Manufacturer X, 18 3/4 15k6.625" OD, 0.813" wall Z-140Shop conditions - no correction for MASP or Hydrostatic
Observations (cont’d)
• Metallurgical advances in drill pipe• S-135 grades are now produced with improved ductility
• Z-140 and V-150 grades • Higher strength, lower ductility, brittle fracture • More common in deepwater• Will ductility improve as it did with S-135?
• Material Test Reports• What material tests produce the most accurate shear
predictions?
Shear Examples – Low & High Shear Examples – Low & High DuctilityDuctility
Low ductility or brittle pipe (left) and high ductility pipe (right). Low ductility or brittle pipe (left) and high ductility pipe (right).
The high ductility pipe required almost 2,000 psi (over 300K lb) The high ductility pipe required almost 2,000 psi (over 300K lb) more to shear than the low ductility pipe even though the more to shear than the low ductility pipe even though the grades were the same, S-135. grades were the same, S-135.
The brittle pipe had cracking on the sides and did not collapse The brittle pipe had cracking on the sides and did not collapse as much as the ductile pipe.as much as the ductile pipe.
Pipe GeometrySince the 2004 study…• Larger OD pipes, thicker walls• Longer internal upsets and tool joints• Increase in verifications for concentric
tubulars, completion strings, wirelines, etc.
• Maximum fold-over limit in some model BOP models
Observations (cont’d)• Shear test repeatability
• Same grade & dimension, different vendor - may produce different test results
• Same pipe heat – variations in measured yield strength, UTS, and percent elongation
• Same pipe – variations in properties along the length of a single joint
• New vs. used (premium) pipe• Variations in shear test measurements
• Wall thickness • Testing Protocol –
• Shear AND Seal• Successful pressure tests – LP and HP
• Shop tests don’t replicate pipe stress conditions down hole.
Observations (cont’d)
• Subsea accumulator volume - shear pressure available for emergency functions
• Evolution of ram geometry₋ Replaceable blade components₋ Low force geometries₋ Pipe Centering
Industry Observations
• Keeping track of drill pipe on the rig – not easy
• Sharing of data – has improved in recent years
• Attention to unusual loading conditions• Side load• Bending load• Drill string in tension, compression, or torsion
GTC Shear Study
Lloyd’s Energy Group Technology Centre (GTC)Sinagapore
Objectives of Singapore GTC• Providing a catalyst for accelerating growth• Engagement with clients and government via
collaborative projects• Enhancing technical edge by focusing on R&D
Themes – Technology Readiness Level (TRL) 4-6• Developing complementary technology to
Southampton GTC • Providing facilities for internal and client training• Providing a mechanism for technology and skills
transfer
Shear Ram Reliability Study Phase 1 Objectives
1. Develop FEA modeling method using fracture theory and determine what material tests are required to obtain accurate results vs. actual shear tests of same pipe.
2. Evaluate the relationship between material properties and forces applied during BOP shearing scenarios.
3. Evaluate the relationship between thin-wall and thick walled tubulars.
4. Collect and analyze joint industry shearing data for all grades of tubulars, BOP models, and shearing ram configurations.
5. Repeatability/variance of shear pressures for a given set of drill pipe.
Target Outcome(s)/Benefits
• Develop or refine shear ram calculations and modelling techniques based on empirical evidence, using appropriate statistical methods, and determine appropriate factors of safety.
• Develop more accurate mathematic models for predicting shear capability, and statistical reliability
Project Motivation• Shear prediction is currently empirical – loosely based on DET and
OEM test data directly or indirectly. Different formulas for each OEM.• Most of the OEMs and LRED currently use variations of the
Distortion Energy fracture theory. • Anecdotal results show that the theoretical shear pressures are
much higher than actual shear tests in majority of cases, previous exception cases noted.
• For a given grade of pipe, there appears to be a rather large distribution of test results for force required to shear the pipe.
• Effects of ductility variation for a given nominal yield pipe• Industry is rapidly changing – new pipe grades, improving quality
within pipe grades, new ram designs. • Prediction based on historical data becomes outdated. No method for
new situations.
Project Goals
• Scientific: Understand shearing, verify theoretical modeling with new fracture and plasticity theory.
• Practical: Explore variation of shear force within one pipe, within one heat batch, within a pipe grade.
• Long term: develop theoretical prediction tool based on standard material testing.
Fracture Theory and FEA Modeling
• Application of a different fracture theory in Engineering Mechanics Literature (Mohr- Coulomb Criterion) – crack initiation as an extension of plasticity theory.
• FEA Modeling – element removal when fracture criterion is met – simulated crack initiation and propagation.
• Critical is the determination of plasticity and fracture coefficients from material testing.
Plasticity Theory
Distortion Energy Theory
The distortion energy theory says that failure occurs due to distortion of a part, not due to volumetric changes in the part (distortion causes yielding, but volumetric changes due not).
Distortion Energy Theory is less conservative than Maximum Shear Strength Theory (Tresca Criterion), but more conservative than the Maximum Normal Stress Theory (von Mises Yield Criterion)
Assumes compressive and tensile yield criteria are equal
F = 0.577 x SF = 0.577 x SY Y x Ax A
Where:Where:F = Force, lbsF = Force, lbsSSYY = material tensile yield strength, = material tensile yield strength, psipsi0.577 converts 0.577 converts tensile yield to sheartensile yield to shearA = cross-sectional area of drill pipe, A = cross-sectional area of drill pipe, inin22
Does the distortion energy theory accurately model fracture of newer, stronger, less ductile drill pipe?
Is there a better way to model increasingly more brittle fracture characteristics, in order to calculate force (hydraulic operating pressure) required to shear a particular tubular?
MIT Research, 2007 - 2012
• Have applied a different fracture theory to predict material failures in automotive, structural, and naval applications
• The Mohr-Coulomb fracture theory, aka the Coulomb Criterion
• Applied a different methodology to traditional Finite Element Modeling.
• Traditional FEA does not address initiation of cracks, but only propagation of cracks
• This approach takes into account crack initiation, and then incorporates the removal of the element from the model once yield criteria is exceeded
Mohr–Coulomb Yield (failure) Criterion(aka Coulomb Criterion)
Similar to Maximum Shear Strength Theory (Tresca Criterion), but take also applies to materials for which the compressive strength far exceeds the tensile strength
Mostly used geotechnical and structural engineering to determine shear strength and fracture angle
Source: MIT Paper
Coulomb Criterion Applied to Finite Element Modeling (FEA)Research Phase 1
Phase 1 Methodology
• Create advanced material test coupons from pipe • Preferably on fish that have already been tested
• Data analysis to get material coefficients from material tests.
• Plug those material coefficients in FEA modeling of BOP/Pipe shearing
• Compare those FEA results against actual shear test results and calculations using existing Distortion Energy Theory techniques
Material Testing to support the MCC
Material Testing results are then mapped and a 3-D best fit is determined
This determines the yield surface as predicted by the Coulomb Criterion
Source: MIT Paper
FEA Model
That material property data is then applied to every element in the FEA model.
Source: MIT Paper
Seek minimum adequate input set
• Material constants needed for FEA can be determined based on variable amount of input data from material testing.
• Determine minimum adequate data input set.1) MTR data (Yield, UTS, % elongation)2) Tensile curve3) Compression curve4) Torsion Curve5) Notched Tensile coupon6) Tensile coupon with central hole
7) Charpy
Variability
• Correlate FEA results against current theoretical calculation methods and actual shear test results
• Repeatability/variance of shear pressures for a given set of drill pipe.
• Variations in shearing force:1) Within one pipe2) Among pipes from the same heat/metallurgical batch “identical MTR row”3) Among various heats on the Same Purchase order4) Within a pipe grade (S-135, Z-140, V-150)
Current Project Status
• FEA Model in Development
• Establishing JIP
• Obtaining shear test data
• Corresponding material test data
Coulomb Criterion Applied to Finite Element Modeling (FEA)
Future Phases of Research
Practical Applications
Future Proposed Extension of the Study – Practical Applications1. Shear Prediction tool possible with existing MTR
data, pipe & ram geometry.2. Shear prediction tool possible if additional test(s)
added to MTR standard.• Provide recommendations for modifications to
standard industry shear testing and material testing protocols, if warranted.
3. Investigate the effects of loading on the drill string and how that affects force required to shear
• Tension, compression, bending, torsion, “Side Load”
Future Proposed Extension of the Study – Practical Applications (cont’d)4. Evaluate the effectiveness of existing shear designs
relative to of complex tubular geometries, such as VIT, concentric tubulars, wirelines, etc.
5. Have a theoretical method for looking at new materials6. Have a theoretical method for looking at alternate rams
ram geometries.7. Ability to affect multiple shears prior to changing out
ram blocks and rubber goods.8. Ability to shear tool joints using casing shear rams or
modified blind shear rams. 9. Shearing at depth or in a hyperbaric pressure chamber
BOP Performance Signature Curves
Use of fiber optic strain gauges as a diagnostic tool
Full trace of pressurization and make up of rams on solid steel mandrel.M
icro-
Stra
in
Time milliseconds
Applications of the Technology
• BOP Use Cases• Shear Testing• Establishing healthy state vs. known failure signature
data• Long term potential for real time monitoring
• Other non-BOP use cases• Tensioners• Compensation• Riser stress monitoring
• Non-invasive• Intrinsically safe• Easily calibrated
Acknowledgements
• Ted Cole• Andy Frankland• Manfred Lin• Chris Tolleson• Allan Turner• Greg Childs• Jeff Sattler
• A*Star• http://www.micronoptics.com/ • Micron Optics• http://www.a-star.edu.sg/
• Students, Faculty and Staff at MIT
References
• International Journal of Fracture, “Application of extended Mohr-Coulomb criterion to ductile failure,”
• Yuanli Bai, Thomasz Wierzbicki, May 2009
• International Journal of Plasticity, “A new model of metal plasticity and fracture with pressure and Lode dependence,”
• Yuanli Bai, Thomasz Wierzbicki, 2007
• MIT Thesis Paper, “Numerical Analysis of a Shear Ram and Experimental Determination of Fracture Parameters”
• Evangelos Koutsolelos, 2012
• “Mini Shear Study“ • West Engineering Services, 2002
• “Shear Ram Capabilities Study for the US Minerals Management Service, Rev 1”
• WEST Engineering Services, November 2004
Integrating ModuSpec and WEST Engineering Servicesto advance excellence in drilling safety, integrity and performance
For more information, please contact:
Covey HallGlobal Manager for Consulting Services
Lloyd’s Register Energy – DrillingLloyds Register Drilling Integrity Services, Inc.1330 Enclave Parkway, Suite 200Houston, TX 77077T +1 832-295-7154E [email protected] www.lr.org/drilling
