New Technologies for BOP Shearing09 October 2013

Covey HallGlobal Manager for Consulting ServicesLloyd’s Register Energy – Drilling

Agenda

• Motivation for the study

• GTC Shear Study

• Ongoing project

• Future project phases

• Acknowledgements

• References

History2003 and 2004 Shear StudiesPerformed by WEST Engineering for the MMS

Understanding the Shear Function

Last resort is to shear pipe and secure the well with the sealing shear ram.

Failure to shear could result in a major safety and/or environmental event.

Improved strength, larger and heavier drill pipe adversely affects the ability to successfully shear and seal.

Actual 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 Shear Blades crushing the drill pipe and beginning the shearing (or breaking) operation.

Observations as a Third Party Verifier

• There is a small but significant percentage of shear tests where the actual test exceeds the OEM calculation method.

• Degree of 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

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? Tensile? Charpy?

Shear Examples – Low & High Ductility

Low ductility or brittle pipe (left) and high ductility pipe (right).

The high ductility pipe required almost 2,000 psi (over 300K lb) more to shear than the low ductility pipe even though the grades were the same, S-135.

The brittle pipe had cracking on the sides and did not collapse 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

• What does the distribution look like? What are the important variables?

• 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

• Testing Protocol –

• Shear AND Seal

• Successful pressure tests – LP and HP

• Normal shop tests don’t replicate pipe stress conditions down hole.

Observations (cont’d)

• Attention to unusual loading conditions

• Side load

• Bending load

• Drill string in tension, compression, or torsion

• Evolution of ram geometry₋ Replaceable blade components

₋ Low force geometries

₋ Pipe Centering

Shear Study Being Conducted byLloyd’s Energy Group Technology Centre (GTC)Singapore

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.

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

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.

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

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 SY x A

Where:F = Force, lbsSY = material tensile yield strength, psi

0.577 converts tensile yield to shearA = cross-sectional area of drill pipe, in2

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.

Has been applied to modeling steel in ship hulls in recent years.

Source: MIT Paper

Coulomb Criterion Applied to Finite Element Modeling (FEA)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

Material data(From LR/vendor)

Mathematical analysis(IHPC)

Calibrate model parameters Ci

σe

εeεf

Benchmark failure criterion

Shear ram FE model

Shear force & stress profile

Load condition

Project Procedure

First stageSecond stage

FEA Model

That material property data is then applied to every element in the FEA model, and the simulation is then run.

Very preliminary FEA analysis….

Very preliminary FEA analysis….

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) Variations in yield, ultimate strength, elongation, ductile/brittle fracture, etc Within one pipe

2) Among pipes from the same heat/metallurgical batch “identical MTR row”

3) Among various heats on the Same Purchase order –

4) 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 Applications

1. Shear Prediction tool possible with existing MTR data, pipe & ram geometry.

2. Shear prediction tool possible if additional test(s) added to MTR standard (compressive, torsion, charpy, etc.)

• 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 materials

6. 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.

Acknowledgements

• Ted Cole

• Andy Frankland

• Manfred Lin

• Greg Childs

• Jeff Sattler

• A*Star• http://www.a-star.edu.sg/

• Micron Optics• http://www.micronoptics.com/

• 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 covie.hall@lr.orgW www.lr.org/drilling