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Torpedo Piles for Gulf of Mexico Applications
OBJECTIVE: Develop and calibrate a method to predict penetration and pullout capacity for torpedo anchor piles. Torpedo piles could be used in the Gulf of Mexico as anchors for temporary and permanent mooring systems and as conductors for deepwater wells. This work will produce data from laboratory-scale and field-scale model tests so that design methods can be validated and calibrated.
INTRODUCTION:Recently, US operators have shown an increased interest in using torpedo piles for anchoring deepwater facilities. They provide a potentially economic alternative to conventional anchors. Petrobras has reported the successful use of torpedo piles both as anchors and more recently as well conductors.
Fugro (a geotechnical consultant) is currently sponsoring a 2-year long research effort at the University of Texas on the methods to predict torpedo pile penetration and performance. This research is intended to address fundamental concepts ands is not directed at a particular, proprietary type of anchoring system. Applications could include a variety of pile types and even surface conductors for deepwater wells.
This ongoing research project started in September 2005 and is expected to be completed by September 2007. The project consists of four phases. The first phase consists of a thorough review of the literature about torpedo piles and other seafloor penetrator experiments. The second phase consists of developing a set of design models to predict the penetration and the capacity of torpedo piles as a function of seafloor velocity, pile geometry and soil shear strength. The third phase consists of conducting a series of 1:30 model torpedo pile experiments at The University of Texas at Austin using their large soil bed facilities. The data will be used to calibrate the design models. The final phase will consist of performing a limited number of offshore field tests using a 0.3-m-diameter, 6-m-long torpedo test pile. These data will be used to further calibrate and validate the design models in field conditions.
A JIP has been recently formed with support from Fugro, ExxonMobil and Shell to fund the offshore test. The cost of the offshore test alone is approximately $150,000. Participants have agreed in principal to MMS participation for a minimal participation fee. MMS will be given access to the confidential data that are produced, will be able to review and provide comments for project reports, and will be given an opportunity to provide guidance to the research effort. The confidential information will remain proprietary to and publishable by Fugro, ExxonMobil, and Shell.
BENEFITS TO MMS & INDUSTRY: Torpedo piles can provide a significant economic advantage for anchoring mooring systems in deepwater. It is beneficial both for MMS and industry to develop a fundamental and common understanding of torpedo pile behavior before a project-specific design is developed and needs to be evaluated by MMS. This project affords this opportunity to the MMS to provide input and have timely access to results at a minimal cost.
DEPLOYMENT OF RESULTS: The results will be deployed in project reports, technical papers and a set of calibrated design methods.
PROJECT ORGANIZATION & TIMING:PROJECT PLAN (2006-2007):
Scope and Plan: Additional laboratory model data will be obtained. The predictive models will be calibrated with laboratory data. The field tests will be conducted, and the data will be used to validate the calibrated design models.
PRINCIPAL INVESTIGATOR (S) & OTHERS INVOLVED IN PROJECT:PI(s): Robert B. Gilbert, post-Doctorate research assistant.
DATE: June, 2007Project Title: Torpedo Piles JIP
MMS Project: 575 TO Number: 39736
Project PI: Robert Gilbert
COTR: L. Medley
Estimated Completion Date: 9/1/2007
Project Description:
Develop and calibrate a method to predict penetration and pullout capacity for torpedo anchor piles. Torpedo anchor piles could be used in the Gulf of Mexico as anchors for temporary and permanent mooring systems and as conductors for deepwater wells. This work will produce data from laboratory-scale and field-scale model tests so that design methods can be validated and calibrated.This ongoing research project started in September 2005 and is expected to be completed by September 2007. The project consists of four phases. The first phase consists of a thorough review of the literature about torpedo piles and other seafloor penetrator experiments. The second phase consists of developing a set of design models to predict the penetration and the capacity of torpedo piles as a function of seafloor velocity, pile geometry and soil shear strength. The third phase consists of conducting a series of 1:30 scale model torpedo pile experiments at The University of Texas at Austin using their large soil bed facilities. The data will be used to calibrate the design models. The final phase will consist of performing a limited number of offshore field tests using a 0.3-m-diameter, 6-m-long torpedo test pile. These data will be used to further calibrate and validate the design models in field conditions.
A JIP has been formed with support from Fugro, ExxonMobil and Shell to fund the offshore test. The cost of the offshore test alone is approximately $150,000. Participants have agreed in principal to MMS participation for a minimal participation fee. MMS will be given access to the confidential data that are produced, will be able to review and provide comments for project reports, and will be given an opportunity to provide guidance to the research effort. The confidential information will remain proprietary to and publishable by Fugro, ExxonMobil, and Shell.Progress:
Phase 1 is complete and Phase 2 is 95% complete, with the prediction model for the penetration of the torpedo pile having undergone evaluation in 36 model anchor tests at The University of Texas at Austin’s soil test bed facility. A plot of predicted versus measured penetrations is provided in Figure 1 below. The results indicate the predicted penetration embedments are generally within +/- 15 percent of the measured values.
A plot of the predicted versus measured vertical pull-out capacity from tests performed so far is provided in Figure 2. The vertical pull-out capacities were measured after the initial set-up was complete (generally 48 hours after installation). The predicted capacities were obtained using the API design method for a driven pile; both the undisturbed undrained shear strength (solid points in Fig. 2) and the remolded undrained shear strength (open points in Fig. 2) were used with the API method. The measured vertical pull-out capacities are best matched using the API method with the remolded undrained shear strength. These results indicate that there has apparently been some “permanent” (at least up until 48 hours after installation) disturbance of the soil in the vicinity of the pile caused by the dynamic penetration and that this disturbance reduces the vertical pull-out capacity. Ongoing tests are directed at investigating if and how this disturbance affects the lateral capacity. Preliminary results indicate that it does not affect the lateral capacity or the combined axial-lateral capacity provided that the load is applied at an angle other than vertical (say 15 degrees off from vertical). Since practical applications with torpedo piles will generally not involve a purely axial load, this effect of soil disturbance may be more relevant to interpreting laboratory and field data (where tests have generally been conducted with pure axial loads) than to design practice.
Phase 3 is also 50% percent complete. Another round of 24 model anchor tests that focus on pile capacity under lateral loading conditions is pending the consolidation of a new test bed. Results from those tests are expected by August 2007. Phase 4 still awaits a test site suitable for all of the JIP participants.
Reports and Publications:
1. Audibert, J.M., Morvant, M.N., Won, J.Y., Gilbert, R.P. 2006. “Torpedo Piles – Laboratory and Field Research,” International Society of Offshore and Polar Engineers, San Francisco, June 2006, Paper No. 2006-PCW-03.2. The following article was presented in the November 2006 issue of Offshore magazine: “Torpedo piles show promise as cost-effective solution for deepwater mooring in GoM.”
Date: December, 2006Project Title: Torpedo Piles JIP
MMS Project: 575 TO Number: 39736
Project PI: Robert Gilbert
COTR: L. Medley
Estimated Completion Date: 9/1/2007
Project Description:
Develop and calibrate a method to predict penetration and pullout capacity for torpedo anchor piles. Torpedo anchor piles could be used in the Gulf of Mexico as anchors for temporary and permanent mooring systems and as conductors for deepwater wells. This work will produce data from laboratory-scale and field-scale model tests so that design methods can be validated and calibrated.This ongoing research project started in September 2005 and is expected to be completed by September 2007. The project consists of four phases. The first phase consists of a thorough review of the literature about torpedo piles and other seafloor penetrator experiments. The second phase consists of developing a set of design models to predict the penetration and the capacity of torpedo piles as a function of seafloor velocity, pile geometry and soil shear strength. The third phase consists of conducting a series of 1:30 model torpedo pile experiments at The University of Texas at Austin using their large soil bed facilities. The data will be used to calibrate the design models. The final phase will consist of performing a limited number of offshore field tests using a 0.3-m diameter, 6-m long torpedo test pile. These data will be used to further calibrate and validate the design models in field conditions.
A JIP has been formed with support from Fugro, ExxonMobil and Shell to fund the offshore test. The cost of the offshore test alone is approximately $150,000. Participants have agreed in principle to provide MMS with limited access to results.Progress:
Phase 1 is complete and Phase 2 is 50% complete, with the prediction model for the penetration of the torpedo pile having undergone evaluation in the first round of 24 model anchor tests at The University of Texas at Austin’s soil test bed facility. The capacity prediction model is under development. Phase 3 is also 50% percent complete. Another round of 24 model anchor tests is pending the consolidation of a new test bed. Results from those tests are expected by May, 2007. Phase 4 awaits a test site suitable for all of the JIP participants.Reports and Publications:
The following paper was presented at the International Society of Offshore and Polar Engineers June, 2006 conference in San Francisco, California: “Torpedo Piles – Laboratory and Field Research”The following article was presented in the November 2006 issue of Offshore magazine:
“ Torpedo piles show promise as cost-effective solution for deepwater mooring in GoM.”
Progress Reports: June 2007 December 2006
