Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Risk Assessment of Surface vs. Subsurface BOP’s on Mobile Offshore Drilling Units

Prinicipal Investigators:

Jerome Schubert and Mahmood Amani

Sponsor:

Minerals Management Service

Completion Date:

August, 2006

Final Report ID#

A172(Click to view final report abstract)

OBJECTIVE:

We propose to study the applicability and risk of applying this technology to waters such as the Gulf of Mexico. In this study we intend to determine the risk of utilizing not only surface BOPs in floating operations, but also the advisability of using subsurface shear rams that may be needed to shear the drillstring during an emergency such as an unplanned disconnect.

INTRODUCTION:

In an attempt to mitigate many of the problems associated with deepwater drilling, some operators such as Woodside Energy Ltd., Shell, TOTAL, and Unocal have either considered using or have used surface BOPs with small diameter, high pressure risers in floating drilling operations. The myriad of problems associated with drilling in deep water have been extensively covered in the literature. Some of the problems that this technology can help to alleviate are directly associated with the large diameter marine risers currently being utilized.

As water depth increases, the weight of conventional risers increases to a point that only a very few fifth generation floating rigs have the capability to drill in ultra-deep water. The deck loads increase tremendously, the volume of mud required to fill the riser increases, and the choke line friction increases to a point to where successfully circulating a kick from the well becomes almost impossible. The small diameter, high pressure riser can alleviate the deck load requirements, reduce the volume of mud required, and eliminate the high choke line friction pressure experienced with conventional marine risers. This will also, minimize the problems associated with riser gas.

However, this is relatively new technology, and there is inherent risk in applying any new practices. Even though this technology is relatively new, it has been successfully applied in a number of international locations, mostly in calm waters, where currents are low, and storms are not common. Now, some operators would like to apply this technology to waters that are susceptible to high currents, and storms.

We propose to study the applicability and risk of applying this technology to waters such as the Gulf of Mexico. In this study we intend to determine the risk of utilizing not only surface BOPs in floating operations, but also the advisability of using subsurface shear rams that may be needed to shear the drillstring during an emergency such as an unplanned disconnect.

BENEFITS TO MMS AND THE OIL & GAS INDUSTRY:

MMS would have an important document to help assess the risk of utilizing relatively small diameter, high pressure risers and surface BOP systems with and without subsurface shear rams. This document will aid the MMS in their approval process of applications to drill submitted by the operators that propose the use of this technology in the Gulf of Mexico and other areas of the U.S. OCS. The Oil & Gas Industry would have accesses to a well written document that could be utilized by drilling engineers and companies alike as a guideline for the risk of utilizing surface BOPs and high pressure risers on MODUs.

DEPLOYMENT OF RESULTS:

The results of this work will be conveyed to OTRC, the MMS, and the petroleum industry through an M.S. Thesis, conference presentations, publication in trade journals, progress reports, and a final progress report. All final versions of thesis and reports will be provided to the OTRC and MMS upon completion of the progress.

PROJECT PLAN:

Scope and Plan:
1. A literature review to assess the state of the art in the use of surface BOPs on Mobile Offshore Drilling Units, MODUs. We will study the equipment that is currently being utilized by these operators and drilling contractors; where this technology is being applied; as well as sea conditions (e.g. current, wave height, and storm frequency and severity). We will compare the sea conditions where surface BOPs are utilized on MODUs to those in the Gulf of Mexico.
2. We will perform an analysis of the frequency of riser failures for both conventional large diameter risers as well as the smaller diameter high pressure risers. We will also review the causes of the failures. However, we do not intend to perform the failure analysis ourselves, just review the analysis performed by others.
3. Based on this failure analysis, we will determine the proper risk evaluation tools that are available today and analyze the risk of utilizing a surface BOP system in deep water on a MODU.
4. Based on the above risk analysis, we will determine the value and/or need for subsea shear rams to be used with high pressure risers and surface BOP systems. We will finish this task with a shorter analysis of the risk involved with utilizing the subsea shear rams.
5.We will document the results of this work in a final report that will be provided to the OTRC and the MMS. The final report will include all M.S. theses written on the project.

 
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