Risk Assessment of Surface vs. Subsurface BOP’s on Mobile Offshore Drilling
Units
Jorge Melendez, Jerome J. Schubert, and Mahmood Amani, Texas A&M University

Executive Summary

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 Blowout Preventers, BOP, 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.

The Harold Vance Department of Petroleum Engineering at Texas A&M University was contracted by the U.S. Minerals Management Service through the Offshore Technology Research Center to conduct a comparative risk assessment of the use of Surface Blowout Preventer Systems and High Pressure Risers vs. conventional Subsea Blowout Preventer Systems and drilling risers in the Gulf of Mexico Environment.