Abstract

Since the inception of deep water operations, drilling riser seal component failures have been a persistent problem worldwide. Traditionally these failures have required that the drilling riser be pulled, the affected seals replaced and then the drilling riser re-installed; resulting in substantial rig down time and expense to the operators and service companies. Seal-Tite International has developed a unique array of pressure activated sealants able to withstand the high pressure and extreme temperature conditions associated with subsea drilling and production operations. The sealant is polymerized by the differential pressure created through the leak sight. The polymerization process only occurs in the sealant that passes through the leak sight; all other sealant remains liquid and can be circulated out of the well with no damage to any of the well components. Subsequent to extensive testing, pressure activated sealant technology was utilized to repair a leaking joint in a drilling riser choke line at approximately 4200 ft water depth in the Gulf of Mexico. The leak was repaired and the client was able to continue and complete drilling operations with no downtime. The riser was tested to operating pressure every three days for the duration of the drilling operation with no leaks observed.

Introduction

In the drilling of deepwater wells, the floating drilling equipment is connected to the seafloor wellhead by means of a riser. This riser consists of the main bore housing the drill string and tools, as well as several ancillary pipes providing the function of choke line, kill line, boost line, and hydraulic power to the subsea BOP's. The riser is made up of numerous sections which are flanged together to provide the total length required. Typically the pressure barriers at each flange are provided by metal-to-metal seals, elastomeric seals or some combination of the two. Each connection must be tested and proved able to withstand the pressure requirements for full functionality during the most critical period of well control operations.

Root cause analysis of rig downtime revealed that drilling riser leaks were a very significant percentage of the overall total. While minor leaks could be tolerated in some instances, critical well control components such as the choke line and kill line must pass stringent pressure test criteria on a routine basis. Failure to pass the test criteria resulted in significant downtime to locate the leak area, disconnect and pull the riser to replace the faulty seals, and then re-run the riser and reconnect it to the wellhead. On a worldwide basis, the financial impact of this downtime exceeded 2 $MM. Transocean identified this area as a priority for development of best practice equipment and procedures in order to minimize future downtime.

Seal-Tite International's pressure-activated sealant technology has been used with success in oilfield leak repair since 1995. However the vast majority of applications were associated with producing wells. Testing and job histories specifically for deepwater drilling operations were minimal. Transocean's Process Improvement Team approached Seal-Tite to learn whether riser leaks were a potentially valid application, and if so to develop a test protocol to qualify the sealant for eventual use.

Testing Program

The objective of the test program was to set up a riser choke/kill line connection and subject it to leak damage similar to that observed on prior leaks. Seal-Tite's pressure activated sealant would be used to repair the leak. The damaged connection would then be subjected to pressure tests similar to that required on the actual location to verify the durability of the seal.

Transocean provided to Seal-Tite a typical pin-and-box connection from a 4″ I.D. riser choke line. The open ends of the tubes were seal-welded and injection/pressure monitoring ports were added. Due to the significant separation forces that high pressure testing would create, a containment frame was constructed to house the connections and allow safe observation of the testing activities. Below in Figures 1, 2 and 3 are photographs of the box connection, pin connection and the testing frame.

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