This paper describes the equipment and procedures used to install welded conductors on Shell U.K. Exploration and Production's Tern Platform located in 550 feet of water in the North Sea. The equipment and procedures which were used allowed conductors to be installed without interrupting drilling and producing operations. This method of installing conductors is more economical than conventional methods and allows conductors to be installed at a schedule dictated by the progress and success of the drilling program.
The placement of conductors into offshore platforms can be divided into three separate operations defined as follows: 'Installation' refers to placement of the conductor down to a penetration in the sea-bed achieved by the conductor's own weight. 'Drive' refers to achieving further penetration by means of an impact or vibratory hammer. 'Drill/drive' refers to achieving further penetration by using a combination of drilling a lead hole and driving with an impact or vibratory hammer. This paper focuses on the equipment and procedures used in the 'installation' of conductors in the Tern platform, that is, to a penetration achieved by the conductor's own weight.
The placement of conductors in offshore platforms is typically accomplished with a crane barge during the installation of the platform, with the drilling rig as part of the drilling program, or with a combination of the two approaches. The choice as to which method to use is influenced by several factors:
Cost of crane barge or drill rig spread vs. speed of installation. While crane barges typically have a higher day rate than drilling rigs, they can install several conductor strings simultaneously and can handle longer section lengths than a drilling rig.
If the drilling and completion program is more successful than planned, several unused, but paid for, conductors which were installed by the crane barge will be left stockpiled in the platform.
By making conductor installation part of the drilling program, the conductors can be installed in an "as-needed" basis, thus, there is no stockpiling of conductors in the platform.
The increased speed of conductor installation by crane barges allows wells to be brought on-line sooner.
Conductors for the Tern platform were installed by using a conductor jacking spread provided by Marine Contractor Services, Inc. in conjunction with Varco-BJ Ltd. and adapted for use on the Tern platform by the operators Shell Expro, the Shell/Esso U.K. North Sea joint venture.
On the platform, the conductor jack was set up adjacent to the drilling rig as shown in Figs. 4 and 5. Because this equipment can operate independently of the rig, conductors were installed while drilling operations were ongoing.