van Bilderbeek, B.H., Plexus Ocean Systems/Ingram Cactus Company Plexus Ocean Systems/Ingram Cactus Company Milne, I.F., Plexus Ocean Systems/Ingram Cactus Company Plexus Ocean Systems/Ingram Cactus Company Copyright 1991, Offshore Europe.
During the summer of 1988, Plexus Ocean Systems, Ltd. installed the first adjustable mandrel-type wellhead system on a well drilled for Occidental Offshore Pool Harbour with the jack-up rig Inter Ocean II.
The adjustable hanger technology was devised to obviate the need for removal of the BOP stack during surface hanger installation procedures. Conventional technology to that date was limited to procedures. Conventional technology to that date was limited to using slip-type surface equipment when mudline hangers were required in the casing program.
The Adjustable Hanger System received formal recognition when Plexus was awarded the 1987 Scottish Offshore Achievement Plexus was awarded the 1987 Scottish Offshore Achievement Technology Award and the 1989 Special Meritorious Award for Engineering Innovation presented by Petroleum International.
The paper reflects on three (3) years of operational experience gained from sixty-one installations drilled for eighteen different operators in water depths varying from 110 to 300 feet. The data offers insight into the practicality of this new technology which features time saving elements plus superior technical solutions to achieve real safety improvements. The Adjustable Wellhead Technology will be shown to be cost effective in exploration as well as production applications.
The concept of a jack-up drilling system designed to eliminate the need to lift the Blow-Out Preventor Stack (BOP) to install casing hangers was conceived from the desire to introduce a new product into the wellhead market. It was our intention to establish a technological identity for which our company would be recognized in the long term.
From years of experience in jack-up drilling operations, it had become apparent that jack-up wellhead equipment was in need of a new approach. As conventional equipment relies on slip and seal technology, much time is wasted removing and reinstalling BOP's. As an additional consequence, deep wells are left unprotected while casing is being suspended raising questions about the safety aspects of these procedures.
The adjustable hanger design project offered the ideal opportunity to receive research and development support from the United Kingdom government and an industry partner.
The proposed system offers several advantages:
* Reduced installation time thus improving economics.
* Increased safety for both the drilling crew and the environment by performing the entire installation through the BOP.
* Improved technical design which positions the wellhead annular seals between machined surfaces rather than against the often irregular O.D. of the casing.
The following paper aims to demonstrate that the above objectives were met by the adjustable wellhead Jack-Up Drilling System.
Data, compiled over a three year period, incorporates more than sixty (60) wells drilled by eighteen (18) different operators in water depths varying from 110 to 300 feet. Well records produced an average installation time savings of 15.75 hours per well for a typical 30" × 20" × 13-3/8" × 9-5/8" program. Depending upon the area of operation, these time savings have accounted for substantial reductions in wellhead expense.
However, the most important aspects of the adjustable wellhead are its technical superiority over conventional systems and improved safety for both workers and the environment.
In jack-up drilling operations, frequent use is made of mudline suspension equipment as a means to support well casing at the ocean floor. This enables a jack-up rig to move off location leaving the well protected under abandonment caps installed in selected hangers. Such a temporarily suspended well can be reentered by means of a subsea wellhead conversion or by reengaging tieback risers to a production platform.
The use of mudline hangers introduces the requirement to land casing at a location away from the wellhead. As no systems were available capable of landing at two locations simultaneously, the standard solution was to support casing at the surface location using slips and seals.