RIASSUNTO
Abstract
The reasons behind Statoil choosing to include continuous circulation in HPHT Managed Pressure Drilling operations in the Kvitebjørn Field in the North Sea are explained. The paper will also discuss the preparations for the operation and the equipment and manpower required to enable the Continuous Circulation System to be installed and operated on the platform. Results recorded by the drilling team during the drilling period are described. Reference is also made to other applications of the Continuous Circulation System.
Introduction
The Continuous Circulation System (CCS) allows drill pipe connections to be made up or broken out without stopping drilling fluid circulation to the drillstring. Uninterrupted circulation is particularly beneficial when drilling pressure sensitive formations where adding or removing the dynamic component of the circulating pressure destabilizes the pressure conditions in the well bore, causing hole problems, lost time and additional costs.
The design, development and past application of the CCS are covered in SPE 90702, SPE 102851 and SPE 102859.
The core of the CCS is a pressure vessel constructed from three blow-out preventer (BOP) bodies surmounted by a snubbing device which can apply sufficient torque to make or break drillpipe connections and control the vertical movement of the disconnected drill pipe against the dirculating pressure. The pressure vessel (Main Unit) contains three sets of rams, blind in the centre and pipe rams top and bottom, the lower set being upside down to contain pressure from above. When in use the Main Unit is located on the rotary table with the drillstring passing through it. To make/break a connection while continuing to circulate, the drillstring is landed in slips connected to the Main Unit and the pipe rams closed, isolating the tooljoint before filling the cavity between the rams with drilling fluid at circulating pressure. The snubber then breaks the connection and allows the pin to rise under control before closing the blind rams. Circulation continues through the open drillpipe box below the blind rams and is closed to the Top Drive, before bleeding off the pressure above the blind rams and opening the upper pipe rams to allow the next stand/joint of pipe to be picked up. The procedure is reversed to make the new connection.
The principle attributes of the CCS are:
• Only one modification to the rig is required to instal the system.
• No changes or additions to the drillstring are needed.
• All connection operations are safely confined within a pressure container constructed from conventional blow-out preventer components.
• The connection process is ""hands off??.
The CCS can be used on any rig equipped with Top Drive and with sufficient height clearance within the derrick to allow a drill pipe stand to be raised 3m above the Rotary Table for access into or withdrawal from the Main Unit.
It can be used to drill with open annulus returns or in conjunction with MPD rotating BOP, closed annulus systems.
The earliest commercial application of the CCS was the successful re-entry and deepening of a high pressure gas discovery well offshore Egypt in 2005, (SPE 102859³). Since then it has found application in re-entering and deepening HPHT gas wells offshore Norway for two major operators and is currently being introduced to drilling operations offshore Brazil.
This paper will:
• Discuss the reasons for using the system to drill the reservoir sections in the Kvitebjørn wells
• Describe the installation and operation of the system
• Review the results of the operation and any lessons learned.