This article describes the various issues to be considered for planning an offshore rig move.
1. Well/Jacket Status
Well Plugging Prior to Rig Move
- If the current well path is less than 100 ft from any of the existing wells on the jacket, the wells shall be plugged with deep set plug and BPV. After closing SCSSV, pressure above SCSSV to be bled of to 100 psi and after installation of BPV, pressure above to be bled off to zero psi.
- Wells other than mentioned above shall be plugged with BPV. After closing SCSSV, pressure above SCSSV to be bled off to 100 psi and after installation of BPV pressure above to be bled off to zero psi.
- All the Xmas tree valves to be closed after ensuring zero pressure in the Xmas tree. All annulus pressures to be bled off and all the annulus valves to be closed.
- SCSSV and wire cutting actuator's control lines to be removed/de-pressurised and blind plugs to be installed.
- Well Services shall co-ordinate with Drilling Supervisor on the rig and shall check and bleed off pressures, if any, in the Xmas tree and annuli within 24 hours prior to the rig move.
Wellhead Preparation prior to Rig Move
- Flowlines and gas lift lines to be de-pressurised on all wells on the jacket.
- All annuli to be de-pressurised and all annulus valves to be closed.
- For the well(s) planned to be worked over, flow lines and gas lift lines to be de-pressurised, removed and spaded off with blind(s). Choke in the Xmas tree bean box to be removed.
Jacket Preparation prior to Rig Move
- Gin pole/pedestal jib to be removed.
- Navigation Lights and solar panel to be removed.
- Shut-down panels of the adjacent wells to be positioned away, at safer place, and provided with protective cover, if required.
- Flowlines, gas-lift lines, telemetry lines, instrument lines and adjacent Xmas trees to be provided with steel covers to safeguard them against dropped objects. This may not be required on two-deck jackets. Xmas tree steel cover to have an 18in diameter opening for BPV installation/retrieval or other wireline operations.
2. Location Preparation
Workover Drawings
Introduction
- When a rig has to be moved to a jacket which has one or more flowlines connected, a workover drawing is required. This large scale drawing includes:
- jacket topdeck lay-out
- jacket heading
- wellhead location(s)
- routing of flowlines with accurate measurements of offsets (doglegs) (has to be measured by divers)
- distance of rig footprints from flowlines.
Drawing Description
The rig is projected to scale on the workover drawing, in the anticipated final position.
Distances from flowlines/subsea wells to rig legs are measured accurately. These distances must be not less than 25 ft. If necessary the proposed rig heading must be adjusted so that the distances of minimum 25 ft between rig/jacket and leg/flowline are guaranteed.
Long Term Considerations
Improving Field Layout
Proposed flowline layouts and jacket locations are forwarded by Engineering and Petroleum Engineering respectively for approval by Marine. Discussions should take place between these departments, and Marine should carry out an accurate study with regard to:
- jacket heading
- rig heading
- possibilities for anchor-handling during the final positioning of rigs
- availability of anchoring space for supply boats or a supply boat mooring buoy
- minimum space required for rig manoeuvring
- consideration of future field development, as far as possible.
Design of New Jackets
When jackets or flowlines have to be situated in such locations that only a rig with thrusters can be used (ie., no anchor handling), Petroleum Engineering must be notified and future Drilling Sequences arranged accordingly. Memos and minutes of meetings must be copied and filed for future reference.
The size of jackets has been the subject of considerable discussion in the past. It is important to closely monitor the design of jackets and positioning of conductors prior to installation to ensure that drilling operations can be carried out by the rigs available.
3. Moving Rig
Timing of Moves
After the rig is handed over to the Senior Barge Engineer (by Drilling, Petroleum Engineering or Production) for the final rig move preparations, the
Onsite Marine Officer reports the timing and actual weather to the Marine Manager.
The Marine Manager, in close liaison with the Meteorological Department Representative, the Onsite Marine Officer and Senior Barge Engineer, decides on the time of commencement for the move.
Timing of each move will be judged individually with due consideration to
- weather
- current
- field lay-out
- location of rig departure and arrival site
- seabed conditions etc.
Departures and arrivals at congested locations, eg., jackets, production complexes, flowlines, etc. will normally be done in daylight only. Departures, arrivals and normal towage in open water areas clear of obstructions may be done at any time day or night.
Weather Limits
Rig moves are subject to suitable weather and a favourable forecast for the duration of the entire move. Predicted wind speeds should not normally exceed 15 knots and swell/sea heights should be less than four feet. This limit may be varied depending on:
- wave types and period ie., long swell or short waves or a combination of both
- nature and composition of seabed, eg., hard (B.H. field) or soft (I.S. field)
- proximity of other structures/flowlines from old and/or new rig location
- required positional accuracy on new location, ie., jacket or new drilling location.
Radio Communication
The Marine Officer is responsible for the rig move radios; proper charging or replacing of batteries, and repairs as required. Repairs and ordering of replacement equipment is carried out by
Helicopter Flights
The Marine Officer will normally organise transportation to and from the rig. During rig moves this often entails a special helicopter flight, arranged with TRA.
Helicopters are permitted to land on a rig while afloat, but not during jacking or pre-load operations.
Location Positioning
Prior to moving onto locations, the dive support vessel will ensure the location is marked with a large Norwegian type marker buoy (on a tight rope).
The rig will then pin down as close as possible to the location on the approximate final heading.
A wire is run down from an 'A' frame on the stern of the rig, attached by divers to the wellhead and tensioned to enable accurate final positioning of the rig.
With the rig held in position by the towing vessels the legs are jacked down until they spud with the seabed.
Jacking operations continue to raise the rig up to the desired air gap.
Water is taken onboard to pre-load the rig to achieve maximum leg penetration and this is held for 12 hours.
The pre-load water is dumped and the rig is jacked up to the desired air gap.
The towing tug will remain connected to the rig ready to move until pre-load tests are completed (start dumping pre-load).
The Marine Officer in charge will remain on the rig till the pre-load tests are completed.
When the rig is jacked up and skidded out, the divers will measure the penetration.
4. Well Handovers
It is essential to establish a formal procedure for the handover of wells and jacket from Production to Drilling Department and from Drilling to Production Department prior to a rig moving onto or off that jacket. This procedure contains:
- wellhead Jacket Inspection Method
- plugging/securing of the wells
- the Handover Certificate
Handover Requirements
Well Services shall prepare a Well Securing Programme in accordance with established procedures and will execute the job in consultation and co-ordinate with PD, EM.
Rig move co-ordination meeting shall be arranged by Marine Department, attended by representatives from Production, Engineering, Transport and Drilling Department to discuss and agree on all activities required prior to rig move.
De-pressurising of tubing, flowarms and annuli shall be completed by Well Services Supervisor following plugging of well by wireline.
Flowarms and other equipment shall be removed by Engineering and Wellhead Supervisor as required.
When the Drilling Supervisor and Wellhead Supervisor are fully satisfied that the jacket is de-pressurised and in all respects safe for the rig to move, the “Hand Over Certificate” shall be signed and faxed to Doha base.
After completion of drilling operations, and prior to rig move when Wellhead Supervisor and Toolpusher are fully satisfied that the jacket is de-pressurised and in all respects safe for the rig to depart, the Hand Over Certificate shall be signed and faxed to Doha base.
After rig move, Wireline section shall unplug the well(s) if required.