Minimum standards, which must be complied with and specifies general practices that enable the planning, safe and successful execution of coiled tubing operations.
PLANNING
1. Coiled tubing operations on live wells need a very thorough preparation and essential parameters have to be taken into consideration during the preparation.
2. Last drift run done in the well if the operation takes place in a production well. Note that if the last drift run is older than 6 months and if the well has produced since, a new drift run and top sediment run has to be done to assess the feasibility of a CT intervention.
3. When a Coiled Tubing unit is installed on a well the installation become a combine installation where Simultaneous operations are going to take place.
4. In case a tapered CT string is used, ensure it is homogeneous and that the limit resistance of each part is similar.
5. Check that the CT string has not been cut and welded, in such case it looses its sour service resistance unless the weld has been heat treated.
6. A minimum of 2 barriers is mandatory at any time or sequence of the operation.
7. The CT BHA should be equipped with dual check valves, disconnecting device and circulating valve on each run.
8. In hot wells, the buckling of the tubing string must be evaluated and run simulation (Drag forces) must be done by the service company to assess the feasibility of the operation.
9. Preferably chose a unit equipped with a devise Checkling the ovality of the CT during operation as a dissymmetry would impact drastically the CT collapse resistance.
10. A stack up schematic of the equipment over the well must be done to ensure there is enough space on location to perform safely the operation.
11. Specialised competent personnel is required to supervise CT operations.
12. For offshore operation the heaviest load must be compared to the crane capacity (it is often the CT reel).
13. The job history of the CT must be QA/QC to ensure it won’t reach its limits during the CT operations
– The cost of a new reel is far cheaper than a work-over.
14. Some CT operations may require notifications to the local authorities.
15. All CT equipment must be certified: like lifting equipment, pressure containing equipment, tank, etc.
JOB PREPARATION
1. During a safety meeting involving all personnel, ensure that everybody is made aware of:
- Operations objectives
- Role and responsibilities of each individual
- Permit to work procedures
- Equipment lay out
- Danger related to chemical
- Emergency response procedure
- Simultaneous operation risk assessment.
2. BOP and stuffing box: function test all rams, Check that all functions (Close all rams) can be done with the power pack shut down.
3. Pressure test BOP to maximum expected wellhead pressure.
4. Check the power pack Emergency Shut Down.
5. Check the chain tension – operate in low and high gear against CT and look for marks on CT.
6. Check that the reel brake function properly.
7. Check the depth counter is working properly.
8. Pump the disconnecting ball through the CT to establish volume and proper drift.
9. Check the good working condition of the gooseneck rollers.
10. Ensure the reliability of the weight indicator during the rig up of the gooseneck and after by performing a pull test.
11. When positioning the CT unit on site, ensure that the angle of the CT from the reel is less than the maximum capacity of the gooseneck to avoid excessive bending.
12. Ensure that disconnecting ball and the ball use to open a circulating valve above the BHA are on site and clearly identified.
JOB PROCEDURES
1. A detailed programme covering as a minimum the following points must be approves by the Well Operation Manager prior to start the installation:
- Detailed list of all equipments to be installed showing dimension and weight
- Lay out of the CT and associated equipment on the location
- Well production and service history including logging wire line operation (Drift runs, Top sediment, etc)
- Well diagram showing all details of the casings and completion
- Well deviation and profile
- Diagram of the BHA to be run with the CT and associated list of fishing equipment available on site
- Operational limits of the equipment in term of tension, collapse, burst. This for the Well, for the CT and for the surface equipment
- The operational limits of the CT must be calculated taking into consideration the triaxial stresses – Von Misses Ellipse
- Where the reference point (zero depth) has to be taken (Rotary table, X-tree, Swab valve…).
2. When running in hole perform a pull test every 300m (1000ft) and compare the result to the drag simulation done by the service company. If the result diverge too much – i.e. the tension seen during the pull tests are superior to the calculated tension – and if the gap increase at each check point, the decision can be made to abort the operation as it is likely that the CT will end up stuck in hole.
3. If several runs are made, change the pulling tests location to avoid to generate too much fatigue at the same point of the CT string.
4. Never exceed the safe operating limits of the equipment.
5. When running in hole do not tag more than 1500lbs.
6. When pulling out of hole always stay within the Von Misses Ellipse stress limits of the concerned part of the CT string.
EMERGENCY PROCEDURES
Different scenarios must be covered when preparing the SIMOPS – What to do if:
- Platform Emergency shut down when CT is out of hole
- Platform Emergency shut down when CT is in the hole
- Leak in Coiled Tubing at Surface
- Leak at Coiled tubing below surface
- Leak in Surface Check Equipment – Stuffing Box leaks
- Surface leak other than the stuffing box
- Failure of the injector – CT run in hole under its own weight
- Failure of the injector – CT run out of hole under the well pressure
- Coiled Tubing collapse at surface – This situation generates leak at stuffing box
- Coiled Tubing breaks at surface
- Coiled Tubing reel back tension motor fails – The sffect is that the Ct will unspool
- Coiled Tubing stuck in hole
- Power pack failure