This article highlights the guidelines which shall be followed during tripping and drilling in order to avoid taking kicks. During any open hole operation the mud level in the well shall always be full.
Prevention While Drilling
The following guidelines shall be observed during drilling:
- Warning signs that a kick has occurred while drilling are discussed in this section. At the Driller’s discretion, or under well-specific standing instructions, any one or a combination of these shall justify performing a flowcheck. During the flowcheck, the pipe shall be positioned at the correct hang-off height for the annular and the string rotated slowly (use trip tank). Flowchecking is mandatory in the following circumstances:
- Unexplained increase in mud level in the active system.
- Increase in percentage returns from flowline.
- Drilling breaks at the top of reservoir section exceeding 2 ft in length.
- Free communication flow between Driller, Derrickman and Mud Logger shall be maintained. This shall be monitored by the Drilling Supervisor.
- The mud weight shall be monitored for any reduction which may indicate incorporation of formation fluids.
- The vacuum degasser shall be run if gas is present in mud to prevent a build up of entrained gas progressively lowering the mud weight.
- Connection gas peaks shall be closely monitored for increases between successive connections. Other pore pressure indicators shall also be continuously monitored, to give early warning of increasing pore pressures.
- Regular examination of returned cuttings (in shale zones) shall be made to check for cavings.
Prevention Prior to Tripping
The following shall be carried out prior to tripping :
1. Circulate and condition the hole to ensure that:
- Entrained gas or cuttings are circulated out.
- Mud weight is correct and consistent in the pit and at the flowline.
- Rheology will not cause excessive swab/surge pressures.
2. Line up and inspect the trip tank.
- All line-up valves and flow paths shall be checked and function tested for leaks.
- The level indicator shall be inspected for smooth running and the tank shall be filled before commencing the trip.
- A trip record sheet shall be prepared. The Driller shall be told the reason for the trip and of any indicators of increasing pore pressure or a near balance condition.
3. A backup inside BOP ready for use and crossovers for drill collars etc shall be available close to the rig floor. This shall be used in the event that the drillpipe safety valve does not hold pressure, or if stripping in the hole is required and no dart sub is in the string.
4. Every attempt shall be made to cure static losses prior to tripping out of the hole. The approval from the Head of Onshore/Offshore Operations shall be obtained in the event that the losses are still occurring prior to pulling out.
5. The mud logging and rig floor monitors shall be accurately set with alarms activated before commencement of the trip.
6. The well shall be flow checked for 10 minutes prior to pumping the slug to ensure the well is stable with the ECD effect removed.
7. A slug shall be pumped. This enables the pipe to be pulled dry and the hole to be accurately monitored. The slug shall be mixed to maintain a minimum of five stands of dry pipe and shall be accurately displaced.
The following precautions shall also be in place prior to tripping:
- All rigs shall have a ‘stabbing valve’ complete with lifting arms immediately accessible on the drill floor which can be quickly attached to the drillpipe
- A flapper type safety ‘gray valve’ shall also be available on the rig floor and shall be installed on top of the full bore ball valve (kelly cock) when stripping into the hole.
- Suitable short crossovers from the 'kelly cock' to other connections in the string (e.g., smaller DP connections in the case of a tapered string) should also be easily accessible on the drill floor and installed on the kelly cock for the pipe currently being pulled or run through the table. A suitable lifting plug (hollow) and air winch should be fitted if the Kelly-cock/X-over combination cannot be easily handled by 2 persons.
Mud System monitoring
- During tripping the trip tank shall be used for accurate measurement of mud volume changes.
- While running in/pulling out checks shall be made to ensure that the trip tank volume changes correspond to the appropriate pipe displacement. A trip sheet shall be prepared prior to the trip and filled in at regular intervals during the trip. (Mud volume and trip tank changes shall be clearly displayed on the rig floor).
- Excessive swab and surge pressures shall be avoided by careful attention to pulling and running speeds.
Note: Calculations can be provided by the drilling Engineer/logging contractor to determine Swab and Surge pressures for both drillstring and casing string. These should be used to determine maximum safe tripping speeds.
- At the start of a trip out, the Drilling Supervisor shall be on the rig floor to witness proper hole fill up and verify that all measures are in place and applied properly. He shall be on the rig floor for at least the first ten stands pulled or until significant over-pulls have ceased.
- If swabbing is expected; do not pump a pill until the string is free of over-pulls.
- If the first 5 stands do not take the right amount of fill up fluid, the bit shall be run back to bottom and the hole circulated again.
- When pulling "wet" stands, a mud saver shall be used and the mud returned to the trip tank in order to check if the hole has taken the right amount of fluid.
Swabbing
To prevent a kick due to swabbing the following Standard Procedure shall be adhered to:
1. Under normal circumstances, CIRCULATE bottoms up (or until the hole is clean) prior to starting a trip in open hole. CHECK returns for hydrocarbon indications.
2. Driller and Contract Toolpusher to CHECK and CALIBRATE trip tank prior to pulling out of the hole.
3. PERFORM flow check for 10 minutes (witnessed by the Drilling Supervisor and Contractor Toolpusher) prior to pumping a heavy pill.
Note: DO NOT pump the heavy pill until the string is free of overpulls and a minimum of 10 stands off bottom.
If hydrocarbons/gas have been encountered or if the hole condition is suspect then the Company Drilling Supervisor and Contractor Toolpusher shall be present for the initial trip (minimum ten stands or until inside previous casing) to witness the correct filling of the hole using the trip tank.
Excessive surge and swabbing pressures shall be avoided by controlled pulling and running speeds. In the event that swabbing is observed or if there is doubt as to whether the hole is taking the correct amount of fluid CONTINUE with step 4.
4. RIH to bottom. CHECK for flow. MONITOR the trip tank for signs of the well beginning to flow. If the well is seen to be flowing, CLOSE in the well and STRIP in hole using the volumetric stripping method.
5. CIRCULATE bottom’s up.
6. CONTACT Operations Engineer and DISCUSS the situation.