The hole conditioning guidelines described in this article should be adhered to in order to safely and successfully run the casing/ liner into the open hole.
Structural Casing
Driven or pre-installed: No hole conditioning necessary
Conductor Casing
- Hole section drilled with seawater/high viscosity sweeps/native clay system with returns to sea bed
- At casing point circulate and condition the mud at the maximum rate until shakers are clean, gas levels are acceptable and mud is in specification
- Sweep the hole with a 100-200bbl high viscosity pill
- Flowcheck
- Perform a wiper trip back to the Drive Pipe shoe, monitoring drags and hole fill
- At casing point circulate shakers clean and condition the mud if necessary.
- Spot high viscosity pill on bottom if necessary
- Flow check and pull out of the hole - strapping pipe using steel line measurements
Surface, Intermediate and Production Casings
- Hole section drilled with returns to surface
- At casing/liner point circulate and condition the mud until shakers are clean, gas levels are acceptable and mud is in specification
- Flow check
- Perform a check trip back to the previous casing/liner shoe, monitoring drags and hole fill
- At casing/liner point circulate shakers clean and condition the mud if necessary, monitoring gas levels (pump high viscosity pill if necessary)
- Calibrate the rig pump efficiency during the conditioning trip prior to pulling out of the hole to run casing.
- Flow check
- pull out of the hole - strapping out using steel line measurement
- Log hole if programmed - a further wiper trip may be necessary if logging highlights poor hole conditions
Remedial Actions
If poor hole conditions are evident during the hole conditioning operations, further remedial preventative actions shall be considered:
- performance of further wiper trips
- conditioning the drilling fluid for greater inhibition, lubricity or mud weight (Rheology should be lowered ie., YP and Gel Strengths)
- modification of the centraliser programme, including stand-off review.
Hole and Mud Condition
- The hole and mud must be in good condition in order to help prevent stuck pipe and improve the likelihood of a successful cement job.
- Mud properties shall be adjusted to obtain the highest level of displacement of mud by cement capabilities.
- Prior to cementing a minimum of casing and annular capacity plus 50% shall be circulated. The well shall be circulated until the shakers are observed to be clean.
- Mud rheology shall be reduced as follows:
- YP<20lb/100 ft2 , 10 minute gel strength < 25lb/100 ft2