BH19 Cuttings Transport and Borehole Cleaning
Hole cleaning should be assessed as an operating outcome, supported by observations and an appropriate drilling method. An annular-velocity calculation can describe part of the case, but a single calculated number cannot establish that a changing hole is being cleaned effectively.
Use geometry carefully
The ideal annular area depends on the bore diameter and the outside diameter of the drill string. The recovered geometry guide provides the calculation. Real holes may differ from the assumed circular dimensions, and different assemblies may occupy different sections of the return path. Record those limitations rather than presenting the ideal area as a measured downhole condition.
Use a stated airflow basis. Reference-volume flow divided by area and local actual gas flow divided by area do not describe the same quantity. In a return containing gas, water and solids, a simple gas calculation does not establish the motion of all phases.
Describe the observed returns
A useful field log connects the observation to depth, tooling, operating state and time. Record changes in the appearance or continuity of returns, relevant water observations and any associated changes in measured operating conditions. Keep the description factual and leave the diagnosis separate.
Avoid interpreting one surface observation as proof of a particular downhole cause. If conditions depart from the approved method, the contractor’s responsible specialist should determine the next action. This guide does not prescribe universal flushing durations, velocity targets or pressure increases.
Review the whole operating interval
For performance comparison, include drilling time, cleaning time and interruptions. A fast penetration interval may not represent better overall performance if it is followed by additional recovery or cleaning work. Compare completed, accepted work against the full elapsed and operating records.
When proposing a tooling or compressor change, identify what result is expected and how the change will be assessed. Record the baseline first. Without a comparable baseline, a larger compressor can be credited for improvement that actually came from a changed formation or another simultaneous adjustment.
Prepare a review request
Provide the hole and drill-string dimensions, hammer details, available airflow evidence and a dated operating log. Include the contractor’s approved cleaning method and any deviation that prompted the enquiry. Manufacturer-specific operating guidance must be checked for the actual tooling.
Discuss the air requirement: use the project enquiry brief and attach the relevant interval records. Continue to Wet-Hole Drilling when water becomes a material part of the return conditions.
Related pages: Bore Diameter vs Air Requirement · Annular Velocity · Wet Hole Drilling and Water Ingress