Can any one advice on Standards and Policies for requirement of 36" Diverter for Jack up Rig.
Can anyone share the experience using 36" diverter.
If originally 36" diverter is not the part of rig equipment. What is the availability of 36" Diverter for a shallow Jack up rig drilling Operation in Middle east area.
What are the mitigations if we could avoid using the same. I mean, drilling a pilot hole etc.
If the Pilot hole is drilled and confirmed no shallow gas!! Is it require to drill the 36" hole with 36" Diverter ON.
36" hole section is planned to drilled to @ 2400ft.
Appreciate your comments and help
Thank you Steve and Thank you Rajiv for your comments and great information.
As for mitigations, the best way is to avoid shallow gas altogether.
Make sure that the operator optimizes the preliminary shallow gas investigations prior to the rig move. Depending on field specifics, in particular, water depth and ease of access to the location, different techniques can be used, including High resolution surveys combined with 2D and 3D shallow seismic surveys with specific reprocessing for shallow structures.
Look at the concept of drilling small pilot holes for shallow gas investigations. In Asia this has been done by drilling 4-1/2” holes to the required depth with a floating DP vessel. It is considered an acceptable and reliable method of shallow gas detection and major problem prevention. The pilot holes can be left after drilling and it generally does not take long to drill to 2500 ft. If gas is encountered simply move the vessel away from the well.Recommendation is to do everything to avoid shallow gas. If shallow gas is indicated on the surveys position the rig outside the shallow gas areas. this may require directional drilling to reach the initial target(s).
Remember that surface diverter equipment is not designed to withstand an erosive shallow gas flow for a prolonged period (and probably never will). Surface diverters are only used as a means of "buying time" to evacuate the drilling rig. Pretty much all of the diverters fail after shallow flow starts. Shallow gas is from a zone with high permeability and will flow at high rates. The bigger the hole size the bigger the flow rates.
Dynamic kills of shallow gas with existing rig pump equipment are generally only successful if a small pilot hole (8-1/2" or smaller) is drilled and immediate pumping at maximum rates is applied in the early stage of the influx. If the hole unloads it will be impossible to kill, the erosion will increase the hole size and the rig pumps will not have sufficient capacity to kill the well.
Drilling a 36” hole and encountering shallow gas means that the well cannot be killed so you have to prove that there is no gas by drilling a pilot hole(s).
Once you do start drilling make sure that the procedures are in place for maintaining well control. Restrict the penetration rates. Particular care should be taken to avoid an excessive build-up of solids in the hole which could cause formation breakdown and losses. Drilling with heavier mud returns could also obscure indications of drilling through higher pressured formations. The well may kick while circulating the hole clean. Restricted drilling rates also minimize the penetration into the gas bearing formation which in turn minimizes the influx rate.
Every effort should be made to minimize the possibility of swabbing. Pumping out of the hole at optimum circulating rates is recommended for all upward pipe movements (e.g. making connections and tripping). Especially in larger hole sizes (i.e. larger than 12") it is important to check that the circulation rate is sufficiently high and the pulling speed sufficiently low to ensure that no swabbing will take place. A Top Drive System will facilitate efficient pumping out of hole operations. The use of stabilizers will also increase the risk of swabbing, hence the minimum required number of stabilizers should be used.
Remember when it comes to shallow gas prevention is
better than the cure.