Nelson - below is a response from one of our Registered Non-members, Chris White, MD of Signspread Ltd:
My immediate reaction to using this new type of gas sealing DP for DSTs, is that time savings running/retrieving the test string using this special DP would only be achievable if the DP string was used to actually drill the reservoir section. Most rigs provide the drill strings as part of their package, so there would almost certainly be an added rental cost involved covering the provision of the special gas-tight seal DP which would apply from a couple of weeks before the well is spudded, to allow time for the string to be cleaned and inspected, consequently a full drill string rental charge would apply for more than the duration of well drilling, coring, logging, testing, and possibly suspension.
I would strongly caution against using tubulars which have been subject to drilling stresses (applied torque and tensile loads) as a production string, which is what a DST string is by definition. Additionally, the internal wall of the DP will not be clean, especially as it will probably be used to cement through. Using the Iron Roughneck to make/break connections is an obvious time saver, however nearly all DST Downhole Tool connections are now 3½” PH-6 Hydril which has a much lower make-up torque than 3½” DP connections. Consequently, tubing tongs will still be required to accurately torque the finer threads of those components. Personal experience has taught that mixing multiple thread types and torques in the same string almost always leads to a lost time event.
It has been proven many times that using specialised and dedicated equipment improves performance by reducing down-time which drives down costs. Commonly, DSTs are performed in a cemented Liner, so if operations are planned correctly, the tubing test string can be run in singles, pressure tested, and retrieved and racked in stands while other operations like waiting on cement, and offloading, spotting, and hooking-up the surface Well Test Package, are ongoing. If you are fortunate enough to be using a dual-derrick drilling unit, the dedicated test string can be assembled and tested using the offline derrick which can also be used to make up sub-assemblies of DST tools.
If you need any assistance planning your well evaluation operations, please feel free to contact me.