Some wells are drilled primarily to retrieve cores. This puts a lot of pressure on the drilling engineers to find methods that moves the recovery factor beyond that of good luck. This coring case is presented because it gave full core recovery AND also provided for documentation of the vibration challenges from MWD recordings.
In the Icewine prospect south of Prudhoe Bay, severe vibrations developed when crossing formation boundaries down towards the coring point. The operator decided to fly in Tomax tools with the aim of improving the situation.
The 4 ¾” OD, 10 inch stroke, X-Series AST paid for its airfare by delivering full core recovery: in mixed rock, it is paramount to avoid vibrations that can crack the laminar column inside the core barrel. If pieces of the core come free, they will most likely jam the barrel. In this case, the AST was kept in the BHA for the remainder of the well, using ordinary BHAs.
The MWD data was able to document how the AST eliminated the previous vibration problems and also improved drilling efficiency (ROP).
The result from the coring was promising and the full recovery improved the accuracy of the resulting analysis.