Abstract
Annulus frictional pressure losses can be significant in certain application and should be considered in the planning phase to correctly calculate a meaningful safety margin for kick tolerance. Kick tolerance is an integral part of the well construction workflow. The formation, casing and well control equipment should withstand the pressure when shutting in and circulating a given kick volume to surface. At its simplest, the kick tolerance will be calculated based on the pressure in the well when the kick front is at the casing shoe, giving the highest pressure load at the shoe.
Safety margins are factored in by adding a given additional pressure as a safety factor in the calculations. This is often a pre-defined value in the technical requirements within the company. In deep water applications, the choke line frictional pressure losses are normally evaluated and can also be included, but in operations onshore or in shallow waters these frictional pressure losses are often excluded. Annulus friction pressure losses are often neglected entirely because they are considered insignificant or considered to be an extra safety factor.
Conventional well control procedures normally start the kick circulation by ramping up the pumps to speed while keeping the choke pressure constant. This procedure implies that any frictional pressure losses in the annulus and choke lines will be added to the wellbore pressure (considered a "nice to have" safety margin). An additional safety margin may be applied before starting the actual circulation, by pumping a few strokes into the shut in well to give some additional overpressure. This additional pressure does not represent a problem if it is accounted for in the planning phase, but, if not considered it could impose a risk to the operation if the actual kick tolerance in the operation is less than the calculated. In deep wells, typically with high mud density, the frictional pressure losses in the annulus can be significant, also at the slow circulation rates during a kick circulation. The standard safety margin applied in planning may or may not match this reality.