Kick Tolerance

Safety factor used in Well Design and Construction

Kick tolerance in drilling well design refers to the maximum volume of formation fluid (or "kick") that can enter the wellbore without exceeding the pressure limits of the weakest formation in the well. It is a critical parameter in well control and safety, ensuring that the well can handle unexpected influxes of formation fluids and circulate them out, without fracturing the formation or causing a blowout.

In general terms, the weakest point of the formation is at the previous casing shoe, however when drilling in a known area or near other production wells, there could be deeper and weaker formations due to depletion which should be taken into account.

In order to calculate kick tolerance, two different phases need to be considered, and then the worst case assumed.

- The kick whilst around the BHA (smallest annular capacity therefore potentially the highest gas height for a given volume)

- The kick whilst being circulated out and at the shoe (gas expansion will increase the volume size although this can be offset by the larger annular capacity)

Kick Tolerance if often quoted as dependent on hole size and will vary across different regulations and company policies. A generic kick tolerance scheme could be similar to below

Since kick tolerance is a generic design criteria, in circumstances where it cannot be met, special measures can be considered to increase kick detection, such as the use of MPD or advanced kick detection meters in the flowline. When drilling the well, if circumstances change, such as a lower than expected shoe FIT/LOT, then kick tolerance needs to be re-evaluated to ensure the next section is still safe to drill