Page 459 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:29 PM Page 435

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Appendix:1

Calculating Kick Tolerances

Assumptions
For each hole section the volume of gas influx that can be safely
handled has to be calculated to safely reach the next casing point.
These calculations take the worst-case scenario and make assumptions
about the likely formation pore pressure to calculate the influx volume.
The worst case for a kick occurring is at the greatest depth—when
the next casing point has been reached. To determine the minimum
shoe strength required to reach this, some assumptions are made.
For an exploration or appraisal well in a relatively or completely
unknown field, assume that the kicking formation may have a pore
pressure gradient of 10% higher than the mud gradient (increase this if
circumstances warrant). Therefore, a planned mud gradient of 0.5
psi/ft will assume a pore pressure gradient at casing point of 0.55 psi/ft.
For a development well in a known area, assume that the kicking
formation may have a pore pressure equal to the mud gradient.
Therefore, it is assumed that any kick is most likely to be a swabbed
influx.

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