All hydrostatic pressure-related calculations should be based on true vertical depth values. This means that the standpipe kill graph of a deviated well has a different curve as compared to the graph prepared for a vertical well due to the behaviour of Pdp. It applies only for phase I (balanced method), since the standpipe pressure remains constant for the other phases.

1. Kick control in deviated wells

When the standpipe kill graph for a deviated well is constructed according to the procedure outlined in Section 2.3.4.15 (vertical hole), higher than required bottom hole pressures will occur in phase I during well killing. Especially in deep, highly deviated holes, and horizontal wells, this overbalance can be relatively high and should be taken into account.

The procedure to construct the phase I standpipe kill graph for a deviated well is as follows:

1.Plot the initial standpipe pressure at time, volume or strokes zero.

2.Calculate and plot the standpipe pressure when the new mud has reached the bit (end of phase I).

3.Calculate and plot the standpipe pressures which occur at the beginning and end of each build-up and/or drop-off section at the appropriate position in the graph.

4.Connect the points obtained in 1), 2) and 3) with a straight line. This line represents the standpipe pressure whilst pumping the new mud from surface to bit.

Well control formulae used throughout Section 2.3 also apply for deviated wells as long as the hydrostatic pressure-related calculations are based on true vertical depths. A simple approach for taking the deviation angle into account is to project the deviated hole into a vertical section to obtain equivalent hydrostatic heads for specific volumes and to apply 'adjusted annular capacities' when using the standard well control formulae. A "Driller's Method" example of this approach is given in Section 6.14

2. Kick control in horizontal wells

In principle, well control calculations for deviated wells also apply for horizontal wells. However, a bottom hole angle of 90 degrees for the horizontal section cannot be used in the calculations, because of practical arithmetical reasons. An assumed bottom hole angle of 89 degrees should be used instead. For hydrostatic pressure-related calculations the TVD of the "deepest" part of the horizontal section should be used.

Most well control methods are also applicable to horizontal wells. However, when the string is off bottom, or when circulation at bottom is not possible, well control options become limited, because the volumetric method or bullheading are most likely unsuccessful or not very effective in the horizontal section.

Other kick control considerations for horizontal wells are:

·When a kick is encountered, the influx will take place over the entire exposed horizontal reservoir section at once.

·The overbalance at the "beginning" of the horizontal reservoir is the same as the "end" of the horizontal reservoir.

·Possible dispersion effect in the horizontal section will take place (depending on hole and flow conditions) which may result in long circulating times to get the mud in the well gas free and filled with the proper weight mud.

·Lower than expected annular pressures will occur due to the dispersion effect.

·A proper standpipe kill graph for a deviated well should be used to ensure that the correct bottom hole pressure is applied during the well killing process.

·If well programming is done correctly, the most likely kicks which may occur are swab kicks, since formation pressures are known.

·In principle, well control situations should not be critical since the casing is set directly above the production zone.