Page 282 - Drilling Technology in Nontechnical Language

Chapter 11 – WELL CONTROL 273

It can now be said that, ignoring the requirement to maintain bottomhole
pressure equal to formation pressure, when circulating starts, the pressure
will be 500 psi, and when kill mud reaches the bottom of the well, the
circulating pressure will be 563 psi. Once heavy mud is at the bottom,

hydrostatic pressure from the mud in the drillstring is sufficient to balance
formation pressure. This phase of the kill operation, from starting to pump
heavy mud until heavy mud reaches the bottom, is called phase 1.
In order to maintain bottomhole pressure equal to formation pressure,
extra pressure must be applied (by the choke) during phase 1. Holding
pressure on the choke will affect the pressure in the entire system, including
the pump pressure. This extra pressure on the pump starts at the original
drillpipe pressure (500 psi) and will decrease to zero by the time heavy
mud reaches the bit. In a vertical well, this decrease is linear; for each
barrel pumped, the extra pressure will reduce by the same amount. The
volume inside the drillstring is known; it works out to be 139 bbl.
The initial circulating pressure equals the slow circulating rate pressure
plus the shut-in drillpipe pressure. Initial circulating pressure therefore is
500 psi + 500 psi = 1,000 psi. Final circulating pressure is PC .
2
A table and graph of pump strokes against pump pressure for phase 1

is then constructed (see fig. 11–11).

Fig. 11–11. Vertical well kill phase 1 graph

_Devereux_Book.indb 273 1/16/12 2:12 PM