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290 Well Control for Completions and Interventions
400 psi.
Gas 4500 ft TVD
Gas 3000 psi.
5000 ft TVD
Figure 7.16 Gas migration.
WHCIP 5 3000 ð0:052 3 4500 3 10Þ 5 660 psi
BHP will be:
BHP 5 P res 1 ðð0:052 3 FDÞ 3 ðTVD res TVD gas ÞÞ
where:
BHP: the bottom hole pressure in psi.
TVD res : TVD of the reservoir (Fig. 7.16).
BHP 5 3000 1 ð0:052 3 10Þ 3 ð5000 4500Þ 5 3260 psi
If the gas bubble was allowed to migrate to the surface, shut-in pres-
sure would rise to the original BHP of 3000 psi. Actual BHP would
increase to:
3000 psi 1 ð0:052 3 5000 3 10Þ 5 5600 psi
7.6 PROCEDURE FOR CONTROLLING GAS MIGRATION
Since gas can migrate quickly, it is often necessary to reduce surface
pressure whilst preparing to kill the well. Notable characteristics of gas
migration include:
• Can occur any time the well is shut-in with gas present (either when
the well is shut-in intentionally or the flow path is mechanically
plugged or blocked).