Page 297 - Well Control for Completions and Interventions
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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).
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