of the guard intervals 206 and 207 the example pressure controller 505 of fig5 actively controls the pump 315 to maintain the guard interval pressure p g1 of the guard interval 206 based on the inner interval pressure p s and the wellbore pressure p w for example the pressure controller 505 adapts and or maintains the guard interval pressure p g1 to be substantially equal to the inner interval pressure p s to reduce the mechanical stresses experienced by the inner packer 210 when the wellbore to drawdown pressure difference is large the example controller 505 adapts the guard interval pressure p g1 to distribute the pressure difference between the outer packer 212 and the inner packer 210 the pressure p g1 of the guard interval 206 is measured by the example pressure gauge 330 likewise the example pressure controller 510 of fig5 actively controls a pump 315 b which is substantially identical to the example pump 315 to maintain the guard interval pressure p g2 of the second guard interval 207 based on the inner interval pressure p s and the wellbore pressure p w the pressure p g2 of the guard interval 207 is measured by a pressure gauge 330 b which is substantially identical to the pressure gauge 330 while in some examples the pressures p g1 and p g1 are maintained at substantially the same pressure the pressures p g1 and p g1 may be maintained at different pressures for example.