pressure is below fracture closure pressure consider pumping back bull heading any gained volume into formation to prevent formation fluids or gas from contaminating the fluid in the annulus and coming to the surface upon filling the drill pipe the following sequence is performed 1 the pipe rams are opened 2 the lower choke fail safe valves are opened and 3 the mud pumps 146 are brought online to pump drilling fluid commensurate with the drilling rate the slips are then pulled and the pipe broken down quickly while drilling the present invention requires maintaining an equivalent circulating density on the well through the manipulation of mud density and frictional pressure losses influenced by e g mud flow rate mud theological properties pipe rotation etc such that ecd d tvd d air u00d7 u03c1 fluid u03b4p compressibility u03b4p friction gt fcp eq 5 ecd d tvd d air u00d7 u03c1 fluid u03b4p compressibility u03b4p friction lt fpp eq 6 where it is understood that the requirement in eq 5 is essential whereas the requirement in eq 6 is merely desirable the following additional definitions are used in eqs 5 and 6 ecd is the equivalent circulating density in psi or pa and u03b4p friction is the frictional pressure losses due to mud circulation in psi or pa during operations.