a sufficiently high pressure can distort or collapse the casing a counteracting pressure within the annular space 344 in the casing can offset the effects of the external water pressure and minimize pressure differences for example the pressure differences can be minimized by flowing a fluid of similar density as sea water into the annular space to lessen the pressure gradient between the internal and external surfaces of the casing however pressures necessary to drill into a subsea formation in the wellbore 330 may necessitate different pressures than those pressures required to offset the water pressure on the casing 326 a drilling head 114 such as the embodiment shown in fig1 can be mounted between the casing and the wellbore the pressure assisted packer 310 engages the drill string 110 and creates a first zone 316 above the packer 310 and a second zone 318 below the packer a first set of pressures can be controlled in the first zone 316 to offset the pressures from the water as the casing increases in depth a second set of pressures can be controlled in the second zone 318 to enable effective drilling into the various formations and production zones fig1 is a cross sectional schematic view of another embodiment of the drilling head 114 having members similar to those described in the embodiment shown in fig9 and 10 an upper body 350 is coupled to a lower body 280 with flanges 284 294 or other coupling members alternatively the upper body 350 and the lower body 280 can be made as a unit with or without the flanges a bearing housing 362 similar to bearing housing.