Method and apparatus for balancing subsea internal and external well pressures

Claim 2

In a method of maintaining a pressure balance between internal and external subsea well pressures during drilling, entry and reentry operation conducted from a floating vessel remote from the subsea well including the step of injecting gas into the subsea well in amounts sufficient to cause the density of the well fluids below the surface of the sea to approximate the density of sea water, the improvement comprising the additional steps of: sensing the pressure differential at said subsea well between internal well bore pressure and external water pressure and controlling the amount of gas injected into said well bore to minimize the magnitude of said pressure differential being sensed.

Claim 3

In a method of maintaining a pressure balance between internal and external subsea well pressures during drilling, entry and reentry operations conducted from a floating vessel remote from the subsea well wherein drill mud is circulated from the vessel into the well during drilling operations and is returned to the vessel via a mud return line including the steps of establishing two or more fluId flow lines between the floating vessel and the bore of the subsea well, returning drill mud to the floating vessel from the well bore via one or more return lines of said fluid flow lines and injecting gas into the subsea well through one or more injection lines of said fluid flow lines in amounts sufficient to lower the density of said drill mud in said one or more return lines to approximate the density of sea water, the improvement comprising the additional step of: applying a back pressure on said well bore by pumping drill mud down one or more of said lines to balance the internal and external well pressures when the internal well pressure falls below that of the surrounding sea water.

Claim 4

In a method of maintaining a pressure balance between internal and external subsea well pressures during drilling, entry and reentry operations conducted from a floating vessel remote from the subsea well wherein drill mud is circulated from the vessel into the well during drilling operations and is returned to the vessel via a mud return line including the steps of establishing two or more fluId flow lines between the floating vessel and the bore of the subsea well, returning drill mud to the floating vessel from the well bore via one or more return lines of said fluid flow lines and injecting gas into the subsea well through one or more injection lines of said fluid flow lines in amounts sufficient to lower the density of said drill mud in said one or more return lines to approximate the density of sea water, the improvement comprising the additional step of: applying a back pressure on said well bore by pumping drill mud down one or more of said lines to balance the internal and external well pressures when the internal well pressure falls below that of the surrounding sea water.

Claim 5

The method of claim 2 comprising the additional step of: sensing the pressure differential at said subsea well between the pressure within said one or more return lines at said well and the surrounding water pressure, and controlling the amount of drill mud introduced back into said well through said lines to minimize the magnitude of said pressure differential.

Claim 6

The method of claim 3 comprising the additional step of: opening the well bore to the surrounding sea water to allow removal of and re-entry of well tools when the internal and external well pressures are in balance.

Claim 7

In a subsea well drilling apparatus including a drill string and drilling mud return line, each run from a floating vessel over a subsea well location to subsea drilling equipment at the well location, a blowout preventer means for sealing the well bore about the drill string within the well during drilling operations and gas supply line means run from said floating vessel and connected into said well bore below said blowout preventer means for injecting gas into the drilling mud to reduce its density as it is returned from said well to the floating vessel via said mud return line, the improvement comprising the provision of: valve means in said gas supply line means at a location therein adjacent said subsea well for controlling the supply of gas to said well bore through said supply line means and pressure differential sensing and valve control means in association with said valve means for operating said valve means in response to a pressure differential between the pressure in said gas supply line on the well bore side of said valve means and the pressure of the surrounding sea water.

Claim 8

In a subsea well drilling apparatus including a drill string and drilling mud return line, each run from a floating vessel over a subsea well location to subsea drilling equipment at the well location, a blowout preventer means for sealing the well bore about the drill string within the well during drilling operations and gas supply line means run from said floating vessel and connected into said well bore below said blowout preventer means for injecting gas into the drilling mud to reduce its density as it is returned from said well to the floating vessel via said mud return line, the improvement comprising the provision of: valve means in said gas supply line means at a location therein adjacent said subsea well for controlling the supply of gas to said well bore through said supply line means and pressure differential sensing and valve control means in association with said valve means for operating said valve means in response to a pressure differential between the pressure in said gas supply line on the well bore side of said valve means and the pressure of the surrounding sea water.

Claim 9

In a subsea well drilling apparatus including a drill string and drilling mud return line, each run from a floating vessel over a subsea well location to subsea drilling equipment at the well location, a blowout preventer means for sealing the well bore about the drill string within the well during drilling operations and gas supply line means run from said floating vessel and connected into said well bore below said blowout preventer means for injecting gas into the drilling mud to reduce its density as it is returned from said well to the floating vessel via said mud return line, the improvement comprising the provision of: valve means in said mud return line in a location therein adjacent said subsea well for controlling the back flow of mud from said return line back into said well bore; and pressure differential sensing and valve control means in association with said valve means for operating said valve means in response to a pressure differential between the pressure in said mud return line on the well bore side of said valve means and the surrounding sea water pressure.

Claim 10

In a subsea well drilling apparatus including a drill string and drilling mud return line, each run from a floating vessel over a subsea well location to subsea drilling equipment at the well location, a blowout preventer means for sealing the well bore about the drill string within the well during drilling operations and gas supply line means run from said floating vessel and connected into said well bore below said blowout preventer means for injecting gas into the drilling mud to reduce its density as it is returned from said well to the floating vessel via said mud return line, the improvement comprising the provision of: valve means in said mud return line in a location therein adjacent said subsea well for controlling the back flow of mud from said return line back into said well bore; and pressure differential sensing and valve control means in association with said valve means for operating said valve means in response to a pressure differential between the pressure in said mud return line on the well bore side of said valve means and the surrounding sea water pressure.

Claim 11

The method of claim 1 comprising the additional steps of: opening said well bore to the surrounding sea water and running a well tool between said well bore and said floating vessel through said sea water and the opened well bore.

Claim 12

The method of claim 2 comprising the additional steps of: opening said well bore to the surrounding sea water and running a well tool between said well bore and said floating vessel through said sea water and the opened well bore. >