Abstract An improved system for offshore drilling is disclosed which is particularly useful in those operations where a floating vessel is situated at the surface of a body of water and circulation of drilling fluid is accomplished by introducing drilling fluid into a drill string extending from the vessel into a borehole in the floor of the body of water and returning it through a separate conduit to the vessel. A surface detectable signal is generated which is proportional to the hydrostatic head exerted by the drilling fluid within the return conduit. Hydrostatic head of the drilling fluid within the return conduit is controlled in response to the signal, as by injecting gas into the conduit near its lower end, to regulate the hydrostatic head of the fluid in the borehole.
In a method of drilling wherein a floating vessel is situated at the surface of a body of water and drilling fluid is introduced into a drill string extending from the vessel into a borehole in the floor of the body of water and returned to the vessel through a separate conduit which conduit is provided with means for injecting a gas thereinto near its lower end, the improvement comprising measuring the hydrostatic pressure of the drilling fluid within said return conduit beneath the gas injection point and adjusting the pressure gradient of the fluid contained within the return conduit to maintain the hydrostatic pressure of the drilling fluid within the borehole at a level sufficient to counterbalance formation pressure without exceeding its fracture gradient.
Claim 2
Dependent Claim
125 words
In a method of drilling wherein a floating vessel is situated at the surface of a body of water and drilling fluid is introduced into a drill string extending from the vessel into a borehole in the floor of the body of water and returned to the vessel through a separate conduit which conduit is provided with means for injecting a gas thereinto near its lower end, the improvement comprising measuring the hydrostatic pressure of the drilling fluid within said return conduit beneath the gas injection point and adjusting the pressure gradient of the fluid contained within the return conduit to maintain the hydrostatic pressure of the drilling fluid within the borehole at a level sufficient to counterbalance formation pressure without exceeding its fracture gradient.
Claim 3
Dependent Claim
12 words
The method of claim 1 wherein said gas is an inert gas.