Patent Application
20230031939
This invention relates to the general subject of connecting sections of riser pipe for drilling oil or gas wells in deep water.
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The field of this invention is that drilling risers for deep water blowout preventer systems are major pieces of capital equipment landed on the ocean floor in order to provide a conduit for the drill pipe and drilling mud while also providing pressure protection while drilling holes deep into the earth for the production of oil and gas. The typical blowout preventer stacks have an 18¾ inch bore and are usually of 10,000 psi working pressure. The blowout preventer stack assembly weighs in the range of five hundred to eight hundred thousand pounds. It is typically divided into a lower blowout preventer stack and a lower marine riser package.
The lower blowout preventer stack includes a connector for connecting to the subsea wellhead system at the bottom on the seafloor and contains several individual ram type blowout preventer assemblies, which will close on various pipe sizes and in some cases, will close on an open hole with what are called blind rams. Characteristically there is an annular preventer at the top, which will close on any pipe size or close on the open hole.
The lower marine riser package typically includes a connector at its base for connecting to the top of the lower blowout preventer stack, it contains a single annular preventer for closing off on any piece of pipe or the open hole, a flex joint, and a connection to a riser pipe which extends to the drilling vessel at the surface.
The purpose of the separation between the lower blowout preventer stack and the lower marine riser package is that the annular blowout preventer on the lower marine riser package is the preferred and most often used pressure control assembly. When it is used and either has a failure or is worn out, it can be released and retrieved to the surface for servicing while the lower blowout preventer stack maintains pressure competency at the subsea wellhead system 36 on the ocean floor.
The riser pipe extending to the surface is typically a 21 inch O.D. pipe with a bore larger than the bore of the blowout preventer stack. It is a low pressure pipe and will control the mud flow which is coming from the well up to the rig floor, but will not contain the 10,000-15,000 psi that the blowout preventer stack will contain. Whenever high pressures must be communicated back to the surface for well control procedures, smaller pipes on the outside of the drilling riser, called the choke line and the kill line, provide this function. These will typically have the same working pressure as the blowout preventer stack and rather than have an 18¾-20 inch bore, they will have a 3-4 inch bore. There may be additional lines outside the primary pipe for delivering hydraulic fluid for control of the blowout preventer stack or boosting the flow of drilling mud back up through the drilling riser.
The time to make up individual bolting on riser connectors has always been a time consuming addition to the expensive day rates of offshore operation.
The object of this invention is to provide a connector for the drilling riser which can be made up by the operation of a single bolt.
A second object of this invention is to provide a multi-section clamp with relatively uniform make-up around the perimeter of the connection.
A third object of this invention is to provide a connector which reduces the tendency for the portions of the clamp adjacent to the bolt to be more highly loaded than the remainder of the clamp.
Another objective of this invention is to eliminate the high stress drag on making up clamp connectors at the interfaces.
Referring now to
Below the drilling riser 22 is a flex joint 30, lower marine riser package 32, lower blowout preventer stack 34 and subsea wellhead system 36 landed on the seafloor 38.
Below the subsea wellhead system 36, it can be seen that a hole was drilled for a first casing string, that string 40 was landed and cemented in place, a hole drilled thru the first string for a second string, the second string 42 cemented in place, and a hole is being drilled for a third casing string by drill bit 44 on drill string 46.
The lower Blowout Preventer stack 34 generally comprises a lower hydraulic connector for connecting to the subsea wellhead system 36, usually 4 or 5 ram style Blowout Preventers, an annular preventer, and an upper mandrel for connection by the connector on the lower marine riser package 32.
Below outside choke or kill line 26 is a choke and kill (C&K) connector 50 and a pipe 52 which is generally illustrative of a choke or kill line. Pipe 52 goes down to choke or kill valves 54 and 56 which provide flow to or from the central bore of the blowout preventer stack as may be appropriate from time to time. Typically a kill line will enter the bore of the Blowout Preventers below the lowest ram and has the general function of pumping heavy fluid to the well to overburden the pressure in the bore or to “kill” the pressure. The general implication of this is that the heavier mud will not be circulated, but rather forced into the formations. A choke line will typically enter the well bore above the lowest ram and is generally intended to allow circulation to circulate heavier mud into the well to regain pressure control of the well.
Normal drilling circulation is the mud pumps 60 taking drilling mud 62 from tank 64. The drilling mud will be pumped up a standpipe 66 and down the upper end 68 of the drill pipe 46. It will be pumped down the drill pipe 46, out the drill bit 44, and return up the annular area 70 between the outside of the drill pipe 21 and the bore of the hole being drilled, up the bore of the casing 42, through the subsea wellhead system 36, the lower blowout preventer stack 34, the lower marine riser package 32, up the drilling riser 22, out a bell nipple 72 and back into the mud tank 64.
During situations in which an abnormally high pressure from the formation has entered the well bore, the thin walled drilling riser 22 is typically not able to withstand the pressures involved. Rather than making the wall thickness of the relatively large bore drilling riser thick enough to withstand the pressure, the flow is diverted to a choke or kill line 26. It is more economic to have a relatively thick wall in a small pipe to withstand the higher pressures than to have the proportionately thick wall in the larger riser pipe.
When higher pressures are to be contained, one of the annular or ram Blowout Preventers are closed around the drill pipe and the flow coming up the annular area around the drill pipe is diverted out through choke valve 54 into the pipe 52. The flow passes up through C&K connector 50, up choke or kill line 26 which is attached to the outer diameter of the central pipe 24, through choking means illustrated at 74, and back into the mud tanks 64.
On the opposite side of the drilling riser 22 is shown a cable or hose 28 coming across a sheave 80 from a reel 82 on the vessel 84. The cable 28 is shown characteristically entering the top of the lower marine riser package. These cables typically carry hydraulic, electrical, multiplex electrical, or fiber optic signals. Typically there are at least two of these systems, which are characteristically painted yellow and blue. As the cables or hoses 28 enter the top of the lower marine riser package 32, they typically enter the top of control pod to deliver their supply or signals. When hydraulic supply is delivered, a series of accumulators are located on the lower marine riser package 32 or the lower Blowout Preventer stack 34 to store hydraulic fluid under pressure until needed.
Referring now to
Control panel 96 is shown to control the reel 82. Centralizer 98 would be used to control the position of the riser as it is being pulled in currents to prevent it from be pushed into the side of the rotary table by the currents. Fairings 100 can be used to provide a better flow profile and reduce the drag forces on the riser. Winch 102 and chain 104 indicate that the fairings are of a “run through” type which means they are independently supported from the drilling rig, can be run after the riser is in the water, and can remain in place when most of the riser is retrieved, rather than the style which are fixed to individual riser joints.
Referring now to
Buoyancy module sections 130 and 132 are shown attached to the lower end of the conventional riser joint 116 and buoyancy module sections 134 and 136 are shown attached to the upper end of conventional riser joint 112. The conventional riser joints are 70 ft. long and the flotation modules are conventionally 129″ long. Six sections of the 129″ long flotation are attached to each riser joint, leaving a gap of 60″ or 5 feet in the area of the connection. The space on the upper end of conventional riser joint 112 is used for the insertion of support dogs when running the riser. The larger space on the bottom of the adjacent riser joint 116 is used for the insertion of a hydraulic make-up wrench when running the riser. It is conventional to use 6 support dogs, giving 6 spaces for bolts between the outside fluid lines.
Referring now to
Passageway 250 has not received an outside fluid line, but rather is shown as providing a passageway for other services. These services can be to lower instrumentation 252 on a wire 254 such as is shown to measure vortex induced vibration in a riser. Alternately passageway 250 can provide a passageway all the way to the bottom like the vacuum tubes used in banks. A hose can be lowered down to deliver hydraulic fluid. A control connector can be lowered on a control line to provide backup control for a blowout preventer stack in case of controls difficulties. A “Go-Devil” on simple weight can be dropped to actuate a single function in an emergency situation. Basically passageway 250 becomes a utility passageway for anything which needs to be done along or at the bottom of the riser.
A receptacle 260 at the upper end of lower riser pipe 262 is engaged by nose 264 on the lower end of upper riser pipe 266. Seals 268 seal between receptacle 260 and nose 264. The upper end of lower riser pipe 262 has a clamping profile 270 and the lower end of upper riser pipe 266 has a clamping profile 272. Clamp segments 274 engage the clamping profiles 270 and 272. Tension band 276 urges clamp segments 274 into engagement with clamping profiles 270 and 272 to secure the connection.
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The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
