Shearable drill pipe method and apparatus

The method of shearing drill collars used in the drilling of oil and gas wells, comprising providing an outer sleeve of a first material for carrying structural loads, providing a second material within the outer sleeve which is lower in shear strength and is greater in unit weight than the first material, and providing a hole in the second material for the circulation of fluids.

TECHNICAL FIELD

This invention relates to the method of shearing drill pipe for drilling oil or gas wells, especially in deep water.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

The drill bit for drilling oil and gas wells is facilitated by having a heavy load applied to assist in crushing and pulverizing the formation being drilled. The formation material must be reduced to particles small enough that the flow of drilling mud up to the surface will carry it to the surface. Drill collars are connected to the drill bit to provide the heavy load for this purpose.

The drill bit and drill collars are part of a drill string which also includes drill pipe which extends to the drilling rig at the surface.

The drill pipe which extends to the surface is thin walled. Its primary design requirement is to support the weight of the drill string including the drill collars during running and retrieving of the drill string.

Conversely, the drill collars are at the bottom of the drill string and they only support themselves. The drill pipe can be 20,000 feet long or longer and drill collars seldom exceed 1,000 feet in length. Although the drill collars are heavier, there is much more length in drill pipe, and the drill pipe must support the drill collars and the drill pipe.

Drill collars have as small a bore as practical and as large an outer diameter as is practical so that they will be heavy. The drill collars have metal sealing threaded connections on each end. These threaded connections are benefited by being made of high strength steel. As a result the entire drill collar is made of high strength steel. They are extremely strong as a result, but do not have a requirement for being extremely strong. They are characteristically so strong that the average person presumes they need to be strong, because they always are.

A problem resulting from this is that the thick cross section of high strength steel cannot be sheared by the blind shear rams in the primary well control device, the blowout preventer stack. The blind shear rams are to cut the pipe in the bore and seal across the bore to keep a well from blowing out. When as much as 1000 feet of drill collars pass in front of the blind shear rams, the well bore literally cannot be closed.

On land or platform wells this is not a major concern as in unexpected pressure situations there is always a closable valve on the top of the drill string except for the short time for making connections at the surface. For the annular area between the outside diameter of the drill string in the well and the bore of the blowout preventer stack, there are annular and ram type blowout preventers which are well known in the art and can be closed to seal this annular area.

In deepwater drilling situations from a floating vessel the situation is different. In the worst case scenario the vessel can be blown off location or can have a steering computer accidental drive off when you are in an unexpected pressure situation. If this happens when the drill collars are in the bore in front of the blind shear rams, you cannot close the blowout preventers and you cannot let go of the pipe string. In other words you have a blowout.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is to provide a drill collar which can be sheared with conventional blowout preventer shear rams.

A second object of this invention is to provide drill collars of a higher unit weight such that the length of the drill collars to provide a desired weight on the bit will be reduced.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1, a view of a complete system for drilling subsea wells20is shown in order to illustrate the utility of the present invention. The drilling riser22is shown with a central pipe24, outside fluid lines26, and control lines28.

Below the drilling riser22is a flex joint30, lower marine riser package32, lower blowout preventer stack34and wellhead36landed on the seafloor38.

Below the wellhead36, it can be seen that a hole was drilled for a first casing string, that string40was landed and cemented in place, a hole drilled thru the first string for a second string, the second string42cemented in place, and a hole is being drilled for a third casing string by drill string44which includes drill bit45, heavy weight drill collars46, and lighter weight drill pipe47.

The lower Blowout Preventer stack34generally comprises a lower hydraulic connector for connecting to the subsea wellhead system36, 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 package32.

Below outside fluid line26is a choke and kill (C&K) connector50and a pipe52which is generally illustrative of a choke or kill line. Pipe52goes down to valves54and56which 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 pumps60taking drilling mud62from tank64. The drilling mud will be pumped up a standpipe66and down the upper end68of the drill pipe47. It will be pumped down the drill pipe47, out the drill bit45, and return up the annular area70between the outside of the drill pipe47and the bore of the hole being drilled, up the bore of the casing42, through the subsea wellhead system36, the lower blowout preventer stack34, the lower marine riser package32, up the drilling riser24, out a bell nipple72and back into the mud tank64.

During situations in which an abnormally high pressure from the formation has entered the well bore, the thin walled central pipe24is 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 line26. 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 valve54into the pipe52. The flow passes up through C&K connector50, up pipe26which is attached to the outer diameter of the riser24, through choking means illustrated at74, and back into the mud tanks64.

On the opposite side of the drilling riser24is shown a cable or hose28coming across a sheave80from a reel82on the vessel84. The cable28is shown characteristically entering the top of the lower marine riser package32. 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 hoses28enter the top of the lower marine riser package32, they typically enter the top of the control pod to deliver their supply or signals. When hydraulic supply is delivered, a series of accumulators are located on the lower marine riser package32or the lower Blowout Preventer stack34to store hydraulic fluid under pressure until needed.

Referring now toFIG. 2, conventional drill collar100comprises a central thick wall section102, an upper female thread104, a lower male thread106, an upper sealing shoulder108and a lower sealing shoulder110.

Referring now toFIG. 3, a cross section ofFIG. 2is shown along lines “3-3” showing the thick cross section required to be sheared.

Referring now toFIG. 4, a half section of the drill collar120of the present invention is shown being made of a thin wall formed tube122with an upper thread124, a lower thread126, upper sealing shoulder128and lower sealing shoulder130. Ring132lands on shoulder134and supports thin walled tube136. Heavy weight material such as lead138is melted and poured into the area between tube122and thin walled tube136.

Referring now toFIG. 5, a cross section ofFIG. 4is shown along lines “5-5” showing the majority of the section required to be sheared is of the lower shear strength material such as lead. As the density of steel is 0.283 lbs. per cubic inch and the density of lead is 0.410 lbs. per cubic inch, lead is approximately 45% heavier than steel. This means that the length of the drill collars of this invention could be up to 45% shorter than conventional drill collars.

Referring now toFIG. 6, a drill collar140of this invention is shown with a portion of a second drill collar142attached at thread144. This illustrates that even the connection of the drill collar of this invention has a smaller cross section of steel than that of a conventional drill collar such as is shown inFIG. 2.

Referring now toFIG. 7, a simple thin wall tube150is shown which can be used as material for a portion of the drill collar of the present invention.

Referring now toFIG. 8, tube150ofFIG. 7is rolled tube160to a suitable profile, with some forging upset occurring at locations162and164where thicker cross sections will be beneficial for machining. This is especially important when the connections are tapered threads.

Referring now toFIG. 9, is shown with the rolled tube160ofFIG. 8is a machined tube170with a lower thread172, an upper thread174, a lower sealing shoulder176, an upper sealing shoulder178, and an internal shoulder180.

Referring now toFIG. 11, lead190is poured into the assembly ofFIG. 10and allowed to solidify. As lead tends to shrink when solidifying, percentages of bismuth, antimony, and tin can be added to eliminate the shrinkage or to cause a slight expansion if desired. Alternately, a temporary tube can be placed in the bore for molding and then be removed.