ADAPTED MUD LINE SUSPENSION SYSTEM

A wellbore system includes a mudline suspension system arranged to provide a pressure rating sufficient for performing operations within a wellbore. The wellbore system includes a conductor pipe installed through a subaquatic surface location, and at least one casing string hung from an interior of the conductor pipe into the wellbore. A split casing string extends through the at least one casing string, includes a downhole liner portion hung from a lower end of the at least one casing string and an uphole tieback portion sealed to an interior surface of the lower liner portion. A wellhead supports the split casing string, wherein the upper tieback portion of the split casing string is hung from the wellhead.

FIELD OF THE DISCLOSURE

The present disclosure relates to a mudline suspension system for supporting casing within a wellbore and, more specifically, the disclosure relates to mudline suspension systems adapted to maintain structural integrity when subjected to greater subsurface pressures than mudline suspension systems may have been rated.

BACKGROUND OF THE DISCLOSURE

Hydrocarbon resources are often located below the earth's surface, sometimes tens of thousands of feet below the surface. Sometimes hydrocarbon fluids, e.g., oil and/or gas, reside in terrestrial locations and sometimes in geologic formations that lie beneath a body of water. In order to extract the hydrocarbon fluid, wellbores may be drilled through the geologic formations to access subterranean hydrocarbon reservoirs. The wellbores may be drilled vertically, and also deviated from vertical, to access the hydrocarbon fluids.

The wellbores may be cased to protect the integrity of the wellbores and the surrounding geologic formations. Casing strings may be fixed in place by injecting cement into an annulus defined between the casing and the surrounding geologic formation. Where a smaller casing string extends through a larger casing string, cement may be injected into an annulus between the outer diameter of the smaller casing string and the inner diameter of the larger previous casing string. For some applications, a liner may be installed in place of a casing string. A primary distinction between a liner and casing is that casing extends from the bottom of the hole to the surface and is supported by a wellhead, whereas liner only runs as high as the previous casing string and is anchored within the previous casing string.

Mud Line Suspension (MLS) systems are often utilized in offshore wellbore construction, where casing is secured within a conductor pipe at the mudline or seabed. An MLS system generally includes a series of concentric hangers equipped with load supporting shoulders that transfer the weight of each casing string to the conductor and the sea bed. MLS systems provide operators with flexibility of temporarily abandoning a wellbore and tying back to the well at a later dated as needed.

MLS systems are generally categorized according to mechanical loads and pressures that the MLS systems are designed to handle. Standard configurations include a 5,000 psi (5M) rated Mud Line Compact (MLC) system and a Mud Line Long (MLL) system rated to 15,000 psi (15M) capacity. In some instances, a need may arise to subject an MLS system to greater loads than the rating of the MLS system. Additionally, a standard MLS configuration may not be the most cost-effective solution for every application.

SUMMARY OF THE DISCLOSURE

According to an embodiment consistent with the present disclosure, a wellbore system includes a conductor pipe installed through a subaquatic surface location. At least one casing string is hung from a mudline suspension profile defined within an interior of the conductor pipe, and the at least one casing string extends into a wellbore defined below the conductor pipe. A split casing string extends through the at least one casing string and includes a downhole liner portion hung from a lower end of the at least one casing string below the mudline suspension hanger profile and an uphole tieback portion sealed to an interior surface of the lower liner portion and passing upwardly through the mudline suspension hanger profile. A wellhead is defined above the mudline suspension hanger profile, and the upper tieback portion of the split casing string is hung from the wellhead such that the uphole tieback portion bypasses the mudline suspension hanger profile.

According to another embodiment consistent with the present disclosure, a method of conducting operations in a wellbore includes (a) installing a conductor pipe through a subaquatic surface location into a geologic formation below the subaquatic surface location, (b) hanging at least one casing string from a mudline suspension hanger profile defined within an interior of the conductor pipe into the wellbore, (c) hanging a downhole liner portion of a split casing string from a lower end of the at least one casing string below the mudline suspension hanger profile, (d) passing an uphole tieback portion through the mudline suspension profile to an interior of the downhole liner portion and (c) supporting the uphole tieback portion from a wellhead installed above the mudline suspension profile such that the uphole tieback portion bypasses the mudline suspension hanger profile.

DETAILED DESCRIPTION

Embodiments in accordance with the present disclosure generally relate to mudline suspension (MLS) systems that employ components of a standard MLS system but are adapted to accommodate greater loads than the standard MLS system. For example, a standard MLS system may be rated to 5000 psi (5M) at a 9⅝″ casing hanger profile, while a modified casing configuration as described herein may elevate the pressure rating to 10,000 psi (10M) by bypassing the 9⅝″ casing hanger profile.

Mudline suspension systems of the present disclosure include an intermediate casing string in a wellbore that is split into a lower cemented liner and an upper tieback portion supported at the wellhead to bypass a lower rated mudline suspension hanger profile. For example, the upper tieback portion may “bypass” the mudline suspension hanger profile by passing through the mudline suspension hanger profile without being supported thereby and without being coupled thereto. In some specific embodiments, 30-inch, 18⅝-inch and 13⅜-inch casing hangers of a standard MLC system are used and a 9⅝-inch casing is split to bypass a 5,000 psi (5M) rated mudline suspension hanger profile. The resulting MLS system may be rated a 10,000 psi (10M) capacity. In some embodiments, a 9⅝-inch tieback portion of the split casing may be cemented into place, and the wellbore may be completed by tying back to a 7-inch liner supported by a 9⅝-inch liner portion of the split casing. In other embodiments, the 9⅝-inch tieback portion may not be cemented into place, and the wellbore may be completed by removing the 9⅝-inch tieback portion and tying back to a 13⅜-inch casing.

FIG.1is a schematic diagram of an example wellbore system100that may embody or otherwise employ one or more principles of the present disclosure. In the illustrated embodiment, the wellbore system100includes a Mudline Suspension (MLS) system102extending below a subaquatic surface location “S,” such as a seabed or lake bottom. The MLS system102supports a wellbore104extending through a geologic formation “G.” In the illustrated example, the wellbore104is substantially vertical. In other embodiments, aspects of the disclosure may be practiced in a wide variety of vertical, directional, deviated, slanted and/or horizontal portions therein, and may extend along any trajectory through the geologic formation “G.”

A platform106is positioned above a water surface “W” and may facilitate drilling the wellbore104and installing the MLS system102. In the example embodiment illustrated, the platform106is a jack-up rig supported on the geologic formation “G.” In other embodiments, the platform106may include a ship or other platform floating on the water surface “W” without departing from the scope of the disclosure. The platform106supports a drilling rig110thereon for handling a drill pipe112. The drill pipe112may be extended into the wellbore104through a conductor pipe130that extends between the platform106and the geologic formation “G.” The drill pipe112may be rotated to drill the wellbore104using techniques recognized in the art. The platform106also supports a surface wellhead118and a BOP stack120to contain drilling fluids and protect drilling personnel while the wellbore104is being drilled. Once the wellbore104is complete, the platform106may be removed, and/or the wellbore104may be temporarily suspended as described in greater detail below.

The MLS system102generally supports the weight of casing strings within the wellbore104at the subaquatic surface “S” and provides the ability to disconnect and reconnect from the wellbore104as needed. The MLS system102includes a mudline suspension hanger profile124defined within the conductor pipe122at or near the subaquatic surface “S.” The conductor pipe122may have a 30-inch nominal diameter and may be set 200 feet (or at an alternate depth determined to be within a service capacity of the conductor pipe122) into the geologic formation “G” below the subaquatic surface “S.” The conductor pipe122may be installed through the subaquatic surface “S” with a pile driver, by drilling or by alternative methods. The surface wellhead118may be coupled to an upper end of the conductor pipe122or other tubulars while drilling or other operations are being conducted in the wellbore104. As described in greater detail below, when drilling is completed and the MLS system102is fully installed, the conductor pipe122may be severed (cut) at the mudline suspension hanger profile124, and an upper portion122aof the conductor pipe122may be removed. A lower portion122bof the conductor pipe122may remain in place, and may receive a corrosion cap (not shown) or other protective structures when the wellbore104is temporarily suspended.

A surface casing string128may be extended concentrically within the conductor pipe122from the surface wellhead118and into the wellbore104. An upper portion128aof the surface casing string128extends between the platform106and the mudline suspension hanger profile124. A lower portion128bof the surface casing string128may be supported on a landing shoulder308(FIG.3) defined within the conductor pipe122at the mudline suspension hanger profile124. The surface casing string128may have a nominal diameter of 18⅝ inches and may extend to a depth of about 650 feet (or to an alternate depth determined to be within a service capacity of the surface casing string128) in some embodiments. The length and depth of the casing strings described herein may vary depending on the casing size and strength, and the external forces (e.g., hydrostatic gradient (pore pressure) and internal pressures (drilling fluid weight)) experienced by the casing strings. Any specific values given herein for the length or depth of a casing string are exemplary only.

The lower portion128bof the surface casing string128may be cemented into place, e.g., an annulus130defined between the lower portion128bof the surface casing string128and the lower portion122bof the conductor pipe122and geologic formation “G” may be filled with cement. Other casing strings described herein may similarly be cemented in place. The surface casing string128may have a pressure rating of 1,500 psi (or an alternate pressure rating indicating a maximum operating pressure of the surface casing string128) to permit drilling and other wellbore operations below the surface casing string128.

Within the surface casing string128, a first intermediate casing string132may be extended from the surface wellhead118and into the wellbore104. An upper portion132aof the first intermediate casing string132extends between the platform106and the mudline suspension hanger profile124. A lower portion132bof the first intermediate casing string132may be hung at the mudline suspension hanger profile124and cemented in place. Specifically, the lower portion132bof the first intermediate casing string132may be hung from an interior shoulder316(FIG.3) on an interior of the surface casing string128. In other example embodiments, the lower portion132bof the first intermediate casing string132may be hung from an interior surface of the conductor pipe122at the mudline suspension hanger profile124. The first intermediate casing string128may have a nominal diameter of 13⅜ inches and a pressure rating of 4,500 psi (or an alternate pressure rating indicating a maximum operating pressure of the first intermediate casing string132). The first intermediate casing string132may extend to a depth of about 2,500 feet (or to an alternate depth determined to be within a service capacity of the first intermediate casing string132) in some example embodiments.

A second intermediate casing string134may be extended concentrically through the first intermediate casing string132from the surface wellhead118and into the wellbore104. An upper portion134aof the second intermediate casing string132extends between the platform106and the mudline suspension hanger profile124. A lower portion134bof the second intermediate casing string132may be hung from the mudline suspension hanger profile124and cemented in place. The second intermediate casing string134may have a nominal diameter of 9⅝ inches and a pressure rating of 5,000 psi (or an alternate pressure rating indicating a maximum operating pressure of the second intermediate casing string134). The second intermediate casing string132may extend to a depth of about 4,500 feet (or to an alternate depth determined to be within a service capacity of the second intermediate casing string134) in some example embodiments.

As illustrated inFIG.1, in some example embodiments, a liner136may be hung from a lower end of the second intermediate casing string134. The liner136may have a nominal diameter of 7 inches and may extend to a depth of 7,000 feet (or to an alternate depth determined to be within a service capacity of the liner136) in some embodiments. The liner136may be supported by a liner hanger138on an interior of the second intermediate casing string134. An open-hole portion140of the wellbore104may be provided below the liner136.

The MLS system102may have a pressure rating of 5,000 psi for operations within and below the second intermediate casing string134. The upper portions122a,128a,132aand134amay each be removed when these operations are complete, and the MLS system102may be capped at the mudline suspension hanger profile124to temporarily suspend the wellbore104.

Referring now toFIG.2, an example MLS system202is described, which may be rated for subsurface pressures of up to 10,000 psi for applications where an anticipated subsurface pressure within a wellbore falls between 5,000 psi and 10,000 psi. The MLS system200includes many of the same components as the MLS system102ofFIG.1, and thus may be best understood with reference thereto. For example, the conductor pipe122, mudline suspension hanger profile124, surface casing string128and first intermediate casing string132may each be identically constructed and arranged as in the MLS system102(FIG.1). Rather than a second intermediate casing string134extending to the mudline suspension hanger profile124, however, the MLS system202includes a split casing string204disposed within the first intermediate casing string132.

The split casing string204includes a downhole liner portion210and an uphole tieback portion212. The downhole liner portion210may have a nominal diameter of 9⅝ inches, and may be cemented in place to a depth of about 4,500 feet in some example embodiments, similar to the second intermediate casing string134(FIG.1). However, rather than being supported near the mudline suspension hanger profile124, the downhole liner portion210is supported by a liner hanger214disposed at or near a lower end of the first intermediate casing string132. The uphole tieback portion212couples to the downhole liner portion210at a Polished Bore Receptacle (PBR)218defined within an interior of the downhole liner210. The uphole tieback portion212is sealed to the downhole liner portion210with a seal assembly (not shown) and extends through the mudline suspension hanger profile124. An upper end of the uphole tieback portion212may be secured to the surface wellhead118(seeFIG.4). In other embodiments, the upper end of the of the uphole tieback portion212may be secured to the conductor pipe122above casing hangers310,312(FIG.3) in the mudline suspension hanger profile124.

In some example embodiments, the uphole tieback portion212may be cemented in place, e.g., by filling an annulus220between the first intermediate casing string132and the uphole tieback portion212with cement. In other example embodiments, the annulus220may be devoid of cement such that the uphole tieback portion212is left un-cemented to facilitate removal of the uphole tieback212from the first intermediate casing string132. Once the split casing string204is installed, the MLS system202may be rated at 10,000 psi.

In some example embodiments, as illustrated inFIG.2, the liner136may be hung from a lower end of the downhole liner portion210. As described above, the liner136may have a nominal diameter of 7 inches and may extend to a depth of 7,000 feet (or to an alternate depth determined to be within a service capacity of the liner136). The liner136may be supported by a liner hanger138arranged on an interior of the downhole liner portion210such that the lowermost end of the MLS system202is similar in construction to the MLS system101ofFIG.1.

Referring now toFIG.3, illustrated is a partial schematic view of the MLS system202installed in a wellbore304. The conductor pipe122is installed through the subaquatic surface location “S” into the geologic formation “G.” The conductor pipe122may extend through a mud layer G1, an unconsolidated earth layer G2and a rock layer G3of the geologic formation “G.” As illustrated inFIG.3, the conductor pipe122has been severed to define an upper edge306at or near the subaquatic surface location “S.” An upper portion of122aof the conductor pipe122has been removed. The mudline suspension hanger profile124is defined within the conductor pipe122, and includes a landing shoulder308at a depth D1, which may be within the rock layer G3in some embodiments. For example, the depth D1may be about 15 feet below the subaquatic surface location “S.”

The landing shoulder308may support first and second casing hangers310,312of the mudline suspension hanger profile thereon. The first and second casing hangers310,312may be carried to the landing shoulder308by the upper portions128a,132aof the surface casing string128and the first intermediate casing string132, respectively. The upper portions128a,132amay remain in place, connecting the surface wellhead118to the wellbore304, until such time the wellbore304is to be temporarily suspended. As illustrated inFIG.3, the upper portions128,132have been removed from the first and second casing hangers310,312. The first casing hanger310engages a landing ring314, which rests on the landing shoulder308. The second casing hanger312is supported on an interior shoulder316defined within the first casing hanger310. The first casing hanger310supports the lower portion128bof the surface casing string128in the wellbore304and the second casing hanger312supports the lower portion132bof the first intermediate casing string132in the wellbore304.

The uphole tieback portion212of the split casing string204extends radially within the first intermediate casing string132. The uphole tieback portion212extends upwardly through the subaquatic surface “S,” bypassing the mudline suspension hanger profile124, and upward for a second distance D2to the surface wellhead118. In some embodiments, the distance D2may be about 168 feet including a water depth D3of about 60 feet and a distance D4above the water surface “W” (generally referred to as the air gap) of about 108 feet. The uphole tieback portion212may be supported by the surface wellhead118.

Referring now toFIG.4, illustrated is a partial cross-sectional view of the surface wellhead118with the uphole tieback portion212supported therein. The surface wellhead118includes a casing head402to which a riser404or conductor pipe122is secured. The casing head402may be threaded onto the top of the riser404, or the casing head402and the riser404may be welded to one another in some embodiments. A casing hanger406is supported on a shoulder408within the casing head402, and a casing spool410is secured to an upper end of the casing head402enclosing the casing hanger406within an interior of the surface wellhead118. The casing hanger408supports the upper tieback portion212therein such that the upper tieback portion212may bypass the mudline suspension hanger profile124(FIG.3) by passing therethrough and without being supported thereby.

Referring now toFIG.5, and with continued reference toFIGS.1-4, a procedure500is described for installing the mudline suspension system202. Initially at step502, the conductor pipe122is installed through the subaquatic surface location “S.” The conductor pipe122may be driven into the geologic formation “G” with a pile driver or similar mechanism, or alternatively, the wellbore304may be drilled to a depth of about 200 feet (or to an alternate depth determined to be within a service capacity of the conductor pipe) and the conductor pipe122may be inserted into the wellbore304. At step504, the wellbore304may be drilled to a subaquatic depth through the conductor pipe122, e.g., to a depth of about 650 feet (or an alternate depth determined to be within a surface capacity of the surface casing string128). The surface casing string128may then be hung on the landing shoulder308of the conductor pipe and cemented in place in the wellbore304. With the surface casing string128installed, the wellbore304may then be rated at 1,500 psi.

At step506, the wellbore304may be extended to a depth sufficient to accommodate the first intermediate casing string132, e.g., 2,500 feet (or an alternate depth determined to be within a surface capacity of the first intermediate casing string132). The first intermediate casing string132may then be run into the wellbore304and hung within the surface casing string128. The first intermediate casing string132may then be cemented into place, and the wellbore may then be rated at 4,500 psi.

At step508, the wellbore304may be extended to a depth sufficient to accommodate the downhole liner portion210of the split casing string204, e.g., 4,500 feet (or an alternate depth determined to be within a surface capacity of the downhole liner portion210). The downhole liner portion210may then be run into the wellbore304and hung on liner hanger214at a lower end of first intermediate casing string132. The downhole liner portion210may then be cemented into place.

At step510, the upper tieback portion212of the split casing string204may be stabbed into the PBR218defined within the lower liner portion210. A seal may be established within the PBR218, e.g., with a seal assembly (not shown) carried by the upper tieback portion212. The upper tieback portion212may be hung from the surface wellhead118to bypass the mudline suspension hanger profile124. In other embodiments, the upper tieback portion212may be hung from the conductor pipe122, riser404or another location above the mudline suspension hanger profile124. Then the wellbore304may then be rated at 10,000 psi. At step512, the upper tieback portion212may optionally be cemented into place by filling annulus220with cement.

The procedure500may then proceed to step514where operations may be conducted in the wellbore304(with a rating of 10,000 psi) through the split casing string204. For example, the wellbore304may be extended to a depth sufficient to accommodate the liner136, e.g., 7,000 feet (or an alternate depth determined to be within a surface capacity of the liner136). The liner136may be hung from liner hanger138at lower end or the lower liner portion210.

At step516, the wellbore304may be suspended. In embodiments where the upper tieback portion212has been cemented into place, the upper tieback portion212may be cut within the conductor pipe122. Portions of the upper tieback portion212above the cut may then be removed from the wellbore304. In embodiments where the upper tieback portion212has not been cemented into place, the entire upper tieback portion212may be removed from the wellbore304. Appropriate plugs and or caps (not shown) may be installed within the wellbore304or at the mudline, e.g., at the subaquatic surface location “S” for safety and to protect the wellbore304, and the wellbore304may be temporarily abandoned or suspended.

At step518, further operations may be conducted in the wellbore304by reconnecting to the wellbore304. For example, the uphole tieback portion212may be re-stabbed into the PBR218in embodiments where the uphole tieback portion212was removed. Alternatively, an additional tieback (not shown) may be provided to connect the uphole tieback portion212to the surface wellhead118in embodiments where the uphole tieback portion212was cut within the wellbore304.

It should be appreciated that the steps of procedure500may be conducted in alternate orders. Also not every step may be performed in every procedure employing the MLS system202.