Patent Abstract:
A subsea riser disconnect assembly  10  may be actuated from a drilling rig DR by axial movement of an upper riser  35  relative to a lower riser  28 , for disconnecting the upper riser  35  from the lower riser  28 . A subsea riser valve assembly  20  may be actuated from the drilling rig DR by axial movement of the upper riser  35  relative to the lower riser  28 , for sealing an interior portion of the lower riser  28  and well bore WB below the subsea riser valve assembly  20 . A drill pipe disconnect  30  may be actuated from a drilling rig DR, either onshore or offshore, for disconnecting an upper portion of drill pipe  236  from a lower portion of drill pipe  240 . The drill pipe disconnect  30  may be actuatable by hydraulic and/or mechanical forces applied to the drill pipe disconnect  30  from the drilling rig DR. The drill pipe disconnect  30  may be compatible for use with or without the subsea riser disconnect assembly  10  and/or the subsea riser valve assembly  20 . The component assemblies of this invention may improve the efficiency and lower the cost of recovering hydrocarbons by reducing drilling costs and time requirements. Also, the ability to relatively quickly disconnect a floating rig from a well may enhance the safety of persons and equipment facing hostile weather conditions or other emergency situations.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/382,762 filed on Mar. 06, 2003 now U.S. Pat. No. 7,040,406 which is a divisional of Ser. No. 09/569,609 filed on May 10, 2000, U.S. Pat. No. 6,557,637. 

   FIELD OF THE INVENTION 
   The present invention relates to drilling subsea wells, and typically from a floating drilling rig. More particularly, this invention relates to a subsea riser disconnect equipment and techniques for sealingly connecting a lower riser extending downward into and fixed within a subsea well bore with an upper riser extending downward from the floating drilling rig, such that the upper riser may be disconnected from the fixed lower riser during adverse weather or other rig move-off conditions. 
   BACKGROUND OF THE INVENTION 
   Subsea wells are increasingly important to hydrocarbon recovery operations. Numerous land-based wells have been drilled, but the percentage of hydrocarbons recovered from land-based wells is steadily decreasing in some parts of the world. Jack-up rigs have been used offshore for decades to drill wells subsea to recover oil, but jack-up rigs are practically limited to drilling operations in relative shallow water of several hundred feet. As water depth increases other drilling rig options may be required to facilitate drilling and well completion operations. In addition to an increase in the number of off-shore wells being drilled, in more recent years an increasing number of wells are being drilled in deeper water and at increasing costs. Accordingly, drilling from offshore rigs, e.g., drilling ships, semi-submersibles, jack-ups, drilling barges or submersible rigs has significantly increased in recent years. The economics associated with drilling offshore remains, however, a primary reason why more wells are not drilled offshore. Particularly, in drilling exploratory wells where financial risk and commercial hydrocarbon uncertainty may severely impact the economics for drilling such wells, costs and may be more critical in determining whether any wells are drilled at all, and how many may be drilled. 
   The majority of offshore or marine drilling rigs utilize riser sections as the outermost tubular between the rig and the seafloor, with the riser sections typically being bolted, clamped, mechanically fixed by dog-type latch mechanisms or otherwise connected. Riser sections conventionally include hydraulic lines spaced outwardly of the assembled riser pipe for operating the blow out preventer (BOP) and subsea ram stack located above the mud line. During an emergency or in anticipation of adverse weather conditions, the subsea BOP may be closed and the rams hydraulically activated to seal off the well bore. Prior to closing the rams, the drill pipe may be threadably disconnected above or below the BOP stack utilizing a back off tool or back off method, or the drill pipe may be sheared by the shear ram assembly. In some applications, acoustically or electrically activated subsea accumulators have been used to replace the hydraulic lines which commonly are run along side the riser pipe. The subsea BOP stack assembly used during deep water drilling operations may contribute significantly to the cost of drilling a well and a substantial amount of expensive rig time may be expended running in and removing the riser pipe sections and related well control equipment. 
   The above disadvantages associated with drilling from floating drilling rigs have long been known. Accordingly, some drilling or operating companies may recommend “riser-less drilling” for certain deep water applications. A subsea pump may be provided to return the drilling fluid to the surface in a separate flow line. Riser-less drilling still has to contend with the high cost of the BOP stack and hydraulic operation of this equipment. Several wells have been successfully drilled from a floating drilling rig, while using a riser, wherein the BOP is placed on the drilling rig rather than subsea. To date, however, these wells practically are limited to geographic areas where and/or seasons when there is a reduced likelihood of adverse weather conditions which would require the floating drilling rig to relatively quickly disengage a portion of the riser, e.g., an upper riser from the lower riser. In these applications, however, elimination of the subsea BOP stack may result in significant cost savings when drilling a well. Further savings may be realized by using conventional threaded casing for a riser rather than flange-type riser pipe sections. Less area on the drilling vessel is required to store casing having the same nominal diameter as the riser pipe sections since conventional riser pipe sections include both flanges and hydraulic lines which are eliminated when using casing as the riser. 
   Typically, subsea BOP stacks are installed on the riser string. The BOP stack may be required to provide a subsea method of isolating a lower portion of the riser and well bore from the riser above the BOP stack. Stress in the riser typically includes the weight of the riser and the weight of the subsea BOP. Subsea BOP stacks may weigh in excess of 400,000 pounds. The weight of the BOP stack plus the weight of a riser sufficiently strong enough to deploy such stack and meet operational requirements necessitates that risers are inherently heavy pieces of equipment which may exert high levels of stress and strain on the drilling and on the riser sections. These effects may be even more pronounced in deep water applications. In deep water installations, installation of a typical riser system may require calm weather and well in excess of a week to install, and in excess of a week to retract. In addition to the subsea riser and BOP stack, electrical and hydraulic umbilical lines are typically deployed concurrently, to control and operate the BOP stack, choke and kill line valves, and hydraulic disconnects if present. Deployment and recovery of this equipment and the rig time involved all contribute significantly to well costs, as daily rental rates for semi-submersible drilling rigs may exceed $240,00 per day. Premature disconnection of a portion of the riser can likewise be expensive and time consuming, such as may be necessary in advance of hostile weather conditions, broken mooring chain or slipping mooring anchor. 
   If drill pipe is in a well bore and it becomes necessary to seal the interior of the well bore, pipe rams or shear rams in the BOP stack may be closed on the drill string to confine pressure and fluid within the well bore. In the event it becomes necessary to disconnect an upper portion of the drill pipe from a lower portion of the drill pipe, the drill pipe may be unthreaded at a tool joint, or cut with a chemical cutter or explosive charge. If pipe is stuck, the free point may be estimated by a free point calculation technique. Each of these disconnect methods requires time to determine free points, deploy appropriate tools on wire line, such as a “string shot,” a free-point tool, a chemical cutter or jet-shot explosive charge. Multiple attempts and re-calculations may be required. The process can be time consuming and frustrating and may still result disconnecting at an undesirable disconnect point. Reconnecting after disconnecting can be even more exasperating, time consuming and expensive, and even impossible. 
   Disadvantages of the prior art are overcome by the present invention. An improved method of drilling from a floating drilling rig is hereinafter disclosed. A subsea riser disconnect is provided for connecting and disconnecting a lower riser from an upper riser. 
   SUMMARY OF THE INVENTION 
   This invention provides means and equipment for relatively quickly, physically disconnecting a floating drilling rig from a subsea well in a manner that may be operationally and economically more efficient than prior art equipment and techniques. In the event hostile weather conditions, rig conditions or well conditions threaten the safety or operating capabilities of an offshore drilling rig or work over vessel, the rig or vessel may be disconnected and moved out of harms way. The rig may later return to the well location and reconnect to the disconnected members. This invention provides means and equipment for installing a riser system and well control system which may provide for a more cost effective offshore drilling and/or work over operations than is available under prior art. Such improvements may reduce the costs to find, develop and produce hydrocarbons. 
   In one embodiment, this invention generally includes three primary components: a) a maritime or subsea riser disconnect for disconnecting and reconnecting an upper portion of the riser with a lower portion of the riser, b) a subsea riser valve for sealing off an interior of a well bore below the riser valve, and c) a drill pipe disconnect for disconnecting and reconnecting an upper portion of the drill pipe with a lower portion of the drill pipe. 
   Subsea Riser Disconnect 
   A preferred embodiment of a subsea riser disconnect includes an apparatus and means which disconnects an upper portion of the subsea riser from a lower portion of the riser, through axial movement of the upper riser relative to the lower riser. The upper riser and the lower riser may be collectively referred to as a riser system. The subsea riser disconnect may be positioned at substantially any point within the riser system, e.g., between the drilling rig and the mud line. The subsea riser is preferably accessible to either a remotely operated vehicle (ROV) or a diver, in order that a riser disconnect lockout device may be operated if needed. The subsea riser disconnect may facilitate placing the blow out preventer and well control stack (BOP) either on the rig or suspended from but relatively near the rig. 
   A preferred embodiment of a riser disconnect may include a male disconnect member secured to the lower end of the upper riser, and a female disconnect member secured to the upper end of the lower riser. The male disconnect member may include a seal mandrel and seal elements for providing a hydraulic seal between the male disconnect member and female disconnect member. The male disconnect member may also include a collet mechanism to facilitate latching and unlatching the male and female disconnect members. A lockout device may be included to prevent inadvertent actuation of the subsea riser disconnect, such as during initial installation of the riser disconnect and riser system. Manipulation of the lockout may be externally performed, such as by ROV, diver or otherwise. 
   The female riser disconnect member may include a seal bore receptacle for sealingly receiving the seal mandrel within the seal bore receptacle, and a circumferential collet groove may be included in an inner surface of the female riser disconnect for engaging collet dogs. A conical shaped entry guide may be included on an upper end of the lower riser disconnect member to guide the male disconnect member into the female disconnect member during subsea connection of the male and female disconnect member. 
   Manipulation of the riser disconnect latch may be performed by axial motion or reciprocation of the upper riser relative to the lower riser. (The terms “axial reciprocation, reciprocation, axial motion, axial, or similar variations of these terms, as used herein may be defined to be substantially synonymous, and include linear displacement of a first component relative to a second component, substantially along a common linear axis, in a first direction and/or second direction, but not necessarily consecutively in both directions during a single manipulation period.) The latching collet mechanism of the riser disconnect may be manipulated between the collet latch position and the collet unlatch position by alternately applying tension and releasing tension in the riser disconnect by the drilling rig. 
   In an initial installation, the riser latch mechanism, including the collet mechanism, may be positioned in the coIlet latch position. After the riser system is installed and cemented in position within the well bore, tension may be applied to the riser system at the riser disconnect to securely retain the latched engagement between the male and female disconnect members. 
   To disconnect the male and female disconnect members, such as in advance of an approaching storm, tension in the riser disconnect may be relaxed allowing the male disconnect member to move axially downward relative to the female disconnect member, thereby unlatching the collet mechanism. The upper riser may be subsequently raised, separated from and suspended above the lower riser. The rig may then be moved and/or the upper riser recovered to the rig. 
   To reconnect the riser disconnect, the male disconnect member may be guided by the entry guide into engagement with the female disconnect member and the collet mechanism re-latched. Tension may be applied and maintained in the riser system to retain the latched configuration during operations until it is desirable to again disconnect the riser disconnect system. Upon completion of well work operations, the female disconnect member with the male disconnect member (plus a subsea riser valve, if run) may be typically recovered together by normally cutting the riser below the mud line with either an explosive charge, a chemical cutter or a mechanical cutter. 
   If desired, the riser disconnect and lower riser may be drilled into position in the sea bed while the well bore for the lower riser is being drilled. This may be accomplished by a number of means, for example preferably by positioning the lower riser on the sea bed with a riser disconnect and portions of an upper riser attached or to be attached substantially during drilling operations, and running a string of drill pipe, a drill bit and/or an under reamer bit through the deployed riser assembly and rotating the riser string with the bit while drilling the lower riser into the seabed. Alternatively, the drill string may substantially swivel or rotate within the riser while the riser may not rotate or may rotate independently from the drill string, while drilling the lower riser into the sea bed for cementing and permanent placement of the lower riser. The drill bit and drill string may then be retrieved back to the rig. Those skilled in the art of well drilling operations will appreciate that there are a number of other means for drilling in the lower riser. An alternative embodiment for the riser disconnect provides non-rotational engagement grooves in order to rotate the riser with the drill string. 
   In an another alternative embodiment, the upper riser may include the female disconnect member and related components, while the lower riser provides the male disconnect member and related components. An alternative embodiment may also provide the seal members within the female member while the male seal member provides a substantially smooth sealing surface on a mandrel. 
   It is an object of the present embodiment to improve the economics of drilling, completion and work over operations from an offshore rig by providing a more economical method of equipment optimization and use. An embodiment provides apparatus and means for placing the wellhead and BOP system substantially on the rig. In a preferred installation, a riser system may be utilized which employs riser joint connections secured by means and apparatus other than by flanges and bolting, such as a threaded riser consisting of joints of well casing, or a groove locked connection. Such equipment usage and arrangement may also save a considerable amount of time in retracting and deploying the upper riser. In addition, a flex joint may be provided either above or below the riser disconnect to accommodate riser angular displacement. 
   It is also an object of this embodiment to provide apparatus and means to relatively quickly disconnect an upper riser from a lower riser to facilitate moving the rig out of harms way. This embodiment provides a riser disconnect system which may be actuated by merely reciprocating the upper riser relative to the lower riser. 
   It is further an objective of this embodiment to provide a riser disconnect apparatus which may be easily and reliably manipulated from the rig. Manipulation of the riser disconnect between the riser latch position and the riser unlatch position may be performed by simple axial reciprocation of the riser disconnect from the rig. Moving the BOP stack near the rig may also assist in economic riser deployment and recovery. 
   It is a feature of this preferred embodiment to provide a riser disconnect system which may be reconnected after disconnecting the male and female disconnect members. The riser disconnect system of this embodiment may be repeatedly connected and disconnected. 
   It is another feature of this embodiment that the riser disconnect may be manipulated between the connected and disconnected positions without subsurface hydraulic and/or electrical umbilical lines. Although such lines may optionally be employed for other purposes, the riser disconnect does not require them. 
   It is also a feature of this embodiment that the riser disconnect system may be locked in the riser latch or unlocked from the riser latch position. The riser system, including the riser disconnect may be installed while the riser disconnect is locked in the latched position, and after installation the riser disconnect may preferably remain unlocked, while riser tension maintains the disconnect in a latched configuration. 
   These advantages may enhance deep water operations by facilitating employment of an improved, more cost effective riser and drilling system which may save considerable time and costs. The subsea riser disconnect may provide for placing the BOP stack on or suspended just below the rig or drill ship, thereby effectively eliminating placing the BOP stack on the ocean floor. By minimizing the number of subsurface hydraulic and electric umbilical lines, connectors, and kill and choke lines, several days of rig time may be saved. The preferred drilling equipment configuration and alternative embodiments thereof, as disclosed herein, may be particularly applicable for drilling and completing exploratory or other wells where well costs are a key consideration and where the well may not be intended for production after well testing. 
   It is also a feature of this embodiment that the riser disconnect system may be employed with re-entry risers as well as drilling and completion risers. Although the preferred embodiment is illustrated generally in terms of use with a drilling riser installation, the concepts and apparatus for riser disconnect manipulation by axial reciprocation methods may be applied equally well to risers used in completion and re-entry operations following well completion. 
   Subsea Riser Valve 
   A preferred embodiment of a subsurface riser valve includes an apparatus and methods for sealing the interior of a well bore, below the riser valve, through axial movement of the riser above the riser valve (generally, the upper riser) relative to the riser below the riser valve (generally, the lower riser). The subsea riser valve may be positioned at substantially any point along a riser system, preferably below the riser disconnect such that the riser valve may be closed in conjunction with or prior to disconnection of a riser disconnect. The subsea riser valve may also provide a subsea method of well control, such that the BOP stack may be positioned on the rig. 
   A preferred embodiment of the subsurface riser valve provides for the riser valve as a distinct, stand-alone piece of equipment which may be employed separately or in combination with riser and/or drill pipe disconnect apparatus. The riser valve is preferably used in combination with the riser disconnect, such that the riser valve is positioned below the riser disconnect in order that the interior of a lower riser and well bore below the riser valve may be hydraulically isolated and confined. The lower end of a riser valve may be sealingly connected to the upper end of a lower riser, a well casing, a well head or other subsea component. The upper end of the subsea riser valve may be directly or indirectly secured to the lower end of the subsea riser disconnect. 
   The subsea riser valve includes a valve housing enclosing a valve sealing member, and a valve actuation mandrel telescopically extending from the upper portion of the riser valve. A linkage or connector may moveably connect the valve sealing member and the valve actuation mandrel. The riser valve may be biased closed and may be opened in response to axial tension in the riser system. A lockout device similar to the lockout device described on the riser disconnect above, may be included with the riser valve apparatus, to lock the riser valve in either the valve opened or valve closed positions. 
   The riser valve may be locked in the opened position during installation of the riser system to allow the riser to fill with fluid and to allow circulation of fluids or slurries through the string prior to applying tension in the valve system. When the riser valve and riser system are properly positioned, installed and cemented, tension may be exerted on the riser valve to maintain the valve sealing member in the valve opened position. Prior to closing the valve sealing member, components within the through bore of the riser valve may be removed from within the through bore of the riser valve, such that the valve sealing member may freely move between the valve closed and valve opened positions. 
   It is an objective of this embodiment to provide an apparatus and means for sealing the interior of a riser and well bore below the riser in response to axial motion of the upper riser string. To close an opened valve sealing member, axial tension in the riser system may be relaxed such that the weight of the riser and the resulting closing biasing force may close the riser valve, effectively sealing the well bore below the riser valve. To open the riser valve, axial tension may be applied to the upper riser and valve actuation mandrel sufficient to overcome the riser weight and closing bias force. The riser valve may be opened and closed repeatedly as needed during well operations. 
   It is an object of this embodiment that the riser valve may be used in conjunction with the riser disconnect to provide a mechanically actuated riser disconnect and well control system for connecting a drilling rig to a subsea well bore. Such mechanically actuated system may assist in facilitating placing the BOP stack and related well control equipment on or near the drilling rig. Such arrangement may significantly decrease well costs by eliminating hydraulic and/or electrical umbilical lines between subsea equipment and the rig. Concurrent and subsequent axial movement of the riser may also unlatch and disconnect the upper riser from the lower riser. The rig and upper riser may thereafter be removed from the situs of the well, while the subsea well control valve remains to contains well pressure and fluids within the well bore. 
   It is also an object of this embodiment to provide a subsea riser valve which may be manipulated between the opened and closed positions without hydraulic or electrical lines. Mechanical movement within the valve mechanism is provided by axial movement of the riser system, thereby effectively eliminating the need for hydraulic or electrical actuation of the valve sealing member. 
   It is a feature of this embodiment that the riser valve provide a full bore opening through bore. The preferred riser valve, including the valve sealing member may provide an ID that is not less than the minimum ID of either or both of the upper riser and lower riser. 
   It is another feature of this embodiment that the preferred riser valve may be provided as a separate, stand alone device, such that the riser valve may be used alone in a riser system, or a riser disconnect may be combined with a stand-alone riser valve and/or other separate devices. Alternatively, the riser valve may be integrated into a common housing with a riser disconnect apparatus. Both apparatus may be compatible for use as an integrated tool combining both the riser valve and the riser disconnect in a common housing or body, as both may be compatibly manipulated by axial tension applied at the drilling rig. 
   It is also a feature of this embodiment that the riser valve may be installed inverted from the preferred orientation described above, such that the valve actuation mandrel is connected to the lower riser, casing or well head. In either the preferred or an inverted embodiment, the riser valve may be manipulated with tension in the upper riser. 
   An additional feature of other embodiments of this invention is that the riser valve components may be varied such that the valve sealing member may be of a type other than a ball type sealing member, such as plug type rotational cylinder members, or gate type sealing members, or flapper type sealing members. Alternative embodiments for a riser valve may be configured for manipulating each of these types of sealing members from axial movement of the upper riser relative to the lower riser. 
   Drill Pipe Disconnect 
   Apparatus and method are disclosed for connecting and disconnecting an upper portion of a drill pipe string above a drill pipe disconnect apparatus from a lower portion of a drill pipe string below the disconnect apparatus. The drill pipe disconnect may be positioned at substantially any point along the drill string wherein it may be convenient or desirable to disconnect a portion of the drill pipe string from the remainder of the string. Such disconnection may be required in conjunction with disconnecting a subsea riser disconnect, and/or in conjunction with closing a subsea riser valve, such as may be desirable in advance of relocating the rig due to approaching threatening weather. 
   The drill pipe disconnect is preferably used in conjunction with the subsea riser disconnect and/or the subsea riser valve. Prior to closing a riser valve and/or disconnecting a riser disconnect, rather than pull the entire string of drill pipe above the riser valve, it may be prudent to temporarily abandon the portion of the drill pipe string which is below the riser valve and the drill pipe disconnect. In such event, the drill pipe disconnect may be disconnected at a point below the riser valve, and the upper disconnected portion of drill pipe pulled up to above the riser valve, such that the riser valve may be closed and the riser disconnect subsequently disconnected. 
   The drill pipe disconnect may be selectively operable to mechanically disconnect or connect the upper and lower portions of a drill pipe string, in response to movement of a latch mechanism, while also providing axial and rotational strength commensurate with the strength of the drill pipe in use. Non-rotational engagement components may be included within the drill pipe disconnect to carry rotational stresses in the drill string. 
   A preferred embodiment of a drill pipe disconnect apparatus may generally include a male drill pipe disconnect member and a female drill pipe disconnect member. The male disconnect member may include a collet mechanism to latch and unlatch the male and female disconnect members. A latch sleeve may be included, which is movable between a collet latch position and a collet unlatch position. When the latch sleeve is in the collet unlatch position, the male drill pipe disconnect member may be released from engagement with the female drill pipe disconnect member. 
   The male and female disconnect members of the drill pipe disconnect may be secured within a drill pipe string by connections provided on each end of the drill pipe disconnect. In a preferable embodiment, the upper end of the male disconnect may include a threaded box type tool joint, while the lower end of the female disconnect may include a threaded pin type tool joint. 
   A preferred method of operation for the drill pipe disconnect generally includes providing and operating a first assembly and a second assembly, which is a modification of the first assembly. The first assembly may typically be employed for an initial drill pipe disconnect installation. Thereafter, subsequent to disconnecting the drill pipe assembly and recovering the male drill pipe disconnect member to the rig, the second assembly may be installed. The second assembly is provided by substituting a male reconnect member for the male disconnect member, to reconnect the male reconnect member with the female disconnect member. Thereafter, if desired the male reconnect member and the female disconnect member may be re-unlatched from one another. 
   The first assembly for the drill pipe disconnect may be installed in a drill pipe string, such that the col let mechanism and latch sleeve are in the collet latch position. A shear pin may secure the position of the latch sleeve within a male disconnect housing, in the collet latched position. The string of drill pipe including the drill pipe disconnect may be repeatedly inserted into and withdrawn from a well bore as needed, such as when “tripping pipe,” with the drill pipe disconnect apparatus threadably secured within the drill string. 
   In the event it becomes desirable to disconnect the drill pipe disconnect and temporarily or permanently abandon a lower portion of drill pipe within the well bore, an unlatching ball or other closure device may be dropped through the upper portion of drill pipe, from the rig floor. The unlatching ball may sealingly seat on the unlatching seat such that hydraulic pressure may be applied to the drill string from the rig to cause the latch sleeve to shear the shear pin and move downward to a position where the collet dogs may unlatch from engagement with the female disconnect member. The male drill pipe disconnect member may then be telescopically withdrawn from the female disconnect member, and the male disconnect member and upper portion of drill pipe withdrawn to the rig. 
   To reconnect the male disconnect member with the female disconnect member, the male second assembly of the male disconnect member may be provided with a positionable latch sleeve that includes two unlatch grooves, shear pins that provide for two shearing actions, a latching seat and an extension tube on the latch sleeve. The male disconnect member may subsequently be engaged with the female disconnect member in the well bore. A latching ball may then be dropped through the drill pipe string for sealingly seating on a latching seat in the latch sleeve. The latching seat may be secured within the latch sleeve by shear pins. Hydraulic pressure may be applied within the drill string, sufficient to shear the double shear pins at a first shear point. The latch sleeve may then move downward from a collet unlatch position to a collet latch position, such that the male and female disconnect members are again securely latched together. 
   Hydraulic pressure within the drill string may be further increased to until the shear pins which secure the latch seat within the latch sleeve are sheared, allowing the latch seat and latching ball to be ejected downward from within the latch sleeve. The extension tube on the latch sleeve may receive or catch the ejected latch seat and latching ball. The extension tube may provide a plurality of ports to hydraulically interconnect the upper and lower portions of the interior of the drill pipe. A hydraulic conduit is thereby provided through the drill pipe through bore such that fluid may be circulated through the upper and lower portions of the drill pipe string. The latch seat and latching ball may remain within the extension tube. As an alternative, instead of shearing the latch seat pins and ejecting the latch seat and latching ball and receiving the latch seat and latching ball within the extension tube, the latch ball may be recovered to the surface. Fluid may be circulated down the drill pipe/casing annulus and back up through the drill bit and drill pipe to reverse flow the latching ball back to the surface of the rig. 
   In the preferred embodiment, to re-unlatch the male drill pipe disconnect from the female drill pipe disconnect, a re-unlatching ball may be dropped for sealingly seating on a re-unlatching seat. Hydraulic pressure applied within the drill pipe through bore may shear the double shear pins at a second point and allow the latch sleeve to move downward to a re-unlatch position, wherein the male disconnect member may be withdrawn from the female disconnect member and recovered to the rig. For subsequent re-engagement, the male disconnect member may be again re-dressed as described above for reconnection. 
   The drill pipe disconnect apparatus and/or method may be utilized in either an off-shore installation or a land based installation. In a land based installation, the drill pipe disconnect may provide for a disconnect point in the drill pipe string, such as may be desirable to provide above a geologic trouble spot or near a casing seat above an open hole section. It may be desirable to provide a convenient disconnect device at a point in the drill string where backing off or disconnecting otherwise may be difficult or impossible to achieve, particularly in deep wells or along long horizontal well bore sections. 
   It is an object of this embodiment to provide a method of operation and an apparatus for disconnecting an upper portion of a drill pipe string from a lower portion of the drill pipe string in a quick, reliable manner. The preferred disconnect method and apparatus disclosed herein facilitates providing a relatively simple and reliable disconnection point within a drill pipe string. Some of the components and mechanisms relied upon for operation of this embodiment are recognized as generally reliable mechanisms, such as a collet mechanism, shear pinned components, and ball and seat type hydraulic seals. 
   It is also an object of this embodiment to provide a drill pipe disconnect apparatus and method which may be manipulated without relying upon back-off tools, back-off methods, external manipulation devices or destruction of drill pipe to disconnect. This embodiment provides method and apparatus for disconnecting an upper section of a drill pipe string from a lower section of the drill pipe string by dropping a ball and applying hydraulic pressure to unlatch a latch mechanism. The drill pipe disconnect can also be actuated with a portion of the drill string off the bottom of the well bore. To disconnect the drill pipe disconnect mechanism with the drill string off bottom of the well bore, disconnection may only require that a higher pressure be applied to the interior of the drill pipe string above the dropped ball. 
   It is a feature of this embodiment that an apparatus and method are provided for reconnecting the upper and the lower drill pipe sections after they have been disconnected. In this embodiment the upper and lower drill pipe sections may be re-engaged and then re-latched by dropping a ball and applying hydraulic pressure to securely re-latch the upper and lower drill pipe sections. 
   It is also a feature of this embodiment that the re-latched drill pipe sections may subsequently be unlatched again, thereby facilitating repeated disconnects and reconnects as desired. The drill pipe reconnect and disconnect apparatus and methods are simple and reliable to operate and may save time and costs in disconnecting a drill pipe string at a pre-determined location. 
   It is yet another feature of this embodiment that the drill pipe disconnect may provide an apparatus and method for rotating the drill string. Non-rotational engagement members are provided which may provide rotational strength within the disconnect apparatus which is substantially equivalent to the strength of the drill pipe. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified pictorial representation of a drilling rig, a riser assembly, a riser disconnect, a riser valve, a string of drill pipe, and a drill pipe disconnect in a drilling installation. 
       FIG. 1A  is a pictorial illustration of a riser male disconnect member disconnected from a female riser disconnect member, with an upper portion of drill pipe disconnected from a lower portion of drill pipe. 
       FIG. 2  is a cross-sectional view of an upper portion of a riser disconnect assembly illustrated in cross-section. 
       FIG. 2A  is a side view of a riser disconnect lockout as shown in  FIG. 2 , in a locked orientation. 
       FIG. 3  is a cross-sectional view of lower portion of the riser disconnect assembly illustrated in  FIG. 2 . 
       FIG. 3A  is an enlarged view of a collet mechanism illustrating a collet mechanism in a latched position. 
       FIG. 4  is an enlarged half-section illustration of the riser disconnect collet mechanism generally illustrated in  FIG. 3 . 
       FIG. 5  is a cross-sectional view of a riser disconnect lockout wherein the left half of  FIG. 5  illustrates the lockout mechanism in the locked orientation and the right half of  FIG. 5  illustrates the lockout mechanism in the unlocked orientation. 
       FIG. 5A  is a side view of the riser disconnect lockout shown in  FIG. 2 , in cross-section through the lockout pin illustrating retainers, grooves and stop dimples. 
       FIG. 6  is a cross-sectional top view of a riser valve assembly, illustrating a ball pivot and the ball linkage adapter. 
       FIG. 6A  is a side view of a ball type sealing member shown in  FIG. 6 , illustrating an engagement groove and engagement pin arrangement. 
       FIG. 7  is a cross-sectional view of a subsea riser valve assembly, with a valve ball in the opened position. 
       FIG. 8  is a cross-sectional top view of a subsea riser valve assembly illustrating a riser valve lockout device and a valve mandrel guide. 
       FIG. 9  is an enlarged half-sectional view of a subsea riser valve with a valve ball in a closed position. 
       FIG. 10  is a cross-sectional view of a drill pipe disconnect in the collet latched position initially installed, including an unlatching ball. 
       FIG. 11  is a cross-sectional view of the drill pipe disconnect illustrated in  FIG. 10 , with the latch sleeve moved downward to the collet unlatch position. 
       FIG. 12  illustrates a lower end of a second assembly, a male reconnect member separated from the upper end of a female disconnect member, with the female disconnect member illustrating non-rotational engagement grooves. 
       FIG. 13  is a cross-sectional view of a drill pipe disconnect with the second assembly, a male reconnect member engaged with the female disconnect member, in the collet unlatch position with a latching ball seated. 
       FIG. 14  is an enlarged illustration of the disconnect shown in  FIG. 13 , with the latch sleeve displaced downward in the collet latch position. 
       FIG. 15  is an enlarged illustration of a portion of the disconnect shown in  FIG. 13 , with the latch ball and latch seat ejected into the latch sleeve extension. 
       FIG. 16  is a cross-sectional illustration of a drill pipe disconnect with a re-unlatching ball seated and the latch sleeve moved downward to the collet re-unlatch position. 
       FIG. 17  is a cross-sectional view of a drill pipe disconnect collet mechanism illustrating collet dogs engaged with a female disconnect member and illustrating the fingers connecting the latch mandrel with the collet engagement ring. 
       FIG. 18  is a cross-sectional view of a riser disconnect embodiment including a non-rotational key engagement head which is engaged with a non-rotational key. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a generalized, suitable application for a subsea riser disconnect, a subsea riser valve and a drill pipe disconnect according to the present invention. In one embodiment, this invention includes three principle assemblies, namely: 1) a subsea riser disconnect assembly  10 , 2) a subsea riser valve assembly  20 , and 3) a subsea drill pipe disconnect assembly  30 . Each of these three principle assemblies may be provided in a drilling installation, separate and apart from or in combination with any or both of the other principle assemblies, or primary components. As disclosed subsequently, safety mechanisms may be included within each principle assembly to prevent inadvertent operation of that assembly. 
   Each of these three primary components  10 ,  20 ,  30  may be employed individually or in conjunction with one or both of the other primary components. And each of these three components generally include a through bore extending through the component along a central axis  15 . The central axis  15  may substantially be common to each and all components. (It is understood and assumed throughout this disclosure, that all seals may be both hydraulic seals and pneumatic seals, notwithstanding the fact that a particular seal may be simply designated as a hydraulic seal or otherwise. It is also understood and assumed that all connections, secured components, attachments or otherwise joining of two or more components may effect a seal, unless designated otherwise. It is further understood and assumed that the terms drilling rig, rig, work over rig, and drill ship, semi-submersible and related terms may be used interchangeably and not in limitation.) 
   One or more portions of a preferred embodiment of a sub-sea riser disconnect assembly  10  are illustrated in  FIGS. 1 ,  1 A,  2  and  3 , for sealingly connecting a lower riser  28  extending downward from above the mud line ML through a seabed SB and into a subsea well bore WB with an upper riser  35  extending downward from a drilling rig DR to the lower subsea riser  28 . The drilling rig DR may include floating types of drilling rigs DR such as a drill ship and a semi-submersible rig. The position of the drilling rig DR is not fixed with respect to the location of the wellbore WB. The lower subsea riser  28  may be secured within the wellbore WB, e.g., by a cementing operation, such that the riser disconnect assembly  10  may be selectively activated to disengage and/or reengage a lower end  37  of the upper riser  35  from an upper end  19  of the lower riser  28 . 
   The subsea riser disconnect assembly  10 , the subsea valve assembly  20 , the drill pipe  36 , the drill pipe disconnect  30  and the wellbore WB may each include a through bore and a central axis  15 . Both the through bore and the central axis  15  may be substantially aligned along a common central axis  15 . 
   The riser disconnect assembly  10  includes a male disconnect member  12 , which may be secured to the lower end  37  of the upper riser  35 , and has a central axis aligned along the axis  15 . The riser disconnect assembly  10  also includes a female disconnect member  18  for axially receiving the male disconnect member  12  therein. The female disconnect member  18  may be secured to upper end  19  of the lower riser  28 . The riser disconnect assembly  10  may provide a full bore opening, such that the minimum ID of the through bore of the riser disconnect assembly  10  is equal to or greater than the ID of at least one of the upper  35  and lower  28  riser sections. Those skilled in the art will appreciate that a riser may generally be comprised of tubular components having a common through bore for providing a conduit that connects a drilling rig DR with a downhole DH portion of a well bore WB that typically extends below the lower end of the riser, where a portion of the lower end of the riser is secured within the seabed, below the mud line ML. 
   Riser Disconnect Male Member 
   As illustrated in  FIGS. 1 ,  2  and  3 , a seal assembly  14  may provide a pneumatic seal in the connection between the outer surface of the male disconnect member  12  and a mating inner surface of the female disconnect member  18 . The male component of the seal assembly  14  includes an upper seal mandrel  42 , which may be connected to a lower end  19  of the upper riser  35  by a riser connector collar  41 . A lower end of the upper seal mandrel  42  may be connected to an upper end of a lower seal mandrel  56 . The lower end of the lower seal mandrel  56  in turn may be connected to a seal retainer  61 , which may be connected to latch mandrel  62 . The upper end of the latch mandrel  62  may be connected to the lower end of the seal retainer  61 , while the lower end of the latch mandrel  62  may generally include the lower end of the male disconnect member  12 . A commonly known latch J-slot groove  63 , as shown in  FIG. 3 , may be included in the outer surface of the latch mandrel  62 , and may circumferentially surround the latch mandrel  62 , in either the pattern shown or another desired pattern. 
   One or more seal elements  54 , also commonly known as packing elements, may be positioned axially along the outer surface of the lower seal mandrel  56 , between the upper seal mandrel  42  and the seal retainer  61 . The seal elements  54  may circumferentially encompass the outer surface of the lower seal mandrel  56  and may include an alternating arrangement of a variety of seal materials in alternative embodiments. The seal elements  54  need not be axially continuous along the lower seal mandrel  56 , and may be positioned in sets, at axial intervals along the male component and female component. The female component of the seal assembly  14  may include a seal bore receptacle  58  for engaging the seal elements  54 . The female disconnect member  18  is discussed in detail below. 
   A riser interconnection device  40  may be included for releasably securing the male disconnect member  12  with the female disconnect member  18 . The riser interconnection device  40  may be actuatable in response to axial reciprocating movement of the upper riser  35  relative to the lower riser  28  from a connect position to a release position or from a release position to a connect position. This reciprocating movement may be effected by movement of the upper riser  35  at the drilling rig DR. In the release position, the male disconnect member  12  and the female disconnect member  18  may be uncoupled, thereby permitting mechanical separation of the upper riser  35  from the lower riser  28 , as discussed below. 
   Referring to  FIGS. 1 ,  3  and  4 , the riser interconnection device  40  may include a collet mechanism  60  for releasably interconnecting the male disconnect member  12  with the female disconnect member  18 . Components of the collet mechanism  60  included in the male disconnect member  12  may include a collet latch sleeve  72 , a latch pin  74  and the collet locking sleeve  80 . The collet latch sleeve  72  may include a plurality of collet arms  76 , and each collet arm  76  may include a collet dog  78  for engaging a collet groove  82 . The collet groove  82  may be provided in the inner surface of a latch housing sleeve  84  of the female disconnect member  18 . The collet latch sleeve  72 , a plurality of collet arms  76  and corresponding plurality of latch dogs  78  may be circumferentially spaced about the external surface of the latch mandrel  62  for selectively interconnecting the plurality of collet dogs  78  with the collet groove  82 . The collet latch sleeve  72 , the plurality of collet arms  76  and the latch dogs  78  may be axially and rotationally moveable about the common central axis  15 , with respect to the latch mandrel  62 . 
   One or more latch pins  74  may be secured in the collet latch sleeve  72 . The latch pins  74  may protrude radially inward from the inner surface of the collet latch sleeve  72  toward the central axis  15  for a distance sufficient for the latch pins  74  to engage the latch J-slot groove  63 , in the outer surface of the latch mandrel  62 . The intrusion of latch pins  74  into the J-slot groove  63  may not exceed the depth of the latch J-slot groove  63 . The plurality of collet arms  76  and collet dogs  78  are preferably made integrally part of the collet latch sleeve  72 . The plurality of collet arms  76  and collet dogs  78  extend downward from the collet latch sleeve  72 . The collet locking sleeve  80  may be immovably secured to the lower end of the latch mandrel  62 , below the collet latch sleeve  72 . 
   A portion of the collet locking sleeve  80  may extend axially upward along the outer surface of the latch mandrel  62  for a sufficient distance such that, with the riser disconnect assembly  10  in the latched position, a tapered portion  81  of the collet locking sleeve  80  may be circumferentially positioned between an inner surface of the collet dogs  78  and an outer surface of the latch mandrel  62 . The tapered portion  81  of the collet locking sleeve  80 , which is between the inner surface of the collet dogs  78  and the outer surface of the latch mandrel  62 , may also be referred to as the collet engaging ring  81 . An outer surface of the collet engaging ring  81  includes the tapered surface which may taper upward to a circumferential upper edge. A load bearing shoulder at bottom of the collet dog  78  may be supported on load bearing shoulder at lower end of collet engaging ring  81  of collet locking sleeve  80  when the riser disconnect assembly  10  is in the latched position. A load bearing shoulder at top of the collet dog  78  may be supported on load bearing shoulder at upper end of a collet engagement groove  82  when riser disconnect assembly  10  is in the latched position. 
   Riser Disconnect Female Member 
   Referring to  FIGS. 1 ,  2 ,  3  and  4 , the lower riser  28  extends upward from the mud line ML, generally toward the drilling rig DR. The lower end of the lower riser  28  may be connected to a well casing  32  which extends through a seabed and into a subsea wellbore WB. The female disconnect member  18  may include the latch housing sleeve  84 , a seal bore receptacle  58 , and an entry guide  34 . The latch housing sleeve  84  may also include the female portion of the collet mechanism  60 , e.g., the collet groove  82  for coupling with the companion male components of the collet mechanism  60 . A casing end of the latch housing sleeve  84  may be attached to the upper end of a well casing  32  or other component. A latch end of the latch housing sleeve  84  may include a collet groove  82  circumferentially within the inner surface of the latch housing sleeve  84  for releasably receiving and securing the collet dogs  78  of the male disconnect member  12 . 
   The latch end of the latch housing sleeve  84  may be attached to the lower end of the seal bore receptacle  58 . An entry guide  34  may be secured to an upper end of the seal bore receptacle  58 , and may assist in aligning the male disconnect member  12  with the female disconnect member  18  during reconnection of the male disconnect member  12  and female disconnect member  18 . An entry guide retainer  52  may be used to secure the entry guide  34  to the seal bore receptacle  58 . The entry guide  34  may extend upward toward the water surface from the point of attachment to the female disconnect member  18 , with a frustoconically expanding circumference, thereby forming a generally cone shaped receptacle defined by surface  38 . 
   Riser Disconnect Lockout Mechanism 
   In addition to the latch mechanism and seal components, the riser disconnect assembly  10  may include a riser disconnect lockout  50  to prevent inadvertent or unintentional disengagement of the male disconnect member  12  from the female disconnect member  18 . The riser disconnect lockout  50  may typically be used in the locked configuration only during the initial connection, installation and cementing of the upper and lower riser assembly, when compressive forces may be experienced due to running, installing and cementing the casing  32  and/or the riser disconnect assembly  10 . The riser disconnect lockout  50  may otherwise normally remain in the unlocked position since the applied axial tensile forces in the upper riser  35  prevent disconnection of the male disconnect member and the female disconnect member. Referring to  FIGS. 2 ,  2 A, the riser disconnect lockout  50  may preferably be comprised of a shouldered pin and groove assembly. The riser disconnect lockout  50  preferably may be provided on the male disconnect member  12 , axially between the riser connector collar  41  and the lower seal mandrel  56 . 
   Referring to  FIGS. 1 ,  2 ,  2 A,  3 ,  3 A,  4 ,  5 ,  5 A one or more lockout grooves  43  may be circumferentially provided on the outer surface of the upper seal mandrel  42 , each lockout groove to accommodate a lockout pin  46 . The one or more grooves  43  may each have a long axis which is aligned axially up and down along the upper riser  35 , substantially parallel with the central axis  15 . Each groove  43  includes a circular portion, at the lower end of the groove  43 , the circular portion having a diameter that is larger than the width of the groove  43 , as shown in  FIGS. 2A and 5 . A riser disconnect lockout housing  48  may be circumferentially positioned on the external surface of the upper seal mandrel  42 , the riser disconnect lockout housing  48  being axially moveable along the central axis  15 , on the outer surface of the upper seal mandrel  42 . 
   A riser disconnect lockout pin  46  may be provided for each lockout groove  43 . Referring to  FIGS. 2A ,  5 , and  5 A, the riser disconnect lockout pin  46  may include a round shaped upset providing lockout upset shoulders  45  and having two opposing flat sides where opposing portions of the round shaped upset are removed to provide the flat sides, on an inner end of the riser disconnect lockout pin  46 , the rounded portion provided along a major axis between the rounded ends and having a length that is larger than the diameter of the pin  46 , and a minor axis between the two flat sides which is substantially equal to the diameter of the pin  46 . Each lockout pin  46  may extend from inside of the riser disconnect lockout housing  48 , through a pin port  51  and may be furnished with a square socket for engagement with an ROV operating wrench (not shown). The round shaped portion of the riser disconnect lockout pin  46  remains inside of the riser disconnect lockout housing  48  in the respective lockout groove  43 . 
   As illustrated in  FIGS. 5 ,  5 A, spring loaded and/or threaded or otherwise secured retainer pins  49  may be positioned within the riser disconnect lockout housing  48  to engage a retainer groove  53  in each lockout pin  46  to provide resistance to the pin  46 . Such configuration may thereby prevent inadvertent rotation of the pin  46 . In addition the retainer groove  53  may only be provided circumferentially around a portion of the outer surface of the lockout pin  46 , such as ninety degrees, in order to provide rotational stop positions to ensure proper rotational orientation of the lockout pin  46 . Stop dimples  88 , as shown in  FIG. 5A , may be provided on a portion of the lockout pin  46  to ensure proper respective locked and unlocked lockout pin  46  orientation. 
   A lockout sleeve  44  may be concentrically disposed around a portion of the upper seal mandrel  42 . An upper end of the lockout sleeve  44  may engage the riser disconnect lockout housing  48 , and a lower end of the lockout sleeve  44  may engage the upper end of the seal bore receptacle  58 . The lockout sleeve  44  is axially moveable with respect to the upper seal mandrel  42  when lockout  50  is in the unlocked position. 
   An alternative embodiment for a riser disconnect may include an apparatus to facilitate rotating an upper riser, a riser disconnect and a lower riser, substantially in unison to drill the lower riser into position in the sea bed. A bit  39  or under reamer bit may be positioned near the lower end of the lower riser  28 . Referring to  FIG. 18 , a tubular, generally female, non-rotational key engagement head  340  may be secured to a female riser disconnect member to receive and engage a non-rotational key member  346 . The non-rotational key member  346  may be secured to an outer surface of a mandrel, such as a lockout sleeve  344 , which may be concentrically disposed around an upper seal mandrel  342 . The female non-rotational key engagement head  340  may include a tapered upper surface, which may be referred to as an upper key guide surface  345 , to guide insertion of the male member into non-rotational engagement with the female disconnect member. An extension mandrel  359  may support the female non-rotational key engagement head  340  and may support an entry guide  334 . An upper end of a seal bore receptacle  358  may connect with the lower end of the extension mandrel  359 . An extension mandrel adapter ring  360  may connect the seal bore receptacle  358  and the extension mandrel  359 . Such embodiment may facilitate rotating a lower riser with an upper riser which may be connected by a riser disconnect  10 . The non-rotational key engagement head  340  and non-rotational key member  346  components, or variations thereof such components, may be employed for purposes other than drilling in the lower riser  28 , such as rotating the lower riser in preparation for and/or during cementing operations, or to rotationally manipulate the lower riser  28  and/or upper riser  35 . 
   Riser Disconnect, General Operation 
   Referring to  FIGS. 1 ,  2 ,  2 A,  3 ,  3 A,  4 ,  5  and  5 A, the riser disconnect assembly  10 , is generally operable by axial motion of the attached upper riser  35  relative to the lower riser  28 , using the drilling rig DR to effect axial motion or reciprocation. The male disconnect member  12  is latched into engagement with the female disconnect member prior to riser installation. When the riser disconnect assembly  10  is installed on a well as part of a riser assembly and in the connected and latched position, the upper riser  35  and lower riser  28  are normally under a tensile load, typically around one-hundred thousand pounds of force, between the drilling rig DR and the well casing  32 , that extends into the wellbore WB and is cemented therein. The tapered portion or collet engaging ring  81  is circumferentially spaced between the inside of the plurality of collet dogs  78  and the outer surface of the latch mandrel  62 , causing the collet dogs to be engaged in the collet groove  82 . The tensile load on the male disconnect member  12  is carried through the collet locking sleeve  80  into the collet dogs  78  as a compressive load, through engagement of the collet locking sleeve  80  with the collet dogs  78 . The compressive load in the collet dogs  78  is transferred to the female disconnect member  18  through the engagement of the collet dogs  78  with the collet groove  82 , the collet groove  82  being a component of the female disconnect member  18 . In such riser tensile load configuration, the latch pin  74  is in a latched position  66  within the latch J-slot groove  63 . A load bearing shoulder at bottom of the collet dog  78  may be supported on load bearing shoulder at lower end of collet engaging ring  81  of collet locking sleeve  80  when the riser disconnect assembly  10  is in the latched position. A load bearing shoulder at top of the collet dog  78  may be supported on load bearing shoulder at upper end of a collet engagement groove  82  when riser disconnect assembly  10  is in the latched position. 
   The load bearing lockout shoulders  45  of each riser disconnect lockout pin  46  are preferably normally positioned within the circular, lower portion of the respective lockout groove  43  and in a rotational orientation such that a long axis between the rounded end portions  47  of the lockout pin  46  may be axially aligned parallel to a long axis of the lockout groove  43 . In such orientation, the male disconnect member  12  may be unlatched from the female disconnect member  18 . Tensile load in the upper riser  35  may not act directly upon the riser disconnect lockout pin  46 . When in the locked orientation, the lockout pin  46  may prevent any compressive forces in the riser from inadvertently unlocking the riser disconnect assembly  10 , in that the load bearing shoulders  45  are not aligned to move along the lockout grooves  43 , as is otherwise required to disconnect the riser disconnect assembly  10 . The locked orientation may normally be used only in initial installation of the casing  32 , riser disconnect assembly  10 . Otherwise the lockout pin  46  will typically remain in the unlocked orientation. 
   When the riser disconnect lockout  50  is in the locked position, as illustrated in the left half of  FIG. 5 , compressive forces in the upper riser  35  prohibit an unlocking axial movement of the upper riser  35  relative to the lower riser  18 . Compressive forces tending to axially move the upper riser  35  relative to the lower riser  28 , such as may be experienced during riser installation, will transfer from the upper seal mandrel  42  to the load bearing lockout shoulders  45  of the lockout pin  46 , and from the lockout pin  46  to the riser disconnect lockout housing  48 . When applying compressive forces substantially at the riser disconnect assembly  10 , the riser disconnect lockout housing  48  will compressingly engage an upper portion of the lockout sleeve  44 , which in turn will compressingly engage an upper portion of the seal bore receptacle  54 . The seal bore receptacle  54  is an immovable component of the lower riser  28 . If the lockout pin is in the unlocked orientation, axial movement of the upper riser  35  relative to the lower riser  28  will result, thereby permitting disconnecting the riser disconnect assembly  10 . If the lockout pin  46  is in the locked orientation, substantially no axial movement of the upper riser  35  relative to the lower riser  28  will result, thereby preventing inadvertent disconnecting of the riser disconnect assembly  10 . The lockout pin  46  is preferably in the locked orientation during running and installation of the casing  32 , the lower riser  28  and upper riser  35 . After cementing operations are complete and tension is applied to the riser disconnect assembly  10 , a remotely operated vehicle (ROV), diver or other means may be employed to orient the disconnect lockout pin  46  to the unlocked orientation. Well operations may normally be carried on with the riser disconnect lockout  50  in the unlocked orientation. 
   Riser Disconnect, Unlatching and Disconnecting Operation 
   In the embodiment illustrated in  FIGS. 1 ,  2 ,  2 A,  3 ,  3 A,  4 ,  5  and  5 A, to unlatch and disconnect the upper riser  35  from the lower riser  28 , the tensile load in the riser assembly may be relaxed and converted to a compressive load at the riser interconnection device  40 . If the lockout pin  46  is oriented in the locked position the riser disconnect lockout  50  must be unlocked, such as by ROV or diver, before the riser disconnect operation may be performed. The load bearing shoulders  45  of each riser disconnect lockout pin  46 , which are positioned within the circular, lower portion of the respective lockout groove  43 , may be rotated 90 degrees to a rotational orientation where the long axis portion of the lockout pin  46  providing the load bearing shoulders  47 , is aligned parallel to the long axis of each respective lockout groove  43 . When the riser disconnect lockout pin  46  is oriented in the unlocked position, axial downward displacement of the upper seal mandrel  42  relative to the lockout sleeve  44  is permitted, such that each lockout groove  43  in the upper seal mandrel  42  may axially move along the respective lockout pin  46  during the axial disconnect movement of the upper riser  35 . 
   As the upper riser  35  is axially moved downward, the male disconnect member  12  moves downward within the female disconnect member  18 . Such displacement results in relative movement of the latch J-slot groove downward along the latch pins  74 . As downward movement continues, the latch pins  74  move from the latched position  66  in the latch J-slot groove  63  to the collet disengage position  64 , and the collet latch sleeve  72 , the latch pin  74 , the plurality of collet arms  76  and the collet dogs  78  move axially and rotationally to the collet disengage position  64 . As the latch mandrel  62  and connected collet locking sleeve  80  move downward, the tapered portion or collet engaging ring  81  of the collet locking sleeve  80  is moved downward and out from between the collet dogs  78  and latch mandrel  62 . The collet dogs  78  may thereby move radially inward toward the latch mandrel  62  and out of engagement with the collet groove  82 . At that point, the male disconnect member  12  is unlatched from the female disconnect member  18 , but is not disconnected. 
   To disconnect the male disconnect member  12  from the female disconnect member  18 , an axial tensile force is applied by the drilling rig DR or other means, to the upper riser  35 . As the upper riser  35  moves upward relative to the lower riser  28 , the J-slot groove  63  in the latch mandrel  62  moves upward relative to latch pins  74 , from the collet disengage position  64  to the latch disconnect position  68 . Because the latch disconnect position  68  is relatively higher than the latch connect position  66 , the collet latch sleeve  72  and collet dogs  78  are prohibited from moving downward along the outer surface of the latch mandrel  62  sufficiently to permit the collet dogs  78  to engage the collet locking sleeve  80 . Thereby, during disconnection of the upper riser  35  from the lower riser, the collet dogs remain disengaged in the annulus between the outer surface of the latch mandrel  62  and the inner surface of the seal bore receptacle  58 . The components of the male disconnect member  12 , including the riser disconnect lockout  50 , the upper and lower seal mandrels  42 ,  56 , the seal elements  54 , the riser interconnection device  40  and the collet mechanism  60  may be extracted from the seal bore receptacle  58 . The upper riser may be suspended from or removed to the drilling rig DR, leaving the lower riser in place on the well casing  32 . 
   Riser Disconnect, Re-Connecting and Latching Operation 
   In the embodiment illustrated in  FIGS. 1 ,  2 ,  2 A,  3 ,  3 A,  4 ,  5  and  5 A, to reconnect and latch the upper riser  35  to the lower riser  28 , the upper riser  35  may be lowered from the drilling rig DR toward the lower riser  28 . The male disconnect member  12  should be guided into and through the entry guide  34 , to compressively set in the female disconnect member  18 . 
   As the unlocked male disconnect member  12  is axially moved downward through the female disconnect member  18 , such displacement results in relative movement of the latch J-slot groove downward from the unlatched or disconnect position  68 , along the latch pins  74 . As downward movement continues, the latch pins  74  move from the unlatched or disconnect position  68  in the latch J-slot groove  63  to a top position  67 , resulting in the collet latch sleeve  72 , the latch pins  74 , the plurality of collet arms  76  and the collet dogs  78  moving axially and rotationally on the latch mandrel. As the latch mandrel  62  and connected collet locking sleeve  80  move downward, the collet dogs  78  will engage the collet groove  82 . The male disconnect member  12  may bottom out on an upset surface  87  in the latch housing sleeve  84 . 
   To re-latch the riser interconnection device  40 , tension may be applied to the upper riser  35  from the drilling rig DR, such that the upper riser  35  may begin to move upward relative to the lower riser  28 . As the latch mandrel  62  begins moving upward, the latch pins  74  remain alternatively axially immobile, due to the collet dogs  78  engaged within the collet groove  82 . The latch J-slot groove  63  will move upward relative to the latch pins  74 , repositioning the latch pins  74  from the top position  67  to one of the latch engaged positions  66 . As the latch pins  74  approach the latch engaged position  66 , the collet locking ring  81  may circumferentially slide between the inside of the collet dogs  78  and the outside of the latch mandrel  62 . The collet dogs  78  may thereby move radially outward toward the latch housing sleeve  84 , forcing the collet dogs  78  to fully engage the locking groove  82 . At that point, the male disconnect member  12  is securely reconnected and latched into the female disconnect member  18 . Tension is preferably sustained within the upper riser  35  from the drilling rig DR in order to maintain the riser interconnection properly in the latched position. 
   The riser disconnect lockout  50  typically remains in the unlocked orientation during drilling operations. In the event it is alternatively desired to lock the riser disconnect lock  50 , a remotely operated actuator, diver or other means are used to reorient the riser disconnect lockout pin  46  to a locked position. From the typically unlocked position, the load bearing shoulders  45  of each riser disconnect lockout pin  46 , which, (with the riser in tension) are normally positioned within the circular, lower portion of the respective lockout groove  43 , may be preferably rotated 90 degrees to a rotational orientation where the long axis of the round portion  47  of the lockout pin  46  which includes the load bearing shoulders  45 , is aligned perpendicular to the long axis of each respective lockout groove  43 . Such locked orientation of the lockout pins  46  prohibits axial downward displacement of the upper seal mandrel  42  relative to the lockout sleeve  44 , thereby locking the riser disconnect in a latched position. 
   Alternatively, the riser disconnect assembly  10  and lower riser  28  may be drilled into position in the sea bed while the well bore WB which is to accommodate insertion of the lower riser therein is being drilled. This may be accomplished by a number of means known within the industry. The lower riser  28 , upper riser  35  and the riser disconnect assembly  10  may be rotated substantially in unison, from the drilling rig DR. Additionally, rotating the lower riser  28  may be desirable in the event a ledge is encountered while installing the lower riser, wherein it may be desired to rotate the lower riser in order to assist insertion of the lower riser in a hole or well bore. An alternative embodiment of a riser disconnect assembly  10  for accomplishing such objectives is illustrated in  FIG. 18 , and disclosed above. 
   Alternatively, depending upon water depth, the riser disconnect  10 , the lower riser  28  and/or the upper riser  35 , or a portion thereof as determined by water depth, may be positioned on the seabed. A string of drill pipe  36 , a drill bit  39  and/or an under reamer bit may be deployed through the positioned riser assembly and the drill string  36  may rotate the riser string along with the bit  39  while drilling the lower riser  28  into the seabed. Those-skilled in the art of well drilling operations will appreciate that there are a number of other means for drilling in the lower riser  28 . 
   In another alternative embodiment of the riser disconnect assembly  10 , the seal elements  54  may be positioned within one or more grooves in the inner wall of the seal bore receptacle  58 , as opposed to being carried upon the generally male component, the lower seal mandrel  56 . In such alternative configuration, the lower seal mandrel may then provide a generally smooth outer surface for insertion and sealing with the seal elements  54 . 
   Another alternative embodiment may include a riser flex joint (not shown) connected to the male or female component of the riser disconnect assembly  10 . The flex joint may be connected in the riser string between one of the riser connector collar  41  and one of the upper riser  35  and the lower riser  28 , or between the latch housing sleeve  84  and the other of the upper riser  35  and lower riser  28 , depending upon orientation of the riser disconnect assembly  10 . 
   As an alternative to use with floating drilling rigs DR, such as semi-submersibles and drill ships, the subsea riser disconnect may be used with other types of drilling rigs, such as submersibles, drilling barges or jack-up type drilling rigs. In the event the riser disconnect point is sufficiently far above the mud line, when the riser disconnect is disconnected, buoyancy cans (not shown) may be attached to the lower riser below the riser disconnect and above the mud line ML. Other alternative embodiments may provide for employing an embodiment of the riser disconnect assembly on production wells, development wells and wells other than exploratory or test wells. 
   Riser Valve Assembly 
     FIGS. 1 ,  6 ,  6 A,  7 ,  8  and  9  illustrate a suitable embodiment for a subsea riser valve assembly  20  according to the present embodiment. The subsea riser valve assembly  20  may be used as a stand alone device in a subsea riser installation or may be used in conjunction with the subsea riser disconnect assembly  10 . In an installation where the subsea riser valve assembly  20  is employed in conjunction with the subsea riser disconnect assembly  10 , the two components may be configured as a common component assembly, as generally illustrated in  FIG. 1 , or preferably as two separate component assemblies, as generally illustrated in  FIGS. 2 ,  3 ,  7  and  9 . The riser valve assembly  20  may provide a full bore opening when the valve seal element is in the opened position, such that the minimum ID of the through bore of the riser valve assembly  20  is equal to or greater than the ID of one or both of the upper  35  and lower  28  riser. The riser valve assembly  20  may provide a method for isolating the lower riser  28  prior to disconnecting and removing the upper riser  35  from the lower riser  28 , and thereby closing in the well bore WB below the riser valve assembly  20 . 
   Those skilled in the are will appreciate that a riser valve  20  is generally a part of a riser system that includes an upper  35  and lower riser  28 , and that the riser valve may thereby include components generally having tubular properties, such as a through bore. Additionally, it may be appreciated that the riser valve  20  may include components which may be similar to components found in valves. 
   In an application wherein the riser valve assembly  20  is a distinctly separate component from the riser disconnect assembly  10 , the subsea riser valve assembly  20  may be preferably installed in an upper portion of the lower riser  28 . The lower riser  28  may be comprised of well casing  28 , which extends downward through a seabed and into the subsea wellbore WB where the lower riser is secured by cementing the lower riser  28  within the wellbore WB. The lower riser  28  may include or may be partially comprised of threaded well casing pipe  32 . 
   The subsea riser valve assembly  20  may include components for selectively closing off the through bore in the lower riser, thereby hydraulically isolating and enclosing the interior of the lower riser  28  and the wellbore WB below the lower riser  28 .  FIG. 7  illustrates a cross-sectional view of a preferred embodiment for a subsea riser valve assembly  20 , with the riser valve assembly  20  in the opened position.  FIG. 9  illustrates an enlarged half-section view of the riser valve, with the riser valve assembly  20  in the closed position. A preferred embodiment includes valve housing components  110 ,  112 ,  114 , and  134 , a valve sealing member  120 , a valve actuating mandrel  118 , and components  128  and  130  which connect the valve actuating mandrel  118  and the valve sealing member  120 . The subsea riser valve assembly  20  may be actuated between the valve opened position and the valve closed position by axial movement of the upper riser  35  relative to the lower riser  28 , by the drilling rig DR or by other means. The riser valve assembly  20  preferably is designed to fail closed such that tension on the riser assembly and the subsea riser valve assembly  20  is required to maintain the subsea riser valve in an opened position. Thus, under normal operating conditions, the subsea riser valve requires tensile force between the upper and lower ends of the riser valve assembly  20 . Releasing the tension or compressing the riser string at the riser valve assembly  20  may preferably result in closure of the riser valve assembly  20 . 
   Referring to  FIGS. 1 ,  6 ,  6 A,  7 ,  8  and  9 , a preferred orientation for the subsea riser valve provides for installing the subsea riser valve assembly  20  with the valve actuating mandrel  118  connected to the upper riser  35  and with a lower valve housing  110  connected to the casing  32  extending below the mud line ML, with the casing  32  comprising a portion of the lower riser  28 . In such orientation, a lower end of a lower valve housing  110  may be secured, such as by threaded connection, to an upper end of a well bore casing  32 . A lower end of a central valve housing  112  may be secured, such as by threaded connection, to an upper end of the lower valve housing  110 . An upper valve housing  114  may be secured to an upper end of the central valve housing  112 , while a lower end of a valve mandrel housing  116  may be secured to an upper end of the upper valve housing  114 . A lower end of the valve actuating mandrel  118  may telescopically penetrate the upper end of the valve mandrel housing  116  and into an upper end of the upper valve housing  114 . An upper end of the valve actuating mandrel  118  may be secured to the lower end of the upper riser  35 . 
   The riser valve assembly  20  includes a valve sealing member  120  that may be actuated in response to movement of the valve actuating mandrel  118 . In a preferred embodiment, the valve sealing member  120  is a ball type sealing member, being rotatable about a ball axis  121 . Ball pivots  126  may extend along the ball axis  121 , from the generally spherically shaped valve sealing member  120  to maintain orientation during rotation of the sealing member  120  between a valve opened position and a valve closed position. The ball type sealing member  120  includes a through bore that provides a generally continuous through bore through the riser assembly and the riser valve assembly  20 , when the riser valve is in the valve opened position. 
   The valve sealing member  120  is generally positioned between the upper  114  and lower  110  valve housings, and within the central valve housing  112 . The valve sealing member may move rotationally on the ball pivots  126 , which in turn may be mounted within one or more ball mounts for supporting the ball pivots  126  during valve manipulation. The upper portion of the lower valve housing  110  may include a lower valve seat  122  to provide a hydraulic seal between the lower valve housing  110  and the valve sealing member  120 . An upper valve seat  124  may be included to provide a hydraulic seal between the upper valve housing  114  and the valve sealing member  120 . One or more seat engagement springs  141  may be provided to enhance the hydraulic seal between the valve sealing member  120  and the lower seat  122 . Wafer type corrugated springs, or other types of seal enhancement mechanism may be employed to effect seal enhancement. 
   The valve actuating member  118  may be connected with the valve sealing member  120  with a valve link pin  130  and a link pin adapter  128 . The valve actuating mandrel  118  may include an annular support ring  134  with a plurality of valve link sockets  137 , preferably two valve link sockets  137 , providing one on each side of the actuating member  118 . The each respective annular support ring  134  may move axially within one a respective mandrel guide groove  132 , within the inner surface of the valve mandrel housing  116 . The annular support rings  134  may be connected to an upper end of a valve link pin  130 . A retainer  136  may be provided on the upper end of each valve link pin  130  to secure the valve link pin  130  within the its respective valve link socket  137 . The valve link pin  130  may extend downward from the annular support ring  134  and penetrate the upper valve housing  114  through an upper valve housing passageway  117 , and extend below the upper valve housing  114  to connect with a link pin adapter  128 . The link pin adapter  128  may be moveably disposed within the central valve housing  112  to axially reciprocate along a link pin adapter passage  119 . The link pin adapter  128  may include a link pin adapter projection  131  to engage the valve seal member  120  in a seal member engagement groove  133 , as illustrated in  FIG. 6A . 
   To prevent rotation of the valve actuating mandrel  118  relative to the mandrel housing  116 , one or more mandrel guides  146  may be positioned within corresponding grooves provided in both the outer surface of the valve actuating mandrel  118  and the inside surface of the valve mandrel housing  116 , as illustrated in  FIGS. 7 and 8 . The mandrel guides may be secured to the mandrel housing  116  with mandrel guide retainers  140  for each respective mandrel guide  146 . The valve actuation mandrel  118  may axially reciprocate along the one or more relatively immovable mandrel guides  146 . A preferred embodiment provides two mandrel guides  146  and two mandrel guide retainers  140 . 
   In a preferred embodiment, the riser valve assembly  20  is designed to remain closed until sufficient tension may be applied to the riser valve assembly  20  to actuate the valve sealing member  120  to the opened position. During installation of the riser valve assembly  20 , the lack of sufficient tension may prevent the valve sealing member  120  from remaining in the valve opened position. To retain the riser valve in a valve opened position during riser installation, and at any time subsequent to installation, a riser valve lockout assembly  150  may be included. The riser valve lockout assembly  150  may be provided within the valve mandrel housing  116  to act upon the valve actuating mandrel  118  to prevent axial displacement of the valve actuating mandrel  118  relative to the mandrel housing  116 . The riser valve assembly  20  may be locked or may remain unlocked, when the valve sealing member  120  is in either t valve opened position or the valve closed position. 
   Referring to  FIGS. 1 ,  7 ,  8  and  9 , one or more valve lockout grooves  151  may be circumferentially provided on the outer surface of the mandrel housing  116 , each lockout groove  151  to accommodate a respective lockout device  153 . The combination of a lockout groove  151  plus a lockout device  153  may constitute a lockout assembly  150 . The one or more valve lockout grooves  151  may each have a long axis which is aligned axially up and down along the valve actuating mandrel  118 , substantially parallel with the central axis  15 . Each groove  151  includes a circular portion at the lower end of the groove  151  and at the upper end of the groove  151 , each circular portion having a diameter that is larger than the width of the groove  151 . The riser valve lockout device  153  is axially moveable along the central axis  15 , on the outer surface of the valve actuating mandrel  118 . 
   The riser lockout device  153  may include a lockout pin  148 , a lockout pin adapter  154  and a lockout pin connector bolt  152  connecting the lockout pin  148  and the lockout pin adapter  154 . The riser lockout pin  148  may be substantially round shaped with a pair of opposing flat sides, such that the round shoulders may provide a pair of upset shoulders  147  on the riser valve lockout pin  148 . The round ends of the lockout pin  148  may be axially located along a major linear axis through the lockout pin, the long axis having a length that is longer than the length of a minor axis which extends between the flat sides of the lockout pin  148 . The length of the minor axis may be substantially equal to the diameter of the lockout pin adapter  154 . Each valve lockout device  153  may extend from inside of a lockout groove  151 , outward through a pin port  157  in the valve mandrel housing  116 . The rounded end portion  147  of the riser valve lockout device  153  may remain inside of the groove  151  on the outer surface of the riser valve actuating mandrel  118 . In an unlocked orientation, the lockout pin adapter  154  may slide in lockout groove  151 , along a grooved but non-recessed portion  138  of the valve mandrel housing  116 . 
   As illustrated in  FIG. 8 , and generally referring to the illustration depicted in  FIG. 5A , spring loaded retainer pins  159  may be positioned within the riser valve mandrel housing  116  to engage a retainer groove  167  and/or stop dimple  88  on an outer surface of each lockout pin adapter  154  and may thereby prevent inadvertent rotation of the lockout device  153  and may assist the ROV, diver or other actuator in properly aligning the upset shoulders  147  on the lockout pin  148  with respect to the lockout groove  151 . The retainer groove  167  and/or stop dimple  88  may only be provided circumferentially around a portion of the outer surface of the lockout pin adapter  154 , such as substantially ninety degree portions of the lockout pin adapter  154 . 
   The riser valve lockout assembly  150  functions similar to the riser disconnect lockout disclosed above. As lockout pin  148  is rotated, such as by ROV or diver, within one of the upper or lower circular portions of the lockout groove  151  to the valve locked orientation, the upset shoulders  147  are oriented so as not to be axially moveable through the narrow portion of the lockout groove  151 . The resulting inability of the lockout device  153  to move axially along the lockout groove  151  provides the capability to lock the valve  20  in either a valve opened or valve closed position, depending upon whether the lockout device  153  is engaged in the upper or lower circular portion, respectively, of the lockout groove  151 . This assembly may provide the ability to install the riser valve assembly  20  in either a valve opened or a valve closed position. 
   In an alternative embodiment, a valve sealing member may be generally positioned within a valve housing which includes component variations from a valve housing discussed above that includes the upper  114  and lower  110  valve housings, and the central valve housing  112 . In an alternative embodiment, a central valve housing may be included as an integral portion of a lower valve housing or an upper valve housing. 
   Riser Valve Operation 
   The subsea riser valve assembly  20  is preferably an independent, stand-alone device which may be inter-connected with numerous other devices or related riser components, such as the riser disconnect, a riser flex joint, or other subsea equipment. The riser valve assembly  20  is preferably installed in tandem with the riser disconnect assembly  10 , such that the riser disconnect is positioned axially above the riser valve assembly  20 . Both assemblies,  10 ,  20 , are generally inter-connnectably and operationally compatible, as both may be actuated through application and/or reduction of axial tensile force.  FIG. 1  generally illustrates a preferred embodiment for a riser valve assembly  20  installation. 
   A subsea riser valve assembly  20  as illustrated in  FIGS. 1 ,  6 ,  7 ,  8  and  9 , may be actuated through riser axial reciprocation at the drilling rig DR. The lower valve housing  110  of the riser valve assembly  20  may be connected to the upper end of a lower riser  28 . The lower riser  28  may be comprised of one or more joints of well casing pipe  32  of sufficient length that the lower riser  32  may be positioned within a well bore WB such that an upper portion of the lower riser  28  and the riser valve assembly  20  remain externally accessible above the mud line ML to an ROV, actuator or diver, e.g., to lock or unlock the valve lockout assembly  150 . The upper end of the valve actuating mandrel  118  may be directly or indirectly secured to the upper riser  35 , which extends substantially from the riser valve assembly  20  to the drilling rig DR. 
   The riser valve assembly  20  is preferably actuated to mechanically fail closed and to remain in the valve closed position, in the absence of a tensile force applied to the riser valve assembly  20  to maintain the riser valve assembly  20  in the opened position. During installation, the riser valve assembly  20  may be positioned in the valve opened orientation and the lockout device  153  rotated to the locked position, within the lower circular portion of the lockout groove  151 , to allow fluid to fill the upper  35  and lower  28  risers and to facilitate circulation of fluids, slurrys and/or cement through the upper and lower riser. 
   The lower riser  28  may be anchored within the well bore WB by placing cement in the annulus between the well bore WB and the outer surface of the well casing  32 . After the cement hardens, tension may be applied by the drilling rig DR, to the upper riser  35 , the riser disconnect assembly  10 , the riser valve assembly  20  and the portion of the lower riser  28  that is not cemented in the well bore WB. When tension is applied to the subsea riser valve assembly  20 , the valve lockout device may be rotated to the valve unlocked position. The riser lockout device  153  preferably remains rotationally oriented in the unlocked position during drilling and well work operations, such that the riser valve assembly  20  may be closed within a relatively short period of time by releasing tension in the upper riser  35 . 
   Referring to  FIGS. 6 ,  6 A,  7 ,  8  and  9 , during riser valve assembly  20  closing operations, as tension is released in the upper riser  35  the weight of the upper riser  35  may provide an axially downward force acting upon an upper portion of the valve actuation mandrel  118 . The downward compressive forces acting upon the valve actuation mandrel  118  may cause the valve actuation mandrel  118  to telescopically move downward within the valve mandrel housing  116  and the upper valve housing  114 . Downward movement of the actuation mandrel  118  may be limited by interference between the top of the valve lockout groove  158  and the valve lockout device  153 . 
   The link pin adapter projection  131  on the link pin adapter  128 , which is secured to the lower end of the valve link pin  130 , is moveably engaged with the valve sealing member  120 . As the valve link pin  130  moves downward, the link pin adapter projection  131  may act generally tangentially upon the valve sealing member  120  to effect rotation of the valve sealing member  120  from an opened position to a closed position. The mere weight of components above the riser valve assembly  20 , in the absence of tension in the upper riser  35 , may provide a “fail closed” biasing effect to the sealing member  120 . In an alternative embodiment of a riser valve assembly  20 , a separate and/or additional biasing force may be provided, such as a spring, which may also contribute to closing the riser valve assembly  20 . The biasing effect in either the preferred or an alternative embodiment may serve to close the riser valve sealing member  120  on demand or in the event of loss of tensile force, and to maintain the riser valve assembly  20  in a closed position, such as when the upper riser  35  may be separated and removed from the riser valve assembly  20 . 
   To open a preferred embodiment of the riser valve assembly  20 , tensile force may be applied to the valve actuation mandrel  118 . As the valve actuation mandrel  118  is telescopically extended from within the upper valve housing  114  and the valve mandrel housing  116 , the link pin  130  and link pin adapter  128 , which connect the valve actuation mandrel  118  and the valve sealing member  120 , engage the valve sealing member  120  to cause the valve sealing member  120  to rotate from the valve closed position to the valve opened position. A lower valve seat  122  may form a hydraulic seal between the moveable valve sealing member  120  and the lower valve housing  110 . An upper valve seat  124  may form a hydraulic seal between the moveable valve sealing member  120  and the upper valve housing  114 . On O-ring seal  115  may provide a hydraulic seal between the lower end of valve actuation mandrel  118  and the upper valve housing  114 . 
   In an alternative embodiment of a riser valve assembly, the valve sealing member may be of a type other than a ball type sealing member, such as a gate type sealing member, a plug or cylinder type sealing member or a flapper type sealing member. These alternative type of sealing members may require variations and modifications on the linkage apparatuses required to effect valve manipulation between the valve opened position and the valve closed position, by axial motion or reciprocation of the valve actuation mandrel  118 . 
   In other alternative embodiments, the riser valve assembly  20  may be inverted from the preferred embodiment, such that the valve actuation mandrel  118  is secured to the well casing  32  and a valve body, such as the lower valve housing  110 , is secured to the upper riser  35 . Axial reciprocation of the upper riser  35  would nevertheless effect movement of the valve body relative to the valve actuation mandrel  118 , thereby effecting manipulation of the valve sealing member  120  between the valve opened position and the valve closed position. 
   An alternative embodiment for the subsea riser valve assembly  20  may integrate the subsea riser valve and subsea riser disconnect assembly  10  into a substantially single assembly which includes both components  10 ,  20 . In such assembly, both the subsea riser disconnect assembly  10  and subsea riser valve assembly  20  may share common housing components. 
   As an alternative to positioning a subsea riser valve assembly  20  substantially adjacent and below a subsea riser disconnect assembly  10 , the subsea riser valve may be installed at any point in a riser assembly, including the lower riser  28  and the upper riser  35 , where it may be desirable to provide a valve for closing off an interior portion of a riser through bore. 
   Drill Pipe Disconnect 
     FIGS. 1 , and  10  through  17  illustrate suitable embodiment for a drill pipe disconnect  30  according to the present invention. The drill pipe disconnect  30  may be used offshore and onshore, along a string of drill pipe  36  used in drilling a subterranean well. In an offshore installation, the drill pipe disconnect may be employed in a drilling installation which also employs a riser disconnect assembly  10  and a subsea riser valve assembly  20 . In general, the drill pipe disconnect  30  provides a means for selectively disconnecting an upper portion of a drill pipe string  36  from a lower portion of the drill pipe string  36 , while leaving the lower portion of the drill pipe string  36 , e.g., within the well bore WB being drilled. The drill pipe disconnect  30  also generally includes an interconnection means which provides for rotating the drill pipe string  36  and for axially transmitting tension and compression in the drill pipe string  36 , through the drill pipe disconnect  30 . 
   The drill pipe disconnect  30  may be hydraulically or otherwise actuated between latched and unlatched positions. After disconnection of the drill pipe disconnect  30 , the drill pipe disconnect  30  may be reconnected, e.g., by hydraulic actuation of the latch mechanism. 
   In a preferred embodiment, a drill pipe disconnect  30  may be employed in a subsea installation and in conjunction with a subsea riser disconnect assembly  10  and a subsea riser valve assembly  20 . The drill pipe disconnect  30  may be secured within the drill pipe string  36  such that when a drill bit  39  or lower end of the drill pipe string  36  is on or near the bottom of the well bore WB, the drill pipe disconnect  30  may be positioned below the subsea riser valve assembly  20  and the riser disconnect assembly  10 . In such configuration, the drill pipe string  36  may be disconnected at the drill pipe disconnect  30 , and the upper portion of the drill pipe string  36  may be pulled above the subsea riser valve assembly  20  in order that the subsea riser valve assembly  20  may be closed, thereby sealingly isolating the well bore WB and the lower portion of the drill pipe string  36  within the well bore WB. 
   A preferred embodiment of the drill pipe disconnect  30 , as illustrated in  FIGS. 10 through 17 , provides for male and female interconnection components. In addition, the preferred embodiment provides for a non-rotational engagement mechanism to facilitate rotational strength in the drill pipe disconnect  30 , and a collet mechanism for providing axial engagement and disengagement of the male and female interconnection components. The male interconnection component may generally be referred to as the male disconnect member  205 , while the female interconnection component may generally be referred to as the female disconnect member  215 . Each of the male disconnect member and female disconnect may include a through bore and a central axis  215  which may be a common to the disconnect members when the drill pipe disconnect  30  is connected. 
   The male disconnect member  205  may be secured to the lower end of an upper portion of drill pipe  236 . An upper end of an upper latch sleeve housing  210  may be secured to the lower end of the upper portion of drill pipe  236 . The lower end of the upper latch sleeve housing  210  may be secured to the upper end of a male drill pipe disconnect housing  212 . A lower end of the male drill pipe disconnect housing  212  may be secured to the upper end of a latch mandrel  222 . The lower end of the latch mandrel  222  may include a latch mandrel collet engaging ring  237 . (Referring to  FIGS. 10 and 17 , the latch mandrel collet engagement ring  237  is preferably an integral portion of the latch mandrel  222 , which is distinguished with a separate component number ( 237 ) and name to assist in clarifying this disclosure.) A latch sleeve  216  may be moveably positioned within the through bore of the male disconnect member  205 . The outer surface of the latch sleeve may be moveably engaged with the inner surfaces of each of the upper latch sleeve housing  210 , the male drill pipe disconnect housing  212 , the latch mandrel  222  and the latch mandrel collet engaging ring  237 . The lower end of the latch sleeve  222  may axially extend below the lower end of the latch mandrel collet engaging ring  237 , such that the lower end of the latch sleeve  216  defines the lower end of the male disconnect member  205 . 
   A collet mechanism  230  may be included on the male disconnect member  205  for selectively securing and unsecuring the male disconnect member  205  with the female disconnect member  215 . The collet mechanism  230  includes a collet ring secured to and circumferentially encompassing a portion of the outer surface of the latch mandrel  222 . A plurality of collet fingers  231  may be spaced circumferentially around the latch mandrel  222 , with an upper end of each respective collet finger  231  secured to the collet ring  229 , and a lower end of each respective collet finger  231  secured to a respective collet dog  232 . The plurality of collet dogs  232  may be positioned near the lower end of the latch mandrel  222 , and extend inwardly through square windows  237  positioned in latch mandrel  222  to contact outer surface of latch sleeve  216  such that, in a latched position, the collet dogs  232  may engage the female disconnect member  215  in a collet engagement groove  239 . 
   A shear pin retainer ring  218  may be provided radially between the outer surface of the latch sleeve  216  and the inner surface of the male drill pipe disconnect housing  212 , and axially below the upper latch sleeve housing  210  and axially above the latch mandrel  222 . The shear pin retainer ring  218  may house one or more shear pins  220  which engage both the shear pin retainer ring  218  and the latch sleeve  216  for prohibiting the latch sleeve  216  from axial movement until the shear pins  220  are selectively sheared. 
   A collet unlatch groove  224  may circumferentially encompass the outer surface of the latch sleeve  216 , such that alignment of the collet unlatch groove  224  with the plurality of collet dogs  232  may provide for radially receiving the collet dogs  232  within the unlatch groove to provide for disconnection of the male disconnect member  205  and the female disconnect member  215 . An axial position of the latch sleeve  216  wherein the collet unlatch groove  224  on the latch sleeve  216  is aligned with the plurality of collet dogs  232  may generally be referred to as a collet unlatch position. When the collet unlatch groove  224  is not aligned with the collet dogs  232 , such that the collet dogs  232  are caused to engage the collet engagement groove  239  of the female disconnect member  215  by an the latch sleeve  216 , such axial position of the latch sleeve  216  may generally be referred to as a collet latch position. 
   When the male disconnect member  205  is engaged with the female disconnect member  215 , a male frustoconical surface  244  substantially on the lower end of the latch mandrel collet engaging ring  237  engages a companion female frustoconical surface  234  in the female disconnect member  215 . Engagement of the frustoconical surfaces  234 ,  244  provides compressive load bearing shoulders between the male disconnect member  205  and the female disconnect member  215 . Downward axial movement thereafter of the latch sleeve  216  relative to the latch mandrel  222  effects manipulation of the drill pipe disconnect  30  between the collet latch position and the collet unlatch position. During movement of the latch sleeve  216 , the latch sleeve may telescopically and sealingly penetrate a lower portion of the through bore of the female drill pipe disconnect housing  228  axially below the female frustoconical surface  234 . The inner surface  245  of the lower portion of the through bore of the female drill pipe disconnect housing  228  which receives the latch sleeve  216 , in combination with seal  246  may provide a moveable hydraulic seal between the female disconnect housing  228  and the latch sleeve  216 . 
   An upper surface of the latch sleeve  216  may include an unlatching seat for sealing engagement with an unlatching ball  208 . Pressurized engagement of the unlatching ball  208  on the unlatching seat may permit shearing of the shear pins  220  and axial downward of movement of the latch sleeve  216  relative to the latch mandrel  222 . 
   The outer surface of the latch sleeve  216  may include a circumferential first shear pin retainer ring groove  260  having a first shear pin retainer upper stop surface  264 . The first shear pin retainer ring groove  260  may circumferentially accommodate the shear pin retainer ring  218 . The shear pin retainer ring  218  includes an upper retainer ring stop surface  262 . After shearing the shear pins  220 , axial downward movement of the latch sleeve  216  relative to the latch mandrel  222 , from the collet latch position to the collet unlatch position, is halted by interference between the upper retainer ring stop surface  262  and first shear pin retainer ring groove upper stop surface  264 . Such interference position of the latch sleeve  216  relative to the latch mandrel  222  may properly align the collet unlatch groove  224  with the collet dogs  232 , in the unlatch position, to permit disconnecting the male disconnect member  205  and the female disconnect member  215 . 
   The female disconnect member  215  may include a receptacle bore  241  for receiving the male disconnect member  205 . The collet engagement groove  239  may be positioned circumferentially in an inner wall of the receptacle bore  241 . A female non-rotational engagement member  227 , as illustrated in  FIGS. 10 and 12 , may be included with the female disconnect member  215  for engaging a companion male non-rotational engagement member  226 , the male non-rotational engagement member  226  being a component secured to the male disconnect member  205 . The lower end of the female disconnect member  215  may be engaged with an upper end of the lower portion of drill pipe  240 . 
   Seals  246 ,  247 , packing or other sealing devices may be included to provide hydraulic seals between the male disconnect member  205 , male reconnect member  225  and female disconnect member  215 , and between the latch sleeve  216 ,  266  and the upper latch sleeve housing  210 . It will be apparent to one skilled in the art that a wide variety of seals and component variations are conceivable and may be applied to apparatus and embodiments of this invention. Consequently, not all seals may be illustrated and/or discussed in this disclosure. 
   Drill Pipe Disconnect Assembly Configured for Re-Connection and Re-Unlatching 
   In a preferred embodiment for the drill pipe disconnect  30 , when the drill pipe disconnect  30  has been disconnected and the male disconnect member  205  recovered to the drilling rig DR, before reconnecting the male disconnect member  205  with the female disconnect member  215 , the male disconnect member  205  may be replaced with a male reconnect member  225 .  FIGS. 13 ,  14 ,  15  and  16  illustrate a preferred embodiment for the redressed male reconnect member  225 . The redressed male reconnect member  225  generally includes similar components as the original male disconnect member  205  with the following modifications. 
   The male drill pipe disconnect housing  212  may be replaced with a male drill pipe disconnect housing  261  which provides ports for insertion of one or more shear pins which may be sheared at two positions on each shear pin (discussed below) or with two separate sets of shear pins. The original latch sleeve  216  is replaced with a latch sleeve  266  that provides an additional collet unlatching groove, referred to as a collet re-unlatching groove  274 , circumferentially on the outer surface of the latch sleeve  266  and axially above the original collet unlatch groove  224 . The radially raised circumferential surface between the collet unlatch groove  224  and the collet re-unlatch groove  274  may be referred to as the collet latch surface  263 . The latch sleeve  266  includes an additional groove  275  substantially adjacent the first shear pin retainer groove  260 , the additional groove being referred to as the second shear pin retainer groove  275 . The second shear pin retainer groove  275  may be located on the outer surface of the latch sleeve  266 , axially between a bottom surface of the shear pin retainer ring  268  and a latch mandrel upper stop surface  270 , and may circumferentially encompass the outer surface of the latch sleeve  266 . The second shear pin retainer groove  275  may permit movement of the latch sleeve  266  between a collet latch position and a collet re-unlatch position. The shear pin retainer ring  268  may include a port for providing two separate sets of shear pins or a set of double position shear pins  269 . The double position shear pin  269  may extend from a series of aligned ports, from the male drill pipe disconnect housing  261  through the shear pin retainer ring  268 , and into an annular groove in the outer surface of the latch sleeve  266 . 
   As illustrated in  FIG. 13 , a latching seat  285  for sealingly seating a latching ball  286  thereon may be included near the lower end of the latching sleeve  266 , with the latching seat  285  secured to an inner surface of the latch sleeve  266  in the latch sleeve through bore, with the latching seat  285  secured by one or more latching seat shear pins  287 . When latching the male disconnect member  205  with the female disconnect member  215 , the latching ball  286  may sealing engage the latching seat  285  in order that the latch sleeve may axially move from a collet unlatch position to a collet latch position after shearing the first set or the portion of the double shear pin  269  extending through shear pin retainer  268  into the annular groove in the outer surface of the latch sleeve  266 . Shearing the one or more latching seat shear pins  287  may provide means for ejection of the latching seat  285  and latching ball  286  from within the latch sleeve  266  after movement of the latch sleeve  266  from the collet unlatch position to the collet latch position. 
   The upper end of a latch sleeve extension tube  280  may be secured to the lower end of the latch sleeve  266  to receive and retain the latching seat  285  and latching ball  286  after the latching seat  285  and latching ball  286  are sheared and ejected from within the latch sleeve  266 . A plurality of slots or ports  282  may be provided in the latch sleeve extension mandrel  280  to allow circulation of fluid within the through bore of the drill pipe string  36 . A ball and seat catcher  284  may be provided near the lower end of the latch sleeve extension tube  280  to catch and retain the ejected latching seat  285  and latching ball  286  within the latch sleeve extension tube  280 , as illustrated in  FIG. 16 . 
   Alternatively, the latch sleeve  266  may be furnished with an integral non-shearing latching seat  266  and with no latch sleeve extension mandrel  280 . When employing this version of a latch sleeve, the latching ball  286  may be flowed to the surface by reverse circulating fluid after shifting the latching sleeve from the unlatch position to the re-latch position. 
   Drill Pipe Disconnect and Reconnect Operation 
   Referring to  FIGS. 1 and 10  through  16 , in the preferred first embodiment for initial installation of the drill pipe disconnect  30 , the male disconnect member  205  and female disconnect member  215  may be connected as illustrated in  FIG. 10 , excluding the unlatching ball  208 , and installed in a drill pipe string  36 . The latch sleeve  216  may be axially positioned such that the collet dogs  232  are engaged in the collet engagement groove  239 , thereby securing the male drill pipe disconnect member  205  with the female drill pipe disconnect member  215 . The axial position of the latch sleeve is secured by one or more shear pins  220 . The drill pipe disconnect  30  may be positioned at an axial point in the drill string from which it may be desirable to disconnect, such as below a subsurface riser disconnect assembly  10 , below a subsurface riser valve assembly  20 , or above a trouble spot in a wellbore where it may be desirable to disconnect an upper portion of the drill pipe  236  from a lower portion of the drill pipe  240 . 
   To disconnect the male disconnect member  205  from the female disconnect member  215 , the collet mechanism unlatches. Fluid may be circulated through the wellbore WB sufficiently to remove cuttings and other debris. The drill pipe disconnect may be manipulated with the drill pipe set off on bottom, or suspended off bottom in the wellbore by the upper portion of the drill string, thereby allowing the lower disconnected portion of drill pipe to fall subsequent to disconnection. In a preferred embodiment, an unlatching ball  208  may be dropped from the drilling rig DR, through the through bore of the upper portion of drill pipe  236  to sealingly seat on the unlatching seat  209 , on a substantially top surface of the latch sleeve  216 . Pressure may be applied by the drilling rig DR to the through bore of the upper portion of drill pipe  236  to a first release pressure which creates sufficient axial force upon the latch sleeve  216  to shear pins  220  between male drill pipe disconnect housing  212  and latch sleeve  216  to axially move the latch sleeve downward from a collet latch position to a collet unlatch position. In the collet unlatch position, the plurality of collet dogs  232  may move radially inward within the circumferential collet unlatch groove  224 , thereby allowing the male disconnect member  205  to be telescopically removed from the female disconnect member  215 . 
   The upper portion of drill pipe  236  may then be recovered to the drilling rig while leaving the lower portion of drill pipe  240  within the well bore WB. To avoid pulling a “wet string,” a drain groove  213  may be provided in the upper portion of the upper latch sleeve housing  210  and one or more drain ports  211  may be provided in the upper portion of the latch sleeve  216  to allow fluid in the upper portion of drill pipe  236  to drain while the upper portion of drill pipe  236  is being removed to the drilling rig DR. 
   In a subsea installation, a subsea riser valve may be closed above the female disconnect member  215  in order to confine pres sure and fluid with the wellbore WB. In addition, a subsea riser disconnect assembly  10  may be disconnected such that the upper riser  35  may be recovered to the drilling rig DR or the rig may be moved with the upper riser suspended below the drilling rig DR. 
   To reconnect the upper portion of drill pipe  236  with the lower portion of drill pipe  240 , the male disconnect member  205  may be replaced or redressed with male reconnect member  225  as described previously. The replaced male reconnect member  225  may be telescopically inserted into the female disconnect member  215 , as illustrated in  FIG. 13 , excluding the latching ball  286 . During such insertion, the collet dogs  232  may be recessed into the collet unlatch groove  224  on an outer surface of the latch sleeve  266 . The latch sleeve  216  in the male reconnect member  225  may be properly, axially positioned in the unlatch configuration by engagement of upper surface  273  on the outer surface of the latch sleeve  216  and a lower surface of the shear pin retainer  268 . During the telescopic insertion of the male reconnect member  225  into the female disconnect member  215 , the male non-rotational engagement member  226  may telescopically engage the female non-rotational engagement member  227  to facilitate unitary rotation of the drill pipe string  236 ,  240 . 
   To latch the male reconnect member  225  with the female disconnect member  215 , a latching ball  286  or other closure device, may be dropped or otherwise deployed from the drilling rig DR, through the through bore of the upper portion of drill pipe  236  to sealingly seat on the latching seat  285 . Pressure may be applied to the fluid in the through bore of the upper portion of drill pipe  236 , upon the latching ball  286  and latching seat  285 , to a latching pressure. The latching pressure is sufficient to shear a first shear position on the double position shear pin  269  or first set of separate shear pins, between the latch sleeve and shear pin retainer ring  268 . When the first shear position on the double shear position shear pin  269  shears, or the first set of separate shear pins shears, the latch sleeve  266  may axially move downward from the collet unlatch position to the collet latch position. Downward movement of the latch sleeve  266  may be arrested when the first shear pin retainer groove upper stop surface  264  interferes with or engages the upper retainer ring stop surface  262 . 
   At such axial position of the latch sleeve, the collet latch surface  263  on the outer surface of the latch sleeve  266  may engage an inward portion of each collet dog  232 , causing each collet dog  232  to remain positioned radially outward and engage the collet unlatch groove  224 . The collet dog stop surface  233  engages the collet dogs  232  to prohibit axial separation of the male reconnect member  225  and the female disconnect member  215 , and the load bearing shoulder at the bottom of collet dogs  232  may engage a load bearing upper side of the collet engagement ring  237  portion of the latch mandrel  222 , thereby securing the male reconnect member  225  with the female disconnect member  215 . 
   After latching the collet mechanism  230 , pressure in the upper drill pipe  236  through bore may be further increased from the latching pressure to a ball and seat ejection pressure. The ball and seat ejection pressure may be sufficient to cause the axial downward force upon the latching ball  286  and latching seat  285  to shear the latching seat shear pin  287 . When the latching seat shear pin  287  is sheared, the latching seat  285  and latching ball  286  may move axially downward through the through bore in the lower portion of the latch sleeve  266 , out of the lower end of the latch sleeve  266 , through an upper portion of the latch sleeve extension tube  280  and into a lower portion of the latch sleeve extension tube  280 . The ejected latching ball  286  and latching seat  285  may be caught within the lower portion of the latch sleeve extension tube  280  and retained therein by the ball and seat catcher  284 . One or more ports  282  through the latch sleeve extension tube  280  may permit transmission of fluid through the drill pipe  36  and drill pipe disconnect  30  through bore, to a bit or other tool on the lower end of the drill pipe  36 . As an alternative to shearing the latching seat  285  and latching ball  286  and ejecting the same into latch sleeve extension tube  280 , the ball  286  may be recovered to the surface by other means, such as reverse circulating fluid or with tools, prior to shearing the seat  285 . 
   Such configuration thereby represents the normal operating configuration for a preferred embodiment of the drill pipe disconnect  30 , after reconnection of the male reconnect member  225  with the female disconnect member  215 . 
   To disconnect the drill pipe disconnect  30  a second time, as illustrated in  FIG. 16 , a re-unlatching ball may be dropped through the through bore in the upper portion of drill pipe  236  for sealingly seating on the re-unlatching seat  259 , the re-unlatching seat positioned substantially on an upper surface of the latch sleeve  266 . Pressure may be applied in the through bore of the upper portion of drill pipe  236  to a re-unlatching pressure. The re-unlatching pressure may be sufficient to cause the axial downward force on the re-unlatching seat  259  and re-unlatching ball  258  to shear the second set of separate shear pins or the double shear position shear pin at the second shear position. When the second separate set of shear pins or the double shear position shear pin  269  is sheared at the second shear position, the latch sleeve may move axially downward from a collet latch position to a collet re-unlatch position. In the collet re-unlatch position, the collet dogs  232  may be aligned with the collet re-unlatch groove  274  such that the collet dogs may move radially inward toward the latch sleeve  266  and partially recess in the collet re-unlatch groove  224 . Downward movement of the latch sleeve may be arrested by engagement of the lower retainer ring stop surface  271  with the latch mandrel upper stop surface  270 . The male reconnect member  225  may be telescopically withdrawn from the female disconnect member by axial tensile force at the drilling rig DR, permitting recovery of the upper portion of drill pipe  236  to the drilling rig DR. 
   Alternative embodiments for the drill pipe disconnect may provide components and means for manipulating components similar to the latch sleeve  216  or  266  other than balls and seats, and hydraulic pressure, such as by mandrel or bars on wire line, or other wireline conveyed tools. Recovery of balls or other manipulating devices may be employed to avoid leaving a ball in the drill pipe disconnect during well drilling or operations, or when pulling the upper portion of drill pipe  236  after disconnecting, to avoid recovering a “wet string.” An alternative embodiment functions by dropping a retrievable device to seal on one or more of the seats for manipulation of the latch sleeve  216 ,  266 , which may thereafter be retrieved on wireline to avoid leaving a latching ball in the drill pipe disconnect  30 . A dart or standing valve may alternatively be dropped in lieu of a ball. An embodiment may include means for recovering the latching ball after manipulation of the latch sleeve  266 , such as with a magnet or by reversing fluid flow to retrieve the ball in a catcher or basket for ball retrieval. 
   The drill pipe disconnect  30  may be manipulated between latched and unlatched positions, with the drill pipe string  36  set off on bottom of the well bore WB. Also, the drill pipe disconnect  30  may be manipulated between latched and unlatched positions with the drill pipe suspended off of bottom of the well bore WB, in the well bore WB. The weight of the drill pipe suspended below the disconnect may merely require additional hydraulic pressure to disconnect when the drill pipe is suspended off bottom of the well bore WB. 
   In alternative embodiments for the drill pipe disconnect  30 , the collet mechanism may be replaced with a different mechanical or hydraulic latch mechanism, such as a grapple type mechanism. Also, the male disconnect member  205 ,  225  and female disconnect member  215  may be inverted such that the male disconnect  205 ,  225  may be secured to the lower portion of drill pipe  240  and the female disconnect member  215  may be secured to the upper portion of drill pipe  236 . Alternative embodiments may also be assembled with components which interconnect by means other than generally male and female interconnecting components. 
   The drill pipe disconnect  30  is generally applicable to drilling wells both onshore and off-shore. In addition, although the drill pipe disconnect device is generally referred to herein as a drill pipe disconnect, this device may also be employed with drill pipe used in work over operations, with a “work string” that is generally tubular. The drill pipe disconnect may be positioned below a BOP stack to facilitate disconnecting the drill pipe at a location in the drill string which may be relatively close to the rig, such that subsequently, blind rams may be closed, thereby sealing the interior of the well bore below the BOP stack. Such time saving option may be desirable in a well control situation. Such action may also minimize the amount of pipe that must be tripped out of the well to the rig floor. 
   The drill pipe disconnect device may be alternatively adapted for use in setting liners or other downhole tubular members wherein it may be desirable to reliably disconnect an upper portion of tubulars from a lower portion of tubulars to leave the lower portion of tubulars within the wellbore. 
   The disconnect device as disclosed herein may also be usefully employed as a safety device for drilling in high risk environments where the risk of sticking pipe, collapsing a well bore, key-seating the drill pipe in the well bore or other drilling hazard risks losing a lower portion of the pipe in the hole. In such instances, this device may be positioned within the tubular string such that the disconnect device may remain above the hazard point to provide a quick and reliable disconnect point uphole from the hazardous well bore region. 
   Non-rotational engagement may be alternatively provided by components other than male and female engaging components, such as interlocking keys, dogs or otherwise. Where male and female non-rotational components engaged, the male component may be secured to either the upper portion of drill pipe or to the lower portion of drill pipe, with the female non-rotational engagement component secured to the other of the upper and lower portion of drill pipe. 
   The drill pipe disconnect may provide the ability to further extend an “extended reach” well bore beyond the point at which all of a drill pipe string may be recovered to the rig by tensional force. In such instance where an open-hole completion may be economically feasible, a lower portion of the drill pipe string may be abandoned within a lower section of the well bore, and the upper portion of the drill string recovered. 
   An alternative embodiment of the drill pipe disconnect may provide for manipulating a latch sleeve by a mechanism other than hydraulically with balls and seats. A latch sleeve may be manipulated by a standing valve, dart or rod that may sealingly engage a seat for hydraulic manipulation of the latch sleeve. Such standing valve, dart or rod may be recoverable on wireline or otherwise, such as reverse pumping the component out of the drill pipe string. A weight bar or rod may engage a load bearing shoulder with sufficient mass weight force to manipulate the latch sleeve. Alternative embodiments may eliminate the latch sleeve altogether and provide for a collet or other latch and unlatch mechanism which does not require a latch sleeve component to effect engagement of the upper and lower disconnect members. 
   An embodiment of a drill pipe disconnect may be provided which eliminates the latch seat, latch ball and extension tube, thereby providing an open through bore, through the disconnect tool. Such open through bore may provide access for tools, instruments and materials which would not other wise pass through the ports in the extension tube, to pass through the disconnect device to the lower portion of drill pipe. 
   Shear pins may be eliminated in favor of other retainer and release components. The drill pipe disconnect may be configured for manipulation between latch and unlatch positions by a combination of axial, rotational and hydraulic forces. Alternative embodiments may also be configured which provide for replacement of each double shear pin with two separate shear pins. 
   The embodiments described herein and other embodiments of this invention are disclosed in an absence of hydraulic lines between these embodiments and a drilling rig. It is a significant benefit of this invention that hydraulic lines between the rig and downhole assemblies may be omitted. It may be appreciated by one skilled in the art that hydraulic lines may alternatively be provided for various uses or applications, including the disclosed assemblies or embodiments, or with other components or assemblies employed in conjunction with these embodiments. For example, an application for concurrently employing hydraulic lines in conjunction with employment of one or more of the disclosed assemblies may be elected in a shallow water installation, or to provide additional manipulating force to a riser valve sealing member to shear drill pipe. Hydraulic lines are not intended for preclusion from use, however, the disclosed embodiments may provide a more attractive alternative which permits excluding hydraulic lines. 
   It may be appreciated that various changes to the details of the illustrated embodiments, methods and systems disclosed herein may be made without departing from the spirit of the invention. While preferred embodiments of the present invention have been described and illustrated in detail, it is apparent that still further modifications and adaptations of the preferred and alternative embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, which is set forth in the following claims.

Technology Classification (CPC): 4