Patent Description:
Operations performed in a well often requires exact depth control. When such operations are to be carried out deep down in the well on components previously installed it is not possible to control the depth from surface. The workstring that is used to convey tools down the well for performing the well operation is subjected to factors such as compression, stretch and thermal expansion. Hence, simply keeping track of the length of the workstring entering the well will not give a good enough control of the depth of the tools. The length of the workstring is often several thousand meters and tools in the bottom hole assembly typically have to be positioned within a few meters. For some applications the error margin is far less and in the range of centimetres.

When a production tubing, a casing or a liner string is installed in a well an exact tally is recorded. The tally comprises the serial number, the exact length and specifics of every tubular that makes up the string. Hence, the exact length between components of the string can be found in the tally and when the components are not too far from each other the effect of stretch, compression and thermal expansion etc. is negligible. Thus, components that can be sensed or recognized from surface can be used to locate the exact depth of other nearby components in the well.

Typically pup joints or radioactive markers are installed in the well to be used for depth control later. For locating pup joints or radioactive markers specialized tools are needed which are not always possible or desirable to include in a toolstring. Another possibility is to use protrusions in the well such as the PBR on the top of a liner. To locate the top of the PBR a component with a larger OD is included in the toolstring often referred to as a no-go. The no-go has a larger OD than the ID of the protrusion. A drawback of using a no-go is that the toolstring cannot pass the protrusion. In case the next step in the operation requires running further into the well there is no other option than pulling out of hole to remove the no-go.

<CIT> describes a downhole tool with a bridge plug releasably coupled to a casing cutting tool. The bridge plug is set within a wellbore and the casing cutting tool may be used in a milling or perforating operation during a single downhole trip of the downhole tool. A method for using a downhole tool includes setting the bridge plug in a wellbore and performing a casing cutting operation during a same downhole trip.

<CIT> describes a casing recovery in which clean-up of the outer casing above the inner casing is performed on the same trip in the wellbore as cutting and pulling a section of the inner casing. A bottom hole assembly (BHA) includes a spear for gripping a casing that is going to be cut, a casing cutter and at least one clean-up tool, for removing binding material above casing that is going to be cut.

<CIT> describes a method and apparatus for landing and orienting selected tools to selected depths within a well casing. The well casing is provided with a plurality of casing nipples located at selected depths with each of the landing and orienting joints defining a differing internal landing profile. A landing orientation tool is adapted to be run into the casing and has an outer tubular body mandrel positioning a plurality of landing dogs for landing engagement with a matching landing profile. The tool being run will pass through non-matching landing and orienting joints and will land only when its landing dogs have a landing profile matching the profile of a landing and orienting joint.

<CIT> describes an axial position-controlled operation toolstring wherein support means in the form of plate like members , are pivotally mounted in slots and adapted to seat on the upper end of well equipment. The support means is maintained in a position for seating on the upper end of the well equipment W, such position being as illustrated in the US patent. The support means is maintained in such position by the release means. Such release means is preferably in the form of a shear pin which extends through the support means within the slots and into a skirt.

<CIT> describes an apparatus for cutting and retrieving an offshore well casing, the casing comprises a seal assembly retrieval tool for releasing a seal assembly of a well casing, a casing spear in mechanical communication with the seal assembly retrieval tool, a mud motor connected to the spear, and a casing cutter driven by the mud motor.

One object of the invention is to provide a downhole toolstring and a method for performing a precision cut to cut loose a section of a tubular below a protrusion in a well and thereafter retrieving said section.

Another object of the invention is to provide a method and a toolstring for cutting the slips of a liner to loosen it from the casing and retrieve the PBR.

The invention relates to an axial position-controlled operation toolstring (<NUM>) for conducting an axial position-controlled operation for releasing a pipe component (<NUM>) in a well,.

The toolstring can further comprises a mud motor arranged for rotating said casing cutter tool.

The toolstring can further comprise a rotatable taper mill.

The toolstring can comprise a spaceout pipe string arranged above or below said mud motor.

The tag sub can comprise a mandrel and said tag sub's tag dogs can be arranged in and protruding from slots in the mandrel, said tag dogs can be arranged for collapsing into said slots when weight-loaded on said protrusion.

The tag dogs can be fixed in said mandrel with shear pins arranged for being sheared out by said weight loading against said protrusion so as for said tag dogs to slide upwardly and inwardly in said slots.

The toolstring can further comprise a no-go sub arranged above said spear, closer than the distance (L).

The mandrel can have an axial through bore so as for conducting flow from the above drill pipe string to said mud motor and said cutter tool.

In another aspect the invention relates to a method for conducting an axial position-controlled operation in a well.

Step f) can include running said pipe spear into said cut free pipe component until a no-go sub lands on said protrusion.

Step d) can include rotating said knives by rotating the drill pipe string from surface or rotating said knives by running a mud motor that is included in the toolstring above the casing cutter tool.

The pipe component can be a polished bore receptacle, and the knives can cut the slips and/or the slips lock thus freeing said polished bore receptacle.

Embodiments of the present invention will now be described, by way of example only, with reference to the following figures, wherein:.

The relative terms "above" and "below" used throughout this description in relation to the position of the different components of the toolstring shall be understood as referring to the order in which the components are installed and inserted into the well from topside/surface, although the actual position after entering the well may be different, as the direction of the wellbore may deviate from vertical.

In one embodiment the toolstring <NUM> comprises a casing cutter tool <NUM>, a tag sub <NUM>, a spear <NUM> and a drill pipe string <NUM>.

The casing cutter tool <NUM> comprises knives <NUM> and is configured to cut through a tubular surrounding the casing cutter tool <NUM>.

The tag sub <NUM> is placed above the cutter tool <NUM>. The purpose of the tag sub <NUM> is to land on a particular protrusion in a well. When the tag sub <NUM> lands, the driller knows that the toolstring has reached a particular depth. The tag sub <NUM> comprises a mandrel <NUM> and tag dogs <NUM> that can collapse radially into dog slots <NUM>. This enables the tag sub <NUM> after collapsing the tag dogs <NUM> to enter a tubular with a smaller ID than before collapsing the tag dogs <NUM>. In one possible embodiment each tag dog <NUM> is secured in a dog slot <NUM> in the mandrel <NUM> by screws or bolts with a predefined shear value. The dog slots <NUM> are axial slots along the outside of the mandrel <NUM>. The depth of the dog slots <NUM> increases towards the end of the mandrel <NUM> that is intended to point upwards in the well (the end that points towards the surface). The tag dogs <NUM> are secured towards the shallow end of the dog slots <NUM>. When a weight above a predetermined threshold is set down in the drill pipe string <NUM> while the tag dogs <NUM> is resting on a protrusion <NUM> in the well, the shear screws or bolts will shear and the tag dogs <NUM> will slide up towards the deepest end of the dog slots <NUM>, thus collapse /retract into the mandrel <NUM>. A ratchet mechanism, springs or similar can be used to keep the tag dogs <NUM> in position after the shear screws or bolts is sheared so the tag dogs <NUM> are kept in the collapsed configuration.

The tag sub <NUM> needs to be spaced out so that the knives <NUM> of the casing cutter tool <NUM> gets the desired depth from the protrusion that the tag dogs <NUM> are landed on. For spacing out, crossovers, pup joints and pipe joints can be used as during any other operation that requires a particular space out.

The spear <NUM> is placed above the tag sub <NUM> in the toolstring <NUM> and is configured to grip a section of a tubular cut loose by the casing cutter tool <NUM>. Various types of spears <NUM> can be used such as an Itco Spear.

In a preferred embodiment the toolstring further comprises a no-go sub <NUM> above the spear <NUM>. The purpose of the no-go sub <NUM> is to prevent the spear <NUM> to move down deeper than the depth of the cut that is made. The purpose of said no-go sub <NUM> is to prevent the spear <NUM> from ending up further below the protrusion <NUM> than the distance (L), i.e. below the cut-free pipe component <NUM>. When the weight is set down for shearing the tag dogs <NUM> out the drill pipe string <NUM> is in compression and when the tag dogs <NUM> are sheared the toolstring <NUM> can suddenly move down. In case the distance between the protrusion and the cut is relativly short, it can happen that the spear <NUM>, due to this sudden movement, will be moved past the cut. The no-go sub will prevent this from happening.

The described toolstring <NUM> is particularly suitable for cutting of a PBR (Polished Bore Receptacle) at the top of a liner and retrieving said cut loose PBR to surface. The top of the liner/PBR is secured to the casing by PBR slips <NUM> (liner hanger) and the PBR <NUM> is extending into the casing above said PBR slips <NUM>. For various reasons it might be needed to cut said slips to release the liner from the casing and pull the PBR to the surface. To be able to release the liner from the casing a cut must be made exactly in the region of the PBR slips <NUM> to sever the slips lock / slips mechanism <NUM>. The error margin for where the cut is to be made is very small and often in the range of centimeters. To make such a cut, a reference point down in the well must be used to position the knives <NUM> of the casing cutter <NUM>.

Since the top of the liner PBR is typically several thousand meters down in the well it is desirable to perform both the cut and the retrieval of the top of the liner on one trip into the well. If the top of the liner is at <NUM>-meter measured depth (mMD), this will be <NUM>- <NUM> hours or more of tripping time saved if the operation can be done on one trip compared to two trips.

Before the cut is made it is not desirable to enter the PBR <NUM> with a spear <NUM>. In particular, it is not desirable to enter the PBR <NUM> with a spear <NUM> and land on the PBR <NUM> with a no-go sub <NUM> above the spear <NUM>. This is since for some types of spears <NUM> it is necessary to set down weight to disengage. With a no-go sub resting on the top of the liner it will not be possible to set down weight to disengage the spear <NUM> if it has engaged the PBR <NUM>. In such a case the toolstring <NUM> will be stuck in the hole if the cut is not successful.

The operational sequence for retrieving the PBR can be as follows.

Assemble the toolstring (the BHA) on surface/drill floor as seen in <FIG>. The knives <NUM> should be spaced out from the tag sub <NUM> so that the length L of the space out is equivalent to the length between the top of the PBR <NUM>, i.e. the top of protrusion <NUM>, and the center of the slips lock/mechanism <NUM> of the PBR slips <NUM>.

Run the toolstring <NUM> into the well on the drill pipe string <NUM>.

Enter the PBR <NUM> with the toolstring <NUM> and land the tag sub <NUM> on the protrusion <NUM>, the top of the PBR <NUM> as seen in <FIG>. The tag dogs <NUM> are in their extended position, as when resting on the top of the PBR <NUM>, is seen in an enlarged view in <FIG>.

Rotate the knives <NUM> to cut the liner and to sever the slips lock <NUM>. The rotation of the knives <NUM> can either be done by rotating the whole toolstring <NUM> from surface or by using a downhole motor as seen in <FIG>.

Weight load the dogs <NUM> by setting down weight in the drill pipe string <NUM> while the dogs <NUM> are resting on the top <NUM> of the PBR <NUM>. The dogs <NUM> will be set up to shear at a predetermine force. When reaching the predetermined force, the dogs <NUM> will collapse as seen in <FIG>. The tag sub <NUM> with the collapsed tag dogs <NUM> is seen in an enlarged view in <FIG>.

Running the spear <NUM> into the PBR <NUM> until the no-go sub <NUM> rests on the top of the PBR <NUM>, thus positioning the spear <NUM> inside the cut-off PBR <NUM> as seen in <FIG>. The operation can also be performed without a no-go sub <NUM>, then the spear <NUM> is run inside until the spear slips/grapples are inside the PBR <NUM> and stopped before they reach the cut. How desirable it is to include a no-go sub <NUM> in the toolstring <NUM> depends mainly on the depth of the PBR <NUM> and the distance between the top <NUM> of the PBR <NUM> and the cut, thus the no-go sub <NUM> is considered an optional feature.

Engage the spear <NUM> in the PBR <NUM>.

Claim 1:
An axial position-controlled operation toolstring (<NUM>) for conducting an axial position-controlled operation for releasing a pipe component (<NUM>) in a well, comprising from below and up:
- a casing cutter tool (<NUM>) comprising knives (<NUM>);
- a tag sub (<NUM>) with tag dogs (<NUM>) arranged for landing on a protrusion (<NUM>) in said well
- a pipe spear (<NUM>);
- a drill pipe string (<NUM>),
wherein said knives (<NUM>) of said casing cutter tool (<NUM>) are spaced out a predetermined initial distance (L) below the tag dogs (<NUM>) of the tag sub (<NUM>). said pipe component (<NUM>) is a polished bore receptacle (<NUM>), and the knives (<NUM>) are arranged to cut slips (<NUM>) and/or a slips lock (<NUM>) of said polished bore receptacle (<NUM>) thus freeing said polished bore receptacle (<NUM>), and
wherein said tag dogs (<NUM>) of said tag sub (<NUM>) are arranged for being collapsible by weight loading against said protrusion (<NUM>),
wherein said tag sub (<NUM>) comprises a mandrel (<NUM>) and said tag sub's (<NUM>) tag dogs (<NUM>) are arranged in and protruding from slots (<NUM>) in the mandrel (<NUM>), said tag dogs are arranged for collapsing into said slots (<NUM>) when weight-loaded on said protrusion (<NUM>)
wherein said tag dogs (<NUM>) are fixed in said mandrel (<NUM>) with shear pins arranged for being sheared out by said weight loading against said protrusion so as for said tag dogs (<NUM>) to slide upwardly and inwardly in said slots (<NUM>).