Patent Description:
When a hydrocarbon production well reaches the end of its economic or technical viability, it is plugged and abandoned. As all the wells associated with a particular hydrocarbon production platform become abandoned, the platform can be decommissioned and removed.

One particular type of offshore platform structure is a Gravity Base Structure or GBS, which are prevalent in North Sea oil fields. <FIG> and <FIG> show schematically a Gravity Base Structure of the type found in the North Sea. The Gravity Base Structure, shown generally at <NUM> , comprises a number of storage cells <NUM> that stand on the seabed. The storage cells <NUM> are formed from steel reinforced, pre-stressed concrete, and are substantially cylindrical and arranged in a honeycomb formation. In this example, three cells extend in to legs <NUM> which support the top sides <NUM> of the platforms. The remaining sixteen cells are used for oil/water separation and oil storage.

In a typical example, the cells <NUM> have an approximate outer diameter of around <NUM> meters, and are approximately <NUM> meters high. At the upper end, each cell has an elliptical domed surface. The cells are flooded and held at a lower internal pressure which is lower than the seawater ambient pressure. This keeps the concrete forming the cells in compression. Typically, the pressure inside the cells is <NUM> bar (approximately <NUM> Psi) below the seawater ambient pressure.

<FIG> is a sectional view through cell number nineteen and leg number one of the GBS of <FIG> and <FIG>. The leg <NUM> comprises a cell draw down system <NUM> which functions to introduce fluids into the internal volume of the storage cell via a flowline <NUM>, and an extraction system <NUM> for removal of hydrocarbons. Ballast sand 8a and sediments 8b are present in the bottom of the cell volume. When the cell is substantially depleted, a volume of oil <NUM> is present at the top of the cell volume above the relatively high density seawater and it is necessary to remove this so-called attic oil from the cell volume prior to removal of the cell.

There is a need for a method and apparatus for accessing the storage cell in a manner which is safe, effective, convenient, and economical. Furthermore, there is a need for safe, effective, convenient, and economical methods and apparatus for removal of stored oil from a storage cell.

<CIT> discloses a method and apparatus for securing a conduit to relatively inaccessible structures, for example, oil tanks on submerged ships. The method involves providing a conduit with a neck, temporarily securing the conduit to the surface, for example by means of magnets, etc, drilling a hole through the structure and passing the neck of the conduit through the hole in the structure, and passing an expander device through the neck of the conduit through the hole in the structure to widen a portion of the internal passage of the conduit in the region of the neck.

It is amongst the aims and objects of aspects of the invention to provide an apparatus which meets the above-described needs in storage cell access and/or remediation applications.

It is amongst the aims and objects of aspects of the invention to provide an apparatus for securing equipment to a concrete component of an offshore structure.

Further aims and objects of the invention will become apparent from the following description.

According to an aspect of the invention, there is provided an anchor hub for providing an access point in a capping plate of a hydrocarbon storage cell, the anchor hub comprising: a main body comprising an upper opening, a lower opening and a throughbore extending between the upper and lower openings, the main body comprising a lower portion configured to be located in and extend into a blind hole formed in an upper surface of the capping plate;.

Preferably, the anchor hub comprises an upper portion which is upstanding from an upper surface of the capping plate. The upper portion may provide the attachment point for an item of process or flow equipment.

Alternatively, or in addition, the anchor hub may comprise a seal between an upper portion of the anchor hub and an upper surface of the capping plate.

The anchor hub may comprise an upper connector, which may be a connector for a valve manifold.

Preferably, the throughbore of the anchor hub comprises a seat for a sealing plug.

In embodiments of the invention, the throughbore of the anchor hub enables the passage of a drilling apparatus through the anchor hub, operable to drill through the blind hole and penetrate the capping plate.

The one or more anchor ring assemblies may comprise a plurality of segments, which together form a ring disposed around a lower portion of the body.

Preferably, the anchor hub comprises a pair of anchor ring assemblies axially separated on the main body. The pair of anchor ring assemblies may be connected via a plurality of bolts. The bolts may be tensioning bolts, and may be designed to be tightened to bring the anchor ring assemblies towards one another in an axial direction of the hub.

The one or more anchor ring assemblies may comprise a tapered profile, which may correspond to a tapered profile of the main body. Relative axial movement of an anchor ring assembly with respect to the main body may result in radial displacement of the anchoring ring.

According to a further aspect of the invention, there is provided apparatus for accessing a hydrocarbon storage cell, the apparatus comprising an anchor hub as described above, and a valve manifold attachable to the attachment point of the anchor hub such that the valve manifold is in communication with the throughbore of the anchor hub.

In examples, the valve manifold comprises:.

The valve manifold preferably comprises a throughbore with sufficient to receive a drilling tool, and may comprise a seat for a drilling apparatus. The valve manifold may comprise an upper connector configured for connection to a drilling apparatus.

In one embodiment, the at least one isolation valve is operable to be actuated by an ROV torque bucket. Alternatively, the at least one isolation valve is operable to be actuated by a diver.

Preferably, the valve manifold comprises upper and lower isolation valves in the throughbore of the apparatus.

The valve manifold may comprise a flow port or flow conduit which is in fluid communication with the throughbore between the upper and lower isolation valves.

The flow port or conduit may be coupled to a third isolation valve in a flow line.

The present disclosure also provides a subsea installation comprising:.

The subsea installation may comprise a valve manifold connected to the anchor hub.

The present disclosure also provides a drilling apparatus for use with the anchor hub described above. The drilling apparatus comprises:.

The drilling apparatus may comprise a carriage configured to move axially within the internal volume defined by the support elements with the drill shaft and drill bit.

The drilling apparatus may comprise a torque reaction block, the torque reaction block configured to be rotationally keyed with the support frame. The torque reaction block may be axially movable with respect to the support frame, and may be integral, or may be unitary, with the carriage.

Preferably, the torque reaction block comprises a plurality of recesses, and the recesses may be shaped and positioned to locate the support elements.

Preferably, the drilling apparatus comprises a lower bearing assembly, which may be configured to permit rotation and axial movement of the drill shaft. The drilling apparatus may comprise a centraliser, which may be disposed at the lower bearing assembly. The centraliser may comprise a sacrificial material.

The drilling apparatus may comprise a seat configured to prevent downward movement of the drill shaft and drill bit beyond a predetermined distance. The seat may be configured to receive the carriage. The seat and the carriage may be configured to locate together to form a seal. The seat and/or the carriage may be provided with sealing elements.

Preferably, the support frame is open, and it may provide flow spaces for fluid to flow freely between the internal volume and a volume outside of the support frame.

The drill shaft may be at least partially hollow. The drilling apparatus may provide a fluid circulation through the drill shaft and/or drill bit.

As described above, <FIG>, <FIG> are representative of a drilling rig with a hydrocarbon storage facility to which the anchor hub of the present invention may be applied. A primary objective of the invention is to provide equipment for the safe and cost-effective access of a hydrocarbon storage cell, to facilitate remediation of attic oil from the cell, and accordingly, exemplary embodiments of the invention will be described in that context. It will be appreciated that aspects of the invention may be used in alternative applications, for example, the anchor hub may provide an attachment point for an item of equipment, on a surface of a concrete structure of an offshore installation, including but not limited to a leg or foundation.

<FIG> shows schematically an overview of equipment <NUM> used to form an opening in a subsea hydrocarbon storage cell. The equipment comprises an anchor hub <NUM> shown in a loose condition 60A and a tightened condition 60B respectively. The equipment also comprises a valve manifold <NUM>, configured to be connected to the anchor hub <NUM>, and a drilling tool <NUM>, configured for attachment on an upper coupling of the valve manifold <NUM>. The drilling tool is shown in a first condition 80A in which the internal drill components are retracted and a second condition 80B, in which the internal drilling components are extended.

The equipment shown in <FIG> is designed to provide an isolated attachment and access point for safe and efficient penetration of a hydrocarbon storage cell, and subsequent remediation or disposal of hydrocarbons. An overview of an access method will be described with reference to <FIG> and the subsequent drawings which show equipment details.

This example method will be described in the context of a Remotely Operated Vehicle (ROV) -based operation; in other words one which predominantly uses ROVs to carry out subsea operations with reduced and/or minimal diver support. Typically, such operations take place in relatively deep water; in sea conditions which diver operations are undesirable; or over extended periods which may be unsuitable for diver-based work. However, alternative embodiments of the invention may have an increased reliance on diver-based operations, as will be clear from the following description.

<FIG> shows schematically an initial stage of a storage cell access operation. Storage cell, generally shown at <NUM>, comprises a main wall and a domed upper surface <NUM> with a central opening <NUM>. The opening is filled with a prefabricated concrete slab <NUM>, and a capping plate <NUM> fills the opening and extends outwards over the wall of the domed surface <NUM> of the cell. The capping plate is formed from concrete, and is approximately <NUM> to <NUM> thick.

The upper surface <NUM> of the capping plate <NUM> has a rough hand-tamped finish, and over the lifetime of the storage cell, debris and marine fouling has accumulated on the surface. In stage one of the operation, a work-class ROV <NUM> is deployed to the storage cell <NUM> and is used to clean the upper surface of the capping plate <NUM>. In this example, the cleaning is carried out by the jetting of high pressure seawater to the surface of the capping plate to remove debris and accumulated material such as drill cuttings.

When the surface <NUM> of the capping plate is cleaned, a plug drilling apparatus <NUM> is deployed from surface and landed on the cleaned surface of the concrete plug. The plug drilling apparatus is shown in more detail in <FIG>. The apparatus <NUM> comprises a gravity base <NUM> which supports the apparatus on the capping plate <NUM>, and a pillar <NUM> extending upwardly from the gravity base <NUM> and supporting the drilling components. The gravity base <NUM> comprises a central aperture <NUM> for extension of the drilling components through the gravity base, and a number of integrated pegs with dedicated hydraulic motors (neither being shown) in the gravity base <NUM> to retain the apparatus in position on the concrete cap. The drilling components of the apparatus <NUM> comprise a drill motor <NUM>, drill shaft <NUM> and core bit <NUM>, which are supported over the central aperture <NUM> aligned in parallel with the pillar by a pair of laterally extending swing arms <NUM>.

Drilling operations may be carried out via the work class ROV <NUM>, which provides a source of hydraulic power for the drilling apparatus. The core bit <NUM> is a cylindrical sleeve comprising at its lower end <NUM> cutting serrations which, when the bit is rotated by the drill motor via the drill shaft and when down weight is applied, penetrate the surface of the concrete cap to drill out an annular recess to the penetrating depth of the bit.

When the core bit <NUM> has penetrated the concrete cap to the required depth, the column of concrete within the core bit is removed by pulling the core bit upwards. A formation <NUM> at the distal end of the core bit functions as a core catcher to engage the concrete, enabling it to break a concrete plug from the surrounding capping plate, which can then be retrieved by upward movement of the drilling components to leave a blind hole <NUM> in the capping plate.

<FIG> shows the drilling apparatus <NUM> on the capping plate, having removed a concrete plug using the drilling apparatus <NUM> in the manner described above.

The next stage of the operation, shown most clearly in <FIG>, is the installation of an anchor hub <NUM> into the blind hole <NUM> of the capping plate. The anchor hub of this embodiment of the invention is shown most clearly in <FIG> and <FIG>.

The anchor hub <NUM> comprises a substantially cylindrical body <NUM> having an upper portion <NUM> and a lower portion <NUM>. The upper portion <NUM> is formed to an outer diameter which is greater than the outer diameter of the lower portion <NUM>. The lower portion is sized to be received in the blind hole <NUM> in the capping plate, whereas the upper portion is designed to be upstanding from the surface <NUM> of the capping plate to provide an attachment point for additional equipment. A shoulder <NUM> is defined at a lower edge of the upper portion <NUM> and provides an abutment surface for the surface <NUM> of the capping plate.

The anchor hub <NUM> comprises a central throughbore <NUM> which extends through the upper and lower portions. Partway along the throughbore, the inner diameter is reduced from a relatively large inner diameter to a relatively smaller inner diameter. The transition between the large and small inner diameter proportions defines a seat <NUM> for equipment inserted into the anchor hub during use. Inwardly protruding locking members <NUM> are located in the lower portion below the seat <NUM>, and provides a second locating formation for landing and/or locking equipment inserted into the hub during use. The outer surface of the anchor hub is also provided with an annular locating groove <NUM> for the attachment of additional equipment in use.

The upper portion <NUM> of the anchor hub defines an annular body through which are formed a plurality of circumferentially-distributed holes <NUM> which provide access for anchoring bolts <NUM>. The anchoring bolts are oriented longitudinally and parallel to the axis of the hub, and are distributed around the exterior of outer surface of the lower portion of the hub.

The anchoring bolts <NUM> extend between and connect upper anchoring ring assembly <NUM> and lower anchoring ring assembly <NUM>. The upper and lower anchoring ring assemblies are axially separated on the lower portion of the anchor hub. The lower anchoring ring assembly <NUM> is substantially annular and is located around the lower portion <NUM> at a lower end <NUM> of the anchor hub. Upper anchoring ring assembly <NUM> is substantially annular and is located around the lower portion at an axial position between the upper portion <NUM> and the lower anchoring ring assembly <NUM>.

Each of the upper and lower anchoring ring assemblies is formed from a number of part annular segments, which together form a split annular ring. The number of part-annular segments corresponds to the number of anchor bolts <NUM> (which in this case is eight).

Each of the upper and lower anchoring ring assemblies <NUM>, <NUM> has a tapered or conical profile which corresponds with an outer surface profile of the lower portion of the anchor hub at the point at which it is mounted. In the case of the lower anchoring ring <NUM>, the inner surface of the anchoring ring is shaped such that the inner diameter decreases moving from an upper end <NUM> of the anchor hub to a lower end <NUM> of the anchor hub. The inner surface of the lower anchoring ring therefore has the shape of the inner surface of a truncated cone. The corresponding shape on the lower portion <NUM> of the main body is an outer diameter which decreases moving in a direction from the upper end of the anchor hub to the lower end of the anchor hub.

The upper anchoring ring <NUM> has an inner surface profile which has an inner diameter which increases in a direction from the upper end <NUM> of the anchor hub to the lower end <NUM> of the anchor hub. The corresponding profile on the lower portion of the main body has an increased outer diameter moving from an upper end of the anchor hub to a lower end of the anchor hub. The segments of the upper and lower ring assemblies therefore each function as cooperating wedges, joined by the anchoring bolts. Outer surface of the lower and upper anchoring rings are provided with arrangements of axially distributed ridges <NUM>, <NUM>.

Between the ring assemblies is disposed a sealing arrangement <NUM>. The sealing arrangement comprises a compressible elastomeric material <NUM>, which is oversized, and which in use is compressed to provide a seal between the anchor hub <NUM> and the hole in which it is located. It will be appreciated that a wide range of sealing configurations may be used within the scope of the invention. In this embodiment, the anchor hub is also provided with a port <NUM> which provides fluid communication between the internal throughbore 65of the anchor hub and the seal arrangement. The port enables a liquid sealant to be pumped from the throughbore into the sealing arrangement to enhance the seal.

In use, the anchor hub <NUM> is located in the blind hole <NUM> in the capping plate <NUM>. Conveniently, this can be achieved by using the gravity base and support pillar of the drilling apparatus <NUM>. A second set of swinging support arms (not shown) may support the anchor hub <NUM> off-axis from the bore, and when the drilling phase is complete, the drilling components can be swung away from the bore axis, before the support arms for the anchor hub <NUM> are swung into place over the bore axis to lower the anchor hub into the bore. It will be appreciated that in alternative embodiments, other mechanisms may be used for lowering the anchor hub into the bore.

With the anchor hub <NUM> in the bore, in the position shown in <FIG>, the lower end of the hub supports the weight of the hub, the upper and lower anchoring ring assemblies <NUM>, <NUM> are axially separated and the shoulder <NUM> defined at the lower edge of the upper portion <NUM> is upstanding from the surface of the concrete cap. The drilling apparatus <NUM> (if used) is removed by recovery to surface using a recovery line and the assistance of a ROV. The anchoring bolts <NUM> are then sequentially tightened by accessing the bolts through the holes <NUM> in the upper portion <NUM>. The tightening of the bolts brings the upper and lower anchoring rings axially closer together, causing the separate ring segments to ride up on the corresponding tapered profile of the lower member <NUM>. The anchoring ring elements therefore move radially outwards to engage with the wall of the blind hole <NUM> and anchor the hub <NUM> in position. Axial movement of the upper and lower rings also causes compression of the elastomeric seal elements <NUM>.

<FIG> is a section through the anchor hub in a tightened and anchored condition with the seal elements compressed. Optionally, port <NUM> could be used to pump additional liquid sealant into the sealing arrangement <NUM>. Alternatively, or in addition, sealant material could be provided at the base of the throughbore <NUM> in the anchor hub, to seal between the lower end <NUM> of the hub and the bottom of the hole <NUM>.

With the anchor hub <NUM> secured in the bore, the upper portion of the anchor provides an attachment point with a connector <NUM> for additional equipment as now will be described.

The next stage in the access operation is the location and installation of the valve manifold <NUM> onto the anchor hub. The valve manifold <NUM> is deployed from surface and landed on the anchor hub <NUM> with the assistance of a work class ROV <NUM>.

<FIG> shows the features of the valve manifold <NUM> in more detail. The valve manifold of this embodiment is configured as a double block isolation valve arrangement. A lower connector <NUM> is configured to be mounted on the connector <NUM> defined by the upper portion <NUM> of the anchor hub <NUM>. The lower connector <NUM> comprises a dog and window locking arrangement, in which an ROV (not shown) is operated to raise or lower the locking dogs to enable ball bearings to extend into or be retracted from the annular groove <NUM> on the anchor hub connector <NUM>.

An upper male connector <NUM> is provided for the connection of additional equipment. In this case, the upper connector <NUM> is identical to the connector <NUM> defined by the upper portion <NUM> of the anchoring hub. A longitudinal throughbore <NUM> extends between the upper and lower connectors. Between the upper and lower connectors are arranged upper and lower isolation valves <NUM>, <NUM>, which in this embodiment are ball valves configured to be actuated by ROV torque buckets <NUM>. Located between the upper and lower valves is a port <NUM> which is configured to be connected to a flowline <NUM> via an ROV operated isolation valve <NUM> and an optional check valve <NUM>. With the upper and lower isolation valves <NUM>, <NUM> open, the valve manifold provides full bore access to the anchoring hub <NUM>. This facilitates intervention through the valve manifold <NUM>, for example to insert a macerator, agitator, or pump into the storage cell to facilitate removal of materials.

With the valve manifold <NUM> in place, the port <NUM> is used to pressure test each of the isolation valves via a hot stab operated from the ROV.

To complete the access operation, it is necessary to drill through the base of the blind bore <NUM> to penetrate the storage cell. This is achieved using drilling tool <NUM>, which is lowered from the surface and again landed with the assistance of a ROV, as shown in <FIG>. The drilling tool <NUM> will be described in more detail with reference to <FIG>.

The drilling components of the tool may be free to drop under their own weight to the lower position as shown in <FIG>, or may be retained in the upper position shown in <FIG>.

The drilling tool <NUM> comprises a drill shaft <NUM> coupled to a drill bit and a drill support frame <NUM>. The drill bit is a conventional core bit comprising a core catcher at its lower end. Provided on the drill support frame <NUM> is a lower connector <NUM>, which is of the same type as the connector <NUM> on the valve manifold <NUM>, and is designed to be connected to the upper connector <NUM> of the manifold. The lower connector <NUM> comprises a dog and window locking arrangement to secure the drilling tool <NUM> on the valve manifold.

At an upper end of the drill support frame <NUM>, a tie <NUM> supports four drill support bars <NUM> which extend from the lower connector <NUM> to the tie <NUM>. The tie <NUM> retains the support bars <NUM> in a position which defines a central bore through which the drill shaft <NUM> moves between extended and retracted positions. The support frame <NUM> also comprises an intermediate tie <NUM> with joins the support bars on their exterior.

Located above the lower connector is a bearing assembly <NUM> which enables the drill shaft to be freely rotated in the drill support frame. Above the bearing assembly <NUM> is a seat <NUM> which is configured to receive a carriage <NUM> of the drilling components. Below the bearing assembly and extending through the lower connector <NUM> is a centraliser <NUM> which is received in the bore defined by the valve manifold connector <NUM>, and defines a throughbore for the passage of the drill shaft <NUM>. The centraliser is a sleeve formed from a sacrificial material, such as a plastic, which facilitates longitudinal alignment of the drill during the early stages of drilling, but which may be damaged during the course of drilling.

The drilling tool carriage <NUM> is shaped to be accommodated within the drill support frame <NUM>, and comprises recesses (not shown) arranged around the outer surface of a torque reaction block <NUM>. The recesses correspond to the position and profile of the support bars <NUM>. The carriage <NUM> supports and carries a hydraulic drill motor <NUM>, which is powered by a hydraulic hose <NUM> that runs out of the drilling tool behind the drill motor and carriage. The carriage <NUM> is able to slide with respect to the support bars, but due to interaction of the block and the bars, is rotationally keyed with respect to the support frame.

Disposed between the drill shaft <NUM> and the torque reaction block <NUM> is an arrangement of ports <NUM> which provides through connection through an interior of the drill shaft and the open space between the support bars. A lower surface of the carriage <NUM> is provided with a seal <NUM> for sealing the carriage <NUM> against the seat <NUM> when in a lowered position.

The drilling operation proceeds as follows. With the drilling tool <NUM> located on the valve manifold block <NUM> , and the first and second isolation valves <NUM>, <NUM> fully open, the drill shaft <NUM> extends into the valve manifold block and into the blind hole <NUM> to the base of the blind hole. Valve <NUM> is opened, and a vacuum is drawn on the port <NUM> by a pump (not shown) powered from surface or a local ROV, causing circulation of seawater through the open structure of the drill support frame <NUM>, and into the hollow drill shaft <NUM> via the ports <NUM>, and out of the port <NUM> to be returned to the sea. The hydraulic drill motor <NUM> is powered from surface or a local ROV to cause the drill shaft <NUM> and bit to rotate.

The weight of the drill shaft, in conjunction with the low pressure drawn through the valve <NUM>, provides sufficient weight-on-bit to progress the drilling of a hole through the base of the blind hole. The carriage <NUM> slides downwards on the support bars, carrying with it the drill motor <NUM> and the distal end of the hydraulic hose <NUM> as the drill bit progresses through the concrete capping plate. When the drill penetrates the concrete capping plate to access the storage cell <NUM>, a pressure differential between the hydrostatic pressure and the storage cell pressure (the latter being relatively low pressure) causes the drill shaft <NUM> and carriage <NUM> to be drawn downwards until the lower surface of the carriage engages with the seat <NUM> and seals the ports <NUM>, preventing further inflow of seawater. Valve <NUM> is closed to prevent inflow of seawater through the port <NUM>.

With the storage cell now penetrated, the drill bit and shaft <NUM> are ejected into the storage cell, as shown in <FIG> (although they may be retained and recovered). The valve <NUM> is vented to partially pressure balance the system and ease the pulling of the drill shaft <NUM> and carriage <NUM> against the seal with the seat <NUM>. With the carriage fully retracted, it is latched against the support frame (latch not shown) and the isolation valves <NUM>, <NUM> in the valve manifold block are closed. The port <NUM> enables pressure testing of the valve manifold block, and optionally the valve manifold can be flushed by liquid or gas to remove any hydrocarbons from the flow lines. The drilling tool may then be decoupled from the valve manifold block and retrieved to surface.

The drilling tool <NUM> has a number of benefits in the envisaged applications to the penetration and/or access of a hydrocarbon storage cell. Firstly, by adopting a staged process of forming a blind hole and a secondary penetrating bore, the penetration distance required by the drill <NUM> is relatively low. This enables the use of a compact and relatively lightweight drilling tool. This is in contrast with a conventional drilling approach which would require the use of heavy drilling equipment, deployed to and supported by the upper surface of the storage cell.

The two stage process may also enable performance of the operation on multiple storage cells at convenient times. For example, multiple blind holes may be sequentially formed on adjacent storage cells during one phase of operation, prior to penetration drilling being carried out in a second phase. This facilitates optimal use of resources. This is in contrast with convention single stage drilling, which may take a considerable amount of time from start to finish with no convenient point to pause or interrupt the operation.

By providing an anchor hub installed into a hole the capping plate in a first phase, a secure, sealed attachment point for isolation and process equipment is provided. Significantly, this equipment is not required to seal against the relatively coarse upper surface of the capping plate. To do so would require a time-consuming and technically challenging surface polishing operation, so that the surface is sufficiently smooth to enable drilling equipment to be sealed on the surface.

The drilling support frame is designed to provide sufficient support to the drilling equipment, but remaining weak enough to be distorted or damaged if impacted during use, for example by a ROV or another subsea object or item of mobile infrastructure. This prevents large forces being transferred to the valve manifold and/or capping plate of the storage cell.

A further advantage arises from the distribution of support elements around the drill access. This is in marked contrast to a conventional pillar drilling tool, in which support pillars are provided on a single axis offset from the drilling axis. Providing support frame elements arranged around the drill axis results in equipment with reduced bulk, reduced footprint, which may be easier to manipulate and handle by personnel at surface, divers and/or ROVs.

The foregoing description relates to a method of providing penetration and access to a hydrocarbon storage cell, and results in the provision of an access point in the form of an anchor hub <NUM> and an isolation valve manifold <NUM>. The valve manifold provides a connection point for a hose connector to enable hydrocarbons to be transferred from and/or to the storage cell during a remediation operation.

An example of such a hose connector assembly is shown in <FIG>, generally at <NUM>. The hose connector assembly <NUM> comprises a lower connector <NUM>, which is of the dog and window locking type described above in the context of the valve manifold and the drilling tool. The hose connector assembly comprises a T-piece <NUM> defining a throughbore <NUM> between the lower connector <NUM> and an upper flange plate <NUM>. A blind flange <NUM> is joined to the flange plate to close the throughbore.

A side arm <NUM> of the T-piece <NUM> comprises a side bore <NUM> to a side flange <NUM>. Joined to the side flange <NUM> is a receptacle <NUM> of a hot stab connector <NUM>, which enables the coupling of a transfer hose <NUM> with the hose connector assembly <NUM>.

The hose connector assembly <NUM> is configured for attachment to a vertically oriented hot stab, which has an elbow joint for connection to a horizontally-oriented hose. The configuration of the hose connector assembly <NUM> also enables convenient coupling of a hose to the valve manifold while maintaining full bore access to the manifold via the throughbore <NUM> if required. This facilitates intervention through the valve manifold <NUM>, for example to insert a macerator, agitator, or pump into the storage cell to facilitate removal of materials, optionally while a hose is connected.

An alternative hose connector assembly is shown in <FIG> of the drawings, generally depicted at <NUM>, and configured for attachment to a horizontally-oriented hot stab for in-line or on-axis connection to a horizontally-oriented hose. The hose connector assembly <NUM> comprises a lower connector <NUM>, which is of the dog and window locking type described above in the context of the valve manifold and the drilling tool. In this embodiment, the hose connector assembly lacks a T-piece, and instead defines an axial throughbore <NUM> between the lower connector <NUM> and an upper flange plate <NUM>. Joined to the upper flange plate <NUM> is a receptacle <NUM> of a hot stab connector <NUM>, which enables the coupling of a transfer hose <NUM> with the hose connector assembly <NUM>.

It will be appreciated that a variety of different anchor hubs may be used in different embodiments of the invention. Examples of anchor hubs in different forms are shown in <FIG>.

Referring to <FIG>, the anchor hub <NUM> is similar to the anchor hub <NUM>, and will be understood from <FIG> and <FIG> and the accompanying description. In particular, the anchor hub <NUM> comprises upper and lower rings <NUM>, <NUM> with inner tapered surfaces which correspond to tapered surfaces on the outer surface of the main hub body <NUM>. The rings <NUM>, <NUM> are brought together by the tightening of anchor bolts, and compress an intermediate seal arrangement <NUM>. The anchor hub <NUM> differs from the hub <NUM> of <FIG> in that the upper portion <NUM> of the anchor hub comprises a J lock spigot <NUM> for mounting equipment, such as a valve manifold, on the concrete capping plate.

<FIG> is a sectional view through an anchor hub according to an alternative embodiment of the invention, generally shown at <NUM>. This embodiment is again similar to the anchor hubs <NUM> and <NUM> of <FIG> and <FIG> in that it has an arrangement of corresponding tapered profiles. However, this embodiment differs in that the upper and lower tapered rings <NUM>, <NUM> are solid rings, and a segmented anchor ring <NUM> is arranged around the exterior of the main body <NUM> of the anchor and rings <NUM>, <NUM>. In use, the anchor hub <NUM> is internally actuated by a threaded engagement of the main body with the lower anchor ring <NUM>. This causes the lower anchor ring to move axially upwards and forces the external anchor ring <NUM> to engage the bore. The upper portion of the anchor hub provides a flange attachment.

<FIG> is a sectional view through an anchor hub <NUM> according to a further alternative embodiment of the invention. In this embodiment, the anchor hub is formed from the core drill bit itself, which is retained in the concrete capping plate. The anchor comprises a hollow cylinder <NUM> which forms an annular groove during drilling. The upper part of the anchor hub is provided with a J lock spigot <NUM> for mounting equipment, such as a valve manifold. A resin is pumped into the micro-annulus between the core bit and the concrete capping plate in order to seal between the lower end of the sleeve and the plate.

This configuration has the advantage of fewer operation steps in order to mount the hub, but does require drilling through the full thickness of the capping plate in the subsequent drilling operation in order to penetrate the storage cell.

<FIG> is a sectional view through an anchor hub <NUM> according to a further alternative embodiment of the invention. In this embodiment, the anchor hub is mounted into a blind hole. The main body <NUM> of the hub is externally bolted to the capping plate via a flange <NUM>. Sealing elements <NUM>, <NUM> are provided beneath the flange plate and surrounding the lower portion of the anchor in axially separated positions. The upper portion of the anchor hub is provided with a J lock spigot <NUM> for the mounting of equipment, such as a valve manifold.

As noted above, a principal application of the apparatus described above, including the anchor hub of the present invention, is in the remediation of hydrocarbons from the storage cell, and a remediation method will be described with reference to <FIG>, with additional equipment details shown in <FIG>.

<FIG> shows the top of a second storage cell <NUM>, which has an anchor hub <NUM> installed in a blind hole in a capping plate <NUM>. The storage cell <NUM> is the same as the storage cell <NUM>, and the blind hole is formed by the method described with reference to <FIG>. The anchor hub <NUM> in this example is the anchor hub <NUM> of <FIG>, and as shown in <FIG> has been fixed into the capping plate to provide access and attachment point.

<FIG> shows a valve manifold <NUM> and drilling tool <NUM> deployed from surface and landed with the assistance of ROV <NUM>. The valve manifold <NUM> is shown in more detail in <FIG>. The manifold comprises a main body <NUM>, and a lower connector <NUM>, which in this case is configured for attachment to a J lock spigot of the anchor hub <NUM>. A throughbore <NUM> extends from the lower connector <NUM> to an upper opening <NUM>, which includes a guide funnel <NUM> for assisting with the placement of the drilling apparatus <NUM> in the manifold <NUM>. Between the upper opening <NUM> and the lower connector <NUM> is an isolation valve <NUM>, which in this case is a ball valve operable to be actuated by a ROV torque bucket <NUM>. Disposed between the upper opening <NUM> and the valve <NUM> is a seat <NUM> defined by a reduced inner diameter. The seat provides a landing point for the drilling tool <NUM> and a sealing plug running tool. Disposed between the isolation valve <NUM> and the lower connector <NUM> is a side conduit <NUM> which extends from the throughbore <NUM> to a side flange <NUM>. The side flange <NUM> is configured for the attachment of a hot stab hose connection receptacle <NUM>, in this case in a vertical orientation, which enables a ROV to connect a hot stab of a transfer hose <NUM> to the valve manifold (<FIG>).

The valve manifold <NUM> also provides a guide for the drilling tool <NUM> to drill a hole which penetrates the storage cell <NUM>. The drilling tool <NUM> is similar in form and function to the drilling tool <NUM> described in detailed reference to <FIG>, <FIG> and will not be described in detail here. However, the drilling tool <NUM> differs in that a lower bearing assembly on the drilling support frame is configured to be received in the seat <NUM>. The lower bearing assembly of the drilling tool is located on the seat, and provides support and centralisation for passage and rotation of the drill shaft.

The drilling tool <NUM> is operated to drill a hole through the base of the blind hole and into the storage cell. The method of drilling is similar to the method described with reference to <FIG>, <FIG> and will not be described in detail here. However, in this embodiment, the drilling of the penetrating hole is performed with the side conduit <NUM> of the valve manifold <NUM> connected to a storage cell <NUM> which has already been penetrated.

In this example, the cell <NUM> is to be remediated by transferring hydrocarbons contained in the storage cell <NUM> to a disposal cell, which in this case is cell <NUM>. Cell <NUM> has been provided with an anchor hub <NUM> and valve manifold <NUM> by the method described with reference to <FIG>. <FIG> shows schematically the equipment installed on the remediating cell <NUM> and the disposal cell <NUM>. With the hose <NUM> connecting the valve manifolds <NUM> and <NUM>, the isolation valves <NUM> and <NUM> are opened to provide fluid communication between the internal volume of the storage cell <NUM> and the manifold <NUM>. The relatively low pressure of the cell <NUM> draws seawater through the open structure of the drill support frame, and into the hollow drill shaft via ports, and through the hose <NUM> to the disposal cell <NUM>. The low pressure also causes the drill shaft and core bit of the drilling tool <NUM> causes the drill shaft and carriage to be drawn downwards until the lower surface of the carriage engages with a seat.

When the storage cell is penetrated, pressure is equalised between the cell <NUM> and the cell <NUM>, and the valve <NUM> is closed to prevent further in-flow of seawater. The drill bit and drive shaft are ejected into the cell. The carriage of the drilling apparatus <NUM> is retracted and latched in an upper position, enabling isolation valve <NUM> to be closed, and the drilling apparatus <NUM> to be removed.

The storage cell <NUM> is now ready to be remediated. On the valve manifold <NUM> of the disposal cell <NUM> is mounted a transfer pump assembly <NUM>. The pump assembly comprises a progressive cavity multiphase pump and a connector which corresponds to the upper connector <NUM> of the valve manifold. The pump assembly <NUM> comprises a viewing window to enable a ROV (or diver) to monitor the fluid being pumped through the assembly. With the transfer hose <NUM> installed between the valve manifold <NUM> and the valve manifold <NUM>, the isolation valves <NUM> and <NUM> of manifold <NUM> are opened, and power is provided to the pump via the ROV <NUM>. The low pressure on the inlet side of the pump <NUM> causes hydrocarbons to be drawn from the remediating cell <NUM> along the transfer hose and through the valve manifold <NUM> into the disposal cell <NUM>. The ROV monitors the fluid being pumped through the pump assembly, until it is observed that seawater (rather than hydrocarbons) is being pumped through the transfer hose <NUM>. The remediating cell is isolated, and the transfer hose is flushed into the disposal cell. The remediating cell valve manifold <NUM> is pressure tested, and the hose connector is removed from the valve manifold, ready for transfer to another remediating cell.

<FIG> shows an optional step of injecting dispersible chemicals into the remediating cell via a second hose <NUM>, which in this case is run from surface.

When the hydrocarbons have been successfully remediated from cell <NUM>, the cell <NUM> can be plugged and capped. <FIG> shows a sealing plug and running tool assembly <NUM> which is deployed from surface and landed with the assistance of the ROV <NUM>. The sealing plug and running tool assembly <NUM> is shown in more detail in <FIG>. The running tool <NUM> comprises a cylindrical sleeve <NUM> with a lower seal assembly <NUM>, shaped and sized to fit into the seat <NUM> defined by the valve manifold <NUM>. A shaft <NUM> extends through the sleeve <NUM> and the seal assembly <NUM> to support a plug <NUM> at its lower end. In use, the sealing plug and running tool assembly <NUM> is received in the upper part of the valve manifold <NUM>, and the lower seal assembly is landed on the seat. The seal is pressure tested, and subsequently the shaft <NUM> is extended to mount the sealing plug <NUM> in an upper part of the anchor hub <NUM>. With the plug set, the equipment is again pressure tested, and the shaft <NUM> is removed from the sealing plug <NUM> to leave it in the anchor hub <NUM>. The running tool <NUM> is then recovered to surface through the valve manifold.

With the sealing plug <NUM> in place, the valve manifold <NUM> is removed from the anchor hub and recovered to surface. A blind cap is installed over the anchor hub, and optionally the anchor hub is capped with concrete to complete the plugging and capping operation. The storage cell <NUM> is then fully remediated.

It will be appreciated that the steps depicted in <FIG> may be repeated for multiple storage cells. Each time, oil contained in the remediating cell is transferred to a disposal cell. Conveniently, the pump assembly can remain in place on the valve manifold of the disposal cell while the transfer hose is relocated to valve manifold installed on the various remediating cells. The operational sequence may be repeated until all cells have been remediated of attic oil, with the contents transferred to the disposal cell.

Subsequently, when it is necessary to remediate the disposal cell, a hose may be deployed from surface and connected to the valve manifold of the disposal cell. A surface or subsea pump is operated to remove the attic oil from the disposal cell, before the hose is removed. The sealing and plugging operations described with reference to <FIG> may then be repeated to plug and cap the remediated disposal cell.

The methods described above are primarily ROV operated, but it will be appreciated that alternatively the operational steps, or at least some of them, may be performed by a diver. Some modifications to the equipment may be necessary to facilitate convenient diver operation. <FIG> is an alternative example of a valve manifold, which is configured for diver-based operations. The valve manifold, generally shown at <NUM>, is similar to the valve manifold <NUM>, and will be understood from <FIG> and the accompanying description. The valve manifold <NUM> is shown installed on an anchor hub, which is the anchor hub <NUM> described with reference to <FIG>. The valve manifold <NUM> comprises upper and lower isolation valves <NUM>, <NUM>, and an intermediate port <NUM> coupled to an isolation valve <NUM>. The upper and lower connectors of the valve manifold are flange plate connectors, which may be attached by the diver. The valves <NUM>, <NUM> and <NUM> function in a similar way to valves <NUM>, <NUM> and <NUM>, although are provided with manually actuated levers <NUM>, <NUM>, <NUM> to facilitate diver-based operations.

Referring to <FIG>, there are shown sequentially the steps of installing an anchor hub on a storage cell, penetrating the storage cell, and remediating the storage cell. The sequence shown is similar to the sequences shown in <FIG> and <FIG>, but differs in that they are primarily operated by divers.

In <FIG>, a diver <NUM> operates the drilling apparatus <NUM> to form a blind hole in the capping plate <NUM>. In <FIG>, the diver installs a valve manifold <NUM> on an anchor hub <NUM> in the blind hole. In <FIG>, a drilling apparatus <NUM> is located in the valve manifold, and the diver performs the drilling operation to penetrate the storage cell.

<FIG> shows diver-supervised remediation of a storage cell <NUM> to a disposal cell <NUM>, the latter having a transfer pump assembly <NUM> installed. The diver monitors the transfer of fluids through the transfer hose <NUM> via a viewing window provided in the hose connector assembly <NUM>.

In <FIG>, injection of dispersible chemicals is carried out by the connection of the surface hose <NUM> to the valve manifold assembly <NUM>' by the diver, and in <FIG>, the diver operates a sealing plug and running tool assembly <NUM> to plug the anchor, and then caps the anchor following removal of the valve manifold <NUM>' and drilling equipment <NUM>.

The invention provides an anchor hub for accessing a hydrocarbon storage cell and/or removing hydrocarbons therefrom. An access method comprises installing the anchor hub in a capping plate of the hydrocarbon storage cell, and drilling a bore to penetrate an internal volume of the storage cell by passing a drilling apparatus through the anchor hub. A removal method comprises providing a first hydrocarbon storage cell comprising a first anchor hub and providing a second hydrocarbon storage cell comprising a second anchor hub. The first and second anchor hubs are connected to one another with a flowline, and hydrocarbons are pumped from an upper portion of an internal volume of the second hydrocarbon storage cell to an internal volume of the first hydrocarbon storage cell. The anchor hub in one aspect of the invention comprises a main body comprising an upper opening, a lower opening and a throughbore extending between the upper and lower openings. The main body comprises a lower portion configured to be located in and extend into a blind hole formed in the capping plate. Securing means are configured to fix the lower portion of the anchor hub in the blind hole. An annular seal is arranged around the lower portion to provide a seal between the lower portion and the blind hole. An attachment point is provided for connecting an item of process or flow equipment to the anchor hub such that the item of process or flow equipment is in communication with the throughbore.

The invention provides apparatus for accessing and/or removal of hydrocarbons from a storage cell in a manner that is safe, effective, convenient, and economical.

The two stage access and penetration process enables performance of the operation on multiple storage cells at convenient times optimising use of resources. By providing an anchor hub installed into a blind hole the capping plate in a first phase, a secure, sealed attachment point for isolation and process equipment is provided. Significantly, this equipment is not required to seal against the relatively coarse upper surface of the capping plate. The drilling support frame is designed to provide sufficient support to the drilling equipment, but prevents large forces being transferred to the valve manifold and/or capping plate of the storage cell.

It will be appreciated that various combinations of the above-described equipment and method steps may be used in alternative embodiments to suit a particular application or environment. For example, diver-oriented operations may be interchanged with ROV-based operations in certain embodiments. Modifications to the process and/or flow equipment can be made to render it suitable for use with different anchor hubs or connector types.

Claim 1:
An anchor hub (<NUM>, <NUM>, <NUM>, <NUM>) for providing an access point in a capping plate (<NUM>) of a hydrocarbon storage cell (<NUM>), the anchor hub (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a main body (<NUM>) comprising an upper opening, a lower opening and a throughbore (<NUM>) extending between the upper and lower openings, the main body comprising a lower portion (<NUM>) configured to be located in and extend into a blind hole (<NUM>) formed in an upper surface of the capping plate (<NUM>);
securing means configured to fix the lower portion (<NUM>) of the anchor hub (<NUM>, <NUM>, <NUM>, <NUM>) in the blind hole (<NUM>),
an annular seal (<NUM>, <NUM>, <NUM>, <NUM>) arranged around the lower portion to provide a seal between the lower portion (<NUM>) and the blind hole (<NUM>); and
an attachment point for connecting an item of process or flow equipment to the anchor hub (<NUM>, <NUM>, <NUM>, <NUM>) such that the item of process or flow equipment is in communication with the throughbore (<NUM>);
characterised in that the securing means comprises one or more anchor ring assemblies that function as wedges or slips, and are configured such that relative axial movement of an anchor ring assembly with respect to the main body results in engagement of an anchor element with the blind hole.