Patent Description:
Prior art includes fully all-electric subsea trees. One such all-electric subsea tree is disclosed in SPE Article, SPE-<NUM>-MS, published on SPE Offshore Europe Conference & Exhibition, <NUM>-<NUM> September <NUM>, Aberdeen, United Kingdom. Here it is described that an all-electric subsea well consists of an electric subsea Christmas tree, electric downhole safety valve, and associated subsea control modules. Valve control is established via an electric cable. Umbilicals used in hydraulic subsea operations are complex, difficult to install, and highly expensive. Replacing hydraulic fluid tubes by an electric cable within the umbilical can provide a <NUM>% cost savings over a <NUM>-km step-out. The technology also improves control of environmental impact by removing the risk of hydraulic fluid release.

A downhole safety valve is functioning as one of the barriers in the well, and is an important element. Normally such a valve will be tested for operation at regular intervals. An electrically operated downhole safety valve would normally be equipped with an A and B (redundant) electric operation system. In the event both of these fail in providing power to the downhole safety valve, the well is shut in and cannot be reopened until power (and communication) is re-established. One possible way of alleviating this is to install two electric downhole safety valves in series within the well. For hydraulically operated trees with a hydraulic operated downhole safety valve, there are provisions for setting an in-tubing insertable hydraulically operated downhole safety valve by wireline operations, to gain the same functionalities and barriers as the non-functional production tubing installed downhole safety valve.

The downhole safety valve (DHSV) is a primary well barrier element located in the "upper" completion string and comprises a valve unit and an actuator. The purpose of the downhole safety valve is to prevent uncontrolled flow of fluids from the reservoir and up the tubing in an emergency situation by closing the valve. The downhole safety valve is also sometimes referred to as surface controlled subsea safety valve (SCSSV).

For a hydraulically operated tree, the downhole safety valve is normally a hydraulically operated valve. The two major types of hydraulic operated downhole safety valves which comprises a flapper are the tubing retrievable surface controlled subsurface safety valve (TRSCSSV) and the wireline retrievable surface controlled subsurface safety valve (WRSCSSV).

The TRSCSSV is installed as part of the tubing string with threaded connections at the upper end (box) and lower end (pin) of the valve. This concept maintains the inside diameter (ID) of the production tubing string also through the safety valve.

The backup for the TRSCSSV for a hydraulic system is the WRSCSSV, which WRSCSSV is a wireline retrievable surface controlled subsurface safety valve. The WRSCSSV is basically a smaller diameter version of the TRSCSSV with main application as through-tubing conveyed means for remediation of TRSCSSV failures. The WRSCSSV is normally installed within the TRSCSSV taking advantage of the existing hydraulic line. The WRSCSSV is also named insert hydraulic downhole safety valve (DHSV).

For an electric tree or for a tree with an electric downhole safety valve, there are no hydraulic lines down to the position of the electric downhole safety valve as there is not need for a hydraulic connection as the valve is electrically operated, i.e. there is no hydraulic present and there is no hydraulic access. In other words, for an originally installed electric downhole safety valve which is electrically operated there are no provisions in the well for providing hydraulics to the position of the electrically operated electric downhole safety valve as there are no need for hydraulics. Such a safety valve would also normally have both an A and B (redundant) operation systems.

Prior art includes <CIT>, <CIT>, <CIT> and <CIT>.

<CIT> relates to a bypass diverter sub including a housing defining a flow passage, a control line bypass piston arranged within a control line bypass bore defined in a wall of the housing, and a balance line bypass piston arranged within a balance line bypass bore defined in the wall. An outer magnet is disposed within a magnet chamber and is operatively coupled to the control and balance line bypass. A flow tube profile is positioned within the flow passage and provides an inner magnet magnetically coupled to the outer. The flow tube profile is movable between a first position, where control line and balance line pressures circulate through the bypass diverter sub to a subsurface safety valve, and a second position, where the control line pressure is diverted into the flow passage and the balance line pressure is diverted into a balance line jumper conduit.

<CIT> relates to a production assembly and method for controlling production from production tubing supported by a tubing hanger in a well including a wellhead. The assembly includes a function spool engaged with the wellhead and a tree engaged with the function spool. The tubing hanger is landable in the tree bore such that the production tubing is supported in the well by the tree. A function mandrel separate from the tubing hanger is engaged with the production tubing and positionable inside the function spool bore. The function mandrel includes a passage connected to a line extending into the well that is connectable with a port in the function spool such that communication with a downhole component through the line is allowable from outside the function spool.

<CIT> relates to a system and method for communicating hydraulic control to a wireline retrievable downhole device. The system utilizes a tubing retrievable downhole device having a hydraulic chamber. A radial cutting tool is selectively located within the tubing retrievable downhole device to cut a fluid passageway between the hydraulic chamber and the interior of the tubing retrievable downhole device. Thereafter, when the wireline retrievable downhole device is positioned within the tubing retrievable downhole device, hydraulic control is communicated to the wireline retrievable downhole device through the fluid passageway to actuate the wireline retrievable downhole device.

<CIT> relates to a system which supplies electrical power to a remote electrical device. The system includes an AC/DC voltage converter coupled to the AC voltage source for converting an AC voltage from the AC voltage source to a high DC voltage output at a first location. The AC/DC voltage converter comprises a plurality of AC/DC voltage converter components which, on the input side thereof, are connected in parallel with the AC voltage source and which, on the output side thereof, are connected serially to an electric conductor. The electric conductor extends to a plurality of voltage converters at a remote location having inputs connected serially to the electrical conductor and having outputs providing an appropriate voltage to the electrical device.

A problem may rise in the electric subsea trees or in any tree (electric or hydraulically operable) having an original installed electric downhole safety valve, in the event that the electric access to the electric downhole safety valve is (for any reason) restricted or fully prevented so that the redundant B system of the electric system does not work as the A system is not working, hence the electric downhole safety valve does not work properly.

It is an object of the invention to provide an alternative fallback solution for a tree and well with an electrically operable electric downhole safety valve, in the case the electric downhole safety valve does not work properly.

The invention is set forth in the independent claims, while the dependent claims describe other characteristics of the invention.

In all embodiments, as defined in the independent apparatus claim and in the independent method claims, a hydraulically operable insert hydraulic downhole safety valve is set in a subsea production system with a X-mas tree and originally electric downhole safety valve.

According to the invention there is an electric subsea tree, also referred to as an electric tree or an all-electric subsea tree within the oil and gas industry, which is characterized in that it is electrically operated and that a traditional umbilical with a hydraulic fluid line as used in the oil and gas industry is superfluous because the operation of the valves in the electric subsea tree is done by electric communication/power only.

The production system comprises an electrically operated downhole safety valve, and since the system originally is intended to operate electrically, the system does not comprise a fluid or hydraulic line from the electric downhole safety valve to a power source on the seabed or at surface. According to the invention there is a need for a hydraulic source for the operation of a hydraulically operable insert hydraulic downhole safety valve and the source for hydraulics as used in the invention is arranged subsea, either being connected to surface or positioned on the seabed at or close to the subsea tree. This is the case in all embodiments of the invention.

The insert hydraulic downhole safety valve contingency solution used with Electric DHSV will provide different technologies for primary and contingency solutions and does not involve any common mode failures.

Although tubing retrievable downhole safety valves are installed in order to be able to shut down a well, there may be situations where it is desirable to test whether the safety valve is capable of shutting down a well (i.e. whether the valve is capable of performing its required function). The tubing retrievable downhole safety valves are tested at predetermined intervals where an operator instructs the safety valve to close, verifies that the safety valve has closed, instructs the safety valve to open, and verifies that the safety valve has opened. For an electrically operable downhole safety valve there are normally two electric modes of operation, A and B, where B would be acting as contingency for A in case that fails. In case both fails there are no further contingency solutions. The present invention provides for such a contingency solution by making provisions for and installing a wireline retrievable hydraulically operated downhole safety valve within the tubing of the production system. The production system may be full-electrical production system with an all-electric or electric tree.

For the electrically operated tubing retrievable downhole safety valve the fall back is the electric B channel. For hydraulically operated tubing retrievable safety valves the procedure is to insert an insert hydraulic downhole safety valve into the hydraulically operated tubing retrievable downhole safety valve. This insert hydraulic downhole safety valve is normally set such that it forces the hydraulically operated tubing retrievable downhole safety valve open in order to avoid sudden unintentional fully or partly closure of the flow in the production tubing.

According to the invention, it is described a method of operating a subsea production system, the system comprising an electric subsea tree connected to a subsea well, a production tubing in the well, and an electrically operable electric downhole safety valve, the electric subsea tree comprises a through-going bore forming part of a fluid line in the subsea production system down to a position at or close to the electric downhole safety valve, wherein the method comprises, in case of malfunction in operation of the electric downhole safety valve, the steps of:.

Thus, according to the invention, the electric subsea tree and tubing are prepared during original installation with a through-bore communicating from an opening at the outside of the tree to an opening at the position of the electric downhole safety valve via the through-going bore.

The procedure assumes contingency hydraulic line from the Xmas tree to a landing profile at the electric safety valve that was originally installed with the production tubing later combined with a fluid conduit from existing infrastructure in the field comprising either hydraulic or chemicals distribution or later installed subsea hydraulic power unit at seabed, and a control unit in communication with the insert hydraulic downhole safety valve.

The Electric DHSV may be equipped with redundant electrical supply and actuator components so this system will be more fault tolerant than a traditional hydraulic DHSV.

Conventional Wireline Retrievable insert hydraulic downhole safety valves (i.e. WRSCSSV) are normally prepared for being installed on wireline, thus already field-proven insert hydraulic downhole safety downhole valves may be used.

The hydraulic operable insert downhole safety valve is preferably run on wireline, but it may also be run on coiled tubing, drill string or other through tubing elements.

The subsea tree is an electric subsea tree. Alternatively, not part of the invention, the subsea tree may be a hydraulically operated subsea tree.

The system may comprise an implement profile below the electric subsea tree, and the method may comprise a step of:.

The implement profile may comprise a shoulder, a landing profile or other additional no-go elements installed with the production tubing. The implement profile is preferably at the same position as the point or opening for the through bore of the hydraulics and is pre-installed but not normally used. It may be a plugged hydraulic access point in the tubing in the event the electric downhole safety valve fails and the insert hydraulic downhole safety valve shall be used instead.

If Tubing Retrievable Electric DHSV system fails: Install Wireline installable hydraulic DHSV in a landing profile above TRSCSSV by means of Riserless Well Intervention (RLWI) or rig tooling. This will be the same procedure as currently used for (hydraulic) TRSCSSVs.

The implement profile may be arranged between the electric subsea tree and the electric downhole safety valve, and the method may comprise a step of:.

The implement profile may be provided in the electric downhole safety valve, and the method may comprise a step of:.

The method may further comprise, prior to the step of operating the hydraulically operable insert hydraulic downhole safety valve, a step of:.

The method may comprise, prior to the step of operating the hydraulically operable insert hydraulic downhole safety valve, a step of:.

Hydraulic fluid is in this context not limited to conventional hydraulic fluids, but may be any fluid available in the field, such as MEG, MeOH, scale inhibitor, corrosion inhibitor and even seawater, either directly applicable or conditioned as required, filtered, deoxygenized, desalted, etc..

This setup provides a hydraulic fluid line in the annulus, i.e. outside of the production tubing. The pre-made bore may be pre-drilled or formed by other means and may be plugged with a temporary plug which is removed only if the electric downhole safety valve malfunctions and the setting of the insert hydraulic downhole safety valve is required. A hydraulic fluid line is prepared when installing the production tubing, which the hydraulic fluid line extends from an input port at a position outside of the subsea tree to the point of setting (e.g. the implement profile).

The HPU can be installed using a ROV. If using ROV, prepare ROV installable HPU with electric control circuit for one DHSV function.

Install HPU and plug in control circuit while Wireline/coiled tubing installation of the insert hydraulic downhole safety valve is performed. This operation will be offline and not cost extra vessel time.

It is further described a subsea production system comprising:.

The system may further comprise a tubing hanger, wherein the tubing hanger comprises a hydraulic connection hydraulically connecting a first side of the tubing hanger with an opposite second side of the tubing hanger, wherein the hydraulic connection forms part of the hydraulic fluid line.

It is further described an electric subsea tree comprising:.

It is further described an electric downhole safety valve comprising an implement profile configured for receiving a hydraulically operable insert hydraulic downhole safety valve, and wherein the electric downhole safety valve further comprises a through-going opening for hydraulic fluid for hydraulically operating the hydraulically operable insert hydraulic downhole safety valve.

These and other characteristics of the invention will be apparent from the enclosed drawings, wherein;.

<FIG> is an overview of the main components forming part of the subsea production system according to the invention, including a subsea tree connected to the subsea well, a production tubing in the well, and an electric downhole safety valve in the well. <FIG> shows the situation before the insert hydraulic downhole safety valve has been installed in the well. The electric downhole safety valve typically has a lock open mechanism, which secures that access to the well is achieved at any time without the risk of uncontrolled closing of the bore in the production tubing. The subsea tree can be an electric subsea tree or a hydraulic subsea tree.

<FIG> is an enlarged view of section A in <FIG>, showing more details of the electric downhole safety valve.

<FIG> shows an example of a typical prior art hydraulic tubing retrievable surface controlled subsurface safety valve (TRSCSSV) <NUM> which is a hydraulic operated downhole safety valve with flapper <NUM>. The main functional components of the TRSCSSV <NUM> typically includes a housing <NUM>, a flapper function <NUM>, a power spring <NUM>, a hydraulic piston <NUM>, a hydraulic chamber <NUM>, a flow tube <NUM>, a control line <NUM>, and a nipple profile <NUM> for insert hydraulic downhole safety valve (e.g. insert valve run on wireline). The end of the control line <NUM> is connected to the valve inlet connection port which is a threaded connection with metal-to-metal seal. This is normally done on the platform before subsea deployment. It could also be done onshore and sent to the platform as pre-made assembly. The entire control line <NUM> is tested before the TRSCSSV <NUM> is run downhole with the production tubing (not shown in the figure but the TRSCSSV <NUM> forms part of the production tubing). In order to protect the control line <NUM> when run downhole, it is typically clamped to the outside of the production tubing while being run down hole. Most TRSCSSV <NUM> uses a single control line <NUM> for valve opening and the power spring <NUM> for valve closure because this gives the fail-safe close function upon hydraulic power supply failure. In a similar manner will an electric operated production installed downhole safety valve be configured and operated, as stay open while being feed electric power and automatic close when losing the power source.

<FIG> shows an example of a typical prior art hydraulic wireline retrievable surface controlled subsurface safety valve (WRSCSSV) <NUM> which is an insert hydraulic downhole safety valve with flapper <NUM>. The main functional modules of the WRSCSSV <NUM> typically includes a housing 25w, a flapper 24w, a power spring 26w, a hydraulic piston 27w, a hydraulic chamber 28w, a control line 30w, a flow tube 29w, hydraulic seals (upper and lower sealbores) 34w, and a nipple profile 31w for insert hydraulic valve (e.g. insert valve run on wireline). The WRSCSSV <NUM> is a wireline retrievable surface controlled subsurface safety valve, also named insert WRSCSSV. The WRSCSSV <NUM> is basically reduced bore version of the TRSCSSV <NUM> with main application as through-tubing conveyed means for remediation of TRSCSSV failures. The WRSCSSV <NUM> is normally installed within the TRSCSSV <NUM> taking advantage of the existing hydraulic line. The WRSCSSV is installed on wireline into applicable nipple 31w in the production tubing (not shown in <FIG>). This nipple 31w is normally a part of the complete TRSCSSV assembly ready for installation. The WRSCSSV <NUM> will as an inserted valve have a reduced bore ID through the valve compared to the TRSCSSV and the tubing string.

Referring to <FIG>, if experiencing a leak in the hydraulic TRSCSSV <NUM>, the operator may run an exercise tool to force flow tube <NUM> to an upper position. Then an inflow test of the TRSCSSV <NUM> is performed as a standard procedure, including increasing the pressure above the TRSCSSV <NUM> over a predetermined period time. When the inflow test has been performed, any debris causing the flow tube <NUM> not to close properly is removed. If the TRSCSSV <NUM> is still leaking, install WRSCSSV <NUM>. This sequence includes:.

In the following different methods of operating a subsea production system according to the invention will be described in greater detail. The methods and associated subsea production system and electric subsea tree have many common features with the installation sequence described in relation to <FIG>, however according to the present invention, due to the fact there is an electric subsea tree with no hydraulic fluid to the surface, the TRSCSSV has been changed with an electrically operable electric downhole safety valve. As indicated above, in <FIG> it is an overview of the main components forming part of the electric subsea production system according to the invention, including an (all)-electric subsea tree connected to the subsea well, a production tubing in the well, and an electric downhole safety valve in the well. <FIG> shows the situation before the insert hydraulic downhole safety valve has been installed in the well.

<FIG> shows an electric downhole safety valve <NUM> comprising an implement profile <NUM> configured for receiving a hydraulically operable insert hydraulic downhole safety valve without the hydraulically operable insert hydraulic downhole safety valve installed.

<FIG> shows an electric downhole safety valve <NUM> comprising an implement profile <NUM> configured for receiving a hydraulically operable insert hydraulic downhole safety valve <NUM> with the hydraulically operable insert hydraulic downhole safety valve <NUM> installed.

<FIG> shows an example of an subsea production system <NUM>, the system <NUM> comprising an electric subsea tree <NUM> connected to the subsea well <NUM>, a production tubing <NUM> in the well <NUM>, and an electrically operable electric downhole safety valve <NUM>. The electric subsea tree <NUM> comprises a through-going bore <NUM> configured to support a hydraulic fluid line <NUM> in the electric subsea system <NUM>. The hydraulic fluid line <NUM> extends from an input port <NUM> at a position outside of the subsea tree <NUM> to a point of setting <NUM> at a position at or close to the electric downhole safety valve <NUM>. The point of setting <NUM> is shown as being the same position as the implement profile <NUM> for landing the insert hydraulic downhole safety valve <NUM>. The hydraulic fluid line <NUM> extends outside of the production tubing <NUM> but inside the well <NUM>. A hydraulic fluid source in the form of a subsea hydraulic power unit <NUM> and a control unit subsea <NUM> have been lowered subsea to a position at or close the electric subsea tree <NUM>. The subsea hydraulic power unit <NUM> is connected to the input port <NUM> and the hydraulic fluid line <NUM> is connected to the insert hydraulic downhole safety valve <NUM> at the point of setting <NUM>. As such, a hydraulic connection between the subsea hydraulic power unit <NUM> and the insert hydraulic downhole safety valve <NUM>, via the hydraulic fluid line <NUM>, has been established. In case hydraulic infrastructure is already in place in the field the subsea high-pressure unit may not be required.

A remotely operated vehicle <NUM> connected to a surface facility <NUM> via a connection line <NUM> may be used in assisting installation of subsea hydraulic power unit <NUM> and when connecting e.g. subsea hydraulic power unit <NUM> to input port <NUM>.

<FIG> shows an example of a tubing hanger to be used with the production system of <FIG>. The tubing hanger comprises a hydraulic connection <NUM> hydraulically connecting a first side of the tubing hanger <NUM> with an opposite second side of the tubing hanger, wherein the hydraulic connection forms part of the hydraulic fluid line. The tubing hanger <NUM> further comprises standard connections when used in a subsea production system <NUM>, including connections or ports to surface controlled subsea safety valve A (eSCSSV A) <NUM>' and surface controlled subsea safety valve B (eSCSSV B) <NUM>".

The invention has been explained with reference to non-limiting embodiments. For example, any subsea tree with an electric downhole safety valve can be used, including an electric subsea tree, an all-electric subsea tree and a hydraulic subsea tree. Furthermore, a skilled person will understand that there may be made alternations and modifications to the embodiment that are within the scope of the invention as defined in the attached claims.

Claim 1:
A method of operating a subsea production system (<NUM>), the system comprising an electric subsea tree (<NUM>) connected to a subsea well (<NUM>), a production tubing (<NUM>) in the well (<NUM>), and an electrically operable electric downhole safety valve (<NUM>), the electric subsea tree (<NUM>) comprises a through-going bore (<NUM>) forming part of a fluid line (<NUM>) in the subsea production system (<NUM>) down to a position at or close to the electric downhole safety valve (<NUM>), characterized in that the method comprises, in case of malfunction in operation of the electric downhole safety valve (<NUM>), the steps of:
- installing a hydraulically operable insert hydraulic downhole safety valve (<NUM>) into the well for positioning within the production tubing (<NUM>);
- connecting the insert hydraulic downhole safety valve (<NUM>) to the fluid line (<NUM>) at a point of setting (<NUM>) in the subsea well (<NUM>), for operation of the insert hydraulic downhole safety valve (<NUM>);
- operating the insert hydraulic downhole safety valve (<NUM>) from a position outside the subsea tree (<NUM>) by using the fluid line (<NUM>) which extends from an input port (<NUM>) at a position outside of the electric subsea tree (<NUM>) to the point of setting (<NUM>) in the subsea well via the through-going bore (<NUM>).