This invention concerns a method to prevent or reduce corrosion within the monopile- transition piece (MP-TP) connection of an offshore structure, such as a wind turbine foundation, for example through the application of a non-structural, gel-based material.

Figure 1 is a schematic of a MP-TP foundation structure. Monopile 1 is driven into the seabed 2 to provide the base of the foundation structure. Transition piece 3 is placed on the monopile 1 with a MP-TP connection 4. Water 5 is present and in contact with monopile 1 and transition piece 3. Grout 6 is typically deployed to prevent oxygenated water contacting the MP-TP connection 4. This is to prevent corrosion on the bolts connecting the monopilel and the transition piece 3. Any corrosion to these bolts could have a significant impact on the long term structural integrity of the wind turbine. Additionally, some form of lower backstop 7 may be present to assist in the grout 6 placement.

Conditions that offshore foundation structures may experience are harsh and dynamic. Temperatures can vary from -20 deg C to 40 deg C, dependent on geography, with challenges including strong waves, sea ice and corrosive (oxygenated and conductive) seawater making grouting operations very difficult. Often the weather conditions significantly limit the time of year grouting operations can be conducted due to the temperature required for grout to set. Additionally, grouting operations take a long time, with final strength often taking 28 or more days to achieve. In this time, the grout may shrink/expand at a different rate to the surrounding metal structure, creating voids between the grout 6 and monopile 1 and/or transition piece 2. This can be exacerbated by mechanical cracks appearing in the grout. This leaves the monopile/transition piece connection 4 vulnerable to corrosion from oxygenated seawater and may significantly reduce the lifetime of the foundation structure and, as such, the wind turbine. Additionally, the cost of repairing a poorly executed grout job is significant and often impracticable.

It is in this context that the present disclosure has been conceived.

In accordance with an aspect of the present disclosure there is provided a method of installing an offshore foundation structure in a body of water. The offshore foundation structure may be an offshore foundation structure for a wind turbine. The method comprises driving a monopile into a ground surface offshore. The monopile extends from the ground surface through the body of water towards an upper surface of the body of water. The method comprises securing a further member to the monopile via a connection assembly to form the offshore foundation structure. The method comprises providing a liquid into a seal region defined between the monopile and the further member. The liquid is in contact with the monopile and the further member to resist ingress of water from the body of water surrounding the offshore foundation structure to the connection assembly. The liquid is immiscible with water and is configured to remain flowable, at least intermittently, throughout operation of the offshore foundation structure.

Thus, the liquid in the seal region can substantially prevent or even completely prevent water from the body of water entering a passage defined between the monopile and the further member and reaching the connection assembly. In particular, where the connection assembly comprises corrodible elements, such as bolts, the operational life of the connection assembly can be extended by reducing or even completely preventing contact between the water and the connection assembly. Furthermore, where the water is oxygenated, the liquid can prevent or at least reduce the amount of oxygen released from the oxygenated water coming into contact with the connection assembly to cause corrosive oxidisation of one or more components of the connection assembly. Therefore, the lifetime of the offshore foundation structure can be increased without requiring frequent and/or complex maintenance.

In contrast, where grout is used to seal the seal region, the grout cures into a non-flowable solid after initial installation which can prevent a perfect seal being provided, meaning that water, and/or oxygen can penetrate through the seal region to reach the connection assembly, reducing the lifetime of the connection assembly of the offshore foundation structure. By ensuring that the liquid will remain flowable, or will return to a flowable state if the liquid becomes temporarily non-flowable due to environmental conditions, the efficacy of the seal in the seal region can be improved. Furthermore, by ensuring that the liquid is immiscible with water, mixing between the liquid and the water from the body of water can be prevented, increasing an effectiveness of the liquid as a seal between the water and the connection assembly.

It will be understood that an offshore foundation structure is substantially any foundation providing structural support for a structure to be located offshore.

A monopile will be understood to be a structural element to be driven into a ground surface subsea to support the load of an offshore structure, typically an above-surface offshore structure. In some examples, the monopile may be one of several separate piles all driven into the ground surface subsea to together support the load of an offshore structure.

The further member may be substantially any further component to transmit the load from the rest of the offshore structure to the monopile. In some examples, the further member may be the rest of the offshore structure itself. The method may further comprise topping-up the liquid during an operational life of the offshore foundation structure. Thus, where the liquid is consumed or leaks away over time, the protective effects can be maintained by providing further liquid into the seal region. In some examples, the method may comprise replacing the liquid during an operational life of the offshore foundation structure.

Viewed from another aspect, the present disclosure provides an offshore foundation structure to be installed in a body of water. The offshore foundation structure may be an offshore foundation structure for a wind turbine. The offshore foundation structure comprises: a monopile to be driven into a ground surface offshore and to extend from the ground surface through the body of water towards an upper surface of the body of water; a further member to be secured to the monopile via a connection assembly; and a seal region defined between the monopile and the further member and comprising a liquid in contact with the monopile and the further member. The seal region is arranged to resist ingress of water from the body of water surrounding the offshore foundation structure to the connection assembly. The liquid is immiscible with water and is configured to remain flowable, at least intermittently, throughout operation of the offshore foundation structure.

Thus, as described with reference to the method, the use of the liquid in the seal region can protect the connection assembly of the offshore foundation structure from corrosion by the water in the body of water.

Although it has been described that the liquid is configured to remain flowable, at least intermittently, throughout operation of the offshore foundation structure, it will be understood that in some examples this could be expressed as the liquid being formulated to remain in the liquid phase. Alternatively, this could be expressed as the liquid being formulated not to chemically react with the water to form a solid.

It will be understood that the features described hereinafter can be combined with either or both of the offshore foundation structure or the method of installing the offshore foundation structure described hereinbefore.

The liquid may be to substantially prevent ingress of water from the body of water surrounding the offshore foundation structure to the connection assembly. The liquid may be to completely prevent ingress of water from the body of water surrounding the offshore foundation structure to the connection assembly.

The offshore foundation structure may further comprise a source of the liquid separate from the seal region. The source of the liquid may be configured to be in fluid communication with the seal region. Thus, where the liquid is consumed or leaks away over time, the protective effects can be maintained by providing further liquid from the source of the liquid into the seal region.

The source may be provided above the seal region. The source may be provided at the further member. The source may be a container storing further liquid. In some examples, the source of further liquid may be provided from a ship, arranged to transfer liquid to the seal region of the offshore foundation structure intermittently.

The offshore foundation structure may comprise a flow control member to control flow of the liquid between the source of the liquid and the seal region. The flow control member may control flow of the liquid from the source to the seal region. The flow control member may comprise a controllable valve. The flow control member may comprise a pump.

The liquid may be a flowable liquid. The liquid may be a gel. It will be understood that the term gel is taken to cover substantially any liquid which is not flowable in the absence of external forces. Significantly, the liquid may deform to substantially prevent cracks or other passageways appearing to allow fluid communication of liquids or gases from the body of water through the seal region to the connection assembly. In other examples, the liquid may be a non-gelled liquid.

The liquid may have a viscosity greater than that of water at any given operating temperature of the offshore foundation structure.

The liquid may be oil-based. Thus, the liquid is typically immiscible with water.

The liquid may be formulated to remain in the liquid phase for at least one month in the seal region. The liquid may be formulated to remain in the liquid phase for at least one year in the seal region. The liquid may be formulated to remain in the liquid phase for at least ten years in the seal region. The liquid may be formulated to remain in the liquid phase indefinitely in the seal region during operation of the offshore foundation structure. The liquid may be formulated to not become a solid during operation of the offshore foundation structure. As used herein, the term “solid” will be understood to mean any state of matter in which the matter substantially maintains its shape, even when subject to external forces.

The liquid may not become a solid for at least one month after application of the liquid to the seal region. The liquid may not become a solid for at least one year after application of the liquid to the seal region.

The further member may comprise a shroud portion arranged, when the further member is secured to the monopile, to extend over an upper portion of the monopile. The seal region may be defined at least partially between the shroud portion of the further member and the upper portion of the monopile. Thus, the upper portion of the monopile is arranged to extend within the further member.

A sealed void may be defined by an internal surface of the further member above the shroud portion, and by an upper surface of the liquid in the seal region. Thus, the connection assembly may only be in fluid communication with atmosphere and/or the body of water via the seal region, and fluid communication between the connection assembly and atmosphere and/or the body of water may be prevented by provision of the liquid in the seal region.

The connection assembly may be in the sealed void.

The connection assembly may comprise one or more threaded fasteners to secure the further member to the monopile. The one or more threaded fasteners may be one or more bolt fasteners. The one or more threaded fasteners may be formed from a material susceptible to corrosion when exposed to sea water. The one or more threaded fasteners may be formed from a material susceptible to corrosion when exposed to oxygen.

The offshore foundation structure may further comprise one or more seal members arranged to prevent escape of the liquid in the seal region towards the body of water. Alternatively or additionally, the one or more seal members can ensure that mixing between the liquid in the seal region and the body of water is prevented. In the absence of one or more seal members, it is possible that liquid in the seal region could be lost from the offshore foundation structure were the water level of the body of water to drop below a lowest level of the shroud of the further member. It will be understood that sufficient drops in water level can occur temporarily, for example during extreme weather, resulting in particularly large waves.

The liquid may comprise gas-filled microspheres. Thus, an overall density of the liquid may be reduced. Furthermore, the voids created in the liquid by the gas-filled microspheres cause the transmission of sound waves through the liquid to be reduced. In this way, the transmission of sounds from the structure, such as the wind turbine, mounted on the offshore foundation structure to the monopile, the body of water and/or the ground surface of the body of water may be reduced. Therefore, acoustic sensor techniques can be used on the monopile to detect accurate placement and/or positioning of the liquid in the seal region. The microspheres may be formed from glass.

The microspheres typically have a true density between 0.1 and 0.9 g/cm ³ , more preferably from 0.14 to 0.5 g/cm ³ , most preferably between 0.14 and 0.45 g/cm ³ . The glass microspheres are typically formed from a chemically stable soda-lime borosilicate. The glass microspheres typically have a crush strength of more than 1300 kilopascals. The crush strength may be no more than 210 megapascals.

The liquid may be non-aqueous. The liquid may comprise a viscosified oil. The liquid may comprise at least one of a hydrocarbon oil (synthetic or refined), linear alkanes, branched alkanes, vegetable oil, vegetable oil esters, fatty acid esters, di-acid esters (such as adipic, glutaric and succinic acid esters), fish oil, lanolin or silicone oil.

The liquid may be from a recycled source. Alternatively, the liquid may be previously unused.

The liquid may comprise a viscosifying agent to increase a viscosity of the oil. A more viscous liquid is beneficial to reduce turbulence of the liquid in the presence of waves and reduce ability of dynamic conditions to displace the liquid in the seal region.

The viscosifying agent may comprise at least one of hydrophobic silica, a block copolymer (such as Kraton G1702, Kraton A1535 or Kraton A1536 block copolymer), and a metal- phosphate ester complex. The viscosifying agent may impart shear thinning properties and may also provide increased strength as the liquid is left static. The viscosifying agent may be mixed with an oil of the liquid to create the liquid on land prior to shipment to offshore or may be added in-situ and in stages to the oil of the liquid to create the liquid offshore. Dependent on the source of oil and logistics, both pre-made liquid and in-situ manufactured liquid may have advantages. Storage of viscosifying agents (sometimes referred to as gelling agents) on the offshore foundation structure may allow for regular replacement of the liquid without storing vast quantities of material offshore. A suitable example of hydrophobic silica is Reolosil. A suitable example of metal-phosphate ester complex is iron(iii) and an octyl decyl phosphate ester.

The liquid may be substantially non-toxic. Thus, any leakage of the liquid to the environment, such as to the body of water, will not have significant environmental effects. The liquid may comprise vegetable oil.

The liquid may comprise an oxygen scavenger. Thus, any oxygen can be absorbed by the liquid, improving the protection of the connection assembly from corrosion by oxygen. The liquid may comprise, as an oxygen scavenger, at least one of a sulphite, a bisulphite, sulphur dioxide, a reductive metal, a sacrificial metal, an electron-rich organic molecule, a neutral organic electron donor and an anionic electron donor.

The liquid may comprise a biocide. Thus, degradation of the liquid can be substantially prevented. Where the liquid comprises an oil, the biocide may be at least one of an isothiazolone, an aldehyde such as glutaraldehyde, a quaternary ammonium salt such as DDAC, a carbamate such as IPBC, an oxazolidine, bronopol, and acetamide organic alcohols and organic acids. Although also possible, it may be less preferable to use a quick kill biocide such as DBNPA.

The liquid may comprise antioxidants to prevent degradation of the oil. The liquid may comprise a primary antioxidant. The primary antioxidants may be a synthetic free radical scavenger. The primary antioxidant may comprise at least one of butylated hydroxytoluene, butylated hydroxyanisole, propyl gallate and t-butylhydroquinone. The liquid may comprise a secondary antioxidant. The secondary antioxidant may be a less strong free radical scavengers than the primary antioxidant. The secondary antioxidant may comprise at least one of ascorbic acid, ascorbyl palmitate, carotenoids, and citric acid and redox active and/or chelating organic molecules.

The insulator gel may comprise a surface active agents. The surface active agent may comprise at least one of a non-ionic surfactant, an alcohol alkoxylate, a fatty acid ester, imidazoline, a cationic surfactant, an anionic surfactant and a polymer such as an EO-PO block copolymer.

A density of the liquid may be less than 1000kg/m ³ . Thus, the liquid is less dense than the water in the body of water, and so will naturally float on the surface of the water, ensuring that the liquid is always between the body of water and the connection assembly in the seal region.

The offshore foundation structure may be for a wind turbine. The body of water may be the sea.

The liquid may be an electrical insulator. Thus, the body of water can be insulated from any electrical currents generated in the further member as a result of operations of the offshore structure supported on the offshore foundation structure. For example, where there is a fault in the offshore structure causing electrical current to be conducted to the further member, the electrical current will not be passed to the body of water via the liquid in the seal region.

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a schematic of an example connection to a monopile for an offshore structure according to the prior art;

Figure 2 shows a schematic of an example connection to a monopile for an offshore structure in accordance with an embodiment of the present disclosure; and Figure 3 shows a flowchart illustrating a method of installing an offshore foundation structure as disclosed herein.

Figure 2 shows a schematic of an example connection to a monopile for an offshore structure in accordance with an embodiment of the present disclosure. The offshore foundation structure comprises, similar to that shown in Figure 1 , a monopile 17, a further member 12 in the form of a transition piece 12 and a connection assembly 14 in the form of a MP-TP connection 14. The monopile 17 is to be driven into a ground surface below a body of water offshore and extends from the ground surface, through the body of water towards an upper surface 16 of the body of water. The further member 12 is secured to the monopile 17 via the connection assembly 14 to form the offshore foundation structure. In this example, the connection assembly 14 comprises one or more threaded fasteners in the form of bolts (not shown) to secure the further member 12 to the monopile 17. In addition to the example shown in Figure 1 , the offshore foundation structure shown in Figure 2 comprises a container 8 containing a liquid 9, typically in the form of insulator gel

9, to provide a source of the liquid. The container 8 is connected to a flow control device

10, The container 8 and the flow control device 10 are each positioned outside of the further member 12, on top of the further member 12 or on a level 11 within the further member 12. In this example, the container 8 and the flow control device 10 are positioned spaced above the connection assembly 14, within the further member 12, at a level 11.

The flow control device 10 is connected to a conduit 13 in the form of a hose 13 which runs down to the level of or below the connection assembly 14. The liquid 9, for example insulator gel 9, can be poured, pumped or placed into a seal region defined between the monopile 17 and the further member 12 to a chosen level which may be dictated by a series of seals or backstops 15. The liquid 9 is lighter than water and does not chemically react to form a solid; this provides a barrier to oxygenated water getting between the monopile 17 and the further member 12 and causing corrosion to the connection assembly 14.

The insulator gel has a density less than seawater; the gel has a density less than 1 .02 g/cm ³ at 0 °C. The gel has a density greater than 0.4 g/cm ³ at 0 °C.

The insulator gel is non-aqueous and may consist of a non-aqueous fluids such as a viscosified oil, preferably a hydrocarbon oil (synthetic or refined), linear alkanes, branched alkanes, vegetable oil, vegetable oil esters, fatty acid esters, di-acid esters (such as adipic, glutaric and succinic acid esters), fish oil, lanolin or silicone oil. The non-aqueous fluid may be from a recycled source or may be previously unused. To increase viscosity of the oil, reduce turbulence of the oil in the presence of waves and reduce ability of dynamic conditions to displace the insulator gel, a viscosifying agent is added to the oil. g

The viscosifying agent may consist of hydrophobic silica, a block copolymer (such as Kraton G1702, Kraton A1535 or Kraton A1536 block copolymer, each available from Kraton Corporation of Houston, Texas, USA), or a metal-phosphate ester complex. The viscosifying agent may impart shear thinning properties and may also provide increased gel strength as the insulator gel is left static. The viscosifying agent may be mixed with the oil of the insulator gel to create an insulator gel on land prior to shipment to offshore or may be added in situ and in stages to the oil of the insulator gel to create the insulator gel offshore. Dependent on the source of oil and logistics, both pre-made insulator gel and in situ manufactured insulator gel may have advantages. Storage of gelling agents on the transition piece 12 may allow for regular replacement of insulator gel without storing vast quantities of material offshore. An example of hydrophobic silica is Reolosil. An example of metal-phosphate ester complex is consists of iron(iii) and an octyl decyl phosphate ester.

The insulator gel may also consist of an oxygen scavenger, such as a sulfite, a bisulfite, sulfur dioxide, a reductive metal, a sacrificial metal, an electron-rich organic molecule, a neutral organic electron donor or an anionic electron donor.

Additionally, the insulator gel may be treated with a biocide to prevent degradation of the oil, such as an isothiazolone, an aldehyde such as glutaraldehyde, a quaternary ammonium salt such as DDAC, a carbamate such as IPBC, an oxazolidine, bronopol, and acetamide organic alcohols and organic acids. It is less preferable to use a quick kill biocide such as DBNPA.

The insulator gel may also contain primary and secondary antioxidants to prevent degradation of the oil, most usually when the oil is vegetable oil based. Primary antioxidants may come from synthetic free radical scavengers, such as butylated hydroxytoluene, butylated hydroxyanisole, propyl gallate and f-butylhydroquinone. Secondary antioxidants may be less strong free radical scavengers than primary antioxidants, including ascorbic acid, ascorbyl palmitate, carotenoids, and citric acid and redox active and/or chelating organic molecules.

The insulator gel may also contain glass microspheres. The glass microspheres typically have a true density between 0.1 and 0.9 g/cm ³ , more preferably from 0.14 to 0.5 g/cm ³ , most preferably between 0.14 and 0.45 g/cm ³ . The glass microspheres typically consist of a chemically stable soda-lime borosilicate. The glass microspheres typically have a crush strength of more than 1300 kilopascals, but no more than 210 megapascals. The glass microspheres, contain a gas. The voids created in the insulator gel utilising glass microspheres may also reduce ability for the transmission of sound waves through the insulator gel. These voids may reduce the sound propagated from the turbine to the monopile, seawater and/or seabed. The lack of sound propagation through the gel may also be used to provide an interference to detect placement and/or positioning of the insulator gel. An example of glass microsphere is K20 glass microsphere from 3M.

The insulator gel may consist of surface active agents; the surface active agents may include non-ionic surfactants, alcohol alkoxylates, fatty acid esters, imidazolines, cationic surfactants, anionic surfactants and polymers such as EO-PO block copolymers.

A flowchart illustrating a method of installing an offshore foundation structure in a body of water is shown in Figure 3. The method 100 comprises providing liquid in contact with a monopile and a further member to substantially prevent ingress of water to a connection assembly connecting the monopile to the further member. Specifically, the method 100 comprises a first step 110 of driving a monopile into a ground surface offshore. The monopile, when driven into the ground surface is arranged to extend from the ground surface, through the body of water, towards an upper surface of the body of water. The method 100 further comprises a second step 120 of securing a further member to the monopile via a connection assembly. When the further member is secured to the monopile via the connection assembly, the offshore foundation structure is formed. The method 100 further comprises a third step 130 of providing a liquid in contact with the monopile and the further member. The liquid is provided into a seal region defined between the monopile and the further member. The third step 130 ensures that the ingress of water to the connection assembly from the body of water surrounding the offshore foundation structure is substantially prevented. In this example, the method 100 further comprises a further step 140 of topping-up the liquid. The liquid can be topped-up during an operational life of the offshore foundation structure, for example if the liquid in the seal region leaks out to the environment, or becomes less effective. In some examples, the liquid can be replaced instead of or in addition to being topped-up.

The following describes a variety of embodiments by which such a material can be created. One approach is based on vegetable oil.

A vegetable oil, with Newtonian viscosity and with a low melting point, below 0 °C and above -30 °C such as soyabean (soybean) oil is mixed with one to fifteen percent by weight hydrophobic fumed silica, an example of fumed silica being Reolosil. The oil and fumed silica is mixed with sufficient time and shear to produce a gel, typically no more than 4 hours. The resultant gel is non-Newtonian and shear thinning. The gel is non-aqueous and as such non- or low-conducting to electricity. The insulator gel may develop additional gel strength when left static without shear. The insulator gel decreases in viscosity with an increase in temperature. The gel increases in viscosity with an decrease in temperature. The gel does not cure to form a grout or solid. Below the melting point of the insulator gel, a solid product may form. Above the melting point of the insulator gel and below 0 °C, the insulator gel may cloud and form a paste-like gel, rather than a smooth, free-flowing gel. The typical viscosity of the gel is represented in Table 1 , which was recorded using a Chandler 3500 viscometer, with rotor 1, bob 2, spring 1 configuration.

Table 1 Viscosity profile of Soyabean oil-based insulator gel

By changing the type of oil, a product with different density and melting point can be created. This may be used to control the depth at which the insulator gel sits in the water column. In another embodiment, a lightweight insulator gel was prepared using a linear alkane. A linear alkane such as SIPDRILL 2/0 from SIP Ltd may be used. The oil may be heated, typically to 70 °C, with stirring and to this oil a block copolymer may be added.

The block copolymer may be based on a styrene monomer and one or two other monomers from ethylene, propylene or butadiene. The copolymer may be a Kraton block copolymer. The block copolymer may be added at 1 to 5% by weight of oil. The block copolymer may yield in the oil at elevated temperatures to form a clear solution which upon cooling forms a shear thinning base gel. Then density of such a base gel is generally less than 1.0 g/cm ³ and greater than 0.7 g/cm ³ . To the gel may be added surface active products to assist the suspension of solids. The surface active products may be non-ionic. The non-ionic products may be polyethylene-glycol diesters. The polyethylene-glycol diester may be PEG 400 dioleate and may be added at between 0.1 and 0.5 percent by weight of the oil. The surface active products may be cationic. The cationic products may be imidazolines. The imidazolines may be a TOFA-DETA imidazoline. Two surface active agents may be used at the same time; one surface active agent may be non-ionic and one may be cationic; the combination surfactants may be PEG 400 dioleate and TOFA-DETA imidazoline; the combined surface active agents may be used together at between 0.1 and 0.5 percent. To the base gel may be added glass microspheres with a true density between 0.1 and 0.9 g/cm ³ . Typically, the glass microspheres will have a density of 0.1 to 0.45 g/cm ³ . The glass spheres may be XLD, S or K grade glass microspheres by 3M. The glass microspheres are typically mixed with a folding mechanical action and may also be mixed using baffles to create eddies within the gel. The resulting insulator gel will have a density less than 0.7 g/cm ³ and greater than 0.4 g/cm ³ . Table 2 shows several formulations of lightweight insulator gel that may be prepared, utilising linear alkane and vegetable oil. Table 2 Low density insulator gel examples

In terms of insulating properties, Table 3 demonstrates the insulation properties of oil- based formulations vs seawater, measured on a HI 2550 with HI-76310 conductivity probe, calibrated to 0.01 mS/cm resolution. This demonstrates the electrical insulation provided in a marine environment with this disclosure, without the need to introducing a solid- forming product. These oil-based gels remain as fluids, are compliant to structural changes in operational temperatures and do not form brittle solids which may shrink or expand at a different rate the steel structures. If the fluid expands/shrinks due to temperature changes, it is still a non-brittle fluid which fills the annular diameter around the MP-TP connection, removing the possibility of seawater induced corrosion. Table 3 Fluid conductivity examples at 20 degrees Celsius

In summary, there is provided a an offshore foundation structure in a body of water. The method (100) comprises driving (110) a monopile (17) into a ground surface offshore. The monopile (17) extends from the ground surface through the body of water towards an upper surface (16) of the body of water. The method (100) further comprises securing (120) a further member (12) to the monopile (17) via a connection assembly (14) to form the offshore foundation structure. The method (100) further comprises providing (130) a liquid (9) into a seal region defined between the monopile (17) and the further member (12). The liquid (9) is in contact with the monopile (17) and the further member (12) to substantially prevent ingress of water from the body of water surrounding the offshore foundation structure to the connection assembly (14). The liquid (9) is substantially immiscible with water. The liquid (9) is configured to remain flowable, at least intermittently, throughout operation of the offshore foundation structure. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the disclosure are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The disclosure is not restricted to the details of any foregoing embodiments. The disclosure extends to any novel one, or any novel combination, of the features disclosed in this specification

(including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.