An apparatus for indicating a characteristic of a subsea environment

Abstract

An apparatus 400 for indicating a characteristic of a subsea environment, comprising a detection component 202 that undergoes a visual change in response to detection of a characteristic, and a mounting unit 204 to hold the detection component, and a viewing port (208, fig.3a) enabling visual inspection of the visual change. The change may relate to colour, opacity or light. The detection component may comprise a dissolvable component. The characteristic may be temperature, pH or a chemical present. The apparatus may monitor subsea well integrity and comprise a handle 302 compatible with an autonomous underwater vehicle.

Description

The present disclosure relates to an apparatus for indicating a characteristic of a subsea environment. In particular, the present disclosure relates to an apparatus for indicating a characteristic of a subsea environment comprising a detection component and a mounting unit. BACKGROUND It can be useful to detect characteristics of a subsea environment. For example, for environmental purposes or for the monitoring of undersea equipment such as subsea wells. Useful characteristics to detect include, but are not limited to, the presence of a specific chemical or chemicals, pH, and temperature. Figure 1(a) is a schematic of a subsea hydrocarbon well apparatus 5 as is known in the prior art (WO 2019 / 215438). The apparatus 5, e.g. a drilling system or a production system, facilitates access to or extraction of a resource, such as oil or natural gas, from a sub-surface reservoir 35 through a well 40. The apparatus 5 is generally depicted as an offshore drilling apparatus 5 including a drilling rig 10 on the sea surface 6, coupled with a riser 15 to a blowout preventer (BOP) 20 and a wellhead assembly 25 installed at the well 40. The wellhead assembly is located on the seabed 30 and is connected to a sub-surface 35 casing scheme 45 previously installed for the purpose of producing hydrocarbons. At the end of the productive life of a subsea oil or gas well, there is typically a requirement to make the well safe and to remove production-related infrastructure from the seabed. Several techniques exist and are under development for the sequence of activities generally referred to as decommissioning a well, including Plugging and Abandonment (P&A). These activities might include creating multiple barriers between the sub-surface reservoir (which might be a considerable distance below the seabed) and the wellhead location on the seabed through which previous drilling and production activities have been performed. Figure 1(b) is a schematic of a decommissioned well 101 as is known in the prior art (WO 2019 / 215438). In the schematic there is shown a mechanical bridge plug 80, a cement plug 85, a volume of kill fluid 90, a mechanical bridge plug 95, a cement plug 100, a volume of kill fluid 105, a mechanical bridge plug 110, and a cement plug 115. Although multiple barriers are created during decommissioning between a reservoir and the external environment, there are multiple potential leak paths that can result from processes including corrosion of the metalwork such as the casing and / or deformation caused by geological movement. Examples of potential leak paths include mico-annuli at the interface between casing and cement caused by channels and the presence of materials such as wax, scale, oil and dirt; connected pores, cracks and channels caused by permeability in cement; and through perforations of casing caused by corrosion and mechanical deformation. Such leak paths may occur at any depth within the well arrangement and give rise to the propagation or migration of hydrocarbons 130 through the sub-surface geology 35. The sub-surface post-decommissioning leak path example 120 shown in Figure 1(b) may give rise to leaked material 135 emerging from the seabed 30 into the subsea environment. Whereas leaks may occur along the axis of the predecommissioned well bore 125, they may also remain close to the casing scheme or take any other path of least resistance to the seabed 30 such as paths 130. Upon completion of well decommissioning activities, it may therefore be desirable to monitor the environment around a well site for an extended period to provide reassurance that a well’s integrity is secure and that hydrocarbons from the reservoir are not leaking into the subsea environment. Several conventional systems are currently available to address this requirement, using approaches including active acoustics, bio sensors, capacitance, fibre optics, fluorescence, optical sniffers, optical cameras and passive acoustics. An example of a leak from a reservoir is shown in Figure 1(b) where leak paths 130 are related to breaches of well barriers, but path 131 is not, as it occurs below the first barrier 80 and thus originates within the reservoir (being the material previously installed by the bull heading procedure). WO 2019 / 215438 describes a passive detection system for use in monitoring the integrity of abandoned, suspended and / or decommissioned subsea wells or carbon dioxide sequestration reservoirs. Such a system can achieve differentiation of the source of a leak thus minimising the probability of false alarms. This is achieved by using a tracer fluid 145 that is mixed with well kill fluid 90,105 so that the presence and detection of said tracer fluid 145 in the external environment means it can only have come from within a well which has suffered a loss of integrity. An example of this tracer fluid 145 is referred to as Sentinel Well Integrity Fluid Tracer (SWIFT) 145, available from Sentinel Subsea Limited of Aberdeen, UK. This fluid 145 may be supplied in concentrated or diluted form, pre-mixed with well kill fluid 90,105 or added to kill fluid 90,105 as the fluid 90,105,145 is pumped into a well during decommissioning activity. It is desirable that SWIFT 145 has the following properties: it is not a naturally occurring material, so that it cannot be mistaken for any other substance, compound, fluid or particle that would be found in the subsea environment; it is inert with any material that might be in the well, e.g. cement, steel, alloys and casing; it is environmentally benign and does not pose a risk to human handlers. There are multiple mechanisms by which SWIFT 145 may migrate from a kill fluid 90,105 zone into a subsea environment. For example, rising naturally through any available leak path 130 in the same way as reservoir hydrocarbons; driven by reservoir pressure, i.e. by the force of the hydrocarbons leaking from the reservoir past the installed barriers; or chemically or mechanically liberated from the kill fluid 90, 105 as it comes into contact with leaking hydrocarbons, at which point SWIFT 145 is optionally bound chemically or mechanically to the hydrocarbons leaking from the reservoir past the barriers and carried to the subsea environment in combination with the hydrocarbons. Preferably SWIFT 145, or the material of interest that is being monitored, is less dense than water / sea water (or less dense than the sea water in the vicinity of the seabed where the monitoring apparatus is positioned), and therefore has a natural tendency to rise under its own inherent buoyancy. The system disclosed in WO 2019 / 215438 provides passive monitoring of SWIFT 145 (or other predetermined chemicals that will provide the required properties to alert an operator to a loss of well integrity in the subsea environment). Whereas active monitoring systems are available to detect the presence of hydrocarbons or tracer fluids using a myriad of techniques, these generally require the use of active systems (therefore electrical power), sensors, processors and communication channels. The passive detection of SWIFT 145 (or other appropriate predetermined chemical) is achieved by the use of one or more materials that react to the presence of SWIFT 145 (or other predetermined material) and thus provide a detection mechanism. The passive detection of SWIFT 145 is achieved by the use of one or more materials that react to the presence of SWIFT 145. Several example embodiments are presented in WO 2019 / 215438. Figure 1(c) is a schematic of a beacon release mechanism 200 that is triggered upon interaction with SWIFT 145 (or other pre-determined chemical) thereby providing a mechanism for alerting an operator to a leak from a decommissioned well, such as the well 101 shown in Figure 1(b) (WO 2019 / 215438). In this example, the beacon release mechanism 200 attachment bracket is a simple ring 280 and the assembly is prevented from moving under buoyancy force 275 by trigger rod 285. In this embodiment, the trigger rod 285 directly restrains the beacon assembly 265 and the failure of the trigger rod 285, upon completion of a reaction and degradation process when the trigger rod 285 is in contact with SWIFT 145 (or another predetermined chemical), allows the beacon assembly 265 to ascend. When the beacon release mechanism 265 reaches the sea surface it may then notify an operator that there is a leak from the well 101. In summary, the systems presented in WO 2019 / 215438 and illustrated in Figures 1(b) and 1(c) operate by gathering fluids of interest (liquid or gas) and directing these fluids to a chamber where they interact with and degrade trigger materials that restrain a buoyant beacon. Although the above relates to decommissioned wells, it is also useful to monitor suspected leaks from wells during their active lifecycle. Production wells may temporarily halt operation due to the presence or suspected presence of a leak. These leaks may be of non-hydrocarbon fluids such as control fluids or flow assurance chemicals but nonetheless are of sufficient concern that the operator is obliged to investigate. Shutdown of a well for multiple days can lead to a loss of significant amounts of money. Such a leak may be observed by a submersible vehicle such as a remotely operated underwater vehicle (ROV) and may appear as a “haze” on the screen of an ROV. The inability to characterise the nature of the leak from a visual inspection of the haze can mean that multiple investigations are required to properly assess the composition of the haze. These investigations would typically be carried out using crude apparatuses, leading to unsatisfactory results. There is also a safety concern in relation to these investigations. If a gas leak is observed, with samples of the gas being captured by a traditional ROV-held funnel-into-bottle method, then the bottle is typically returned to surface. The bottle thereafter poses a hazard since that vessel then contains pressure. It is generally preferred by operators to avoid putting pressurised vessels onto helicopters for transfer to land but sometimes this is necessary to enable a chemical analysis to be performed. For example, the vessel may then be transferred to a laboratory for isotope analysis, e.g. to confirm the presence of thermogenic gas. This process represents a delay in characterising the gas, it introduces a risk to personnel and equipment, and it can be costly. It will be appreciated that the above examples primarily relate to the detection of chemicals from subsea wells. However, as discussed previously chemical detection may also be desirable for other applications. Similarly, it may be desirable to identify other characteristics of a subsea environment such as pH and temperature. SUMMARY It is desirable to provide an improved system for detecting one or more characteristics of a subsea environment. According to a first aspect of the disclosure there is provided an apparatus for indicating a characteristic of a subsea environment a first detection component configured to detect a first characteristic of the subsea environment, and undergo a visual change in response to detection of the first characteristic, and a mounting unit comprising a first mounting component configured to hold the first detection component, and a first viewing port configured to permit visual inspection of the visual change of the first detection component, thereby indicating the detection of the first characteristic within the subsea environment. Optionally, the visual change of the first detection component is a colour change, or an increase in opacity, or a decrease in opacity, or emission of light. Optionally, the first detection component comprises a first inner material, and a first outer material, the first outer material at least partially encasing the first inner material, wherein the first outer material is configured to at least partially dissolve as a result of the first characteristic, thereby exposing the first inner material. Optionally, the visual change of the first detection component is a colour change, or an increase in opacity, or a decrease in opacity, or emission of light, and a visual change is exhibited by the first inner material after its exposure to sea water, thereby providing the visual change of the first detection component. Optionally, the first characteristic relates to a temperature of the subsea environment. Optionally, the first characteristic is the temperature of the subsea environment being greater than a first threshold temperature value, less than the first threshold temperature value, or approximately equal to the first threshold temperature value. Optionally, the first characteristic relates to a pH value of the subsea environment. Optionally, the first characteristic is the pH value of the subsea environment being greater than a first threshold pH value, less that the first threshold pH value, or approximately equal to the first threshold pH value. Optionally, the first characteristic is the presence of a first pre-determined chemical. Optionally, the first pre-determined chemical comprises a tracer fluid, and / or a thermogenic gas, and / or a biogenic gas, and / or methane, and / or a hydrocarbon, and / or methanol, and / or monoethylene glycol, and / or a control fluid, and / or carbon dioxide. Optionally, the tracer fluid is Sentinel Well Integrity Fluid Tracer (SWIFT). Optionally, the hydrocarbon is a liquid hydrocarbon. Optionally, the apparatus is configured to monitor the integrity of a subsea well or a fluid sequestration site by indicating that the first pre-determined chemical has been detected. Optionally, the first detection component is configured to undergo a chemical reaction that results in the visual change in response to detection of the first characteristic. Optionally, the mounting unit comprises a handle configured to permit holding by a submersible craft. Optionally, the submersible craft is a remotely operated underwater vehicle (ROV) or an autonomous underwater vehicle (AUV). Optionally, the mounting unit comprises an enclosure that comprises the first viewing port, and the first mounting component is configured to hold the first detection component within the enclosure. Optionally, the enclosure comprises a first aperture for receiving a volume of fluid. Optionally, the enclosure comprises a second aperture for permitting flow of the volume of fluid into the enclosure via the first aperture and out of the enclosure via the second aperture. Optionally, the mounting unit comprises a collection component comprising an input portion comprising an input aperture arranged to capture a volume of fluid, and an output portion arranged to provide the volume of fluid to the first detection component via the first aperture of the enclosure. Optionally, the input aperture of the collection component is larger than the first aperture of the enclosure. Optionally, the mounting unit comprises a first window coupled to the first viewing port. Optionally, the first window is substantially optically transparent. Optionally, the first window comprises hardened glass. Optionally, the first mounting component comprises the first window, the first detection component being held by the first window. Optionally, the mounting unit comprises a first additional viewing port configured to permit visual inspection of the visual change of the first detection component. Optionally, the mounting unit comprises a first additional window coupled to the first additional viewing port. Optionally, the first additional window is substantially optically transparent. Optionally, the first additional window comprises hardened glass. Optionally, the mounting unit is configured to hold the first detection component between the first window and the first additional window. Optionally, the mounting unit comprises an attachment portion for attaching the apparatus to a subsea tree. Optionally, the mounting unit comprises a stand for standing the apparatus on the sea floor. Optionally, the stand is in a tripod configuration. Optionally, the apparatus comprises a second detection component configured to detect a second characteristic of the subsea environment, and undergo a visual change in response to detection of the second characteristic, Optionally, the first mounting component is configured to hold the second detection component, and the first viewing port is configured to permit visual inspection of the visual change of the second detection component, thereby indicating the detection of the second characteristics within the subsea environment. Optionally, the mounting unit comprises a second mounting component configured to hold the second detection component, and a second viewing port configured to permit visual inspection of the visual change of the second detection component, thereby indicating the detection of the second characteristic within the subsea environment. Optionally, the visual change of the second detection component is a colour change, or an increase in opacity, or a decrease in opacity, or emission of light. Optionally, the second detection component comprises a second inner material, and a second outer material, the second outer material at least partially encasing the second inner material, wherein the second outer material is configured to at least partially dissolve as a result of the second characteristic, thereby exposing the second inner material. Optionally, the visual change of the second detection component is a colour change, or an increase in opacity, or a decrease in opacity, or emission of light, and a visual change is exhibited by the second inner material after its exposure to sea water, thereby providing the visual change of the second detection component. Optionally, the first characteristic and / or the second characteristic relates to a temperature of the subsea environment. Optionally, the first characteristic is the temperature of the subsea environment being greater than a first threshold temperature value, less than the first threshold temperature value, or approximately equal to the first threshold temperature value, and / or the second characteristic is the temperature of the subsea environment being greater than a second threshold temperature value, less than the second threshold temperature value, or approximately equal to the second threshold temperature value. Optionally, the first characteristic and / or the second characteristic relates to a pH value of the subsea environment. Optionally, the first characteristic is the pH value of the subsea environment being greater than a first threshold pH value, less than the first threshold pH value, or approximately equal to the first threshold pH value, and / or the second characteristic is the pH value of the subsea environment being greater than a second threshold pH value, less that the second threshold pH value, or approximately equal to the second threshold pH value. Optionally, the first characteristic is the presence of a first pre-determined chemical and / or the second characteristic is the presence of a second pre-determined chemical. Optionally, the first pre-determined chemical comprises a tracer fluid, and / or a thermogenic gas, and / or a biogenic gas, and / or methane and / or a hydrocarbon, and / or methanol, and / or monoethylene glycol, and / or a control fluid, and / or carbon dioxide, and / or the second pre-determined chemical comprises the tracer fluid, and / or the thermogenic gas, and / or the biogenic gas, and / or methane, and / or the hydrocarbon, and / or methanol, and / or monoethylene glycol, and / or the control fluid, and / or carbon dioxide. Optionally, the tracer fluid is Sentinel Well Integrity Fluid Tracer (SWIFT) Optionally, the hydrocarbon is a liquid hydrocarbon. Optionally, the apparatus is configured to monitor the integrity of a subsea well or a fluid sequestration site by indicating that the first pre-determined chemical and / or the second pre-determined chemical have been detected. Optionally, the first detection component is configured to undergo a chemical reaction that results in the visual change in response to detection of the first characteristic and / or the second detection component is configured to undergo a chemical reaction that results in the visual change in response to detection of the second characteristic. Optionally, the mounting unit comprises an enclosure that comprises the first viewing port and the second viewing port, the first mounting component is configured to hold the first detection component within the enclosure, and the second mounting component is configured to hold the second detection component within the enclosure. Optionally, the mounting unit comprises a first window coupled to the viewing port and a second window coupled to the viewing port. Optionally, the first and second windows are substantially optically transparent. Optionally, the first mounting component comprises the first window, the first detection component being held by the first window, and the second mounting component comprises the second window, the second detection component being held by the second window. According to a second aspect of the disclosure there is provided a method of indicating a characteristic of a subsea environment, using the apparatus of the first aspect. It will be appreciated that the method of the second aspect may include features set out in the first aspect and can incorporate other features as described herein. BRIEF DESCRIPTION OF THE DRAWINGS The disclosure is described in further detail below by way of example and with reference to the accompanying drawings in which: Figure 1(a) is a schematic of a subsea hydrocarbon well apparatus as is known in the prior art, Figure 1(b) is a schematic of a decommissioned well as is known in the prior art, Figure 1(c) is a schematic of a beacon release mechanism; Figure 2(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment, in accordance with a first embodiment of the present disclosure, Figure 2(b) is a schematic of the apparatus after detection of the predetermined characteristic, Figure 2(c) is a schematic cross section of a specific embodiment of the detection component, Figure 2(d) is a schematic cross section of the detection component after the outer material has dissolved, Figure 2(e) is a photograph of an apparatus in accordance with a specific embodiment of the present disclosure; Figure 3(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment, in accordance with a second embodiment of the present disclosure, Figure 3(b) is a schematic of the apparatus having the detection component and some parts of the mounting unit removed; Figure 4(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment, in accordance with a third embodiment of the present disclosure, Figure 4(b) is an alternative schematic of the apparatus of Figure 4(a), Figure 4(c) is a schematic of an apparatus for indicating a characteristic of a subsea environment, in accordance with a fourth embodiment of the present disclosure, Figure 4(d) is an alternative schematic of the apparatus of Figure 4(c); Figure 5(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment, in accordance with a fifth embodiment of the present disclosure, Figure 5(b) is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with a sixth embodiment of the present disclosure; Figure 6(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with a seventh embodiment of the present disclosure, Figure 6(b) is a schematic showing a reverse side of the apparatus, for a specific embodiment of the apparatus of Figure 6(a), Figure 6(c) is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with an eighth embodiment of the present disclosure, Figure 6(d) is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with a ninth embodiment of the present disclosure; Figure 7(a) is a schematic exploded view of an apparatus for indicating a characteristic of a subsea environment in accordance with a tenth embodiment of the present disclosure, Figure 7(b) is a schematic of the apparatus showing a front view, Figure 7(c) is a schematic of the apparatus showing a first perspective view, Figure 7(d) is a schematic of the apparatus showing a second perspective view, Figure 7(e) is a schematic of the apparatus showing a third perspective view, Figure 7(f) is a schematic of the apparatus showing a first interior view, Figure 7(g) is a schematic of the apparatus showing a second interior view, Figure 7(h) is a schematic of the apparatus showing a third interior view, Figure 7(i) is a schematic cross section of the apparatus; Figure 8(a) is a schematic of a specific embodiment of the apparatus in accordance with an eleventh embodiment of the present disclosure, Figure 8(b) is a schematic of a specific embodiment of the collection component, Figure 8(c) is a schematic cross section of the specific embodiment of the collection component, Figure 8(d) is a schematic of a view from above of the specific embodiment of the collection component, Figure 8(e) is a schematic of the specific embodiment of the apparatus attached to a surface, Figure 8(f) is a schematic of the specific embodiment of the apparatus attached to a subsea tree, Figure 8(g) is a schematic of the specific embodiment of the apparatus attached to a subsea tree; Figure 9(a) is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with an twelfth embodiment of the present disclosure, Figure 9(b) is a schematic of the apparatus from an alternative view point. Figure 9(c) is a schematic cross section of the apparatus, Figure 9(d) is a schematic cross section of the apparatus from an alternative view point, Figure 9(e) is a schematic of the apparatus showing a side view, Figure 9(f) is a schematic of the apparatus viewed from above, Figure 9(g) is a top-down schematic of the apparatus; and Figure 10 is a schematic of an apparatus for indicating a characteristic of a subsea environment in accordance with a thirteenth embodiment of the present disclosure. DETAILED DESCRIPTION Figure 2(a) is a schematic of an apparatus 200 for indicating a characteristic of a subsea environment, in accordance with a first embodiment of the present disclosure. It will be appreciated that the characteristic may be referred to as a “predetermined" characteristic. The apparatus 200 comprises a detection component 202 that is configured to detect the pre-determined characteristic of the subsea environment, and then undergo a visual change in response to detection of the characteristic. The apparatus 200 further comprises a mounting unit 204 that comprises a mounting component 206 that holds the detection component 202 during operation. The mounting unit 204 further comprises a viewing port 208 that enables the detection component 202 to be visually inspected. This can enable a user to observe the visual change of the detection component 202 that is indicative of the detection of the characteristics within the subsea environment. Therefore, the apparatus 200 can function as a visual indicator of the detection of the pre-determined characteristic. The detection component 202 may, for example, undergo a chemical reaction that results in the visual change. Figure 2(b) is a schematic of the apparatus 200 after detection of the predetermined characteristic. In Figure 2(b), the detection component 202 is shown with a different hatching pattern when compared to the component 202 in Figure 2(a) to indicate the visual change. It will be appreciated that in specific embodiments, the visual change of the detection component 202 may be irreversible, in that after the detection component 202 is no longer being exposed to the characteristic the visual change remains. However, in further embodiments, the visual change may be reversible, where the appearance of the detection component 202 returns to its initial appearance after it stops being exposed to the characteristic. In further embodiments, the detection component 202 may undergo different visual changes based on the characteristic or characteristics that it is exposed to. In further embodiments, two or more detection components 202 may be used, each to identify a different characteristic. The visual change may, for example, be: a colour change; an increase or decrease in opacity; or an emission of light, such as a fluorescence. In a specific embodiment, the colour change may be observable by a human user simply looking directly at the component 202. The colour change may be observable in an image acquired, for example, by a camera controlled by an ROV. In specific embodiments, the colour change may be observable in the reflection and / or transmission spectrum of the detection component 202. In further embodiments, the visual change may only be observable using imaging equipment as may be held and operated using an ROV. For example, the visual change may occur outside of the visible wavelength range, such as at ultraviolet or infrared wavelengths. For example, where a visual change occurs at infrared wavelengths, an infrared camera may be used to observe the visual change. Figure 2(c) is a schematic cross section of a specific embodiment of the detection component 202 as may be used in any of the embodiments described herein, in accordance with the understanding of the skilled person. The detection component 202 comprises an inner material 210 and an outer material 212. The inner material 210 is fully encased by the outer material 212. In further embodiments, the inner material 210 may only be partially encased by the outer material 212. In the present example, the outer material 212 is configured to at least partially dissolve as a result of exposure to the pre-determined characteristic, thereby exposing the inner material 210. Figure 2(d) is a schematic cross section of the detection component 202 after the outer material 212 has dissolved. The dissolving of the outer material 212 results in a visual change to the detection component 202 as now the inner material 210 can be observed. In a specific embodiment, the inner material 210 may be a different colour from the outer material 212 such that there would appear to be a colour change to the detection component 202 after exposure to the pre-determined characteristic. In a further embodiment, the inner material 210 may visually change when exposed to sea water. For example, after the dissolving of the outer material 212, the inner material 210 would then be exposed to sea water, which could result in a visual change such as a colour change. It will be appreciated that in a specific embodiment, small and localised penetration of the outer material 212 can allow sea water to gain access to the inner material 210, which could then exhibit the visual change. By way of example, we may consider the characteristic to be detected as being the presence of a pre-determined chemical, where the pre-determined chemical is a tracer fluid. As discussed previously, a tracer fluid can be used with a well kill fluid, where the presence of the tracer fluid can be indicative of a well losing integrity. Examples of tracer fluids are described in WO2019215438A1. Examples of emulsions that may be suitable for use as tracer fluid include those based on a range of solvents, surfactants, fluorophores, and dyes, including: Solvents: Ethyl acetate, methyl ethyl ketone (Butanone / MEK), N-Methyl-2-pyrrolidone (NMP), toluene; Surfactants: Triton X-100, polysorbate 80, decyl polyglucose; Fluorophores: Nile blue, Auramine O, eosin; and Dyes: Cobalt blue A suitable outer material 212 that dissolves in the presence of a specific tracer fluid can be provided. For example, the outer material 212 may be formed from polyfmethyl methacrylate) (PMMA) or polyvinyl acetate (PVA). For example, the outer material 212 being formed using PMMA (wholly or partially) may be used for the detection of a tracer fluid comprising surfactant / solvent mix of 1:4 polysorbate 80 to ethyl acetate, with <0.05 vol. % of Auramine 0 and cobalt blue. In this example, the outer material 212 would dissolve in the presence of the specific tracer fluid, thereby exposing the inner material 210. The inner material 210 itself may indicate the visual change, for example by having a distinct colour that would become exposed after the dissolving of the outer material 212. In a further embodiment, the inner material 210 itself may undergo a visual change (such as a colour change) when it is exposed to sea water, when the outer material 212 dissolves. The inner material 210 may, for example, comprise anhydrous copper sulphate, which changes from pink to blue when exposed to sea water. It will be appreciated that the detection component 202 of the embodiments described herein may be inert in sea water. In specific embodiments of the present disclosure, the detection component 202 may only be partially inert in sea water. For example, where the detection component 202 comprises the inner material 210 and the outer material 212, the outer material 212 may be inert in sea water (but dissolve in the presence of the pre-determined characteristic) whilst the inner component may be reactive in sea water (and exhibit a colour change when in contact with sea water, as discussed previously). It will be appreciated that the present embodiment relates to a detection component 202 comprising two layers (the inner material 210 and the outer material 212). In a further embodiment, the detection component 202 may comprise a single layer that dissolves in the presence of the pre-determined characteristic, with the change of appearance or absence of the detection component 202 itself being a visual indication of the detection of the pre-determined characteristic. Figure 2(e) is a photograph of an apparatus 214 in accordance with a specific embodiment of the present disclosure. In the present example, the detection component 202 is mounted on a window, which may function as the mounting unit 204. The detection component 202 may be disc-shaped as in the present example. In a specific embodiment, the characteristic that is detected may relate to temperature. For example, the characteristic may be the temperature of the subsea environment being greater than a threshold temperature value, less than the threshold temperature value, or approximately equal to the threshold temperature value. The detection component 202 may comprise one or more materials that are responsive to temperature. For example, the detection component 202 may comprise a shape memory alloy that is thermoresponsive. Such materials may hold different shapes at different temperatures, and therefore can provide a visual indication of temperature. An example of a shape memory alloy that is responsive to temperature is nickel titanium (also known as nitinol). In a further embodiment, the detection component 202 may comprise a material that is soluble at one temperature, and insoluble at another temperature, thereby providing a visual indication of a temperature change. In a specific embodiment, the detection component 202 being responsive to temperature may comprise polyacrylamides such as poIy(N-isopropylacrylamide). By way of example, for a detection component 202 having the structure presented in Figures 2(c) and 2(d), the outer material 212 may dissolve in seawater when exposed to a temperature greater than 10°C, thereby exposing the inner material 210 that has a distinctive and bright colour when exposed to seawater. Therefore, when the temperature exceeds 10°C (the threshold temperature value) the detection component 202 would exhibit a clear colour change as could be seen by observer, thereby indicating the occurrence of the subsea environment exceeding 10°C. In a further embodiment, the characteristic that is detected may relate to the pH value of the subsea environment. For example, the characteristic may be the pH value of the subsea environment being greater than a threshold pH value, less that a threshold pH value, or approximately equal to a threshold pH value. The detection component 202 may comprise one or more materials that are responsive to pH. For example, the detection component may comprise a polymer that swells or collapses in response to changes in pH, thereby providing a visual indicator of a pH change. In further embodiments, the detection component may comprise a halochromic material that changes colour as a result of a change in pH. In specific embodiments, the detection component 202 may comprise a pH indicator such as resazurin, resorcin blue or alizarin yellow. By way of example, for a detection component 202 having the structure presented in Figures 2(c) and 2(d), the outer material 212 may dissolve in seawater when exposed to a pH value less than 7, thereby exposing the inner material 210 that has a distinctive and bright colour when exposed to seawater. Therefore, when the pH value falls below 7 (the threshold pH value) the detection component 202 would exhibit a clear colour change as could be seen by observer, thereby indicating the occurrence of the subsea environment falling below a pH of 7. It will be appreciated that pH may be a secondary indicator indicative of the presence of carbon dioxide (CO2). In a further embodiment, the characteristic that is detected is the presence of a predetermined chemical in the subsea environment. For example, the pre-determined chemical may comprise one or more of a tracer fluid, a thermogenic gas, a biogenic gas, methane, a hydrocarbon, methanol, monoethylene glycol, a control fluid, carbon dioxide. The tracer fluid may, for example, be SWIFT. The hydrocarbon may, for example, be a liquid hydrocarbon. The detection component 202 may comprise one or more materials that are responsive to a specific pre-determined chemical, thereby enabling the detection component 202 to give a visual indication of the pre-determined chemical being detected. It will be appreciated that one or more materials suitable for the detection of each of the aforementioned pre-determined chemicals will be well known to the skilled person. For example, for the detection of methanol, the detection component 202 may comprise polymethacrylates such as poly(2-hydroxyethyl acrylate). In a specific embodiment, the apparatus may be used to monitor the integrity of a subsea well or fluid sequestration site by indicating that the pre-determined chemical has been detected. For example, for a detection component 202 having the structure presented in Figures 2(c) and 2(d), the outer material 212 may dissolve when exposed to a trace fluid (such as the tracer fluid 145 as described previously), thereby exposing the inner material 210 that has a distinctive and bright colour when exposed to seawater. Therefore, when the tracer fluid is detected, the detection component 202 would exhibit a clear colour change as could be seen by an observer, thereby indicating the present of the tracer fluid 145 in the subsea environment which may be indicative of a decommissioned subsea well leaking. In summaiy, in the present example as applied to monitoring of a subsea well, the inner material 210 is a reactive material encased by the outer material 212 which is reactive only to specific fluids of interest. The inner material 210 is such that it changes when exposed to water (including seawater) and typically that characteristic change will be a colour change or some other clearly visible trait. The material 212 encompassing the inner material 210 is the material that is sensitive to the fluid of interest (the “pre-determined chemical”). These fluids of interest may include, but are not limited to, SWIFT, thermogenic gas, a biogenic gas, methane, liquid hydrocarbon, methanol, MEG, control fluids, and CO2. On exposure to the fluid of interest the encasing material 212 will (over a period time) react to that fluid and be degraded. When there is sufficient degradation to allow water to penetrate through the outer material 212 to reach the inner material 210 then a reaction occurs which may, for example, turn the inner material 210 from one colour to another or from clear to opaque or vice-versa. As discussed previously ROV inspection can take a long time to conduct an inspection and there are safety concerns in extracting chemicals for analysis outside of the subsea environment. Embodiments of the present disclosure can accelerate inspection by instructing the ROV to look only at specific areas of interest, for example by looking at one or more detection component 202 of the present disclosure, and confirming the condition of the detection components 202. Triggering of a specific detection component 202 may indicate the presence of a specific fluid. In being able to report that discs are unchanged, an operator has greater confidence and knowledge to share with authorities. Furthermore, by having the detection components 202 sensitive to specific chemicals, there is eliminated the requirement to extract the chemicals for analysis outside of the subsea environment, thereby improving safety over known systems. Figure 3(a) is a schematic of an apparatus 300 for indicating a characteristic of a subsea environment, in accordance with a second embodiment of the present disclosure. Figure 3(b) is a schematic of the apparatus 300 having the detection component 202 and some parts of the mounting unit 204 removed. In the present example, the mounting unit 204 comprises a handle 302 to permit holding of the apparatus 300 by a submersible craft such as an ROV or an autonomous underwater vehicle (AUV). Specific embodiments described herein are described primarily as being used with an ROV. However, it will be appreciated that the embodiments of the present disclosure may also be used with other submersible craft, such as an AUV, in accordance with the understanding of the skilled person. In the present example, the mounting unit 204 comprises a window 304 that is coupled to the viewing port 208. The window 304 may be substantially optically transparent and may comprise hardened glass. It is generally time consuming and therefore expensive to interface electronic systems with ROVs. Specific embodiments of the apparatuses described herein do not require specialised equipment to be fitted to an ROV for operation. For example, the handle 302 can be used by a typical ROV without requiring modification of the ROV. Figure 4(a) is a schematic of an apparatus 400 for indicating a characteristic of a subsea environment, in accordance with a third embodiment of the present disclosure. Figure 4(b) is an alternative schematic of the apparatus 400. Figure 4(c) is a schematic of an apparatus 401 for indicating a characteristic of a subsea environment, in accordance with a fourth embodiment of the present disclosure. Figure 4(d) is an alternative schematic of the apparatus 401. The apparatus 401 is an alternative configuration to the apparatus 400. To aid in the clarity of the drawings, the reference numerals for the mounting component 206 and the viewing port 208 have been omitted. In the present examples, there are five further detection components 402, 404,406, 408, 410. Each of the detection components 402-410 is mounted to a mounting component and is viewable via a viewing port. It will be appreciated that further embodiments may comprise one or more detection components with related mounting components and viewing ports, and the present embodiment is provided as one example having multiple detection components. Two or more of the detection components 202, 402-410 may be responsive to a different characteristic. The characteristics may relate to temperature, relate to pH or may be the presence of a pre-determined chemical, as described previously. For example, each detection component 202, 402-410 may exhibit a visual change when exposed to different chemicals, therefore providing a simple visual indication of the local chemical environment. Two or more of the detection components 202, 402-410 may exhibit the same or different visual changes. The visual changes may, for example, be a colour change, an increase in opacity, a decrease in opacity or emission of light. At least one of the detection components 202, 402-410 may be implemented using the structure as illustrated in Figure 2(c) and Figure 2(d), where the outer material 212 enclosing the inner material 210 and reacts as previously described. The apparatuses 300, 400, 401 may function as "cartridges" with replaceable detection components. It will be appreciated that specific embodiments may use different handle configurations to support a range of ROV manipulators. Handles may have different lengths to allow for the insertion of the apparatus 300, 400, 401 into usually inaccessible places, e.g. between the bottom of a tree and the wellhead on which it is installed. In specific embodiments, the “cartridges" may be fitted to other styles of equipment which are intended to be mounted for short to mid-term periods in a static location, e.g. on a tree. Although in the present embodiment the detection components 202, 402-410 are separate and distinct discs, in a further embodiment a single structure, such as a single disc may comprise two or more detection components, each responsive to different characteristics. Figure 5(a) is a schematic of an apparatus 500 for indicating a characteristic of a subsea environment, in accordance with a fifth embodiment of the present disclosure. In the present embodiment, the apparatus 500 comprises the specific embodiment of the mounting unit 204 as shown in Figures 4(a) and 4(b), with an alternative handle 302 configuration and further comprising a stand 502 that, in the present example, has a tripod configuration. Figure 5(b) is a schematic of an apparatus 504 for indicating a characteristic of a subsea environment in accordance with a sixth embodiment of the present disclosure. In the present embodiment, the apparatus 504 comprises the specific embodiment of the mounting unit 204 as shown in Figures 4(c) and 4(d), and further comprising the stand 502. The mounting unit 204 may also comprise a sonar reflector 506 for vehicle navigation and support. The mounting unit 204 may also comprise a weighting unit to assist in preventing the toppling of the stand 502 when deployed on the sea floor. Figures 5(a) and 5(b) show 2 different styles of configuration of multiple disc detectors: a linear arrangement of 6 (Figure 5(a)) and another arrangement of 3 x 2 are shown (Figure 5(b)), with any number being feasible and suitable for further embodiments of the present disclosure. Specific embodiments may use an array of tripods (for example using the apparatuses 500, 504), with tripods being installed on the seabed perhaps covering an extensive area with each individual unit expected to provide coverage for a particular zone of influence. The overall tripod assemblies are capable of indicating the presence or influence of multiple fluids of interest. Such an approach might be advantageous when monitoring the integrity of a CCS site, for example, in that some of the discs may be responsive to carbon dioxide whereas others are responsive to different levels of acidity, e.g. pH indicators. In this “array of monitors" scenario, it is envisaged that an ROV would fly between the tripods to visually inspect the status of the discs or, as is now increasingly the case, AUVs might be used where an automated vehicle conducts the visual checks automatically before returning to its garage to dock and download the observations whilst recharging. Specific embodiments of the tripod arrangements may comprise a sonar reflector to provide additional navigational support to the AUV or the ROV pilot. This is typical of subsea practice. For the tripod type scenario a deployment example may use a basket that would be lowered from a vessel to the seabed and an ROV used to take one tripod at a time out of the basket to place it in the monitoring position. Such an approach to deployment is common and saves a lot of tripping time between seabed and vessel. It will be apparent that one of the characteristics of the tripod approach is taking advantage of subsea currents to move fluids of interest from remote sources to the monitor. Figure 6(a) is a schematic of an apparatus 600 for indicating a characteristic of a subsea environment in accordance with a seventh embodiment of the present disclosure. The mounting unit 204 may comprise an enclosure 601 comprising the viewing port 208, with the mounting component 206 being configured to hold the detection component 202 within the enclosure 601. The enclosure 601 forms an enclosed volume which the detection component 202 is held within. The enclosure 601 may be formed whilst still permitting viewing within the enclosure 601 by having the mounting unit 204 comprise the window 304 coupled to the viewing port 204. The window 304 may be optically transparent and may comprise hardened glass. In an alternative embodiment the mounting component 206 may comprise the window 304 such that that detection component 202 may be held by the window 304. In the present embodiment the enclosure 601 comprises an aperture 602 for receiving a volume of fluid 604. The aperture 602 provides a fluid path into the enclosure 601. The enclosure 601 may further comprise an aperture 606 for enabling the volume of fluid 604 to pass outside of the enclosure 601. In operation, the volume of fluid 604 passes into the enclosure 601 via the aperture 602 and over the surface of the detection component 202. The detection component 202 can then detect the characteristic of the subsea environment via its interaction with the volume of fluid 604. The volume of fluid 604 may then pass through the aperture 606 to exit the enclosure 601. When the apparatus 600 is immersed in sea water, the use of two apertures 602, 606 provides a fluid path from outside the enclosure 601, over the detection component 202 and then back out of the enclosure 601. This can provide a continuous flow of the volume of fluid 604 through the enclosure 601 for interaction with the detection component 202. It will be appreciated that in a further specific embodiment, the aperture 606 may be omitted such that the apparatus 600 comprises only a single aperture (the aperture 602). In such an embodiment, the aperture 602 may be unidirectional, in that it only permits the volume of fluid 604 to enter the enclosure 601, or the aperture 602 may be bidirectional, in that it may permit the volume of fluid 604 to both enter the enclosure 601 and to leave the enclosure 601. Figure 6(b) is a schematic showing a reverse side of the apparatus 600, for a specific embodiment of the apparatus 600 having an additional viewing port 605 in the back of the mounting unit 204. In the present example, the mounting unit 204 is a cubic structure with viewing ports 208, 605 on opposite sides. However in further embodiments the viewing ports may be on different sides, and furthermore, there may provided more than two viewing ports. It will also be appreciated that the mounting unit 204 may have a structure other than the cubic structure of the present embodiment, in accordance with the understanding of the skilled person. The mounting unit 204 may comprise an additional window 607 coupled to the viewing port 605. The additional window 607 may be optically transparent and may comprise hardened glass. In the present embodiment, the mounting unit 204 is configured to hold the detection component 202 between the windows 304, 605. Figure 6(c) is a schematic of an apparatus 608 for indicating a characteristic of a subsea environment in accordance with an eighth embodiment of the present disclosure. In the present embodiment, the mounting unit 204 comprises a collection component 610 comprising an input portion 612 comprising an input aperture 614 arranged to capture the volume of fluid 604. The collection component 610 further comprises an output portion 616 arranged to provide the volume of fluid 604 to the detection component 202 via the aperture 602. The collection component 610 may be in a funnel configuration, such that the input aperture 614 is larger than the aperture 602 to enable the volume of fluid 604 to be collected over an area that is wider than the aperture 602. It will be appreciated that the collection component 610 may be implemented as part of any of the embodiments described herein, and in accordance with the understanding of the skilled person. Figure 6(d) is a schematic of an apparatus 618 for indicating a characteristic of a subsea environment in accordance with a ninth embodiment of the present disclosure. In the present embodiment, the mounting unit 204 comprises an attachment portion 620 that may, for example, be used for attachment to a subsea tree. Figure 7(a) is a schematic exploded view of an apparatus 700 for indicating a characteristic of a subsea environment in accordance with a tenth embodiment of the present disclosure. Figure 7(b) is a schematic of the apparatus 700 showing a front view. Figure 7(c) is a schematic of the apparatus 700 showing a first perspective view. Figure 7(d) is a schematic of the apparatus 700 showing a second perspective view. Figure 7(e) is a schematic of the apparatus 700 showing a third perspective view. Figure 7(f) is a schematic of the apparatus 700 showing a first interior view. Figure 7(g) is a schematic of the apparatus 700 showing a second interior view. Figure 7(h) is a schematic of the apparatus 700 showing a third interior view. Figure 7(i) is a schematic cross section of the apparatus 700. The enclosures in which the discs are mounted, as shown in Figures 7(a)-7(i) are designed such that the fluid of interest is able to pass across the face of the detection material. This may be caused by flow of the fluid of interest e.g. a buoyant or nonbuoyant fluid rising or falling through the apparatus 700, or by the apparatus 700 being moved through the water by a subsea vehicle. In the present examples hardened glass is placed on either side of the reactive discs (whilst leaving a gap of several mm to allow fluid to flow across the discs). By utilising simple manufacturing techniques, enclosures can be created either as a single piece (after manufacturing, sealing adhesives, welding etc is complete) or as mechanically secured cartridges which can be disassembled only by those in possession of the necessary specialised tooling to remove special keyed fasteners. Figure 8(a) is a schematic of a specific embodiment of the apparatus 700 comprising the collection component 610 and the attachment portion 620, in accordance with an eleventh embodiment of the present disclosure. The attachment portion 620 comprises adjustable elements that are provided in the mountings such that pre-configuration of the assembly allows for avoidance of obstructions on the tree. A compliant spring 801 is also shown between a magnetic lock 803 and the disc so that should the pilot bump the tree with the disc during manoeuvring then the spring 801 allows for several degrees of movement without causing damage. Similarly, a bumper bar is shown around the top of the hopper to help minimise damage to the disc arrangement. Figure 8(b) is a schematic of a specific embodiment of the collection component 610. Figure 8(c) is a schematic cross section of the specific embodiment of the collection component 610. Figure 8(d) is a schematic of a view from above of the specific embodiment of the collection component 610. Figure 8(e) is a schematic of the specific embodiment of the apparatus attached to a surface 800. Figure 8(f) is a schematic of the specific embodiment of the apparatus 700 attached to a subsea tree 802. Figure 8(g) is a schematic of the specific embodiment of the apparatus 700 attached to a subsea tree 804. The collection component 610 may be referred to as "a hopper". The attachment portion 620 may comprise a switchable magnetic lock which allows the unit to be attached or removed from a metal surface. There are examples of trees where leaks are known or suspected but where access is limited by pipework or clashes with other valve access requirements. The example shown would be deployed in the port manipulator of a standard workclass ROV such that the box marked U / L ('locked’ / ‘unlocked’) is placed flush against the face of the tree in a position that the hopper for the disc is located (in the example shown) underneath the item of interest. The starboard manipulator is used to move the handle from unlocked position to locked position thus activating the magnet and allowing the pilot to release the unit and continue to do other work whilst the monitoring is taking place. It will be appreciated that the apparatus 700 can be used upside down or the disc can be installed in a different orientation in order that positively buoyant materials can be captured and passed across the face of the discs. By maintaining the alignment of the disc to be in the same plane as that of the main flow of the hopper the disc remains visible to pilots during operations. This contrasts with other examples such as the ROV held detectors (for example, the apparatus 300,400, 401) which may be used in a more dynamic manner where the fluid of interest may move at right angles to the detection discs. In the present examples, the flow pattern is arranged through the disc apertures such that the fluid of interest passes across the face in the usual manner. In specific embodiments, the collection component 610 may be remote from the detection disc cartridge if, for example, it would otherwise be obscured by other tree equipment when in the monitoring position. For example, a simple tube may be used to connect the collection component 610 to the aperture 602. It will be appreciated that by either installing units in multiples on the seabed using a tripod approach or by using magnetic clamps to attach detector discs to other assets, such as trees, monitoring is ongoing even with the ROV reassigned to other duties. It is feasible that if a programme of work over 1 or 2 shifts is required then the discs might be installed around a tree at the beginning of the work and 12 / 24 hours later a return to that tree will allow an assessment of the condition of the detectors. Monitoring periods could thus be a few hours or many months, but they do not tie up ROVs or delay vessel schedules. In known instances ROVs have been held on station for an entire shift trying to monitor a leak or suspected leak - this is an expensive way of monitoring as it limits operations by the vessel and the e-tire day rate could be expended on one task instead of being split over many tasks. In short, embodiments of the present disclosure free up ROVs for other work. By providing a solution that can be held in place (if necessary for several hours] a result can be obtained at source in pseudo real-time and the issues of known systems are mitigated. Similarly, by deploying multiple detection discs on a tree (perhaps pre-emptively rather than in response to concerns about specific locations) an operator is able to demonstrate to all interested stakeholders (including regulators) that the tree is being monitored in a rigorous manner. Figure 9(a) is a schematic of an apparatus 900 for indicating a characteristic of a subsea environment in accordance with an twelfth embodiment of the present disclosure. Figure 9(b) is a schematic of the apparatus 900 from an alternative view point. Figure 9(c) is a schematic cross section of the apparatus 900. Figure 9(d) is a schematic cross section of the apparatus from an alternative view point. Figure 9(e) is a schematic of the apparatus 900 showing a side view. Figure 9(f) is a schematic of the apparatus 900 viewed from above. Figure 9(g) is a top-down schematic of the apparatus 900. Although shown with three detection mechanisms and related viewing ports, it will be appreciated that further embodiments may comprise one or more detection mechanisms with related viewing ports in accordance with the understanding of the skilled person. Embodiments of the present disclosure using two or more detection components (for example, as shown in Figures 4(a)-(d) and Figure 9(a)-9(g)). may be used to provide a gradient indicator of a variable, such as pH, by having different detection components responsive to different characteristics. Multiple use cases are possible with the apparatus 900. The ROV can move through the water to search for evidence of specific fluids. In another case the ROV can hold station with the funnel 610 above the item of interest (if the fluid has a specific gravity <1) or (if the specific gravity is >1) it can position the funnel 610 such that the fluid passes down through the funnel 610 and into the chamber where it might react with the detection discs 202, 402, 404 in the same manner as the other styles of equipment. By holding the unit at an angle the ROV can seek to monitor the fluid in front of it as it is flown through the subsea environment. This allows the indication of when the vehicle passes through a cloud of material such as monoethylene glycol (MEG). Reaction times for detector discs may be driven by several factors and in certain cases, such as for the detection of a chemical within a cloud of material, a single fast pass through a material cloud may be insufficient to acquire a detection indication. In this case the vehicle could then reverse course, having exchanged the contaminated disc indicator for a fresh one taken from a holster on the vehicle, and backtrack at a much lower speed in order that a more precise location of the source of the leak (such as from a buried pipeline) is discovered. Figure 10 is a schematic of an apparatus 1000 for indicating a characteristic of a subsea environment in accordance with athirteenth embodiment of the present disclosure. The apparatus 1000 is configured to provide a gradient as an indication of a characteristic and may be implemented as part of any of the apparatuses described herein in accordance with the understanding of the skilled person. In the present example, there is provided a disc that has been divided into four sections, with each section being one of the detection components 202, 402, 404, 406 that are each responsive to a different characteristic. In further embodiments, there may be provided a single disc being further divided, or divided into fewer sections. Furthermore, the shape of the combined detection components may be something other than a disc. In a specific embodiment there may be provided a grid of detector cells incorporated into a single disc with each region of that grid being approximately 2 cm2 and with each section being representative of 0.1 pH change. In a specific embodiment, there may be provided an apparatus comprising multiple discs divided as shown in Figure 10, with each disc being responsive to a different range of values, e.g. from 8.2 to 7.9. These ranges would be typical of normal seawater becoming more acidic (strictly speaking less alkaline) which is a secondary indicator of the presence of carbonic acid and therefore CO2. Each section of the grid of a single disc can change state independent of its neighbour. What then becomes apparent from a distance is what level of alkalinity / acidity is present in that region. This concept is not just applicable to CO2 type applications but can be used in other areas where the range of interest is different. One example being cementing top holes subsea where the alkalinity being targeted is nearer 9.5, therefore a disc's range is likely to be from 8.6 to 10. In this instance this allows operators to stop pumping cement at an opportune time and avoid wasting cement. Whereas monitoring is currently done using expensive electronic systems, these are not necessarily always relied upon or working. Pumping excess into the wellbore is an expensive exercise which could therefore be avoided by simple, passive means as provided by embodiments of the present disclosure. In summary, in specific embodiments of the present disclosure, by using a long-arm ROV detector (either with or without a funnel attachment) to get into difficult to reach or see places (optionally with additional battery powered lights and video style cameras attached), the flow of materials across the detection components, optionally in the form of discs, can be used to identify either positively or negatively whether an observed fluid has a particular characteristic or not. For example, the presence of a specific chemical, pH or temperature. Using embodiments of the apparatus as described herein, issues of known systems, for example delays in chemical characterisation, safety problems and costs, are avoided and it is simply a case of the ROV picking up the item of interest in a manipulator and deploying it to site. A vessel can be equipped with more than one apparatuses of the present disclosure and cases of pre-configured ready-to-use detection discs can be swapped out at short-notice and in a very short time scale for each operation. Embodiments of the present disclosure may be used for hot tap monitoring. Hot taps are usually used as a temporary measure and work-around for intervention tasks and can be removed after that work is complete. In some circumstances, however, there can be long-term use of a hot tap and providing a means of ensuring that the integrity of the tap is sound is another level of reassurance for an operator if challenged by third parties such as regulators. Embodiments of the present disclosure may be used for shorter-term monitoring. For example, from a few hours up to a year. Further embodiments may be used for longer term monitoring. Various improvements and modifications may be made to the above without departing from the scope of the disclosure.

Claims

1. An apparatus for indicating a characteristic of a subsea environment:a first detection component configured to:detect a first characteristic of the subsea environment; andundergo a visual change in response to detection of the first characteristic; anda mounting unit comprising:a first mounting component configured to hold the first detection component; anda first viewing port configured to permit visual inspection of the visual change of the first detection component, thereby indicating the detection of the first characteristic within the subsea environment.

2. The apparatus of claim 1, wherein the visual change of the first detection component is:a colour change; oran increase in opacity; ora decrease in opacity; oremission of light.

3. The apparatus of claim 1, wherein the first detection component comprises:a first inner material; anda first outer material, the first outer material at least partially encasing the first inner material; wherein:the first outer material is configured to at least partially dissolve as a result of the first characteristic, thereby exposing the first inner material.

4. The apparatus of claim 3, wherein:the visual change of the first detection component is:a colour change; oran increase in opacity; ora decrease in opacity; or emission of light; anda visual change is exhibited by the first inner material after its exposure to sea water, thereby providing the visual change of the first detection component.

5. The apparatus of any preceding claim, wherein the first characteristic relates to a temperature of the subsea environment.

6. The apparatus of claim 5, wherein the first characteristic is the temperature of the subsea environment being:greater than a first threshold temperature value;less than the first threshold temperature value; orapproximately equal to the first threshold temperature value.

7. The apparatus of any of claims 1 to 4, wherein the first characteristic relates to a pH value of the subsea environment.

8. The apparatus of claim 7, wherein the first characteristic is the pH value of the subsea environment being:greater than a first threshold pH value;less that the first threshold pH value; orapproximately equal to the first threshold pH value.

9. The apparatus of any of claims 1 to 4, wherein the first characteristic is the presence of a first pre-determined chemical.

10. The apparatus of claim 9, wherein the first pre-determined chemical comprises: a tracer fluid; and / ora thermogenic gas; and / ora biogenic gas; and / ormethane; and / ora hydrocarbon; and / ormethanol; and / ormonoethylene glycol; and / ora control fluid; and / or carbon dioxide.

11. The apparatus of claim 9 or 10 being configured to monitor the integrity of a subsea well or a fluid sequestration site by indicating that the first pre-determined chemical has been detected.

12. The apparatus of any preceding claim, wherein the mounting unit comprises a handle configured to permit holding by a submersible craft.

13. The apparatus of any preceding claim, wherein:the mounting unit comprises an enclosure that comprises the first viewing port; andthe first mounting component is configured to hold the first detection component within the enclosure.

14. The apparatus of claim 13, wherein the enclosure comprises a first aperture for receiving a volume of fluid.

15. The apparatus of claim 14, wherein the enclosure comprises a second aperture for permitting flow of the volume of fluid into the enclosure via the first aperture and out of the enclosure via the second aperture.

16. The apparatus of claim 14 or 15, wherein the mounting unit comprises:a collection component comprising:i) an input portion comprising an input aperture arranged to capture a volume of fluid; andii) an output portion arranged to provide the volume of fluid to the first detection component via the first aperture of the enclosure.

17. The apparatus of any of claims 13 to 16, wherein the mounting unit comprises a first window coupled to the first viewing port.

18. The apparatus of claim 17, wherein the first mounting component comprises the first window, the first detection component being held by the first window.

19. The apparatus of claim 17, wherein the mounting unit comprises a first additional viewing port configured to permit visual inspection of the visual change of the first detection component.

20. The apparatus of claim 19, wherein the mounting unit comprises a first additional window coupled to the first additional viewing port.

21. The apparatus of any preceding claim, wherein the mounting unit comprises an attachment portion for attaching the apparatus to a subsea tree.

22. The apparatus of any of claims 1 to 21 wherein the mounting unit comprises a stand for standing the apparatus on the sea floor.

23. The apparatus of any preceding claim, comprising:a second detection component configured to:detect a second characteristic of the subsea environment; and undergo a visual change in response to detection of the second characteristic,24. The apparatus of claim 23, wherein the mounting unit comprises:a second mounting component configured to hold the second detection component; anda second viewing port configured to permit visual inspection of the visual change of the second detection component, thereby indicating the detection of the second characteristic within the subsea environment.

25. A method of indicating a characteristic of a subsea environment, using the apparatus of any preceding claim.

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