MUON based imaging and detection of fluids, gases and natural solids

Abstract

A borehole muon detector (100, 200, 500, 600, 602) for deployment in wellbores comprises a cylindrical housing (104); a processing section (120), dedicated for data processing; at least one detection section (106, 206) with at least two detection means (102, 202, 302, 312), wherein each detection means (102, 202, 302, 312) is preferably a coextruded support (306, 316) and scintillator (304, 314) structure. A method of detecting muons comprises providing at least one borehole muon detector (100, 200, 500, 600, 602); position the at least one borehole muon detector in a well bore; measuring the trajectory and velocity of the muons in the muon detector.

Description

[0001] MUON BASED IMAGING AND DETECTION OF FLUIDS, GASES AND NATURAL SOLIDS

[0002] 1. Field of the invention

[0003] This invention relates to a borehole muon detector for deployment in wellbores, and a method of detecting muons.

[0004] 2. Background

[0005] In the field of underground exploration and surveillance, the concept of muon detection has emerged as a robust and non-invasive measurement technique. Muons are elementary particles and are being created under the effect of cosmic rays in the Earth’s atmosphere. They can travel through the Earth’s surface and might be subject to deceleration when they interact with matter. The rate of energy loss due to the deceleration depends on the medium with which the muon interacts. Approximately 10,000 muons are passing through an area of a square meter in each minute on the surface of the Earth, thus delivering an abundance of muons suitable for detection.

[0006] Muons are primarily detected using a specialized device made from plastic scintillator material. When a muon enters the scintillator, it deposits energy which is then converted into photons. These photons generate a pulse of light that is subsequently transformed into an electrical pulse by photosensors next to the scintillator. The use of muon detectors with many scintillators allows for a precise mapping of the trajectory and speed of a muon as it passes through the detector, thus providing a precise knowledge of the path and attenuation experienced by the muon before it passes through the detector. In this way, it is possible to determine which materials, of which densities and with which properties, are present on the path between the Earth's surface and the detector.

[0007] US 8 288 721 B2 discloses techniques, apparatus and systems for detecting particles such as muons for imaging applications. Subtraction techniques are described to enhance the processing of the muon tomography data. In CA 3 091465 Al a borehole muon detector for muon radiography or geotomography is provided, the borehole muon detector including a substantially cylindrical housing, which defines a bore, a pair of end caps, each end cap sealing an end of the cylindrical housing and a plurality of sealed drift tubes which are longitudinally disposed in the bore of the housing to form a bundle of drift tubes.

[0008] It is disadvantageously here, that scintillators are generally difficult to manufacture and usually made of cost-intensive materials and separated from their mounting and support means. In the field of muon detectors, scintillators are often cumbersome and difficult to integrate. Thus, there is a demand for cheaper and yet efficient muon detectors for borehole applications.

[0009] In view of the foregoing, there is a need for improved borehole muon detectors. It is thus an object of the present invention to overcome some or all the deficiencies of the prior art.

[0010] 3. Summary

[0011] The above objects are at least partially achieved by the subject matter of independent claim 1. Preferred embodiments are the subject of the dependent claims, and the skilled person will find clues to other suitable aspects of the present invention in the overall disclosure of the present application.

[0012] An aspect of the invention relates to a borehole muon detector for deployment in wellbores, comprising: a cylindrical housing; a processing section, dedicated for data processing; at least one detection section with at least two detection means, wherein each detection means is preferably a coextruded support and scintillator structure.

[0013] Such a borehole muon detector can be used in geological surveying to detect changes in density, or the presence of materials based on muon detection, which can be important in identifying oil, gas, or mineral deposits. The cylindrical design of the housing makes it easy to deploy the detector in existing wellbores, thereby leveraging the infrastructure already in place for exploration or monitoring activities. The optional coextruded support and scintillator structure in each detection means is enhancing the durability and effectiveness of the muon detectors, which is particularly valuable in the harsh envi- ronments typical of wellbores. This integration not only simplifies the assembly and maintenance of the detector but also improves its performance in detecting muons with high precision, offering important advantage in subsurface exploration.

[0014] In a preferred embodiment, the detection means are circumferentially arranged in the housing in at least a first and a second circle, wherein the first circle has a bigger radius than the second circle and the second circle is arranged concentric in the first circle.

[0015] Such a structural design enhances the muon detector's capability to provide detailed and layered muon flux data from the surrounding geological structure. By having detection units arranged in concentric circles with varying radii, the detector can capture a more nuanced and detailed cross-sectional muon density profile. This configuration not only increases the overall sensitivity of the muon detector but also improves its accuracy in identifying variations in material density and structure. Such a detailed understanding is important for applications like mineral exploration or monitoring changes in geological formations, providing a clear advantage in environments where traditional exploration methods might be less effective or more invasive.

[0016] This embodiment can be improved, when the first circle comprises at least 15 detection means and the second circle comprises at least 5 detection means, and the number of detection means is higher in the first circle than in the second circle.

[0017] Such an arrangement enhances the detector's functionality by providing a gradient of detection capabilities, with e.g., a denser detection grid in the wider circle. This differential in detector density allows for a more detailed analysis of muon data at different radial distances from the center of the borehole. Such an arrangement is beneficial for creating a detailed image of the geological structures surrounding the borehole, improving the accuracy of detecting and mapping mineral deposits, cavities, or other geological features.

[0018] This embodiment can further be improved, when the number of detection means in the first circle is at least 2 times the number of the detection means in the second circle, preferably at least 2,5 times, even more preferably at least 3 times. Such a distribution strategy would significantly enhance the detector's ability to capture detailed, high-resolution muon data from the area closest to the borehole wall. The increased number of detection means in the first circle ensures a higher data collection rate from this area. Such a setup is particularly useful in detailed subsurface mapping, where precision in detecting density changes can lead to more accurate identification of resources such as minerals, water, oil, or gas.

[0019] In another preferred embodiment, at least one detection means has the shape of a cuboid, preferably a rectangular cuboid.

[0020] Detection means shaped as rectangular cuboids facilitate an optimal arrangement within the cylindrical housing, allowing for maximum coverage and efficient use of space. The rectangular cuboid shape is particularly beneficial because it can be tightly packed with minimal wasted space, thereby increasing the density of the detection array without sacrificing the detector's overall size and deployability. This configuration also aids in creating a uniform detection environment, ensuring that muon data is consistently captured across the detector's volume, which is important for accurate geological assessments and resource exploration. The cuboid shape contributes to the detector's robustness and durability, which are necessary characteristics for equipment used in the challenging conditions of borehole environments.

[0021] In a further preferred embodiment at least one detection means comprises a rectangular cross-section wherein the detection means is twisted along a helical path.

[0022] Such a feature involves the helically twisted detection means, which optimizes the detection of muons in three-dimensional space within the confines of the borehole. The helical arrangement allows the detector to cover more area within a compact space, capturing muons traveling in different directions and thus providing a more comprehensive data set about the surrounding geological formations. This is particularly advantageous in borehole environments, where space is limited, and effective use of every available dimension is crucial. The helical configuration of the detection means can significantly improve the resolution and depth of geological imaging, facilitating better decision-making in resource exploration and monitoring. The helical path, combined with the rectangular cross-section, ensures a structured approach to muon detection, enhancing both the structural integrity and the operational efficacy of the detector in challenging subsurface conditions.

[0023] In a further preferred embodiment at least one detection means has the shape of a cylinder, preferably a round cylinder.

[0024] Detection means in the shape of a round cylinder would enhance the muon detector's functionality by allowing for uniform detection capabilities in all radial directions from the detector's center. This uniformity is important in environments like wellbores, where detecting variations in muon flux from all directions can provide valuable insights into the surrounding geological structures. The cylindrical shape of the detection means ensures that the device can capture muons effectively regardless of their trajectory, leading to more accurate and reliable data collection. Moreover, the cylindrical form contributes to the structural durability of the detection means, making it more resistant to the pressures and stresses typical of borehole environments. This characteristic is advantageous in ensuring the long-term operational integrity of the detector under harsh conditions.

[0025] In a further preferred embodiment at least one detection means comprises a cross section in form of a circular sector.

[0026] Using detection means with a circular sector cross-section allows for an efficient and compact arrangement of multiple detection units within the cylindrical housing. This setup ensures that the detector can utilize every available space without leaving gaps that could result in detection blind spots. By arranging these sector-shaped detection means around a central point or axis, the detector can provide a comprehensive and continuous radial coverage, important for capturing a full spectrum of muon data across the borehole. This configuration not only optimizes the detector's sensitivity and resolution by ensuring that no area is left uncovered but also enhances the precision of geological assessments by providing detailed and consistent data across the detector's operational radius.

[0027] In a further preferred embodiment, the housing comprises a circular cross section. Featuring a housing with a circular cross-section enhances the overall operational efficiency and practical application of the muon detector in borehole environments. The circular design allows for uniform orientation and deployment, which is important in the rotational symmetry of wellbores. This symmetry ensures that the detector can be efficiently and effectively used in various orientations without concerns about alignment or incorrect positioning, which can be important for accurate data gathering and analysis. Furthermore, the circular shape helps in achieving a compact and robust design, minimizing potential obstructions and maximizing the stability of the detector within the wellbore, thus ensuring consistent performance under various subsurface conditions.

[0028] In a further preferred embodiment, the support and scintillator structure are formed by the same base material, preferably one or a combination of polystyrene, polyvinyl toluene, polyethylene naphthalate.

[0029] The use of a singular material composition for both the support structure and the scintillator within the detection means simplifies the manufacturing process. This uniformity in material choice can lead to better mechanical and optical properties, as the integration of the support and scintillator into a single form factor eliminates interfaces that could disrupt scintillation or structural integrity. Using materials like polystyrene, polyvinyl toluene, or polyethylene naphthalate ensures that the detection means are not only effective in detecting muons but also durable enough to withstand the harsh environmental conditions found in boreholes. These materials are chosen for their ability to produce light (scintillation) when hit by muons, thus ensuring high sensitivity and accuracy in muon detection. The use of a single material across the support and scintillator also optimizes the manufacturing process, potentially reducing costs and complexity in producing these specialized detection units.

[0030] In a further preferred embodiment, the support structure comprises a reflective surface configured and dedicated to reflecting photons into the scintillator, wherein the surface is preferably white and opaque.

[0031] By reflecting photons that may have otherwise escaped, such a surface ensures a higher photon retention within the scintillator, thereby increasing the scintillation light available for detection. Such a feature is important in maximizing the sensitivity and accuracy of the muon detector, as the increased light output directly translates to better detection capabilities. The use of a white and opaque surface is optimal for achieving these reflective properties, as it prevents photon absorption and disperses light uniformly back into the scintillator. This design enhancement not only improves the performance of the detection means but also contributes to the overall reliability and effectiveness of the muon detection system in the challenging and varied environments of borehole applications.

[0032] This embodiment can further be improved when the reflective surface comprises titanium dioxide.

[0033] Titanium dioxide is well-known for its high refractive index and strong ultraviolet light resistance, making it an ideal choice for maximizing the reflection of photons back into the scintillator. This enhances the scintillation process, ensuring that more light is available for the accurate detection of muons. The use of titanium dioxide, which is typically white and opaque, aligns with the desired characteristics for optimal photon reflection, as previously noted. Its application on the support structure not only boosts the detector's efficiency in capturing and analyzing muon data but also contributes to the robustness and longevity of the equipment, particularly important in the harsh environmental conditions of borehole applications.

[0034] In a further preferred embodiment, the total number of detection means inside a detection section is in the range i to 1200, preferably in the range 30 to too, even more preferably in the range 50 to 75.

[0035] Utilizing for example a detection section containing 50 to 75 detection means strikes a balance between providing sufficient density for high-resolution data collection and maintaining manageable complexity and cost of the detector. By specifying a range, the design can be adapted based on specific operational requirements or environmental conditions. Having 50 to 75 detection means per section ensures that the detector can capture a comprehensive data set across various angles and orientations, enhancing the accuracy and detail of geological assessments. This density is particularly effective for detailed imaging of subsurface structures, improving the ability to detect and analyze variations in material composition and density. The specified range allows for scalability and customization in different geological and operational scenarios, making the detector versatile for use in diverse wellbore conditions. In a further preferred embodiment, the detector comprises at least two, preferably at least 4, more preferably at least 8, even more preferably 16 and most preferably at least 32, detection sections and the detection sections are stacked on top of each other in the insertion direction of the housing.

[0036] Such a vertical stacking optimizes the use of space within the cylindrical housing and allows for a comprehensive scanning of the borehole environment over its entire depth. Each section can be precisely calibrated to detect muons at different depths or geological layers, providing a detailed vertical profile of the subsurface conditions. This configuration is particularly beneficial for deep wellbore applications where understanding geological variations at different depths is important for effective resource exploration and evaluation. The use of numerous stacked detection sections enhances the resolution and accuracy of the data collected, allowing for a more nuanced analysis of the muon measurements and thereby improving the ability to detect differences in rock density, voids, or other geological features. This design also facilitates redundancy and increases reliability, as multiple sections can independently verify muon data, ensuring consistent and accurate results across the entire depth of the borehole.

[0037] In a further preferred embodiment, the length of the housing is in the range 0.2 m to 2.6m, preferably in the range 2 m to 2.4 m, more preferably in the range 2.1 m to 2.3 m.

[0038] Such a length is for example optimal for a balance between ease of handling and deployment in a variety of borehole sizes, and sufficient space to accommodate multiple detection sections for comprehensive data collection. The specified length ensures that the detector can be easily integrated into existing infrastructure without requiring extensive modifications to the borehole setup. This optimal length also allows for the efficient stacking of multiple detection sections within the housing, as described in the previous claim, facilitating detailed and layered geological analysis over the detector's entire length.

[0039] In a further preferred embodiment, the outer diameter of the housing is in the range 10 mm to 240 mm, preferably in the range 40 mm to 80 mm, more preferably in the range 50 mm to 70 mm. Such a diameter range is for instance particularly well-suited for standard borehole operations, allowing for smooth insertion and retrieval without compromising the structural integrity of the wellbore or the housing itself. This size range also optimizes the space available for internal components, including multiple stacked detection sections, ensuring that each section can function efficiently within the cylindrical housing. The specified diameter range facilitates a good balance between maximizing internal volume for detection capabilities and maintaining an outer size that is practical for typical borehole environments. This ensures that the detector can operate effectively, providing high-quality, reliable data for geological analysis and resource exploration.

[0040] In a further preferred embodiment, the weight of the detector is in the range i kg to 20 kg, preferably in the range 12 kg to 18 kg, more preferably in the range 14 kg to 16 kg.

[0041] Such a weight range is for example optimal for ensuring that the detector is substantial enough to withstand the physical demands and environmental stresses encountered in borehole applications, such as pressure, temperature variations, and potential impacts during insertion and retrieval. Simultaneously, keeping the weight within this specific range ensures that the device remains manageable for operators to handle manually if necessary, and compatible with standard deployment machinery used in wellbores.

[0042] In a further preferred embodiment, the power consumption of the processing section during operation is in the range 0.1 W to 9 W, preferably in the range 3 W to 7 W, more preferably in the range 4 W to 6 W.

[0043] Such a range could be ideal as it balances the need for sufficient power to process data accurately and efficiently, with the need to conserve energy, extending the operational lifespan of the detector on a single power source or battery. The specified power consumption range ensures that the detector can run effectively for extended periods, which is particularly important for continuous monitoring tasks in borehole applications. Operating within this power range also reduces the thermal footprint of the device, minimizing heat generation that could potentially affect the detector's performance or the integrity of its components. This energy-efficient design enhances the practical!- ty of deploying the muon detector in varied geological settings, where reliable and sustained operation is critical.

[0044] In a further preferred embodiment, the detector further comprises a seismic detector for merging muon detection data with seismic data.

[0045] The muon detector equipped with a seismic detector leverages the combined strengths of both muon and seismic detection technologies. Muon detection provides detailed density profiling of the geological structures, while seismic data offers insights into the layers and faults within the Earth. The integration of these data types enables a multi-faceted approach to subsurface exploration, enhancing the ability to detect and characterize resources like natural solids such as rocks and / or minerals in addition to gases and fluids such as- water, or oil. It also improves the accuracy of detecting voids, cavities, and other anomalies that might not be clearly discernible through single-method detection. This capability is especially valuable in complex geological environments where precise and robust data analysis is important for successful exploration and safe operation.

[0046] Another embodiment of the invention is a method of detecting muons, the method comprising: providing at least one borehole muon detector according as described in the foregoing; position the at least one borehole muon detector in a well bore; measuring the trajectory and velocity of the muons in the muon detector.

[0047] Such a method involves deploying the borehole muon detector in a wellbore to gather detailed data on muons passing through the Earth. By measuring both the trajectory and velocity of muons, the detector can provide insights into the density and composition of the subsurface materials, as muons are affected by the density of the matter they pass through. Such a method is effective for geological exploration, such as identifying mineral deposits or assessing the integrity of geological structures. The integration of muon and seismic data, as facilitated by the seismic detector component of the muon detector, enhances the precision and reliability of the subsurface assessments.

[0048] The method is further improved, when the at least one borehole muon detector is positioned in a well bore in a depth shallower than 300 m, preferably shallower than 800 m, more preferably shallower than 1500 m. At such exemplary depths, the Earth's overburden provides a natural filter that affects the muon flux, allowing only muons with higher energies to penetrate. This variation in muon flux and energy with depth can be used to derive detailed information about the density and composition of geological layers. By positioning the detector for instance shallower 1500 meters, the accuracy and sensitivity of the muon detection are significantly enhanced, making it ideal for detailed geological assessments such as the identification of dense mineral deposits or the mapping of geological discontinuities. This method enhances the capability of muon detection for deep-Earth exploration, where traditional methods might not be as effective or feasible.

[0049] The method can even further be improved, when the at least one borehole muon detector is configured to estimate the concentration of fluids and / or gases in the Earth's subsurface to the side or above the detector by measuring the subsurface density.

[0050] Using the borehole muon detector to measure the density variations in the subsurface environment can be correlated with different concentrations of fluids and / or gases like carbon dioxide. By analyzing how muons are deflected and absorbed by the subsurface materials, the detector can provide an indirect measurement of e.g., carbon dioxide concentrations. This capability is important for monitoring geological storage sites for carbon sequestration projects, where accurate tracking of carbon dioxide movement and concentration is important for assessing the efficacy of the storage and the integrity of geological containment barriers.

[0051] The method can be further improved, when the at least one borehole muon detector is configured to estimate the degree of storage or mineralization of fluids and / or gases in the Earth's subsurface to the side or above the detector by measuring changes in the subsurface density.

[0052] Such a method leverages the muon detector's ability to provide detailed density profiles of the subsurface environment. By analyzing the muon data for density variations, scientists can infer the extent of for instance carbon dioxide plume movement or mineralization. This process is important for carbon capture and storage (CCS) as well as mineralization (CCM) technologies, where injected carbon dioxide is expected to be stored in a saline aquifer, depleted reservoir or mineralized over time, effectively trapping it in a solid, sta- ble form within geological formations. Monitoring the degree of mineralization is important for evaluating the long-term viability and safety of CCS and CCM strategies.

[0053] The method can be further improved, when the at least one borehole muon detector is configured to estimate the material properties of natural solids such as rock in the Earth's subsurface to the side or above the detector, preferably the density of natural solids.

[0054] By analyzing how muons are deflected or absorbed by different materials, the detector can infer the density and other related material properties of the for instance rock formations around and above the detector. This is particularly valuable in applications such as assessing the stability of rock for tunneling projects, evaluating potential drilling sites in oil and gas exploration, or understanding geological structures. The ability to determine rock density non- invasively through muon detection provides an important advantage over more traditional methods, which may require physical core sampling or other intrusive techniques.

[0055] To improve the method further, the at least one borehole muon detector is embedded in a cement casing of a wellbore.

[0056] Such a placement ensures that the detector has a fixed, stable position from which to continuously monitor muon flux and gather data on the surrounding geological formations. The cement casing not only protects the detector from physical damage but also minimizes noise and interference from the wellbore environment, which can enhance the accuracy of the muon measurements. This setup is particularly useful for long-term monitoring applications, such as tracking changes in subsurface structures or assessing the efficacy of carbon sequestration processes over time. Embedding the detector in the wellbore's cement casing represents an innovative approach to enhancing the functionality and longevity of muon detection systems in geological exploration and monitoring scenarios.

[0057] To improve the method further, at least two borehole muon detectors are arranged in a fishbone configuration to increase the spatial detection area. Such a fishbone configuration allows for comprehensive coverage of the geological features surrounding the wellbore, providing a more detailed and extensive data set. By deploying multiple detectors in this manner, it becomes possible to capture insights about the subsurface environment, enhancing the ability to detect and analyze variations in geological formations, track changes over time, and assess different material properties at various locations. This setup is advantageous for complex geological assessments, such as evaluating the potential for natural resource extraction or monitoring the integrity and impact of geological storage sites for carbon sequestration. The fishbone arrangement maximizes the use of space within the wellbore while minimizing the need for multiple independent drilling operations, thus offering a more efficient and less invasive approach to subsurface exploration and monitoring.

[0058] This method is improved, when the at least two borehole muon detectors are positioned in a well bore in a depth below 1500 m.

[0059] Such a depth for the fishbone configuration enables thorough coverage of the geological features around the wellbore, resulting in a more detailed and extensive dataset in deeper depths. By arranging multiple detectors in this depth, insights can be gathered about the subsurface environment, improving the detection and analysis of geological formation variations, tracking changes over time, and assessing material properties at various locations even below 1500 m. The term "below” in that sense means depths deeper than 1500 m, for instance 1600 m.

[0060] This method can be further improved, when at least two borehole muon detectors are mechanically linked together to form a chain.

[0061] Such a chained arrangement allows the detectors to maintain a specific relative positioning, which ensures consistent and reliable data collection as the assembly moves through different geological layers or as it is manipulated to explore various sections of a borehole. This configuration is especially useful for conducting detailed, linear scans of geological formations, providing a sequential, integrated view of the subsurface properties. The chain formation also facilitates the deployment and retrieval of multiple detectors simultaneously, enhancing operational efficiency and reducing the time and effort required for setup and data collection. Additionally, this approach can provide a robust framework for detectors, offering added structural support and stability with- in the challenging environment of a wellbore. This method is ideal for extensive and comprehensive muon detection applications, such as long-range geological mapping or continuous monitoring of subsurface conditions over extended periods.

[0062] To improve the method even further at least two borehole muon detectors are mechanically linked together to form a bundle, wherein the diameter of the bundle is bigger than the diameter of the cylindrical housing of one borehole muon detector.

[0063] Such a cylindrical bundle shows an overall increased diameter. The increased diameter of this bundle allows for a broader cross-sectional area to be covered by the detectors as they collect data from the surrounding geological formations. This is beneficial for extensive spatial monitoring and mapping of subsurface properties such as rock density and mineralization. The bundling of detectors maximizes the use of the borehole space, allowing for denser data collection and potentially reducing the number of drilling sites required for comprehensive subsurface analysis. This configuration is ideal for projects requiring high-resolution imaging of geological structures, offering enhanced detection capabilities that can lead to more accurate geological assessments. Additionally, deploying detectors in a bundle can improve the overall durability and stability of the system within the borehole, protecting the detectors against the harsh environmental conditions commonly found in deep-Earth exploration.

[0064] The method is further improved, when at least two borehole muon detectors are electrically linked together to form a connection for electrical signal and power transport.

[0065] Such a method would involve connecting at least two borehole muon detectors via electrical cables or wireless communication interfaces that allow for the seamless transfer of power and data signals. This connectivity ensures that all linked detectors can share power resources and data insights, enabling a cohesive functioning unit. The electrical linking of detectors simplifies the infrastructure required for power supply and data management, as signals can be for instance routed through a central hub, reducing the complexity and increasing the reliability of the system. This approach is advantageous in extensive monitoring setups or in challenging operational environments where maintaining individual power supplies and data connections for each detector would be impractical or inefficient.

[0066] 4. Brief description of the figures

[0067] In the following, preferred embodiments of the disclosure are disclosed by reference to the accompanying figures.

[0068] Fig. 1: illustrates a borehole muon detector set according to the invention in a cross-sectional view.

[0069] Fig. 2: shows an exemplary arrangement of concentrically aligned detections means according to the invention.

[0070] Fig. 3A: depicts a schematic view of a detection means in the form of a circular sector.

[0071] Fig. 3B: depicts a schematic view of a detection means in the form of a square section.

[0072] Fig. 4: shows the relationship of between the muon radiation intensity and the detection depth below the Earth’s surface.

[0073] Fig. 5: depicts an exemplary fishbone configuration of borehole detectors in a schematic view.

[0074] Fig. 6: illustrates the surveillance of CO2 with borehole muon detectors in a schematic view.

[0075] 5. Detailed description of the figures

[0076] The subsequent sections provide a detailed description of the invention, referencing the accompanying illustrations for clarity. The descriptions represent examples only and are not intended to limit the invention's scope. Identical reference numerals across the figures and text denote the same components. The illustrations may not reflect actual size or scale; their dimensions, proportions, and depictions of elements might be enhanced for better understanding and visual convenience.

[0077] Figure 1 illustrates an exemplaiy borehole muon detector too according to the invention. A processing section 120 is arranged inside a cylindrical hous- ing 104 and electrically attached to at least three detection sections 106. Each detection section 106 comprises a multitude of detection means 102. On top and below the muon detector 100 are mechanical links 110 and electrical links 112. The detection means 102 is a coextruded support and scintillator structure.

[0078] Main parts of the detector 100 are housed within a cylindrical structure in form of a housing 104, which is beneficial for borehole instruments to facilitate easy insertion and operation within the cylindrical confines of a wellbore. The processing section 120 is located inside the cylindrical housing 104, this section is important for handling and processing the data collected by the detection means 102. It is electrically connected to other components to manage data flow and analysis effectively. There are at least three detection sections 106 distributed along the length of the detector. Each section contains multiple detection means 102, which are the functional units responsible for detecting the muons. The detection means 102 are the operational units within each detection section that directly interact with muons. They capture muon data such as trajectory and velocity, which are important for the subsequent data processing and analysis. The mechanical links 110 and the electrical links 112 are positioned at the top and bottom of the muon detector too, these links are designed for both mechanical stability and electrical connectivity. The mechanical links 110 ensure the physical integrity of the detector when deployed, especially when multiple detectors are linked in series or in a bundle. The electrical links 112 are necessary for the transfer of power and data signals between linked detectors or to the surface. The integration of a dedicated processing section 120 within the detector too allows for immediate and efficient processing of muon detection data, enhancing the speed and accuracy of subsurface evaluations. The distribution of multiple detection sections 106 along the detector too optimizes the spatial coverage of muon detection, ensuring a comprehensive analysis of the surrounding geological structures.

[0079] Figure 2 depicts an exemplary muon detector 200 with concentrically arranged detection means 202. The detector 200 comprises at least six detection sections 206, wherein each detection section comprises 21 detection means 202. Six detection means are arranged in an inner circle 210 and 15 detection means are arranged in an outer circle 208. A muon trajectory 10 is depicted on its way through the muon detector 200. Here, the detection means 202 are shaped as rectangular cuboids.

[0080] The detector 200 features detection means 202 organized in concentric circles, which is a strategic setup to capture muon data from different angles and directions, enhancing the spatial resolution of the data. There are at least six detection sections 206 in the detector 200, with each section containing 21 detection means 202. Such an arrangement can ensure comprehensive coverage and high sensitivity to muon activity. Within each detection section 206, six detection means 202 are arranged in a smaller, inner circle 210, while 15 detection means 202 are placed in a larger, outer circle 208. This configuration not only maximizes the detector's spatial coverage but also varies the density of detection means 202, which can be important for resolving different muon flux intensities and patterns. Having multiple detection sections 206 with a number of detection means 202 enhances the detector's ability to gather extensive data within a single pass, improving the efficiency and accuracy of subsurface mapping and monitoring. The specific layout of detection means 202 in inner 210 circles and outer circles 208 facilitates a nuanced approach to capturing muon trajectories, enabling precise measurements of muon attenuation and absorption, which are important for accurate density and material property estimations.

[0081] Figure 3A depicts a schematic view of a detection means 302 in the form of a circular sector. The scintillator 304 is arranged between the bars of the support structure 306.

[0082] The detection means 302 is designed in the form of a circular sector, similar to a slice of a cake. This shape is ideal for composing a full circular detection array when multiple sectors are combined, efficiently using the internal space of the cylindrical detector housing. The support structure 306 comprises bars that hold the scintillator 304 in place, ensuring its stability and optimal positioning within the detection means 302. The support structure 306 is necessary for maintaining the integrity and functionality of the scintillator during operational conditions.

[0083] Figure 3B depicts a schematic view of a detection means 312 in the form of a square section. The support structure 316 is arranged around the scintillator 314- The square cross-section of the detection means 312 allows for efficient packing, maximizing the use of space. This design can be beneficial when arranging multiple detection means, ensuring uniform coverage and minimizing gaps. The support structure 316 ensures that the scintillator is securely held in place, which is important for consistent and reliable detection of muons. It can also help to protect the scintillator from damage and misalignment, which could otherwise affect the accuracy of muon detection.

[0084] Figure 4 shows the relationship of between the muon radiation intensity 400 and the detection depth below the Earth’s surface. It is clear, that the deeper Earth muons travel below the Earth’s surface, the lower is their intensity.

[0085] This is because muons lose energy and are absorbed by the material they pass through: the deeper the material layer, the greater the attenuation of muon intensity. This relationship between muon intensity and depth allows to calibrate muon detectors for different depths, optimizing them for specific geological conditions. By measuring how muon intensity varies with depth the density and composition of the materials the muons have passed through can be deducted.

[0086] Figure 5 depicts an exemplary fishbone configuration 5000 of borehole detectors 500 in a schematic view. The borehole 50 has various branches 50 that branch off from the main borehole 50 in various angles. In each branch sits a borehole muon detector 500 and the borehole muon detectors 500 are all connected with each other with electrical links 512.

[0087] The main borehole 50 is the primary shaft into which the borehole muon detectors 500 are initially deployed. Extending from the main borehole 50, the branches 52 are drilled at various angles to cover a broader area and provide more detailed subsurface data. Here, each branch holds one borehole muon detector 500. The borehole muon detectors 500 are placed in each branch 52, and these detectors might be located to maximize the geological information gathered from different segments of the Earth surrounding the main borehole. The electrical links 512 connect all the borehole muon detectors 500 with each other, facilitating the efficient transmission of power and data between the units. By deploying the detectors 500 in a fishbone configuration 5000, an enhanced spatial coverage is achieved in the geological structures surrounding the main borehole 50. Figure 6 illustrates the surveillance of carbon dioxide (CO2) stored in the subsurface with borehole muon detectors in a schematic view. On the top of the Earth’s surface 630 is a CO2 injection tank 622, which injects CO2 in the CO2 storage location 620 below the Earth’s surface. A borehole 60 comprises a chain of detectors 610, the chain 610 comprising at least six borehole muon detectors 600. A second borehole 62 comprises a chain of detectors 612, the chain 612 comprising at least six borehole muon detectors 602. The trajectory 10 of a muon through the Earth’s surface is depicted.

[0088] Located at the Earth's surface 630, the CO2 injection tank 622 is responsible for injecting CO2 into a designated storage area 620 below the Earth's surface 630. The tank facilitates the controlled delivery of CO2 into the subsurface, where it is intended to be temporarily or permanently stored. The CO2 storage location 620 is the subsurface zone where injected CO2 is stored. The boreholes 60 and 62 house the chains of muon detectors 610 and 612. Each borehole allows placement of the detectors 600 and 602 close to or within the CO2 storage area 620. Each chain 610 and 612 consists of at least six borehole muon detectors 600 and 602. These detectors are linked together to form a continuous monitoring system that can detect and analyze changes in the density of the subsurface environment, which may indicate movement, leakage or mineralization of CO2. The use of chains of muon detectors in boreholes allows for ongoing surveillance of the CO2 storage.

[0089] Reference list: io: muon trajectory

[0090] 50, 6o, 62: borehole

[0091] 52: branches

[0092] 100, 200, 500, 600, 602: borehole muon detector

[0093] 102, 202, 302, 312: detection means

[0094] 110: mechanical links

[0095] 112, 512: electrical links

[0096] 120: processing section

[0097] 104: cylindrical housing

[0098] 106, 206: detection section

[0099] 208: outer circle

[0100] 210: inner circle

[0101] 304, 314: scintillator

[0102] 306, 316: support structure

[0103] 400: muon intensity

[0104] 610, 612: chain of detectors

[0105] 620: CO2 storage

[0106] 622: CO2 injection tank

[0107] 630: Earth’s surface

[0108] 5000: fishbone configuration

Claims

CLAIMS1. A borehole muon detector for deployment in wellbores, comprising: a cylindrical housing; a processing section, dedicated for data processing; at least one detection section with at least two detection means, wherein each detection means is preferably a coextruded support and scintillator structure.

2. The borehole muon detector according to claim i, wherein the detection means are circumferentially arranged in the housing in at least a first and a second circle, wherein the first circle has a bigger radius than the second circle and the second circle is arranged concentric in the first circle.

3. The borehole muon detector according to claim 2, wherein the first circle comprises at least 15 detection means and the second circle comprises at least 5 detection means, and the number of detection means is higher in the first circle than in the second circle.

4. The borehole muon detector according to the claims 2 or 3, wherein the number of detection means in the first circle is at least 2 times the number of the detection means in the second circle, preferably at least 2,5 times, even more preferably at least 3 times.

5. The borehole muon detector according to any of the preceding claims, wherein at least one detection means has the shape of a cuboid, preferably a rectangular cuboid.

6. The borehole muon detector according to any of the preceding claims, wherein at least one detection means comprises a rectangular crosssection and wherein the detection means is twisted along a helical path.

7. The borehole muon detector according to any of the preceding claims, wherein at least one detection means has the shape of a cylinder, preferably a round cylinder.

8. The borehole muon detector according to any of the preceding claims, wherein at least one detection means comprises a cross section in form of a circular sector.

9. The borehole muon detector according to any of the preceding claims, wherein the housing comprises a circular cross section.

10. The borehole muon detector according to any of the preceding claims, wherein the support and scintillator structure are formed by the same base material, preferably one or a combination of polystyrene, polyvinyl toluene, polyethylene naphthalate.

11. The borehole muon detector according to any of the preceding claims, wherein the support structure comprises a reflective surface configured and dedicated to reflecting photons into the scintillator, wherein the surface is preferably white and opaque.

12. The borehole muon detector according to claim 11, wherein the reflective surface comprises titanium dioxide.

13. The borehole muon detector according to any of the preceding claims, wherein the total number of detection means inside a detection section is in the range 1 to 1200, preferably in the range 30 to too, even more preferably in the range 50 to 75.

14. The borehole muon detector according to any of the preceding claims, wherein the detector comprises at least two, preferably at least 4, more preferably at least 8, even more preferably 16 and most preferably at least 32, detection sections and the detection sections are stacked on top of each other in the insertion direction of the housing.15- The borehole muon detector according to any of the preceding claims, wherein the length of the housing is in the range 0.2 m to 2.6m, preferably in the range 2 m to 2.4 m, more preferably in the range 2.1 m to 2.3 m.

16. The borehole muon detector according to any of the preceding claims, wherein the outer diameter of the housing is in the range 10 mm to 240 mm, preferably in the range 40 mm to 80 mm, more preferably in the range 50 mm to 70 mm.

17. The borehole muon detector according to any of the preceding claims, wherein the weight of the detector is in the range 1 kg to 20 kg, preferably in the range 12 kg to 18 kg, more preferably in the range 14 kg to 16 kg.

18. The borehole muon detector according to any of the preceding claims, wherein the power consumption of the processing section during operation is in the range 0.1 W to 9 W, preferably in the range 3 W to 7 W, more preferably in the range 4 W to 6 W.

19. The borehole muon detector according to any of the preceding claims, wherein the detector further comprises a seismic detector for merging muon detection data with seismic data.

20. A method of detecting muons, the method comprising: providing at least one borehole muon detector according to any of the preceding claims; position the at least one borehole muon detector in a well bore; measuring the trajectory and velocity of the muons in the muon detector.

21. The method of detecting muons according to claim 20, wherein the at least one borehole muon detector is positioned in a well bore in a depth shallower than 300 m, preferably shallower than 800 m, more preferably shallower than 1500 m.

22. The method of detecting muons according to any of the claims 20 or 21, wherein the at least one borehole muon detector is configured to estimate the concentration of fluids and / or gases in the Earth's subsurface to the side or above the detector by measuring the subsurface density.

23. The method of detecting muons according to claims 20 to 22, wherein the at least one borehole muon detector is configured to estimate the degree of storage or mineralization of fluids and / or gases in the Earth's subsurface to the side or above the detector by measuring changes in the subsurface density.

24. The method of detecting muons according to any of the claims 20 to 23, wherein the at least one borehole muon detector is configured to estimate the material properties of natural solids (such as rock) in the Earth's subsurface to the side or above the detector, preferably the density of natural solids.

25. The method of detecting muons according to any of the claims 20 to 24, wherein the at least one borehole muon detector is embedded in a cement casing of a wellbore.

26. The method of detecting muons according to any of the claims 20 to 25, wherein at least two borehole muon detectors are arranged in a fishbone configuration to increase the spatial detection area.

27. The method of detecting muons according to claim 26, wherein the at least two borehole muon detectors are positioned in a well bore in a depth below 1500 m.

28. The method of detecting muons according to any of the claims 20 to 27, wherein at least two borehole muon detectors are mechanically linked together to form a chain.

29. The method of detecting muons according to any of the claims 20 to 28, wherein at least two borehole muon detectors are mechanically linked together to form a bundle, wherein the diameter of the bundle is biggerthan the diameter of the cylindrical housing of one borehole muon detector.

30. The method of detecting muons according to any of the claims 20 to 29, wherein at least two borehole muon detectors are electrically linked together to form a connection for electrical signal and power transport.

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