Embedded optical fiber system for multicomponent borehole geophysical measurement

Abstract

Systems and methods for embedded optical fiber system for multicomponent borehole geophysical measurement that can include a sensing head; a set of winding guides routed in an inclined path around the sensing head; and a set of optical fibers, where at least one optical fiber is routed along a path of a winding guide in the set of winding guides.

Description

EMBEDDED OPTICAL FIBER SYSTEM FOR MULTICOMPONENT BOREHOLEGEOPHYSICAL MEASUREMENTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of U.S. Provisional Application No. 63 / 621,319, filed on 16-JAN-2024, which is incorporated in its entirety by this reference.TECHNICAL FIELD

[0002] This invention relates generally to the field of geophysical sensing and more specifically to a new and useful system and method for an embedded optical fiber system for multicomponent borehole strain measurement.BACKGROUND OF THE INVENTION

[0003] There is ever increasing interest in improving sensing and monitoring of underground phenomena associated with human activity, such as well operations for fluid extraction or storage, as well as natural processes such as seismicity and volcanic activity. Strainmeters such as the Sacks-Evertson dilatometer (a reluctance transducer) and / or a Gladwin tensor strainmeter have been used in the past, but these sensing technologies lack the sensing fidelity, bandwidth, configurability, and robustness to be used for advanced applications and long-term operation. Some may only provide one discrete measurement interval when deployed in a borehole. These sensing technologies additionally are limited in their availability.

[0004] Thus, there is a need in the geophysical sensing field to create a new and useful system and method for an embedded optical fiber system for multicomponent borehole geophysical measurement. This invention provides such a new and useful system and method.BRIEF DESCRIPTION OF DRAWINGS

[0005] FIGURE 1 is a schematic representation of a system.

[0006] FIGURE 2 is a detailed schematic representation with a partial cross-sectional view of a sensing element.

[0007] FIGURE 3 is a vertical cross-sectional representation of a portion of a sensing element with winding guides inset into the sensing head 110.

[0008] FIGURE 4 is a top cross-sectional view illustrating the winding patterns and stress concentrators of a system variation.

[0009] FIGURES 5A-5E are exemplary cross-sectional views of different winding guide patterns.

[0010] FIGURE 6 is a perspective view of an inclined helical path of an optical fiber with an elliptical cross section.

[0011] FIGURE 7 is a perspective view of three inclined helical paths of optical fibers with elliptical cross sections offset from each other.

[0012] FIGURE 8 is a schematic representation of two instances of sensing tools used in-line of each other.

[0013] FIGURES 9 and 10 are flow diagrams of exemplary methods.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The following description of the embodiments of the invention is not intended to limit the invention to these embodiments but rather to enable a person skilled in the art to make and use this invention.1. Overview

[0015] A system and method for a geophysical measurement function to use a fiber optic-based measurement tool to sense and monitor deformation of the ground with high resolution. The system employs a novel design of the sensing element to allow for the embedding of one or more optical fibers and the modification of its material properties such that the system can resolve geophysical conditions oriented along one ormore axes of deformation. In particular, the systems and methods may be used for monitoring a variety of geophysical conditions.

[0016] In one particular variation, the system and method may be implemented as a strainmeter for use within a borehole (from subsurface drilling) and used in measuring a strain tensor within the ground. The system may measure deformation in situ. The system and method maybe implemented as a meter for any suitable type of geophysical sensing. Additionally, the system may measure multiple components such as vertical strain and horizontal strain in multiple orientations. The system and method can preferably provide a measurement of a geophysical tensor using a passive optical fiber sensing solution, thereby functioning as a multi-directional point sensor. Furthermore, the design of the system and method enables such optical sensing that is spread out over a length of a sensing unit.

[0017] The sensed strain signals may be used to estimate the geometry, as well as the hydraulic and elastic properties of a geologic reservoir. The sensor data input may be used to characterize a variety of subsurface conditions such as fluid flow, strain, seismic stress, pressure, and / or other properties. For example, the system maybe used to monitor the location of injected fluids or other sources of disturbances.

[0018] The systems and methods may be used in a variety of applications and fields such as active well operations monitoring (e.g., for pumping or injection of fluids), hydraulic fracture operations monitoring, active-source geophysical surveys of subsurface imaging, monitoring loads applied to the ground surface (person, vehicle, etc.), monitoring natural processes (e.g., earthquakes, volcanic processes, ambient environmental processes like precipitation and barometric pressure fluctuations, etc.), and / or other areas of use.

[0019] The system preferably includes one or more sections where optical fiber is wound in an inclined helical path. The helical path in some variations has an elliptical cross section but other biased shape profiles may alternatively be used. There may be multiple windings with biased (e.g., elliptical) cross sections oriented for different sensing directions. As one design variation, the system may include one or more inclined helical grooves or guides with an elliptical cross section that serve as winding guides for the desired number of optical fibers.

[0020] As another design variation, the system may include defined voids or regions at one or more locations through the sensing element that can be filled with differing materials to modify the strain or force transfer to the optical fibers. These function as stress concentrator structures to enhance the sensing capabilities of the system. The voids may additionally or alternatively serve as conduits through the system, which may, in some variations, be used for connecting multiple system instances in-line within a well.

[0021] The system may be used as a geophysical sensor to sense a variety of geophysical phenomena, such as displacement, stress, strain, strain rate, velocity, pressure, deformation, vibration, or any poroelastic, acoustic or seismic phenomena in the subsurface.

[0022] The system maybe used in place of a geophone, seismometer, accelerometer, extensometer, Fiber Bragg Grating system, Distributed Acoustic Sensing system, Distributed Strain Sensing system, or pressure transducer.

[0023] The system may be used as a geophysical sensor at shallow well depths to monitor fluid migrations at much greater depths. The system may be used to characterize geologic storage reservoirs, conventional petroleum reservoirs or aquifers, and / or other subsurface ground regions. In particular, the system maybe used to detect and monitor leakage pathways in a geologic storage reservoir. The system for example maybe used to monitor for leaks from geologic carbon storage reservoirs.

[0024] The system and method may provide a number of potential benefits. The system and method are not limited to always providing such benefits and are presented only as exemplary representations for how the system and method may be put to use. The list of benefits is not intended to be exhaustive, and other benefits may additionally or alternatively exist.

[0025] As one potential benefit, the system is a passive sensing approach that may be implemented without downhole electronics. The system may use optical fiber with optical fiber interferometry for measuring. This may make the system particularly robust for the intense downhole environments.

[0026] As another potential benefit, the system may be more easily manufacturable, which can enable the system to be produced in a cost-effective manner such that it maybe deployed more widely. Additionally, the system may be well adapted for deployment alongside existing downhole systems used for petroleum and / or carbon storage operations.

[0027] As another potential benefit, the system may enable enhanced sensing capabilities. The system could enable sensing at different well intervals (e.g., sensing at multiple distinct well interval regions). The system may enable sensing geophysical properties (e.g., strain) along multiple axes / orientations. In some variations, multiple instances of the system may be used in series (at different downhole positions) such that sensing can be conducted at different depths. The system may additionally enable high resolution sensing, which in some variations can be implemented as real-time sensing.

[0028] As another potential benefit, the system may provide better subsurface leak detection as a result of sensor sensitivity and enhanced capabilities for monitoring a site. The system maybe able to detect small leaks and / or detect leaks more quickly.2. System

[0029] A system for a downhole optical sensor system may include a sensing head 110 and optical fiber 130 wrapped in a helical pattern around the sensing head 110. In particular, the wrapping pattern may be configured for multiple oriented inclined helically wrapped fibers with a cross-section pattern having a biased shape such as an elliptical shape. This can result in enhanced optical interrogation for measuring geophysical properties like strain in multiple orientations / directions.

[0030] The system may be specifically used for a downhole optical sensing system for geophysical. The system may be compatible and used in connection with other geophysical drilling technologies.

[0031] In one variation, the system for a downhole optical sensing system can include a sensing head 110, a set of winding guides 120 routed in an inclined path around the sensing head no; and a set of optical fibers 130, where at least one optical fiber is routed along a path of a winding guide in the set of winding guides.

[0032] The optical fiber 130 is integrated into the downhole bore device by being wound in a carefully controlled, inclined helical pattern. The pattern can have a constantor varied cross sectional shape profile that is biased in one or more directions. The bias enables better optical sensing of strain or other forces along a particular direction / dimension. As described herein, an elliptical shape is one example of a biased shape profile that may be used as the cross-sectional shape. The ellipse is used as a primary example herein, though alternative biased shape variations such as those discussed herein may alternatively be used. As such, as one skilled in the art could appreciate, reference to an elliptical shape profile does not limit the description to such a shape profile and alternative biased shape profiles may alternatively be used.

[0033] Using an elliptical helical wrapping pattern aligned in different orientations results in deformations of the fiber (e.g., changes in length) differing depending on the directions of the strain or deformations experienced at the sensing head 110. There may be a different fiber for each direction / orientation. In some variations, the system maybe configured for sensing in two or more orientations. For example, optical fibers 130 with helical patterns with cross-sectional shape profiles oriented in two distinct orientations maybe used for sensing in two orientations. In another example, optical fibers 130 with helical patterns with cross-sectional shape profiles oriented in three distinct orientations may be used for sensing in three orientations.

[0034] The system may be used in connection with an optical interrogator 140 and an additional or integrated analysis system that may be configured for use with the optical sensing system. The optical interrogator 140 functions to transmit and / or receive light through the optical fibers of the system so as to perform optical fiber interferometry. The system maybe used with any suitable type of optical interrogator 140. The optical fiber 130 can extend up to interface with the optical interrogator 140 or some system to manage optical sensing. The optical interrogator 140 may periodically or continuously read measurements. In some implementations, an optical interrogator 140 may make redundant measurements for improving accuracy of a reading. The optical interrogator 140 may also take one-off measurements in response to some triggering event.

[0035] In some variations, the sensing head 110 may include a winding guide with defined cavity, recesses, protruding guides, or other suitable structural features to establish the helical winding pattern along the sensing head 110.

[0036] The system may additionally include a set of stress concentrators 150 integrated within the helical winding pattern of the winding guide 120 / optical fibers 130 to enhance optical sensing of deformations / strain.

[0037] The helical pattern of optical fibers 130 wrapped around the sensing head 110 (as guided by the winding guides 120) may be embedded within a protective housing such as an external pressure casing 112 described herein or directly adhered or integrated into a bore surface. The system may include additional coatings or buffer layers around the fiber, which may be included to enhance durability and thermal stability.

[0038] The system is preferably used to measure a strain tensor and / or displacement field. More generally, the system may be used to measure any suitable geophysical measurement. This geophysical measurement can be a tensor with multiple directional components. The system may additionally include additional sensing elements that can be integrated into the sensing head or other component.

[0039] In particular, the system maybe applied to sense subsurface conditions to better monitor fluid migrations at much greater depth. This may be used to characterize geologic storage reservoirs, conventional petroleum reservoirs, and / or aquifers or any type of geologic formation. The system maybe used to detect reservoir conditions including but not limited to presence of evidential leakage pathways and / or leakage out of reservoirs.

[0040] The system is preferably used and installed as a subsurface geophysical sensor system. The sensing element may be installed at shallow depths, though they may be used at any suitable depth.

[0041] The sensing head 110 functions as the main structure where sensing occurs. The sensing head 110 is preferably configured to be deployable in a borehole. Accordingly, the sensing head 110 is designed to be exposed to the subsurface environment where it may experience strain, temperature, and / or other conditions. The sensing head 110 maybe used to measure strain, pressure, temperature, and / or other subsurface conditions.

[0042] The sensing head 110 can be a component with a design profile for being deployed downhole. It may be designed to fit within a well pipe or around a well pipe. Itmay alternatively be part of a section of pipe deployed down hole. The sensing head no can be an axially integrated measurement system. In one exemplary variation, the sensing head no may additionally be part of some other downhole equipment serving an additional function in addition to the sensing capabilities enabled through the system herein. As an axially integrated sensing element, the sensing head no can be designed to have a defined through channel which may function to avoid obstructing use of a pipe.

[0043] The sensing head 110 maybe a substantially cylindrical structure made of a material or materials suitable for down hole environments. In one variation, a main structural component of the sensing head no maybe a stainless-steel cylinder.

[0044] A sensing head no may include optical fiber windings for measurement of multiple orientations. The different orientations are preferably orthogonal orientations though any suitable set of orientations may be used.

[0045] A sensing head no may alternatively include fiber windings configured for one orientation. In this variation, the system may make use of multiple sensing heads no with each head having their primary sensing orientation arranged so that a desired set of orientations may be monitored using multiple sensing heads no. The multiple sensing heads no maybe integrated within one integrated component. Alternatively multiple instances of the sensing system can be used in combination where multiple instances can be used at different sections of a well.

[0046] The sensing head 110 may be designed in a variety of heads. As one variation the sensing head 110 includes at least a sensing element for use with optical fiber. In another variation, the sensing head no may include a sensing element that includes or is a winding guide as described herein.

[0047] In some variations, the sensing head no is a sensing element with the wound optical fiber that is encased or otherwise interfaces with an external pressure case 112. The external pressure case 112 as shown in FIGURE 1 functions as a protective casing for use in a borehole. The external pressure casing may encase the sensing head and provide an external structural barrier that shields the optical fiber from direct exposure to the downhole external environment. Strain and stress can preferably be mechanically transferred through the external pressure casing 112 for sensing by the system.

[0048] The sensing head 110 with the external pressure casing maybe deployed in a borehole and coupled to the surrounding formation using an expanding cement mixture or by being driven into an undersized hole. Deformation of the enveloping material due to external forces (e.g., fluid injection into a nearby reservoir) can be transmitted through the pressure case and to the sensing element that is bonded to the inner diameter of the external pressure casing. The sensing element contains one or more lengths of optical fiber whose length(s) change due to deformations in the pressure case caused by strain changes in the formation.

[0049] The winding guide 120 functions to enforce or otherwise guide optical fibers 130 in a designed winding pattern. As discussed, the winding pattern around the sensing head 110 is preferably an inclined helical pattern that is axially aligned with the sensing head 110 (and thereby substantially axially aligned with a cross section of a bore hole).

[0050] -A winding guide 120 can be disposed on and extend in an inclined path around the sensing head 110. The path is preferably a circumnavigating helical or spiraling inclined path. This path may also be a continuous loop that goes from a top (or proximal) end of the sensing head 110 to a bottom (or distal) end of the sensing head no and back to the top so that an optical fiber can be routed so that both ends of the fiber are terminated at or above the top of the sensing head 110 (e.g., at an optical interrogator 140).

[0051] In a variation where the system includes an optical interrogator 140, the optical fibers 130 can interface with the optical interrogator 140 on both ends of each optical fiber 130. As such, each optical fiber maybe wound to form a continuous optical path from the optical interrogator system, through at least one winding guide in the sensing head 110, and back to the optical interrogator system 140. This continuous optical path is routed through or along a path defined by the winding guide(s) 120.

[0052] In some variations, the system includes a set of winding guides 120. The winding guide 120 can include one or more guides. Accordingly, the set of winding guides 120 maybe a singleton set where it is a set of a single winding guide 120.However, in other variations, the set of winding guides 120 can include multiple winding guides 120 with individually customized paths around the sensing head no.

[0053] A winding guide 120 could be a groove or recessed channel with a width greater than the diameter width of the optical fiber 130. As shown in a cross -sectional representation of FIGURE 3, the winding guides 120 maybe inset grooves in the side of the sensing head no or some other structural body of a winding guide 120. The optical fiber can be wrapped and set to a desired path. The winding guide 120 extends along or at least partially defines the winding path. A channel variation of a guide maybe recessed into an outer surface of the winding guide 120. A guide variation could alternatively be formed by a channel protruding out from a main outer surface of the winding guide 120. In other variations, the guide could be a ridge restricting fiber movement at least partially. An outer wrapping or covering may secure or lock optical fiber windings into place after the winding is established. The guide may be continuous along the path. A guide may alternatively be intermittent or otherwise include breaks.

[0054] As an alternative variation, the optical fiber 130 may be wrapped without any pre-existing winding guide 120. Instead the manufacturing process of the system may wrap the optical fibers 130 in a desired path around a sensing head 110. In such variation, the position of the optical fibers 130 may then be fixed or restricted by some other material or structure that can fix or lock the position of the optical fibers 130. For example, an external layer be adhered, deposited, molded, or otherwise formed on top of wrapped optical fibers 130.

[0055] The winding guide 120 defines an inclined path around the sensing head 110. More specifically, the inclined path is an inclined helical path, where the winding guide promotes a spiraling circumnavigating path around the sensing head 110. Being an inclined helical path can mean structural elements of the winding guide 120 (recessed cavities, defined tunnels, protruding guides, etc.) fully or partially define an inclined helical path. The defined path can define a spiral path down the sensing head and return spiral path up the sensing head.

[0056] This helical configuration can define the path of the winding guide and thereby the path of the routed optical fiber 130 such that the path is spirally wrapped around the longitudinal axis of the device at an inclined / oblique angle relative to the longitudinal axis. As shown in FIGURE 6, a winding guide 120 maybe used to promote a resulting inclined helical path of an optical fiber. The inclination angle of the helix maybe specifically engineered to optimize strain sensitivity and minimize external interference, ensuring accurate signal transmission and data collection. The helical pattern may also be used to enhance sensing along a targeted dimension.

[0057] As a result of the path of the winding guide(s) 120, the optical fiber 130 is integrated into the downhole bore device by being wound in a carefully controlled, inclined helical pattern. The helical pattern of the winding guide 120 thereby enforces, promotes or otherwise results in a conforming path of the optical fiber. As such the optical fiber may similarly be described as being routed around the sensing head 110 with similar paths.

[0058] The routing path of the optical fiber forms a continuous helical loop that progresses along the length of the tool. The angle of inclination of the helix may vary depending on the application requirements, such as maximizing sensitivity in a particular stress or strain direction.

[0059] The pitch (i. e. , the angle of inclination) and spacing of the helical path may be adjusted or used to alter sensing capabilities or properties of the tool. These parameters may be constant throughout the length of the device, or they may vary in a tailored gradient to address region-specific sensing requirements. For example, a tighter pitch could be applied in sections of the bore expected to experience higher stress concentrations, while a looser pitch could be employed in more stable sections to reduce material usage and manufacturing complexity.

[0060] In some variations, the cross-sectional profile of the optical fiber path is elliptical rather than circular. Accordingly, the inclined helical path may have an elliptical cross-section (i.e., substantially elliptical cross section) of a longitudinal axis of the sensing head no. This cross-sectional shape is the shape formed from a projected view of the winding guide path (or optical fiber) viewed perpendicular to the longitudinal axes.

[0061] This elliptical profile may enhance the coupling efficiency of stress or strain into the fiber core, biasing sensing along one dimension or direction. The major and minor axes of the elliptical cross-section can be aligned strategically to amplify specific stress responses and / or reduce undesired modes of interaction.

[0062] As used herein, the term 'substantially elliptical' refers to a cross-sectional shape that approximates an ideal ellipse with deviations that do not exceed 10% of the geometric properties of a perfect ellipse, as measured by the aspect ratio, perimeter deviation, or focal point alignment. Specifically, a shape may be considered substantially elliptical if its major-to-minor axis ratio deviates by no more than ±10%, the perimeter deviation is less than 10% when compared to a corresponding perfect ellipse, or the mean squared error of a best -fit ellipse determined by least -squares fitting is less than X. As discussed, other shapes may also be used.

[0063] More generally, the cross-sectional shape of the helical pattern may be a biased shape. A biased shape may include substantially elliptical shapes, rose shapes, cardioid shapes, and / or other non-circular shapes that would serve as biased shape profiles as shown in examples of FIGURES 5A-5E. Accordingly, the helical path may have a rose, cardioid, or other biased-shape cross-section along the longitudinal axes of the sensing head 110.

[0064] A substantially biased shape used for the cross-sectional shape of the winding guide 120 functions to create biased reactions to stress and strain experienced by the optical fiber 130 following the path of the winding guide 120. As used herein, 'biased shapes' refer to any non-circular closed forms that exhibit directional asymmetry, where geometric properties such as radius or curvature vary non-uniformly with angular direction. This includes, but is not limited to, substantially elliptical shapes, rose-like shapes characterized by sinusoidal radial oscillations, and cardioid-like shapes with heart-like profiles. Such shapes are distinguished by their preferential extension or compression along one or more axes, quantified by a radial variation exceeding 10% relative to a reference geometry or by other mathematical measures of asymmetry.

[0065] Cardioid-like shapes may refer to shape profiles, such as the example of FIGURE 5C, characterized by a heart-like appearance, mathematically represented as r = a(i + cos(0)) or equivalent formulations. Rose-like shapes may refer to shape profiles, such as the example of FIGURE 5E, characterized by sinusoidal radial oscillations, described mathematically as r = acos(k0) or similar expressions, where k determines the number of lobes.[oo66] As shown in the examples, any number of suitable winding guide patterns may be formed. In FIGURE 5A, three winding guides form three elliptical cross- sectional shape profiles offset by 6o°. In FIGURE 5B, two elliptical cross sectional shape profiles are offset by 90°. Alternative forms may also be used such as the biased-shape with a tear-like shape profile shown in FIGURE 5D.

[0067] In some variations, the biased shape may vary or change. Different sections may follow different biased shape patterns. Alternatively, a biased shape gradient may have gradually varied shape profile parameters as a function of position in the longitudinal direction.

[0068] The system may include a set of winding guides 120 which may include a singleton set of winding guides 120 with a single winding guide but may also include multiple winding guides 120 (e.g., at least two winding guides), wherein each winding guide 120 maybe configured to orient optical fibers along distinct paths. The multiple winding guides are configured with offset orientations of elliptical cross-sections, allowing optical fibers to sense one or more geophysical property like strain in multiple directional orientations. In particular, the biased-shape profiles may be offset to align in different directions. In the exemplary variation of an elliptical cross-sectional profile, the minor and major axes of elliptical cross sections of two winding guides 120 maybe aligned in different directions. For example, these maybe aligned with offsets that are offset by 90°, 6o°, 450, 30°, or some other suitable angular offset.

[0069] The path of a winding guide 120 is preferably an axially aligned helical path. The helical path may make several circumnavigating paths around a defined center. When there are multiple winding guides 120, they maybe substantially axially aligned but could alternatively have different axial centers.

[0070] Multiple winding guides 120 be offset such that the optical fiber paths do not intersect directly routed. As shown in the example of FIGURE 7, three inclined helical winding guides 120 that have elliptical cross sections offset by 6o° can promote three separate paths for optical fibers wrapped around the sensing head 110. In some variations, multiple winding guides may have intersecting paths, but the optical fibers maybe wrapped so that they overlay each other.

[0071] Different approaches maybe used to avoid direct intersections of the optical fiber when wrapped around the winding guides 120. In one variation, the pitch of an elliptical winding guide (or other path for the optical fiber) in the axial direction maybe larger than the space occupied by the grooves of the paths from the other offset azimuths. In this way all the paths, assuming they are the same (e.g. all ellipses) follow each other up the cylinder without intersecting.

[0072] In another variation, the system may use configuration with the diameters of each subsequent angular path at least one fiber diameter larger than the previous. In this way the fiber from a second path lays over a first, and a third over the first and second, and so on.

[0073] In one variation, the winding guide may be directly integrated into the body of the sensing head no. In this variation, the sensing head 110 maybe a structural body and the winding guide(s) may be structural features of that body.

[0074] In another variation, the winding guide maybe a component that connects or otherwise interfaces with the sensing head 110 and / or an external casing 112. In one such variation, the winding guide 120 may include a central cavity such that the winding guide 120 functions as a sleeve that can go around an inner pipe or structure. Similarly, variations of the winding guide 120 may be such that the winding guide 120 fits within an external pipe or structure such as an external pressure case.

[0075] In another variation, the winding guide(s) 120 may be machined or otherwise manufactured onto an outer surface of a sensing head 110. Subtractive manufacturing, additive manufacturing, and / or molding maybe used. For example, a CNC lathe maybe used to mill the helical winding patterns onto a steel pipe. In another example, the winding guide 120 and / or a structure of the sensing head 110 maybe 3D printed or otherwise produced.

[0076] In one variation, the sensing head 110 may include defined guides for fiber winding integrated into the structure of the sensing head no. For example, a sensing head 110 that is 3D printed may include internal defined open channels through which optical fiber may be threaded.

[0077] In another variation, the sensing head 110 may have a base structure and then an outer casing molded or encased around the base structure so as to fix the winding pattern of the fiber cable.

[0078] The optical fiber cable or more succinctly the optical fiber 130 functions as an optical connection between the sensing head 110 (or site of sensing) and a connected optical interrogation system. The optical fibers 130 additionally functions as a conduit for sensing strain and deformation by way of its change in optical properties resulting from deformation. One or more optical fibers are preferably used.

[0079] The system may include one or more optical fiber cables that establish a continuous roundtrip optical path from the interrogator to the sensing head 110 and back to the optical interrogator. In some variations, this is a single continuous optical fiber cable. In other variations, it may be a series of interfacing optical fiber cables. Any suitable type of optical fiber cable may be used. Preferably, the optical fiber cable is one suitable for the optical path required for the desired depths of sensing and can survive conditions of the host environment.

[0080] The number of optical fibers contained within the cable may depend on the number of sensed orientations and / or the number of sensing heads 110. In a variation with multiple winding guides 120, at least one optical fiber may be operably associated with the set of winding guides 120, wherein each optical fiber 130 is routed to follow the path defined by at least one winding guide 120 in the set of winding guides 120. In one variation, there is one single optical fiber for a given path. In another variation multiple optical fibers may be guided along the same path either as individual fibers or as an integrated bundle of optical fibers.

[0081] In one variation, the optical fiber is bundled as a cable that includes the input and output portions of the optical fiber making the path from an optical interrogator to the sensing head 110. When the optical fiber reaches or is in proximity to the sensing head 110, the optical fibers of the cable can be separated to follow their helical path before looping back into the cable.

[0082] As the sensing head 110 may be deployed at some depth within a well, the optical fibers 130 may be bundled into an integrated cable that is passed through connecting equipment to a proximal end of a sensing head 110. The integrated cable ofoptical fibers 130 may be separated to be routed through their corresponding winding guides 120 at the sensing head 110. A return path of optical fibers 130 may similarly be integrated into the same integrated cable or into its own collected cable. Alternatively individual optical fibers, bundles of fibers, or other sub-groupings of optical fiber cables may be used.

[0083] The optical fibers 130 maybe connected, optically coupled, or otherwise integrated with an optical interrogator system 140, which maybe configured to analyze signals transmitted through the optical fibers 130. The optical interrogator 140 functions as an active system that facilitates analyzing the optical signals transmitted through the optical fibers to measure and interpret geophysical property data. The optical interrogator 140 may include a light source, photodetectors, and a signal processing unit. The optical interrogator 140 maybe configured to emit a light signal into the optical fibers 130, where the light propagates through the fibers 130 embedded within the sensing head. Variations in the light's physical properties (including but not limited to phase, intensity, frequency / wavelength, and polarization), as a result of strain-induced changes in the fibers' geometry, maybe detected by the interrogator 140. Other light properties such as nonlinear and quantum properties may also be modified by the applied stress and used for monitoring. With different optical fibers having different winding paths configured for biased detection in different directions / dimensions, the optical interrogator 140 (and / or another analysis system) may process the collected signals to extract precise measurements of geophysical properties like strain along different axes. The optical interrogator 140 may connect to the optical fibers via direct splicing and / or high-precision connectors ensuring minimal signal loss and high fidelity in data transmission. It operates using optical sensing principles such as homodyne or heterodyne interferometry as well as Brillouin or Rayleigh scattering techniques, leverages advanced algorithms to deliver real-time monitoring and high-resolution data from the subterranean environment. The integration of the optical interrogator 140 into the system may thus facilitate continuous, accurate, and remote sensing capabilities, essential for geophysical monitoring and analysis.

[0084] The optical interrogator 140 may include multiple channels for individually interrogating different optical fiber paths. Alternatively, the optical interrogator 140 maybe able to switch between interrogating different connected optical fibers.

[0085] In some variations, an isotropic winding guide 120 maybe sufficient for resolving directional strains. In some variations, though, the system design may include features to modify the strain transfer to one or more of the optical fiber windings. As one variation, this maybe achieved in the system by including stress concentrator features. Accordingly, the system may include a set of stress concentrators 150, which may extend longitudinally through the sensing head no. A stress concentrator 150 functions to amplify or otherwise alter experienced deformation of optical fiber 130 within the sensing head 110. This can make the system more sensitive to deformations. The set of stress concentrators 150 may include one or more stress concentrators 150.

[0086] The stress concentrators 150 may be design features oriented at different points within or next to the cross-sectional patterns of the optical fiber winding path. These design features will generally extend longitudinally through the length of the sensing head 110. In some variations, stress concentrators 150 may extend longitudinally through the entirety of the sensing head 110. In some variations, a stress concentrator 150 may extend only partially through the sensing head no.

[0087] The stress concentrators 150 preferably introduce a non-uniform mechanical response within the sensing head such that deformations are not substantially uniformly experienced through the system. As such the mechanical properties of a stress concentrator 150 can differ from mechanical properties of a main material of the sensing head 110.

[0088] In one variation, a stress concentrator 150 may be the inclusion and / or exclusion of stress rods or materials such as shown in Figures 2 and 3. A given stress concentrator 150 may serve to increase the compliance (i.e., decrease the stiffness) of the sensing element by leaving a stress rod locations empty (air void), or decrease the compliance for high stress applications by using a high stiffness material for the stress rods. It would also be possible to create one or more directions where the strain transfer could be increased or decreased by varying the stress rod stiffnesses or be made completely anisotropic by having each rod be of a different stiffness.

[0089] In one variation, at least one stress concentrator 150 of a set of stress concentrators comprises a solid material extending longitudinally through the sensing head 110. In some variations, all stress concentrators 150 comprise a solid material. The stress concentrator 150 maybe a fully solid material. For example, the stress concentrator 150 maybe a solid rod made of a material (e.g., steel or other rigid material) that differs from a material of the sensing head 110 or winding guide 120. The stress concentrator 150 may alternatively be a partially solid structure such as a pipe, structured meta material, or some other body with solid material and defined voids.

[0090] In another variation, at least one stress concentrator 150 of a set of stress concentrators maybe a defined void within material of the sensing head 110 (or winding guide 120). The defined void may establish an opening running fully or partially through the sensing head no in the longitudinal direction. In one variation, all stress concentrators maybe defined voids.

[0091] A stress concentrator 150 that is a defined void may be used as a conduit for optical fiber that maybe passed through the sensing head no / tool to another instance of another sensing head 110 / tool. Additionally or alternatively, other cabling or components maybe passed through such a void stress concentrator 150. These other types of cabling and / or components may be used for any suitable purpose.

[0092] The stress concentrators may be strategically positioned relative to the cross- sectional shape profile of the winding pattern.

[0093] There may be various arrangements of any such stress concentrator 150 features. As shown in the example of FIGURE 2, FIGURE 3, and FIGURE 4, two types of stressing elements include “intra-lobe" and "inter-lobe", where the "lobe" is the high curvature end of the ellipse. There may also be a central stress concentrator.

[0094] In one variation with an elliptical cross-sectional shape profile, the stress concentrators may be positioned in voids within the helical patterns as shown in the cross-sectional view of the example in FIGURE 4. In one variation, at least one stress concentrator 150 of the set of stress concentrators maybe positioned within a lobe of an elliptical cross-section of a winding guide. This may be characterized as an interlobe stress concentrator. An inter-lobe stress concentrator 150 could be used to change the response of one wrap relative to the other.

[0095] In another variation, at least one stress concentrator 150 of the set of stress concentrators is positioned between lobes of elliptical cross sections of two adjacent winding guides. This may be characterized as an intralobe stress concentrator. An intralobe stress concentrator 150 could be used to modify the off-axis sensitivity of a given wrap.

[0096] The stress concentrators may also be used strategically within other biased shape profiles of the winding patterns. Also, while these exemplary stress concentrators 150 are shown as circular cylinders, they could be of arbitrary shape (ellipse, rose, cardioid, etc.) and asymmetric shapes could be arbitrarily oriented.

[0097] In another alternative variation, the winding guide 120 or other supporting structure of the sensing head 110 may have a shape profile that similarly functions to concentrate stress or otherwise alter dispersion of deformations to amplify the resulting deformation on optical fibers.

[0098] The system description above primarily focuses on a single instance of a sensing tool. In some applications, the system may additionally include multiple instances of the sensing tool which may be used in series or at different points within a downhole well. This may include two or more system instances.

[0099] In such a variation, the system may include a system like above (a first sending head 110’ equipped with a first set of winding guides 120’, and a set of optical fibers 130 with a first subset of optical fibers 130’ routed along the first set of winding guides 120’), and further comprising a second sensing head 110” equipped with a second set of winding guides 120”, wherein the set of optical fiber 130 comprises a second subset of optical fibers 130” routed along the second set of winding guides 120” as shown in FIGURE 8. In some variations, the first sensing tool instance may additionally include a stress concentrator 150 with a defined void, wherein the second subset of optical fibers 130” are further routed through the defined void of the at least one stress concentrator 150. In other variations, the first sensing tool instance may include some other defined void in the sensing head 110 through which the second subset of optical fibers 130” maybe routed. In this way the optical fibers wound around one sensing head may be pass through openings in the preceding downhole equipment. Any number of sensing tool instances may be combined. These different sensing toolinstances can enable sensing at different depths. While this variation describes a second system instance being used, any suitable number of instances may be used. Accordingly, the optical fiber 130 may pass through any suitable number of system instances.

[0100] An exemplary variation of the system including the external pressure casing shown in FIGURE 1 and a detailed view of a sensing element is shown in Figure 2. The main body of the sensing element shows a winding guide, which in this shown variation is a cylindrical sensing head with three inclined helical grooves of elliptical cross section cut into it. Each groove accepts one optical fiber and is vertically offset from the previous groove such that the fibers maybe slotted into position to not wrap directly over one another. Figure 4 shows a transparent top view of the sensing element that shows the elliptical cross section of the inclined helical grooves.

[0101] One potential purpose of the winding guide 120 is to guide one or more fibers along inclined helical path(s) of elliptical cross section such that the strain transferred to the fiber(s) in the assembled sensing element will depend on the direction under which external stresses are applied. The mechanism for this is due to the elliptical shape of the wraps since a stress applied to the long axis of the ellipse will impinge on a longer length of fiber than a stress applied to the short axis. Using the vertically oriented ellipse in Figure 4 as an example, the amount of fiber exposed to a horizontal stress is greater than a vertical stress since the curvature of the fiber is much lower along the vertical axis than the horizontal axis. While the example shown in Figures 2 and 3 show only three fibers, at least six may be used to resolve the six components of the elastic strain tensor. An arbitrary number of fibers may be used for redundancy or to make multiple measurements of a particular orientation or set of orientations. As shown in FIGURE 4, one exemplary variation of the system may include a set of differing stress concentrators 150 positioned in different sections to concentrate stress. Other suitable arrangements and configurations of stress concentrators 150 maybe used.

[0102] The various features and variations described herein may be used in a variety of combinations. Mention of one variation does not preclude using another variation, and many features and variations may be used in combination within a system.3- Method

[0103] The system described herein may be manufactured or otherwise produced by forming a sensing tool with optical fiber following a winding pattern with the inclined helical pattern with a biased shape cross-sectional pattern. As shown in FIGURE 9, a method of producing a downhole optical geophysical sensor may include: forming a set of winding guides where each winding guide in the set of winding guides form a continuous inclined helical path around a sensor head body S110; and winding optical fiber along each winging guide of the set of winding guides S120.

[0104] Block S110, which includes forming a set of winding guides where each winding guide in the set of winding guides form a continuous inclined helical path around a sensor head body, functions to establish structural features in a body (e.g., the sensing head) that can be used to guide the path of an optical fiber. The shape of the winding guide can be similar to a winding guide path or optical fiber path described above for the system

[0105] As discussed, some variations will have multiple winding guides. As such block S110 may include forming multiple winding guides that have a path with an elliptical cross-section or some alternative biased-shape cross-section. The elliptical (or other biased-shape cross sections may be offset by aligning the shapes in different directions. In the case of an elliptical cross-section, a major and minor axes of the ellipses for different winding guides may be aligned in different directions, offset with some angular offset (e.g., 90°, 6o°, 450, 30°, or other suitable angular offset).

[0106] The winding guide can be a variety of physical features that mechanically promote positioning of an optical fiber with some desired path. In one variation, forming the set of winding guides may include creating a winding guide as a recessed groove. In another variation, forming the set of winding guides may include creating a winding guide as a defined cavity. In another variation, forming the set of winding guides may include creating a winding guide as a protruding structure.

[0107] Forming the winding guide may use a variety of manufacturing processes and techniques including additive and / or subtractive manufacturing. In one variation, forming the set of winding guides may include 3D printing the sensor head body with integrated structures of the set of winding guides. In another variation, forming the set of winding guides comprises manufacturing the sensor head body with integratedstructures of the set of winding guides through subtractive manufacturing. This may include milling or otherwise using some cutting or subtractive technique. As another alternative, the sensing head no or some structural winding guide that can be integrated with a sensing head may be cast or molded.

[0108] Block S120, which includes winding optical fiber along each winging guide of the set of winding guides, functions to wind optical fibers along an inclined helical path with a biased-shape cross-sectional pattern. At least one optical fiber can be routed through each winding guide. An optical fiber can be routed from a proximal end to a distal end of a winding guide and then back to the proximal end.

[0109] In some variations, the method may be performed without winding guides and therefore without process block S110. An optical fiber maybe carefully wound and fixed in place about a sensing head. This may include carefully winding optical fibers in place and then casting, molding, or otherwise applying some external layer fixing the optical fibers in place.

[0110] In some variations, the method may include forming stress concentrators within the sensing head and / or winding guide. The stress concentrators can be a physical feature (e.g., defined void, tube, or rod) extending longitudinally through the sensing head.

[0111] When using the sensing tool, the method may further include interconnecting the optical fiber(s) to an optical interrogator S130 as shown in FIGURE 10. A method including operation of the device may include optically interrogating optical properties of the optical fibers 130, analyzing the signals and determining a stress or strain measurement.

[0112] When multiple sensing tool instances are used, the method may include routing optical fiber through a longitudinal cavity (“through-hole”) of one sensing head 110. The longitudinal cavity maybe a defined void of a stress concentrator or possibly a central defined through-hole.4. Examples

[0113] Hereafter are described different examples of system and method variations.These examples are not intended to limit the systems and / or methods and theirvariations and does not include every variation and combination of variations of the systems and methods described herein.

[0114] Example 1: A system for a downhole optical sensing can include a set of winding guides routed in an inclined path around the sensing head; a set of optical fibers, where at least one optical fiber is routed along a path of a winding guide in the set of winding guides. The system can serve as a downhole optical sensing system for geophysical measurement.

[0115] Example 2: The system of example 1, wherein the inclined path is an inclined helical path.

[0116] Example 3: The system of example 2, wherein the inclined helical path has an elliptical cross-section, rose cross section, cardioid cross-section, and / or other suitable biased-shape cross-section along a longitudinal axis of the sensing head.

[0117] Example 4: The system of one of examples 1-3, further comprising an optical interrogator system. The optical interrogator system may be configured to analyze signals transmitted through the optical fibers.

[0118] Example 5: The system of example 4, wherein each optical fiber is wound to form a continuous optical path from the optical interrogator system, through at least one winding guide in the sensing head, and back to the optical interrogator system.

[0119] Example 6: The system of one of examples 1-5, wherein the set of winding guides comprises multiple winding guides each configured to orient optical fibers along distinct paths."

[0120] Example 7: The system of one of examples 1-6, wherein the multiple winding guides are configured with offset orientations of elliptical cross-sections, allowing optical fibers to sense strain in multiple directional orientations.

[0121] Example 8: The system of one of examples 1-7, further comprising a set of stress concentrators extending longitudinally through the sensing head.

[0122] Example 9: The system of one of examples 1-8, wherein at least one stress concentrator of the set of stress concentrators is a defined void within material of the sensing head.

[0123] Example 10: The system of one of example 1-9 further comprising a second sensing head equipped with a second set of winding guides, wherein the set of opticalfiber comprises a subset of optical fibers routed along the second set of winding guides; and further routed through the defined void of the at least one stress concentrator in the first sensing head (i.e., the first sensing head)

[0124] Example 11: The system of one of examples 1-8, wherein at least one stress concentrator of the set of stress concentrators comprises a solid material extending longitudinally through the sensing head.

[0125] Example 12: The system of example 11, wherein the at least one stress concentrator is a solid rod.

[0126] Example 13: The system of example 11, wherein the at least one stress concentrator is a pipe or tube with an internal opening running longitudinally through the stress concentrator.

[0127] Example 14: The system of one of examples 8-13, wherein at least one stress concentrator of the set of stress concentrators is positioned within a lobe of an elliptical cross-section of a winding guide.

[0128] Example 15: The system of one of examples 8-13, wherein at least one stress concentrator of the set of stress concentrators is positioned between lobes of elliptical cross sections of two adjacent winding guides.

[0129] Example 16: The system of one of examples 1-15, further comprising an external pressure casing that encases the sensing head.

[0130] Example 17: A method of producing a downhole optical geophysical sensor comprising: forming a set of winding guides where each winding guide in the set of winding guides form a continuous inclined helical path around a sensor head body; winding optical fiber along each winging guide of the set of winding guides. Example 17 may be used in connection with producing, implementing, or otherwise enabling the system examples 1-16.

[0131] Example 18: The method of example 17, wherein forming the set of winding guides comprises forming multiple winding guides that have a path with an elliptical cross-section, where the elliptical cross sections are offset aligning the elliptical shapes in different directions. In the case of an elliptical shape, the major and minor axes of the elliptical shapes maybe aligned in different directions offset by some angle (e.g., 90°, 6o°, 450, 30°, or other offsets).

[0132] Example 19: The method of one of examples 17-18, wherein forming the set of winding guides comprises creating a winding guide as a recessed groove.

[0133] Example 20: The method of one of examples 17-18, wherein forming the set of winding guides comprises creating a winding guide as defined cavities.

[0134] Example 21: The method of one of examples 17-18, wherein forming the set of winding guides comprises creating a winding guide as protruding structures.

[0135] Example 22: The method of one of examples 17-21, wherein forming the set of winding guides comprises 3D printing the sensor head body with integrated structures of the set of winding guides. More generally this forming the set of winding guides comprises producing winding guides through additive manufacturing.

[0136] Example 23: The method of one of examples 17-21, wherein forming the set of winding guides comprises manufacturing the sensor head body with integrated structures of the set of winding guides through subtractive manufacturing. This may include milling (e.g., via CNC machining). Alternatively, forming the set of winding guides may comprise casting or molding a sensing head or other structure with formed winding guides.

[0137] Example 24: The method of one of examples 17-23, further comprising interconnecting the optical fiber to an optical interrogator.

[0138] Example 25: The method of example 24, further comprising at the optical interrogator, interrogating optical properties of the optical fibers.

[0139] Example 26: The method of one of examples 17-25, wherein there are multiple sensing tool instances comprising, routing cable through a longitudinal cavity (“through-hole”) of one sensing head (such as a defined void of stress concentrator).

[0140] As used herein, first, second, third, etc. are used to characterize and distinguish various elements, components, regions, layers and / or sections. These elements, components, regions, layers and / or sections should not be limited by these terms. Use of numerical terms may be used to distinguish one element, component, region, layer and / or section from another element, component, region, layer and / or section. Use of such numerical terms does not imply a sequence or order unless clearly indicated by the context. Such numerical references maybe used interchangeable without departing from the teaching of the embodiments and variations herein.

[0141] As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the embodiments of the invention without departing from the scope of this invention as defined in the following claims.

Claims

CLAIMSWe Claim:

1. A system for a downhole optical sensing comprising: a sensing head; a set of winding guides routed in an inclined path around the sensing head; and a set of optical fibers, where at least one optical fiber is routed along a path of a winding guide in the set of winding guides.

2. The system of claim 1, wherein the inclined path is an inclined helical path.

3. The system of claim 2, wherein the inclined helical path has an elliptical crosssection along a longitudinal axis of the sensing head.

4. The system of claim 1, further comprising an optical interrogator system.

5. The system of claim 4, wherein each optical fiber is wound to form a continuous optical path from the optical interrogator system, through at least one winding guide in the sensing head, and back to the optical interrogator system.

6. The system of claim 1, wherein the set of winding guides comprises multiple winding guides each configured to orient optical fibers along distinct paths."7. The system of claim 6, wherein the multiple winding guides are configured with offset orientations of elliptical cross-sections, allowing optical fibers to sense strain in multiple directional orientations.

8. The system of claim 1, further comprising a set of stress concentrators extending longitudinally through the sensing head.

9. The system of claim 8, wherein at least one stress concentrator of the set of stress concentrators is a defined void within material of the sensing head.

10. The system of claim 9 further comprising a second sensing head equipped with a second set of winding guides, wherein the set of optical fiber comprises a subset of optical fibers routed along the second set of winding guides; and further routed through the defined void of the at least one stress concentrator in the sensing head.

11. The system of claim 8, wherein at least one stress concentrator of the set of stress concentrators comprises a solid material extending longitudinally through the sensing head.

12. The system of claim 8, wherein at least one stress concentrator of the set of stress concentrators is positioned within a lobe of an elliptical cross-section of a winding guide.

13. The system of claim 8, wherein at least one stress concentrator of the set of stress concentrators is positioned between lobes of elliptical cross sections of two adjacent winding guides.

14. The system of claim 1, further comprising an external pressure casing that encases the sensing head.

15. A method of producing a downhole optical geophysical sensor comprising: forming a set of winding guides where each winding guide in the set of winding guides form a continuous inclined helical path around a sensor head body; winding optical fiber along each winging guide of the set of winding guides.

16. The method of claim 15, wherein forming the set of winding guides comprises forming multiple winding guides that have a path with an elliptical cross-section, where the elliptical cross sections are offset by aligning the elliptical shapes in different directions.

17. The method of claim 16, wherein forming the set of winding guides comprises 3D printing the sensor head body with integrated structures of the set of winding guides.

18. The method of claim 16, wherein forming the set of winding guides comprises manufacturing the sensor head body with integrated structures of the set of winding guides through subtractive manufacturing.

19. The method of claim 16, further comprising interconnecting the optical fiber to an optical interrogator.

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