Three-dimensional waveguide sensors for sample analysis

Systems and methods for measuring a characteristic of a fluid are provided. The system includes a plurality of waveguides embedded in a substrate, and an exposed surface of the substrate comprising a portion of a side surface of at least one of the plurality of waveguides. The system also includes a sensitized coating in the at least one of the plurality of waveguides. The exposed surface is curved in a direction perpendicular to a light propagation in the waveguide. A method of fabricating a system as above is also provided.

BACKGROUND

The present disclosure relates to sensors incorporating waveguides in a three-dimensional (3D) substrate for use in the oil and gas industry. More specifically, the present disclosure relates to interferometry-based chemical sensors to measure fluid samples relevant in the oil and gas industry.

Chemical sensors using planar waveguide arrays in a Mach-Zehnder interferometer configuration have gained popularity for their high sensitivity. However, planar geometries are incompatible with the relatively large and circular cross-sections of optical fibers used to reach the depths of some wellbores in oil and gas exploration and extraction operations. In such downhole environments, the fragile complexion of planar waveguide arrays becomes a hindrance, as alignment procedures need to be enhanced. Also, planar waveguide arrays are more susceptible to stress, strain, high temperatures, and high pressures commonly encountered in downhole applications.

DETAILED DESCRIPTION

The present disclosure relates to sensors incorporating waveguides in a three-dimensional (3D) substrate for use in the oil and gas industry. More specifically, the present disclosure relates to interferometry-based sensors to measure fluid samples relevant in the oils and gas industry.

Measurement of fluid samples, as disclosed herein, includes measuring a characteristic or analyte of relevance in the sample. Embodiments as disclosed herein make use of the optical interaction between a sample with a first portion of an electromagnetic radiation. An associated sensor combines an interacted first portion of the electromagnetic radiation with a second portion of the electromagnetic radiation to produce a signal in a photo-detector. An analyzer determines changes in the signal and correlates the changes with a presence, absence, or a change in the characteristic in the sample. In that regard, the embodiments disclosed herein interferometrically combine the interacted first portion and the second portion of the electromagnetic radiation (e.g., as in a Mach-Zehnder type interferometer). Sensors of a type consistent with the present disclosure may include chemical sensors, pH sensors, biological sensors, and other environmentally sensitive devices such as physical sensors correlating an optical signal to a fluid density.

As used herein, the term “characteristic” refers to a chemical, mechanical, or physical property of a substance. The characteristic of a substance may include a quantitative or qualitative value of one or more chemical constituents or compounds present therein or any physical property associated therewith. Such chemical constituents and compounds may be referred to herein as “analytes.” Illustrative characteristics of a substance that can be detected with the sensors described herein can include, for example, chemical composition (e.g., identity and concentration in total or of individual components), phase presence (e.g., gas, oil, water, etc.), impurity content, pH, alkalinity, viscosity, density, ionic strength, total dissolved solids, salt content (e.g., salinity), porosity, opacity, bacteria content, total hardness, transmittance, combinations thereof, state of matter (solid, liquid, gas, emulsion, mixtures, etc.), and the like.

As used herein, the term “substance,” “sample,” “sample substance,” or variations thereof, refers to at least a portion of matter or material of interest to be tested or otherwise evaluated using embodiments described herein. The substance includes the characteristic of interest, as defined above. The substance may be any fluid capable of flowing, including particulate solids, liquids, gases (e.g., air, nitrogen, carbon dioxide, argon, helium, methane, ethane, butane, and other hydrocarbon gases, hydrogen sulfide, and combinations thereof), slurries, emulsions, powders, muds, glasses, mixtures, combinations thereof, and may include, but is not limited to, aqueous fluids (e.g., water, brines, etc.), non-aqueous fluids (e.g., organic compounds, hydrocarbons, oil, a refined component of oil, petrochemical products, and the like), acids, surfactants, biocides, bleaches, corrosion inhibitors, foamers and foaming agents, de-foamers, breakers, scavengers, stabilizers, clarifiers, detergents, a treatment fluid, fracturing fluid, a formation fluid, or any oilfield fluid, chemical, or substance as found in the oil and gas industry.

As used herein, the term “optically interact” or variations thereof refers to the reflection, transmission, scattering, diffraction, interference, or absorption of electromagnetic radiation either on, through, or from one or more processing elements, a substance being analyzed by the processing elements, or a polarizer. Accordingly, optically interacted light refers to electromagnetic radiation that has been reflected, transmitted, scattered, diffracted, interfered, or absorbed by, emitted, or re-radiated, for example, using a sensitized coating, but may also apply to optical interaction with a substance or a polarizer. In operation, a sensor as described herein is capable of distinguishing electromagnetic radiation related to a characteristic of interest of a substance from electromagnetic radiation related to other components of the substance.

Embodiments disclosed herein include sensors for measuring a characteristic of a sample substance by interacting electromagnetic radiation with the sample substance. Sensors based on interferometry show high sensitivity. An interferometer, in embodiments consistent with the present disclosure, splits coherent electromagnetic radiation into at least two portions that effectively travel different optical paths before being recombined and detected. An optical path length is defined as the product of the refractive index of the material the radiation or light is propagating through and the physical propagation distance or length. For waveguides, the effective refractive index used in the calculation of optical path length is based on the propagation velocity of waves in the waveguide. The difference in the optical path lengths between a first portion and a second portion of the electromagnetic radiation creates a change in interference fringe pattern upon recombination. The fringe pattern carries information regarding a sample property of interest (e.g., substance or analyte concentration among many others). The fringe pattern provides a sensitive measure of the phase shift induced by propagation of radiation under the presence (or absence) of an analyte of interest. Accordingly, interferometric techniques as disclosed herein allow for enhanced sensitivity at very low concentrations of the analyte of interest.

Embodiments as disclosed herein use interferometry with chemically sensitized optical waveguides to enhance detection sensitivity while maintaining device simplicity and compactness. In extreme environmental conditions, a waveguide structure embedded in a 3D substrate is well suited for interferometry. The oil and gas industry may benefit from such embodiments by using already deployed fiber optic cables and infrastructure in oil wells and pipelines. Embodiments as disclosed herein may be used in the inspection and maintenance of oil and gas pipelines used for long-haul transportation, or within refineries and storage facilities.

Embodiments in this disclosure combine existing technologies used in the manufacturing of optical fibers to form waveguides on interior and exterior surfaces of a 3D substrate. Pairs of waveguides are formed into Mach-Zehnder interferometers. A coating to selectively absorb, capture, bind, or otherwise immobilize a target analyte (i.e., characteristic) is applied to one arm of the Mach-Zehnder interferometer while the reference arm remains uncoated. In some embodiments, coherent light illuminates one end of the 3D substrate and launches light into both sensing and reference arms. Since one arm is coated and one is not, the quantity of the target analyte absorbed, captured, bound, or immobilized will cause a change in phase difference at the output of the two arms. Light leaving the two arms will spread out or diffract as it propagates through free space, overlapping and forming an interference pattern on an optical detector. The interference pattern observed at the detector, or a received irradiance of a single detection point is a function of the analyte absorbed, captured, bound, or immobilized in the coated arm.

Sensors as disclosed herein incorporate a plurality of waveguides into a 3D structure arranged in various configurations to detect one or more properties of a downhole environment. Sensitivity and specificity of sensors as disclosed herein are enhanced by coating alternating waveguide channels with a sensitized coating layer or film. The sensitized coating can be located on an outer surface or an inner surface of the 3D structure, depending on the configuration of the sensor. In either configuration, the sensitized coating is located on a surface exposed to the sample. Some embodiments include one or more different sensitized coatings to interact with one or more analytes of interest in the sample. In this sense, combinations for analyte detection are unlimited, as functional coatings are identified for different target analytes of interest. The interaction of an analyte with a sensitized coating causes a change in the refractive index of the coating. The change in the coating refractive index changes the propagation constant of the coated waveguide. Some embodiments use the interaction of an evanescent field from a propagating waveguide mode with the sensitized waveguide surface to change an interference pattern between the light emanating from the sensitized waveguide and light emanated from a reference waveguide. This change is generally proportional to analyte concentration.

A sensitized coating is activated when it absorbs, binds, attaches, or adheres to a target analyte(s) such that the refractive index of the sensitized coating changes. This changes the propagation constant of the sample waveguide, thereby giving rise to a phase shift of light (i.e., electromagnetic radiation) emerging from the sample waveguide. If an interferometer is constructed containing the sample waveguide and an uncoated reference waveguide, the output of the interferometer changes in response to activation of the sample waveguide by the presence of the target analyte. An analyzer determines a target analyte concentration based on the change in the interference pattern. Embodiments disclosed herein include arrangements of sample and reference waveguides to make an interferometry configuration simple to adapt for field applications and for simultaneous measurement of multiple target analytes.

In some embodiments, the plurality of waveguides forms an array having a circular cross-section relative to the light propagation in the waveguides. This configuration makes the sensor suitable for downhole and pipeline applications in the oil and gas industry. Embodiments consistent with this disclosure include small and robust chemical sensors that use relatively low power and are relatively inexpensive to fabricate. Furthermore, sensors according to this disclosure have the ability to measure a plurality of sample characteristics of interest simultaneously with no moving parts.

FIG. 1illustrates an exemplary measurement system101including a sensor100incorporating waveguides114in a 3D substrate105, according to some embodiments. In embodiments consistent with the present disclosure, sensor100may be a chemical sensor configured to detect the presence and/or concentration of one or more chemical analytes of interest in a sample. Sensor100includes a light source102, and a beam splitter element104to separate the electromagnetic radiation emitted from the light source102into a first electromagnetic radiation110sand a second electromagnetic radiation110r. Beam splitter element104may be any type of phase-preserving beam splitter as known to those of ordinary skill in the art. For example, beam splitter element104may be a fiber beam splitter or a beam splitter prism. Light source102may be a lamp, an LED, a laser, an electromagnetic radiation emitter, or even solar light. Sensor100includes a detector118that provides a signal to analyzer160. The coherence length of the electromagnetic radiation emitted by light source102is desirably as long as or longer than the maximum difference in optical path lengths splitter element104to detector118. Analyzer160includes a processor circuit161and a memory circuit162. Analyzer160may also be configured to control light source102.

According to some embodiments, at least one of waveguides114includes a surface that is exposed to a fluid150in a container170. In some embodiments container170is a closed container that houses fluid150. Some embodiments include an open container170having an inlet and an outlet so that fluid150is circulating or otherwise in motion. In some embodiments, fluid150may include a mixture of oil, gas, water, and mud (i.e., drilling fluid) commonly found in downhole environments associated with an oil and gas platform in the oil and gas industry. In other embodiments, however, fluid150may include a blood sample, and fluid container170may be a vile, a test tube, or a blood vessel in a patient's body. Further according to some embodiments, fluid150may be a food product, such as milk or water, and container170may be a bottle or package. In some embodiments container170may be a pipeline, a tube, or a conduit. For example, container170may be an oil or gas pipeline, a water pipeline for agricultural irrigation or drainage, a blood vessel, or another tissue in the human body. Container170may also be a line or fluid passage in a downhole tool or downhole sensor, or a sensor located at the surface.

FIG. 2Aillustrates a cross-sectional view of an exemplary sensor200aincorporating waveguides in a 3D substrate205a, according to some embodiments. Chemical sensor200aincludes sample waveguides214sand reference waveguides214rembedded in or otherwise positioned on substrate205a. Waveguides214sand214rare collectively referred to hereinafter as waveguides214. Sample waveguides214sinclude a sensitized coating212,222,232, and242. Reference waveguides214rare similar in all respects to sample waveguides214, except for sensitized coatings212,222,232, and242. It is desirable that sensitized coatings212,222,232, and242provide a linear, reversible, secure, and high target specificity.

In some embodiments, substrate205aincludes a preform, re-shaped using techniques well-known in the optical fiber industry. Accordingly, in some embodiments, 3D substrate205ais a glass cylinder. It should be noted that the cross-section of the final 3D substrate205ais a scaled down version of the preform. In embodiments where the preform is a solid rod-like structure, waveguides214could be located along the outer diameter (OD) of the rod. To efficiently propagate electromagnetic radiation, waveguides214are formed of a material having a higher refractive index (n1) than the material in substrate205awith refractive index (n2, i.e., n2<n1).

Sensing channels210,220,230, and240are indicated by dashed lines. For each sensing channel210,220,230, and240, the signal portions of the electromagnetic radiation are injected into or otherwise conveyed through signal waveguides214s, and the reference portions of the electromagnetic radiation are injected into or otherwise conveyed through reference waveguides214r. Ideally, the coherent light illuminating for both reference and sensing waveguides should be in phase. For each sensing channel210,220,230, and240an output electromagnetic radiation from waveguide214sforms an interference pattern with an output electromagnetic radiation from waveguide214r. An interference pattern for each of sensing channels210,220,230, and240can be measured independently. Thus, sensor200acan measure a plurality of analytes either simultaneously or overlapping in time. Waveguides214sinclude sensitized coatings212,222,232, and242on a side of the waveguide exposed to the outside or 3D substrate205a. Each of sensitized coatings212,222,232, and242may be selected to chemically interact with a target analyte.

FIG. 2Billustrates a cross-sectional view of a chemical sensor200bincorporating waveguides214in a hollow or cylindrical 3D substrate205b, according to some embodiments. Sensor200bis similar to chemical sensor200a, and operates under the same principles. In that regard, chemical sensor200bdiffers from sensor200ain that substrate205bis a hollow, 3D structure. Furthermore, in sensor200bwaveguides214are disposed along the inner diameter (ID) of substrate205b. Accordingly, fluid150is contained or flowing through a lumen or cavity207defined within hollow substrate205b.

FIGS. 2A and 2Bshow the arrangement of waveguides214on an exposed surface of a 3D substrate to form sensing channels210,220,230, and240as a plurality of interferometers arranged in a 3D configuration. More particularly, a 3D configuration in substrates205aand205bincludes a cross-section and a length, where the length extends along a longitudinal axis of a wellbore in oil and gas exploration and extraction operations. In some embodiments, the exposed surface is in contact with fluid150. More generally, the exposed surface is coupled to the substance containing an analyte of interest for measurement. The exposed surface may be external to an internal diameter of the 3D substrate (e.g., substrate205a) or contained within the internal diameter of the 3D substrate (e.g., substrate205b). In embodiments consistent with the present disclosure, the exposed surface may include a side surface of each waveguide214, or at least one of waveguides214. More generally, the exposed surface may include a side surface of at least one of waveguides214, and a portion of the 3D substrate. Advantageously, the cylindrical geometry of sensors200aand200bmatches the general symmetry of downhole and pipeline inspection tools in the oil and gas industry. More generally, the exposed surface of the 3D substrate may be curved in a direction perpendicular to a light propagation in waveguides214(i.e., the outer diameter inFIG. 2Aand the inner diameter inFIG. 2Bare perpendicular to waveguides214). In some embodiments, the outer diameter (OD) of 3D substrates205aand205bis between about 1/16″ and about ⅛″. The cross-sectional dimension of waveguides214may be on the order of the size of the wavelength of light propagating through the waveguides. In that regard, waveguides214may be single mode or multimode waveguides, without limiting the embodiments disclosed herein.

WhileFIGS. 2A and 2Billustrate waveguides214having a somewhat square profile, the specific cross-sectional shape and size of waveguides214is not limiting. Rather, waveguides214may have any cross-sectional shape and size as desired for efficient electromagnetic radiation propagation and efficient fabrication. In that regard, the cross-sectional shape and size of each pair of waveguides214sand214rwithin each one of sensing channels210,220,230, and240is similar or the same.

Sensitized coatings212,222,232, and242may include hydrophobic or hydrophilic gels. Accordingly, either by swelling or shrinking, a change in the refractive index and the geometry of waveguides214sinduces a phase shift in the sample portion of radiation propagating therethrough. In some embodiments, the sensitized coating212,222,232, and242is a porous material that is filled or emptied by the target analyte. A hydrophilic gel will shrink or swell in the presence of water or oil in fluid150. Likewise, a hydrophobic gel may shrink or swell in the presence of water or oil in the fluid. Thus, a chemical sensor as disclosed herein may be used to measure water and oil content in a water/oil mixture.

In some embodiments, sensitized coatings212,222,232, and242target gaseous hydrocarbons ranging from methane to hexane, and other hydrocarbons and related chemical species of relevance to the oil and gas industry. In such embodiments, sensitized coatings212,222,232, and242may include a thin polymer layer related to the selected hydrocarbon. Moreover, in some embodiments coatings212,222,232, and242may include embedded nanoparticles to enhance target specificity, such as metal nanoclusters, quantum dots, and plasmon resonant schemes. Other embodiments include coatings212,222,232, and242having ion sensitivity for applications such as pH sensors.

Analytes or characteristics that may be of relevance for targeting with sensors as disclosed herein include Iron ions or Alkaline metals dissolved in fluid150. In some embodiments, it is desirable to measure gaseous concentrations in fluid150, such as CO2or Methane (CH4). More generally, sensors consistent with embodiments disclosed herein may include pollutants, agrochemicals, nerve agents, explosives, pharmaceuticals, and controlled substances (e.g., illegal drugs).

Accordingly, sensors as disclosed herein may have multiple applications depending on the target analyte in fluid150. For example, applications for measuring bacteria contamination in fluid150include specific bacterial antibodies in sensitized coatings212,222,232, and242. Moreover, in some embodiments a sensor as disclosed herein includes at least one of coatings212,222,232, and242sensitized with an antibody having affinity to certain types of cancer cells, or to a carcinoembryonic antigen (CEA). More generally, sensitized coatings212,222,232, and242may target pathogens associated with a disease such as a bacterium, a unicellular microorganism, a strand of nucleic acid (e.g., DNA or RNA), a protein or a peptide. Other examples of target pathogens for sensitized coatings212,222,232, and242include, but are not limited to,Bacillus anthracis(Anthrax),Mycobacterium tuberculosis lipoarabinomannan(LAM),Vibrio cholerae, Escherichia Coli(E. Coli), or the Influenza virus. Other biological agents targeted by sensitized coatings212,222,232, and242include spores, toxins, viruses, and water borne pathogens. Accordingly, coatings212,222,232, and242may include covalently bonding an antibody or antigen on the exposed surface of waveguides214. Thus, sensors as disclosed herein are configured to determine a unicellular microorganism presence in a sample, or a unicellular microorganism concentration in the sample.

Other examples for the use of sensors as disclosed herein include DNA sensors having short, single-stranded (desoxyribonucleicacid) DNA oligonucleotides grown on the surface of a quartz or silica waveguide214. Sensitized coatings212,222,232, and242for use in biological sensing may include material layers such as silane-based self-assembled monolayers. Accordingly, silane-based monolayers may be sensitized by amine radical termination including a mixture of carboxylic acid-terminated polyethylene glycol (PEG) chains.

In fluid150, sensitized coatings212,222,232, and242may reach equilibrium with a target analyte concentration after a given response time. It is desirable that the equilibrium be reached below a saturation point for a plurality of ligands included in sensitized coatings212,222,232, and242. In that regard, when target analyte concentration increases, it may be desirable that the coating response increases at a first rate. When target analyte concentration decreases, it is desirable that the coating response decreases at an equivalent second rate. Accordingly, it is desirable that sensitized coatings212,222,232, and242have a reversible and linear response to target analyte concentration. Thus, it is desirable that sensitized coatings212,222,232, and242reach an equilibrium point that is proportional to analyte concentration in fluid150. Response times and saturation points vary substantially from one type of sensitized coating to another. In general, it is desirable that sensitized coating212,222,232, and242have a fast, linear, and reversible response.

In order to correct for aging and degradation effects in sensitized coatings212,222,232, and242, some embodiments include periodic calibration procedures on sensors200aand200b. Furthermore, some embodiments include a heater to drive back the sensitized coating to a baseline (or unsaturated) value. Some embodiments include calibration measurements to determine sensor replacement or when to refresh or clean the sensitized coating.

FIG. 3Aillustrates a cross-sectional view of an exemplary sensor300aincorporating waveguides214in 3D substrate205a, according to some embodiments. Sensor300ais similar to sensor200a, described in detail above (cf.FIG. 2A). Sensor300aincludes sensing channels310,320,330and340. Sensing channel310includes sensitized coating212, and therefore has a similar function as sensing channel210in sensor200a. Likewise, sensing channel320includes sensitized coating222, and therefore has a similar function as sensing channel220in sensor200a. Sensing channel330includes sensitized coating232, and therefore has a similar function as sensing channel230in sensor100a. Moreover, sensing channel340includes sensitized coating242, and therefore has a similar function as sensing channel240in sensor200a.

As illustrated, sensing channels310and340share a first reference waveguide214r, and sensing channels320and330share a second reference waveguide214r. Thus, sensor300amakes an efficient use of the total number of waveguides214embedded in 3D substrate205a. Accordingly, sensor300aincreases the possible number of analytes detected simultaneously by reducing the total number of reference waveguides214r.

FIG. 3Billustrates a cross-sectional view of a chemical sensor300bincorporating waveguides214in hollow 3D substrate205b, according to some embodiments. Sensing channels310,320,330, and340inFIG. 3Bare as described in detail above in reference toFIG. 3A. Substrate205bis as described inFIG. 2Babove.

More generally, embodiments consistent with the present disclosure use a single reference waveguide with multiple sample waveguides for detection of multiple analytes of interest. Furthermore, multiple analyte detection may be performed simultaneously or overlapping in time.

FIG. 4illustrates a chemical sensor400incorporating waveguides214(shown as waveguides214rand214s) in an exterior surface of 3D substrate205a, according to some embodiments. Sensor400includes 3D substrate205ainserted into a housing401containing fluid150flowing past sensor400from a fluid inlet405to a fluid outlet407. Coherent light illuminates an input side of 3D substrate205aand detectors418and438positioned at an output side of 3D substrate205aread the individual interferometers formed by signal channels310and330. While not limiting, some embodiments of sensor400include a 3D substrate205aof about 1″ to 2″ in length.

A signal electromagnetic radiation410sis coupled or otherwise conveyed into waveguide214sand interacts with sensitized coating212. As a result, a sample output signal412semerges from waveguide214s. A reference electromagnetic radiation410ris coupled or otherwise conveyed into waveguide214rto form a reference output signal412r. Sample output signal412soptically interacts with reference output signal412rto form interference pattern415. Detector418measures a property of interference pattern415. The distance between detector418and the end of waveguides214is selected to capture a specific portion of interference pattern415. In some embodiments, detector418may be placed in the near field (about a few wavelengths away from the end of waveguides214), to have greater sensitivity to changes in interference pattern415. Further, in some embodiments, detector418may be placed with a sensitive area overlapping a peak in interference pattern415. Some embodiments may include detector418with a sensitive area overlapping a dark node of interference pattern415. Moreover, in some embodiments a sensitive area of detector418may overlap a transition region in interference pattern415, the transition region including a portion of a peak and a portion of a dark node. In yet other embodiments, detector418may include a sensor array including a linear array of optical fibers, each optical fiber connected to a remote photo detector. In such a configuration, waveguides214may also be remotely illuminated and interrogated via fiber (e.g., from the surface in downhole applications); thus, sources and detectors can be located remotely, according to some embodiments. For downhole applications, this means at the surface, away from the harsh downhole environment that is not amenable to light sources and detectors.

In a similar manner, a first electromagnetic radiation430s, and a second electromagnetic radiation430rare coupled or otherwise conveyed into waveguides214sand214r, respectively. A sample output signal432sis the result of interaction between first electromagnetic radiation430sand sensitized coating232. Accordingly, sample output signal432sinteracts with reference output signal432rto form interference pattern435. Detector438measures a property of interference pattern435.

In one or more embodiments, electromagnetic radiation410s,410r,430s, and430ris part of a collimated, coherent beam of light illuminating the left hand side of the structure. Some embodiments may include electromagnetic radiation410scoherent with electromagnetic radiation410ras part of a focusing beam. Other configurations of electromagnetic radiation410sand electromagnetic radiation410rmay include non-collimated beams. Accordingly, interference patterns415and435may be formed as sample output signal412sand reference output signal412reach propagate through free space.

In some embodiments, an optical element (not shown) may be placed between the output side of waveguides214and detector418. For example, in some embodiments a micro-lens array may be placed between waveguides214and detector418to more efficiently direct interference pattern415to the sensitive area in detector418. Detector418may be a single receiver to determine the brightness or irradiance of a central interference fringe in pattern415in configuration where the central fringe is approximately Gaussian in shape. Accordingly, pattern415moves up and down with respect to detector418inFIG. 4in response to phase differences between sample output signal412sand reference output signal412rexiting waveguides214sand214r, respectively. Alternately, detector418may include an array of sensors used to better determine the position of the central fringe and secondary interferences in pattern415, which may be also be analyzed to determine the phase difference. Detector418may include a lens to focus the central area of interference pattern415onto an optical fiber, or a plurality of optical fibers. Accordingly, light forming interference pattern415can be transmitted to a remote photodiode sensor via the optical fiber, or the plurality of optical fibers receiving at least a portion of interference pattern415at a selected location.

In embodiments consistent with the present disclosure, detectors418and438may include a plurality of sensitive areas in a detector array. Thus, detectors418and438may collect a portion of interference patterns415and435, respectively, and perform a detailed analysis or computation. In embodiments consistent with the present disclosure, detectors418and438may be included in a detector array. In some embodiments, the entire body of sensor400may be immersed in fluid150to perform simultaneous or time overlapped measurements of multiple analytes. In yet other embodiments, only a portion of the OD in substrate205amay be exposed to the fluid (e.g., the portion exposing sensing channel210) at a given moment. In such a configuration, sensor400may incorporate a rotating mechanism to rotate substrate205aabout its longitudinal axis to perform a second measurement (e.g., rotating substrate205ato expose sensing channel220). Accordingly, in some embodiments housing401maintains detectors415and435in a desired position relative to 3D substrate205a. In some embodiments, substrate205amoves longitudinally inside housing401so that a fresh portion of coatings212and232is exposed to fluid150.

FIG. 5illustrates a sensor500incorporating waveguides214in an interior surface of a 3D substrate205b, according to some embodiments. InFIG. 5, fluid150flows from an inlet505to outlet507through a portion within an inner diameter of substrate205b.FIG. 5depicts one sensing channel210for illustration purposes only. A plurality of sensing channels may be included, consistent with embodiments disclosed herein (e.g., channels210,220,230,240, cf.FIG. 2B, or channels310,320,330, and340, cf.FIG. 3B).

FIGS. 4 and 5illustrate a Mach-Zehnder configuration where a beam splitter is replaced by illuminating waveguides214sand214rwith coherent, collimated light. Another advantageous feature in some embodiments of chemical sensors400and500is that output light412sand412ris combined in free space propagation into interference pattern415as in a “two slit” interference pattern. Accordingly, embodiments of chemical sensors consistent withFIGS. 4 and 5are compact, simpler and cheaper to fabricate than existing interferometric waveguide based chemical sensors.

FIG. 6Aillustrates a cross-sectional view of a chemical sensor600aincorporating waveguides214in an exterior surface of a 3D substrate205a, according to some embodiments. A mask605ain sensor600aoverlaps transparent portions that are not waveguides214on the side of sensor600aincluding the optical output of waveguides214. Mask605aimproves the signal-to-noise ratio (SNR) from the output of waveguides214.

FIG. 6Billustrates a cross-sectional view of a chemical sensor600bincorporating waveguides214in an interior surface of a 3D substrate, according to some embodiments. A mask605b(best seen inFIG. 6C) included in sensor600boverlaps the end of the sensor tube, serving a similar purpose as mask605ain sensor600a, above (cf.FIG. 6A).

Masks605aand605bblock background electromagnetic radiation that may propagate through the bulk of 3D substrates205aand205band may confuse the interference pattern formed at the detectors (e.g., interference patterns415and435, cf.FIG. 4). In that regard, masks605aand605bmay be formed of a material that is opaque or substantially opaque to the electromagnetic radiation propagating through waveguides214. Masks605aand605blimit the illumination from light source102mostly to waveguides214. Accordingly, masks605aand605bavoid illumination of the entire 3D structure, which is glass in some embodiments. In some embodiments, the portion of the cross section of the 3D structure occupied by waveguides214is small in comparison to the entire cross section of the 3D structure. Accordingly, masks605aand605bincrease the optical interferometric signal over a background optical signal, thus facilitating phase difference detection between waveguides214rand214s.

FIG. 6Cillustrates a side view of sensor600aofFIG. 6Aand sensor600bofFIG. 6B, according to some embodiments. As shown inFIG. 6C, mask605ais disposed on a surface of substrate205afacing detectors418and438(cf.FIG. 4). Likewise, mask605bis disposed on a surface of substrate205bfacing detector418(cf.FIG. 5).

FIG. 7illustrates a flow chart including steps in a method700for fabricating a sensor incorporating waveguides in a 3D substrate, according to some embodiments. The sensor in method700may include a 3D substrate having a cross-section and a length, the substrate supporting a plurality of waveguides embedded in the substrate (e.g., waveguides214in sensors100a,100b,300a, and300b, cf.FIGS. 2A, 2B, 3A, and 3B, respectively). The substrate may further include an exposed surface having at least a portion of a side surface of each waveguide, and sensitized coatings in the portion of the side surface of at least one of the plurality of waveguides (e.g., sensitized coatings212,222,232, and242). Methods consistent with the present disclosure may include at least one of the steps in method700, and not others. Likewise, methods consistent with method700may include all the steps in method700, in addition to other steps. Moreover, the specific order of the steps illustrated inFIG. 7is not limiting of different embodiments consistent with method700. In that regard, methods consistent with method700may include steps as illustrated inFIG. 7performed in different order, or at least two or more steps overlapping in time, or even two or more steps performed simultaneously.

Step702includes forming the 3D substrate in a shape that fits into a fluid container, such that the 3D substrate may have at least one surface exposed to the fluid. Accordingly, in some embodiments step702may include using a preform in the shape of a solid or hollow rod structure. Step702may also include selecting a material having a given index of refraction for the preform (e.g., n2). Step702should also include forming longitudinal regions with a higher refractive index than the bulk regions. The regions with higher refractive index will form the waveguides, after drawing the preform down to its final size. For example, step702may include selecting a 3D structure made of glass. Step704includes forming at least two channels on an exposed surface of the 3D substrate. The at least two channels in step704will become waveguides once the preform is formed into a waveguide structure, when the preform is drawn to its final size. Accordingly, step704may include selectively increasing the index of refraction of the selected portions of the preform (i.e., the at least two channels) to a value n1(n2<n1). In some embodiments, step706includes doping portions of the glass preform with heavy ions, or illuminating portions of the glass preform with electromagnetic radiation (such as ultra-violet radiation, or X-ray radiation). A preform as used in steps702through704may be on the order of ½ to 3 inches in diameter, according to some embodiments. Step704may include depositing, growing, fusing, inserting, or otherwise embedding channels with higher refractive index than the majority of the preform, in the preform. Step706includes heating and drawing the 3D substrate to reduce an outer diameter (OD) of the waveguide structure. Furthermore, step706may include heating and pulling the modified preform to a desired length in a draw tower.

Step708includes applying a sensitive coating on an exposed side of one of the waveguides. Accordingly, step708may include depositing a chemically sensitive coating using a chemical vapor deposition (CVD) technique. Other techniques for thin layer deposition as used in the semi-conductor and biomedical industries may be included and otherwise employed in step708. Step710includes disposing a mask on surfaces of the 3D substrate. Accordingly, in some embodiments step710includes disposing the mask on a surface that will face the detector. Furthermore, in some embodiments step710includes disposing a mask also in a surface of the 3D substrate facing the source of collimated light. In that regard, step710enhances removal of an optical background from a signal measured by the detector.

Step712includes disposing a detector at a selected position relative to an optical output of each of the at least two waveguides. Accordingly, step712may include disposing the detector so that the sensitive area of the detector overlaps a peak, or a dark node in an interference pattern formed by the waveguides embedded in the 3D substrate. Moreover, step712may include disposing the detector so that the sensitive area of the detector overlaps a portion of a peak and a portion of a dark node in the interference pattern. Step712may further include disposing the 3D substrate including the waveguides, and the detector, in a housing that protects the chemically sensitive coating and maintains the detector in the desired position.

FIG. 8illustrates a flow chart including steps in a method800for measuring a characteristic of a sample using a sensor, according to some embodiments. Method800may include using a light source, a beam-splitter, a sensor, and a detector in an interferometer configuration (e.g., light source102, beam-splitter104, sensor100, and detector118, cf.FIG. 1). Alternatively, the input beam splitter may be omitted by illuminating both waveguides of a sensing interferometer by a single, collimated, coherent beam that overlaps the two waveguides. The sensor may include a substrate having a cross-section and a length, the substrate supporting a plurality of waveguides embedded in the substrate (e.g., substrates205aand205b, and waveguides214, cf.FIGS. 4 and 5). An exposed surface of the substrate includes least a portion of a side surface of each of the plurality of waveguides. The plurality of waveguides includes at least a sensing channel having a sample waveguide and a reference waveguide (e.g., sensing channels210,220,230, and240, cf.FIGS. 2A, B). Accordingly, the sample waveguide may include a sensitized coating in a side surface that is included in the exposed surface of the substrate (e.g., sensitized coatings212,222,232, and242, cf.FIGS. 2A, B). Moreover, method800may be performed by an analyzer including a processor circuit executing commands stored in a memory circuit (e.g., analyzer160, processor circuit161, and memory circuit162).

Methods consistent with the present disclosure may include at least one of the steps in method800, and not others. Likewise, methods consistent with method800may include all the steps in method800, in addition to other steps. Moreover, the specific order of the steps illustrated inFIG. 8is not limiting of different embodiments consistent with method800. In that regard, methods consistent with method800may include steps as illustrated inFIG. 8performed in different order, or at least two or more steps overlapping in time, or even two or more steps performed simultaneously.

Step802includes exposing a sensitive surface of the sensor to a fluid. In some embodiments, step802includes allowing a target analyte to reach equilibrium on the sensitive surface of the sensor. Step804includes directing a first portion of light through a first waveguide in the sensor. In some embodiments, step804may further include splitting a coherent light beam using a beam splitter element and selecting the first portion of light from a first port in the beam splitter. Step806includes directing a second portion of light through a second waveguide in the sensor. Accordingly, step806may include selecting the second portion of light from a second port in the beam splitter. In some embodiments, steps804and806take place simultaneously.

Step808includes obtaining a phase relation between the first portion of light and the second portion of light at the output of the first and second waveguides. Accordingly, step808may include placing a phase retardation element in the optical path length of the first portion of light or the second portion of light between the light source and at least one of the first and second waveguides. In some embodiments, step808may include selecting a light beam having a coherence length longer than a length of the waveguides in the sensor. In some embodiments, step808includes splitting a light beam from a light source into the first portion of light and the second portion of light with a phase-preserving beam splitter element. Accordingly, step808includes obtaining a phase difference that results from the different phase velocities (i.e. optical path lengths) between a sensitized waveguide and a reference waveguide, as disclosed herein.

Step810includes detecting an interference signal with the detector. In some embodiments, step810includes detecting a portion of the interference signal comprising at least one of a peak, a dark node, or a portion of a peak and a dark node. In some embodiments, step810may include determining an interference pattern using an array of sensitive areas in the detector, or an array of detectors. Accordingly, step810may include detecting an interference pattern with a two-dimensional detector array. Furthermore, in some embodiments step810includes detecting an interference pattern with a one-dimensional detector array. And step812includes determining the characteristic of the sample based on a change in the interference signal from the detector. In some embodiments, step812includes determining an analyte concentration based on a change in the interference signal from the detector. Accordingly, step812may include finding the characteristic of the sample in a lookup table having a list of characteristics of the sample and a list of changes in interference signal values.

FIG. 9illustrates an exemplary drilling system900employing a sensor901incorporating waveguides in a 3D substrate, according to some embodiments. Sensor901may be the same as or similar to any one of sensors100,200a,200bdescribed in detail inFIG. 1and inFIGS. 2A-2Babove. Boreholes may be created by drilling into the earth902using drilling system900. Drilling system900may be configured to drive a bottom hole assembly (BHA)904positioned or otherwise arranged at the bottom of a drill string906extended into the earth902from a derrick908arranged at the surface910. The derrick908includes a kelly912used to lower and raise the drill string906.

The BHA904may include a drill bit914operatively coupled to a tool string916which may be moved axially within a drilled wellbore918as attached to the drill string906. During operation, drill bit914penetrates the earth902to form wellbore918. BHA904provides directional control of drill bit914as it advances into the earth902. Tool string916can be semi-permanently mounted with various measurement tools such as a measurement-while-drilling (MWD) tool and a logging-while-drilling (LWD) tool, and sensor901may form part of one of the MWD or LWD tools to obtain downhole measurements of drilling conditions. In other embodiments, the measurement tools may be self-contained within the tool string916, as shown inFIG. 9. In some embodiments, tool string916may include a fiber optic cable coupling a light source at surface910to sensor901(e.g., light source102, cf.FIG. 1). The fiber optic cable may be configured to convey electromagnetic radiation to sensor901(e.g., electromagnetic radiation110sand electromagnetic radiation110r, cf.FIG. 1).

Fluid or “mud” from a mud tank920may be pumped downhole using a mud pump922powered by an adjacent power source, such as a prime mover or motor924. The mud may be pumped from the mud tank920, through a stand pipe926, which feeds the mud into the drill string106and conveys the same to the drill bit914. The mud exits one or more nozzles arranged in the drill bit914and in the process cools the drill bit914. After exiting the drill bit914, the mud circulates back to the surface910via the annulus defined between the wellbore918and the drill string906, and in the process returns drill cuttings and debris to the surface. The cuttings and mud mixture are passed through a flow line928and are processed such that a cleaned mud is returned down hole through the stand pipe926once again. Sensor901may be configured to measure characteristics of the mud near where drill bit914forms wellbore918. In that regard, mud in the wellbore near drill bit914may be the fluid to which sensor901is exposed, for measurement (e.g., fluid150, cf.FIGS. 1, 4 and 5). In that regard, measurement procedures using sensor901may include any one or all of the steps in a method for measuring a characteristic of a sample using a sensor as disclosed herein (e.g., method800, cf.FIG. 8).

Although drilling system900is shown and described with respect to a rotary drill system inFIG. 9, those skilled in the art will readily appreciate that many types of drilling systems can be employed in carrying out embodiments of the disclosure. For instance, drills and drill rigs used in embodiments of the disclosure may be used onshore (as depicted inFIG. 9) or offshore (not shown). Offshore oil rigs that may be used in accordance with embodiments of the disclosure include, for example, floaters, fixed platforms, gravity-based structures, drill ships, semi-submersible platforms, jack-up drilling rigs, tension-leg platforms, and the like. It will be appreciated that embodiments of the disclosure can be applied to rigs ranging anywhere from small in size and portable, to bulky and permanent. Further, although described herein with respect to oil drilling, various embodiments of the disclosure may be used in many other applications. For example, disclosed methods can be used in drilling for mineral exploration, environmental investigation, natural gas extraction, underground installation, mining operations, water wells, geothermal wells, and the like. Further, embodiments of the disclosure may be used in weight-on-packers assemblies, in running liner hangers, in running completion strings, etc., without departing from the scope of the disclosure.

FIG. 10illustrates a well system1000employing a sensor1001incorporating waveguides in a 3D substrate, according to some embodiments. Sensor1001may be the same as or similar to any one of sensors100,200a,200bdescribed in detail inFIG. 1and inFIGS. 2A-Babove. As illustrated, well system1000may include a service rig1020that is positioned on the earth's surface1040and extends over and around a wellbore1060that penetrates a subterranean formation1080. Service rig1020may be a drilling rig, a completion rig, a workover rig, or the like. In some embodiments, service rig1020may be omitted and replaced with a standard surface wellhead completion or installation. Moreover, while well system1000is depicted as a land-based operation, it will be appreciated that the principles of the present disclosure could equally be applied in any sea-based or sub-sea application where service rig1020may be a floating platform or sub-surface wellhead installation, as generally known in the art.

Wellbore1060may be drilled into subterranean formation1080using any suitable drilling technique and may extend in a substantially vertical direction away from the earth's surface1040over a vertical wellbore portion1100. At some point in wellbore1060, vertical wellbore portion1100may deviate from vertical relative to the earth's surface1040and transition into a substantially horizontal wellbore portion1120. In some embodiments, wellbore1060may be completed by cementing a casing string1140within wellbore1060along all or a portion thereof. As used herein, “casing string” may refer to any downhole tubular or string of tubulars known to those skilled in the art including, but not limited to, wellbore liner, production tubing, drill string, and other downhole piping systems.

System1000may further include a downhole tool1160conveyed into wellbore1060. Downhole tool1160may be coupled or otherwise attached to a conveyance1180that extends from service rig1020. Conveyance1180may be, but is not limited to, a wireline, a slickline, an electric line, coiled tubing, or the like. In some embodiments, device1160may be pumped downhole to a target location within wellbore1060using hydraulic pressure applied from service rig1020at surface1040. In some embodiments, downhole tool1160may be conveyed to the target location using gravitational or otherwise natural forces. Downhole tool1160can be semi-permanently mounted with various measurement devices such as sensor1001. In some embodiments, conveyance1180may include a fiber optic cable coupling a light source at surface1040to sensor1001(e.g., light source102, cf.FIG. 1). The fiber optic cable may be configured to convey electromagnetic radiation to sensor1001(e.g., electromagnetic radiation110sand electromagnetic radiation110r, cf.FIG. 1).

Even thoughFIG. 10depicts downhole tool1160as being arranged and operating in horizontal portion1120, embodiments disclosed herein are equally applicable for use in portions of wellbore1060that are vertical, deviated, or otherwise slanted. Moreover, use of directional terms such as above, below, upper, lower, upward, downward, uphole, downhole, and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure, the uphole direction being toward the surface of the well and the downhole direction being toward the toe of the well.

Those skilled in the art will readily appreciate that the methods described herein, or large portions thereof, may be automated at some point such that a computerized system may be programmed to design, predict, and devices that are more robust for compact optical systems operating in extreme environments. Computer hardware used to implement the various methods and algorithms described herein can include a processor configured to execute one or more sequences of instructions, programming stances, or code stored on a non-transitory, computer-readable medium. The processor can be, for example, a general purpose microprocessor, a microcontroller, a digital signal processor, an application specific integrated circuit, a field programmable gate array, a programmable logic device, a controller, a state machine, a gated logic, discrete hardware components, an artificial neural network, or any like suitable entity that can perform calculations or other manipulations of data. In some embodiments, computer hardware can further include elements such as, for example, a memory (e.g., random access memory (RAM), flash memory, read only memory (ROM), programmable read only memory (PROM), electrically erasable programmable read only memory (EEPROM)), registers, hard disks, removable disks, CD-ROMS, DVDs, or any other like suitable storage device or medium.

Executable sequences described herein can be implemented with one or more sequences of code contained in a memory. In some embodiments, such code can be read into the memory from another machine-readable medium. Execution of the sequences of instructions contained in the memory can cause a processor to perform the process steps described herein. One or more processors in a multi-processing arrangement can also be employed to execute instruction sequences in the memory. In addition, hard-wired circuitry can be used in place of or in combination with software instructions to implement various embodiments described herein. Thus, the present embodiments are not limited to any specific combination of hardware and/or software.

As used herein, a machine-readable medium will refer to any medium that directly or indirectly provides instructions to a processor for execution. A machine-readable medium can take on many forms including, for example, non-volatile media, volatile media, and transmission media. Non-volatile media can include, for example, optical and magnetic disks. Volatile media can include, for example, dynamic memory. Transmission media can include, for example, coaxial cables, wire, fiber optics, and wires that form a bus. Common forms of machine-readable media can include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, other like magnetic media, CD-ROMs, DVDs, other like optical media, punch cards, paper tapes and like physical media with patterned holes, RAM, ROM, PROM, EPROM and flash EPROM.

A. A sensor for measuring a characteristic of a substance that includes a substrate having a cross-section and a length, a plurality of waveguides embedded in the substrate, the substrate providing an exposed surface, the exposed surface comprising a portion of a side surface of at least one of the plurality of waveguides, and a sensitized coating positioned on the exposed surface of the at least one of the plurality of waveguides.

B. A method for fabricating a sensor that includes forming a substrate in a three-dimensional shape, arranging at least two waveguides on an exposed surface of the substrate, applying a sensitive coating on an exposed side of one of the at least two waveguides, the exposed side being adjacent the exposed surface, and disposing a detector at a selected position relative to an optical output of each of the at least two waveguides.

C. A method for measuring a characteristic of a substance that includes exposing a surface of a sensor to the substance, the sensor including a substrate, a plurality of waveguides embedded in the substrate, and a sensitized coating positioned on a portion of at least one of the plurality of waveguides, directing a first portion of light through a first waveguide of the plurality of waveguides and thereby generating a first output signal, directing a second portion of light through a second waveguide of the plurality of waveguides and thereby generating a second output signal, obtaining a phase relation between the first portion of light and the second portion of light at an output of the first and second waveguides, generating an interference signal by combining the first and second output signals, detecting at least a portion of the interference signal with a detector, and determining the characteristic of the substance based on a change in a feature of the interference signal detected with the detector.

Each of embodiments A, B, and C may have one or more of the following additional elements in any combination: Element 1: wherein the exposed surface is curved in a direction perpendicular to a light propagation in the waveguide. Element 2: further comprising a detector arranged to receive an interference pattern generated from two waveguides of the plurality of waveguides, and configured to generate a signal corresponding to a change in an interference pattern, the change in the interference pattern induced by the characteristic of the substance. Element 3: wherein the interference pattern is formed in a free space between the detector an optical output of the waveguides. Element 4: wherein the sensitized coating comprises one of a chemically sensitive layer, a biologically sensitive layer, a hydrophilic layer, or a hydrophobic layer. Element 5: wherein the plurality of waveguides comprise a sample waveguide having the sensitized coating positioned thereon and being optically coupled with a signal electromagnetic radiation portion, a reference waveguide adjacent the sample waveguide and being optically coupled with a reference electromagnetic radiation portion, the reference radiation having a determined phase relation with the sample radiation. Element 6: further comprising a second sample waveguide being optically coupled with a second signal electromagnetic radiation portion, wherein the second signal electromagnetic radiation portion has a determined phase relation with the reference electromagnetic radiation portion. Element 7: further comprising a mask applied to the substrate to prevent background radiation in the substrate from reaching a detector. Element 8: wherein the sensitized coating targets one of the group consisting of water, gas, oil, methane, a hydrocarbon, a unicellular microorganism, an iron ion, and an alkali metal. Element 9: wherein the plurality of waveguides include at least a sample waveguide and a reference waveguide, the sensor further comprising a detector array to measure at least a portion of an interference pattern generated by the sample waveguide and the reference waveguide. Element 10: wherein the sensitized coating is configured to contact a substance including a target analyte. Element 11: wherein the substrate is cylindrical and the exposed surface is positioned at an inner diameter of the substrate.

Element 12: further comprising disposing a mask on a surface of the substrate that faces the detector. Element 13: further comprising heating and drawing the substrate to reduce an outer diameter (OD) of the waveguide structure. Element 14: wherein the at least two waveguides include a sample waveguide and a reference waveguide, the method further comprising determining an interference pattern for light emerging from the sample waveguide and the reference waveguide to select a position for disposing the detector. Element 15: further comprising overlapping a sensitive area of the detector with at least one of a peak of the interference pattern, a dark node of the interference pattern, and a portion of a peak and a dark node of the interference pattern.

Element 16: wherein exposing the sensitive surface of the sensor comprises allowing a target analyte to reach equilibrium on the sensitive surface of the sensor. Element 17: wherein obtaining a phase relation between the first portion of light and the second portion of light comprises splitting a light beam from a light source into the first portion of light and the second portion of light with a phase-preserving beam splitter element. Element 18: wherein detecting the interference signal with the detector comprises detecting a portion of the interference signal comprising at least one of a peak, a dark node, or a portion of a peak and a dark node. Element 19: wherein detecting the interference signal with the detector comprises coupling at least a portion of the interference signal to an optical fiber and transmitting the coupled portion to a remotely located detector. Element 20: wherein obtaining a phase relation between the first portion of light and the second portion of light comprises illuminating the first and second waveguides with a collimated and coherent light. Element 21: wherein determining the characteristic of the substance comprises finding the characteristic of the substance in a lookup table having a list of characteristics of the substance and a list of changes in interference signal values. Element 22: wherein determining the characteristic of the substance comprises determining at least one of a water concentration, a gas concentration, an oil concentration, a water-to-oil ratio, a methane concentration, or a hydrocarbon concentration, a unicellular microorganism presence or a unicellular microorganism concentration.