Evanescent wave downhole fiber optic spectrometer

1. Field of the Invention The present invention generally relates to wellbore tools and in particular to apparatus and methods for estimating wellbore fluid property.

2. Description of Related Art Oil and gas wells have been drilled to depths in the range of a few hundred meters to as deep as eight kilometers. A large portion of current drilling activity involves directional drilling that includes drilling drills from the vertical by a few degrees up to the horizontal to increase hydrocarbon production from underground earth formations.

Information on underground formations traversed by the borehole can be obtained by any number of techniques. Some techniques used to obtain formation information include obtaining one or more core samples from underground formations and obtaining one or more fluid samples produced from underground formations. These sampling are collectively referred to herein as training sampling. Modern fluid sampling includes several downhole tests and sometimes fluid samples are taken for surface laboratory testing. However, the high costs of oil and gas exploration create a big trend toward improved methods and devices for downhole testing.

What is needed, therefore, are improved methods and apparatus for fluid well bottom testing. Preferably,

Petition 870190070224, of July 24, 1919, p. 4/34

2/22 methods and apparatus that provide users with capabilities to quickly identify constituents of a fluid sample.

SUMMARY OF THE INVENTION An embodiment of the invention includes an apparatus for estimating a property of a downhole fluid, the apparatus includes: an optical fiber that receives a light source and includes an uncoated portion adapted to contact with the fluid; a photodetector for receiving optical signals from the portion; and a spectrometer to obtain an evanescent spectrum of portion fluid.

[006] Another embodiment of the invention includes a method for estimating a property of a downhole fluid, the method includes: selecting a downhole spectrometer that includes an optical fiber with at least one uncoated portion; that at least partially contacts the portion in the downhole fluid; receive light emitted from a light source through the optical fiber; estimate an evanescent spectrum of fluid from the received light; and estimate property from the spectrum.

An additional embodiment of the invention includes a system for characterizing a fluid in a downhole environment, the system includes: at least one light source for input of an optical fiber having an uncoated portion adapted to contact with the fluid; a photodetector for receiving optical signals from the portion; a spectrometer for obtaining an evanescent spectrum of fluid from the portion; and an electronic unit adapted to receive evanescent spectrum information and characterize the fluid.

BRIEF DESCRIPTION OF THE DRAWINGS For a detailed understanding of the present disclosure, reference should be made to the following detailed description of the various non-limiting embodiments, taken in conjunction with the accompanying drawings, in which like elements were given similar numerals and

Petition 870190070224, of July 24, 1919, p. 5/34

3/22 where:

[009] Figure 1 represents aspects of a profiling cable system for profiling in a borehole;

Figure 2 depicts aspects of a system for profiling during drilling;

Figure 3 depicts aspects of a fiber optic spectrometer useful for characterizing petroleum;

Figure 4 represents aspects of another embodiment of the fiber optic spectrometer useful for characterizing petroleum; and Figure 5 is a flowchart offering an exemplary method for characterizing fluid (s) with the downhole spectrometer.

DESCRIPTION OF THE INVENTION Methods and apparatus are described herein for at least one of analyzing a downhole fluid and identifying constituents of the fluid by collecting evanescent wave optical absorption spectra. The techniques provided make use of an optical fiber immersed or at least partially close to the fluid. Exemplary optical fibers include those made from silicon, germanium and sapphire. The techniques are particularly well suited for medium infrared spectroscopy and can be used to estimate issues such as the percentage of oil-based sludge contamination as well as hydrogen sulfide (H2S), carbon dioxide (CO2) concentrations as well as methane, ethane, propane and butane concentrations.

Now for context, an exemplary apparatus for oil and gas exploration is considered. Figure 1 schematically illustrates aspects of a profiling cable apparatus used for oil and gas exploration. In the example shown, a borehole 110 or borehole

Petition 870190070224, of July 24, 1919, p. 6/34

Borehole 110 traverses subsoil materials which may include various underground formations 102. borehole 110 may be filled or at least partially filled with a fluid mixture comprising various gases, water, drilling fluid and forming fluids which they are native to underground formations penetrated by borehole 110. Such fluid mixtures are referred to herein as "borehole fluids" or "borehole fluids". The terms "innate fluid" and "natural fluid" as used herein refer to fluids that exist naturally or are extracted from underground formations 102 and unique to any mixture or substantial contamination with fluids not naturally present in the formation, such as fluid. drilling

In this non-limiting example, a formation assessment tool 120 is conducted in the well borehole 110 using a profiling cable 104. Placing and withdrawing of the profiling cable can be accomplished by an energized winch driven by a service truck 108, for example. Profiling cable 104 may be a shielded cable carrying data and power conductors to power the forming evaluation tool 120 and to provide two-way data communication between the tool processor 112 and a loadable controller 114 by the service truck 108. In general, the profiling cable 104 is loaded from a coil 116 by a pulley 118 supported by a tower 122. Coil 116 may be loaded by truck 108 as shown for shore operations, a subsea marine platform or any other suitable furniture or fixed support structure. Controller 114 may include a processor, such as within a computer or a microprocessor, data storage devices such as solid state memory and magnetic tapes, peripherals such as input devices.

Petition 870190070224, of July 24, 1919, p. 7/34

5/22 data and display devices and other circuits for controlling and processing data from the training evaluation tool 120. Surface controller 114 may further include one or more computer programs embedded in a processor-readable computer-readable medium in controller 114 to execute instructions contained in computer programs to perform the various methods and functions associated with processing data from the processor. training assessment tool 120. It may also be useful in profiling to identify fluid phases in the wellbore and to identify which phases (gas, water, oil) are being produced from a particular borehole.

A lower portion of the forming assessment tool 120 may include an assembly of several tool segments that are joined end to end by helical sleeves or mutual compression joints 124. A suitable tool segment assembly for the present invention may include a power unit 126 which may include one or more than one hydraulic power unit, an electric power unit or an electromechanical power unit. In the example shown, a forming fluid puller 128 is coupled to the forming evaluation tool 120 below the power unit 126. A large displacement motor / pump unit 130 may be offered below the forming fluid puller 128. for line drainage. A similar motor / pump unit 132 having a smaller displacement volume may be included in the tool at a suitable location, such as below the large volume pump, to quantitatively monitor the fluid received by the formation assessment tool 120. One or More sample tank compartment sections 134 may be included to hold fluid samples from the small volume pump 132. Each compartment section 134 may have several sample tanks.

Petition 870190070224, of July 24, 1919, p. 8/34

136. In several embodiments to be described in more detail below, the formation assessment tool 120 includes a downhole spectrometer 300. The downhole spectrometer 300 may be used in both embodiments during the formation. perforation as in the form of cable forming.

Forming fluid extractor 128 generally includes an extendable suction probe 138 which is opposed by orifice wall feet 140. Both suction probe 138 and opposite feet 140 may be hydraulically or electromechanically extendable to engage firmly to the well borehole wall.

Figure 2 schematically illustrates a non-limiting example of a drilling system 200 in a metering during drilling (MWD) arrangement according to various non-limiting embodiments of the description. A tower 202 supports a drill string 204, which may be a coiled pipe or a drill pipe. The drill string 204 may carry a wellbore assembly (BHA) 220 and a drill bit 206 at a distal end of the drill string 204 to drill the borehole 110 through various earth formations and subsoil materials.

Drilling operations according to various embodiments may include pumping drilling fluid or "mud" from a mud tank 222, and using a circulation system 224, which circulates the mud through an internal hole in the drill string. 204 The mud exits the drill string 204 in drill bit 206 and returns to the surface through an annular space between drill column 204 and the inner wall of borehole 110.0 drilling fluid is designed to provide hydrostatic pressure that is higher. that the formation pressure to prevent bursts. Pressurized drilling fluid may further be used to drive a drilling motor 208 and may provide lubrication for various elements of the

Petition 870190070224, of July 24, 1919, p. 9/34

7/22 drill string 204.

In the non-limiting embodiment of FIG. 2, BHA 220 includes a formation assessment tool 120 substantially similar to the formation assessment tool 120 described above and shown in figure 1.

A formation evaluation tool during drilling 120 may carry a fluid extractor 128 that includes an extendable suction probe 138 and opposite feet 140. In various embodiments to be described in more detail below, the formation evaluation tool 120 includes wellbore spectrometer 300. Wellbore spectrometer 300 can be used in both drilling and profiling cable modalities. Of course, other modalities can be performed in the same way. For example, the downhole spectrometer 300 may be used as a part of a tractor (i.e. a downhole device, independent of a profiling and generally self-propelled cable).

Referring to Figure 3, and with respect to evanescent wave spectroscopy and downhole spectrometer 300, an illustration is provided for better perspective. In Figure 3, an optical fiber 310 generally includes a sheath 301 and a core 302. In this example, which represents some aspects of the downhole spectrometer 300, a portion of the fiber 310 is uncoated. That is, core 302 is exposed and without the coating surrounding it 301. This portion of fiber 310 may be referred to as "uncoated". The exposed core portion 302 is at least partially surrounded by a sample 303 and may be enclosed with or traversing a sample chamber 305 (such as a channel, a cell, a sample line, a volume, a sampling area or similar device). It should be noted that the uncoated portion, although it may be within a

Petition 870190070224, of July 24, 1919, p. 10/34

The sample chamber 305 may be in any area or volume where the sample 303 contacts at least part of a surface of the uncoated portion. The downhole fluid sample 303 may be a flowing fluid or a nonflowing fluid. In general, the fluid may be pumped, ported, added, drained, charged, left or otherwise moved in contact with the uncoated portion for analysis.

A light beam is provided to a fiber interface 310. As light passes through the exposed portion of core 302, light that is incident upon the core / sample interface is partially reflected and partially refracted in sample 303. This occurs if an angle of incidence is less than a critical angle. With an increase in the incidence angle, the reflected light portion is increased, and if the incidence angle exceeds a critical angle, the total internal reflection is performed. The critical angle depends on the refractive index of the core material, m, and the sample material, ri2. A harmonic wave is referred to as the “evanescent wave”. The evanescent wave enters sample 303 at a penetration depth, d_P, and is described by Eq. (1):

d);

Where z represents a normal distance to the interface between sample 303 and core 302, Eo represents the amplitude of a wave at z = 0. A penetration depth, d, in sample 303 is given by Eq. (2) :

= VGit •^27r) (sin^2<9-G2₁/ T2₂)²y (²);

Where λ represents a wavelength of light at core 302 of fiber 310, m represents a refractive index (RI) of core 302, and Π2 represents the refractive index of sample 303. Likewise, and as an example, for an input of θ = 85 (degrees), λ - 2,000 (nm), ni = 1,75 and 1Ί2 = 1,5, the depth of penetration, d_P, is estimated as

Petition 870190070224, of July 24, 1919, p. 11/34

9/22

92.34 nm.

[0027] The fiber optic spectrometer at present includes several adaptations to provide operation in a downhole environment. For example, some materials previously used for medium infrared optical fibers (such as silver halides) are not practical for downhole use as such materials are brittle and easily ruptured. Moreover, such materials have highly unacceptable solubility and reactivity in forming fluids such as brines or crude oils, and such solubility and reactivity increases at the high temperatures found in the downhole environment.

Thus, the teachings of the present offer embodiments of a deep-sea spectrometer that make use of, among other things, high refractive index fiber optic material, little or no solubility, and little or no reactivity in high temperature formation and little absorption over the wavelengths of interest.

The materials selected for the downhole spectrometer 300 generally exhibit a select group of properties, such as, and without limitation, non-adherent, non-corrosive surfaces, high refractive index, insolubility, and other properties as may be desired for. the deep end. Suitable materials for downhole spectrometer 300 generally will not deteriorate at high temperature in the presence of water.

Thus, in some embodiments, a metalloid is used for the wellbore spectrometer 300. A metalloid behaves as a mirror at shorter wavelengths and as a transparent window at longer wavelengths. Metalloid, in one example, silicon, has an added advantage of being an almost unreactive and non-adherent surface, so it's tough

Petition 870190070224, of July 24, 1919, p. 12/34

10/22 both fluid corrosion and contamination by fluid deposits. Germanium is also relatively non-chemically reactive and a suitable material. Silicon and germanium are both semiconductors, so they have a gap in the band, so they operate as a mirror for photons with energy greater than the gap in the band and operate as a transparent window for photons with energy less than the energy of the gap. in the band. Silicon, for example, changes the behavior of a mirror to a window at wavelengths greater than about 1,100 nm and germanium changes from a mirror to a window at wavelengths greater than about 1,800 nm.

In order to provide some context for the teaching of the present, a review of fiber optic fundamentals in relation to the downhole spectrometer is now offered. A principle of fiber optics is that light is fully reflected in a core coating interface if light strikes that interface at an arrival angle that exceeds a critical angle. The fiber core must have a higher refractive index than the coating surrounding the core for the critical angle to exist. However, even in the case of total internal reflection, there is an evanescent field of reflected light that exponentially decays below the nucleus. This means that a portion of the light slightly penetrates the coating to a depth that is less than a few wavelengths. If the coating happens to be so highly absorbent at the wavelengths of light that significant light is absorbed within the evanescent penetration depth, d_Pthen the attenuated reflection spectrum of the coating can be obtained. If a material exhibiting a sufficiently high refractive index for the fiber core is used, then the forming fluid, which at least partially surrounds the core that is inserted, can act as the coating. In this case, an absorption spectrum could be obtained for the forming fluid using the evanescent signal. At

Petition 870190070224, of July 24, 1919, p. 13/34

11/22 fundamental molecular vibrational bands, which occur in the mid-infrared regions of the spectrum (about 2.5 to 11 microns), are several orders of magnitude more absorbent than the overtone and combination bands that occur in the near infrared region ( 0.8 to 2.5 microns) of the spectrum. The effective path length for an evanescent wavelength spectrometer is quite short. It equals the product of penetration depth of only less than a few microns with the number of internal reflections. Because the measured absorbance is the product of effective path length and absorbance, it is preferable to make evanescent wavelength measurements in the high-infrared, mid-infrared region to compensate for short effective path length.

In order to provide a robust downhole spectrometer, the fiber core material must have high chemical and thermal resistance to withstand the hostile downhole environment. The core material should also have a refractive index that is higher than the typical downhole gas brine (RI <1.3) (RI in the range of 1.30 to 1.33) or crude oil (RI in the 1.40 to 1.55). Preferably, it should also have the ability to transmit medium infrared light. Examples of suitable materials include sapphire (RI = 1.75, transmits at wavelengths as long as 5 microns), elemental silicon (RI = 3.4, transmits at wavelengths as long as 11 microns), elemental germanium (RI = 4, transmission at wavelengths as long as 20 microns) and other such materials. Elemental silicon and germanium look like bright metals in the visible region of the electromagnetic spectrum, but become transparent at longer wavelengths (1,100 nm for silicon and 1,800 nm for germanium). The mid-infrared region is of particular interest for use with a downhole spectrometer, and ranges from about 2,500 nm (2.5 microns) to 11,000 nm (11 microns).

Petition 870190070224, of July 24, 1919, p. 14/34

Thus, it can be seen that the selection of fiber optic 310 should consider material properties in core 302 as well as properties of sample 303. Table 1 below provides non-limiting examples of materials suitable for use in core 302 from fiber optic 310 compared to the property of sample materials.

Table 1 Refractive Indexes for Wellbase Spectrometer, m, and Sample,

<td colspan="2">ni = Core Refractive Index</td><td colspan="2">Π2 = Refractive Fluid Index</td>

<td>Sapphire (AI2O3)</td><td> 1,75</td><td>Brine</td><td>1.3 to 1.33</td>

<td>Silicon</td><td> 3,42</td><td>Crude oils</td><td>1.4 to 1.55</td>

<td>Germanium</td><td> 4,00</td><td>Gas</td><td> &lt; 1,3</td>

<td>Boron</td><td> 3,0</td><td colspan="2"></td>

<td>Tellurium</td><td>1.7 to 2.7</td><td colspan="2"></td>

<td>Diamond film</td><td> 2,42</td><td colspan="2"></td>

<td>Gallium and Lanthanum Sulphide</td><td> 2,40</td><td colspan="2"></td>

<td>Rutile (TiO₂)</td><td> 2,56</td><td colspan="2"></td>

<td>Yttrium Aluminum Grenade (YAG)</td><td> 1,82</td><td colspan="2"></td>

Aspects and considerations specific to various materials are not offered. Although it is considered that metalloids are generally appropriate, arsenic, polonium and antimony have not been considered or evaluated for use in the downhole spectrometer 300 due to toxicity issues. However, this does not suggest that these materials could not perform well. On the contrary, it is considered that there is a likelihood that such materials may

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13/22 probably work well since they are members of the metalloid family.

With respect to other materials and considerations for constructing wellbore 300 spectrometer, tellurium thin films have shown favorable properties such as low band gap and infrared region transparency. The diamond exhibits a transmission range of about 300 nm to 2.5 microns and a refractive index of 2.4175 at 0.589 microns, and is insoluble in water. Germanium has a transmission range of about 1.8 to 23 microns, a refractive index of 4.0026 at 11 microns and is insoluble in water. Gallium and lanthanum sulfide is a calcogenated glass, and an alternative to toxic arsenic-based glass, which exhibits a transmission range of about 0.5 to 10 microns and a refractive index of 2.398 at 1.014 microns. Rutile (titanium dioxide) exhibits a transmission range of about 0.43 to 5.0 microns, a refractive index of 2.555 to 0.69 microns and is insoluble in water. Sapphire exhibits a transmission range of about 0.17 to 5.5 microns and a refractive index of 1.75449. Silicon exhibits a transmission range of about 1.2 to 15 microns, a refractive index of 3.4223 at 5 microns and is insoluble in water. YAG (Y3AI5O12 Yttrium Aluminum Oxide) exhibits a transmission range of about 0.21 to 5.5 microns, a refractive index of 1.81523 at 1.06 microns and is insoluble in water.

The downhole spectrometer 300 can be performed in various ways. In one embodiment, optical fiber 310 (such as a silicon fiber or a germanium fiber) is attached to a substrate. The substrate provides mechanical reinforcement that reduces brittleness, as modalities using semi metals are somewhat fragile. In this way, the fiber optic 310 mounted on a general substrate offers users a design that is tolerant to vibration. Some further modalities of vibration tolerant designs include mounting

Petition 870190070224, of July 24, 1919, p. 16/34

14/22 on resilient devices such as motion damping springs and the like.

In some other embodiments, the downhole spectrometer includes a photonic wire waveguide (such as a silicon wire) on a substrate that is very sensitive to residual amounts of sample 303. In additional embodiments, the spectrometer Wellhead 300 includes attenuated reflection optical windows made of silicon or germanium (e.g., windows between about 2 mm and about 3 mm). More specifically, Finite Element Analysis shows that windows made of these semi metals can withstand downhole pressures and temperatures.

In addition, various other physical forms of fiber optic material may be used. More specifically, it is recognized that certain aspects of the teachings of the present are offered in the context of an optical fiber. However, downhole spectrometer 300, in at least some embodiments, may be performed in other ways, such as a thin film waveguide. That is, in some instances, thin films may provide material waveguides that may not meet all downhole performance criteria. For example, thin-film waveguides may offer robust wellbore spectrometer 300 modalities when using materials such as boron, diamond, silicon, germanium, sapphire, brittle, etc. In modalities using thin film waveguides, the material used in the downhole spectrometer may be supported on a rigid substrate and may be prepared by standard wafer processing techniques. These thin films, "optical wires" or "silicon photonics" can act as optical waveguides in the same way as a round optical fiber could, even if they have a different cross section, such as a square or rectangular cross section. Accordingly, as used herein, the terms “optical fiber”, “spectrometer

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15/22 "and other related terms shall be construed by including thin film waveguides in a manner useful for performing evanescent downhole spectroscopy.

Referring now to Figure 4, aspects of another embodiment of the downhole spectrometer 300 are shown. In this example, the downhole spectrometer 300 includes an infrared light source 401 in optical communication with a hollow waveguide 402 for transmitting light on a fiber optic element 403. In some embodiments, at the distal end of the fiber optic element 403, there is a mirror 404, such as a gold mirror 404 at the tip end of the fiber that can be included and used to reflect light in the fiber optic element 403.0 crude oil. , or other fluid to be analyzed, acts as a coating on the fiber and is denoted by the hatch marks between the indicators 403 and 404. The waveguide 402 transmits the reflected light to at least one photodetector 405. The photodetector 405 may include, for example, a plurality of detection elements for oil specific wavelength (s) or other selected wellbore fluid (s). The electronic 410 may be included and used to control light source 401, analyze signals from photodetector 405 and to transmit signals to remote locations as desired.

The photodetector 405 is generally used to receive light emitted from the light source 401 after the light has interacted with the fluid via the return optical fiber 403. In one or more embodiments, the photodetector 405 comprises a single Broadband photodetector responsive to light emitted from light source 401 and / or light reflected on a fluid metalloid interface. In other non-limiting embodiments, photodetector 405 includes a dual layer photodetector responsive to light emitted from light source 401 and / or light reflected at the fluid metalloid interface. A suitable mode for the photodetector

Petition 870190070224, of July 24, 1919, p. 18/34

16/22

405 includes a dual layer photodetector which is a dual layer photodetector of Si and InGaAs. The photodetector 405 provides an output signal indicative of the light received on the photodetector 405 for the electronic unit 42.

In some cases, the photodetector output signal may be an analog electrical signal, so an analog to digital converter may be used to convert the photodetector output signal to a digital signal that is received by a background controller. well inside electronics unit 410 or by surface controller 114. Light emitted from light source 401 may be modulated by a processor within the same controller receiving photodetector output 405 or by a modulator in a separate controller. In the example shown, one modulator / controller is coupled to photodetector 405 and a second modulator / controller is coupled to light source 401. These controllers may be deployed as a single controller without departing from the scope of the description. In other embodiments, the controller or controllers may be located on the surface of the well borehole as described above and shown in Figures 1 and 2 in 114 using any of the various communication methods. Cooling of one or more of these downhole components can be accomplished using a cooling device. The cooling device used may be any one or more of a variety of devices, examples of which include electrothermal, thermal tunneling, sorption cooling, evaporators and a dewar. Cooling is optional where selected components are compatible with the downhole temperature environment.

Cooling may be applied where a component operating temperature is below that of the downhole environment and / or where cooling may improve the performance of the spectrometer.

Petition 870190070224, of July 24, 1919, p. 19/34

17/22 downhole 300. In various embodiments, the light source 401 is compatible with the downhole temperature environment and the cooling device is optional. Cooling, in some cases, increases a signal to noise ratio of photodetector 405 and increases laser brightness where light source 401 includes one or more lasers.

The non-limiting examples of spectrometer tools described herein provide a small, lightweight, fiber optic downhole spectrometer that has substantially higher resolution than conventional spectrometers. In addition, the spectrometer 300 may include in situ calibration capabilities, such as through the use of a positionable reference material and a light source that generates both short and long wavelengths.

In various embodiments, the light source 401 may include one or more broadband light sources such as an incandescent light source together with an optical filter to provide selected wavelengths, or the light source 401 may include one or more light emitting diodes (LEDs). The light source may also use one or more laser diodes. In other embodiments, downhole spectrometer 300 may include one or more light sources 401 which include a combination of light source types. Some modalities can be used as multiple wavelength deployments. For example, an incandescent light and a dual pass filter can be used as a 401 light source to generate two selected wavelengths. Alternatively, dual wavelength diodes or laser diodes may be used. The dual wavelength light can be conducted via optical fiber 403 to a silicon or germanium tip immersed in target fluid within a fluid cell. An anterior 405 double layer photodetector can be used to detect light reflected at the fluid interface. In one embodiment, both wavelengths include

Petition 870190070224, of July 24, 1919, p. 20/34

18/22 a short wavelength light and a long wavelength light, where the short wavelength light is a light having a lower energy than the gap in the metalloid material band and the light of wavelength. Longwave is a light that has a higher energy than the gap in the band of the metalloid material.

As one skilled in the art will appreciate, a "single wavelength" as discussed herein may in fact appear as a wavelength band, such as a peak in a spectrum. Thus, a plurality of wavelengths may actually manifest as a plurality of wavelength bands as effectively discriminated by associated electronics. In addition, the use of various types or combinations of optical filters for refining light and wavelength groups as may be used with the downhole spectrometer 300. In some embodiments, light source 32 may be adjusted to suit multiplex varying wavelengths by time.

The dual wavelength photodetector can provide a short wavelength detector and a long wavelength detector to simultaneously detect the wavelengths reflected at the fluid interface. In some embodiments, when using a fiber having a Si or Ge material and a Si and InGaAs detector, the Si portion of the detector will detect the highest intensity reflections of short wavelength light while the InGaAs portion detector detects reflections of lower intensity of long wavelength light.

With respect to material selection, an advantage of a silicon interface is that a silicon interface provides a soft surface that is resistant to contamination by downhole fluid deposits. In addition, silicon acts as a mirror for light wavelengths less than about 1,100 nm and is substantially

Petition 870190070224, of July 24, 1919, p. 21/34

19/22 transparent for wavelengths greater than about 1,100 nm. This feature is useful in the dual wavelength modalities described above. As described above, germanium is another exemplary metalloid that offers properties suitable for use as fiber optics.

In some embodiments, at least one of the light source 401, the electronic unit 410 and the photodetector 405 may be maintained remotely. For example, at least one of light source 401, electronics unit 410 and photodetector 405 may be provided on the production deck. In such embodiments, users and designers are offered the opportunity to employ a large component arrangement to perform necessary tasks. In such embodiments, communication with downhole spectrometer components 300 may occur across a variety of devices, including, without limitation, wired pipe, fiber, telemetry and the like. In other embodiments, at least one of the light source 401, the electronics unit 410 and the photodetector 405 may be included in the wellbore spectrometer 300 near the sample chamber 305. In the latter embodiments, the downhole spectrometer 300 may make use of components such as downhole power supplies, cooling units and the like.

In general, the downhole spectrometer 300 offers “real time” results. That is, the downhole spectrometer 300 provides results at a rate that is useful for downhole users and operators while using such equipment. Generally, the rate is appropriate for users and operators to make significant decisions regarding the downhole environment and other downhole sequences.

Referring now to Figure 5, an exemplary method for estimating a property of a downhole fluid is shown.

Petition 870190070224, of July 24, 1919, p. 22/34

20/22

In a first stage 501, the method calls for selecting a downhole spectrometer comprising an optical fiber with at least one portion without a coating disposed therein. In a second stage 502, the method requires at least partially to surround the portion in the downhole fluid. In a third stage 503, the method requests to receive light emitted from a light source through the optical fiber. In a fourth stage 504, the method asks to estimate an evanescent spectrum of fluid from the received light. In a fifth stage 505, the method asks to estimate sample property according to the evanescent spectrum.

Having introduced the aspects of the invention, certain advantages of the teachings of the present should become apparent. For example, the presently provided wellbore spectrometer offers simplified fabrication over prior art designs. More specifically, the use of a single fiber avoids the incorporation of optical interface (s) beyond those required between the light source and the photodetector. In addition, the use of a single fiber provides simplified assembly of components. That is, the use of a fiber further avoids complications that occur in the use of components such as reflection crystals that have accompanying geometry requirements. Thus, the wellbore spectrometer supplied herein is generally more physically robust as well as more economical to maintain or replace.

As provided above, this invention provides well bottom fluid analysis by collecting fluid evanescent wave optical absorption spectra, but using silicon, germanium, sapphire or other high temperature and otherwise robust optical fiber. submerged in or at least partially surrounded by the fluid sample. This approach is well suited for spectroscopy.

Petition 870190070224, of July 24, 1919, p. 23/34

21/22 medium infrared sink and to determine issues such as the percentage of oil-based sludge contamination or concentrations of H2S or CO2, methane, ethane, propane and butane and other such petroleum constituents.

In support of the teachings of the present, various analytical components may be used, including a digital system and / or an analog system. The system (s) may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, programs. software, signal processors (digital or analog) and other such components (such as resistors, capacitors, inducers and others) to provide operation and analysis of the apparatus and methods described herein in any of several ways well appreciated in the art. It is considered that these teachings may be, but not necessarily, implemented in conjunction with a series of computer-executable instructions stored in a computer-readable medium, including memory (ROMs, RAMs), optics (CD-ROMs), or magnetic (disks). hard disks), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide equipment operation, control, data collection and analysis, and other required functions relevant to a designer, owner, system user, or other person, in addition to the functions described in this disclosure.

In addition, various other components may be included and required to provide aspects of the teachings of the present. For example, a sample line, sample storage, sample chamber, sample hood, pump, piston, power supply (e.g. at least one of a generator, a remote supply, and a battery), vacuum supply, pressure supply, unit or

Petition 870190070224, of July 24, 1919, p. 24/34

Cooling supply (ie cooling), heating component, motive force (such as a translational force, propelling force or a rotational force), magnet, sensor, controller, optical unit, electrical unit, or electromagnetic unit may be included in support of the various aspects discussed herein or in support of other functions beyond this description.

One of ordinary skill in the art will appreciate that various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, such functions and features, as may be required in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings of the present and a part of the described invention.

Although the invention has been described with reference to exemplary embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for such elements without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt an instrument, situation or material to the teachings of the invention if it deviates from its essential scope. Accordingly, the invention is not intended to be limited to the particular embodiment described as the best mode contemplated for carrying out this invention, but rather to include all embodiments that fall within the scope of the appended claims.