Patent Publication Number: US-2010124313-A1

Title: Methods and apparatus to perform downhole x-ray fluorescence

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates generally to sulfur detection and, more particularly, to methods and apparatus to perform downhole x-ray fluorescence to detect sulfur. 
     BACKGROUND 
     Wellbores are drilled to, for example, locate and produce hydrocarbons. During a drilling operation, it may be desirable to perform evaluations of the formations penetrated by the wellbore. In some cases, a drilling tool is removed and a wireline tool is then deployed into the wellbore to test and/or sample the formation and/or fluids associated with the formation. In other cases, the drilling tool may be provided with devices to test and/or sample the surrounding formation and/or formation fluids without the need to remove the drilling tool from the wellbore. These samples or tests may be used, for example, to characterize hydrocarbons and/or detect the presence of elements, such as sulfur, in formation fluids. 
     Formation evaluation often requires that fluid(s) from the formation be drawn into the downhole tool for testing, evaluation and/or sampling. Various devices, such as probes, are extended from the downhole tool to establish fluid communication with the formation surrounding the wellbore and to draw fluid(s) into the downhole tool. Fluid(s) passing through the downhole tool may be tested and/or analyzed to determine various downhole parameters and/or properties while the downhole tool is positioned in situ, that is, within a wellbore. Various properties of hydrocarbon reservoir fluids, such as viscosity, density and phase behavior of the fluid at reservoir conditions, and/or a presence and/or absence of elements, may be used to evaluate potential reserves, determine flow in porous media and design completion, separation, treating, and metering systems, among others. 
     Additionally, samples of the fluid(s) may be collected in the downhole tool and retrieved at the surface. The downhole tool stores the formation fluid(s) in one or more sample chambers or bottles, and retrieves the bottles to the surface while, for example, keeping the formation fluid pressurized. These fluids may then be sent to an appropriate laboratory for further analysis, for example. Typical fluid analysis or characterization may include, for example, composition analysis, fluid properties and phase behavior, and/or detection of elements. Additionally or alternatively, such analysis may be made at the wellsite using a transportable lab system. 
     SUMMARY 
     Example methods and apparatus to perform downhole x-ray fluorescence to detect sulfur are disclosed. A disclosed example downhole x-ray fluorescence apparatus includes a flowline comprising a flowline wall, an x-ray source, a boron carbide crystal window in the flowline wall to allow x-rays emitted by the x-ray source to pass into a formation fluid in the flowline, and a detector to measure a value representative of a fluorescence of the formation fluid in response to the emitted x-rays 
     A disclosed example method to detect sulfur in a formation fluid includes trapping the formation fluid in a flowline, the flowline having a boron carbide crystal window, passing x-rays through the boron carbide crystal window into the trapped formation fluid, measuring a value representative of a fluorescence of the trapped formation fluid in response to the x-rays, and determining whether the sulfur is present in the formation fluid based on the measured value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, partial cross-sectional view of a downhole wireline tool suspended from a rig and having an internal x-ray fluorescence assembly with the wireline tool. 
         FIG. 2  is a schematic, partial cross-sectional view of a downhole drilling tool suspended from a rig and having an internal x-ray fluorescence assembly with the downhole drilling tool. 
         FIG. 3  is a cross-sectional view of an example manner of implementing the example x-ray fluorescence assembly of  FIGS. 1 and 2 . 
         FIG. 4  illustrates an example process that may be carried out downhole to perform sulfur detection, and/or to implement the example x-ray fluorescence assembly of  FIGS. 1-3 . 
         FIG. 5  is a schematic illustration of an example processor platform that may be used and/or programmed to carry out the example process of  FIG. 4  and/or to implement any of all of the methods and apparatus disclosed herein. 
     
    
    
     Certain examples are shown in the above-identified figures and described in detail below. In describing these examples, like or identical reference numbers may be used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic for clarity and/or conciseness. Moreover, while certain preferred embodiments are disclosed herein, other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. 
     DETAILED DESCRIPTION 
     The example downhole methods and apparatus disclosed herein provide certain advantages for downhole and/or wellbore applications that include, but are not limited to, an ability to withstand and/or operate in the environmental conditions present within a wellbore. More particularly, the example x-ray fluorescence apparatus and methods described herein are able to withstand and/or remain operable while being subjected to pressures as high as 15,000 pounds per square inch (psi) and/or temperatures as high as 150 degrees Celsius (C.). Under such downhole conditions, conventional and/or traditional x-ray fluorescence devices would fail and/or become damaged and, thus, become inoperable. 
       FIG. 1  shows a schematic, partial cross-sectional view of an example downhole tool  10 . The example downhole tool  10  of  FIG. 1  is suspended from a rig  12  into a wellbore  14  formed in a geologic formation G. The example downhole tool  10  can implement any type of downhole tool capable of performing formation evaluation, such as x-ray fluorescence, fluid analysis, fluid sampling, well logging, etc. The example downhole tool  10  of  FIG. 1  is a wireline tool deployed from the rig  12  into the wellbore  14  via a wireline cable  16  and positioned adjacent to a particular geologic formation F. 
     To seal the example downhole tool  10  of  FIG. 1  to a wall  20  of the wellbore  14  (hereinafter referred to as a “wall  20 ” or “wellbore wall  20 ”), the example downhole tool  10  includes a probe  18 . The example probe  18  of  FIG. 1  forms a seal against the wall  20  and draws fluid(s) from the formation F into the downhole tool  10  as depicted by the arrows. Backup pistons  22  and  24  assist in pushing the example probe  18  of the downhole tool  10  against the wellbore wall  20 . 
     To detect elements such as sulfur, the example downhole tool  10  of  FIG. 1  includes an x-ray fluorescence assembly  26  constructed in accordance with this disclosure. The example x-ray fluorescence assembly  26  of  FIG. 1  performs x-ray fluorescence to detect, for example, sulfur present in downhole fluids, such as the formation fluids extracted or drawn from the formation F. The example x-ray fluorescence assembly  26  receives the formation fluid(s) from the probe  18  via an evaluation flowline  46 . An example manner of implementing the example x-ray fluorescence assembly  26  of  FIG. 1  is described below in connection with  FIG. 3 . 
       FIG. 2  shows a schematic, partial cross-sectional view of another example of a downhole tool  30 . The example downhole tool  30  of  FIG. 2  can be conveyed among one or more (or itself may be) of a measurement-while-drilling (MWD) tool, a logging-while-drilling (LWD) tool, or other type of downhole tool that are known to those skilled in the art. The example downhole tool  30  is attached to a drill string  32  and a drill bit  33  driven by the rig  12  to form the wellbore  14  in the geologic formation G. 
     To seal the example downhole tool  30  of  FIG. 2  to the wall  20  of the wellbore  14 , the downhole tool  30  includes a probe  18   a.  The example probe  18   a  of  FIG. 2  forms a seal against the wall  20  and draws fluid(s) from the formation F into the downhole tool  30  as depicted by the arrows. Backup pistons  22   a  and  24   a  assist in pushing the example probe  18   a  of the downhole tool  30  against the wellbore wall  20 . Drilling is stopped before the probe  18   a  is brought in contact with the wall  20 . 
     To detect elements such as sulfur, the example downhole tool  30  of  FIG. 2  also includes the example x-ray fluorescence assembly  26 . The example x-ray fluorescence assembly  26  of  FIG. 2  performs x-ray fluorescence to detect, for example, sulfur that is present in downhole fluids, such as the formation fluids extracted or drawn from the formation F. The example x-ray fluorescence assembly  26  receives the formation fluid(s) from the probe  18   a  via the evaluation flowline  46 . An example manner of implementing the example x-ray fluorescence assembly  26  of  FIG. 2  is described below in connection with  FIG. 3 . 
     While  FIGS. 1 and 2  depict the x-ray fluorescence assembly  26  in the example downhole tools  10  and  30 , the x-ray fluorescence assembly  26  may instead be provided or implemented at the wellsite (e.g., at the surface near the wellbore  14 ), and/or at an offsite facility for performing fluid tests. By positioning the x-ray fluorescence assembly  26  in the downhole tool  10 ,  30 , real-time data may be collected concerning sulfur or other elements present in downhole fluids. However, it may also be desirable and/or necessary to test fluids at the surface and/or offsite locations. In such cases, the example x-ray fluorescence assembly  26  may be positioned in a housing transportable to a desired location. Alternatively, fluid samples may be taken to a surface or offsite location and tested in the x-ray fluorescence assembly  26  at such a location. Data and test results from various locations may be analyzed and compared. 
       FIG. 3  is a cross-sectional view of an example manner of implementing the example x-ray fluorescence assembly  26  of  FIGS. 1 and 2 . Additionally or alternatively, the example x-ray fluorescence assembly  26  of  FIG. 3  may be used to detect sulfur or other elements that are present in formation fluids at the surface, at a wellsite, in a transportable lab, and/or in a fixed-location facility. Fluorescence is an optical phenomenon in which molecular absorption of a photon triggers the emission of another photon with, for example, a longer wavelength. In an example x-ray fluorescence method to detect sulfur in a formation fluid, the formation fluid is subjected to 5.9 kiloelectron volt (keV) x-rays and, in response to the 5.9 keV x-rays, any sulfur that is present within the formation fluid will fluoresce by emitting 2.3 keV x-rays. Thus, the detection and/or measurement of 2.3 keV x-rays emitted by the exposed formation fluid is indicative of the presence of sulfur within the formation fluid. The number of 2.3 keV x-rays corresponds to an amount of sulfur present within the formation fluid. 
     The example x-ray fluorescence assembly  26  of  FIG. 3  comprises a housing  305  and a flowline and/or chamber  310  within and/or through which formation fluid(s)  315  can flow and/or be captured or trapped. The example flowline  310  of  FIG. 3  is fluidly coupled to the example flowline  46  of  FIGS. 1 and 2 , and the example formation fluid  315  of  FIG. 3  is provided to the x-ray fluorescence assembly  26  via the flowline  46 . The example flowline  310  has a flowline wall  320  and one or more valves (not shown) that control the flow of the formation fluid  315  into and/or out of the flowline  310  and/or allow formation fluid  315  to be trapped within the flowline  310 . In some examples, the flowline  310  has a cylindrical and/or rectangular cross-section. 
     To detect elements (e.g., sulfur) and/or compounds (e.g., sulfur dioxide) that are present in the formation fluid  315 , the example x-ray fluorescence assembly  26  of  FIG. 3  includes an x-ray excitation source  325  and one or more detectors, one of which is designated at reference numeral  330 . The example excitation source  325  of  FIG. 3  excites the formation fluid  315  and, thus, any elements or compounds present within the formation fluid  315  with x-rays  335 , which under certain circumstances can cause elements and/or compounds in the formation fluid  315  to floresce (i.e., to emit and/or radiate x-rays  340 ). Whether or not fluorescence occurs depends on the type(s) of x-rays  335  emitted by the excitation source  325  and the type(s) of elements and/or compounds (if any) present in the formation fluid  315 . The amount and/or type(s) of x-rays emitted by the formation fluid  315  and/or elements and/or compounds present in the formation fluid  315  can be measured by the example detector  330  of  FIG. 3 , and used to detect the presence of the elements and/or compounds. The type of x-rays  335  to excite the formation fluid  315  and the type of detector(s)  330  used depends on the type of elements and/or compounds that are to be detected. For example, when exposed to the x-rays  335 , sulfur present within the formation fluid  315  emits characteristic Ka line (i.e., 2.3 keV) x-rays  340 . The amount of 2.3 keV x-rays corresponds to amount of sulfur present within the formation fluid. 
     An example x-ray source  325  comprises a 55Fe (i.e., iron-55) chemical source that emits 5.9 keV x-rays  335 . However, other types of x-ray sources  325  that emit x-rays that are effectively absorbed by sulfur or sulfur containing compounds, and which are able to operate at extreme pressures (e.g., 15,000 psi) and/or extreme temperatures (e.g., 150° C.) may be used. Preferably, the x-rays source  325  has a narrow emission spectrum and generates x-rays  335  have an adequate signal-to-noise ratio (SNR). In some examples, the x-ray source  325  includes a mechanical shutter (now shown) that can be operated (e.g., opened and closed) to selectively irradiate the formation fluid  315 . 
     Example detectors  330  include, but are not limited to, those based on silicon (Si), lithium-drifted silicon (Si(Li)), a silicon PIN photodiode, germanium (Ge), cadmium telluride (CdTe), mercury iodide (HgI2), gallium nitride (GaN), silicon carbide (SiC), and/or chemical vapor deposition (CVD) grown diamond. Regardless of the type of material(s) used to implement the detector  330 , the detector  330  preferably can operate in extreme ambient temperatures (e.g., 150° C.) and/or at extreme operating temperatures (e.g., 150° C.), have high sensitivity to 2.3 keV x-rays  340  pertinent to sulfur detection, and have low/no sensitivity to other (e.g., higher) energy x-rays and/or gamma-rays. A leak current in the detector  330  is caused by the x-rays  340  is the thermal-excitation of electron-hole pairs by the x-rays  340 , and the population of the electron-hole pairs within the materials used to implement the detector  330 . The leak current can be approximated by the following mathematical expression: 
     
       
         
           
             
               
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     where E g  is the bandgap energy the detector  330 , K B  is the Boltzmann constant, and T is temperature. The term E g /T inside the exponential dominates the overall electron-hold populations. Thus, in order to reduce the carrier population, one can reduce the temperature T of the detector  330  and/or increase the bandgap E g  (i.e., using wider bandgap semiconductors). For example, CdTe (E g =1.44 eV) has a larger bandgap than Si (E g =1.11 eV) and Ge (E g =0.66 eV), and has been reported to operate at 70° C. when used to implement the detector  330 . With use of a cooling system  345 , a CdTe-based detector  330  can be used at temperatures over 100° C. and possibly as high as 150° C. GaN and SiC have even larger bandgaps (E g ≈3 eV) and work at even higher temperatures. At an extreme, a vapor deposition grown diamond (E g ≈6 eV) is reported to operate at 250-300° C. The particular material(s) chosen to implement the example detector  330  depends on expected temperatures and the efficiency and/or capability of the example cooling system  345  to reduce the temperature of the detector  330 . 
     To cool the example detector  330 , the example x-ray fluorescence assembly  26  of  FIG. 3  includes the example cooling system  345 . The example cooling system  345  of  FIG. 3  is used to reduce leakage current of the detector  330  by reducing the operating temperature of the detector  330 . Example cooling systems  345  include, but are not limited to, Peltier cooling used locally within the x-ray fluorescence assembly near the detector  330 , a Stirling engine to cool the whole x-ray fluorescence assembly within the example housing  305 , and/or liquid Nitrogen (N). The particular type(s) of cooling system(s)  345  implemented depends on the expected ambient temperature(s) and/or the maximum operating temperature of the detector  330 . 
     To allow the x-rays  335  to pass into the formation fluid  315 , the example flowline wall  320  of  FIG. 3  has a boron carbide crystal window  350 . Likewise, to allow the x-rays  340  to pass from the formation fluid  315  onto the detector  330 , the example flowline wall  320  of  FIG. 3  has a second boron carbide crystal window  355 . Boron carbide crystal is used to implement the example windows  350  and  355  of  FIG. 3 , as boron carbide crystal has low Z components making it relatively transparent (i.e., minimally absorptive) of the 5.9 keV x-rays  335  and the 2.3 keV x-rays  340 , and can operate at extreme pressures (e.g., 15,000 psi) and extreme temperatures (e.g., 150° C.). 
     While in the illustrated example of  FIG. 3 , the windows  350  and  355  are shown on opposite sides of the flowline  310 , they do not need to be so positioned. In general, the positions of the windows  350  and  355 , and as a consequence the positions of the x-ray source  325  and the detector  330 , may be selected based on any number and/or type(s) of criteria such as, for example, mechanical stability of the flowline wall  320 , mechanical packaging issues, electrical control issues, etc. 
     To control the x-ray fluorescence assembly  26 , the example x-ray fluorescence assembly  26  of  FIG. 3  includes an x-ray fluorescence controller  360 . The example x-ray fluorescence controller  360  of  FIG. 3  (a) controls one or more valves to allow the formation fluid  315  to be trapped in the flowline  310 , (b) controls the x-ray source  325  and the detector  330  to measure one or more values representative of the fluorescence of one or more elements and/or compounds present in the formation fluid  315 . The example x-ray fluorescence controller  360  stores the measured values in any type and/or number of memory(-ies) and/or memory device(s), one of which is designated at reference numeral  365 , for later retrieval. Additionally or alternatively, the measured values can be sent to a surface computer (not shown) using telemetry, and/or be analyzed by the example x-ray fluorescence controller  360  to determine the amount of an element and/or compound present in the formation fluid  315 . The example x-ray fluorescence controller  360  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, the example x-ray fluorescence controller  360  may be implemented by one or more circuit(s), programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field-programmable PLD(s) (FPLD(s)), etc. 
     While an example manner of implementing the example x-ray fluorescence assembly  26  of  FIGS. 1 and 2  has been illustrated in  FIG. 3 , one or more of the example interfaces, housing  305 , flowline  310 , flowline wall  320 , windows  350  and  355 , x-ray source  325 , detector  330 , cooling system  345 , x-ray fluorescence controller  360  and/or memory  365  illustrated in  FIG. 3  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the x-ray fluorescence assembly  26  may include interfaces, housings, flowlines, flowline walls, windows, x-ray sources, detectors, cooling systems, controllers and/or memories instead of, or in addition to, those illustrated in  FIG. 3  and/or may include more than one of any or all of the illustrated interfaces, housings, flowlines, flowline walls, windows, x-ray sources, detectors, cooling systems, controllers and/or memories. 
       FIG. 4  illustrates an example process that may be carried out to implement the example x-ray fluorescence controller  360  and/or, more generally, to implement the example x-ray fluorescence assembly  26  of  FIGS. 1-3 . The example process of  FIG. 4  may be carried out by a processor, a controller and/or any other suitable processing device. For example, the example process of  FIG. 4  may be embodied in coded instructions stored on any tangible computer-readable medium such as a flash memory, a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a read-only memory (ROM), a random-access memory (RAM), a programmable ROM (PROM), an electronically-programmable ROM (EPROM), and/or an electronically-erasable PROM (EEPROM), an optical storage disk, an optical storage device, magnetic storage disk, a magnetic storage device, and/or any other medium which can be used to carry or store program code and/or instructions in the form of machine-accessible and/or machine-readable instructions or data structures, and which can be accessed by a processor, a general-purpose or special-purpose computer, or other machine with a processor (e.g., the example processor platform P 100  discussed below in connection with  FIG. 5 ). Combinations of the above are also included within the scope of computer-readable media. Machine-readable instructions comprise, for example, instructions and/or data that cause a processor, a general-purpose computer, special-purpose computer, or a special-purpose processing machine to implement one or more particular processes. Alternatively, some or all of the example process of  FIG. 4  may be implemented using any combination(s) of ASIC(s), PLD(s), FPLD(s), discrete logic, hardware, firmware, etc. Also, some or all of the example process of  FIG. 4  may instead be implemented manually or as any combination of any of the foregoing techniques, for example, any combination of firmware, software, discrete logic and/or hardware. Further, many other methods of implementing the example operations of  FIG. 4  may be employed. For example, the order of execution of the blocks may be changed, and/or one or more of the blocks described may be changed, eliminated, sub-divided, or combined. Additionally, any or all of the example process of  FIG. 4  may be carried out sequentially and/or carried out in parallel by, for example, separate processing threads, processors, devices, discrete logic, circuits, etc. 
     The example process of  FIG. 4  begins with the example x-ray fluorescence controller  360  controlling one or more valves to trap and/or capture the example formation fluid  315  in the example flowline  310  (block  405 ). The controller  360  activates the example x-ray source  325  to irradiate the formation fluid  315  with the x-rays  335  via the window  350  (block  410 ). For example, if a chemical-based x-ray excitation source  325  is used, the controller  360  may operate (e.g., open) a mechanical shutter to irradiate the formation fluid  315 . The example detector  330  measures the amount of x-rays  340  emitted by elements (e.g., sulfur) and/or compounds within the formation fluid  310  that pass through the window  355  and fall incident upon the detector  330  (block  415 ). The controller  360  stores the fluorescence measurement(s) taken by the detector  330  in the memory  365 , and/or determines whether and/or how much sulfur is present in the formation fluid  315  based on the measurements (block  420 ). Control then exits from the example process of  FIG. 4 . 
       FIG. 5  is a schematic diagram of an example processor platform P 100  that may be used and/or programmed to implement the example controller  360  and/or the example x-ray fluorescence assembly  26  described herein. For example, the processor platform P 100  can be implemented by one or more general-purpose processors, processor cores, microcontrollers, etc. 
     The processor platform P 100  of the example of  FIG. 5  includes at least one general-purpose programmable processor P 105 . The processor P 105  executes coded instructions P 110  and/or P 112  present in main memory of the processor P 105  (e.g., within a RAM P 115  and/or a ROM P 120 ). The processor P 105  may be any type of processing unit, such as a processor core, a processor and/or a microcontroller. The processor P 105  may execute, among other things, the example process of  FIG. 4  to implement the example methods and apparatus described herein. 
     The processor P 105  is in communication with the main memory (including a ROM P 120  and/or the RAM P 115 ) via a bus P 125 . The RAM P 115  may be implemented by dynamic random-access memory (DRAM), synchronous dynamic random-access memory (SDRAM), and/or any other type of RAM device, and ROM may be implemented by flash memory and/or any other desired type of memory device. Access to the memory P 115  and the memory P 120  may be controlled by a memory controller (not shown). The memory P 115 , P 120  may be used to implement the example memory  365 . 
     The processor platform P 100  also includes an interface circuit P 130 . The interface circuit P 130  may be implemented by any type of interface standard, such as an external memory interface, serial port, general-purpose input/output, etc. One or more input devices P 135  and one or more output devices P 140  are connected to the interface circuit P 130 . The example output device P 140  may be used to, for example, control the example x-ray source  325 . The example input device P 135  may be used to, for example, collect measurements taken by the example detector  330 . 
     Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.