Abstract:
A method and apparatus for determining the effectiveness of bearing seals in s roller cone drill bit. The bit includes a sensor in optical communication with the bearing lubricant. The sensor includes a light source, an optical filter, and an optical detector arranged so that light interacts with the lubricant, is filtered, and detected, wherein the detected light is indicative of the amount of contaminant within the lubricant. The optical filter is preferably an integrated computing element that filters preselected orthogonal components from the light.

Description:
FIELD 
       [0001]    The present disclosure relates generally to drill bits for boring holes in the earth, and specifically to lubrication systems for roller cone bits. 
       BACKGROUND 
       [0002]    Roller cone bit used in the oil and gas drilling industry typically have sealed ball bearings that are lubricated from a lubricating system. Grease is often used as the lubricant. Of the bearing components, the bearing seal typically has the lowest mean time between failure, so that the bearing seal effectiveness typically determines the life of the bearing system. As the seal wears, the grease may become contaminated with drilling mud and water, which are gradually introduced into the lubrication system. Accordingly, the amount of contaminant fluid within the lubricant indicates the effectiveness of the seal, and when the contaminant reaches a predetermined limit, continued drilling must cease, lest a bearing failure occur that can leave one or more roller cones at the bottom of the borehole and require a costly fishing operating to retrieve them. 
         [0003]    Prior art techniques are known for sensing an impending bearing failure due to a bearing seal failure. In some cases, bearing seal failure is gradual, but in other cases, bearing failure may occur catastrophically with little to no warning. Prior art methods of detecting seal failure may not be sensitive enough predict an imminent seal failure or responsive enough detect a seal failure and rapidly communicate such condition before significant bearing damage occurs. Accordingly, it is desirable to detect seal failure of a roller cone bit in real time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Embodiments are described in detail hereinafter with reference to the accompanying figures, in which: 
           [0005]      FIG. 1  is an elevation view with one-quarter cut away to reveal a longitudinal cross section of a roller cone drill bit according to a present embodiment, showing a bit body having arms terminating in journals, cutter assemblies rotatively mounted to the journals with ball bearings, and an internal bearing lubrication system; and 
           [0006]      FIG. 2  is an enlarged longitudinal cross section of an optical sensor according to a present embodiment for use within the lubrication system of the drill bit of  FIG. 1 , showing a light source, an optical filter and an optical detector located within a cylindrical housing with a transparent window located at one end for immersion in a lubricant. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]      FIG. 1  illustrates a roller cone drill bit  10  that is arranged for including an optical sensor  100 , as shown in  FIG. 2 , which is specifically designed and configured for detecting the presence of water within a grease, lubricant, or other fluid. Bit  10  includes a bit body  12 , which preferably includes arms  14  that terminate as journals  16 . A cutter assembly  20 , typically a roller cone carrying a large number discrete cutters  22 , is rotatively captured on each journal  16 . 
         [0008]    In one embodiment, the interior circumference of cutter assembly  20  has a semi-circular groove  30  formed therein that defines an outer bearing race. Likewise, the outer circumference of journal  16  has a semicircular groove formed therein that defines an inner bearing race  32 . A plurality of hardened ball bearings  34  are received in the circular cavity defined between the inner and outer races  30 ,  32  to rotatively capture cutter assembly  20  upon journal  16 . A ball passageway  36 , which is plugged during ordinary use, is formed between the exterior surface and the circular bearing cavity within each arm  14  to allow the ball bearings to be loaded and unloaded as needed for installation, maintenance, and repair. 
         [0009]    One or more cavities are formed in bit body  12  to serve as a reservoir  40  for lubricant. Reservoir  40  is in fluid communication with the ball bearings  34  and bearing races  30 ,  32 , ideally through a conduit  42  that connects ball passageway  36  to reservoir  40 . A diaphragm, piston, or similar pressure regulation assembly  44  may be provided to pressurize the lubrication system to minimize ingress of contaminants into the bearing assembly. To that end, one or more journal/cutter assembly seals  50  are provided to keep lubricant in and contaminants out of the bearing assemblies. 
         [0010]    A seal failure sensor or monitor  100  ( FIG. 2 ) is positioned to be in fluid communication with the lubricant. In one embodiment, the sensor is positioned in a socket  46  that is fluidly coupled to conduit  42 . However, in other embodiments, the sensor may be positioned elsewhere in the drill bit about the lubricant system. Sensor  100  may be unitary, or it may consist of several discrete parts. 
         [0011]      FIG. 2  is a detailed view of socket  46  of drill bit  10  of  FIG. 1 , showing sensor  100  positioned therein according to one embodiment. Sensor  100  includes a housing  102 , which may be cylindrical and threaded into socket  46 . However, other techniques to mount sensor  100  within bit  10  may be used as appropriate. 
         [0012]    The inner end of housing  102  includes, or is formed by, a window  104 , which preferably forms a fluid tight seal with housing  102  but is transparent to wavelengths of light of interest to the optical sensor  100 . Window  104  is in optical communication, and ideally in physical contact, with lubricant  60 , which may be contained in conduit  42  as shown in  FIG. 2 . Sensor  100  includes a light source  106 , and optical filter  108 , and an optical detector  110 , which are all preferably but not necessarily positioned within housing  102 . The light source  106 , and optical filter  108 , and an optical detector  110  may all be discrete components, or two or more may be conjoined. Regardless, these components are positioned so that light from light source  106  interacts with lubricant, passes through optical filter  108  (either before or after interaction with lubricant  60 , as appropriate), and is received at optical detector  110 . 
         [0013]    As illustrated by arrows, light interaction with lubricant  60  may be by reflection (predominantly at the window/lubricant interface) as shown by arrow  70 , by transmission (with reflection off of the conduit wall), as shown by arrow  72 , or by a combination of these mechanisms. Indeed, the light from light source  106  may also be subject to refraction, diffusion, and absorption so as long as some of the interacted light reaches optical detector  110 . 
         [0014]    Sensor  100  may also contain a processing and telemetry module  120  that is operatively coupled to optical detector  110  for processing signals from optical detector  110  and communicating them to a remote location, for example, the surface of the earth. In this manner, drilling operators can be accurately advised in real time of the amount of water ingress in the bit lubrication system and accordingly, the effectiveness of the seals. Various forms of telemetry may be used, including electric, electromagnetic, acoustic, etc. As such telemetry techniques are well known in the art, further detail regarding telemetry is not provided herein. 
         [0015]    In a first embodiment, each cutter assembly  20  may have an individual, dedicated optical sensor  100 , which is preferably located within each arm  14 . Telemetry may include signals from each sensor, which may be continual or sequential, for example. Alternatively, bit  100  may include a single optical detector  100 , which monitors a common lubrication system that serves all of the cutter assemblies  20  on the bit. 
         [0016]    The principle of operation of sensor  100  is now described: When light interacts with matter, for example via transmission or reflection, it carries away information about the physical and chemical properties of the matter with which it interacted. A property of the light, for example its intensity, may be measured and interpreted to provide information about the matter with which it interacted. That is, the data carried by the light through its intensity may be measured to derive information about the matter. 
         [0017]    In general, it is difficult to convert a simple measurement of light intensity into information because of interfering data. That is, several factors may contribute to the intensity of light, even in a relatively restricted wavelength range. It is often impossible to adequately measure the data relating to one of these factors, because the contribution of the other factors is unknown. 
         [0018]    It is possible, however, to derive information from light. An estimate may be obtained, for example, by separating light from several samples into wavelength bands and performing a multiple linear regression of the intensity of these bands against the results of conventional measurements of the desired information for each sample. In particular, a lubricant sample may be illuminated so that light from the lubricant carries information such as the sample&#39;s water content. Light from each of several samples may be directed to a series of bandpass filters which separate predetermined wavelength bands from the light. Light detectors following the bandpass filters measure the intensity of each light band. If the water content of each lubricant sample is measured using conventional means, a multiple linear regression of several measured bandpass intensities against the measured water content for each sample may produce an equation such as: 
         [0000]        y=a   0   +a   1   w   1   +a   2   w   2   +. . . +a   n w n   (Equation 1)
 
         [0000]    where y is water content, a n  is a constant determined by the regression analysis, and w n  is the light intensity for each wavelength band. 
         [0019]    Equation 1 may be used to estimate water content of subsequent samples of the same lubricant type. Depending on the circumstances, however, the estimate may be unacceptably inaccurate, because factors other than water may affect the intensity of the wavelength bands. Moreover, these other factors may not change from one sample to the next in a manner consistent with water. 
         [0020]    A more accurate estimate may be obtained by compressing the data carried by the light into principal components. To obtain the principal components, spectroscopic data is collected for a variety of samples of the same type of light, for example from illuminated samples of the same type of lubricant. The light samples are spread into their wavelength spectra by a spectrograph so that the magnitude of each light sample at each wavelength may be measured. This data is then pooled and subjected to a linear-algebraic process known as singular value decomposition (SVD). SVD is at the heart of principal component analysis, which is generally well known by routineers in this art apart from the particular teachings of the present disclosure. 
         [0021]    Briefly, principal component analysis is a dimension reduction technique which takes m spectra with n independent variables and constructs a new set of eigenvectors that are linear combinations of the original variables. The eigenvectors may be considered a new set of plotting axes. The primary axis, termed the first principal component, is the vector which describes most of the data variability. Subsequent principal components describe successively less sample variability, until only noise is described by the higher order principal components. 
         [0022]    Typically, the principal components are determined as normalized vectors. Thus, each component of a light sample may be expressed as x n  {circumflex over (z)} n , where x n  is a scalar multiplier and {circumflex over (z)} n  is the normalized component vector for the n th  component. That is, {circumflex over (z)} n  is a vector in a multi-dimensional space where each wavelength is a dimension. Normalization determines values for a component at each wavelength so that the component maintains its shape and so that the length of the principal component vector is equal to one. Thus, each normalized component vector has a shape and a magnitude so that the components may be used as the basic building blocks of all light samples having those principal components. Accordingly, each light sample may be described in the following format by the combination of the normalized principal components multiplied by the appropriate scalar multipliers: 
         [0000]      x 1 {circumflex over (z)} 1 +x 2 {circumflex over (z)} 2 +. . . +x n {circumflex over (z)} n    
         [0000]    The scalar multipliers x n  may be considered the “magnitudes” of the principal components in a given light sample when the principal components have a standardized magnitude as provided by normalization. 
         [0023]    Because the principal components are orthogonal, they may be used in a relatively straightforward mathematical procedure to decompose a light sample into the component magnitudes which accurately describe the data in the original sample. Since the original light sample may also be considered a vector in the multi-dimensional wavelength space, the dot product of the original signal vector with a principal component vector is the magnitude of the original signal in the direction of the normalized component vector. That is, it is the magnitude of the normalized principal component present in the original signal. This is analogous to breaking a vector in a three dimensional Cartesian space into its X, Y and Z components. The dot product of the three-dimensional vector with each axis vector, assuming each axis vector has a magnitude of  1 , gives the magnitude of the three dimensional vector in each of the three directions. The dot product of the original signal and some other vector that is not perpendicular to the other three dimensions provides redundant data, since this magnitude is already contributed by two or more of the orthogonal axes. 
         [0024]    Because the principal components are orthogonal, or perpendicular, to each other, the dot, or direct, product of any principal component with any other principal component is zero. Physically, this means that the components do not interfere with each other. If data is altered to change the magnitude of one component in the original light signal, the other components remain unchanged. In the analogous Cartesian example, reduction of the X component of the three dimensional vector does not affect the magnitudes of the Y and Z components. 
         [0025]    Principal component analysis provides the fewest orthogonal components that can accurately describe the data carried by the light samples. Thus, in a mathematical sense, the principal components are components of the original light that do not interfere with each other and that represent the most compact description of the entire data carried by the light. Physically, each principal component is a light signal that forms a part of the original light signal. Each has a shape over some wavelength range within the original wavelength range. Summing the principal components produces the original signal, provided each component has the proper magnitude. 
         [0026]    The principal components comprise a compression of the data carried by the total light signal. In a physical sense, the shape and wavelength range of the principal components describe what data is in the total light signal while the magnitude of each component describes how much of that data is there. If several light samples contain the same types of data, but in differing amounts, then a single set of principal components may be used to exactly describe (except for noise) each light sample by applying appropriate magnitudes to the components. 
         [0027]    Thus, the principal components of light may be used to accurately estimate information carried by the light. Accordingly, light that has interacted with a test sample of a known material contaminated with an unknown quantity of a known contaminant can be resolved into its principal components and compared to previously-measured principal components of reference samples with known quantities of contaminants to determine the quantity of contaminant within the test sample. This is the operating principle of the present embodiment. 
         [0028]    In a preferred embodiment, optical filter  104  is a multivariate optical element, also known as an Integrated Computing Element (“ICE”), which is specifically designed and structured to detect the amount of water or other contaminant in grease or other lubricant. The design and operation of ICE structures are described in, for example, U.S. Pat. Nos. 6,198,531; 6,529,276; 7,697,141; and 8,049,881, each being owned by the Assignee of the present disclosure, Halliburton Energy Services, Inc., of Houston, Tex. 
         [0029]    The Abstract of the disclosure is solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of technical disclosure, and it represents solely one or more embodiments. 
         [0030]    While various embodiments have been illustrated in detail, the disclosure is not limited to the embodiments shown. Modifications and adaptations of the above embodiments may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the disclosure.