Abstract:
A device for measuring the physical characteristics of a flow within a pipe is disclosed. In one exemplary embodiment, the device comprises a plug attached to two or more strut assemblies, each strut assembly comprising a forward strut, a rearward strut, and a skid having an inner surface that faces the plug, and one or more sensors located on the inner surface of the skid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter herein relates generally to downhole flow meters, and, more particularly, to an improved downhole flow meter capable of measuring the physical characteristics of a flow comprising more than one phase of matter, for example liquid and gas, also known as a multiphase flow meter. 
         [0002]    Flow meters provide critical measurements concerning the characteristics of a flow within a pipe, for example the rate and volume of material flowing through the pipe, as well as pressure and temperature measurements. This is especially true in downhole applications, such as those in which a flowmeter is used to measure material flow in an oil well below the well head. The data produced is used to not only monitor and quantify the well output, but to evaluate overall well conditions and operational performance. Downhole meters must therefore be robust in nature in order to function in the severe environments experienced in downhole applications, for example within widely varying temperature extremes, high flow rates and high pressure, while producing highly accurate measurements in order to properly quantify well production levels and assess operational characteristics. 
         [0003]    Several devices are currently used to perform flow measurements in downhole applications. For example, turbine flow meters use a spinning blade that is placed into a flow within a pipe located below a well head. As the material from the well flows past the blade, the blade turns. A linear relationship exists between the rotational speed of the blade and the flow rate, such that the flow rate can be determined from the speed of the rotation. Additionally, each rotation of the blade results in a given volume of fluid passing the blade, thereby also enabling volumetric measurements of the flow. However, because the blade must be free to rotate, it cannot fully occupy the full inner diameter of the pike within which it is placed, resulting in some of the material passing the meter without being measured, also known as slip. The resulting nonlinearity in the volume of material to blade rotation results in inaccuracies in the measurements. Additionally, because a turbine flow meter utilizes a moving blade, it can be susceptible to breakage and maintenance issues, with loose or broken parts being particularly problematic to downstream components in a given well system. Also, a typical flow within a well contains a mixture of liquid and gas components, such as crude oil, water and natural gas, which a turbine flow meter cannot differentiate between. Accordingly, the accuracy of a turbine flow meter may not be sufficient in all applications, such as where separately quantifying the volumetric amount of crude oil and natural gas a well is producing is required. 
         [0004]    Other techniques used to measure downhole flow include the use of pressure sensors placed along plugs positioned in the center of a pipe beneath the well head. The plug occupies a portion of the pipe diameter through which the flow travels, thereby causing a disturbance in the flow as the fluid and gas move past. By measuring the pressure in the pipe and the differential pressure around the plug the flow rate can be determined. One advantage to this technique is that it eliminates the need for moving parts within the system. However, the results obtained have less accuracy than those obtained using a turbine flow meter. Additionally, measurement accuracy is dependent on positioning the plug in the center of the pipe, which can be difficult to correctly establish and maintain over time in downhole environments. 
         [0005]    It would be advantageous to provide a downhole flow meter that is not only mechanically robust and capable of operating in the severe environment experienced in downhole applications, but which also provides highly accurate measurements of flow characteristics, and which is capable of differentiating between the different phases of matter present in the flow. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    A device for measuring the characteristics of a flow within a pipe is disclosed, in one embodiment comprising a plug having a forward end and a rearward end, two or more strut assemblies, each strut assembly comprising a forward strut having a first end and a second end, the first end of the forward strut being fixably attached to the plug proximate the forward end, a rearward strut having a first end and a second end, the first end of the rearward strut being fixably attached to the plug proximate the rearward end, a skid having an inner surface, the skid being fixably attached to the second end of the forward strut and the second end of the rearward strut such that the inner surface faces the plug, and a sensor located on the inner surface for measuring the characteristics of the flow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of invention. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
           [0008]      FIG. 1  is an exemplary cross-sectional side view of a multiphase downhole meter having electrical impedance spectroscopy (EIS) sensors within a pipe in one embodiment of the invention. 
           [0009]      FIG. 2  is an exemplary cross-sectional side view of a multiphase downhole meter after it has been moved from a pipe of one diameter into a pipe of narrower diameter in one embodiment of the invention. 
           [0010]      FIG. 3  is an exemplary cross-sectional view of a flow facing end of a multiphase downhole meter within a pipe in one embodiment of the invention. 
           [0011]      FIG. 4  is an exemplary cross-sectional side view of a multiphase downhole meter having EIS, ultrasonic and pressure sensors in a pipe in one embodiment of the invention. 
           [0012]      FIG. 5  is an exemplary cross-sectional view of a flow facing end of a multiphase downhole meter having multiple sensors in a pipe in one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows an exemplary cross-sectional side view of a multiphase flow meter  100  having EIS sensors  160  within a pipe  200  in one embodiment of the invention. Pipe  200  can be, for example, any type of hollow conduit. In one exemplary embodiment, multiphase flow meter  100  can comprise a centrally located plug  150  that can comprise a nose  152 , a body  155  and a tail  158 . The nose  152  is oriented to face the oncoming flow and can be conical in shape such that the narrowest portion of the nose  152  extends outwardly from the multiphase flow meter  100  to a forward end  105 , while the widest portion of the nose  152  is connected to the body  155 . The body  155  can be cylindrically shaped and can extend from the nose  152  to the tail  158 . The tail  158  can also be cylindrically shaped and can extend out into the direction of the flow to a rearward end  110 . The shapes of nose  152 , body  155  and tail  158  can be chosen to create desired flow characteristics within the pipe  200 . Additionally, the nose  152 , body  155  and tail  158  can all be integrally connected. Plug  150  can be made of, for example, stainless steel, inconel, other exotic metals, ceramic, or plastic. The material used can be chosen based on various considerations, including its resistance to corrosion and its electrical insulative properties. 
         [0014]    Located proximate the forward end  105  of the plug  150  can be two or more forward struts  130 . Forward strut  130  can be a supportive structure, for example a cylindrical rod, that can be fixably attached to the outer surface of the plug  150 . Forward strut  130  can extend radially with respect to the outer surface of the plug  150  a distance as required by the diameter of the pipe within which the multiphase flow meter  100  is intended to operate. In one embodiment, as shown in  FIG. 1 , forward strut  130  can extend at an acute angle α towards the rearward end  110  with respect to the outer surface of the plug  150 . The end of forward strut  130  opposite the end attached to the plug  150  can be fixably attached to a forward skid end  142  of skid  140 . Skid  140  can be made of for example, stainless steel, inconel, other exotic metals, ceramic, or plastic that is shaped to fit within the inner diameter of the pipe within which the multiphase flow meter  100  is intended to operate. The material used can be chosen based on various considerations, including its resistance to corrosion and its electrical insulative properties. Skid  140  can be of the same diameter and thickness as that of the forward strut  130 , or it can be bigger or smaller depending on a given application. Opposite the forward skid end  142  of skid  140  is a rearward skid end  145 , such that the skid  140  connects the forward strut  130  to a corresponding rearward strut  135 . The rearward skid end  145  is fixably attached to the rearward strut  135 , which extends towards the plug  150  and is fixably attached to the outer surface of plug  150  proximate the rearward end  110 . In one embodiment, as shown in  FIG. 1 , rearward strut  135  can extend from the surface of plug  150  towards the forward end  105  at an acute angle β with respect to the outer surface of the plug  150 . The rearward strut  135  can be the same design and structure as that of the forward strut  130 , such that the forward strut  130  and rearward strut  135  act to support the skid  140  a distance from plug  150  that is determined by the diameter of the pipe  200  within which it is placed. Forward strut  130  and rearward strut  135  can be made of, for example, stainless steel, inconel, other exotic metals, ceramic, or plastic. The material used can be chosen based on various considerations, including its resistance to corrosion and its electrical insulative properties. 
         [0015]    Together, forward strut  130 , skid  140  and rearward strut  135  comprise a strut assembly  120 . Two or more strut assemblies  120  can be attached to the surface of plug  150  such that the strut assemblies  120  work to center the plug  150  within pipe  200 . Both forward strut  130  and rearward strut  135  can be made flexible such that the strut assembly  120  is allowed to flex between a maximum radial distance from the surface of the plug  150  defined by the fully extended length of the forward strut  130  and rearward strut  135 , and a radial distance closer to the surface of the plug  150 , made possible by the flexure of the forward strut  130  and rearward strut  135 . The maximum radial distance of the strut assembly  120  is determined by the largest size diameter pipe within which the multiphase flow meter  100  is designed to operate. The flexibility of the strut assemblies  120  allows the multiphase flow meter  100  to be moved through a pipe of one diameter into a pipe having a smaller diameter, as is often necessary in downhole applications. 
         [0016]      FIG. 2  is an exemplary cross-sectional side view of a multiphase downhole meter after it has been moved from a pipe of one diameter into a pipe of narrower diameter in one embodiment of the invention. As the pipe  200  diameter decreases, the strut assemblies  120  flex inwardly towards to surface of the pipe to accommodate the narrower diameter, as required in many downhole applications. 
         [0017]    With reference again to  FIG. 1 , an inner surface  147  of skid  140  is located on the surface of the skid  140  facing the plug  150 . On inner surface  147  can be one or more electrical impedance spectroscopy (EIS) sensors  160 , which can allow the multiphase flow meter to perform multiphase flow measurements that not only determine the flow rate, but the states of matter comprising that flow. EIS sensors  160  can be placed on the inner surface  147  of multiple strut assemblies  120  such that the EIS sensors  160  have a substantially equidistant spacing around the circumference of the pipe  200 . In other embodiments, the EIS sensors can be spaced apart in only a portion of the inner pipe  200  circumference. In still further embodiments, EIS sensors can be placed on the plug  150 , forward struts  130  or rearward struts  135  or combinations thereof. 
         [0018]      FIG. 3  is an exemplary cross-sectional view of a flow facing end of a multiphase flow meter  100  in a pipe  200  in one embodiment of the invention. With reference to  FIGS. 1 and 3 , two or more strut assemblies  120  can be attached to the outer surface of the plug  150  in any chosen radial pattern such that the skids  140  of the strut assemblies  120  are pressed against the inner wall of the pipe  200  to position the plug  150  in the center of the pipe  200 . Flexibility of the strut assemblies  120  further allows the plug  150  to maintain a central location within a given pipe diameter as the diameter of the pipe changes. 
         [0019]      FIG. 4  is an exemplary cross-sectional side view of a multiphase flow meter  100  having EIS sensors  160 , ultrasonic transmitter  170 , ultrasonic receiver  180 , and pressure sensors  190  in a pipe  200  in one embodiment of the invention. Additional sensing instrumentation can be optionally installed on multiphase flow meter  100  to provide measurement and analysis of additional environmental parameters in the downhole environment. For example, ultrasonic transmitters, receivers and/or transducers can be installed on multiphase flow meter  100  to determine flow rate using ultrasonic transit time or Doppler frequency shift techniques. As shown in  FIG. 4 , an ultrasonic transmitter  170  can be located on the plug  150 , along with a corresponding ultrasonic receiver  180  in order to obtain ultrasonic transit time measurements from which the flow rate can be determined. In other embodiments, an ultrasonic transducer can be located on plug  150  instead of an individual transmitter or receiver. In still further embodiments, ultrasonic instrumentation can be located on any of the forward struts  130 , the rearward struts  135 , or the skid  140 . 
         [0020]    As shown in  FIG. 4 , one or more pressure sensors  190  can be located along the plug  150  in order to determine flow rate using differential pressure techniques. In other embodiments, pressure sensors  190  can be located on any of the forward struts  130 , the rearward struts  135 , or the skid  140 . Other instrumentation that can be located on any of the forward struts  130 , the rearward struts  135 , or the skid  140  can include thermal sensors and torsional densitometers. 
         [0021]      FIG. 5  shows an exemplary cross-sectional view of a flow facing end of a multiphase flow meter  100  having multiple sensors in a pipe  200  in one embodiment of the invention. As shown in  FIGS. 4 and 5 , the shape of plug  150  can be chosen to accommodate various design needs. In one exemplary embodiment, the shape of plug  150  can form a venturi, such that the forward end  105  of nose  152  can gradually increase in diameter in the direction of the rearward end  110 , reach a maximum diameter, and then gradually decrease in diameter until it fixably attaches to the end of the body  155  closest to the forward end  105 . The body  155  of plug  150  can extend towards the rearward end  110  and have a constant diameter less than the average diameter of the nose  152 . The end of the body  155  facing the rearward end  110  can be fixably attached to the forward end  105  facing end of tail  158 . Tail  158  can gradually increase in diameter in the direction of the rearward end  110 , reach a maximum diameter, and then gradually decrease in diameter until it reaches the rearward end  110 . The diameters and geometries of the nose  152 , body  155  and tail  158  can be chosen to accommodate particular design needs and to produce chosen characteristics in the flow. The nose  152 , body  155  and tail  158  of plug  150  can be constructed out of a single, continuous piece of material, and together they can form a venturi such that the plug  150  creates two narrowings of the cross sectional surface area of the pipe  200 , separated by an expansion area having a greater cross sectional surface area. Additional narrowings and expansions can be added to plug  150  to produce additional flow characteristics, for example through the use of a dual venturi shape. 
         [0022]    The gradual narrowing and expanding diameters of the nose  152  and tail  158  form sloped surfaces on plug  150 . Instrumentation, for example, EIS sensors, ultrasonic emitters, transmitters and/or transducers, pressure sensors, and thermal sensors, can be located on the sloped surfaces of plug  150  such that the instrumentation can be angled relative to the flow direction without creating a large flow disturbance. Additionally, the instruments can be angled in such a way as to minimize particle impact and buildup from the flow, thereby enhancing the longevity and accuracy of the instruments. 
         [0023]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.