Abstract:
An oil well production analyzing system receives production fluid samples from the oil well according to an automated sampling schedule. The fluid samples are taken from a pipeline through a sampling apparatus to obtain a representative sample. The representative sample flows into a circulation loop having a circulating pump, a water cut analyzer, and a cylindrical vessel, with interconnecting piping and actuated valves there between, with the actuated valves and the circulating pump controlled by a digital processor. Once a determination of the percentage of water and oil in the sample has been determined, the processor stops the circulating pump and activates a piston in the cylindrical vessel which sweeps the cylindrical vessel of any fluid contained in the vessel in preparation of receiving a subsequent fluid sample from the oil well.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to the on-sight analysis of fluids produced from hydrocarbon producing wells and the measurement of flow rates of those fluids. In particular, the present invention relates to devices which provide real-time determination of the relative components of the fluids produced from hydrocarbon producing wells and the flow rates of each of the relative components, both instantaneous and over a particular period of time. 
         [0002]    A determination of the percentage of water with respect to the volume of total liquids produced by the well—the “water cut”—is important for determination of the economic viability of a well because excessive water production increases lifting and separation expense, plus the produced water must be properly disposed. In addition, an accurate real-time determination of water cut, when used in conjunction with other parameters such as oil gravity and gas liquid ratio, may be utilized to determine the real-time density of the produced fluid. Knowing the real-time density of the produced fluid may be utilized in conjunction with various devices, such as rod string load cells, to determine downhole pressures and real-time production rates. Knowing the water cut of individual wells on a real time basis also facilitates field wide reservoir analysis and management. For example, in a water flood operation, the detection of a sudden increase in a well&#39;s water cut provides useful information regarding the effectiveness of the flood. 
         [0003]    The present well test systems typically require a relatively large test vessel into which the flow from a particular well may be directed by diverting the flow from the field production system into the test system. The test system will allow produced gas to separate from the other produced fluids, and then typically allow oil and water to separate by gravity separation over time. However, particularly with heavy crudes which may have gravities approaching that of water, gravity alone is not always sufficient. Emulsions also present difficulties in determining the relative percentages of water and oil in a well&#39;s production stream. Heat may be applied to the test vessel to assist in separating the oil and water or in breaking up oil and water emulsions. Floatation devices may be utilized which inject large quantities of small-diameter gas bubbles into streams of primarily water such that the gas bubbles attach to oil droplets suspended in the water stream. These separation devices are expensive and typically require a given volume of produced fluid to remain in the test vessel for sufficient time to allow oil and water separation. Before a successive well can be tested, the test system must be purged of produced fluids from the prior test. 
         [0004]    It is known that separation of the free gas phase from the liquid phase in a sample is desired prior to making a water cut determination is made. The American Society for Testing and Materials (“ASTM” and the American Petroleum Institute (“API”) have provided a Standard Test Method for Water and Sediment in Crude Oil by the Centrifuge Method (D 4007) which provides a laboratory procedure for making water cut determinations. This method is generally accurate because, among other reasons, free gas has already separated from the oil. However, this operation is time consuming and requires manual processing of the sample. It is not a method which may be replicated in the field for real time determination of water cut. Instead, the field determination of water cut will typically employ a number of various water cut meters. These meters utilize various operating principles and hardware to make the water cut determination, such as dielectric measurements using radio or microwave frequencies, optical detectors for detecting near infrared wavelengths, and gamma ray based instruments. 
       SUMMARY OF THE INVENTION 
       [0005]    The presently disclosed apparatus ascertains a relative percentage of water contained in a liquid phase of a fluid sample received from an oil well under real-time producing conditions. Embodiments of the disclosed apparatus include a sampling probe which acquires a representative sample of the fluid flowing through a well&#39;s production line. 
         [0006]    The fluid sample may comprise a liquid phase and a gas phase, while the liquid phase comprises an oil component and a water component. Gas separation may occur prior to taking the sample from the well&#39;s production line. Alternatively, embodiments of the present invention provide for gas separation to be achieved through the system itself. 
         [0007]    In one embodiment of the disclosed systems, a pipe receives fluid received from the oil well. A representative sample of the produced fluid is acquired from a sampling apparatus which has one or more probes installed through a wall of the pipe. The sample of the produced fluid flows into the sampling probe when a valve hydraulically connected to the outlet of the sampling probe opens. A circulating pump has an inlet hydraulically connected to the sampling probe. The circulating pump receives the sample of the produced fluid and discharges the sample to a cut analyzer connected to the pump discharge. The cut analyze ascertains the relative percentages of water and oil in the first portion of fluid as it is circulated through the analyzer. 
         [0008]    The sampling apparatus will typically be downstream of an inline mixer. The sampling probe(s) of the sampling apparatus is installed through a wall of the pipe through which the fluid to be sampled is flowing. In one embodiment of the sampling apparatus, a first probe is inserted through a wall of the pipe downstream of an inline mixer. The first probe comprises a first shaft having a first terminal end and a first outlet end. A portion of the first shaft spans substantially across the internal diameter of the pipe. The first shaft further has an internal axial passage which extends from adjacent the first terminal end through to the first outlet end. The first shaft also has a first upstream face facing towards the inline mixer and a first downstream face facing away from the direction of the downstream mixer. The first upstream face of the sampling probe has a solid wall and the first downstream face has plurality of spaced-apart radial slots extending through from the first downstream face to the first axial passage. 
         [0009]    The sampling apparatus may also have a second probe installed through a wall of the pipe downstream of the outlet of the inline mixer. The second probe will substantially have the same structural elements as described above for the first probe. The first probe and the second probe may be installed such that the first probe and second probe are perpendicular to one another. With this configuration, a sample taken by the sampling apparatus will be representative of the fluid flowing through the pipe at the time of the sampling. 
         [0010]    As the sample of produced fluid is circulated through the system, it flows through a cut analyzer, through a vessel inlet and into a cylindrical vessel which is hydraulically connected to the cut analyzer. The liquid phase of the sample, and any remaining entrained or dissolved gas, flows out through an outlet of the cylindrical vessel, such that a circulation loop is defined as the fluid sample is circulated by the circulating pump through the cut analyzer and the cylindrical vessel. 
         [0011]    As the sample is circulated, gas phase components which come out of solution are vented out of the cylindrical vessel through a gas outlet. The sample is circulated through the circulation loop until such time as the water cut analyzer reports consistent relative percentages of water and oil, as determined by specified tolerance values inputted into a processor which controls the system. Once the water cut analyzer reports consistent relative percentages of water and oil according to the pre-determined values, the processor stops the circulating pump and a piston within the cylindrical vessel displaces all fluids contained within the cylindrical vessel in preparation for receipt of the next sample. 
         [0012]    The piston is moveable from a first position to a second position, wherein substantially all fluids contained within the cylindrical vessel are displaced from the cylindrical vessel as the piston moves from the first position to the second position. A first sensor is connected to the cylindrical vessel, where the first sensor ascertains when the piston is in the first position. A second sensor ascertains when the piston is in the second position. 
         [0013]    In this embodiment, the fluid is swept from the sampling cylinder as the piston moves from a “raised” position to a “lowered” position. Fluid is discharged from the cylindrical vessel as the piston moves from the raised to the lowered position. It is to be noted that, as utilized within this disclosure, the terms “raised,” “lowered,” “top,” “bottom,” etc., are made with respect to the orientations of the piston and cylinder as depicted in the figures herein. However, the operation of the system is not dependent upon the components of the system being oriented as depicted in the drawings. Therefore, the use of the terms “raised,” “lowered,” “top,” “bottom,” etc. should be understood to be consistent with the a “raised” piston being in the initial position before it sweeps a cylinder and a “lowered” piston being in its final position after it has swept the cylinder and cleared all fluid from the cylinder. 
         [0014]    It is to be noted that the presently disclosed invention can utilize almost any of the types of devices for the eventual water cut determination. The presently disclosed invention improves the accuracy of these devices by providing a sample, on the fly at real-time conditions, where the sample is essentially gas free and, optionally, heated to API standard temperature for water cut determination. The inventor herein has found that PHASE DYNAMIC water cut analyzers, which utilize the difference between the electrical characteristics of the water and oil to determine water content, are acceptable for use for water cut determination, but other water cut analyzers may be utilized as well. 
         [0015]    A vacuum pump may be connected to the cylindrical vessel to facilitate gas separation as the sample flows through the circulation loop. Alternatively, the vacuum may be applied from an external source, such as a field gas collection system. 
         [0016]    Gas which has been evacuated from cylindrical vessel may be directed to a gathering line and measured through a gas flow meter, and if desired, a gas chromatograph to ascertain the gas stream constituents as discussed below. The gas flow meter may provide output to the processor as well. 
         [0017]    The piston utilized in the cylindrical vessel may be configured with a piston head and seals which efficiently sweep the cylinder clear of all fluids contained within the cylinder, such that there is little or no mingling of samples as each sample is processed through the system. The cylinder wall may be lined with a material which is non-stick and capable of receiving high temperature fluids. 
         [0018]    The sample may be heated within the cylindrical vessel to further effect separation of the gas phase and liquid phase and separation of the liquid phase components. The heating means will typically be of the electrical resistance type, such as heat blanketing wrapped about the cylindrical vessel. However, process heat might also be utilized with cylindrical vessel with a heat exchanger receiving process fluids such as steam or heated liquids. For such embodiments, the cylindrical vessel may be connected to one or more heat sensors which detect, or provide output to the processor which may be utilized to regulate the temperature of the fluid contained within system according to pre-set values. 
         [0019]    It should be understood that all sensors utilized with embodiments of the device may be located outside of the cylindrical vessel, which greatly facilitates maintenance and repair. In addition, the sensors may be of the type which provide output signals compatible for receipt as input to a digital processor for either data collection or control purposes. 
         [0020]    The piston in the cylindrical vessel may be actuated by a variety of actuation devices, including a low voltage servo motor. This motor may be actuated by the digital processor described above, such that a piston operating within the cylindrical vessel operates according to conditions which may be detected by, among other things, the position sensors and temperature sensors described above, as well as flow sensors which may be utilized in the system. Among other possible input received by the processor and in addition to the other devices listed herein, the processor may also receive load information from a polish rod load cell, pressure transducers detecting the pressure of the cylindrical vessel or downhole devices, water salinity from the water cut analyzer, gas flow rates from the gas flow meter, and other devices utilized in the industry. 
         [0021]    The processor may therefore be utilized to manage the flow of a sample through the system, determining the time required to contain a satisfactory liquid sample for water cut determination, as well as controlling piston position, heat, etc. of the system. In these embodiments, the processor controls a plurality of solenoid operated valves to manage the flow of fluids through the system. In addition, the processor may, based upon the data received through the gas meter, gas analyzer, water cut analyzer, etc., calculate a real time fluid density. Once known, the real time fluid density may be utilized in conjunction with a rod string load analyzer to ascertain flow rates and downhole flowing pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows a general schematic of an embodiment of the analyzing apparatus. 
           [0023]      FIG. 2  shows an embodiment of a analyzing cylinder, piston and related components which may be used with the apparatus. 
           [0024]      FIG. 3  shows a process flow diagram for an embodiment of the present invention. 
           [0025]      FIG. 4  shows a perspective view of an embodiment of a cylinder which may be utilized in embodiments of the present invention. 
           [0026]      FIG. 5  shows a perspective view of an embodiment of a piston which may be utilized in embodiments of the present invention. 
           [0027]      FIG. 6  shows a side view of the piston of  FIG. 5 . 
           [0028]      FIG. 7  shows a sectional view taken along line  7 - 7  of  FIG. 6 . 
           [0029]      FIG. 8  shows a portion of an embodiment of the analyzing apparatus showing the location where a sample may be extracted. 
           [0030]      FIG. 9  shows a close-up view of a static mixer and a sampling apparatus. 
           [0031]      FIG. 10  shows an end view of the static mixer and sampling apparatus of  FIG. 9 . 
           [0032]      FIG. 11  shows a perspective view of a sampling probe or quill which may be utilized in embodiments of the presently disclosed analyzing apparatus. 
           [0033]      FIG. 12  shows a side view of the sampling probe of  FIG. 11 , showing a detailed view of the slots. 
           [0034]      FIG. 13  shows a front view of the sampling probe of  FIG. 11 . 
           [0035]      FIG. 14  shows as section view taken along line  14 - 14  of  FIG. 13 . 
           [0036]      FIG. 15  shows a top view of the sampling probe of  FIG. 11 . 
           [0037]      FIG. 16  exemplifies an operator screen of a digital processor which provides data display and/or control of embodiments of the disclosed apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0038]      FIG. 1  schematically depicts an embodiment of the presently disclosed hydrocarbon well production analysis system  100  according to the present invention. A fluid sampling system  200  for obtaining a representative fluid sample from pipeline  10  is described in further detail below. With respect to the hydrocarbon analysis system depicted in  FIG. 1 , the major components of this embodiment include cylindrical vessel  300 , water cut analyzer  400 , gas flow meter  500 , circulating pump  600 , gas compressor  700 , and flow control valve  800 . A digital processor  1000 , not shown in  FIG. 1 , provides, among other things, control of the process flow of the analysis system and reporting of the analysis results. It is to be appreciated that the components of the production analysis system  100  may be relatively small, fitting within an instrument cabinet or mounted on a transportable skid for easy movement between locations. Flow volumes may be relatively small and interconnecting piping may be ½ inch stainless steel tubing. 
         [0039]      FIG. 2  schematically depicts an embodiment of a cylindrical vessel  300  which may be utilized with the present system. The cylindrical vessel may be fabricated from 316 stainless steel. The size of the vessel may change depending upon a variety of factors, such as the gas-oil ratio and viscosity of the test fluid or whether the test fluid is an emulsion. For test fluids requiring little residence time in the system, such as fluids which have already been degasified and/or containing non-emulsified light gravity crude, the cylindrical vessel may be relatively small, perhaps having an outside diameter of 3 inches with an overall height (or length) of 36 inches, resulting in an approximate volume of 1.5 gallons of fluid. However, for low gravity crude (having a gravity approaching the gravity of the produced water), a larger cylindrical vessel will normally be desired. A cylindrical vessel for these applications may have a diameter and height which provides a volume of 10 gallons of fluid or greater. 
         [0040]    The internal surface of cylindrical vessel  300  may be coated with a non-stick liner suitable for high temperature surface, which facilitates the removal of sample fluid from the cylindrical vessel  300 . The cylindrical vessel  300  should be rated for a minimum of 300 psig, assuming a vacuum of 2.0 inches of water is applied to the vessel. The cylindrical vessel  300  may be equipped with a rupture disc (not shown). Cylindrical vessel  300  receives a fluid sample through inlet  302 . Vent  304  provides for the outflow of gas phase components into a gas collection line  510  which may be transmitted to a gas flow meter  500 . 
         [0041]    Cylindrical vessel  300  has a piston  310  which may have o-ring seals  312 . The o-ring seals  312  may be configured as double seals having an adjustable wear backing ring. Piston  310  may have a head portion  314  which has a profile which mates with the profile of the bottom  306  of cylindrical vessel  300 , thereby providing for greater sweep efficiency of the cylindrical vessel  300  by piston  310 . Piston  310  may be actuated by a low voltage servo motor  330 . 
         [0042]    The cylindrical vessel  300  may be heated to promote separation of any free gas, and also to allow the liquid phase components to reach American Petroleum Institute (“API”) standard temperatures for testing water cut through water cut analyzer  400 . The means for heating the sampling cylinder  300  may comprise an electrical resistance heating element, such as in a heat blanket  326  or it utilize process heat in conjunction with a heat exchanger receiving process fluids such as steam or heated liquids. The cylindrical vessel  300  may be connected to one or more heat sensors  328  which detect the internal temperature of the cylindrical vessel  300 . 
         [0043]    Cylindrical vessel  300  has an outlet  324  which is hydraulically connected to the intake of circulating pump  600 , which flow from the outlet controlled by solenoid operated valve  410 . A sampling probe  332  may detect flowing liquid temperature at outlet  324  and provide this information to processor  1000 . 
         [0044]    The fluid sample is circulated through water cut analyzer  400  which determines the relative percentages of water and oil in the circulating liquid phase. Water cut analyzer  400  may provide data output to processor  1000 . Once stable and consistent water cut information is detected by the water cut analyzer  400 , the circulation of the liquid phase through the circuit may be ceased by the issuance of instructions to a motor controller for circulating pump  600 . Once circulation has stopped, automated valve  410  is closed by instructions from processor  1000  and automated valve  610  is opened by instructions from processor  1000  for return of the liquid phase components to a group line. Upon the completion of the water cut analysis, piston  310  may be actuated by servo motor  330  to clear any remaining fluid inside cylindrical vessel  300  for discharge from the disclosed oil well production analyzing system  100  and discharge from the system as desired, such as by return to the group line and gathered with production from other wells. 
         [0045]    Appropriate interconnect piping for the oil well production analyzing system  100  is one half-inch stainless steel tubing with fittings, utilizing stainless steel ASCO solenoid and check valves. The oil well production analyzing system  100  may be configured as a compact skid package to facilitate transportation and installation of the unit. For example, the entire system may be configured into a unit 40 inches long by 40 inches tall by 30 inches wide. 
         [0046]      FIGS. 8 through 15  depicts an embodiment of a fluid sampling system  200  which may be utilized in combination with the presently disclosed well production analysis system  100 . The fluid sampling system  200  provides representative fluid samples to the system  100 .  FIG. 8  depicts a piping configuration  202  which may be utilized in conjunction with embodiments of the well production analysis system  100 . This piping configuration may include a mass flow meter  204  set within a bypass loop  206  into which the fluid sampling system  200  may be installed, where the sample is taken of fluid flowing through pipe  214 . 
         [0047]    Representative fluid samples are received through sampling line  210  by the operation of actuated valve  212  which allows flow of the sample into the well production analysis system  100 . Pipe  214  has a fluid flowing through it as depicted by the arrows. Pipe  214  has an internal diameter D i . The sampling system  200  may be fabricated into the pipe  214  as a segment of the piping. Sampling system  200  has an inline mixer  216 . Inline mixer  216  is a static mixer which allows for continuous blending of fluids within pipe  214  utilizing the energy of the flow stream to generate the mixing. Inline mixer  216  has an inlet  218  and an outlet  220 . 
         [0048]    The fluid sampling system  200  has a probe  222  which is installed into a tee fitting or alternatively into a welded or threaded reinforced branch fitting, such as a WELDOLET or THREADOLET (not shown) which provides access through a wall  224  of the piping segment. The probe  222  is installed immediately adjacent to the outlet  220  of the inline mixer  216 . The reinforced branch fitting or tee fitting may have threads which receive threads  226  of the head  228  of the probe  222 . Head  228  may have attached a fitting  230  having ½ inch MNPT (male national pipe thread) with a flared bevel on the opposite end of the threads  232  which make up into internal threads  234  at the top of head  228 . External threads  226  of head  228  may likewise be ½ inch 
         [0049]    Probe  222  has a shaft  236  which depends from head  228 . The shaft  236  has a terminal end  238  and an outlet end  240 . Terminal end  238  may be plugged as shown in  FIG. 14 , but an axial passage  242  extends from a point immediately adjacent to the plugged end of terminal end  238  through to the outlet end  240  and out of head  228 . As shown in  FIG. 10 , the portion of the shaft  236  extending from terminal end  238  to outlet end  240  spans substantially across the internal diameter D i  of the pipe  214 . 
         [0050]    Shaft  236  has an upstream face  242  which faces toward the outlet  220  of inline mixer  216 . As shown in  FIG. 12 , the upstream face  242  of shaft  236  is solid, i.e., the upstream face  242  has no openings penetrating into axial passage  242 . Opposite upstream face  242  is downstream face  244 . Downstream face  244  has a plurality of spaced-apart radial slots  246 . Slots  246  may extend approximately through half of shaft  236 . Each slot may be spaced 0.2 inches from an adjacent slot. Radial slots  246  penetrate through the wall of shaft  236  to provide a flow path to axial passage  242 , such that a portion of a representative fluid sample enters into shaft  236  only by passing through slots  246  in the downstream face  244 . 
         [0051]    As shown in  FIG. 10 , the fluid sampling system  200  may have a second probe  222  which is identical to the first probe described above. As further shown in  FIG. 10 , the first probe  222  and the second probe  222  may be configured to be perpendicular to one another. 
         [0052]    With the probe(s)  222  configured and installed as described above, a fluid sample taken from pipe  214  will flow into the axial passage  242  of shaft  236  through spaced-apart radial slots  246  on the downstream face  244  of the shaft, with the fluid sample taken along the entire diameter of pipe  214 . If two probes  222  are configured as shown in  FIG. 10 , the sample is being drawn from across a vertical and horizontal axis, each extending across nearly the entire internal diameter of the pipe  214  thereby collecting a sample along the entire flow profile, which is particularly useful for two phase fluid flow, such as a gas phase and a liquid phase, or in fluid flows where gravitational separation of individual components may occur, such as with some hydrocarbon fluids produced from different wells, or from different producing zones of a single well, where the hydrocarbons are combined into a single pipeline. 
         [0053]    Because the radial slots  246  are on the downstream face  244  of the shaft  236 , the sample will be acquired from fluid which has already flowed past the shaft and the radial slots will not be subject to plugging from any solids which may be entrained in the flowing fluid. This configuration further facilitates backwashing of the radial slots  246  when cleaning of the probe  222  is required. 
         [0054]    The dimensions of sampling probe  222  may vary according the size of pipe  214 . By way of example only, the total length of probe  222 , without fitting  230 , may be 4¼ inches, with shaft  226  having a length of 2½ inches extending below threads  226  of head  228 . Shaft  226  may have an outside diameter of ½ inch. Radial slots  246  may extend into shaft  226  by ¼ inch, or half-way through the diameter. Radial slots  246  may be spaced by 0.190 inches from center to center—i.e., each slot spaced less than 0.2 inches from an adjacent slot. 
         [0055]      FIG. 16  schematically shows a display from a digital processor  1000  which may be utilized with embodiments of the well production analyzing system  100 . As exemplified by the schematic of  FIG. 16 , the processor display may show a calculated gross daily production rate, daily oil rate, and water rate, which would be calculated by the processor based upon input received from a load cell or other device. The processor  1000  may also display the water cut for a given sample, the temperatures of the fluid sample at the inlet of the device and the temperature of the liquid sample as it flows to the water cut analyzer  400 . The processor may also display the current pressure and/or vacuum within the cylindrical vessel  300 . Control of the well production analyzing system  100  may also be performed at controls on the digital processor  1000 , where the controls provide for manual or automated operation of the system, or allowing the system to be placed offline. The digital processor  1000  may provide a display which shows the status of the various components, such as the position of the piston  310  inside the cylindrical vessel  300 . 
         [0056]    It is to be appreciated that the cycling of the oil well production analyzing system  100  is controlled by the processor  1000  based upon real time conditions observed through the various sensors and controlled through the actuation of various end devices as determined appropriate by the processor. Thus, operation of the cylindrical vessel  300   0  and the various other control devices may be varied according to the observed conditions and as desired for the particular field. For example, the timing of the sampling and volume of produced fluid tested for a particular well may be adjusted as necessary to obtain consistent and representative information. 
         [0057]    While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.