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 received within a degassing cylinder and separated into a liquid phase and a gas phase, with the liquid phase automatically transferred to a sampling cylinder for water cut analysis. Once the liquid phase has been transferred to the sampling cylinder, a piston within the degassing cylinder automatically evacuates all fluid from the cylinder 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. In particular, the present invention relates to devices and methods which provide real-time determination of the relative components of the fluids produced from hydrocarbon producing wells. In this invention, phase separation and the determination of the relative volumes of each are accomplished by utilizing a pair of vessels in series, where the first vessel eliminates substantially all of the gas phase from a sample by actuation of a piston within the vessel which delivers a degasified sample to the second vessel which further processes the sample and delivers a liquid phase sample to a cut analyzer which ascertains the relative percentages of water and oil in the sample (i.e., the “cut” or “water cut”). 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 . 
         [0002]    The known cut analyzers are most accurate when analyzing a sample which does not have any free gas phase. Free gas in the sample typically results in under measurement of the water cut, so it is desirable to reduce or eliminate any free gas before analysis of the sample. Moreover, the presence of small, but unknown and variable amounts of entrained gases in the sample confound accurate fluid density measurement, which is critical to the extent that fluid density is an inputted variable for downhole monitoring and well diagnostics. 
         [0003]    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, a number of various water cut meters are utilized. 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. 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. 
         [0004]    The common automated mechanisms for gas separation typically require large separators which typically rely upon heat, gravity, mechanical flow dividers (such as baffles), and relatively long holding times to sufficiently separate the gas phase from the liquid phase to obtain an accurate determination of the cut. While portable skid units having relatively smaller separation vessels are known, the accuracy of the water cut determination can be adversely impacted by the relatively small separator size and short time for separation. 
       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. The fluid sample comprises a liquid phase and a gas phase, while the liquid phase comprises an oil component and a water component. The system has a fluid inlet which receives flow from a wellhead or production line from the well. The system also has one or more fluid outlets through which the fluid sample, after being analyzed, is discharged from the system. A plurality of vessels is disposed between the fluid inlet and the fluid outlet, typically in a series configuration, although a parallel configuration might also be utilized. 
         [0006]    Among the vessels disposed between the fluid inlet and fluid outlet are a degassing cylinder and a sampling cylinder. The degassing cylinder is hydraulically connected to the sampling cylinder, typically in a series configuration. The degassing cylinder typically receives substantially all of the fluid sample from the fluid inlet. A piston is disposed within the degassing cylinder, with the piston being moveable from a first position to a second position. As the piston moves from the first position to the second position, substantially all of the liquid phase of the fluid sample is transferred to the sampling cylinder. This operation is similar to the operation of a plunger within a syringe displacing the contents of the syringe through the needle end of the syringe. Gas phase components are vented from the degassing cylinder during this process, where the gas phase may be gathered from the degassing cylinder. Gas gathered from the degassing cylinder and from the sampling cylinder may be commingled in 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 a digital processor. 
         [0007]    The piston 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. 
         [0008]    Once the sample is transferred to the sampling cylinder, the sample may be heated to further effect separation of the liquid phase and gas phase, with gas phase components vented out of the sampling cylinder, where the gas phase may be commingled with the gas phase from the degassing cylinder as described above. The sample may be circulated through the sampling cylinder by a pump connected to an outlet of the sampling cylinder. A water cut analyzer as discussed above is hydraulically connected to the sampling cylinder, where the water cut analyzer receives a liquid sample from the sampling cylinder. The water cut analyzer generates data which allows the determination of the percentage of water, if any, within a liquid sample received from the sampling cylinder. 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. 
         [0009]    In one embodiment, the sampling cylinder comprises a separate piston, similar to that of the degasing cylinder. In this embodiment, the fluid is swept from the sampling cylinder as this piston moves from a “raised” position to a “lowered” position. Fluid is discharged from the sampling cylinder 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 pistons and cylinders 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. 
         [0010]    In one embodiment of the invention the degassing cylinder and/or the sampling cylinder may have sensors which ascertain the position of the piston within the degassing cylinder. For example, the sensors may detect when the piston is in the raised position, where there is a maximum volume of the cylinder available for inflowing fluid. The sensors may also detect when the piston is immediately adjacent to the bottom of the degassing cylinder, which is the position of the piston after it has swept all of the contents from the degassing cylinder. In another embodiment, the sampling cylinder and/or degassing cylinder may comprise heating means. The heating means will typically be of the electrical resistance type, such as heat blanketing wrapped about the sampling cylinder or the degassing cylinder. However, process heat might also be utilized with the sampling cylinder or the degassing cylinder configured with a heat exchanger receiving process fluids such as steam or heated liquids. For such embodiments, the sampling cylinder and/or degassing cylinder may be connected to one or more heat sensors which detect, or provide output which determines, the temperature of the fluid contained within the sampling cylinder and/or degassing cylinder. 
         [0011]    It should be understood that all sensors utilized with embodiments of the device may be located outside of the degassing cylinder and the sampling cylinder, 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. 
         [0012]    In another embodiment of the system, a vacuum may be applied to either the sampling cylinder and/or the degassing cylinder to facilitate the removal of gas phase components from the vessels. As discussed above, these gas phase components may be collected and piped through a flow meter to ascertain the relative volume of the gas phase in the sample. Additionally, the gas phase components may be processed through a gas phase analyzer, such as a chromatography unit. The vacuum may be either applied by a compressor integral to the system, or the vacuum may be applied from an external source, such as a field gas collection system. 
         [0013]    The pistons in the degassing cylinder and the sampling cylinder may be actuated by various actuation devices, including low voltage servo motors. These motors may be actuated by the digital processor described above, such that a piston operating within the degassing cylinder is operating cooperatively with a piston operating within the sampling cylinder, 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 degassing cylinder, the sampling cylinder, 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. 
         [0014]    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 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 
         [0015]      FIG. 1  shows a general schematic of an embodiment of the apparatus. 
           [0016]      FIG. 2  shows an embodiment of a degassing cylinder and related components which may be used with the apparatus. 
           [0017]      FIG. 3  shows an embodiment of a sampling cylinder and related components which may be used with the apparatus. 
           [0018]      FIG. 4  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 
       [0019]      FIG. 1  schematically depicts an embodiment of the presently disclosed oil well production analyzing system  100  according to the present invention. The major components of this embodiment are degassing cylinder  200  and sampling cylinder  300 . Additional components of this embodiment are water cut analyzer  400 , gas flow meter  500 , circulating pump  600 , gas compressor  700 , flow control valve  800 , base member  900 , and processor  1000 . This production analyzing system will typically be connected at position close to an oil well, such that the received fluid sample received by the unit is essentially the same as produced at the wellhead from the well. The sample should be taken downstream of an inline mixer which is present in a flow-line coming from the oil well. An acceptable inline mixer is available through Automated Mechanical Process Systems Inc. of Bakersfield, Calif., part number DM-360. This inline mixer is configured in a spool piece which may be inserted within a well&#39;s production flow- line. For a 2 inch production flow-line, a  3  inch diameter spool is utilized, the spool having a length of approximately  23  inches. This in-line mixer comprises, in respective order from the upstream end: (1) a plurality of mixing vanes having both clockwise and counter-clockwise orientation; and (2) an internal conical structure with the small end of the cone facing upstream, the conical structure having a plurality (e.g., more than twenty) of axially-aligned slots through which the fluid flows. 
         [0020]    It is to be appreciated that the components of the production analyzing system may be relatively small, fitting 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. 
         [0021]      FIG. 2  schematically depicts an embodiment of a degassing cylinder  200  which may be utilized with the present system. The degassing cylinder  200  may be fabricated from  316  stainless steel and will typically 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. The internal surface of degassing cylinder  200  may be coated with a non-stick liner suitable for high temperature surface, which facilitates the removal of sample fluid from the cylinder  200 . The degassing cylinder should be rated for a minimum of 300 psig, assuming a vacuum of 2.0 inches of water is applied to the vessel. The degassing cylinder  200  may be equipped with a rupture disc (not shown). Degassing cylinder  200  receives a fluid sample through inlet  202 . Vent  204  provides for the outflow of gas phase components into a gas collection line  510  for transmission to gas flow meter  500 . 
         [0022]    Degassing cylinder  200  has a piston  210  which may have o-ring seals  212 . The o-ring seals are typically configured as double seals having an adjustable wear backing ring. Piston  210  may have a head portion  214  which has a profile which mates with the profile of the bottom  206  of degassing cylinder  200 , thereby providing for greater sweep efficiency of the degassing cylinder  200  by piston  210 . Piston  210  may be actuated by a low voltage servo motor  230 . The inventor herein has found that a 24 VAC, 1.6 amp, ¼ hp motor is suitable for this service. 
         [0023]    Piston  210  may also have one or more displacement pick-ups  216 . Displacement pick-ups  216  provide a signal which may be detected by displacement sensors such as a displacement sensor  218 , piston down sensor  220 , and piston up sensor  222 . These sensors are positioned to receive signals from the displacement pick-ups when the piston  210  is adjacent to the sensors. The sensors may provide output signals which are conveyed to a processor  1000 , which may be an industrial programmable controller or other processor capable of receiving, storing, and processing input data and providing output instructions based upon the input data. Degassing cylinder  200  may further comprise a means for heating the contents of the cylinder for both promoting gas separation as well as for pre-heating the fluid which is transferred to sampling chamber  300 . The means for heating the cylinder may comprise an electrical resistance heating element, such as in a heat blanket  226  or it utilize process heat in conjunction with a heat exchanger receiving process fluids such as steam or heated liquids. The degassing cylinder  200  may be connected to one or more heat sensors  228  which detect the internal temperature of the degassing cylinder  200 . Output from this sensor  228  may be conveyed to processor  1000 . 
         [0024]    As piston  210  sweeps the interior of degassing cylinder  200 , liquid phase components are forced out of the cylinder through liquid outlet  224  and piped to the inlet of sampling cylinder  300 . Gas phase components are released through vent  204  into a gas collection line  510  for transmission to gas flow meter  500 . Gas separation may be further promoted by applying vacuum to vent  204  by connecting a vacuum line to the vent. For example vent  204  may be connected to the inlet of compressor  700  and a vacuum of a two inch water column applied to the inlet. As discussed below, sampling cylinder  300  has a similar vent  304  which flows into gas collection line  510 . The commingled gas streams from the degassing cylinder  200  and the sampling cylinder  300  may flow through gas flow meter  500 , pressurized by compressor  700  and returned into a group line as controlled by flow control valve  800 . 
         [0025]    Once the liquid phase and gas phase components of the fluid sample are cleared from degassing cylinder  200 , piston  210  is raised to the upper portion of degassing cylinder  200 , with any gas trapped between the piston  210  and the upper portion of the degassing cylinder allowed to escape through vent  208 . Based upon input received by the processor  1000  regarding the completion of the cycle within the degassing cylinder  200  and the status of the of the liquid phase components in the sampling cylinder  300 , the processor will issue instructions to a control valve (not shown) upstream of the degassing cylinder  200  to open and allow a new fluid sample to be received into the degassing cylinder to be processed in a new testing cycle. 
         [0026]      FIG. 3  schematically depicts an embodiment of a sampling cylinder  300  which may be utilized with the present system. For manufacturing and maintenance convenience, sampling cylinder  300  may be manufactured from similar materials as degassing cylinder  200 , and have similar dimensions. Sampling cylinder  300  receives flow through inlet  302 . Vent  304  provides for the outflow of gas phase components into a gas collection line  510  for transmission to gas flow meter  500 . Sampling cylinder  300  is connected at outlet  324  to the intake of circulating pump  600 . A sampling probe  332  may detect flowing liquid temperature at outlet  324  and provide this information to processor  1000 . 
         [0027]    Similar to degassing cylinder  200 , sampling cylinder  300  may comprise a means for heating the contents of the cylinder. This heating will further promote separation of any free gas, and will also 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 degassing cylinder  300  may be connected to one or more heat sensors  328  which detect the internal temperature of the sampling cylinder  300 . 
         [0028]    Liquid phase components are 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 and automated valve  610  is opened for return of the liquid phase components to the group line. Upon the completion of the water cut analysis, piston  310  may be actuated by servo motor  330  to clear any remaining fluid from sampling cylinder  300  for discharge from the disclosed oil well production analyzing system  100  and return to the group line and gathered with production from other wells. 
         [0029]    Sampling cylinder  300  has a piston  310  which may have o-ring seals  312 . Piston  310  may have a head portion  314  which has a profile which mates with the profile of the bottom  306  of sampling cylinder  300 , thereby providing for greater sweep efficiency of the sampling cylinder  300  by piston  310 . Piston  310  may be actuated by a low voltage servo motor  330  similar to that utilized with degassing cylinder  200 , i.e., a 24 VAC, 1.6 amp, ¼ hp motor is suitable for this service. 
         [0030]      FIG. 4  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. 4 , 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 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 degassing cylinder  200  and the sampling cylinder  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 pistons  210 ,  310  inside the degassing cylinder  200  and the sampling cylinder  300 . 
         [0031]    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, the interaction of the degassing cylinder  200  and the sampling cylinder  300  and the various other end 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. 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. 
         [0032]    Appropriate 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. 
         [0033]    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 claims to be filed in the forthcoming utility application.