Abstract:
A method for measuring in-situ the viscosity of a fluid within a vessel using an apparatus using a motor driven impeller paddle immersed in the fluid. A chemical or biological agent is added to the fluid. The impeller paddle is rotated and the rotational positions of impeller drive shaft and the paddle are sensed. The rotational speed of the shaft is determined and the deflection angle of the impeller paddle relative to the shaft is determined. The viscosity of the fluid is determined by a computer from a look up table containing deflection angle for fluids of known viscosities. The measurements are periodically repeated for a predetermined number of iterations to determine the change in viscosity caused by reaction of the fluid with the chemical or biological agent and the results are reported to a user.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is a method to measure the viscosity of a fluid in-situ, such as in a sealed vessel or in a batch reactor or in a flow reactor. The fluid can be a single phase or multiphase fluid, such as a hydrocarbon compound and water in a bacterial enrichment culture. 
       BACKGROUND OF THE INVENTION 
       [0002]    Certain anaerobic bacteria are known to have an ability to metabolize certain hydrocarbon molecules, such as those found in crude petroleum. The anaerobic bacteria break bonds in the hydrocarbon molecule, which results in a reduction of the viscosity of the crude petroleum. To evaluate the action of these anaerobic bacteria, samples of crude petroleum or petroleum and water mixtures are inoculated with an anaerobic bacteria to create an enrichment culture and then tested under controlled temperature conditions over a period of time. Samples are removed periodically from the culture and tested to measure viscosity using prior art methods. This prior art methodology is believed disadvantageous because the sampling disturbs the environment of the culture and results in a reduction in liquid volume. This volume reduction necessitates either larger volume cultures or multiple cultures of a given sample in order to sacrifice a portion of the sample for the viscosity measurement. 
         [0003]    An instrument known as a viscometer is employed to measure the viscosity of a fluid. A number of commercial viscometers are available from a number of vendors, for example, Rheotek, Brookfield or Hydramotion. Using a typical batch viscometer, the fluid material of interest is placed into a cup and a probe is moved in the fluid within the cup. The drag on the probe from the fluid surrounding it can be translated to viscosity. Although some viscometers can use volumes as low 10 cubic centimeters (cc), they are expensive, and are difficult to adapt to sealed vessels such as those used to incubate enrichment cultures. 
         [0004]    When using an in-line viscometer, the fluid material of interest is pumped through a chamber that contains the probe. For example, U.S. Pat. No. 4,750,351 discloses an in-line viscometer that measures a pressure drop across a fixed flow resistance element. This type of viscometer is difficult to adapt to a sealed vessel such as those used to incubate enrichment cultures. 
         [0005]    Another viscosity measurement technique as described in U.S. Pat. No. 5,203,203, uses a spherical ball placed in direct contact with a fluid in a sealed container. The viscosity measurement is effected by measuring the speed at which the ball falls through the liquid. Although potentially adaptable to sealed vessels such as those used to incubate enrichment cultures, a difficulty is encountered with using a spherical ball and controlling its location in order to keep it within the hydrocarbon phase of a multi-phase enrichment culture. 
         [0006]    Prior art methods and apparatus suffer from a number of deficiencies. Prior art methods and apparatus typically do not provide a means to measure the viscosity as a function of rate of shear. The falling ball technique provides no means to independently agitate the fluid in the sealed vessel without disturbing the movement of the spherical ball that is used to measure viscosity. 
         [0007]    Consequently, there is a need to provide an inexpensive method to measure viscosity in-situ in sealed vessels under a variety of shear conditions. There is also a need for a method to measure viscosity in the hydrocarbon phase of an enrichment culture without the need to remove samples from the culture. Another need is for a method to measure viscosity that is not disturbed by any agitation that is required for the enrichment culture or the reaction that is occurring in the sealed vessel. Another need is for a method capable of measuring viscosity in the hydrocarbon phase and not the water phase of the enrichment culture. Another need is for a method that readily accommodates multiple sealed vessels so that both control cultures (or control reactions) and replicate cultures (or replicate reactions) can be run in parallel at the same time under identical conditions. 
       SUMMARY OF THE INVENTION 
       [0008]    A method of measuring viscosity of a fluid in a vessel while chemically or biologically reacting the fluid with an agent, comprising the steps of:
       a) placing a fluid material of interest in a generally cylindrical vessel containing an impeller assembly, the impeller assembly comprising: i) a generally planar impeller paddle, ii) a shaft, iii) a torsional spring, and iv) a drive motor;   b) adding a chemical or biological agent to the fluid material;   c) purging the cylindrical vessel with a desired reaction atmosphere and reacting the reaction agent with the fluid;   d) rotating the impeller paddle at a predetermined rotational speed;   e) sensing the rotational position of the shaft and the rotational position of the impeller paddle;   f) determining the rotational speed of the shaft from the sensed rotational position;   g) determining the deflection angle of the impeller paddle relative to the shaft;   h) determining the viscosity of the fluid from the deflection angle and the rotational speed of the shaft;   i) periodically repeating steps d) through h) for a predetermined number of iterations; and   j) reporting the results to a user.       
 
         [0019]    The calibration of the apparatus for measuring viscosity of a fluid in a vessel is performed by practicing the measurement method in accordance with the invention for a number of fluids having known viscosities, compiling the known viscosities, the deflection angles and the shaft speeds in a look up table stored in a storage device and then accessing the look up table with a computer to determine the viscosity of a fluid. The viscosity may be measured in situ in a sealed vessel without loss of sample or affect on reaction or reactants in the vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]      FIG. 1  is a diagrammatic view showing the components of the apparatus in accordance with the present invention; 
           [0021]      FIG. 2  is a pictorial view showing a viscosity measurement module in accordance with the present invention; 
           [0022]      FIG. 3A  is a sectional view showing details of construction of a rotating impeller assembly of the viscosity measurement module; 
           [0023]      FIG. 3B  is an exploded view of selected components of  FIG. 3A ; 
           [0024]      FIG. 4  is a block diagram view showing the overall operation of the apparatus; 
           [0025]      FIG. 5  is a timing diagram showing the signals used to measure the shaft rotational speed and deflection angle of the paddle; 
           [0026]      FIG. 6  is a block diagram view showing the steps of a method carried out in accordance with the invention to determine relative viscosity; 
           [0027]      FIGS. 7A and 7B  are plots that illustrate how the apparatus was calibrated using Newtonian fluids of known viscosities; 
           [0028]      FIG. 8  is a plot that illustrates the use of the apparatus for an un-inoculated control using fluids with and without water present and measuring their relative viscosities over a period of time; and 
           [0029]      FIG. 9  is a plot that illustrates the use of the apparatus for an inoculated experiment that shows viscosity changes over time and the resulting evaporative losses of light components in the oil. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    The present method is arranged to facilitate the automated measurement of viscosity of a plurality of enrichment culture samples, each in a sealed vessel, without the need to remove any sample material from the sealed vessel or to disturb the environment within the vessel using the apparatus described below. 
         [0031]    A viscosity measurement system  1  comprises a plurality of viscosity measurement modules  10  and a control and measurement system  100 . A viscosity measurement module  10  comprises an agitator assembly  20 , a shaft  30  and a drive motor  40 . The shaft  30  has an axis  30 A, a first end  30 B, a second end  30 C and a middle region  30 M. The shaft  30  is supported in its middle region  30 M in a bushing  50 B mounted to a containment vessel  50 . The agitator assembly  20  comprises a paddle  22  and a low torsion helical spring  24 . The paddle  22  is mounted on the shaft  30  adjacent to the first end  30 A for rotatable motion. The low torsion helical spring  24  has an axis  24 A, a first end  24 B and a second end  24 C. The first end  24 B of the spring  24  is connected to the paddle  22  and the second end  24 C end of the spring is connected to the shaft  30 , as will be described. The second end  30 B of the shaft  30  is connected to the drive motor  40  by a coupling  42 . 
         [0032]    A position sensor assembly  60  comprises a shaft position sensor unit  62  and a paddle position sensor unit  72 . The shaft position sensor unit  62  comprises a magnet  64  mounted on the shaft  30  and a magnetic field detector  66  known as a “Hall-effect sensor” mounted near the shaft  30 . The paddle position sensor unit  72  comprises a magnet  74  mounted on the paddle  22  and a Hall-effect sensor  76  mounted near the paddle  22 . The magnets  64  and  74  are typically rare earth magnets. When the magnets  64 ,  74  pass by the respective Hall-effect sensors  66 ,  76  the Hall-effect sensors generate electrical signals. 
         [0033]    The paddle  22  is mounted on the shaft  30  in such a way that it can freely rotate about the shaft and is driven for rotation by the torsion spring  24  (see  FIG. 3 ). The paddle  22 , the spring  24  and the shaft  30  are configured so that when the paddle  22  is rotated away (i.e., deflected) from its equilibrium position on the shaft  30  it will readily spring back to its equilibrium position when the rotational force is removed. 
         [0034]    The agitator assembly  20  is mounted in a vessel  50  that contains the fluid of interest. The fluid of interest may be any single phase or multiple phase liquid. A chemical or biological agent may be added to the fluid to cause the fluid to chemically react or to change its physical state, such as a change in it viscosity. The additive agent for instance may contain a bacterium innoculum such as that described in conjunction with Example 3. The fluid of interest is typically an enrichment culture comprising a multiple phase liquid (hydrocarbon and water) and a bacterium. The apparatus is arranged in such a way that the enrichment culture can be located around the agitator assembly and at a depth such that the agitator is immersed in the light phase (hydrocarbon phase) of the enrichment culture. 
         [0035]    A plurality of viscosity measurement modules  10  may be connected to a control and measurement system  100  for simultaneous use. 
       Description of the Apparatus 
       [0036]    Referring to  FIG. 1 , a system  1 , comprising a plurality of viscosity measurement modules  10 - 1  through  10 -N and a control and measurement system  100  was constructed to permit simultaneous experiments and viscosity measurements to be carried out. Each viscosity measurement module  10  was electrically connected to the multiport control and measurement system  100 . The control and measurement system  100  comprises a signal multiplexer  300 , a counter circuit  400 , a programmable power supply  500 , a motor selector unit  550  and a computer control unit  600 . 
         [0037]    A well assembly comprising a plurality of viscosity measurement modules  10 - 1  through  10 -N, as pictorially depicted in  FIG. 2 , was fabricated. Each viscosity measurement module  10  comprises a vessel  50  for holding a fluid of interest As may be seen in  FIG. 3  each vessel  50  was made from a length of acrylic tubing having an inside diameter of 1.0 inch and an outside diameter of 1.5 inches, approximately 3.25 inches in length. A bottom end of each vessel  50  was formed by bonding the tube  150  ( FIG. 3A ) to an acrylic plate  160  approximately 0.3125 inches thick. The tubes were mounted in an array on this acrylic plate, the tubes being spaced about 1.625 inches center-to-center. A hole  164  (best seen in  FIG. 3A ) was drilled into the acrylic plate  160  at the center of each tube and tapped, typically with a ⅛ inch National Pipe Thread (NPT), to receive a threaded adapter  170 , such as a male ⅛ inch pipe-to-male Luer Lock adapter (Swagelok Company 29500 Solon Road, Solon Ohio). A stop cock  172 , typically a Biomedical Luer-fittng stop cock, from Popper &amp; Sons, Inc, New Hyde Park, N.Y., was then mounted into the male Luer Lock end of the adapter  170  to permit filling and emptying each vessel  50 - 1  through  50 -N. 
         [0038]    The top of each acrylic tube  150  was bonded, using a suitable adhesive such as a solvent adhesive, to an acrylic top plate  180  approximately 0.3125 inch thick, having an array of 1.0 inch diameter bores  182  centered on each tube  150 . This top plate  180  supports the top of the tubes  150  while provided access to each vessel  50 - 1  through  50 -N. The top plate  180  was counter bored and machined to accept an O-ring  184 , such as a part number 2-217 O-ring made by the Parker Hannifin Corporation, O-Ring Division, of Lexington, Ky. This O-ring was used to effect a seal to a 2.75 inch thick aluminum plate  190  that formed the top of all the vessels  50 - 1  through  50 -N. Machined into this aluminum plate was an array of recesses  192  that were approximately 0.75 inches in diameter and 2.25 inches deep. These recesses were located on the underside of the plate  190  and were in communication with the volume of the vessels  50 - 1  through  50 -N. These recesses  192  provide the volume necessary to hold the components of the agitator assembly  20 , as will be described herein. 
         [0039]    Holes  194  centered on each recess  192  were drilled into the top of the aluminum plate  190  above each vessel  50 - 1  through  50 -N to provide access for the shaft  30 . Each hole  194  was tapped, typically with a ⅛ National Pipe Thread (NPT), to accept a fitting  196 , such as a male ⅛ inch pipe to ⅛ inch female swagelock tube fitting adapter (Swagelok Company, Solon Ohio) which served as a bushing  50 B for each shaft  30 . 
         [0040]    Each shaft  30  was inserted into the female swagelock tube fitting  196 , which permitted free rotation of the shaft. Each shaft  30  was made of a ⅛ inch diameter stainless steel tube approximately 6 inches long. Onto the shaft was mounted a small aluminum drive block  200  ( FIG. 3A ), approximately ⅝ inches long, 0.25 inches thick and 7/16 inches wide. 
         [0041]    This block  200  was machined with a narrow slot  202  and a bore  204 . The bore  204  was drilled to a diameter slightly larger than the shaft to allow it to slide along the ⅛ diameter stainless steel tubing. Two holes were drilled into this block  200 . A first hole  206  was drilled to intersect the slot  202  and tapped to accept a 2-56 set screw. A second hole  208  was drilled through the block  200  into the bore  204  and also tapped to accept a 2-56 set screw  208 S. A first 2-56 set screw  206 S was threaded into the first hole  206  to affix a first end of the low torsional constant spring  24  in the slot  202 . A spring having a part number TO-1114 spring, from Century Spring Corp. of Los Angeles, Calif. is suitable as spring  24 . The second end  24 C of the spring  24  was inserted in the slot  202  and secured with set screw  206 S. When so mounted the spring  24  surrounds the ⅛ inch diameter stainless steel shaft  30  so that the spring&#39;s axis  24 A was coincident with the shaft axis  30 A and so that the first end  24 B of the spring can rotate about the shaft  30  without binding. 
         [0042]    The paddle  22  was machined from a block of aluminum plate approximately 0.25 inch thick, 0.9 inches long and 0.85 inches wide. A slot  222  and a bore  224  were machined into the paddle. The bore  224  was positioned at the center of the paddle along its longitudinal axis. The diameter of this bore (typically 9/64 inch) was such that the paddle  22  could freely rotate on the shaft  30 . The slot  222  was machined into the paddle next to this bore to accept the first end  24 B of the spring  24 . A hole  226  was drilled to intersect the slot  222  and was threaded to accept a 2-56 set screw  226 S. The paddle  22  was slid onto the shaft  30 , the bore  224  permitting it to freely slide and rotate on the shaft  30 . The first end  24 B of the low torsional spring  24  was slid into the slot  222  on the side of the paddle and affixed to the paddle with the set screw  226 S. In this manner, the paddle was free to rotate about the shaft  30  with only the torsional spring used to drive it for rotation. A recess approximately 0.125 inch in width by 0.125 inch deep was machined into one longitudinal edge of the paddle. Into this recess was press-fitted one or more 0.125 inch diameter by 0.0625 thick rare earth magnets  64 , such as those available from Edmund Scientific of Barrington, N.J. 
         [0043]    The portion of the shaft  30  adjacent to the first end  30 B, the aluminum block  200 , the torsional spring  24  and the paddle  22  thus constitute the agitator assembly  20 . The shaft  30  was slid into the recess  192  machined into the aluminum plate  190  and into the male ⅛ inch pipe to ⅛ female swagelock tube fitting adapter  196 . The height of the shaft  30  above the adapter  196  was adjusted so that the top of the paddle  22  extended down below the aluminum plate  190  by about ½ inch. 
         [0044]    The height of the paddle  22  was fixed by attaching the shaft  30  to the shaft  40 S of a DC motor  40 , such as part number 253446 available from Jameco Electronics of Belmont, Calif. using common rubber tubing as a coupler  42 . This DC motor  40  was mounted above the aluminum support plate  190 , its drive shaft directed downward, on a support member such that its shaft  40 S was aligned with the male ⅛ inch pipe to ⅛ female swagelok tube fitting adapter  50 B that was mounted into the top of the aluminum plate  190 . A 0.125 inch diameter by 0.0625 thick rare earth magnet  64  available from Edmund Scientific, was mounted to the shaft  30  just above the adapter  50 B, typically with an epoxy adhesive. 
         [0045]    An agitator assembly  20  and DC motor assembly  40 , as described above, was installed for each vessel  50 - 1  through  50 -N. After every agitator and DC motor was assembled and mounted onto the aluminum plate, the well assembly comprising the vessel  50 - 1  through  50 -N was fastened onto the aluminum plate with the previously mentioned “O” rings making a seal between the top acrylic plate  180  and the aluminum top plate  190 . 
         [0046]    Each first Hall-effect sensor  66 - 1  through  66 -N, such a part number A1321 EUA from Allegro MicroSystems. Inc. of Worcester, Mass., was mounted next to each rare earth magnet  64  on each drive shaft  30  of each respective module  10 - 1  through  10 -N. Each second Hall-effect sensor  76 - 1  through  76 -N was located outside the vessel  50  adjacent the rare earth magnet  74  on the paddle  22  of each respective module  10 - 1  through  10 -N. These Hall-effect sensors were connected by suitable cables to the signal conditioning circuits  80 - 1  through  80 -N of  FIG. 1 . The signal conditioning circuits  80  each comprise buffer amplifier and comparators  68  and  78  and a flip flop  82 . The plurality of modules  10 - 1  through  10 -N were located inside a nitrogen atmosphere box to assure anaerobic operation. 
       The Control and Signal Processing Apparatus 
       [0047]    In operation the computer  600  commands the programmable power supply  500  (the “control motor speed” signal) to set the speed of the motors  40  in each viscosity measurement module  10 . The computer  600  then commands the motor selector unit  550  (the “select motor group” signal) to select one or more motors. 
         [0048]    With the DC motor(s)  40  energized the computer  600  commands the multiplexer unit  300  to select the signals from the corresponding module(s)  10  to measure of shaft rotational speed and the deflection angle of the paddle in each module  10 . The measured rotational speed and the deflection angle were recorded for each module  10  using the computer control unit  600  according to method diagrammed in  FIG. 6 , described below. 
       Electronic Signal Processing 
       [0049]    Attached to the shaft  30  and paddle  22  of the impeller assembly are high strength rare earth magnets  64 ,  74 . The angular rotational positions of the paddle and shaft are sensed by the magnets  64 ,  74  passing by respective Hall-effect sensors  66 ,  76 . 
         [0050]    Rotational shaft speed of the impeller assembly is determined by measuring the shaft rotation interval, i.e., the time between pulses produced by the magnet  64  attached to the shaft of viscometer. As the magnet passes by the Hall-effect sensor  66 , a voltage pulse is generator from the Hall-effect sensor, as seen in  FIG. 5 , the waveform labeled “shaft sensor analog signal”. This signal is feed to a voltage comparator  68  ( FIG. 4 ), which produces a digital pulse. This digital pulse as seen in the waveform labeled “shaft sensor digital signal” of this group may be used to start a counter circuit (in the counter unit  400  in measurement unit  100 ) which counts high frequency clock pulses. After the shaft  30  of the agitator assembly has completed one revolution, the magnet  64  again passes the Hall-effect sensor  66 , generating another voltage signal which generates another digital pulse, which is used to stop the counter circuit. The counter circuit thus measures the time interval between occurrences of the digital pulses (the shaft rotation interval) to determine the rate of rotation of the shaft of the agitator assembly in revolutions per minute. 
         [0051]    The deflection angle of the paddle is determined by measuring the time interval between the signal generated by the passing of the magnet  64  past the sensor  66  (the “shaft sensor analog signal”) and the signal generated by the passing of the magnet  74  attached to the paddle past the sensor  76 , the “paddle sensor analog signal”. 
         [0052]    The paddle sensor analog signal is converted to a digital signal by comparator  78  ( FIG. 4 ) in the manner described above. The digital pulse of the “shaft sensor digital signal” waveform may be used to start a second counter circuit (in the counter unit  400  in the measurement unit  100 ) which counts high frequency clock pulses. The “paddle sensor digital signal” stops the second counter circuit, thus measuring the time between the “shaft sensor digital signal” and the “paddle sensor digital signal” (the “deflection interval”). By calculating the ratio of the “deflection interval” and the “shaft rotation interval” the measurement unit  100  can determine the paddle deflection angle. It should be noted that both the deflection angle and shaft speed are measured in the same rotational period of the shaft to minimize noise in the measurement. 
       The Measurement Method 
       [0053]    As may be seen in block A of the block diagram of  FIG. 6 , one or more fluid(s) of interest are a placed in one or more corresponding vessel(s) and the vessel(s) are purged with inert gas. As seen in block B an impeller assembly is inserted into each corresponding vessel and coupled to a drive motor. Alternatively the fluid(s) may be added to vessel(s) with the impeller assemblies already in place. The user selects the modules  10  to be used, the measurement time intervals, the number of measurements and the motor voltage using the computer control unit  600  as shown in block C. The computer control unit then commands the programmable power supply  500  to produce the selected output voltage and selects one or more drive motors  40  with the motor control unit  550  and energizes the selected drive motor(s). 
         [0054]    The computer control unit then commands the multiplexer  300  to select signals from one or more viscosity measurement modules  10  corresponding to the selected drive motors  40  (block D). After a suitable time interval the signal conditioning unit  80  then detects the motor shaft rotational position and the paddle deflection angle as the impeller assembly rotates. The counter unit  400  measures the shaft rotation interval and the paddle deflection interval. The computer control unit then calculates shaft rotational speed and the paddle deflection angle (blocks F and G). 
         [0055]    Using the shaft rotational speed and the paddle deflection angle, and calibration data for known viscosity fluids the computer control unit calculate the viscosity of the fluid(s) (block H). The steps of blocks D through H are repeated until the selected number of measurements have been completed in accordance with decision block I. 
         [0056]    The computer control unit then reports the rotational speed and the calculated viscosity for each measurement (block J). The computer control unit then can plot the viscosity as a function of time for each sample, if desired, in accordance with block K. 
       EXAMPLES 
       [0057]    Three examples were performed to illustrate the utility and performance capability of this apparatus. Example 1 illustrates how the apparatus was calibrated using Newtonian fluids of known viscosities. Example 2 illustrates the use of the apparatus for an un-inoculated control using real fluids with and without water present to measure their relative viscosities over an extended period of time as would be required for any enrichment culture experiment. Example 3 illustrates the use of the apparatus for an inoculated experiment that shows viscosity changes over time as a result of evaporative losses of light components in the oil. 
       Example 1 
       [0058]    The apparatus and measurement method described above was used on a series of calibration fluids. These fluids were purchased from Brookfield viscosity standards available from Brookfield Engineering Laboratories, Inc, Middleboto, Mass., USA at the following viscosities: 1000 centipoise (cp), 300 cp, 100 cp, 75 cp, 56 cp and 1 cp. For a viscosity of zero, air was used. A fluid volume of 40 ml was placed in each vessel  50 - 1  through  50 - 6 . The deflection angle of the paddle was measured for each fluid at three different shaft rotational speeds: 399, 225 and 166 revolutions per minute (RPM). The top plot of  FIG. 7  shows these deflection angles plotted as a family of curves at each RPM. For example, for the 1000 cp fluid and at shaft speed of 399 RPM, the deflection angle of the paddle was just under 100 degrees from its equilibrium position. At 225 RPM, the paddle had a deflection angle of 58 degrees and at 166 RPM, the deflection angle was 43 degrees. The deflection angle was linearly related to the fluid viscosity as would be anticipated for a Newtonian fluid. This validates the measurement method. The specific deflection angle was measured as a ratio of the change in the deflection angle per unit change in the viscosity of the calibration fluid and is illustrated in the bottom plot of  FIG. 7 . Again, there is a very linear response indicating that the apparatus is functioning correctly. 
       Example 2 
       [0059]    For this example, 40 ml of crude oil was placed in one vessel  50 - 1  of the apparatus. Approximately 14 ml of crude oil and 26 ml of water were placed in a second vessel  50 - 2 . The relative viscosity of the oil phase of each vessel was measured at predetermined intervals for a full week. The relative viscosity was the relative change in the deflection angle of the paddle at a constant shaft speed. As shown in the plot of  FIG. 8 , there was essentially no change in the viscosity of the oil when either in contact with the water or not in contact with the water. 
       Example 3 
       [0060]    For this example, 14 ml of crude oil and 26 ml of water were placed in one vessel  50 - 1  of the apparatus. The same 14 ml of crude oil and 26 ml of water were placed in a second vessel  50 - 2 . In this second vessel, 5 milliliters (ml) of an ATCC strain  33635 , ( Marinobacterium georgiense ) at about 10 8  colony forming units per milliliter (cfu/ml) was used as an inoculum. The relative viscosity was measured each day as the relative change in the deflection angle at a constant RPM for over a month. As shown in the plot of  FIG. 9 , there was a consistent increase in the viscosity of the oil for both the control as well as the inoculated well. This increase in viscosity was subsequently found to be due to evaporative loss of a small part of the oil since the head space in the vessel was vented into the nitrogen atmosphere chamber. 
         [0061]    Those skilled in the art, having the benefit of the teachings of the present invention may impart modifications thereto. Such modifications are to be construed as lying within the scope of the present invention, as defined by the appended claims.