Abstract:
Disclosed is a fluid testing device which utilizes a small, cross-section fluid interface to separate a test fluid chamber from a drive and measuring chamber. The test fluid chamber contains the test fluid and a paddle-type fluid test assembly. The drive and measuring chamber contains a second fluid and assemblies for moving the paddle and for determining the resistance movement. The two chambers are connected together by a narrow cross-section passageway allowing for continuous testing while test fluids are flowed through the test chamber and for successive testing of different samples without breaking down the device between tests. A pair of coaxial shafts extends between the test fluid chamber and the drive and measuring chamber. The shafts are connected together by a spring located in the drive chamber whereby the resistance to movement is determined by measuring the deflection in the spring. The shafts are magnetically coupled to a motor to rotate the shafts.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The invention relates to testing apparatus and methods for conducting tests of compatibility on wellbore fluids and their contaminated mixtures and slurries under specific pressure and temperature conditions and, in particular, apparatus and methods for testing fluid mixtures and slurries for use in subterranean wellbores under simulated wellbore conditions. 
         [0003]    2. Background Art 
         [0004]    When drilling, completing, and treating subterranean hydrocarbon wells, it is common to inject materials fluid form with complex structures, such as, suspensions, dispersions, emulsions and slurries. These injected materials are present in the wellbore with materials such as water, hydrocarbons and other materials originating in the subterranean formations. The materials present in the wellbore will be referred to herein as “wellbore fluids” or “wellbore liquids”. These substances and their mixtures flow rather than plastically deform. The flow of these fluids and mixtures cannot be characterized by a single value, instead the apparent viscosity and shear stress changes due to other factors such as temperature and pressure and the presence of other materials. Indeed, the materials in some mixtures may be characterized as incompatible. Two fluids are incompatible if undesirable physical and/or chemical interactions occur when the fluids are mixed. Many times incompatibility is characterized by apparent viscosity and shear stress. When apparent viscosity of A+B is greater than apparent viscosity of A as well as apparent viscosity of B, they are said to be incompatible at the tested shear rate. 
         [0005]    Cement is routinely inserted to block or seal off fluid flow, isolate hydrocarbon zones and provide support for well casings. Wellbores typically are at elevated temperatures and pressures and contain contaminating fluids and solids. The flow characteristics of various cement mixtures can be tested in the presence of a contaminant, such as, a fluid spacer or drilling mud. In addition, mixtures of spacer fluids and drilling mud can be tested. Other examples, including mixtures of wellbore fluids pumped into the wellbore to carry particulate in suspension to the hydrocarbon bearing formations, are located outside the wellbore. 
         [0006]    It is common to determine optimum wellbore liquids and incompatibility of those liquids in a laboratory by running a series of tests of different liquid mixtures under wellbore conditions. Testing various ratios of mixtures of wellbore liquids is done to replicate the changes in the wellbore concentrations of the fluids. These wellbore liquids and mixtures that have variable viscosity are sometimes called “Non-Newtonian fluids.” Testing a series of samples of actual wellbore mixtures during well treatment is also common. Viscosity, elasticity, shear stress, and consistency are rheological characteristics that need to be measured for a given fluid or mixture. 
         [0007]    Known devices used to test fluids for these characteristics include viscometers, rheometers and consistometer. Testing comprises filling a test chamber with a first mixture, bringing the chamber to pressure and temperature test conditions, and then conducting tests of the fluids characteristics. In prior art devices the successive test of different mixture ratios requires emptying and refilling the test chamber with a different mixture to repeat the test. 
       SUMMARY OF THE INVENTIONS 
       [0008]    The present inventions provide equipment and procedures for successively and accurately testing the compatibility of a series of wellbore fluids, fluid mixtures and fluid slurries in the presence of contaminants and under pressure and temperature conditions existing in the well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The drawing is incorporated into and forms a part of the specification to illustrate at least one embodiment and example of the present invention. Together with the written description, the drawing serves to explain the principles of the invention. The drawing is only for the purpose of illustrating at least one preferred example of at least one embodiment of the invention and is not to be construed as limiting the invention to only the illustrated and described example or examples. The various advantages and features of the various embodiments of the present invention will be apparent from a consideration of the drawing in which: 
           [0010]      FIG. 1  is a diagram of the testing apparatus system of the present invention illustrated in longitudinal section; 
           [0011]      FIG. 2  is a partial section view of another embodiment of the testing apparatus of the present invention; 
           [0012]      FIG. 3  is an enlarged partial section of the drive section of the  FIG. 2  embodiment of the testing apparatus of the present invention; 
           [0013]      FIG. 4  is an enlarged partial section of the  FIG. 2  embodiment of the torsion sensing section of the testing apparatus of the present invention; 
           [0014]      FIG. 4   b  is an enlarged sectional view taken in  FIG. 4  looking in the direction of the arrows of the spring stop of the torsion sensing section of the testing apparatus of the present invention; 
           [0015]      FIG. 5  is an enlarged partial section of the  FIG. 2  embodiment of the fluid interface section of the testing apparatus of the present invention; 
           [0016]      FIG. 5   b  is a partial section taken at right angle to the section of  FIG. 5  showing the fluid interface section of the testing apparatus of the present invention; 
           [0017]      FIG. 6  is an enlarged partial section of the  FIG. 2  embodiment of the sample testing section of the testing apparatus of the present invention; 
           [0018]      FIG. 7  is a perspective view of the  FIG. 2  embodiment of the paddle assembly of the present invention; and 
           [0019]      FIGS. 8   a  and  8   b  are diagrams of alternative embodiments of the fluid waste and source reservoirs of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The present invention provides an improved testing apparatus and method for successively testing a variety of combinations of fluid and solid based additives for use in subterranean hydrocarbon wells. The present invention&#39;s particular applicability is to the testing of various proportional mixtures of drilling mud and fluid spacers and, in addition, the testing of various proportional mixtures of drilling mud, fluid spacers and cement. 
         [0021]    Referring more particularly to the drawings, wherein like reference characters are used throughout the various figures to refer to like or corresponding parts, there is shown in  FIG. 1  one embodiment of the testing apparatus  10  of the present invention. The testing apparatus  10  is a pressure vessel designed to withstand test pressures and temperatures. The testing apparatus  10  can be described as basically comprising a pressure chamber housing assembly  100 , a magnetic drive assembly  200 , a torque spring assembly  300 , a fluid interface assembly  400  and a hot well or sample testing assembly  500 . 
         [0022]    The pressure chamber housing assembly  100  is designed to test a liquid or slurry mixture in an enclosed pressure chamber  102 . The housing is designed to be used in controlled temperature and pressure tests up to subterranean hydrocarbon wellbore operating temperatures as high as about 600° F. and pressures as high as about 50,000 psi. In  FIG. 1 , the housing is illustrated as a single piece pressure vessel, however, it is envisioned that considerations of manufacturing and assembly would require multiple pieces or sections such as is illustrated in the other embodiments described herein. In this particular embodiment the housing is shown with five external ports in fluid communication with the interior of the enclosed pressure chamber  102 . These ports are identified for description by letters A-E. Note that Port E is illustrated in  FIG. 5   b  but is not shown in the section forming  FIG. 1 . 
         [0023]    The enclosed pressure chamber  102  is somewhat hourglass shaped with an upper chamber portion  104  and a lower chamber portion  106  connected together by a relatively reduced or smaller cross-section area or passageway  108 . As can be seen in this embodiment the reduced cross section is a passageway. In any case the reduced cross section portion has a maximum cross-section area which is less than the maximum cross-section area of the first and second chambers. The magnetic drive assembly  200  and torque spring assembly  300  are located in the upper chamber portion  104 . The hot well or sample testing assembly  500  is located in the lower chamber portion  106 . As will be described in more detail hereinafter the fluid interface assembly  400  is located in the passageway  108 . 
         [0024]    Generally, the magnetic drive assembly  200  comprises an embodiment of a drive means for rotating the shaft extending into hot well or sample testing assembly  500 . The magnetic drive assembly  200  transfers power into the pressure chamber  102  to rotate shaft assembly  202 . The shaft assembly  202  in this embodiment is illustrated as being located entirely inside the enclosed pressure chamber  102  and therefore eliminates the need for a rotating seal through the housing wall. A motor sprocket drive assembly  208  is connected by sprocket  205  and an endless belt  204  to mag drive sprocket  220  on magnetic drive assembly  200 . The sprocket assembly  208  includes permanent magnets and is rotationally supported from the upper end of the pressure chamber housing assembly  100  by bearings  210 . 
         [0025]    The shaft assembly  202  comprises an upper portion  216  and lower portion  218  connected together by a resilient member such as a spring. The shaft portions in this embodiment comprise two rigid metallic members, however, it is envisioned that the shaft portions could comprise more than two portions and need not be formed from metallic materials. The shaft assembly  202  is supported in the upper chamber portion  104  by a pair of bearings  212  which in this embodiment a simple cylindrical bushing. Bearing  212  allows the shaft to rotate about a vertical axis. A magnetic follower assembly  214  is carried on the upper end of the shaft assembly  202  adjacent to the sprocket assembly  208 . The magnetic follower assembly  214  contains permanent magnets which are coupled by magnetic forces to the sprocket assembly  208 . It can be seen that as the motor  206  causes the external magnets  224  in the sprocket drive assembly  208  to rotate about the upper end of the pressure chamber housing assembly  100 , the magnets in the magnetic follower assembly  214  will cause the shaft assembly  202  to rotate about a vertical axis. 
         [0026]    By using this magnetic coupling to drive or rotate the shaft assembly  202  the necessity of mounting the shaft to extend through the wall of the pressure chamber housing assembly  100  is eliminated. When testing at extremely high wellbore pressure, it is difficult to control leakage around a shaft extending through rotating seals without applying drag forces to the shaft. It has been found that drive means having seals associated with a through housing shaft mounting can induce error into the torsion measurements; however, in some testing situations seal induced error is not significant. Accordingly, alternative drive means for rotating the shaft could be used in place of the illustrated embodiment. For example, electro magnets could be mounted on the shaft and/or around the housing. As previously described a drive means with a shaft extending through enclosure wall could be used. In the illustrated embodiment, the shaft assembly  202  will be described as divided into an upper shaft portion  216  and a lower shaft portion  218 . It is appreciated that one or any number of shaft portions could be used. 
         [0027]    In the illustrated embodiment, a torsion spring assembly  300  is used as a means to measure drag or the resistance to rotation encountered by the shaft during rotation. In the present embodiment, the shaft upper  216  and shaft lower  218  portions of the shaft assembly  202  are connected together by a spring  302  in the torque spring assembly  300 . Alternatively, instead of torsion springs Cantilevered Pivot Bearings could be used such as those obtained from Riverhawk Company, New Hartford, N.Y. 
         [0028]    The shaft upper portion  216  extends upward and is connected and rotated by the magnetic follower assembly  214 . The shaft lower portion  218  extends down from the upper chamber portion  104  through the fluid interface  402  of the fluid interface assembly  400  and into the lower chamber portion  106  of the hot well or sample testing assembly  500 . The shaft upper portion  216  extends into a bearing  219  mounted on the shaft upper portion  216 . 
         [0029]    Test sample contacting rotating paddle assembly  502  are connected to the lower shaft portion  218  and when moved or rotated through the test sample encounter drag or shear forces caused by the test sample contacting the paddles  502 . As used herein, the term “paddle” is defined generically as any member without any particular shape or size moved in contact with the test fluid to incur a drag or shear force as it moves. An example of another a paddle shape is a cylinder rotated about its axis in the test fluid. In this embodiment the removable cylindrical cup  524  lines the lower chamber portion  106 . In addition, removable vanes  520  are mounted to removable cylindrical cup  524  to interact with the rotating paddle assembly  502 . In this embodiment the paddles, vanes and cup are removable for ease in cleaning. 
         [0030]    The torque spring assembly  300  connects the shaft upper and lower portions  216  and  218  together by torsion spring  302 . If during operation (rotation of the upper shaft portion  216 ) drag is incurred by the lower shaft portion  218 , the torsion spring  302  will allow relative rotation between the lower and upper portions in proportion to the magnitude of resistance encountered. Stop assembly  304  limits rotational deflection of the spring  302  to less than 360 degrees. As will be described, the magnitude of the drag is measured and utilized to determine the characteristics of the fluid being tested in the hot well or sample testing assembly  500 . In the illustrated embodiment, magnets  310  and  312  are connected to the shaft upper portion  216  and shaft lower portion  218 , respectively. Transducers  306  and  308  sense the relative position of magnets as they rotate from which the resistance can be determined. As will be explained the transducers can be connected to a recorder processor  309  to store or convert the transducer outputs to usable data. 
         [0031]    Alternative to the torsion spring  302 , a torsion measuring means could be used which could include a strain gauge on the shaft. It should be appreciated that the resistance to rotation caused by contacting the test sample can be measured by alternative torsion measuring means located external to the pressure chamber housing assembly  100 , in which case the torsion spring assembly is eliminated. For example, the load or torque on the motor can be determined from dynamic electrical measurements of the motor. Alternatively, a torsion measuring assembly can be connected to the magnetic drive assembly or motor. However, the preferred embodiment uses a torsion spring immediately adjacent to the paddle. 
         [0032]    When a sample fluid or mixture is being tested in the hot well or sample testing assembly  500 , the drag or resistance encountered by the sample contacting paddles  502  will be proportional to the shear stress at the rotational speed being tested of the sample. A temperature sensing assembly  504  such as a thermocouple  509  is located inside the pressure chamber housing assembly  100  preferably in contact with the fluid located in the lower chamber portion  106  and centered in the paddle assembly to eliminate drag errors caused by fluid contact with the thermocouple  509 . In addition, a pressure sensing assembly  511  is provided to measure the pressure of the fluid inside the pressure chamber housing assembly  100 . 
       Example A 
       [0033]    An example of a method of utilizing the test apparatus  10  will be described in reference to  FIG. 1  and is illustrative of the present invention used to test a variety of proportional mixtures of test fluids and/or solids X and Y. Hydrocarbon well application examples of components of mixtures to be tested include hydrocarbon liquids and gases, acids, gels, cement, mud, proppant, sand, bauxite spacers and elastomers, clays, slag, fly ash, surfactant, polymers and the like. For example, slurries of proppant from 8 to 100 mesh can be tested. In this example, two fluids in liquid form are tested, however, a variety of proportional mixtures and slurries of two or more fluids and solids could also be tested. Indeed a single fluid could also be tested under different conditions using the present inventions. 
         [0034]    The first step in this example is to manipulate the valves v and pump  526  to inject fluid X from reservoir assembly  700  into the lower chamber portion  106  through Port C. Injection of fluid X continues until it is discharged from open Port B indicating that the lower chamber portion  106  of the hot well or sample testing assembly  500  is filled with fluid X and Fluid X is in contact with paddles  502 . Alternatively, Fluid X could be injected through Port A into the lower chamber  106  until discharge is observed at Ports B and C. 
         [0035]    Next, Ports B and C are closed and pressurizing fluid Z is pumped into either Port E (See  FIG. 5   b ) or Port C until discharge is observed at the Port D. This discharge indicates that gas has been displaced from the upper chamber portion  104  and the upper chamber portion has been filled with fluid. Fluid Z is preferably a liquid that is insoluble and immiscible in fluids X and Y. Fluid Z can be an inert lubricating/pressurizing fluid such as nonflammable mineral oil or the like. 
         [0036]    Pumping fluid Z to fill the upper chamber portion  104  will create a fluid interface  402  at the vertical height Port C intersects the passageway  108 . Fluid interface  402  as used herein means the boundary area where the fluids in the upper and lower chambers are in contact with each other. In this example, it is where fluids X and Z are in contact. Port D is then closed and the fluids contained in the testing apparatus  10  are brought to the desired testing temperature using the electrical heating elements  110  and desired testing pressure using a pump connected to the Port D or E. 
         [0037]    While fluid X is being brought to the desired testing temperature and pressure, the motor  206  is activated to rotate the rotating paddle assembly  502 . To monitor the temperature, a thermocouple  509  is located in chamber  522  with its output connected to the recorder  309 . Also, a pressure sensing assembly  511  is connected to the recorder to monitor the pressure of the test fluid. However, the motor could be activated before the testing temperature and pressure are reached. Drag on the rotating paddle assembly  502  contacting the test liquids (and mixtures) will cause torque in the shaft and relative rotation between shaft upper portion  216  and shaft lower portion  218  as torsion spring  302  flexes. Transducers  306  and  308  will sense (measure) the relative rotation between the upper shaft portion  216  and lower shaft portion  218 . The relative rotation is relational to the apparent viscosity or shear stress of the sample contacting rotating paddle assembly  502  once calibrated. 
         [0038]    To test the mixture of fluids X and Y, a measured amount of fluid Y is pumped from a reservoir assembly  600  through Port A and into chamber  522  the hot well or sample testing assembly  500  while an equal amount is discharged from Port B into the waste reservoir  606 . Preferably, an adjustable back pressure regulator  604  is connected to Port B set to maintain the testing pressure during the adding step. It is important to note that in this and the following examples the fluid interface  402  located in the passageway  108  is not disturbed by the controlled injection and the discharge of fluid. Preferably the fluid Y in reservoir assembly  600  has been preheated and maintained at the testing temperature, so that the resultant mixture of fluids X and Y can be quickly tested at the desired test temperature. Preferably the motor  206  is off during the pumping fluid Y into the test chamber. 
         [0039]    The process performing a series of tests of different mixtures containing progressively higher proportions of fluid Y can be accomplished by utilizing Port A and B and pump  628  to add and remove additional amounts of fluid Y and mixtures of fluids X and Y while pressure regulator  604  maintains pressure in the chamber  106 . It is to be noted that the addition of fluid Y can be accomplished by maintaining the fluid interface  402  undisturbed in the passageway  108 . By utilizing this method a plurality of successive tests can be performed without the necessity of emptying the chamber in the sample testing assembly and without removing and replacing the lubrication/pressurizing fluid Z. It should be appreciated that a variety of types of mixtures and slurries can be tested utilizing the apparatus and methods of the present inventions described herein. 
         [0040]    Alternatively, as illustrated in  FIG. 8   a , the pressure sensing assembly  511   a  and regulator  604   a  could be located on the discharge side of the waste reservoir  606   a . In addition, chamber  608   a  is divided into variable volume sub chambers  610   a  and  612   a  by piston  614   a . Chamber  610   a  is filled with an inert or isolating liquid such as mineral oil and is displaced from the chamber  610   a  as liquid is pumped from hot well assembly  500  and into chamber  614   a , it is noted that the regulator  604   a  and pressure sensor  511   a  are in contact with the isolating liquid rather than the Fluids X and Y. This protects these devices from any damaging fluids being tested. In this embodiment piston  614   a  has a rod  616   a  that extends through the wall of reservoir  606   a  and is connected to a linear volume detector  618   a . Alternatively, the rod extending through the reservoir wall could be eliminated and an inferno sensor could be used to measure the piston&#39;s movement. For example, a linear magnetic displacement sensor could be used. The output of detector  618   a  can be connected to recorder  528  to record the volume of Fluids X and Y pumped. 
         [0041]    As illustrated in  FIG. 8   b , an alternative embodiment for isolating the pump  526   b  from the test fluids. In this embodiment fluid reservoir  700   b  is assembled with a piston  702   b  separates reservoir  700   b  into two chambers  704   b  and  706   b . An isolating liquid such as mineral oil is pumped into chamber  702   b  by pump  526   b  to displace Fluid X from chamber  706   b  and into hot well assembly  500 . A piston rod  708   a  is connected to linear detector  710   b . Preferably the detector  618   a  and  710   b  are “LVDT” which can be obtained from Novotechnik U.S., Inc. of Southborough, Mass. or RDP Electrosense, Inc. of Pottstown, Pa. 
       Example B 
       [0042]    The testing apparatus can also be used to perform a series of tests of samples of well fluids. In this example, the reservoir assembly  600  is connected to a source of well fluids such as, for example, the drilling mud which at the time was being circulated through the well. As in example A, the ports are used to place a first test sample in the lower chamber portion  106 . As described in Example “A” using the ports, a suitable second fluid is placed above the test fluid and the contents of the enclosure are brought to test conditions. The test fluid is then tested. When it is desired to test a second test sample, the second sample is pumped into the lower chamber portion  106  by displacing the first sample and to discharge it from the apparatus into waste reservoir  606 . The fluids remaining in the lower chamber  106  will approach, but not completely reach, a 100% concentration of the second sample. The second sample is then tested. This process can be repeated with succession of different samples. Alternatively, a first test sample can be tested as described and thereafter different proportions of the second fluid added to the sample in chamber  106  and tested successively. 
       Example C 
       [0043]    The apparatus can also be used to perform continuous monitoring (testing) of a fluid as it is pumped through the lower chamber portion by pump  526 . For example, a fluid being pumped into or circulated through a wellbore (or other fluid application) could be continuously sampled and the sample pumped through the lower chamber. With the motor running, the shear forces are constantly measured and recorded along with the temperature and pressure. Ideally, a pressure regulator  604  is connected to the discharge port to maintain the test pressure while the test fluid is being circulated through the lower chamber. 
         [0044]    After the test is completed the lower chamber portion  106  is disassembled and the removable cylindrical cup  524 , vanes  520  and rotating paddle assembly  502  are removed and cleaned. 
         [0045]    Turning now to  FIG. 2 , the details of another embodiment of the testing apparatus  10  will be described. In this embodiment, the pressure chamber housing assembly  100  is made up of an upper subassembly  120 , a middle subassembly  140 , a lower subassembly  160 , a bottom cover  180  and an internal bottom cap  190 . The adjacent subassemblies are connected together in sealed engagement to form the enclosed pressure chamber  102 . The upper subassembly  120  houses the magnetic drive assembly  200 . The middle subassembly  140  houses the torque spring assembly  300  and the fluid interface assembly  400 . The lower subassembly  160 , bottom cover and internal bottom cap  190  house the hot well or sample testing assembly  500 . 
         [0046]    The magnetic drive assembly  200  is illustrated in detail in  FIG. 3 . The magnetic drive assembly  200  serves the purpose of transmitting rotational motion via the shaft assembly  202  to the rotating sample contacting paddle assembly  502 . The use of magnetic forces through the wall of the housing to drive the rotating paddle assembly  502  is preferred because it eliminates the necessity of having a sealed shaft extending through the wall of the housing. The variations in frictional drag caused by packing or seals around a shaft can cause errors in the readings. 
         [0047]    In the  FIG. 3  embodiment, a pulley or sheave  220  is connected through an endless belt or chain to a variable speed motor  206  (illustrated in  FIG. 1 ). The sheave  220  is connected to the external magnetic drive housing  222  by a press fit connection or set screws. Magnetic drive housing  222  encloses a plurality of external magnets  224 . Bearings  210  rotatably mount the magnetic drive housing  222  around the neck portion  122  of upper subassembly  120 . The upper assembly  120  or at least the neck portion  122  is made out of a material with magnetic permeability very close to 1, like Inconel, A-286 or MP35N. This is to ensure that the part  120  transmits all the magnetic flux line for effective coupling but, does not get magnetized during operations. As previously pointed out, the sheave  220  is coupled by an endless belt (not shown in  FIG. 3 ) to a variable speed motor  206 . By energizing the motor, the magnetic drive housing  222  and external magnets  224  are rotated about a vertical axis extending through the center of the neck portion  122 . 
         [0048]    In  FIG. 3 , the upper end of the shaft assembly  202  is illustrated as comprising a mandrel  230  constructed preferably of strong ferromagnetic materials like 17-4 PH stainless steel. Suitable bearings  212  in the form of cylindrical bushings are provided to mount the mandrel  230  for rotation about a vertical axis extending along the center of the neck portion  122 . A plurality of internal magnets  232  are mounted to rotate with the mandrel  230  and are axially positioned adjacent to the external magnets  224 . Internal magnets  232  are magnetically coupled to rotate with the external magnets  224 . A top plug assembly  234  closes off the upper end of the neck portion  122 . In order to remove trapped gases or air, Port D is provided to extend through the top plug assembly  234 . 
         [0049]    The torque spring assembly  300  is illustrated in detail in  FIGS. 4 and 4   b . Basically, in the torque spring assembly  300 , the driven portion of the shaft assembly (mandrel  230 ) is coupled by a torsion spring  302  to the shaft lower portion  218  of the shaft assembly. Housing  324  is connected to rotate with the mandrel  230 . The upper end  318  of the torsion spring  302  is connected at connection  320  to housing  324 . The lower end  314  of the torsion spring  302  is connected at  316  to the shaft lower portion  218 . It will be appreciated that torque is transferred from the motor to the shaft lower portion  218  through the torsion spring  302 . The more resistance to rotation encountered by the sample contacting rotating paddle assembly  502  the more the torsion spring  302  is deformed. This deformation allows the shaft lower portion  218  to rotate with respect to the housing  324 . 
         [0050]    In  FIG. 4   b , a spring stop assembly  304  is illustrated in detail for limiting relative rotation between upper mandrel  230  and shaft lower portion  218 . In this figure the torsion spring  302  is mounted so that the spring  302  tightens to urge the shaft lower portion  218  in a counterclockwise direction. In this embodiment, the spring stop comprises a pair of vertically extending pins  328  mounted to rotate with the shaft lower portion  218  and a horizontally extending removable set screw  330  mounted to rotate with the mandrel  230 . The pins and set screw are positioned to engage when the spring is deflected sufficiently to rotate the set screw and mandrel counterclockwise direction. Interference contact between the pins and screw limit relative rotation. As illustrated, the stop assembly  304  allows about 300° of rotation between the mandrel  230  and the shaft lower portion  218 . 
         [0051]    Magnets  310  and  312  are mounted on the mandrel  220  ( FIG. 3 ) and shaft lower portion  218  ( FIG. 4 ), respectively. A transducer  306  is illustrated, mounted outside the wall of the top neck portion  122 , adjacent to the magnet  310 . The transducer  306  senses the rotation of the magnet  310 . A second transducer  308  is mounted to sense rotation of the magnet  312 . From the relative position of these two magnets the torque in the shaft can be determined. It should be understood that transducers  308  and  310  could be mounted internally rather than externally as illustrated. 
         [0052]    The fluid interface assembly  400  is illustrated in detail in  FIG. 5 . The shaft lower portion  218  is illustrated extending through the passageway  108  in the middle subassembly  140  and into the lower chamber portion  106 . The passageway h as  a substantially reduced cross-section area as compared to the cross sections of the upper and lower chambers. In the illustrated example, passageway  108  is 4.5″ long and has a circular cross section shape and is 5/16 inches in diameter. The shaft lower portion  218  extending through passageway  108  has a circular cross section and is 5/32 inches in diameter. This leaves an annular diametrical clearance of 5/32 inches or 0.057 square inches. The annular clearance is selected to be larger than at least four times the size of the largest solid particle to be tested to prevent clogging of the passageway. For example, if proppant is being tested the clearance needs to be larger than particles from 8 to 100 mesh. The length of the passageway and the small annular clearance combine to prevent fluid mixing between the upper and lower chamber portions at the interface as fluids and slurries are tested and added to and withdrawn from the lower chamber portion  106 . Preferably, the passageway has a length that is at least about equal to or greater than the maximum cross-section dimension of the passageway, which maximum cross-section dimension, for example, is the diameter in a circular cross-section passageway and the diagonal in a square cross-section passageway. 
         [0053]    As illustrated in  FIG. 5 , Ports B and C are aligned at about the same vertical fluid levels. When fluid is pumped into the lower chamber  106 , the fluid will reach and be discharged from open Ports B and C simultaneously. Although this is a preferable configuration, it is important that Port C be located at or above the height of Port B. An internal drilling  404  in middle subassembly  140  connects Port C to the passageway  108 . It is preferable that the internal drilling  404  intersect the passageway  108  at about its center so that the fluid interface  402  can move up or down without leaving the passageway. A pair of internal drillings  406  and  408  connects Port B to the lower chamber portion  106 . Port E is illustrated in  FIG. 5   b  located at the same vertical level as Ports B and C. However, Port E could be at a different vertical level. Internal drillings  410  and  412  connect Port E to the chamber  326  in middle subassembly  140  at a level preferably above the fluid interface  402 . Port E could, of course, be connected to passageway  108  at a location vertically above the fluid interface  402 . 
         [0054]    The hot well or sample testing assembly  500  is illustrated in  FIG. 6 . As can be seen, the shaft&#39;s lower portion  218  extends out of the passageway  108  and into rotating paddle assembly  502 . Shaft lower end  506  contacts and is supported by bearing  507  supported by tubular member  510 . As used herein the term “bearing” is used generically to refer to a device that supports a rotating or sliding part and/or reduces friction—without regard to particular structure of the device and whether the device is a roller, needle or ball bearing, a bushing type bearing, a pivot point contact bearing or the like. Tubular member  510  forms a chamber  522  which is in fluid communication with the lower chamber portion  106 . The tubular member  510  is mounted to extend upward from internal bottom cap  190 . An opening or passageway  512  extends to the lower center of internal bottom cap  190 . 
         [0055]    As illustrated, shaft lower end  506  has a pair of radially extending shaft flanges  514  which engaged slots in the rotating paddle assembly  502  to couple the rotating paddle assembly  502  to rotate with the shaft lower portion  218 . Alternatively, a set screw could be used to couple the rotating paddle assembly to rotate with the shaft. The rotating paddle assembly  502  shown in detail in  FIG. 7  is having a cylindrical body  516  with a plurality of radially extending blades  518 . As shown in  FIG. 6  a plurality of complementary vanes  520  is mounted in the lower chamber portion  106 . While the blades and vanes are illustrated having straight edges, it should be appreciated that the terms “paddle” and “blades” used to indicate the sample contacting portion of the apparatus are defined to include other shapes than those illustrated such as cylindrical or frustoconical shapes and those shown in U.S. Pat. Nos. 6,874,353, 6,782,735 and 7,392,842, which are incorporated herein for all purposes. 
         [0056]    In the  FIG. 6  embodiment, paddle assembly  502  is removably connected to the shaft  218  for ease in cleaning. In addition, vanes  520  are removable for the same reason. 
         [0057]    In operation, as the paddle assembly  502  is rotated by the lower shaft portion  218 , the paddle will contact the fluid located inside the hot well or sample testing assembly  500 . As the paddle rotates, contact with the fluid will apply a torque to the lower shaft portion  218  of the shaft assembly  202 . The magnitude of this torque can be measured by the torque spring assembly  300  from which the characteristics of the fluid being tested can be determined. 
         [0058]    Also, as shown in  FIG. 6 , external Port A is connected to passageway  512  and the chamber  522  formed inside of tubular member  510 . Tubular Member  510  is opened to lower chamber portion  106  at the lowest level to effectively displace the existing fluid. Port A can be used to add fluids to the lower chamber portion  106 . In addition, a temperature sensing assembly  504 , such as, a thermocouple assembly  509 , is mounted as shown with its temperature sensing probe located inside the chamber  522  in contact with the fluid in the lower chamber portion  106 . 
         [0059]    While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods also can “consist essentially of” or “consist of” the various components and steps. As used herein, the words “comprise,” “have,” “include,” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. 
         [0060]    Therefore, the present inventions are well adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the inventions, such a reference does not imply a limitation on the inventions, and no such limitation is to be inferred. The inventions are capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the inventions are exemplary only, and are not exhaustive of the scope of the inventions. Consequently, the inventions are intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects. 
         [0061]    Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an”, as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.