Abstract:
A drilling mud monitoring system includes a single measurement chamber which is filled with a predetermined quantity of drilling mud. The chamber is weighed to provide a value representative of the density of the drilling mud. The time needed for the chamber to drain is measured to provide a value representative of viscosity. The system proceeds through a measurement cycle in which the chamber is filled, weighed, timed, and washed. At the end of the wash step, the weight of the chamber is compared with an empty weight and if the chamber weighs too much, the conclusion is that drilling mud adheres to the chamber so it is washed again. An alarm is sounded if the mud weight is too low and/or too high or in the case of a machine malfunction.

Description:
This invention relates to a method and apparatus for automatically monitoring the density and viscosity of a liquid, such as drilling mud. 
     BACKGROUND OF THE INVENTION 
     Drilling fluids used to drill wells into the earth are commonly called drilling muds because the original drilling fluid was simply water that mixed with clays in the earth to produce a thin natural mud. Typically, drilling mud is pumped down the drill string, through nozzles in the end of the bit and then upwardly in the annulus between the drill string and the wall of the bore hole. Drilling mud has a variety of functions and must accordingly have comparable capabilities. Cuttings generated by the bit are moved away from the bottom of the hole and then upwardly through the annulus to the surface to present a clean rock face to be drilled. The bit is cooled and lubricated by the drilling mud. The mud also forms a wall cake on the exposed face of the well bore to prevent the drilled formations caving into the bore hole. The pressure of fluids in the formations penetrated by the bit is counterbalanced, or at least partially so, by the hydrostatic weight of the mud column in the hole. The drilling mud is modified to prevent undue effects on the bore hole wall, e.g. to prevent shale swelling. In water based muds, materials are added to prevent undue water loss into permeable formations penetrated by the bit. Various materials are added to reduce friction between the drill string and the bore hole wall. An almost endless list of substances have been added to drilling mud for a variety of reasons. 
     Two important characteristics of drilling mud are mud weight and viscosity. Mud weight is important to counterbalance the pressure in permeable formations penetrated so the well does not blow out. In English measurement systems, mud weight is reported in pounds per gallon. Most wells are drilled overbalanced, i.e. the mud weight is sufficient to contain formation pressures. Some wells are drilled underbalanced, i.e. the mud weight is not sufficient to wholly contain formation pressures, so the contents of drilled formations flow into the bore hole and are circulated to the surface. When it is desired to drill overbalanced, mud weights that are too low cause a well to kick or blow out. When it is desired to drill overbalanced, mud weights that are too high normally produce only unnecessary costs although there is a slight danger of causing formations up the hole to break down and take mud. When it is desired to drill underbalanced, mud weights that are too low create an excessive pressure differential across the formation face. When it is desired to drill underbalanced, mud weights that are too high may result in drilling the well overbalanced. In any event, abrupt changes in mud weight are a reliable signal that something is amiss and, in some situations, is a sign that disaster is approaching. 
     Mud weight is conventionally measured with a beam balance having a small metal cup at one end receiving a fixed amount of mud and a sliding weight on a lever arm fixed to the cup. The beam is placed on a pivot and the sliding weight moved along the lever arm until it balances. The density of the mud is read off the lever arm adjacent the slide. Mud weight is controlled by the addition of weight materials to the mud, usually barite which is a naturally occurring barium sulfate or hematite which is an iron oxide. 
     Viscosity of drilling mud is important because it is a measure of the capacity of the mud to move cuttings up the hole and a measure of the gel strength of the drilling mud which is related to the thixotropic capacity of the mud, i.e. the ability to set up as a gel or semi-solid thereby suspending cuttings to prevent them from settling to the bottom of the bore hole when the mud is quiescent. Viscosity is conventionally measured by adding a predetermined quantity of mud to a funnel of predetermined shape, known as a viscosimeter, Saybolt funnel, or viscosity funnel, allowing the predetermined volume to run out of the funnel, and measuring the time for the funnel to empty. Viscosity of drilling mud is typically measured in seconds. With low cost, water based muds, viscosity is controlled by the addition of bentonite which is often called gel. Bentonite is a naturally occurring swellable clay and has been used for decades as the standard viscosifier in drilling muds. Many other materials, such as polymers, are also commonly used. 
     Drilling mud has many other properties that are measured by a technician known as a mud man. These properties include water loss, pH, gel strength, and the like. Although these properties are of importance for a variety of different reasons, to the drilling contractor or person responsible for drilling the well and delivering a logable hole at the least cost, the most important mud characteristics are mud weight and viscosity. 
     It is known in the art to automatically monitor mud weight and/or viscosity of drilling mud as shown in U.S. Pat. Nos. 2,132,015; 2,252,014; 3,074,266 and 5,052,219. 
     SUMMARY OF THE INVENTION 
     In this invention, an automated device is provided to periodically measure the density and viscosity of any suitable liquid, such as solutions, slurries, or suspensions of any type, for example drilling mud, paint, and the like. Although the method and apparatus of this invention are applicable to other liquids, this invention is described in conjunction with drilling mud because that is a particular niche for which the invention has application. 
     A suitable print out is provided, preferably at a remote location, such as the driller&#39;s station, a central office, or a location handy to a drilling consultant. An important feature of this invention is using a single container to weigh a quantity of mud and measure the time it takes for the mud to drain out of the container thereby providing a measure of viscosity. 
     A variety of features allow the device of this invention to produce consistently reliable results: (1) the measuring container is washed at the end of every measurement cycle and, if the weight of the container does not fall to a predetermined empty weight, the container is rewashed; (2) if rewashing does not reduce the weight of the container to its empty weight, the conclusion is that mud solids have adhered to the container which can corrupt subsequent measurements and an alarm is accordingly sounded and the device turned off; (3) an alarm is sounded if the mud weight measures a value which is too low and/or too high; (4) the too low weight and/or the too high weight limits can be set by an operator; (5) in the event the measuring container overflows, the device is shut off and an alarm sounded; (6) when the supply valve to the mud container opens, the weight of the container is monitored so that, if the weight of the container does not increase, the conclusion is made that something is amiss with the supply valve and/or there is a blockage in the mud line; (7) multiple weight measurements are taken and then averaged to provide the reported mud weight; and (8) a relatively large volume of mud is weighed, as compared to the conventional beam balance thereby providing greater accuracy because small errors are not magnified by the multiplication that necessarily goes on to convert the measured value to pounds per gallon. 
     It is an object of this invention to provide an improved method and apparatus for automatically monitoring drilling mud. 
     Another object of this invention is to provide a method and apparatus for measuring the density and viscosity of drilling mud. 
     A further object of this invention to provide apparatus for monitoring drilling mud which is inexpensive and reliable and which produces consistent results. 
     Another object of this invention is to provide an apparatus for measuring drilling mud weight and viscosity which employs a single measuring container. 
     These and other objects and advantages of this invention will become more fully apparent as this description proceeds, reference being made to the accompanying drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the apparatus of this invention; 
     FIG. 2 is an enlarged cross-sectional view of the device of FIG. 1, taken substantially along line  2 — 2  as viewed in the direction indicated by the arrows; and 
     FIG. 3 is a front view of a recorder used with this invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1-2, a mud monitoring device  10  of this invention comprises, as major components, a housing  12 , a chamber or funnel  14  for receiving a quantity of drilling mud, means  16  for delivering a predetermined quantity of mud to the chamber  14 , means  18  for weighing the chamber  14 , means  20  for washing the chamber  14 , and means  22  for controlling operation of the device  10  including monitoring the weighing means  18  and measuring the time for the chamber  14  to drain. 
     The housing  12  is of conventional design and includes a metallic or plastic box having a door  24  mounted for pivotal movement on an axis  26 . A suitable latch or lock (not shown) releasably attaches the door in a closed position. 
     The chamber  14  is preferably in the shape and size of a standard Saybolt or viscosity funnel conventionally used to measure drilling mud viscosity. A standard Saybolt or viscosity funnel has a generally frustoconical shaped side or bottom wall  28 , has an outlet  30  providing an opening  32  that is 0.180 inches in inside diameter, is 14.25 inches tall, and has a slope of 14°. In a conventional viscosity measuring technique, one quart of liquid is poured into the funnel  14  with a finger closing the outlet opening  32 . The user would remove the finger from the outlet opening  32  and measure the time, usually with a wrist watch, needed for the funnel  14  to empty. 
     Ideally, the chamber  14  is a standard Saybolt or viscosity funnel in which the handle  34  is attached to an element  36  of the weighing means  18  by fasteners  38  as will be described more fully apparent hereinafter. Using the standard Saybolt or viscosity funnel as the weighing chamber  14  is an ideal approach because the viscosity of the drilling mud can be determined simply by measuring the time for the funnel to drain which is necessarily part of the weighing cycle. 
     The mud delivery means  16  includes a conduit  40  connected to a mud line of the drilling rig (not shown) with which this invention is used. Desirably, the monitoring device  10  is placed in the mud line leading from the well and a second monitoring device is placed in the mud line leading to the well. In this manner, mud weight and viscosity are measured after the mud is treated and before it is pumped into the well and after the mud exits from the well. The device  10  that measures mud coming from the well is preferably placed upstream of any shale shaker or the like where treatment of the mud affects mud weight and/or viscosity. When placed upstream from the shale shaker, it is desirable to provide a screen through which the liquid mud flows to the device  10  while allowing large solids to bypass the device  10 , as will be pointed out more fully hereinafter. 
     When the control means  22  starts a measurement cycle, a signal is sent to a valve motor  42  which opens a valve  44  thereby delivering drilling mud through an outlet  46  into the funnel  14 . Because mud flow into the funnel  14  is much greater than mud flow out of the opening  32 , the funnel  14  fills. The rate of filling is the difference between the inflow rate through the valve  44  and the outflow rate through the opening  32 . When the liquid in the funnel  14  reaches a predetermined level, the controller  22  sends a signal to the valve motor  42  to close the valve  44 . The liquid level in the funnel  14  is sensed by a sensor  50  of any suitable type providing a signal to the controller  22  over outlet wires  52  which conveniently pass through a metallic support  54  supporting the sensor  50 . The sensor  50  may be a float operated switch, an ultrasonic liquid level detector, or the like. The support  54  may be adjustable to provide a means of adjusting the position of the sensor  50 . 
     The weighing means  18  includes an L-shaped support  56  to which the chamber  14  is fixed. The support  56  includes the vertical element  36  to which the funnel handle  34  is fixed and a horizontal element  60  having an passage  62  opening through the forward edge of the element  60 . The lower end of the funnel  14  extends through the passage  62  and can be removed by deforming the plastic body of the lower end of the funnel  14  and pulling it through the passage  62 . The support  56  is mounted on an arm  64  extending upwardly from a horizontal wall  66  for pivotal movement about an axis  68 . The free end of the horizontal element  60  is accordingly mounted for movement between an operative position abutting a load cell  70  which senses the load applied by the support  56 , the empty funnel  14 , and any drilling mud in the funnel. The load cell  70  connects to the controller  22  by suitable wires  72 . 
     A lock out mechanism  74  is provided to support the element  60  out of contact with the load cell  70  to allow the device  10  to be transported without damaging the load cell  70 . The mechanism  74  accordingly includes a rigid body  76  having a slot  78  of a size to receive the end of the horizontal element  60 . The body  76  is mounted for rotational movement about a vertical axis  80  so the slot  78  moves to a position out of engagement with the element  60  allowing the device  10  to operate and into a position supporting the element  60  thereby preventing damage to the load cell  70  during handling. 
     The washing means  20  includes a conduit  82  connected to a source of relatively clean wash liquid, such as water or diesel fuel, as is available on any drilling rig. Water is used as the wash liquid when the mud is a water based mud, and diesel fuel is used when the mud is an oil emulsion. A spray nozzle  84  is positioned below the top of the funnel  14  and above the level of liquid sensed by the sensor  50  to start weighing and viscosity measurements. The nozzle  84  delivers a large quantity of clean wash liquid to rinse and thereby clean the inside of the funnel  14 . The washing means  20  is controlled by a suitable valve  86  operated by a solenoid or other conventional operator receiving a signal along wires  88  from the controller  22 . 
     A description of the operation of the device  10  reveals a number of important features. It is preferred that the drilling mud be monitored at relatively frequent intervals, e.g. every fifteen minutes. The time between measurement cycles can be incorporated into the controller or may be set in the field in any suitable fashion, as by an input (not shown) on the controller  22  or on a recorder  92 . 
     At the beginning of a measurement cycle, a signal passes from the controller  22  to the valve motor  42 . Because the funnel outlet opening  32  is restricted, the funnel  14  fills rather rapidly and is not particularly flat. For this reason, the sensor  50  detects a rising liquid level in the funnel  14  and the controller  22  closes the valve  44  in response to the rising liquid level. Because of the time delay and because of the volume of liquid in the outlet  46  downstream of the valve, the liquid level in the funnel  14  rises slightly after the sensor  50  detects the liquid level which is selected to shut off the valve  44 . After flow into the funnel  14  stops, the liquid surface in the funnel  14  flattens out and relatively slow flow through the funnel outlet  30  causes the liquid surface to become reasonably flat. As the liquid level in the funnel falls, the sensor  50  detects a predetermined value which is recognized by the controller  22  and used to initiate weighing. 
     Modern load cells are capable of making a large number of measurements in a very short time, e.g. one hundred measurements in a nanosecond. In a nanosecond, very little liquid flows through the restricted outlet opening  32  so a large number of measurements can be made and averaged. Preferably, values which are abnormally high or low can be discarded before averaging the balance. Ideally, the high 5% of the measured values and the low 5% of the measured values are discarded and the balanced averaged to provide a measurement which is transmitted by the controller to a suitable display  94  on the recorder  92  through wires  96  or through a wireless transmitter (not shown). The recorder  92  may be of any suitable type and one may be located at the driller&#39;s station, in a central office location, or in a trailer or other location suitable for a drilling consultant. 
     An important feature of this invention is measuring the chamber  14  when it is empty which is included to mean when it is dry or when it is water wet. This measurement is necessary to determine the density of the mud being monitored because one gets a value from the load cell  70  representative of a full weight and a deduction needs to be made for an empty weight. 
     The liquid level sensed by the sensor  50  to measure the weight of the mud in the funnel  14  is conveniently, but not necessarily, used to measure viscosity. In other words, the liquid level sensed by the sensor  50  as mud is running out of the funnel is the liquid level corresponding to the predetermined volumetric capacity, e.g. one quart, in the funnel. It should be understood, of course, that different liquid levels could be used for weight and viscosity measurements with the necessary adjusting calculations being made by the controller  22 . Viscosity is accordingly simply measured by measuring the time needed for the weight of the funnel to fall from the full weight to the empty weight. In the event the measured weight of the funnel does not fall to the empty weight within a reasonable time, e.g. two minutes, the conclusion is there is some reason the funnel has not emptied, such as a shale particle stuck in the outlet opening. The washing means  20  is turned on to rinse the funnel and the measuring cycle is repeated before recording any of the values. In the event the empty weight on the next measuring cycle does not fall to the empty weight within a reasonable time, an alarm  98  at the recorder  92  is sounded, a message is printed out at the recorder  92 , and the device  10  is turned off. 
     By weighing the funnel  14  when it contains a predetermined large volume, e.g. one or more quarts, the density of the mud in pounds per gallon is obtained simply by multiplying the difference between the full weight and empty weight of the funnel by a factor which is sufficient to raise the volume to a gallon. A preferred volume for the funnel  14  is one quart, which is the volume necessary for a conventional viscosity measurement. The factor necessary to raise the volume to a gallon is accordingly four. Thus, any error in the weighing operation is magnified, using the preferred volume of one quart, only by a factor of four. In a conventional mud weighing balance, the cup capacity is only about four fluid ounces so the multiplication factor is thirty two. Thus, any measurement error in a conventional mud balance is magnified to a much greater extent than in this invention. 
     If viscosity is successfully measured, the date, time of day, mud weight, and viscosity are printed out on a paper  100  exiting from the recorder  92 . 
     At the end of a successful measurement cycle, the controller  22  turns on the washing means  20  to rinse away any drilling mud on the inside of the funnel  14 . The load cell  70  continually measures the load on the horizontal element  60  in the sense that the element  60  continually bears on the load cell  70 . Thus, the weight of the funnel is measured at the end of the wash cycle. In the event the weight of the funnel  14  returns to the empty weight, the conclusion is that the funnel is clean and the device  10  is ready for another measurement cycle. In the event the weight of the funnel does not fall to the empty weight, the conclusion is that the funnel contains some drilling mud residue and the washing means  20  is turned on again. If the weight of the funnel returns to the empty weight, the conclusion is that the funnel is clean and the device  10  is ready for another measurement cycle. In the event the weight of the funnel again does not fall to the empty weight, a message to this effect is printed on the paper  100  by the recorder  92 , the alarm  98  is sounded, and the device  10  is turned off. 
     The device  10  is capable of setting off the alarm  98  in the event mud weight falls too low or becomes too high. Ideally, this value may be set at the recorder  92  by an input  102 . 
     The device includes other features promoting consistently reliable results. In the event the funnel  14  overflows, this condition is detected because the weight of the funnel increases to a point and then stops at a time when the valve  44  is open and the sensor  50  has not yet indicated that the predetermined level is reached. The conclusion is that the sensor  50  has malfunctioned so the alarm  98  is sounded, a message is printed on the paper  100  and the device  10  is turned off. 
     When the supply valve  44  is open and the weight of the container does not increase, the conclusion is that something is amiss with the supply valve and/or there is a blockage in the conduit  40 , or in a screen assembly  104  through which mud flows into the conduit  40 , or that mud flow has stopped for a substantial time for some other reason. After a delay of a few minutes, a message is printed on the paper  100  and the alarm  98  sounded. To avoid sounding the alarm during an intended interruption of mud flow, as when making a connection, several options are feasible. The conduit  40  may connect to part of the mud system where an accumulation of mud exists, e.g. to the inlet box of a shale shaker. In the alternative, a connection may be made from the controller  22  to the rig pumps so that when the rig pumps are stopped, no measurements are taken. 
     Referring to FIGS. 1-2, a screen assembly  104  is provided to remove drilled solids, such as large shale particles, from the mud upstream of the device  10 . The screen assembly  104  comprises a tee  106  in the conduit  40 , an inclined screen  108  in the tee, and a drain  110  leading off from the tee  106  providing a restricted drain hole  112 . When the supply valve  44  is closed, mud passes through the tee  106 , through the drain  110  and out through the drain hole  112 . When the supply valve  44  opens, mud flows through the screen  108 . Any large particles are rejected by the screen  108  and drop into the drain  110 . It would appear that mud located between the tee  106  and the valve  44  is old mud and its presence would affect readings taken by the device  10 . In practice, the volume of mud in the line  40  between the valve  44  and the tee  106  is very small and it flows out of the bottom of the funnel  14  well before any measurements take place. At the end of a measurement cycle, a supply of wash liquid is delivered through a conduit  114  to wash any drilled solids collecting on the screen back into the drain  110 . 
     When the valve  44  is closed, all flow toward the device  10  is diverted to the drain  110 . When the valve  44  opens, almost all flow is diverted to the device  10  because the restricted drain opening  112  provides a much greater restriction to flow than does the valve  44  and piping downstream of the screen assembly  104 . 
     Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.