Abstract:
An apparatus and process to generate a liquid-gas-surfactant foam and to measure its viscosity and enable optical and or electronic measurements of physical properties. The process includes the steps of pumping selected and measured liquids and measured gases into a mixing cell. The mixing cell is pressurized to a desired pressure and maintained at a desired pressure. Liquids and gas are mixed in the mixing cell to produce a foam of desired consistency. The temperature of the foam in the mixing cell is controlled. Foam is delivered from the mixing cell through a viscometer under controlled pressure and temperature conditions where the viscous and physical properties of the foam are measured and observed.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with U.S. Government support under DOE Grant DE FG26-99BC15178 awarded by the United States Department of Energy. The U.S. Government has certain rights in the inventions 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to an apparatus and process to generate a foam under controlled conditions, measure its viscosity and facilitate measurements of its physical properties. In particular, the present invention is directed to a foam generator and viscometer apparatus and a process which is capable of controlling multiple variables during the generation of a foam and allowing the foam to flow under controlled conditions in order to maintain constant foam properties while being measured. 
     2. Prior Art 
     A number of industries, such as the petroleum drilling and production industry use foams for a wide range of tasks. For example, foams are utilized in the petroleum industry for: drilling underbalanced wells, the transport of proppants during fracturing of wells to improve production, to enhance oil recovery from partially depleted reservoirs, and for environmental remediation of underground water. In the case of drilling new wells into low-pressure reservoirs, conventional drilling muds are too heavy and can over-pressurize the porous rock formations and cause “skin damage” that reduces the flow of either crude and/or gas from the well. This problem is avoided by using lighter weight drilling fluids such as foams. 
     In petroleum applications, foam is produced on-site at a drilling and/or production location. The various components of the foam such as liquids and gases are mixed together and then pumped downhole. Accordingly, it is important to know the properties of the foam and to control its characteristics. 
     Additional applications would be in the chemical and pharmaceutical industries. 
     A study of foam properties includes measurements of its viscous properties and its physical properties such as foam texture, which includes bubble size, size distribution, and bubble shape. All instrument that can produce foam under controlled conditions and measure its properties will provide valuable engineering data that can be used in a variety of industries. 
     There have been proposals in the past to study foams and similar liquids. The Bass Patents (U.S. Pat. Nos. 5,306,734 and 5,394,738) disclose a device to study emulsions which includes a fixed volume mixing chamber and conventional flow meters to measure feed rates of oil and water into the mixing chamber. Bass measures viscosity of samples of the emulsion at ambient temperature and atmospheric pressure. 
     Joseph (U.S. Pat. No. 5,301,541) discloses a device and a method for drag determination having a rib surface  20  attached to an inner block  14  and a rib surface  22  attached to a housing  12 . 
     There remains a need for an instrument and a process to generate a foam and measure its physical and viscous properties. The device should be capable of controlling a number of variables independently, such as foam quality (ratio of gas to total fluid volume), pressure, temperature, surfactants and other additives, bubble size and surface roughness. 
     SUMMARY OF THE INVENTION 
     The present invention produces a liquid-gas-surfactant foam by selectively mixing components of various ratios and controlling the resulting bubble size by adjusting the amount of mixing or shear energy applied. It also conveys the foam, at constant pressure and temperature, through a viscometer, and enables optical measurements of the foam&#39;s physical properties. 
     Gas, contained under pressure in a cylinder, is dispensed and delivered through fluid lines. Liquids, including surfactants and additives, are initially premixed in a volume-calibrated container and then introduced via a pump into a mixing cell. Once the desired volume of liquids has been delivered into the mixing cell, pressurized gas is then allowed to flow into the mixing cell, thereby adding a volume of gas to the liquid volume. As the combined volume of liquid and gas increases inside the mixing cell, a piston begins to rise from its resting place upon a stop or stops. 
     Generation of foam is initiated by rotating a propeller driven by a shaft that is rotated by a variable speed motor. Flow within the mixing cell is forced upward in the center of the mixing chamber and thereafter is diverted downward along the sides of the mixing cell by a specially contoured piston. 
     Additional mixing of the foam can be achieved by optionally drawing liquids, gas and foam from either the top or bottom of the mixing cell with a pump and circulating back to the opposite end of the mixing cell. 
     After a satisfactory foam has been generated, valves may be manipulated to direct gas pressure to the top of the piston, thereby forcing a smooth continuous flow of foam from the mixing cell through a viscometer. The rate at which foam flows from the mixing cell may be measured by a linear voltage differential transformer. Foam from the mixing cell enters a fluid line and passes into a Couette-type viscometer having interchangeable elements (stationary cup and a rotor or a rotating sleeve and a stationary bob) with different values of surface roughness. This feature enables studies of the effects of surface roughness on “wall slip” of foams at a solid surface. Fluid flow is controlled by a metering valve located downstream of the viscometer that allows flow rate to be controlled by varying the opening of the valve. The physical properties of a foam may be visually and electronically assessed at four view ports. Two are located near the Generator, and two others are located on the entry and exit sides of the Viscometer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall schematic diagram of a foam generator and viscometer apparatus constructed in accordance with the present invention; 
     FIGS. 2,  3  and  4  provide additional details about three separate sections of the apparatus shown in FIG. 1 for ease of comprehension; 
     FIG. 5 illustrates a sectional view of a piston utilized in connection with a mixing cell of the present invention; and 
     FIG. 6 illustrates an alternate mixing cell having a propeller with a shroud to assist in mixing of components within the mixing cell. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting the scope of the instant invention. 
     While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention&#39;s construction and the arrangement of its components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. 
     FIG. 1 is an overall schematic diagram of the foam generator and viscometer apparatus  10  and process of the present invention. The process includes a mechanism to produce a liquid-gas-surfactant foam by selectively mixing components in various ratios, varying the resulting bubble size by adjusting the amount of mixing or shear energy applied, and measuring the resulting rheological properties and enables optical measurements of the physical properties. As will be described herein, the temperature and the pressure are controlled throughout the entire process. The overall apparatus  10  is illustrated in FIG.  1 . FIGS. 2,  3  and  4  divide the overall apparatus and process into three sections for ease of comprehension. 
     FIG. 2 illustrates the initial portion of the process that deals with dispensing the constituent gases and fluids at the beginning of the process. Gas, contained under pressure in a cylinder  12 , may be dispensed and delivered through a tank valve  14  and a pressure regulator  18 . Nitrogen would be an example of a gas suitable for the present invention although air and other gases may also be used. Pressure inside the gas cylinder  12 , upstream of a pressure regulator  18  will be indicated on pressure gauge  16 . Pressure downstream of the pressure regulator  18  will be indicated and observed on pressure gauge  20 . A pressure regulator  22  may further refine the precise pressure of gas introduced. The final line pressure is measured by a high precision pressure gauge  24 . 
     A pair of fluid lines  32  and  34  are interconnected by fluid line  36 . By manipulation of valves  26 ,  28  and/or  30 , gas may be dispensed through either line  32  or  34 . 
     Liquids, including surfactants and additives, are initially premixed in a volume-calibrated container  40  and then introduced through low-pressure flexible tubing  42  in fluid communication with pump  44 . The pump  44  controls the volume of liquids introduced. In the sequence of operations, the liquids from container  10  are premixed and dispensed into the mixing cell first. Thereafter, gas from the high-pressure gas container  12  is introduced. Arrows  46  and  48  in FIG. 2 illustrate the flow of fluids and the connection with lines  32  and  34 , respectively, in FIG.  1 . 
     FIG. 3 primarily pertains to generation of the foam. Liquids are dispensed through line  32  and through a port  50  into a fluid tight mixing cell  52 . As the volume of liquid increases inside of the mixing cell  52 , a piston  54  begins to rise from its resting place upon a stop or stops  56 . A portion of the mixing cell  52  above the movable piston  54  is assigned reference numeral  17 . A port to vent high-pressure and high-temperature foam to the viscometer  102  is designated as reference numeral  51 . 
     Once a desired volume of liquids has been delivered into the mixing cell  52 , valves  26 ,  30 , and  28  (as shown in FIG. 2) may be manipulated to allow pressurized gas to flow through line  32  thereby adding a volume of gas to the liquid volume in the mixing cell. The piston  54  may be raised to its maximum height within the mixing cell against a cap  58  at the top of the mixing cell. Both the liquids and gas introduced inside the mixing cell are at a selected pressure. The fluids in the mixing cell are then heated to the desired temperature. Seals  59  assist in maintaining a fluid-tight seal between the cap and the mixing cell. 
     Generation of foam is initiated by rotating a propeller  60  driven by A shaft  82  that is rotated by a variable speed motor  62  or other mechanism. A control  64  can be used to control the speed of rotation of the propeller  60 . Flow within the mixing cell is forced upward in the center of the mixing chamber as the propeller picks up and moves liquids, gases and foam from the bottom and propels them upward. The flow encounters the piston and is thereafter diverted downward along the sides of the mixing cell. This recirculation is facilitated by a contoured piston having recessed portions  55  as shown in the partial section view of FIG.  5 . 
     Bubble size can be controlled by varying propeller rotary speed and by selection of propeller design configurations. 
     Additional mixing of the foam can be achieved by optionally drawing liquids, gas and foam from either the top or bottom of the mixing cell with a pump  66  and circulating back to the opposite end of the mixing cell  52 . In one direction, the flow would move through entry port  50 , pump  66  (driven by motor  67 ), valve  68 , flexible hose  70  and a hollow shaft  72  of the piston  54 . Characteristics of the foam, such as bubble size and gas-liquid ratio may be visually and/or electronically assessed at view ports  74  and  76 . 
     After a satisfactory foam has been generated, valves  78 ,  80 , and  26  (shown in FIG. 2) may be manipulated to direct gas pressure to the top of the piston  54  and into line  98 . After pressurizing line  98 , which connects the mixing cell with a viscometer to be discussed, and manipulating valve  106 , a smooth continuous flow of the foam sample is accomplished. 
     As shown in FIG. 3, the apparatus also includes a vent valve  84 , a drain valve  86  and a drain line  88 . 
     A mechanism may be provided to measure movement of the piston  72  such as a linear voltage differential transformer  90  which can be used to measure piston position and rate-of-travel which provides a measure of flow rate of foam from the mixing cell  52 . 
     The apparatus may also include a mechanism to increase and maintain the temperature inside the mixing cell, such as electrical heater  92 , with thermal insulation (indicated by dashed lines  94 ). 
     An alternate configuration of the mixing cell includes, an optional propeller shroud  96  (shown in FIG. 6) which is designed to promote and enhance mixing. 
     Foam exits the mixing cell through fluid line  98 . A view port  100  is provided in line  98  that allows visual and optical measurements of the foam prior to entering the viscometer. 
     FIG. 4 illustrates the apparatus downstream of the mixing cell  52  and includes a viscometer  102 . Foam from the mixing cell enters fluid line  98  and passes into a viscometer cup  104 . Foam can flow as needed, during the viscometer measurement process, in order to compensate for any foam degradation caused by drainage (syneresis) and/or bubble coalescence. Foam flow is controlled by a micrometer valve  106  located downstream of the viscometer which allows flow rate to be controlled by varying the opening of the valve. Pressure is monitored by pressure gauges  110  and  108  (shown in FIG. 3) and is controlled by maintaining a specified gas pressure above the piston  54  of the mixing cell  52 . A portion  2  of the exhaust  2  flow line located between the viscometer  102  and the pressure gauge  112  is designated reference numeral  47  in FIG. 4. A portion of this exhaust line between the needle valve  106  and the waste tank  118  is designated as reference numeral  49 . 
     A view port is located on each side of the viscometer  102  in order to evaluate and compare properties of the foam before and after passing through the viscometer. The foam may be visually and electronically assessed at view port  112 , downstream of the viscometer, for comparisons with the properties, of the foam as it passes through view port  100  (FIG. 3) and immediately prior to entering the viscometer  102 . 
     The foregoing arrangement provides a method to control flow of foam through the apparatus. 
     In a preferred embodiment of the present invention, a modified Couette-type rotary viscometer is employed with either a rotor inside a stationary cup or a stationary bob with an outer rotating sleeve. The internal surfaces of these elements are modified to have a variety of surface roughnesses so the effects of changing wall roughness on foam rheological measurements can be systematically investigated. 
     The viscometer  102  includes a heater  114  that enables control and selection of temperature and thermal insulation (indicated by a dashed surrounding block  116 ) to maintain a uniform temperature inside the viscometer cup  104 . A drain receptacle  118  will receive waste from line  49  exiting the viscometer and from line  88  exiting the mixing cell or any exhausts from containers  12  and  40 . 
     An alternate mechanism may be used to control the rate-of-flow through the viscometer cup. Instead of flowing fluid directly into the drain receptacle  118 , flow may be directed into a pressurized container of such size that all of the liquid and gas components of the foam are contained therein. Flow is then controlled through micrometer valve  106  which would be located on the top of the pressurized container and be used to control flow by allowing only the gaseous phase to be vented. This arrangement permits better control of flow rate rather than having an intermittent flow of liquid and gas passing through the micrometer valve  106 . FIG. 6 illustrates two additional features of the mixing cell. A temperature sensor  57  used to control heating elements  92  and achieve a desired temperature is provided. A shroud  96  surrounds a propeller/impeller is designed to promote better circulation of fluids between the bottom and top of the closed volume within the mixing cell  52 . 
     Whereas, the present invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.