Method and apparatus for foam generation

Abstract

 A foam generation apparatus comprises a tee (10), into which liquid is introduced through the side leg (20) thereof, and a gas is introduced through one (30) of the ends of the main leg of the tee, the generated foam exiting the tee from the other end of the main leg. The side leg of the tee is disposed at substantially a right angle to the main leg, and the gas may be introduced into the main leg through a choke (50).

Description

[0001] It is generally known to employ foams in chemical processes, in the manufacture of elastomeric products, in fire fighting, in agricultural chemical applications and in various uses in the petroleum industry. Among the uses for foam in the latter industry are included acidizing, fracturing, cleanout, and gravel packing. There are numerous foam generating apparatuses employed in the prior art, such as sparger tubes and closed vessels wherein gaseous and liquid products are introduced and mixed in various ways to create a foam. Several such devices of the prior art are disclosed in U.S. Patents Nos. 1,753,429, 2,418,858, 3,979,326 and 4,070,302.

[0002] Problems with the aforesaid prior art devices include their bulk and weight, the relatively high expense of manufacture, as well as the devices' tendency to create foams of uneven quality due to their complexity and the inability of the operator to immediately ascertain changes in foam quality. Moreover, these prior art devices are very unsuitable for generating a foam carrying particles therein, as the introduction of a particle-laden liquid into a prior art foam generator vessel results in immediate and severe erosion due to the scouring action of the particles on the interior of the vessel and associated piping. The inability to generate large volumes of such "dirty" (particulate-laden) foams, is a major detriment to operations such as fracturing or gravel packing an oil or gas well, where it may be beneficial from both a cost and results standpoint to employ a foam as a carrier for the particulate matter. For example, using foam greatly reduces the amount of carrier fluid and expensive additives employed, and in addition places far less hydrostatic pressure on delicate formations such as may be encountered in gas wells, or in unconsolidated formations of wells to be gravel packed.

[0003] Other foam generating devices of a simpler design are also known in the prior art. For example, U.S. Patent No. 3,090,444 discloses a device which draws air through apertures in the side walls of the generator to create a foam; U.S. Patent No. 3,889,764 discloses a foam generator wherein the materials to be foamed impinge on a knife-edge to create turbulence; U.S. Patent No. 4,330,086 discloses a tubular foam generator having a choked liquid flow, downstream of which air is pulled into the generator and the resulting mixture impinged on a transversely set pin and then the inner wall of the generator to create a foam. While, as noted, above, these devices are simpler and more compact than the aforementioned prior art devices, they nonetheless possess inherent disadvantages. For example, the device of U.S. Patent No. 3,090,444 is still somewhat clumsy in design, and takes quite some time and flow distance to effectively create a foam. Moreover, this device, as well as those of U.S. Patents No. 3,889,764 and 4,330,086 are totally unsuitable for the foaming of particulate-laden fluids as the fluid flow would quickly erode the liquid chokes and the knife-edge or pin employed in these devices.

[0004] We have now devised a relatively uncomplex device for foam generation, which device can be relatively easily and inexpensively produced, is wear-resistant by its design and which permits the easy production of foam to the quality desired, even in the case of "dirty" foams.

[0005] According to the invention, there is provided a system for generating a foam product, comprising: means for supplying gas; means for supplying a liquid; foam generating tee means comprising a tubular tee including a main leg and a side leg disposed at substantially a right angle to said main leg; liquid feed manifold means adapted to transmit said liquid from said liquid supply means to said side leg of said tee; gas feed manifold means adapted to transmit said gas from said gas supply means to said inlet end of said tee; and foam discharge piping means for receiving a foam product from said tee.

[0006] The invention also includes a method of generating a foam product, comprising: introducing a liquid stream under pressure into a tubular vessel; introducing a gas stream under pressure into said tubular vessel; impinging said gas stream on said liquid stream in said vessel at substantially a right angle to said liquid stream, whereby a substantially uniform foam product is formed and discharged from said vessel.

[0007] Preferably, a choke means is associated with the main leg of the tee wherein the gas component is introduced, the outlet of the choke means being located proximate the inlet from the side.leg of the tee into the main leg. The foam is generated proximate to and downstream from the intersection of the side leg with the main leg, and the foam leaves the tee at the main leg and opposite the gas inlet end thereof.

[0008] It is believed that, in the method and apparatus of the present invention, a high quality emulsion or foam is generated due to the manner in which the liquid component is forced to make a substantially right-angle turn in its flow path. This change indirection initiates turbulence, at which point the gas component flow induces additional turbulence and provides efficient dispersion of the gas throughout the liquid, producing a high quality emulsion or foam product. In addition to the efficient production of an emulsion or a foam, the impingement of the gas flow at substantially right angles to the liquid flow curtails the erosive effects of the liquid on the inside wall of the tee opposite the inlet for the side leg; this curtailment is particularly critical in the foaming or emulsification of dirty liquids carrying abrasive particulate matter, as without it a hole would quickly be worn through the wall of the tee, or at best a weakened wall area produced which could rupture, causing damage and serious injury.

[0009] In order to more fully understand the nature of the invention, the detailed description set forth hereafter should be read in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a full section elevation of one embodiment of apparatus of the invention; and

FIGURE 2 is a schematic illustration of the placement of an apparatus of the invention in a system employed to generate and introduce a foam into a well bore to be treated.

[0010] Referring now to FIG. 1, the preferred embodiment of the apparatus of the present invention will be described hereafter. Foam generator 10 comprises a generally tubular tee having main leg 8 and side leg 12, side leg 12 defining liquid inlet bore 14 with wall 16. A hammer-up type threaded union, generally indicated at 18 and well known in the petroleum industry, connects liquid discharge piping 20 to side leg 12, piping bore 22 communicating with and being coaxial with liquid inlet bore 14. Circular elastomeric seal 24 is compressed between the end of piping 20 and annular seat 26 surrounding the entrance to fluid inlet bore 14.

[0011] At the left side of FIG. 1, choke nozzle 30 is connected to end 32 of the main leg of foam generator 10 by a hammer-up threaded union, generally referred to by reference numeral 36, circular elastomeric seal 37 being compressed between end 32 of foam generator 10 and the inner end of choke nozzle 30. Choke insert 40 is threaded to choke nozzle 30 at threads 42; the end of choke nozzle 30 extends into gas inlet bore 38 of the main leg which is defined by wall 34. A gas-tight seal between choke nozzle 30 and choke insert 40 is effected by 0-ring 44, maintained in annular recess 46 on the exterior of choke nozzle 30. Choke insert 40 includes outer tubular metal housing 48, which is threaded to choke nozzle 30, which housing 48 carries choke insert 50 having restricted axial bore 52 therethrough. Choke insert 50 may be of any suitable material, such as metal or ceramic (shown in FIG. 1). The inner end 54 of axial bore 52 opens into gas inlet bore 38 of main leg 8. The outer end 56 of axial bore 52 opens into socket 58 in which an allen wrench is used to rotate choke nozzle 30 when it is threaded into foam generator 10. The outer end of socket 58 is open, and communicates with gas discharge piping 60, having bore 62 defined by wall 64, which is connected to choke nozzle 30 by hammer-up threaded union 66, circular elastomeric seal 59 being compressed between the outer end of choke nozzle 30 and the end of gas discharge piping 60.

[0012] The area whereat the fluid and gas streams entering foam generator 10 impinge on each other is generally indicated at 70; to the right of area 70 is foam discharge bore 72, defined by wall 74 of foam generator 76. Foam discharge piping 80 is secured to end 88 of foam generator 10 at the exit of foam discharge bore 72 by threaded hammer-up union 82. Wall 84 of foam discharge piping 80 defines bore 86 within, which coaxially communicates with foam outlet bore 72.

[0013] Area 90, opposite the entry of fluid inlet bore 14, is of somewhat greater wall thickness than walls 16, 34 or 74, for reasons set forth hereafter.

[0014] FIG. 2 is schematically illustrative of a system in which the foam generator of the present invention may be employed at a well site.

[0015] Liquid source 100, which may comprise multiple tanks of liquid with various additives therein, such as surfactants and gelling agents, is connected to liquid feed manifold 102, which may comprise a variety of pipes, valves and joints as used in the art. There may also be included in liquid source 100 a blender to blend particulate matter such as sand, glass or ceramic beads, etc. with a carrier liquid, such an arrangement and the r apparatus therefor being well known in the art. In any event, it should be understood that liquid source 100 may be a source of a "dirty" (particulate-laden) liquid or gel, as is employed in the prior art in acidizing, fracturing, gravel packing or well cleanout operations.

[0016] Pump 104 draws liquid or gel from liquid source 100 through liquid feed manifold 102, greatly increasing its pressure (to several hundreds or even thousands of pounds) and discharging the liquid or gel into liquid discharge piping 20. Pump 104 may be a plunger-type high pressure pump, such as the HT-150 or _HT-400 pumps, employed by Halliburton Services of Duncan, Oklahoma in well treatment operations.

[0017] Gas source 110, depicted schematically at the left side of FIG. 2, may comprise multiple tanks containing liquid carbon dioxide or nitrogen, such as are employed in the art, which feed through gas feed manifold 112, which may comprise a variety of pipes, valves and joints as used in the art, into a pump 114, which may also be an HT-150 or HT-400 pump, employed by Halliburton Services. Pump 114 raises the pressure of the liquified gas and discharges it into gas discharge piping 60. As noted with respect to FIG. 1, liquid discharge piping 20 is connected to side leg 12 of foam generator 10, while gas discharge piping 60 is connected to end 32 of the main leg of foam generator 10 through choke nozzle 30. It should be noted that the gas carried by piping 60 may still be in a liquified state at the time it is introduced into foam generator 10. However, for purposes of clarity the flow thereof is referred to herein as a gas stream.

[0018] Foam discharge piping 80, secured to end 88 of main leg 8, runs from foam generator 20 into well 200, where the mixed gas and liquid is carried via tubing 202 to the level of the well bore where it is discharged and employed in a well treating operation such as been heretofore described and is known in the art.

[0019] The method of foam generation, or more broadly the generation of a product which may comprise a foam product or a liquid/gas emulsion product, is effected in foam generator 10 as follows. A liquid such as water, combined with a liquid such as water, acid, crude oil, diesel, kerosene or other liquid which may have a surfactant and/or a gelling agent combined therewith (gels also being encompassed by the term "liquid" as used herein), is introduced into liquid inlet bore 14, as shown by the arrow in bore 22. This liquid may also carry substantial amounts of particulate material, as r noted previously. A gas such as carbon dioxide or nitrogen (which may be in a liquified state) is introduced as shown by the arrow in bore 62 into the outer end 56 of axial bore 52 of ceramic choke insert 50 secured to end 32 of main leg 8. The gas is accelerated in bore 52 through the Venturi effect, and exits at inner end 54 into gas inlet bore 38 of main leg 8. The accelerated gas stream impinges on the liquid stream at area 70, the gas stream turning the fluid flow at substantially a right angle (depicted by bent arrow) into foam discharge bore 72, the mixing of the gas with the liquid and the turning of the liquid flow direction causing substantially immediate and uniform mixing of the gas and liquid components into an emulsion or foam product. This emulsion or foam product exits foam discharge bore 72 into foam discharge pipe 80, as shown by the arrow in bore 86. This emulsion or foam product is then introduced into a well. While the pressure in the well bore may not be substantially less than that in the injection tubing 202, the emulsion or foam product will tend to form a foam or at the least a gas emulsion due to the warming and vaporization of the initially liquified gas in the product.

[0020] It should be noted that the change in direction of liquid stream greatly reduces the erosive effect of the liquid on the wall of main leg 8 opposite side leg 12. However, as erosion cannot be entirely eliminated, area 90 may be of increased wall thickness to reduce the possibility of failure at that point.

[0021] It should be understood that the apparatus and method of the present invention are not limited in application to foaming or emulsification of any particular liquids or gels, or the use of any particular gases. In fact, the apparatus and method as disclosed herein may be employed in the formation of true emulsions, as well as foams and emulsions which may subsequently become foams due to a lowering of pressure or an increase in temperature transforming the initial product.

[0022] Moreover, the method and apparatus of the present invention are not limited in applicability to the petroleum industry, but may be employed wherever an emulsion or foam is to be formed for any purpose.

[0023] It should be further understood that the introdu- tion of gas into the main leg of the tee of foam generator 10 provides a feature not heretofore known in the art. In contrast to an instance where gas is introduced into the side leg, and may therefore not sufficiently impinge upon and mix with a liquid flow in the main leg, the method and apparatus of the present invention ensure complete mixing due to the radical change in liquid stream direction. The impingement of the gas stream into the liquid stream also reduces the erosive effect of a particulate liquid aimed at the side wall of main leg 8. Moreover, the accelerated, choked gas flow provides a much more effective barrier to the erosive liquid than an unchoked flow. Of course, the degree of choking for optimum performance is a matter of choice depending on the liquids and gases employed, the pressures and flow rates thereof, and the desired quality and texture of the final emulsion or foam product. Such choice of the degree of choking, or otherwise expressed as the diameter of bore 52 relative to that of bore 62, may be empirically determined by the operator. As with the selection of gases and liquids and the pressures and flow rates thereof, such determinations are well within the ability of one of ordinary skill in the art.

Claims

1. A system for generating a foam product, comprising: means (60) for supplying gas; means (20) for supplying a liquid; foam generating tee means (10) comprising a tubular tee including a main leg (8) and a side leg (12) disposed at substantially a right angle to said main leg; liquid feed manifold means (102) adapted to transmit said liquid from said liquid supply means to said side leg of said tee; gas feed manifold means (112) adapted to transmit said gas from said gas supply means to said inlet end of said tee; and foam discharge piping means (80) for receiving a foam product from said tee.

2. A system according to claim 1, for use when said liquid carries particulate material, wherein said liquid supply means comprises: a liquid source, a source of particulate material; and blender means to mix said liquid and said particulate material.

3. A system according to claim 1 or.2, wherein said liquid supply means includes high pressure pump means (104), and/or said gas supply means includes high pressure pump means (114).

.4. A system according to claim 1,2 or 3, wherein said foam generating tee means includes gas choke means (50) in said main leg.

5. A system according to claim 4, wherein said choke means possesses a restricted longitudinal bore (52) having an outlet disposed proximate the junction of said side leg with said main leg, the diameter of said choke means bore being selectively variable.

6. A method of generating a foam product, comprising: introducing a liquid stream under pressure into a tubular vessel; introducing a gas stream under pressure into said tubular vessel; impinging said gas stream on said liquid stream in said vessel at substantially a right angle to said liquid stream, whereby a substantially uniform foam product is formed and discharged from said vessel.

7. A method according to claim 6, wherein said gas stream is accelerated prior to impinging on said liquid stream.

8. A method according to claim 7, wherein said acceleration is effected through choking said gas stream.

9. A method according to claim 6,7, or 8, wherein said liquid carries particulate material therein.

10. A method according to claim 9, wherein said particulate-laden liquid comprises a particulate-laden gel.

Drawing