1. Field of the Invention
The present invention relates to a system for continuously mixing gel fluid that will be used to transport fracturing proppant into a well formation to prop open the formation after fracturing. The system employs a dynamic diffuser to remove air from the fluid as the fluid comes out of a mixer and employs progressive dilution of the fluid after the fluid leaves the dynamic diffuser and travels through a series of hydration tanks. High sheer agitation is used to help mix the gel fluid and dilution fluid as it moves through the hydration tanks. This system allows increased hydration time and more complete hydration of the gel fluid in the limited tank space of skid, truck, or trailer mounted portable equipment than is possible with current gel mixing systems.
2. Description of the Related Art
Currently when mixing guar powder and water to form a liquid gel for use to transport fracturing proppant into a well formation, the mixing is done by a portable mixer and one or more portable hydration tanks. All of the equipment necessary to mix the gel is skid, truck, or trailer mounted so that it can, be transported to the well site. There at the well site, the gel is constantly mixed, transferred to the fracturing blender, and pumped into the well bore. Because the equipment is truck or trailer mounted, the tank volume available for allowing the gel to hydrate after it is mixed with water is limited.
One of the problems with current gel mixing systems is that, without the use of large hydration tanks, the gel is not fully hydrated to the desired viscosity before the gel is transferred to the fracturing blender. Large hydration tanks can not be readily skid, truck or trailer mounted for use at a well site. Without using large hydration tanks, the gel will have a short residence time of the liquid within the smaller skid, truck or trailer mounted hydration tanks which does not allow sufficient time for the gel to become adequately hydrated before it is transferred to the fracturing blender prior to being used in the well.
The present invention addresses these problems by creating a gel concentrate, employing a dynamic diffuser for quickly removing the air from the fluid as the fluid exits the gel mixer, and by progressively diluting the gel concentrate in a series of hydration tanks to maximize hydration time without allowing the gel to become so viscous that it is not easily diluted or pumped. High shear agitation of the fluid between the hydration tanks also helps to increase the hydration rate. By progressively diluting the gel concentrate, residence time and hydration time are maximized in the limited tank space. The result of this new continuous gel mixing system is that the gel is almost fully hydrated when it is transferred to the fracturing blender without the need for an increase in the volume of the hydration tanks.
Some gels hydrate faster than others. This system is useful for both standard gels and fast hydrating gels. With fast hydrating gels, the system can be operated at a higher throughput rate, thus extending the usefulness of the system.
One object of the present invention is to provide a system that continuously mixes guar powder with water to produce a gel.
A further object to the invention is to provide a system that employs high sheer pumps that allow the guar to hydrate into a viscous gel more quickly than prior art systems. When dry guar powder is mixed with water, a thick gelatinous coating is forms around each of the particles of the dry powder as the powder begins to hydrate at its surface. These partially hydrated particles may be called micelles. They are relatively dry in their nucleus and are progressively more fully hydrated at their surface. The high sheer pumps used in the present system tend to disrupt or sheer this gelatinous outer coating off of the micelles. This allows the dryer inner portions and nucleus of the micelles to be contacted with water more quickly, thereby speeding up the hydration process.
Another object of the invention is to increase the hydration time of the gel within the limited hydration tank space.
Still a further object of the invention is to provide a system that does not require special chemicals to accelerate the hydration process. By not requiring special chemicals, some of which are considered harmful to the environment, the end gel product is more economical and more environmentally friendly.
A final object of the present invention is to employ mobile equipment such that the equipment would be truck or trailer mounted and the gel would be produced at or near the well site using the truck or trailer mounted equipment.
The present invention is a gel mixing system that employs a dynamic diffuser for quickly removing the air from the fluid as the fluid exits a traditional gel mixer and employs progressive dilution of a concentrate fluid as it hydrates into a gel in a series of hydration tanks to maximize hydration time without allowing the gel to become so viscous that it is not easily pumped. High shear agitation of the fluid between the hydration tanks helps to increase the hydration rate. Progressive dilution of a concentrate gel in the hydration tanks increases residence time of the gel in the tanks and results in longer hydration time in the limited tank space available. As a result, the present system is able to continuously produce gel that is almost fully hydrated by the time it is transferred to the fracturing blender without the need for an increase in the volume of the hydration tanks.
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The dynamic diffuser 50 pulls the moisture away from the mixer 22 and removes the air by using a high speed rotating impeller 56 that causes the liquid to travel down through the impeller cylinder 48 and to be propelled radially outward at the lower end 68 of the impeller shaft 56. Liquid entering the dynamic diffuser 50 via the inlet pipe 45 provided in the stationary upper portion 46 of the impeller cylinder 48 travels downward between the impeller shaft 56 and the lower portion 52 of the impeller cylinder 48 to the bottom plate 70. From there, the fins 66 on the lower end 68 of the impeller 56 force the liquid horizontally outward so that the liquid exits the impeller cylinder 48 at the flared bottom 64 of the lower portion 52 of the impeller cylinder 48 and strikes against an internal partition wall 76 provided within the dynamic diffuser tank 50. The internal partition wall 76 is cylindrical in shape and secured to the bottom 74 of the dynamic diffuser tank 50. A top 77 of the wall 76 does not extend to the top 78 of the dynamic diffuser tank 50. Thus, the internal partition wall 76 separates the tank 50 into two channels 80 and 82 that connect with each other above the top 77 of the internal partition wall 76. Channel 80 is located outside of the impeller cylinder 48 and between the impeller cylinder 48 and the internal partition wall 76. Channel 82 is located outside the internal partition wall 76 and between the internal partition wall 76 and an outside wall 86 of the dynamic diffuser tank 50.
The air that enters the dynamic diffuser tank 50 with the liquid gel is not propelled outward with the liquid, but rather travels upward within channel 80 where it exits the dynamic diffuser through air exit openings 84 provided in the top 78 of the tank 50 and located just outside the stationary portion 46 of the impeller cylinder 48. The liquid moves through the dynamic diffuser 50 by first traveling upward within channel 80, next traveling over the partition wall 76, and then traveling downward within the channel 82. Arrows inside the dynamic diffuser shown in
The liquid that exits the dynamic diffuser 50 then enters a first hydration tank 92, shown in
Although this first hydration tank 92 is shown separated from the dynamic diffuser tank 50, in practice this first hydration tank 92 may be large enough to completely enclose the dynamic diffuser tank 50 so that the liquid flows directly out of the dynamic diffuser tank 50 into this first hydration tank 92.
The liquid is pumped out of this first hydration tank 92 via a first centrifugal high sheer pump 94A through a first liquid flow line 96A. Each of the centrifugal high sheer pumps 94A, 94B, 94C, and 94D employed in this system 20 increases the hydration rate of the liquid gel. The more inefficient the pump 94A, 94B, 94C, and 94D, the more sheer or disruption occurs in the gel micelles. This helps break down the partially hydrated gel particles or micelles and thus speeds up the hydration process. The first liquid flow line 96A is provided with an first liquid flow meter 98A and intersects with a first dilution water line 36 where the liquid is diluted with water supplied by the first dilution water line 36. The first dilution water line 36 receives water from the suction manifold 26. The water flowing through this first dilution water line 36 flows through a first water flow meter 100A, a first on/off butterfly valve 102A, and a first proportional valve 104A that controls the flow of water through the first dilution water line 36. The mixture of liquid from first liquid flow line 96A and water from the first dilution water line 36 passes through a first static mixer 106A where the liquid and water are mixed to dilute the liquid.
Referring now also to
The second liquid flow line 96B is provided with a second liquid flow meter 98B and intersects with the second dilution water line 38 where the liquid is again diluted with water supplied by the second dilution water line 38. The second dilution water line 38 receives water from the suction manifold 26. The water flowing through this second dilution water line 38 flows through a second water flow meter 100B, a second on/off butterfly valve 102B, and a second proportional valve 104B that controls the flow of water through the second dilution water line 38. The mixture of liquid from the second liquid flow line 96B and water from the second dilution water line 38 passes through a second static mixer 106B where the liquid and water are mixed to further dilute the liquid.
The mixture then enters the third hydration tank 108B via a second passive diffuser 112B that slows down the velocity of the fluid as it enters the third hydration tank 108B. The liquid flows through the baffled third hydration tank 108B to achieve maximum retention and hydration time within the third hydration tank 108B without allowing the gel to become so viscous that it can not be easily pumped. The liquid exits the third hydration tank 108B at a second exit 116B of the third hydration tank 108B and is pumped via a third centrifugal high sheer pump 94C to a third liquid flow line 96C.
The third liquid flow line 96C is provided with a third liquid flow meter 98C and intersects with the third dilution water line 40 where the liquid is again diluted with water supplied by a third water line 40. The third dilution water line 40 receives water from the suction manifold 26. The water flowing through this third dilution water line flows through a third water flow meter 100C, a third on/off butterfly valve 102C, and a third proportional valve 104C that controls the flow of water through the third dilution water line 40. The mixture of liquid from the third liquid flow line 96C and water from the third dilution water line 40 passes through a third static mixer 106C where the liquid and water are mixed to further dilute the liquid.
The mixture then enters the fourth hydration tank 108C via a third passive diffuser 112C that slows down the velocity of the fluid as it enters the fourth hydration tank 108C. The liquid flows through the baffled fourth hydration tank 108C to achieve maximum retention and hydration time within the fourth hydration tank 108C without allowing the gel to become so viscous that it can not be easily pumped. The liquid exits the fourth hydration tank 108C at a third exit 116C of the fourth hydration tank 108C into fourth liquid flow line 96D and is pumped via a fourth centrifugal high sheer pump 94D to the gel discharge manifold 24. Although not illustrated, the liquid gel then is pumped to a fracturing blender for addition of proppant and chemicals before the mixture is pumped into the well bore.
Progressive dilution of the gel in the first hydration tank 92 and the hydration tanks 108A, 108B, and 108C increases residence time of the gel in the tanks 92, 108A, 108B, and 108C and results in longer hydration time in the limited tank volume available. As a result, the present system 20 is able to continuously produce gel that is almost fully hydrated by the time it is transferred to the fracturing blender without the need for an increase in the volume of the hydration tanks.
The mix water flow meters 34A and 34B; the liquid flow meters 98A, 98B, 98C, and 98D; and the water flow meters 100A, 100B, and 100C all monitor flows in the system 20 so that the flows can be controlled by adjusting the proportional valves 104A, 104B, and 104C and by adjusting the pumping rate of the water pumps 30 and 32, thereby controlling the progressive dilution of the gel concentrate by the system 20.
Below is a comparison between a gel created employing the progressive dilution of the present system 20 and a gel created according to current mixing practice. In both cases, the feed rate into tank no. 1 is 67.2 lbs/min of guar powder diluted as shown below. Also, in both cases the output produced is forty (40) barrel per minute (bpm) or 1,680 gallons per minute (gpm) gel fluid at a final concentration of forty (40) lbs guar/1000 gal.
Total residence/hydration time achieved with progressive dilution = 5.2 min.
Total residence/hydration time achieved with current dilution practice = 2.5 min.
For simplification of the examples presented above, the hydration tanks are all shown as equal in size. Hydration tanks do not need to be equal sizes and the dilution amount for each tank does not need to be the same. Individual tank volumes can be adjusted in size to optimize the process. However, the total dilution throughout the process should be the same to create the end desired concentration. Although equal dilution amounts make control of the system easier, if the process is slowed due to well conditions, hydration might proceed too fast in the first tanks. To counter this, faster dilution, i.e. more dilution in first tanks and less dilution in the downstream tanks, would reduce the potential problem. Actually, a control plan can be developed such that the same amount of hydration is developed regardless of the throughput rate. This presents a more complicated control issue, but it should not be a problem with the use of current computers to operate the controls.
Thus, as the foregoing example illustrates, progressive dilution of gel according to the present system 20 allows the hydration time of guar gel to be increased by more than double without changing the capacity of the tanks 92, 108A, 108B, and 108C used for hydration. In more than doubling the hydration time using existing tank capacity, and by employing centrifugal high sheer pumps 94A, 94B, 94C, and 94D between the tanks 92, 108A, 108B, and 108C that are used for hydration, thus increasing the normal hydration rate, this system 20 produces gel that is more fully hydrated than can be achieved with other gel mixing and hydration systems currently used in the industry.
Both
The control illustrated in
The control illustrated in
Each of these control methods has advantages and disadvantages in controlling the progressive dilution of gel in the system 20.
The present method involves both progressive dilution and progressive hydration of the gel in the system 20 to maximize residence and hydration time within limited tank space. The liquid stream that flows from the gel mixer 22 is a non-hydrated first liquid stream that passes into and through the dynamic diffuser 50. The first liquid stream begins to hydrate in the first hydration tank 92 and hydration continues through each of the subsequent hydration tanks 108A, 108B, 108C, etc.
The present method requires the use of a dynamic diffuser 50 that does not rely on the motive energy of the incoming fluid to separate air from the fluid as does a passive diffuser. The present method requires the use of a dynamic diffuser 50 to discharge fluid from the diffuser rather than relying on the motive energy of the incoming fluid. The use of a dynamic diffuser 50 in the present method produces more predictable performance because of the impeller 48, 56, 58 and 66 of the dynamic diffuser 50. Because the operation of well fracturing requires frequent changes in flow of the fracturing gel to the well and may even require that flow of fracturing gel to the well be completely stopped, it is essential for this method that there be a means to keep the hydrating fluid in motion within the diffuser tank 50 and to discharge the same fluid from the diffuser independently from the motive energy, or lack thereof, of the incoming fluid.
For fixed rate flow situations, use of only a passive diffuser is acceptable if the flow is relatively constant and does not stop until the process is complete. However, in variable flow rate conditions such as those present in oil well fracturing, the system and method must be able to operate efficiently in a wide range of flow conditions. If flow is stopped for this method and a dynamic diffuser 50 is not employed to keep the fluid in motion, when the flow needs to be started up again, the fluid in the diffuser tank 50 is stationary and can not start moving again instantaneously. Any attempt to get the fluid moving quickly will result in fluid being belched out the air exit openings 84 of the tank 50. When the present method employs a dynamic diffuser 50, the impeller 48, 56, 58 and 66 of the diffuser 50 keeps the fluid in motion so that it can be pumped out of the system quickly. Fluid inside a diffuser 50 that has become stationary is like a brick wall when attempting to restart flow through the diffuser 50. The inertia of the water is hard to overcome.
Thus it is necessary to keep the hydrating gel in motion in the present method since once the gel stream stops, it is very difficult to resume flow without causing problems such as overflow of the diffuser. Also, it is difficult to change the flow rate without some type of motive energy beyond the normal flow of the fluid through the system. Thus, this method will not work properly if a passive diffuser is substituted for the dynamic diffuser 50 since the dynamic diffuser 50 keeps the hydrating gel constantly in motion in the diffuser tank 50 regardless of the flow output to the well and thereby allows the system and this method to respond quickly to changes in flow demand on the system. The dynamic diffuser 50 keeps the fluid moving or spinning within the diffuser 50 at a constant velocity. The spinning fluid creates centrifugal forces on the fluid that separates air from the denser liquid. The centrifugal forces also create a pressure within the diffuser 50 that causes the fluid to be discharged from the diffuser 50. Thus, the dynamic diffuser 50 is more efficient in removing the air from the fluid, i.e. more consistent and at a higher energy level, and has more power to push the fluid within the diffuser 50 to the outside of the diffuser 50.
The passive diffusers 112A, 112B and 112C are simply devices used to slow the incoming fluid velocity of the fluid streams as those fluid streams enter, respectively, hydration tanks 108A, 108B, and 108C.
Also, this invention begins with a liquid stream produced continuously by mixing a measured amount of dry guar powder with a first volume of water in a gel mixer to form a non-hydrated and highly concentrated first liquid stream coming out of the gel mixer.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of 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 the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.
The present application is a continuation in part application originating from U.S. patent application Ser. No. 10/426,742 for Gel Mixing System filed on Apr. 30, 2003.
Number | Date | Country | |
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Parent | 10426742 | Apr 2003 | US |
Child | 11364705 | Feb 2006 | US |