CA2500500A1 - Mixing device for oil well fracturing fluid - Google Patents

Abstract

This invention is about a mobile device for making fracturing fluid. It meets the oil industry's demand for a mobile, efficient, and reliable equipment to make fracturing fluid directly from guar without taking the mid-step of slurry formation.
The invention has the following features: the upper part of the above-mentioned semi-trailer is an externally-packed compartment, divided into a control cabin and a machine room. The mixing equipment units are installed in the machine room and are controlled from an operation and control console installed in the control cabin. The mixing device is composed of storage and feeding device, water-powder mixer, release tank, static mixer, high-speed stirrer, additive device, and liquid conveyer device.
The device is compact in structure that can be conveniently installed in a compartment on a semi-trailer. Meanwhile, all the equipments are controlled by computers from the control cabin and are reliable and easy to operate.

Description

Description Manual Mixing Device for Oil Well Fracturing Fluid Technical Scope This invention is about a mobile device for making oil well fracturing fluid directly from guar powder without taking the mid-step of slurry formation.
Technical Background Hydraulic fracturing technology has been widely adopted in oil industry to stimulate oil well productivity through increasing extraction rate of petroleum from oil layer and extending oilfield's productive life span. The quality of fracturing fluid plays a vital role in the effectiveness of fracturing operation. The fracturing fluid is made of guar gum (powder) water solution at a certain concentration mixing with additives such as demulsifier, discharge-aiding agent, and viscosity-reducing agent to form an even-spread liquid with desired viscosity.
The fracturing technology has a strict requirement on the quality of fracturing liquid. The main requirements include: 1 ) The proportions of various components in fracturing fluid should be accurate with a maximum tolerance of t2%. 2) All components in fracturing fluid should be thoroughly mixed and no guar lumps should exist in the base liquid.
3) The fracturing fluid is made on fracturing site. 4) The instantaneous viscosity of the fracturing fluid made on site must reach over 90% of the maximum level achieved in laboratory.
5) On-the-site fracturing fluid preparing speed must reach 1.5m3/minute. 6) When making the fracturing fluid on-site, the fluid-making process and equipment must be flexible enough to quickly meet the different demands from fracturing operation under various working conditions.

The above-mentioned requirements define the difficulties in developing an efficient and mobile fracturing-fluid-making device. Conventional fracturing fluid making process mixes water and guar powder to form a condensed guar-water mixture (usually called guar slurry).
as a middle step, from which the guar slurry is diluted to guar solution with desired concentration. The conventional approach has following disadvantages: A) Investment has to be made on workshops and devices including several water tanks, each over 100m2 in capacity in the vicinity of the operation sites. B) The viscosity release is slow. Consequently, the guar slurry has to be store for up to 4 hours before its viscosity reaches the desired level.
C) The distance between the fixed workshop and the operating site is typically 50~200km. If unexpected interruption occurs in the fracturing operation, all the guar slurry (or fracturing fluid) transported from 50-200km away to the site has to be discharged, which results in not only great economic losses but also environmental pollution.
Contents of this Invention This invention is about a device that can be easily transported to the fracturing location to make the fracturing fluid directly from guar powder. It meets all the strict requirements on the fracturing fluid preparation while overcomes the weaknesses in the conventional approach.
The invention, a kind of mobile equipment for making oil well fracturing fluid, is mounted on a semi-trailer and has the following features:
The device consists of a machine room and a control cabin. All the mixing equipment units are installed in the machine room and are controlled through a control console installed in the control cabin. The semi-trailer is designed to be towed by a road tractor.
There are foldable supporting legs on the front and back of semi-trailer.
As illustrated in Figure 1 & Figure 2, the device consists of following working units:
~ Conveyer (3) ~ Feeding device (4) ~ Water-powder mixer (5) ~ Release tank (6) ~ Static mixer (7) ~ High-speed stirrer (8) ~ Additive device (9) ~ Liquid delivery device (Not shown on Figure 1 or 2) The conveyer includes two three-stage conveyer spirals driven by motors. The conveyer spiral on top is connected to the feeding device.
The feeding device includes guar gum reserve tank and granular anti-expansion agent reserve tank. In each tank, a set of motor-driven feeding spirals are installed. An outlet is set at the bottom of guar gum reserve tank, where it leads to a precise feeding spiral driven by a frequency-converting motor The outlet of anti-expansion agent reserve tank is set on the top of release tank.
The water-powder mixer includes:
~ An inlet pipeline, connected (in radial direction) to the outlet of precise feeding spiral.
~ A gradually-narrowing suction chamber, connected to the inlet pipeline.
~ A gradually-expending diffusion chamber, connected to the outlet pipeline.
~ A choke, connected between the suction chamber and the diffusion chamber.
~ A jet pipe, on central line of the suction chamber and the diffusion chamber.
The release tank consists of three cylinders placed one in another whose diameters decrease in sequence. The top of each cylinder is open. The inlet of the out-most cylinder connects to the outlet pipe of water-powder mixer. An outlet is arranged on the bottom of in-most cylinder.
The static mixer includes a mixing chamber formed by zigzag pipelines. The inlet of the mixing chamber connects to an outlet at the bottom of release tank. Several rotating blades are installed at intervals inside the mixing chamber. The neighboring blades are staggered at 90 degree angles with each other and rotate in opposite directions.
The high-speed stirrer includes frame, motor, transmission, stirring rods, and stirring cylinders. The stirring cylinders includes 4~8 layers whose diameters increase gradually from the interior to the external. Supports are arranged between the bottoms of those cylinders. The bottoms of these cylinders are all connected to a vertical delivery pipe. The walls of the odd-numbered cylinders are lower than those of the even-numbered ones.
Discharge holes are opened on the lower part of the odd-numbered cylinder walls. The above-mentioned delivery pipe connects to a feeding pipe. The feeding pipe connects to the outlet of static mixing device. A discharge pipe is set on the out-most cylinder. Several stirring rods are positioned between the layers of cylinders.
The additive device includes a demulsifier reserve tank, a discharge-aiding agent reserve tank, and a viscosity-reducing agent reserve tank. The outlets of these reserve tanks connect to the discharge pipe of the high-speed stirrer.
The liquid delivery device includes a liquid delivery pipe connected to the end of high-speed stirrer discharge pipe. The liquid delivery pipe goes from the middle of the trailer to its bottom. The pipe is divided into two routes and laid along both sides of the semi-trailer to its back, where each rout connects to a section of rotating pipe.
This invention, which adopts the above-mentioned design, has following advantages:
1. It is mobile. The whole device is assembled on a semi-trailer, which is designed to be towed by a road tractor to the fracturing operation site and makes the fracturing fluid on the spot. As a result, it can not only save the investment on the fixed workshops and eliminate the slurry transportation expense accrued in conventional approached but also improve the working efficiency and quality.

2. This device is suit to work in various operating environments and can protects operators and machines from harsh climate conditions. A thermal insulating layer has been placed around the while trailer-compartment, which is segregated into a control cabin and a machine room. As a result, the working temperature can be maintained at above 5°C even if the outdoor temperature drops to -40oC.

3. The design of conveyer mechanism is compact and easy to work with. By adopting two groups of three-stage convey spirals, which shares a same first-stage convey spiral that is free to move up and down, the conveyer adapts well to the limited structural space inside the compartment and saves the construction cost.

4. The feeding device in this invention uses a set of feeding spirals for each reserve tank to work with a precise feeding spiral in providing guar gum for the water-powder mixer and to work with another feeding spiral in providing anti-expansion agent to the release tank. This design is simple, compact, reliable, and easy for repair and maintenance. Furthermore, it prevents the guar gum from caking.

5. The water-powder mixer device in this invention applies the jet principle by adopting a gradually-narrowing suction chamber, a choke and a gradually-expending diffusion chamber. The high-pressure spray of water or guar powder from the jet pipe results in a negative pressure around the jet pipe that sucks the guar powder or water in from the material hole, and the fine water spray and guar powder can be evenly mixed. This design can effectively prevent the guar from caking and rapidly increase the viscosity of the guar solution. It is also discovered through experiments that reducing the choke length to zero can efFectively prevent the guar powder from building up on the choke, which consequently clog the chock.

6. The release tank adopts three cylinders whose diameters decrease in sequence.
The tops of these cylinders are open. When the guar solution flow a round-about way through the release tank, the vast amount of air bubble among the liquid will be pressed and broken in the eddy current. This process releases the air from the liquid so as to facilitate the next stage pumping operation.

7. The unique design of the mixing chamber increases the guar solution's chances of colliding on the pipe wall where the pipe bend and extends the time for which the guar solution stays in the pipeline so as to better release the solution viscosity. This design also improves the blend condition of the solution when the liquid is in between the blades, where it is stirred to rotate clockwise at one time and counterclockwise at next. In particular, the unique design of the rotating blades effectively reduces the viscosity degradation of guar solution.

8. The following designs of the high-speed stirrer gives the liquid a continuous and intense stir as well as effectively increases the times and duration of the liquid being stirred;
A) Multiple-cylinders structure in which the liquid is stirred in sequence by several stirring rods between the layers of the stirring cylinders, which effectively increases the times and duration of the stirs.
B) An interlayer between the bottom of the out-most cylinder and the frame is segregated by a partition board into a feeding area and a discharge area, which makes the whole structure compact.
As a result, the device is capable of releasing over 90% of the maximum viscosity level achieved in laboratory test at a rate of 1.5m3/minute.

9. The dual liquid delivery pipe design in the liquid delivery device enables a non-stop delivery of fracturing fluid to reserve tank vehicles, without having to stop the machine when switching from loading one reserve tank vehicle to loading another.
The different working units of this invention are well integrated into each other to optimize the usage of the space confined by the compartment. The device is mounted on a semi-trailer and its working parts are controlled by a computer in control cabin. This invention meets the oil industry's demand for a reliable, mobile, and efficient fracturing fluid maker.
List of illustrations Figure 1: General Structure Figure 2: Top View of Figure 1 Figure 3: Conveyer Figure 4: Side View of Figure 3 Figure 5: Feeding Device Figure 6: Side View of Figure 5 Figure 7: Water-Powder Mixer Figure 8: Water-Powder Mixer When Choke Length is Zero Figure 9: Release Tank Figure 10: Static Mixer Figure 11: Slotting on the Rotary Blade in Figure 10 Figure 12: Rotary Blades in Figure 10 after Twist Figure 13: High-speed Stirrer Figure 14: Liquid Delivery Device Figure 15: Upward View of Liquid Delivery Pipe in Diagram 14 Detailed Aaalication Scheme As shown in Figures 1 and 2, the whole device consists of a semi-trailer (2) towed by a road tractor. The mixing devices are mounted on a semi-trailer. The upper part of the trailer is an externally-packed compartment with a thermal insulating layer placed at interior. The compartment on the semi-trailer frame (24) is segregated into control cabin (21 ) and the machine room (22). An operation and control console (23) is installed in the control cabin (21 ). The mixing device is installed in the machine room (22).
The mixer in this invention includes: conveyer (3), feeding device (4), water-powder mixer (5), release tank (6), static mixer (7), high-speed stirrer (8), additive device (9), and liquid delivery device (10).
As shown in Figures 1 ~4, the function of conveyer (3) in this invention is to lift powder materials for making water solution from ground level to the feeding device (4) on the semi-trailer. Since two reserve tanks are needed for material conveyance, the conveyer (3) uses two sets of motor-driven three-stage conveying spirals (31, 32, and 33) extend to the tops of both reserve tanks. Meanwhile, since the two kinds of materials can be delivered intermittently, the two sets of second-stage and third-stage conveying spirals can share a same first-stage spiral (31 ). The first-stage spiral (31 ) is designed to move up and down and to rotate. Once the conveyance finished, simply take away the bucket (34) and raise the first-stage spiral to clear the space for other operations.
As shown in Figures 2, 5 and 6, the feeding device in this invention includes two reserve tanks (41, and 42) for guar, and anti-expansion agents. Each reserve tank (41 or 42) are equipped with a set of three feeding spirals (45, 46, and 47) driven by motor via a reducing gear (44). These feeding spirals are positioned parallel to each other, with spirals 45 and 46 on top and the other one (47) at the bottom. The inlets of both reserve tanks (41, and 42) are set on top, to where the third-stage conveying spirals (33) of the conveyer (3) convey the powder materials. The outlet of guar reserve tank (41 ) is set at its bottom in the middle, from where the material is delivered through a cylinder to a precise feeding spiral (49) driven by a frequency converting motor (48), which also precisely controls the material quantity. The outlet of anti-expansion agents reserve tank (42) is set a side, where the anti-expansion agent is directly added to release tank (6) from top by another feeding spiral.
As shown in Figures 1 and 7, the water-powder mixer (5) in this invention has an inlet pipe (51 ) with a material hole (52) at one end to receive materials from the precise feeding spiral (48). The other end of inlet pipe (51 ) connects, in sequence, to a gradually-narrowing suction chamber (53), a choke (54), and a gradually-expanding diffusion chamber (55). A jet pipe (56) is positioned on the centerline of suction chamber (53). The jet pipe (56) connects a water pump (57 on Figure 1 ), which connects to water source.
Experiments show that powder tends to build up at the outlet of choke (54) after the extended use of jet pipe (56), which will eventually clog the jet pipe nozzle.
To overcome this drawback, this invention minimizes the length of choke (54) to enlarge the space of liquid-water mixing chamber while ensuring sufficient negative pressure.
Experiments show that the negative pressure produced is still sufficient to suck the guar powder even when the choke length reduces to zero (as shown in Figure 8). In this extreme case, the water-powder mixing space is the biggest and the powder build up can be greatly alleviated, which is an innovative application of the jet principle. The jet pipe (56) can be use to spurt either water or guar powder. In the case when the jet pipe is used to spurt guar powder, the connections of guar and water supply need be changed so that water will be supplied from the material hole (52). Experiments also show that the jet pipe can be positioned in suction chamber (53), at choke (54), or at the inlet of expansion chamber (55) Figure 9 illustrates the release tank. The function of release tank is to remove the air that enters guar solution during the jet mixing process. The release tank includes three cylinders (61, 62, and 63), one placed in another, whose diameters reduce in sequence.
The top of each cylinder is open for ventilation. Guar solution from the diffusion chamber (55 of Figure 7) of water-powder mixer (5) enters the out-most cylinder (61 ) via the inlet pipe (64). The air goes up and is released from top while guar solution flows downward though the inlets at the bottom of the second cylinder (62). The pump (66 in Figure 1 ) connected to the outlet pipe (65) draws the liquid through the third cylinder on top from the second cylinder and goes to the outlet pipe (65) at the bottom of third cylinder (63). The inlet pipe (64) connects to the out-most cylinder in a position that the pipe is on tangents line of cylinder's interior wall. Several protruding bafflers (not shown in the figures) are installed on the interior wall of the out-most cylinder (6) so that the guar solution enters the cylinder (61 ), rotates around it, collides with the protruding bafflers, and releases the air in it as quick as possible.
Figure 10 illustrates the static mixer, which includes a mixing chamber (71 ) formed by zigzag pipes and several rotary blades (72) in the mixing chamber (71 ). The inlet of mixing chamber (71 ) is connected, via the pipe (73), to the outlet pipe (65) of the release tank (6).
The mixing chamber (71 ) is arranged downward in "S" shape from the top. This design increases the pipe length in a given mixing chamber space. The rotary blades (72) in the mixing chamber (71 ) are formed by round stainless steel sheets {as shown in Fig. 11 ) which are symmetrically slotted (74) in radial direction and the opposite pairs are twisted for 60 degree in opposite directions (as shown in Figure 12). Alternatively, two slots can be opened on the rotary blades (72) and the rotary blades are twisted 60 degree in opposite direction. The axle centers of two neighboring rotary blades (72) are arranged in a staggered way at 90 degree and the two neighboring blades (72) will force the liquid to rotate in opposite directions. Since there is a space in between any pair of neighboring blades, when guar solution flows through the blades, the fluid is forced, under the effect of rotary blades, to self-rotate or self-stir clockwise followed by a counter clockwise self-rotate or self stir. The solution is thoroughly mixed in the gaps between the rotary blades (72).
Figure 13 illustrates that the high-speed stirrer consists of a frame (81 ), stirring cylinders (82), stirring rods (83), a transmission (84), and a motor (85). The stirring cylinders (82) and the motor {85) are all mounted on the frame (81 ). The motor (85) is connected to the stirring rods (83) via transmission (84), which uses four C-type V-belts to transmit the power. The stirring cylinders (82) include six layers {821, 822, 823, 824, 825, and 826).
Each layer is supported by three to six supporting columns at the bottom. A stainless steel pipe (87), served as a delivery pipe, goes through the bottom of each cylinder (821, 822, 823, 824, and 825). Ail the layers are fixed to the delivery pipe (87) with nuts and are integrated as a whole. The walls of odd numbered cylinders (821, 823, and 825) are higher than those of the even numbered ones (822, 824, and 826). Discharge holes are opened on the lower part of even numbered cylinder walls (822, 824, and 826). The inlet of delivery pipe (87) connects to the outlet of the static mixer via a feeding pipe (88). The discharge hole (829) of the out-most cylinder (826) connects to a discharge pipe (89). There are several stirring rods (83) arranged between the layers of cylinders. On the bottom of its frame, there are foundation bolts (not shown in the figures) so that the frame can be installed on the floor of io semi-trailer. An interlayer is added to the space between the frame and the bottom of the out-most cylinder, The interlayer is segregated in to two parts by a partition board (812): the space on one side of the partition board is used as a feeding pipe (88) that connects to delivery pipe (87) while the space on the other side of the partition board (812) connects to discharge hole of the out-most cylinder and serves as discharge pipe (87).
This arrangement makes the whole structure compact, integrated, and convenient for transportation and storage. The number of cylinders layers may change depends on needs.
Similarly, the transmission (84) can use V belts or other scheme(s).
When the high-speed stirrer is operating, the guar solution flows through the feeding pipe (88) and delivery pipe (87) into the first layer cylinder (821 ). Liquid is keeps on being stirred and sheared by the stirring rod (83) while it rises in the first layer cylinder, overflows from top into the second layer (822), where it is stirred and sheared by the stirring rods inside the second layer. The stirring rods in third layer will do the same thing when the liquid flows into third layer cylinder (823) from the discharge hole (827) on the lower part of the second layer cylinder (822). The same repeats in the rest of the layers as guar solution flows through them. After six times of high-speed stirring and shearing, the liquid flows into the discharge pipe (89) from the discharge hole (829) at the bottom of the out-most layer of cylinder and flows out from the discharge pipe (89).
Figure 2 shows that the additive device (9) includes a demulsifier reserve tank (91 ), a discharge-aiding agent reserve tank (92), and a viscosity-reducing agent reserve tank (93).
The outlets of these reserve tanks (91, 92, and 93) all connect to the discharge pipe (89 of Figure 13) of the high-speed stirrer (8 of Figure 2), where they mix with the guar solution and form qualified fracturing fluid.
As illustrated in Figure 14, the liquid delivery device (10) starts at a liquid delivery pipe (11 ) to receive prepared fracturing fluid. The liquid delivery pipe goes from mid semi-trailer to its bottom and is fixed to the frame by suspension clips. At that point, the delivery pipe is divided into two routes (12). These two routes go from both sides of semi-trailer to the back of vehicle, extend to a certain height (13) (as shown in Figures 14 and 15), and each connects to a rotating pipe (14) to facilitate delivering liquid to the reserve tank. Each of the two liquid delivery pipes installs an electric-magnetic valve controlled from control cabin, so that each delivery line can independently deliver the liquid.
This device uses computer to realize centralized working process control. In the control cabin (24), after the operator inputs various parameters such as discharge rate and ingredients from control cabin, the computer will start the device, control the action of the valves, adjust the frequency-altering motor, and control material feeding speed. Meanwhile, the operators can monitor the current system status through the readings on gauges and material level meters.
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Claims (9)

Claims

1. The invention, a kind of mobile device for making oil well fracturing fluid, is mounted on a semi-trailer and has the following features:
The device consists of a machine room and a control cabin. All the mixing equipment units are installed in the machine room and are controlled through a control console installed in the control cabin. The semi-trailer is designed to be towed by a road tractor There are foldable supporting legs on the front and back of semi-trailer frame.
The mixing equipments consist of a conveyer, a feeding device, a water-powder mixer, a release tank, a static mixer, a high-speed stirrer, and an additive device.
The conveyer includes two three-stage conveyer spirals driven by motors. The conveyer spiral on top is connected to the feeding device.
The feeding device includes guar reserve tank and granular anti-expansion agent reserve tank. In each tank a set of motor-driven feeding spirals are installed. An outlet is set on the bottom of guar gum reserve tank, where it leads to a precise feeding spiral driven by a frequency-converting motor. The outlet of anti-expansion agent reserve tank is arranged on the top of release tank by another feeding spiral.
The water-powder mixer includes: an inlet pipeline, connected in radial direction to the outlet of precise feeding spiral, a gradually-narrowing suction chamber, connected to the inlet pipeline, a gradually-expending diffusion chamber, connected to the outlet pipeline, a choke, connected between the suction chamber and the diffusion chamber, and a jet pipe, on central line of the suction chamber.
The release tank consists of three cylinders placed one in another whose diameters decrease in sequence. The top of each cylinder is open. The inlet of the out-most cylinder is connected to the outlet pipe of water-powder mixer. An outlet is set on the bottom of in-most cylinder.
The static mixer includes a mixing chamber formed by zigzag pipelines. The inlet of the mixing chamber is connected to the outlet on the bottom of release tank.
Several rotating blades are installed at intervals inside the mixing chamber. The neighboring blades are staggered at 90 degree with each other and rotate in opposite directions.
The high-speed stirrer includes a frame, a motor, a transmission, stirring rods, and stirring cylinders. The stirring cylinders include 4~8 layers whose diameters increase gradually from the interior to the external. Supports are arranged between the bottoms of those cylinders. The bottoms of these cylinders are all connected to a vertical delivery pipe. The walls of the odd numbered cylinders are lower than those of the even numbered ones. Discharge holes are opened on the lower part of the odd numbered cylinder walls. The above-mentioned delivery pipe connects to a feeding pipe.
The feeding pipe connects to the outlet of static mixing device. A discharge pipe is set on the out-most cylinder. Several stirring rods are installed between the layers of cylinders.
The additive device includes a demulsifier reserve tank, a discharge-aiding agent reserve tank, and a viscosity-reducing agent reserve tank. The outlets of these reserve tanks connect to the discharge pipe of the high-speed stirrer The liquid delivery device includes a liquid delivery pipe connected to the end of high-speed stirrer discharge pipe. The liquid delivery pipe goes from the middle of the trailer to its bottom and is fixed to the trailer by suspension clips. From that point, the pipe is divided into two routes, which go along both sides of the semi-trailer to its back, where the pipes go upward to certain height and each connects to a section of rotating pipe.

2. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: a thermal insulating layer is arranged in the compartment of the trainer.

3. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: the two sets of three-stage conveying spirals of the conveyer use the same first-stage conveying spiral and the first-stage delivery spiral can move up and down.

4. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: there are three parallel feeding spirals for the feeding device, two on the top of the other.

5. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: the length of the choke in the water-powder mixer is zero.

6. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: the liquid inlet of release tank is installed on the tangent line of the out-most cylinder's interior wall. Some bafflers are spirally arranged inside the out-most cylinder.

7. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: the rotary blades of static mixer are made of round sheet which are radially and symmetrically slotted and twisted by 60°.

8. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: the zigzag pipes forming the mixing chamber in the static mixer are arranged spirally in "S" shape.

9. The mobile device for making oil well fracturing fluid described in Clause 1 in Claims for Rights has the following features: an interlayer is arranged on the bottom of the out-most cylinder of high-speed stirrer. A partition board segregates the interlayer into a feeding pipe that connects to the vertical delivery pipe and a discharge pipe connects to the discharge hole on the bottom of the out-most cylinder.