A sand mixing device and method for carbon dioxide pure dry fracturing

Abstract

The application relates to the technical field of oil and gas exploitation equipment, and discloses a sand mixing device and method for carbon dioxide pure dry fracturing. The sand mixing device comprises a working tank, a preparation tank one, a preparation tank two, an induction module and a sand feeding device. A horizontal spiral sand feeder is fixedly connected with a sand outlet of the sand feeding device. The sand outlet of the horizontal spiral sand feeder is fixedly connected with the preparation tank one and the preparation tank two respectively. The bottom of the preparation tank one and the preparation tank two is fixedly connected with the working tank. The bottom of the working tank is fixedly connected with a mixer. The sand mixing device has the advantages that the preparation tank one and the preparation tank two and corresponding control butterfly valves are switched with each other, so that the sand outlet of the working tank can continuously discharge sand; liquid carbon dioxide input through the induction module and a liquid inlet pipeline can guarantee that the pressure and temperature in the working tank are constant, and sand can be continuously added. The sand mixing device for carbon dioxide pure dry fracturing can continuously add sand under pressure, and meets the requirement of the field.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction equipment technology, and in particular to a sand mixing device and method for pure dry carbon dioxide fracturing. Background Technology

[0002] In the field of oil and gas engineering, with the advancement of oil and gas field development technologies, the development of unconventional oil and gas resources such as low-permeability, tight, and shale resources is receiving increasing attention. Fracturing technology, as a major measure for increasing production in unconventional oil and gas fields, has been widely applied both domestically and internationally.

[0003] Carbon dioxide-related fracturing technologies can be categorized into hydraulic fracturing, hybrid fracturing, and pure dry carbon dioxide fracturing, depending on the proportion of water and carbon dioxide. Currently, hydraulic fracturing is the dominant technology, with pure dry carbon dioxide fracturing accounting for a very small percentage. The advantages of pure dry carbon dioxide fracturing technology include: 1. Strong reservoir stimulation capability: Rock fracturing model experiments show that carbon dioxide can effectively increase pore pressure, reduce fracture pressure by 20%-40%, and achieve multi-directional fracturing, improving fracture surface roughness by 15%; Carbon dioxide fracturing can reduce the impact of in-situ stress on fracture propagation, forming a complex fracture network, with a stimulation volume more than 2.6 times that of hydraulic fracturing; 2. No reservoir contamination, especially for water-sensitive reservoirs; 3. Carbon dioxide retained in the formation can aid in crude oil extraction; 4. Some carbon dioxide can also be stored; 5. Finally, it can conserve freshwater resources, which is of great significance for water-scarce regions.

[0004] However, the pure dry carbon dioxide fracturing technology has the following drawbacks: 1. The sand mixing device has high requirements, requiring pressurization and a certain sand delivery capacity; 2. Due to the low viscosity of carbon dioxide, the sand carrying capacity is weak, the sand ratio is small, and the proppant's support effect on the fracture is weak; 3. The carbon source of carbon dioxide is relatively scarce, and the price of carbon dioxide is high, resulting in high fracturing costs; 4. The liquid carbon dioxide storage capacity at the fracturing well site is limited, currently generally around 1000 cubic meters, which cannot guarantee the carbon dioxide fracturing fluid required for large-scale fracturing. Summary of the Invention

[0005] This invention provides a sand mixing device and method for pure carbon dioxide dry fracturing, which overcomes the shortcomings of the prior art and can effectively solve the problem that existing sand mixing devices used in pure carbon dioxide dry fracturing cannot meet the requirement of continuous pressurized sand addition.

[0006] To solve the above problems, one of the technical solutions of the present invention is achieved through the following technology: a sand mixing device for pure dry carbon dioxide fracturing, comprising a working tank, a first preparatory tank, a second preparatory tank, an induction module, and a sand feeding device; the sand outlet of the sand feeding device is fixedly connected to a horizontal spiral sand conveyor, the sand outlet of the horizontal spiral sand conveyor is fixedly connected to the first preparatory tank and the second preparatory tank respectively, the bottom of the first preparatory tank and the second preparatory tank are fixedly connected to the working tank, the bottom of the working tank is fixedly connected to a mixer, and the outside of the mixer is fixedly connected to a medium-pressure manifold and an input manifold respectively; an induction module is fixedly installed on the outside of the working tank, the first preparatory tank, and the second preparatory tank; an inlet pipeline is fixedly connected to the outside of the working tank, the first preparatory tank, and the second preparatory tank; a safety valve and an exhaust valve are fixedly installed on the outside of the working tank, the first preparatory tank, and the second preparatory tank.

[0007] Agitators are fixedly installed on the inner side of the above-mentioned working tank, preparation tank one, and preparation tank two.

[0008] The aforementioned sensing module includes a control unit, a gravity sensor, a pressure sensor, and a temperature sensor. The gravity sensor, pressure sensor, and temperature sensor are all connected to the control unit, and are respectively installed on the working tank, the first preparation tank, and the second preparation tank.

[0009] The aforementioned sand feeding device includes a tubular chain conveyor 1 and a tubular chain conveyor 2. The sand inlets of both tubular chain conveyor 1 and tubular chain conveyor 2 are respectively connected to sand hoppers, and the sand outlets of both tubular chain conveyor 1 and tubular chain conveyor 2 are respectively fixedly connected to the sand inlet of a horizontal spiral sand conveyor.

[0010] The bottom of the aforementioned working tank is fixedly connected to a tee, the bottom of which is fixedly connected to a spiral sand conveyor. The sand outlet of the spiral sand conveyor is fixedly connected to a bypass pipe, and the mixer and the input manifold are fixedly connected through the bypass pipe.

[0011] Control butterfly valves are fixedly installed between the aforementioned horizontal spiral sand conveyor and the first and second reserve tanks, between the first and second reserve tanks and the working tank, between the working tank and the tee, between the spiral sand conveyor and the bypass pipe, and on each inlet pipeline. All control butterfly valves are connected to the control unit.

[0012] The second technical solution of this invention is achieved through the following technology: a sand mixing method for pure dry carbon dioxide fracturing, including two working modes: intermittent sand loading and continuous sand loading, wherein intermittent sand loading includes the following steps:

[0013] Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor and into the preparatory tank 1 and preparatory tank 2;

[0014] Step 2: Once the sensing modules in preparation tank 1 and preparation tank 2 detect that the proppant is full, the sand feeding stops.

[0015] Step 3: Inject liquid carbon dioxide into preparation tank 1 and preparation tank 2 through the liquid inlet pipeline;

[0016] Step 4: When the sensing module detects that the pressure in the preparation tank 1 and preparation tank 2 has reached the set value, open the exhaust valves of preparation tank 1 and preparation tank 2 to empty the gas in the tanks and then close them; continue to inject liquid carbon dioxide into preparation tank 1 and preparation tank 2, and repeatedly open the exhaust valves until the sensing module detects that the temperature in preparation tank 1 and preparation tank 2 has reached the set value, empty the gas in preparation tank 1 and preparation tank 2, and close the exhaust valves;

[0017] Step 4: Inject liquid carbon dioxide fracturing fluid into the input manifold and into the mixer. At the same time, the proppant is output to the mixer and fully mixed with the liquid carbon dioxide fracturing fluid. After mixing, it is output to the fracturing truck through the medium-pressure manifold.

[0018] The continuous sand application process includes the following steps:

[0019] Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor, and then into the working tank via the first and second preparatory tanks;

[0020] Step 2: After the sensing module in the working tank detects that the proppant is full, it stops the sand filling in the second preparation tank, so that the proppant only enters the first preparation tank.

[0021] Step 3: Inject liquid carbon dioxide into the working tank through the inlet line; when the sensing module detects that the pressure inside the working tank has reached the set value, open the exhaust valve of the working tank to empty the gas inside the tank and then close it; continue to inject liquid carbon dioxide into the working tank and repeatedly open the exhaust valve until the sensing module detects that the temperature inside the working tank has reached the set value, then empty the gas inside the working tank and close the exhaust valve.

[0022] Step 4: Inject liquid carbon dioxide fracturing fluid into the input manifold and into the mixer. At the same time, the proppant is output to the mixer and fully mixed with the liquid carbon dioxide fracturing fluid. After mixing, it is output to the fracturing truck through the medium-pressure manifold.

[0023] Step 5: Performed simultaneously with Step 4, after the proppant in Preparatory Tank 1 is filled, close the sand supply in Preparatory Tank 1 and open the sand supply in Preparatory Tank 2 to pressurize and cool the proppant in Preparatory Tank 1. After the pressure and temperature reach the set values, allow the proppant in Preparatory Tank 1 to flow into the working tank.

[0024] Step 6: Start the sand feeding device to continue feeding sand into the preparation tank. The proppant undergoes the above-mentioned cooling, pressurization and venting processes in the preparation tank until the temperature and pressure reach the standard, and then it is output to the working tank.

[0025] Step 7: Output all the proppant that has reached the standard in the preparation tank 2 to the working tank; start the sand feeding device to continue feeding sand into the preparation tank 2. The proppant undergoes the above-mentioned cooling, pressurization and venting processes in the preparation tank 2 until the temperature and pressure reach the standard, and then outputs it to the working tank.

[0026] Step 8: Repeat steps 5 through 7.

[0027] This invention features a simple structure and ease of use. Two tubular chain conveyors vertically and continuously transport proppant into a horizontal spiral sand conveyor. Switching between two preparatory tanks (one and two) and their corresponding control butterfly valves ensures continuous sand discharge from the working tank's discharge port. Liquid carbon dioxide input via a sensing module and inlet pipeline maintains constant pressure and temperature within the working tank, allowing for continuous sand addition. A mixer thoroughly mixes the proppant with the liquid carbon dioxide fracturing fluid, outputting liquid carbon dioxide carrying sand. Therefore, this invention, as a sand mixing device for dry carbon dioxide fracturing in the field, enables continuous pressurized sand addition, meeting on-site requirements. Attached Figure Description

[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0029] Figure 1 This is a schematic diagram of the main structure of the present invention.

[0030] In the diagram: 1-Working tank, 2-Preparation tank one, 3-Preparation tank two, 4-Horizontal spiral sand conveyor, 5-Mixer, 6-Medium pressure manifold, 7-Input manifold, 8-Inlet pipeline, 9-Safety valve, 10-Exhaust valve, 11-Agitator, 12-Gravity sensor, 13-Pressure sensor, 14-Temperature sensor, 15-Tubular chain conveyor one, 16-Tubular chain conveyor two, 17-Sand hopper, 18-Tee, 19-Spiral sand conveyor, 20-Bypass pipe. Detailed Implementation

[0031] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0032] In this invention, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as the positional relationships of front, back, top, bottom, left, and right, which are based on the instructions attached. Figure 1 The orientation of the layout is determined by the direction of the map.

[0033] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0034] Example 1: As Figure 1As shown, the sand mixing device for pure dry carbon dioxide fracturing includes a working tank 1, a first reserve tank 2, a second reserve tank 3, an induction module, and a sand feeding device. The sand outlet of the sand feeding device is fixedly connected to a horizontal spiral sand conveyor 4. The sand outlets of the horizontal spiral sand conveyor 4 are fixedly connected to the first reserve tank 2 and the second reserve tank 3, respectively. The bottoms of the first reserve tank 2 and the second reserve tank 3 are fixedly connected to the working tank 1. The bottom of the working tank 1 is fixedly connected to a mixer 5. A medium-pressure manifold 6 and an input manifold 7 are fixedly connected to the outside of the mixer 5, respectively. An induction module is fixedly installed on the outside of the working tank 1, the first reserve tank 2, and the second reserve tank 3. An inlet pipeline 8 is fixedly connected to the outside of the working tank 1, the first reserve tank 2, and the second reserve tank 3. A safety valve 9 and an exhaust valve 10 are fixedly installed on the outside of the working tank 1, the first reserve tank 2, and the second reserve tank 3.

[0035] The aforementioned inlet pipeline 8 is used to connect with external liquid carbon dioxide and to input external liquid carbon dioxide into the working tank 1 and the reserve tank, thereby cooling the proppant in the working tank 1 and the reserve tank and ensuring that the proppant flowing out of the working tank 1 does not vaporize when it encounters the liquid carbon dioxide fracturing fluid input into the inlet manifold 7; the medium-pressure manifold 6 is used to mix the proppant and the liquid carbon dioxide fracturing fluid and then output the liquid carbon dioxide proppant-carrying fluid.

[0036] The aforementioned exhaust valve 10 is mainly used to discharge the vaporized carbon dioxide gas in the preparation tank and working tank 1; the safety valve 9 is mainly used to ensure that the pressure in the preparation tank and working tank 1 does not exceed the set pressure.

[0037] The sensing module can sense gravity, temperature, and pressure. When adding sand to the preparation tank and working tank 1, the sensing module can sense whether the proppant in the corresponding tank is full by gravity. Once the proppant is full, the sand adding stops. The sensing module can also sense whether the temperature and pressure in the corresponding tank have reached the set values ​​(the set values ​​are pre-set in the sensing module according to the on-site operation).

[0038] The invention can be manufactured in a horizontal position for easy transport of vehicle-mounted equipment; it can also be manufactured in a vertical position for easy operation; and it can also be manufactured as a skid-mounted module for direct assembly at the work site, thereby improving the flexibility of its use.

[0039] During operation, this invention can achieve two technical solutions: intermittent sand application and continuous sand application. The specific working process is as follows:

[0040] 1. Intermittent Sand Filling: The sand filling device transports the proppant to the horizontal spiral sand conveyor 4, and then into the preparatory tank 1 2 and preparatory tank 2 3. Once the sensing modules in preparatory tanks 1 2 and 2 3 detect that the proppant is full (via gravity sensing), sand filling stops. Liquid carbon dioxide is injected into preparatory tanks 1 2 and 2 3 through the liquid inlet line 8. When the sensing modules detect that the pressure in preparatory tanks 1 2 and 2 3 has reached the set value, the exhaust valves 10 of preparatory tanks 1 2 and 2 3 are opened to vent the gas inside the tanks and then closed. The process continues... Liquid carbon dioxide is injected into the first tank 2 and the second tank 3. The exhaust valve 10 is repeatedly opened until the sensing module detects that the temperature in the first tank 2 and the second tank 3 has reached the set value. The gas in the first tank 2 and the second tank 3 is then vented and the exhaust valve 10 is closed. Liquid carbon dioxide fracturing fluid is injected into the input manifold 7 and enters the mixer 5. At the same time, the proppant is output to the mixer 5 and fully mixed with the liquid carbon dioxide fracturing fluid in the mixer 5. After mixing, the mixture is output to the fracturing truck through the medium-pressure manifold 6 to implement the pure dry carbon dioxide fracturing process.

[0041] 2. Continuous Propane Feeding: The proppant feeding device delivers the proppant to the horizontal spiral sand conveyor 4, and then enters the working tank 1 via the first and second preparatory tanks 2 and 3. Once the sensing module in the working tank 1 detects that the proppant is full (via gravity sensing), proppant feeding in the second preparatory tank 3 is stopped, allowing proppant to enter only the first preparatory tank 2. Liquid carbon dioxide is injected into the working tank 1 through the inlet line 8. When the sensing module detects that the pressure in the working tank 1 reaches the set value, the exhaust valve 10 of the working tank 1 is opened to vent the gas inside and then closed. Liquid carbon dioxide is continued to be injected into the working tank 1, and the exhaust valve 10 is repeatedly opened until the sensing module detects that the temperature inside the working tank 1 reaches the set value. Then, the gas inside the working tank 1 is vented, and the exhaust valve 10 is closed. Liquid carbon dioxide fracturing fluid is injected into the input manifold 7 and enters the mixer 5. Simultaneously, the proppant is output to the mixer 5, where it is fully mixed with the liquid carbon dioxide fracturing fluid. After mixing, the mixture is delivered through the medium-pressure manifold 6. The proppant is output to the fracturing truck. Simultaneously, after the proppant in preparatory tank 1 (2) is filled, the sand feeding in preparatory tank 1 (2) is closed, and the sand feeding in preparatory tank 2 (3) is opened. The proppant in preparatory tank 1 (2) is pressurized and cooled. Once the pressure and temperature reach the set values, the proppant in preparatory tank 1 (2) flows into working tank 1. The sand feeding device is activated to continue feeding sand into preparatory tank 1 (2). The proppant undergoes the aforementioned cooling, pressurization, and venting processes in preparatory tank 1 (2) until the temperature and pressure reach the specified values, then it is output to working tank 1. All the proppant in preparatory tank 2 (3) that has reached the specified values ​​is output to working tank 1. The sand feeding device is activated to continue feeding sand into preparatory tank 2 (3). The proppant undergoes the aforementioned cooling, pressurization, and venting processes in preparatory tank 2 (3) until the temperature and pressure reach the specified values, then it is output to working tank 1. The above steps are repeated, switching back and forth between preparatory tank 1 (2) and preparatory tank 2 (3) to ensure that there is always proppant in working tank 1 and that the temperature and pressure in working tank 1 remain constant and reach the set values.

[0042] like Figure 1 As shown, a stirrer 11 is fixedly installed inside the working tank 1, the first preparation tank 2, and the second preparation tank 3.

[0043] The aforementioned agitator 11 is a known technology. The outer sides of the working tank 1, the first preparation tank 2, and the second preparation tank 3 can all be wrapped with heat insulation material. The working tank 1 maintains a low-temperature environment by using agitation and heat insulation. The first preparation tank 2 and the second preparation tank 3 rapidly cool the proppant by using agitation and heat insulation.

[0044] The agitator 11 installed in the working tank 1, the preparatory tank 1 2, and the preparatory tank 2 3 accelerates the heat exchange between the proppant and the liquid carbon dioxide, and prevents sand blockage caused by incomplete removal of the proppant, which would affect normal construction.

[0045] like Figure 1 As shown, the sensing module includes a control unit, a gravity sensor 12, a pressure sensor 13, and a temperature sensor 14. The gravity sensor 12, pressure sensor 13, and temperature sensor 14 are all connected to the control unit. The gravity sensor 12, pressure sensor 13, and temperature sensor 14 are respectively installed on the working tank 1, the preparation tank 1 2, and the preparation tank 2 3.

[0046] The aforementioned control unit can be a known PLC controller, used to receive signal values ​​output by gravity sensor 12, pressure sensor 13, and temperature sensor 14, and compare the received signals with the corresponding signal set values ​​to determine whether the received signal values ​​have reached the set values; gravity sensor 12, pressure sensor 13, and temperature sensor 14 are all known technologies, used to sense whether the proppant in the tank is full and whether the pressure and temperature have reached the set values. When gravity sensor 12 senses that the proppant in working tank 1, preparatory tank 1, or preparatory tank 2 is full, the addition of proppant in that tank is stopped; pressure sensor 13 and temperature sensor 14 are used to monitor whether the pressure and temperature in the corresponding tank have reached the set values.

[0047] like Figure 1 As shown, the sand feeding device includes a tubular chain conveyor 15 and a tubular chain conveyor 2 16. The sand inlets of both the tubular chain conveyor 15 and the tubular chain conveyor 2 16 are connected to sand hoppers 17. The sand outlets of both the tubular chain conveyor 15 and the tubular chain conveyor 2 16 are fixedly connected to the sand inlet of the horizontal spiral sand conveyor 4.

[0048] The sand feeding device uses two existing, well-known tubular chain conveyors, which can meet the sand feeding requirements during construction and can vertically transport the proppant to the target position according to the conveying capacity. The power source of the tubular chain conveyor can be hydraulically driven or electrically driven. By switching between the tubular chain conveyor and the horizontal screw conveyor 4, the sand feeding process is ensured to be continuous and will not affect the pressure in the working tank 1. During operation, the proppant is poured into the sand hopper 17, enters through the sand inlet of the tubular chain conveyor, and is output from the sand outlet of the tubular chain conveyor to the horizontal screw conveyor 4.

[0049] like Figure 1 As shown, a tee 18 is fixedly connected to the bottom of the working tank 1, a spiral sand conveyor 19 is fixedly connected to the bottom of the tee 18, and a bypass pipe 20 is fixedly connected to the sand outlet of the spiral sand conveyor 19. The mixer 5 and the input manifold 7 are fixedly connected through the bypass pipe 20.

[0050] In this process, by using two spiral sand conveyors 19 below the working tank 1 to convey sand to the input manifold 7, a relatively accurate measurement of the added support dosage is achieved; during operation, liquid carbon dioxide fracturing fluid is input through the input manifold 7 to the bypass pipe 20, and further enters the mixer 5.

[0051] like Figure 1 As shown, control butterfly valves are fixedly installed between the horizontal spiral sand conveyor 4 and the preparation tank 1 2 and the preparation tank 2 3, between the preparation tank 1 2 and the preparation tank 2 3 and the working tank 1, between the working tank 1 and the tee 18, between the spiral sand conveyor 19 and the bypass pipe 20, and on each liquid inlet line 8. The control butterfly valves are all connected to the control unit.

[0052] Among them, the preparation tank 1 2 and preparation tank 2 3 are connected to the working tank 1 through a Y-type tee. The control butterfly valve is set on the Y-type tee, thereby ensuring that the compaction of the working tank 1 remains constant by controlling the switching of the butterfly valve.

[0053] The power of each control butterfly valve can be hydraulically driven or electrically driven. By using two preparatory tanks and their corresponding control butterfly valves, the pressure in the working pipe can be kept basically constant. At the same time, by switching between the control butterfly valves, the sand loading process is ensured to be continuous and will not affect the pressure in the working tank 1.

[0054] The control unit receives signal values ​​from the gravity sensor 12, pressure sensor 13, and temperature sensor 14, and compares the received signal values ​​with the corresponding sensor set values. If the received signal value reaches the set value of the corresponding sensor, the control unit controls the corresponding control butterfly valve to open and close. This process is highly automated, thereby improving the working efficiency of the invention.

[0055] Example 2: A sand mixing method for pure carbon dioxide dry fracturing, including two working modes: intermittent sand loading and continuous sand loading. The intermittent sand loading includes the following steps:

[0056] Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor 4 and into the preparation tank 1 2 and preparation tank 2 3;

[0057] Step 2: Once the sensing modules in preparation tank 1 (2) and preparation tank 2 (3) detect that the proppant has been filled, the sand feeding stops.

[0058] Step 3: Inject liquid carbon dioxide into preparation tank 1 2 and preparation tank 2 3 through liquid inlet line 8;

[0059] Step 4: When the sensing module detects that the pressure inside the preparation tank 1 2 and preparation tank 2 3 has reached the set value, open the exhaust valve 10 of the preparation tank 1 2 and preparation tank 2 3 to empty the gas inside the tank and then close it; continue to inject liquid carbon dioxide into the preparation tank 1 2 and preparation tank 2 3, and repeatedly open the exhaust valve 10 until the sensing module detects that the temperature inside the preparation tank 1 2 and preparation tank 2 3 has reached the set value, empty the gas inside the preparation tank 1 2 and preparation tank 2 3, and close the exhaust valve 10;

[0060] Step 4: Inject liquid carbon dioxide fracturing fluid into the input manifold 7 and into the mixer 5. At the same time, the proppant is output to the mixer 5 and fully mixed with the liquid carbon dioxide fracturing fluid in the mixer 5. After mixing, it is output to the fracturing truck through the medium-pressure manifold 6.

[0061] The continuous sand application process includes the following steps:

[0062] Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor 4, and then into the working tank 1 via the first and second preparatory tanks 2 and 3.

[0063] Step 2: After the sensing module in working tank 1 detects that the proppant is full, it stops the sand filling in preparation tank 2 3, so that the proppant only enters preparation tank 1 2;

[0064] Step 3: Inject liquid carbon dioxide into working tank 1 through inlet line 8; when the sensing module senses that the pressure inside working tank 1 has reached the set value, open the exhaust valve 10 of working tank 1 to vent the gas inside the tank and then close it; continue to inject liquid carbon dioxide into working tank 1, and repeatedly open the exhaust valve 10 until the sensing module senses that the temperature inside working tank 1 has reached the set value, then vent the gas inside working tank 1 and close the exhaust valve 10;

[0065] Step 4: Inject liquid carbon dioxide fracturing fluid into the input manifold 7 and into the mixer 5. At the same time, the proppant is output to the mixer 5 and fully mixed with the liquid carbon dioxide fracturing fluid in the mixer 5. After mixing, it is output to the fracturing truck through the medium-pressure manifold 6.

[0066] Step 5: Simultaneously with Step 4, after the proppant in Preparatory Tank 1-2 is filled, close the sand supply in Preparatory Tank 1-2 and open the sand supply in Preparatory Tank 2-3 to pressurize and cool the proppant in Preparatory Tank 1-2. After the pressure and temperature reach the set values, allow the proppant in Preparatory Tank 1-2 to flow into Working Tank 1.

[0067] Step 6: Start the sand feeding device to continue feeding sand into the preparation tank 12. The proppant undergoes the above-mentioned cooling, pressurization and venting processes in the preparation tank 12. After the temperature and pressure reach the standard, it is output to the working tank 1.

[0068] Step 7: Output all the qualified proppant in the preparation tank 2 3 to the working tank 1; start the sand feeding device to continue feeding sand into the preparation tank 2 3. The proppant undergoes the above-mentioned cooling, pressurization and venting processes in the preparation tank 2 3. After the temperature and pressure reach the standard, it is output to the working tank 1.

[0069] Step 8: Repeat steps 5 through 7.

[0070] The amount of sand conveyed can be adjusted and the amount of sand added can be measured by adjusting the rotation speed of the spiral sand conveyor 19.

[0071] The sensing module senses whether the proppant is full using gravity sensor 12; the sensing module senses whether the pressure and temperature have reached the set values ​​using pressure sensor 13 and temperature sensor 14.

[0072] In summary, this invention features a simple structure and ease of use. Two tubular chain conveyors vertically and continuously transport the proppant into the horizontal spiral sand conveyor 4. The switching between the first and second preparatory tanks 2 and their corresponding control butterfly valves ensures continuous sand discharge from the working tank 1. Liquid carbon dioxide input through the sensing module and inlet pipeline 8 maintains constant pressure and temperature within the working tank 1, allowing for continuous sand addition. A mixer 5 thoroughly mixes the proppant with the liquid carbon dioxide fracturing fluid, outputting liquid carbon dioxide carrying sand. Therefore, this invention, as a sand mixing device for use in pure dry carbon dioxide fracturing, enables continuous pressurized sand addition, meeting on-site requirements.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any attempt to rewrite the present invention without creative effort constitutes an infringement. Equivalent substitutions or changes to the technical solutions and concepts of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A sand mixing method for a sand mixing device used in carbon dioxide dry fracturing, the sand mixing device comprising a working tank, a first preparatory tank, a second preparatory tank, an induction module, and a sand feeding device; the sand outlet of the sand feeding device is fixedly connected to a horizontal spiral sand conveyor, the sand outlet of the horizontal spiral sand conveyor is fixedly connected to the first preparatory tank and the second preparatory tank respectively, the bottom of the first preparatory tank and the second preparatory tank are fixedly connected to the working tank, the bottom of the working tank is fixedly connected to a mixer, and the outside of the mixer is fixedly connected to a medium-pressure manifold and an input manifold respectively; an induction module is fixedly installed on the outside of the working tank, the first preparatory tank, and the second preparatory tank; an inlet pipeline is fixedly connected to the outside of the working tank, the first preparatory tank, and the second preparatory tank; a safety valve and an exhaust valve are fixedly installed on the outside of the working tank, the first preparatory tank, and the second preparatory tank. The sensing module includes a control unit, a gravity sensor, a pressure sensor, and a temperature sensor. The gravity sensor, pressure sensor, and temperature sensor are all connected to the control unit. The gravity sensor, pressure sensor, and temperature sensor are respectively installed on the working tank, the first preparation tank, and the second preparation tank. The sand feeding device includes a tubular chain conveyor 1 and a tubular chain conveyor 2. The sand inlets of both tubular chain conveyor 1 and tubular chain conveyor 2 are respectively connected to sand hoppers, and the sand outlets of both tubular chain conveyor 1 and tubular chain conveyor 2 are respectively fixedly connected to the sand inlet of the horizontal screw conveyor. Its features are: Sand mixing methods include two working modes: intermittent sand application and continuous sand application. Intermittent sand application... Includes the following steps: Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor and into the preparatory tank 1 and preparatory tank 2; Step 2: Once the sensing modules in preparation tank 1 and preparation tank 2 detect that the proppant is full, the sand feeding stops. Step 3: Inject liquid carbon dioxide into preparation tank 1 and preparation tank 2 through the liquid inlet pipeline; Step 4: When the sensing module detects that the pressure in the preparation tank 1 and preparation tank 2 has reached the set value, open the exhaust valves of preparation tank 1 and preparation tank 2 to empty the gas in the tanks and then close them; continue to inject liquid carbon dioxide into preparation tank 1 and preparation tank 2, and repeatedly open the exhaust valves until the sensing module detects that the temperature in preparation tank 1 and preparation tank 2 has reached the set value, empty the gas in preparation tank 1 and preparation tank 2, and close the exhaust valves; Step 5: Inject liquid carbon dioxide fracturing fluid into the input manifold and into the mixer. At the same time, the proppant is output to the mixer and fully mixed with the liquid carbon dioxide fracturing fluid. After mixing, it is output to the fracturing truck through the medium-pressure manifold. The continuous sand application process includes the following steps: Step 1: The sand feeding device delivers the proppant to the horizontal screw conveyor, and then into the working tank via the first and second preparatory tanks; Step 2: After the sensing module in the working tank detects that the proppant is full, it stops the sand filling in the second preparation tank, so that the proppant only enters the first preparation tank. Step 3: Inject liquid carbon dioxide into the working tank through the inlet line; when the sensing module detects that the pressure inside the working tank has reached the set value, open the exhaust valve of the working tank to empty the gas inside the tank and then close it; continue to inject liquid carbon dioxide into the working tank and repeatedly open the exhaust valve until the sensing module detects that the temperature inside the working tank has reached the set value, then empty the gas inside the working tank and close the exhaust valve. Step 4: Inject liquid carbon dioxide fracturing fluid into the input manifold and into the mixer. At the same time, the proppant is output to the mixer and fully mixed with the liquid carbon dioxide fracturing fluid. After mixing, it is output to the fracturing truck through the medium-pressure manifold. Step 5: Performed simultaneously with Step 4, after the proppant in Preparatory Tank 1 is filled, close the sand supply in Preparatory Tank 1 and open the sand supply in Preparatory Tank 2 to pressurize and cool the proppant in Preparatory Tank 1. After the pressure and temperature reach the set values, allow the proppant in Preparatory Tank 1 to flow into the working tank. Step 6: Start the sand feeding device to continue feeding sand into the preparation tank. The proppant undergoes the above-mentioned cooling, pressurization and venting process in the preparation tank until the temperature and pressure reach the standard, and then it is output to the working tank. Step 7: Output all the proppant that has reached the standard in the preparation tank 2 to the working tank; start the sand feeding device to continue feeding sand into the preparation tank 2. The proppant undergoes the above-mentioned cooling, pressurization and venting process in the preparation tank 2, so that the temperature and pressure reach the standard, and then output it to the working tank. Step 8: Repeat steps 5 through 7.

2. The sand mixing method for a sand mixing device used in pure dry carbon dioxide fracturing according to claim 1, characterized in that: Agitators are fixedly installed on the inner side of the working tank, preparation tank one, and preparation tank two.

3. A sand mixing method for a sand mixing device used in pure dry carbon dioxide fracturing according to claim 1 or 2, characterized in that: A tee is fixedly connected to the bottom of the working tank, and a spiral sand conveyor is fixedly connected to the bottom of the tee. A bypass pipe is fixedly connected to the sand outlet of the spiral sand conveyor. The mixer and the input manifold are fixedly connected through the bypass pipe. Or / and, a control butterfly valve is fixedly installed between the horizontal spiral sand conveyor and the first and second preparation tanks, between the first and second preparation tanks and the working tank, between the working tank and the tee, between the spiral sand conveyor and the bypass pipe, and on each liquid inlet line. All control butterfly valves are connected to the control unit.

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