Carbon dioxide dry sand fracturing continuous sand adding system and method

Abstract

The invention provides a continuous sand adding system and method for carbon dioxide dry sand adding fracturing. The system comprises a feeding screw, a storage box, a metering conveying screw, a spraying pipe, a stirring machine, a buffer box, a paste pump, a continuous cooling tank, a coil pipe, a main manifold and the like. The method comprises the following steps: raw material conveying, base liquid pumping, proportioning and wet mixing, wet mixed slurry buffering, booster pumping, continuous cooling, mixed conveying and the like. By means of the system and method, continuous sand adding construction of carbon dioxide dry fracturing can be achieved, the sand ratio is accurately controlled, and dry sand adding fracturing construction with the unlimited sand amount, the large sand ratio and the large displacement is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to a system and method for continuous sand addition during carbon dioxide dry sand fracturing. Background Art

[0002] As a new waterless fracturing technology, CO2 dry fracturing with sand uses liquid CO2 as the fracturing medium, and has the advantages of low damage, easy flowback, easy fracture creation, and environmental protection. CO2 dry fracturing with sand is particularly suitable for complex rock formations with low pressure, low permeability, density, and strong water sensitivity. It has a good effect on reservoir transformation with serious oil and gas layer pollution and low water content, and can greatly increase the production of a single well.

[0003] CN106640024A discloses a closed sand mixing device and method. The method adds proppant to the closed sand mixing device before construction, seals the closed sand mixing tank, then adds liquid carbon dioxide for pressurized cooling, and cools the proppant to the same temperature as the liquid carbon dioxide; the amount of sand added in one construction is the effective volume of the closed sand mixing device. If a second sand addition is required, the liquid carbon dioxide in the closed sand mixing tank needs to be discharged first, and then the pressure in the tank is released. After the pressure is released, the closed sand mixing tank is opened and the proppant is added again. After pressurized cooling again, the sand addition operation can be performed. The preparation method of this dry sand adding liquid determines that it can only perform carbon dioxide dry sand adding fracturing construction with quantitative sand addition, and cannot perform construction operations with unlimited sand volume, large sand ratio, and large displacement, which limits the promotion and application of carbon dioxide dry sand adding fracturing technology.

[0004] In order to maximize the production potential of carbon dioxide dry sand fracturing technology and ensure that the construction scale is not affected by the volume of the closed sand mixing device, it is particularly important to develop a system and method for continuous sand addition in carbon dioxide dry sand fracturing. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a system and method for continuous sand addition in carbon dioxide dry sand fracturing. The system and method can realize continuous sand addition construction in carbon dioxide dry fracturing.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a continuous sand adding system for carbon dioxide dry sand fracturing, the system comprising: a storage box, a spray pipe, a mixer, a buffer box, a paste pump, a continuous cooling tank, a coil and a main manifold;

[0007] Wherein, the mixer is provided with a proppant inlet, a base liquid inlet and a wet slurry outlet; the outlet of the storage box is connected to the proppant inlet of the mixer; the spray pipe is arranged in the mixer and is connected to the base liquid inlet; the wet slurry outlet of the mixer is connected to the inlet of the buffer box; the outlet of the buffer box is connected to the inlet of the paste pump; the coil is arranged in the continuous cooling tank; the outlet of the paste pump is connected to the inlet of the coil; the outlet of the coil is connected to the main manifold.

[0008] According to a specific embodiment of the present invention, preferably, the above system further comprises: a feeding screw, wherein the outlet of the feeding screw is connected to the inlet of the storage box.

[0009] In the above system, preferably, the feeding screw comprises a double-screw feeder.

[0010] According to a specific embodiment of the present invention, preferably, the above system further comprises: a metering and conveying screw, through which the outlet of the storage box is connected to the proppant inlet of the mixer. More preferably, the accuracy of the metering and conveying screw is ±0.5%.

[0011] In the above system, preferably, the base liquid inlet of the mixer is connected to a base liquid delivery pipeline, and a metering pump is arranged on the base liquid delivery pipeline. More preferably, the metering pump is a cam rotor pump.

[0012] In the above system, preferably, the mixer comprises a double-screw mixer.

[0013] In the above system, preferably, a rotating mechanism is provided in the buffer box.

[0014] In the above system, preferably, the paste pump comprises a two-stage paste pump, which is two paste pumps connected in series, wherein, according to the material flow direction, the two paste pumps in series are respectively referred to as the first-stage paste pump and the second-stage paste pump.

[0015] In the above system, preferably, a cooling medium is provided in the continuous cooling tank, the cooling medium is liquid carbon dioxide, and the coil is immersed in the cooling medium.

[0016] In the above system, preferably, the continuous cooling tank is provided with a cooling valve, and the cooling valve is used to regulate the temperature in the continuous cooling tank.

[0017] In the above system, preferably, the outer surface of the coil is processed with a spiral groove; more preferably, the cross-section of the spiral groove is U-shaped, and the angle between the extension lines of the two side walls of the spiral groove is 45-60°.

[0018] In the above system, preferably, the length of the coil is 80-120 m.

[0019] A second aspect of the present invention provides a method for continuous sand addition during carbon dioxide dry sand fracturing, wherein the method uses the above-mentioned system for continuous sand addition during carbon dioxide dry sand fracturing to perform continuous sand addition during carbon dioxide dry sand fracturing, and the method comprises the following steps:

[0020] S1. Raw material transportation: The proppant is continuously transported to the storage box, and the proppant in the storage box is transported to the mixer according to the designed dosage ratio;

[0021] S2, base liquid pump injection: while step S1 is being carried out, the base liquid is measured according to the designed dosage ratio and then sprayed into the mixer;

[0022] S3, proportioned wet mixing: the proppant and the base liquid are mixed in a mixer according to the designed proportion to form a wet mixed slurry;

[0023] S4, wet mixed slurry buffering: the wet mixed slurry in the mixer enters the buffer box, where the wet mixed slurry is sheared at high speed and foamed evenly to form foamed wet mixed slurry;

[0024] S5, booster pumping: the foam wet slurry in the buffer tank is continuously pressurized by the paste pump and pumped to the continuous cooling tank;

[0025] S6, continuous cooling: the high-pressure wet mixed slurry flows in the coil in the continuous cooling tank to complete continuous cooling;

[0026] S7. Mixed transportation: The high-pressure and low-temperature wet mixed slurry enters the main manifold and mixes with the liquid carbon dioxide in the main manifold to continuously form the carbon dioxide dry sand-added fracturing fluid, which is then transported to the fracturing truck through the main manifold for continuous sand-added construction.

[0027] In the above method, preferably, in step S1, the proppant comprises a fracturing proppant of 20 to 100 meshes.

[0028] In the above method, preferably, in step S1, the proppant is continuously transported to the storage box by a feeding screw.

[0029] In the above method, preferably, in step S1, the proppant in the storage box is transported to the mixer according to the designed dosage ratio by a high-precision metering and transporting screw.

[0030] In the above method, preferably, in step S2, the base fluid includes a viscosity enhancer specifically for carbon dioxide dry sand fracturing.

[0031] In the above method, preferably, in step S2, quantitatively pumping the base liquid to the mixer according to the designed dosage ratio is achieved by adjusting the operating frequency of the cam rotor pump. More preferably, the operating frequency of the cam rotor pump is controlled to be 15-50 Hz.

[0032] In the above method, preferably, in step S4, the wet mixed slurry is sheared at high speed by a rotating mechanism with a rotation speed of 600 to 1000 r / min in a buffer box, thereby uniformly foaming to form a foamed wet mixed slurry.

[0033] In the above method, preferably, in step S4, the foaming rate of the wet slurry in the buffer box is greater than 280%. The foaming rate refers to the ratio of the volume of the foamed wet slurry formed by the wet slurry to the volume of the wet slurry.

[0034] In the above method, preferably, in step S5, the foam wet slurry is continuously pressurized by a two-stage paste pump, the first-stage paste pump pressurizes the foam wet slurry to 0.5-1.5 MPa, and the second-stage paste pump pressurizes the foam wet slurry pressurized by the first-stage paste pump to 7-10 MPa.

[0035] In the above method, preferably, in step S6, the high-pressure wet slurry is continuously cooled to -15°C to -20°C in a coil having a length of 80 to 120 m.

[0036] In the above method, preferably, in step S6, a cooling medium is provided in the continuous cooling tank, the cooling medium is liquid carbon dioxide at -15°C to -20°C, the coil is immersed in the cooling medium, and the continuous cooling amount of the high-pressure wet slurry is 0.8m 3 / min or above.

[0037] The present invention provides a system and method for continuous sand addition in carbon dioxide dry sand fracturing. The system and method can realize continuous sand addition construction of carbon dioxide dry fracturing, and accurately control the sand ratio, so as to realize dry sand addition fracturing construction with unlimited sand volume, large sand ratio and large displacement.

[0038] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0039] (1) Through continuous pumping of wet slurry from normal pressure to high pressure and continuous rapid cooling from normal temperature to low temperature, continuous preparation of dry sand fracturing fluid is achieved;

[0040] (2) The mixing ratio of proppant and base fluid can be ensured by adjusting the metering conveying screw and metering pump, and the sand ratio can be accurately controlled;

[0041] (3) The low temperature characteristics of liquid carbon dioxide can be used to continuously cool the foam wet slurry formed by the proppant and the base liquid to a set temperature, which simplifies the system structure and greatly reduces the overall power consumption of the system;

[0042] (4) Realize the low-pressure injection of base liquid (viscosity enhancer), completely solve the problem of adding an additional base liquid (viscosity enhancer) dedicated pump truck for high-pressure injection, and at the same time ensure the high sand carrying capacity of liquid carbon dioxide in the ground main manifold;

[0043] (5) The pressure and temperature of the wet slurry can be precisely controlled to ensure that the liquid carbon dioxide in the mixing and transportation step remains in the liquid phase. The resulting sand-added fracturing fluid fully meets the continuous construction requirements of high sand ratio, large sand volume, and large displacement of carbon dioxide dry sand-added fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic structural diagram of a system for continuous sand addition in carbon dioxide dry sand fracturing provided in a specific embodiment of the present invention.

[0045] Figure 2 It is a schematic diagram of the structure of the spiral groove on the outer surface of the coil in a specific embodiment of the present invention.

[0046] Figure 3 A schematic flow chart of a method for continuous sand addition in carbon dioxide dry sand fracturing provided in a specific embodiment of the present invention.

[0047] Description of Figure Numbers:

[0048] 1-storage box; 2-spray pipe; 3-mixer; 4-buffer tank; 5-paste pump; 6-continuous cooling tank; 7-coil; 8-main manifold; 9-feeding screw; 10-metering conveying screw; 11-metering pump; 12-cooling valve; 13-spiral groove. DETAILED DESCRIPTION

[0049] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0050] It should be noted that in the present invention, all directional indications (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0051] Furthermore, unless otherwise expressly specified or limited, “connection” should be understood in a broad sense, including both direct connection and indirect connection through another component.

[0052] In the absence of conflicts, technicians in this field can combine the relevant technical features in the following embodiments according to actual conditions to achieve corresponding technical effects. Specific details of various combinations are not described here one by one.

[0053] On the one hand, the present invention provides a system for continuous sand addition by dry fracturing with carbon dioxide, the structure of which is as follows: Figure 1 shown.

[0054] The system comprises: a material storage box 1, a spray pipe 2, a mixer 3, a buffer tank 4, a paste pump 5, a continuous cooling tank 6, a coil 7 and a main pipe manifold 8;

[0055] Among them, the mixer 3 is provided with a proppant inlet, a base liquid inlet and a wet slurry outlet; the outlet of the storage box 1 is connected to the proppant inlet of the mixer 3; the spray pipe 2 is arranged in the mixer 3 and is connected to the base liquid inlet of the mixer 3; the wet slurry outlet of the mixer 3 is connected to the inlet of the buffer box 4; the outlet of the buffer box 4 is connected to the inlet of the paste pump 5; the coil 7 is arranged in the continuous cooling tank 6; the outlet of the paste pump 5 is connected to the inlet of the coil 7; the outlet of the coil 7 is connected to the main manifold 8.

[0056] In some specific embodiments, the system further comprises: a feeding screw 9 , the outlet of the feeding screw 9 is connected to the inlet of the storage box 1 .

[0057] In some specific embodiments, the feeding screw 9 is a double-screw feeder. Specifically, the double-screw feeder includes two spiral feeding pipes and a transmission mechanism, etc., each spiral feeding pipe is provided with an inlet and an outlet at both ends, a hopper is provided at the inlet, and the transmission mechanism is used to drive the two spiral feeding pipes to operate. The transmission mechanism may include a motor. The double-screw feeder may also selectively include a support mechanism for supporting the double-screw feeder. The present invention preferably uses a double-screw feeder, which can alternately transport sand, that is, after one spiral feeding pipe completes feeding, the other spiral feeding pipe continues to feed, and at the same time, the hopper of the first spiral feeding pipe is filled with proppant, and the cycle continues to achieve continuous transportation.

[0058] In some specific embodiments, the system further comprises: a metering and conveying screw 10, through which the outlet of the storage box 1 is connected to the proppant inlet of the mixer 3. Preferably, the accuracy of the metering and conveying screw 10 is ±0.5%.

[0059] In some specific embodiments, the base liquid inlet of the mixer 3 is connected to a base liquid delivery pipeline, and the base liquid delivery pipeline is provided with a metering pump 11. Preferably, the metering pump 11 is a cam rotor pump.

[0060] In some specific embodiments, the mixer 3 is a double-screw mixer. In the present invention, a double-screw mixer is preferably used to preliminarily mix the proppant and the base liquid to form a wet slurry.

[0061] In some specific embodiments, a rotating mechanism is provided in the buffer box 4. The rotating mechanism may be a rotating mechanism in the prior art, and the present invention does not impose any special limitation on its structure, as long as it can achieve high-speed shearing of the wet slurry to form a foamed wet slurry.

[0062] In some specific embodiments, the paste pump 5 is a two-stage paste pump, which is two paste pumps connected in series. According to the material flow direction, the two paste pumps in series are respectively referred to as the first-stage paste pump and the second-stage paste pump. Preferably, both the first-stage paste pump and the second-stage paste pump are reciprocating paste pumps. The present invention preferably uses a two-stage reciprocating paste pump, which can continuously pressurize the foam wet slurry through rapid reciprocating motion.

[0063] In some specific embodiments, a cooling medium is provided in the continuous cooling tank 6, and the cooling medium is liquid carbon dioxide. The coil 7 is immersed in the cooling medium to achieve continuous cooling of the high-pressure wet slurry.

[0064] In some specific embodiments, the continuous cooling tank 6 is provided with a cooling valve 12, and the cooling valve 12 is used to adjust the temperature in the continuous cooling tank 6. Specifically, by adjusting the opening of the cooling valve 12, the cooling medium liquid carbon dioxide can be regulated to flow out of the continuous cooling tank 6 in the form of gas phase to adjust the temperature in the continuous cooling tank 6, thereby achieving continuous and rapid cooling of the foam wet slurry.

[0065] In some specific embodiments, Figure 2 As shown, the outer surface of the coil 7 is processed with a spiral groove 13. The cross section of the spiral groove 13 is U-shaped, and the angle between the extension lines of the two side walls of the spiral groove 13 is 45 to 60 degrees ( Figure 2 The angle shown in the figure is 60°). Specifically, the spiral groove 13 on the outer surface of the coil 7 can be made by lathe processing. The spiral groove 13 can greatly increase the contact area between the coil 7 and the cooling medium liquid carbon dioxide, accelerate the temperature transfer, and ensure that the wet slurry is quickly cooled when flowing in the coil 7.

[0066] In some specific embodiments, the length of the coil 7 is 80-120 m.

[0067] On the other hand, the present invention provides a method for continuous sand addition during carbon dioxide dry sand fracturing. The method uses the above-mentioned system for continuous sand addition during carbon dioxide dry sand fracturing to perform continuous sand addition during carbon dioxide dry sand fracturing. The process is as follows: Figure 3 shown.

[0068] The method comprises the following steps:

[0069] S1, raw material transportation: the proppant is continuously transported to the storage box 1, and the proppant in the storage box 1 is transported to the mixer 3 according to the designed dosage ratio;

[0070] S2, base liquid pumping: while step S1 is being performed, the base liquid is measured according to the designed dosage ratio and then sprayed into the mixer 3;

[0071] S3, proportioned wet mixing: the proppant and the base liquid are stirred and mixed in the mixer 3 according to the designed proportion to form a wet mixed slurry;

[0072] S4, wet slurry buffering: the wet slurry in the mixer 3 enters the buffer box 4, where the wet slurry is sheared at high speed and foamed evenly to form a foamed wet slurry;

[0073] S5, booster pumping: the normal pressure foam wet slurry in the buffer tank 4 is continuously pressurized by the paste pump 5 and pumped to the continuous cooling tank 6;

[0074] S6, continuous cooling: the high-pressure wet mixed slurry flows in the coil 7 in the continuous cooling tank 6 to complete continuous cooling;

[0075] S7, mixed transportation: the high-pressure and low-temperature wet mixed slurry enters the main manifold 8, mixes with the liquid carbon dioxide in the main manifold 8, continuously forms the carbon dioxide dry sand-added fracturing fluid, and is transported to the fracturing truck through the main manifold 8 for continuous sand-added construction.

[0076] In some specific embodiments, in step S1, the proppant includes a 20-100 mesh fracturing proppant, and specifically, the proppant includes but is not limited to various types of fracturing proppant such as ceramsite, quartz sand, and resin coated sand.

[0077] In some specific embodiments, in step S1 , the proppant is continuously transported to the storage box 1 via the feeding screw 9 .

[0078] In some specific embodiments, in step S1 , the proppant in the storage box 1 is transported to the mixer 3 according to the designed dosage ratio by means of the metering and transporting screw 10 .

[0079] In some specific embodiments, in step S2, the base fluid includes a special viscosity enhancer for carbon dioxide dry sand fracturing. The special viscosity enhancer for carbon dioxide dry sand fracturing can be a viscosity enhancer in the prior art, which can increase the suspension performance of the proppant in the carbon dioxide dry sand fracturing fluid, improve the sand ratio, and reduce the friction resistance of the carbon dioxide dry sand fracturing fluid in the pipeline.

[0080] In some specific embodiments, in step S2, quantitatively pumping the base liquid to the mixer according to the designed dosage ratio is achieved by adjusting the operating frequency of the cam rotor pump. Preferably, the operating frequency of the cam rotor pump is controlled to be 15 to 50 Hz.

[0081] In some specific embodiments, in step S4, the wet mixed slurry is sheared at high speed by a rotating mechanism with a rotation speed of 600 to 1000 r / min in the buffer box 4, thereby uniformly foaming to form a foamed wet mixed slurry.

[0082] In some specific embodiments, in step S4, the foaming rate of the wet mixed slurry in the buffer box 4 is greater than 280%.

[0083] In some specific embodiments, in step S5, the foam wet slurry is continuously pressurized by a two-stage paste pump, the first-stage paste pump pressurizes the foam wet slurry to 0.5-1.5 MPa, and the second-stage paste pump pressurizes the foam wet slurry pressurized by the first-stage paste pump to 7-10 MPa.

[0084] In some specific embodiments, in step S6, the high pressure wet slurry is continuously cooled to -15°C to -20°C in a coil having a length of 80 to 120 m.

[0085] In some specific embodiments, in step S6, a cooling medium is provided in the continuous cooling tank 6, and the cooling medium is liquid carbon dioxide at -15°C to -20°C. The coil 7 is immersed in the cooling medium to achieve continuous cooling of the high-pressure wet slurry. The continuous cooling amount of the high-pressure wet slurry is 0.8m 3 / min or above.

[0086] The technical solutions of the present invention are specifically described below by way of examples, but the present invention is not limited to these examples and can of course be implemented in various modifications within the scope of the gist of the present invention.

[0087] Example 1

[0088] This embodiment provides a system for continuous sand addition during carbon dioxide dry sand fracturing. Figure 1 As shown, the system includes: a storage box 1, a spray pipe 2, a mixer 3, a buffer tank 4, a paste pump 5, a continuous cooling tank 6, a coil 7, a main manifold 8, a feeding screw 9, a metering and conveying screw 10, a metering pump 11 and a cooling valve 12;

[0089] Among them, the outlet of the feeding screw 9 is connected to the inlet of the storage box 1; the inlet of the metering and conveying screw 10 is connected to the outlet of the storage box 1; the mixer 3 is provided with a proppant inlet, a base liquid inlet and a wet slurry outlet; the outlet of the metering and conveying screw 10 is connected to the proppant inlet of the mixer 3; the base liquid inlet of the mixer 3 is connected to a base liquid conveying pipeline, and a metering pump 11 is provided on the base liquid conveying pipeline; the spray pipe 2 is arranged in the mixer 3 and is connected to the base liquid inlet; the wet slurry outlet of the mixer 3 is connected to the inlet of the buffer box 4; the outlet of the buffer box 4 is connected to the inlet of the paste pump 5; the coil 7 is arranged in the continuous cooling tank 6; the continuous cooling tank 6 is provided with a cooling medium, the cooling medium is liquid carbon dioxide, and the coil 7 is immersed in the cooling medium from the inlet to the outlet, which is used to realize continuous cooling of the high-pressure wet slurry; the continuous cooling tank 6 is provided with a cooling valve 12, and the cooling valve 12 is used to adjust the temperature in the continuous cooling tank 6; the outlet of the paste pump 5 is connected to the inlet of the coil 7; the outlet of the coil 7 is connected to the main manifold 8.

[0090] In this embodiment, the feeding screw 9 is a double-screw feeding machine.

[0091] In this embodiment, the accuracy of the metering and conveying screw 10 is ±0.5%.

[0092] In this embodiment, the metering pump 11 is a cam rotor pump.

[0093] In this embodiment, the mixer 3 is a double-screw mixer. The diameter of the spiral stirring rod of the double-screw mixer is 0.6m to 0.8m (the diameter is the diameter including the spiral blade). The rated mixing efficiency of the double-screw mixer can be set to 2m 3 / min.

[0094] In this embodiment, a rotating mechanism is provided in the buffer box 4, and the rotating speed can be 700-1000 r / min.

[0095] In this embodiment, the paste pump 5 is a two-stage paste pump. Both the first-stage paste pump and the second-stage paste pump are reciprocating paste pumps.

[0096] In this embodiment, the volume of the continuous cooling tank 6 can be 25 to 30 m 3 The length of the coil 7 built therein can be 120m and the nominal diameter (DN) can be 114.3mm.

[0097] In this embodiment, if Figure 2As shown, the outer surface of the coil 7 is processed with a spiral groove 13, the cross section of the spiral groove 13 is U-shaped, the angle between the extension lines of the two side walls of the spiral groove 13 is 60°, and the radius R of the circle formed by the arc at the bottom of the spiral groove 13 is 3 mm. Specifically, the spiral groove 13 on the outer surface of the coil 7 can be made by lathe processing. The spiral groove 13 can greatly increase the contact area between the coil 7 and the liquid carbon dioxide, accelerate the temperature transfer, and ensure that the wet slurry is quickly cooled when flowing in the coil 7.

[0098] Example 2

[0099] This embodiment provides a method for continuous sand addition during carbon dioxide dry sand fracturing. The method uses the system provided in Example 1 to perform continuous sand addition during carbon dioxide dry sand fracturing.

[0100] like Figure 3 As shown, the method comprises the following steps:

[0101] S1, raw material transportation: the proppant in the sand tank truck is continuously transported to the storage box 1 through the feeding screw 9, and the proppant in the storage box 1 naturally falls to the metering and conveying screw 10, and is transported to the mixer 3 according to the designed dosage ratio through the metering and conveying screw 10;

[0102] S2, base liquid pumping: while step S1 is being performed, the base liquid is metered by the metering pump 11 according to the designed dosage ratio and then quantitatively pumped, and the operating frequency of the metering pump 11 (cam rotor pump) is controlled to be 38 Hz, and the base liquid is evenly sprayed into the mixer 3 through the spray pipe 2;

[0103] S3, proportioned wet mixing: the proppant and the base liquid are preliminarily stirred and mixed in the mixer 3 according to the designed proportion to form a wet mixed slurry;

[0104] S4, wet slurry buffering: the wet slurry in the mixer 3 enters the buffer box 4, where the wet slurry is sheared at high speed by a rotating mechanism with a rotation speed of 700 to 1000 r / min, and then foamed uniformly to form a foamed wet slurry; the foaming rate of the wet slurry in the buffer box 4 is 295%;

[0105] S5, booster pumping: the normal pressure foam wet slurry in the buffer tank 4 is continuously pressurized by the paste pump 5 (two-stage paste pump), the first-stage paste pump pressurizes the normal pressure foam wet slurry to 0.5-1.5 MPa, the second-stage paste pump pressurizes the foam wet slurry pressurized by the first-stage paste pump to 7-10 MPa, and pumps it to the continuous cooling tank 6;

[0106] S6, continuous cooling: The high-pressure wet mixed slurry flows continuously and uniformly in the coil 7 with a length of 120m in the continuous cooling tank 6. During the flow, the high-pressure wet mixed slurry in the coil 7 exchanges heat with the liquid carbon dioxide at -15℃ to -20℃ outside the coil 7. The temperature in the continuous cooling tank 6 is regulated by adjusting the opening of the cooling valve 12 to continuously and rapidly cool the high-pressure wet mixed slurry to -15℃ to -20℃. The continuous cooling amount of the high-pressure wet mixed slurry is 0.92m 3 / min;

[0107] S7, mixed transportation: a high-pressure, low-temperature and continuous wet slurry is formed at the outlet of the coil 7 and enters the main manifold 8 to mix with the liquid carbon dioxide in the main manifold 8 to continuously form a carbon dioxide dry-type sand-added fracturing fluid. The pressure of the carbon dioxide dry-type sand-added fracturing fluid is 2.5 MPa and the temperature is -15°C to -20°C. The carbon dioxide dry-type sand-added fracturing fluid is transported to the fracturing truck through the main manifold 8 for continuous sand-added construction.

[0108] In this embodiment, in step S1, the proppant includes a 20-100 mesh fracturing proppant, and specifically, the proppant includes but is not limited to various types of fracturing proppant such as ceramsite, quartz sand, and resin coated sand.

[0109] In this embodiment, in step S2, the base fluid includes a special viscosity enhancer for carbon dioxide dry sand fracturing. The special viscosity enhancer for carbon dioxide dry sand fracturing can be a viscosity enhancer in the prior art, which can increase the suspension performance of the proppant in the carbon dioxide dry sand fracturing fluid, improve the sand ratio, and reduce the friction resistance of the carbon dioxide dry sand fracturing fluid in the pipeline.

[0110] The system and method of the above embodiment can realize the continuous sanding construction of carbon dioxide dry fracturing, and accurately control the sand ratio, and the continuous pumping displacement of the proppant is ≥1.0m 3 / min, continuous proppant pumping volume ≥100m 3 , realizing dry sand fracturing construction with unlimited sand volume, large sand ratio and large displacement.

[0111] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A system for continuous sand addition during dry fracturing with carbon dioxide, the system comprising: Storage tank, spray pipe, mixer, buffer tank, paste pump, continuous cooling tank, coil and main manifold; Wherein, the mixer is provided with a proppant inlet, a base liquid inlet and a wet slurry outlet; the outlet of the storage box is connected to the proppant inlet of the mixer; the spray pipe is arranged in the mixer and is connected to the base liquid inlet; the wet slurry outlet of the mixer is connected to the inlet of the buffer box; the outlet of the buffer box is connected to the inlet of the paste pump; the coil is arranged in the continuous cooling tank; the outlet of the paste pump is connected to the inlet of the coil; the outlet of the coil is connected to the main manifold.

2. The system according to claim 1, wherein: The system further comprises: a feeding screw, the outlet of which is in communication with the inlet of the storage box; Preferably, the feeding screw comprises a double-screw feeder; Preferably, the system further comprises: a metering and conveying screw, through which the outlet of the storage box is connected to the proppant inlet of the mixer; more preferably, the accuracy of the metering and conveying screw is ±0.5%; Preferably, the base liquid inlet of the mixer is connected to a base liquid delivery pipeline, and a metering pump is provided on the base liquid delivery pipeline; more preferably, the metering pump is a cam rotor pump; Preferably, the mixer comprises a double screw mixer.

3. The system according to claim 1, wherein: A rotating mechanism is arranged in the buffer box.

4. The system according to claim 1, wherein: The paste pump comprises a two-stage paste pump, which is two paste pumps connected in series.

5. The system according to claim 1, wherein: The continuous cooling tank is provided with a cooling medium, the cooling medium is liquid carbon dioxide, and the coil is immersed in the cooling medium; Preferably, the continuous cooling tank is provided with a cooling valve, and the cooling valve is used to regulate the temperature in the continuous cooling tank; Preferably, the outer surface of the coil is processed with a spiral groove; more preferably, the cross section of the spiral groove is U-shaped, and the angle between the extension lines of the two side walls of the spiral groove is 45-60°; Preferably, the length of the coil is 80 to 120 m.

6. A method for continuous sanding during carbon dioxide dry sand fracturing, the method using the system for continuous sanding during carbon dioxide dry sand fracturing according to any one of claims 1 to 5 to perform continuous sanding during carbon dioxide dry sand fracturing, the method comprising the following steps: S1. Raw material transportation: The proppant is continuously transported to the storage box, and the proppant in the storage box is transported to the mixer according to the designed dosage ratio; S2, base liquid pump injection: while step S1 is being carried out, the base liquid is measured according to the designed dosage ratio and then sprayed into the mixer; S3, proportioned wet mixing: the proppant and the base liquid are mixed in a mixer according to the designed proportion to form a wet mixed slurry; S4, wet mixed slurry buffering: the wet mixed slurry in the mixer enters the buffer box, where the wet mixed slurry is sheared at high speed and foamed evenly to form foamed wet mixed slurry; S5, booster pumping: the foam wet slurry in the buffer tank is continuously pressurized by the paste pump and pumped to the continuous cooling tank; S6, continuous cooling: the high-pressure wet mixed slurry flows in the coil in the continuous cooling tank to complete continuous cooling; S7. Mixed transportation: The high-pressure and low-temperature wet mixed slurry enters the main manifold and mixes with the liquid carbon dioxide in the main manifold to continuously form the carbon dioxide dry sand-added fracturing fluid, which is then transported to the fracturing truck through the main manifold for continuous sand-added construction.

7. The method according to claim 6, wherein: In step S1, the proppant includes a fracturing proppant with a mesh size of 20 to 100.

8. The method according to claim 6, wherein: In step S1, the proppant is continuously transported to the storage box by a feeding screw; Preferably, in step S1, the proppant in the storage box is transported to the mixer according to the designed dosage ratio by a high-precision metering and transporting screw.

9. The method according to claim 6, wherein: In step S2, the base fluid includes a viscosity enhancer specifically for carbon dioxide dry sand fracturing.

10. The method according to claim 6, wherein: In step S2, quantitatively pumping the base liquid to the mixer according to the designed dosage ratio is achieved by adjusting the operating frequency of the cam rotor pump.

11. The method according to claim 6, wherein: In step S4, the wet mixed slurry is sheared at high speed by a rotating mechanism with a rotation speed of 600 to 1000 r / min in a buffer box, thereby foaming evenly to form a foamed wet mixed slurry; Preferably, the foaming rate of the wet mixed slurry in the buffer box is above 280%.

12. The method according to claim 6, wherein: In step S5, the foam wet slurry is continuously pressurized by a two-stage paste pump. The first-stage paste pump pressurizes the foam wet slurry to 0.5-1.5 MPa, and the second-stage paste pump pressurizes the foam wet slurry pressurized by the first-stage paste pump to 7-10 MPa.

13. The method according to claim 6, wherein: In step S6, the high pressure wet slurry is continuously cooled to -15°C to -20°C in a coil having a length of 80 to 120 m.

14. The method according to claim 6, wherein: In step S6, a cooling medium is provided in the continuous cooling tank, and the cooling medium is liquid carbon dioxide at -15°C to -20°C. The coil is immersed in the cooling medium, and the continuous cooling amount of the high-pressure wet slurry is 0.8m 3 / min or above.

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