A system and method for continuous sand addition in a carbon dioxide dry sand fracturing

Abstract

The application provides a system and method for continuous sand adding in carbon dioxide dry sand fracturing. The system comprises a feeding screw, a storage box, a metering conveying screw, a spraying pipe, a mixer, a buffer tank, a paste pump, a continuous cooling tank, a coil pipe and a main pipe junction, etc. The method comprises the following steps: raw material conveying, base fluid pump injection, proportioning wet mixing, wet mixed slurry buffering, pressure boosting pumping, continuous cooling and mixed conveying, etc. The system and method can realize continuous sand adding in carbon dioxide dry sand fracturing, accurately control sand ratio, and realize unlimited sand amount, large sand ratio and large displacement dry sand fracturing construction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas field development, and particularly relates to a system and method for continuous sanding of carbon dioxide dry sand fracturing. BACKGROUND

[0002] As a new waterless fracturing technology, the carbon dioxide dry sand fracturing technology uses liquid carbon dioxide as a fracturing medium, has low damage, easy flowback, easy fracture formation, environmental protection and other advantages. The carbon dioxide dry sand fracturing technology is particularly suitable for low-pressure low-permeability, dense and strong water-sensitive complex rock formations, has good effect on reservoirs with serious oil and gas layer pollution and low water content, and can greatly improve single well production.

[0003] CN106640024A discloses a sealed sand mixing device and method. The method adds proppant into the sealed sand mixing device before construction, seals the sealed sand mixing tank, then adds liquid carbon dioxide for pressurization and cooling, and cools the proppant to the same temperature as the liquid carbon dioxide. The sanding amount of one construction is the effective volume of the sealed sand mixing device. If secondary sanding is required, the liquid carbon dioxide in the sealed sand mixing tank needs to be discharged first, then the pressure in the tank is released, and after the pressure is released, the sealed sand mixing tank is opened to add proppant again, and then pressurization and cooling are performed before sanding operation can be performed. The preparation method of the dry sanding liquid determines that it can only be used for quantitative sanding of carbon dioxide dry sand fracturing construction, and cannot be used for unlimited sanding, large sand ratio and large displacement construction, which limits the popularization and application of the carbon dioxide dry sand fracturing technology.

[0004] In order to maximize the production potential of the carbon dioxide dry sand fracturing technology, it is particularly important to develop a system and method for continuous sanding of carbon dioxide dry sand fracturing, so that the construction scale is not affected by the volume of the sealed sand mixing device. SUMMARY

[0005] To solve the above technical problems, the purpose of the present application is to provide a system and method for continuous sanding of carbon dioxide dry sand fracturing. The system and method can realize continuous sanding construction of carbon dioxide dry sand fracturing.

[0006] To achieve the above purpose, the first aspect of the present application provides a system for continuous sanding of carbon dioxide dry sand fracturing, which comprises: a storage tank, a spray pipe, a mixer, a buffer tank, a paste pump, a continuous cooling tank, a coil pipe and a main pipe junction.

[0007] The stirring machine is provided with a proppant inlet, a base fluid inlet and a wet mixed slurry outlet; the outlet of the storage box is communicated with the proppant inlet of the stirring machine; the spray pipe is arranged in the stirring machine and communicated with the base fluid inlet; the wet mixed slurry outlet of the stirring machine is communicated with the inlet of the buffer box; the outlet of the buffer box is communicated with the inlet of the paste pump; the coil pipe is arranged in the continuous cooling tank; the outlet of the paste pump is communicated with the inlet of the coil pipe; and the outlet of the coil pipe is communicated with the main pipe.

[0008] According to the specific embodiment of the present application, preferably, the system further comprises a feeding screw, and the outlet of the feeding screw is communicated with the inlet of the storage box.

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

[0010] According to the specific embodiment of the present application, preferably, the system further comprises a metering conveying screw, and the outlet of the storage box is communicated with the proppant inlet of the stirring machine through the metering conveying screw. More preferably, the accuracy of the metering conveying screw is ±0.5%.

[0011] In the system, preferably, the base fluid inlet of the stirring machine is connected with a base fluid conveying pipeline, and a metering pump is arranged on the base fluid conveying pipeline. More preferably, the metering pump is a cam rotor pump.

[0012] In the system, preferably, the stirring machine comprises a double-screw stirring machine.

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

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

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

[0016] In the system, preferably, the continuous cooling tank is provided with a cooling valve for regulating the temperature in the continuous cooling tank.

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

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

[0019] The second aspect of the present application provides a method for continuous sanding in carbon dioxide dry sand fracturing, which uses the system for continuous sanding in carbon dioxide dry sand fracturing described above to carry out continuous sanding in carbon dioxide dry sand fracturing, and the method comprises the following steps:

[0020] S1, raw material conveying: continuously conveying the proppant to the storage tank, and conveying the proppant in the storage tank to the mixer according to the designed proportion of the amount;

[0021] S2, base fluid pump injection: while step S1 is being performed, the base fluid is measured according to the designed proportion of the amount and then sprayed into the mixer;

[0022] S3, proportioning and wet mixing: the proppant and the base fluid are mixed in the 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 tank, and the wet mixed slurry is sheared at high speed in the buffer tank to uniformly foam and form a foamed wet mixed slurry;

[0024] S5, booster pumping: the foamed wet mixed 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, mixing and conveying: the high-pressure and low-temperature wet mixed slurry enters the main pipe manifold and mixes with the liquid carbon dioxide in the main pipe manifold to continuously form a carbon dioxide dry sand fracturing fluid, and the carbon dioxide dry sand fracturing fluid is conveyed to the fracturing truck through the main pipe manifold for continuous sanding construction.

[0027] In the method described above, preferably, in step S1, the proppant comprises 20-100 mesh proppant for fracturing.

[0028] In the method described above, preferably, in step S1, the proppant is continuously conveyed to the storage tank by the feeding screw.

[0029] In the method described above, preferably, in step S1, the proppant in the storage tank is conveyed to the mixer according to the designed proportion of the amount by a high-precision metering conveying screw.

[0030] In the method described above, preferably, in step S2, the base fluid comprises a carbon dioxide dry sand fracturing special viscosity enhancer.

[0031] In the above method, preferably, in step S2, the base fluid is pumped into the stirring machine in a designed amount ratio 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 high-speed sheared in the buffer tank by a rotating mechanism with a rotating speed of 600-1000 r / min, and then uniformly foamed to form the foamed wet mixed slurry.

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

[0034] In the above method, preferably, in step S5, the foamed wet mixed slurry is continuously pressurized by a two-stage paste pump, the first-stage paste pump pressurizes the foamed wet mixed slurry to 0.5-1.5 MPa, and the second-stage paste pump pressurizes the foamed wet mixed 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 mixed slurry is continuously cooled to -15℃ to -20℃ in the coil pipe with a length of 80-120 m.

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

[0037] The present application provides a system and method for continuous sand adding in carbon dioxide dry sand fracturing.

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

[0039] (1) The continuous preparation of dry sand fracturing fluid is realized by the continuous pumping of the wet mixed slurry from normal pressure to high pressure and the continuous rapid cooling of the wet mixed slurry from normal temperature to low temperature;

[0040] (2) The proportion of the proppant and the base fluid can be ensured by adjusting the metering conveying screw and the metering pump, and the accurate control of the sand ratio can be realized;

[0041] (3) can take advantage of the low temperature characteristics of liquid carbon dioxide, continuously cooling the foam wet mixed slurry formed by the proppant and the base fluid to a set temperature, simplifying the system structure while greatly reducing the overall power consumption of the system;

[0042] (4) to realize the low pressure end injection of the base fluid (thickening agent), completely solve the problem of additional increase of a base fluid (thickening agent) dedicated pump truck for high pressure end injection, while ensuring the high sand carrying capacity of liquid carbon dioxide in the ground main manifold;

[0043] (5) can accurately control the pressure and temperature of the wet mixed slurry, ensure that the liquid carbon dioxide in the mixing and conveying step remains in a liquid state, and the generated sand fracturing fluid fully meets the continuous construction requirements of carbon dioxide dry sand fracturing with large sand ratio, large sand volume and large displacement. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The structure diagram of the system for continuous sanding of carbon dioxide dry sand fracturing is provided for the specific embodiment of the present application.

[0045] Figure 2 The structure diagram of the spiral groove on the outer surface of the coil in the specific embodiment of the present application.

[0046] Figure 3 The flowchart of the method for continuous sanding of carbon dioxide dry sand fracturing is provided for the specific embodiment of the present application.

[0047] BRIEF DESCRIPTION OF DRAWINGS

[0048] 1-Storage tank; 2-Spraying 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, objectives and beneficial effects of the present application, the technical solutions of the present application will be described in detail below, but it should not be understood as limiting the scope of the present application.

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

[0051] In addition, unless otherwise specified and limited, "connection" should be understood broadly, which includes direct connection and indirect connection through another component.

[0052] In the case of no conflict, the skilled person in the art can combine the relevant technical features in each of the following embodiments according to the actual situation to achieve the corresponding technical effects, and specific combinations are not described here.

[0053] In one aspect, the present application provides a system for continuous sanding in carbon dioxide dry sand fracturing, and the structure of the system is shown in Figure 1 .

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

[0055] The mixer 3 is provided with a proppant inlet, a base fluid inlet, and a wet mixed slurry outlet. The outlet of the storage tank 1 is in communication with the proppant inlet of the mixer 3. The spray pipe 2 is arranged in the mixer 3 and is in communication with the base fluid inlet of the mixer 3. The wet mixed slurry outlet of the mixer 3 is in communication with the inlet of the buffer tank 4. The outlet of the buffer tank 4 is in communication with the inlet of the paste pump 5. The continuous cooling tank 6 is provided with the coil pipe 7. The outlet of the paste pump 5 is in communication with the inlet of the coil pipe 7. The outlet of the coil pipe 7 is in communication with the main pipe junction 8.

[0056] In some specific embodiments, the system further comprises a feeding screw 9, and the outlet of the feeding screw 9 is in communication with the inlet of the storage tank 1.

[0057] In some specific embodiments, the feeding screw 9 is a double screw feeding machine. Specifically, the double screw feeding machine comprises two screw feeding pipes and a transmission mechanism, etc. Each screw feeding pipe is provided with an inlet and an outlet at both ends, and a hopper is arranged at the inlet. The transmission mechanism is used to drive the two screw feeding pipes to operate. The transmission mechanism can comprise a motor. The double screw feeding machine can also selectively comprise a support mechanism for supporting the double screw feeding machine. The present application preferably adopts a double screw feeding machine, which can alternately feed sand, that is, after one screw feeding pipe completes feeding, the other screw feeding pipe continues to feed, while the hopper of the first screw feeding pipe is filled with proppant, which is continuously circulated to realize continuous feeding.

[0058] In some specific embodiments, the system further comprises a metering and conveying screw 10, and the outlet of the storage tank 1 is in communication with the proppant inlet of the mixer 3 through the metering and conveying screw 10. Preferably, the accuracy of the metering and conveying screw 10 is ±0.5%.

[0059] In some specific embodiments, the base fluid inlet of the mixer 3 is connected with a base fluid conveying pipeline, and a metering pump 11 is arranged on the base fluid conveying pipeline. Preferably, the metering pump 11 is a cam rotor pump.

[0060] In some embodiments, the stirring machine 3 is a double helix stirring machine. The present application preferably adopts a double helix stirring machine to preliminarily stir and mix the proppant and the base fluid uniformly to form the wet mixed slurry.

[0061] In some embodiments, the buffer tank 4 is provided with a rotating mechanism. The rotating mechanism can adopt the rotating mechanism in the prior art, and the present application does not specially limit the structure thereof, as long as it can realize high-speed shearing of the wet mixed slurry to form the foamed wet mixed slurry.

[0062] In some 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 series-connected paste pumps are respectively referred to as a first-stage paste pump and a second-stage paste pump. Preferably, the first-stage paste pump and the second-stage paste pump are both reciprocating paste pumps. The present application preferably adopts two-stage reciprocating paste pumps, which can continuously pressurize the foamed wet mixed slurry through rapid reciprocating motion.

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

[0064] In some embodiments, the continuous cooling tank 6 is provided with a cooling valve 12 for regulating the temperature in the continuous cooling tank 6. Specifically, by adjusting the opening degree of the cooling valve 12, the liquid carbon dioxide cooling medium can be regulated to flow out of the continuous cooling tank 6 in the form of gas phase to regulate the temperature in the continuous cooling tank 6, thereby realizing continuous and rapid cooling of the foamed wet mixed slurry.

[0065] In some embodiments, as shown in Figure 2 the outer surface of the coil pipe 7 is provided with a spiral groove 13. The cross section of the spiral groove 13 is U-shaped, and the included angle between the two side walls of the spiral groove 13 is 45-60° (the angle shown in Figure 2 is 60°). Specifically, the spiral groove 13 on the outer surface of the coil pipe 7 can be made by a lathe. The spiral groove 13 can greatly increase the contact area between the coil pipe 7 and the liquid carbon dioxide cooling medium, accelerate the temperature transfer, and ensure that the wet mixed slurry realizes rapid cooling when flowing in the coil pipe 7.

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

[0067] On the other hand, the present application provides a method for continuously adding sand in carbon dioxide dry sand fracturing, which adopts the above-mentioned system for continuously adding sand in carbon dioxide dry sand fracturing to continuously add sand in carbon dioxide dry sand fracturing, and the flow process is as shown in Figure 3 .

[0068] The method comprises the following steps:

[0069] S1, raw material conveying: continuously conveying the proppant to the storage tank 1, and conveying the proppant in the storage tank 1 to the mixer 3 according to the designed proportion of the amount;

[0070] S2, base fluid pump injection: while step S1 is being performed, the base fluid is measured according to the designed proportion of the amount and then sprayed into the mixer 3;

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

[0072] S4, wet mixed slurry buffering: the wet mixed slurry in the mixer 3 enters the buffer tank 4, and the wet mixed slurry is sheared at high speed in the buffer tank 4 to uniformly foam to form a foamed wet mixed slurry;

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

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

[0075] S7, mixing and conveying: the high-pressure and low-temperature wet mixed slurry enters the main pipe manifold 8, mixes with the liquid carbon dioxide in the main pipe manifold 8, continuously forms a carbon dioxide dry sand fracturing fluid, and is conveyed to the fracturing truck through the main pipe manifold 8 for continuous sanding operation.

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

[0077] In some specific embodiments, in step S1, the proppant is continuously conveyed to the storage tank 1 through the feeding screw 9.

[0078] In some specific embodiments, in step S1, the proppant in the storage tank 1 is conveyed to the mixer 3 according to the designed proportion of the amount through the metering conveying screw 10.

[0079] In some specific embodiments, in step S2, the base fluid comprises a carbon dioxide dry sand fracturing special viscosity enhancer. The carbon dioxide dry sand fracturing special viscosity enhancer can adopt the 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 of the carbon dioxide dry sand fracturing fluid in the pipeline.

[0080] In some embodiments, in step S2, the base fluid is pumped into the mixer in a designed amount ratio by adjusting the operating frequency of the cam rotor pump. Preferably, the operating frequency of the cam rotor pump is controlled to be 15-50 Hz.

[0081] In some embodiments, in step S4, the wet mix slurry is high-speed sheared in the buffer tank 4 by a rotating mechanism with a rotating speed of 600-1000 r / min, and then uniformly foamed to form a foamed wet mix slurry.

[0082] In some embodiments, in step S4, the foaming rate of the wet mix slurry in the buffer tank 4 is above 280%.

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

[0084] In some embodiments, in step S6, the high-pressure wet mix slurry is continuously cooled to -15℃ to -20℃ in the coil pipe with a length of 80-120 m.

[0085] In some embodiments, in step S6, a cooling medium is arranged in the continuous cooling tank 6, the cooling medium is liquid carbon dioxide at -15℃ to -20℃, and the coil pipe 7 is immersed in the cooling medium to continuously cool the high-pressure wet mix slurry, and the continuous cooling amount of the high-pressure wet mix slurry is above 0.8 m 3 / min.

[0086] The technical solutions of the present application are specifically illustrated by the following examples, but the present application is not limited to these examples, and various modifications can be made within the scope of the gist of the present application.

[0087] Example 1

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

[0089] The outlet of the feeding screw 9 is communicated with the inlet of the storage tank 1; the inlet of the metering conveying screw 10 is communicated with the outlet of the storage tank 1; the agitator 3 is provided with a proppant inlet, a base fluid inlet and a wet mixed slurry outlet; the outlet of the metering conveying screw 10 is communicated with the proppant inlet of the agitator 3; the base fluid inlet of the agitator 3 is connected with a base fluid conveying pipeline, and a metering pump 11 is arranged on the base fluid conveying pipeline; the spray pipe 2 is arranged in the agitator 3 and communicated with the base fluid inlet; the wet mixed slurry outlet of the agitator 3 is communicated with the inlet of the buffer tank 4; the outlet of the buffer tank 4 is communicated with the inlet of the paste pump 5; the coil pipe 7 is arranged in the continuous cooling tank 6; the cooling medium is arranged in the continuous cooling tank 6, the cooling medium is liquid carbon dioxide, the coil pipe 7 is immersed in the cooling medium from the inlet to the outlet, so as to realize the continuous cooling of the high-pressure wet mixed slurry; the continuous cooling tank 6 is provided with a cooling valve 12, the cooling valve 12 is used for regulating the temperature in the continuous cooling tank 6; the outlet of the paste pump 5 is communicated with the inlet of the coil pipe 7; the outlet of the coil pipe 7 is communicated with the main pipe junction 8.

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

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

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

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

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

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

[0096] In the embodiment, the volume of the continuous cooling tank 6 can be 25-30m 3 , and the length of the coil pipe 7 arranged in the continuous cooling tank 6 can be 120m, and the nominal diameter (DN) can be 114.3mm.

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

[0098] Embodiment 2

[0099] The embodiment provides a method for continuous sand adding in carbon dioxide dry sand fracturing, which adopts the system provided in the embodiment 1 to continuously add sand in carbon dioxide dry sand fracturing.

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

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

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

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

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

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

[0106] ​S6, continuous cooling: the continuous and uniform high-pressure wet slurry flows in the 120m long coil pipe 7 in the continuous cooling tank 6, during the flowing process, the high-pressure wet slurry in the coil pipe 7 exchanges heat with the liquid carbon dioxide outside the coil pipe 7 at-15℃ to-20℃, the temperature in the continuous cooling tank 6 is regulated by adjusting the opening of the cooling valve 12, the high-pressure wet slurry is continuously and rapidly cooled to-15℃ to-20℃, and the continuous cooling amount of the high-pressure wet slurry is 0.92m 3 / min;

[0107] S7, mixed delivery: the high-pressure and low-temperature continuous wet slurry is formed at the outlet of the coil pipe 7, and enters the main pipe manifold 8, mixes with the liquid carbon dioxide in the main pipe manifold 8, continuously forms the carbon dioxide dry sand fracturing fluid, the pressure of the carbon dioxide dry sand fracturing fluid is 2.5MPa, the temperature is-15℃ to-20℃, and the carbon dioxide dry sand fracturing fluid is delivered to the fracturing truck through the main pipe manifold 8 for continuous sanding operation.

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

[0109] In the embodiment, in step S2, the base fluid includes a carbon dioxide dry sand fracturing special viscosity-raising agent. The carbon dioxide dry sand fracturing special viscosity-raising agent can use the viscosity-raising agent 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 of the carbon dioxide dry sand fracturing fluid in the pipeline.

[0110] The system and method of the above embodiment can realize continuous sanding operation of carbon dioxide dry fracturing, accurately control the sand ratio, and continuously pump the proppant with a displacement of ≥1.0m 3 / min, and a continuous pumping amount of ≥100m 3 , which realizes the dry sand fracturing operation with unlimited sand amount, large sand ratio and large displacement.

[0111] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and here it is impossible to enumerate all the embodiments, and any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A system for continuous sand feeding in dry carbon dioxide fracturing, the system comprising: Storage tanks, spray pipes, mixers, buffer tanks, paste pumps, continuous cooling tanks, coils, and main pipe manifolds; The mixer is equipped with a proppant inlet, a base liquid inlet, and a wet slurry outlet; the outlet of the storage tank is connected to the proppant inlet of the mixer; the spray pipe is located inside 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 tank; the outlet of the buffer tank is connected to the inlet of the paste pump; the continuous cooling tank is equipped with the coil; 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. The buffer tank is equipped with a rotating mechanism, which can achieve high-speed shearing of the wet slurry to form foamed wet slurry; The continuous cooling tank is provided with a cooling medium, which is liquid carbon dioxide, and the coil is immersed in the cooling medium. The continuous cooling tank is equipped with a cooling valve, which is used to regulate the temperature inside the continuous cooling tank.

2. The system according to claim 1, wherein, The system further includes a feeding screw, the outlet of which is connected to the inlet of the storage bin.

3. The system according to claim 2, wherein, The feeding screw includes a twin-screw feeder.

4. The system according to claim 1, wherein, The system further includes a metering conveying screw, the outlet of the storage tank being connected to the proppant inlet of the mixer via the metering conveying screw.

5. The system according to claim 4, wherein, The accuracy of the metering and conveying screw is ±0.5%.

6. The system according to claim 1, wherein, The mixer has a base liquid inlet connected to a base liquid delivery pipeline, and a metering pump is installed on the base liquid delivery pipeline.

7. The system according to claim 6, wherein, The metering pump is a cam rotor pump.

8. The system according to claim 1, wherein, The mixer includes a twin-helix mixer.

9. The system according to claim 1, wherein, The ointment pump includes a two-stage ointment pump, which consists of two ointment pumps connected in series.

10. The system according to claim 1, wherein, The outer surface of the coil is machined with spiral grooves.

11. The system according to claim 10, wherein, The cross-section of the spiral groove is U-shaped, and the included angle between the extension lines of the two sidewalls of the spiral groove is 45~60°.

12. The system according to claim 1, wherein, The length of the coil is 80~120m.

13. A method for continuous proppant addition in dry carbon dioxide fracturing, wherein the method employs the system for continuous proppant addition in dry carbon dioxide fracturing as described in any one of claims 1-12, and the method comprises the following steps: S1. Raw material conveying: The proppant is continuously conveyed to the storage tank, and the proppant in the storage tank is conveyed to the mixer according to the designed dosage ratio; S2, Base Liquid Pumping: While step S1 is being performed, the base liquid is metered according to the designed dosage ratio and then sprayed into the mixer; S3, Wet Mixing: The proppant and base liquid are mixed in a mixer according to the designed ratio to form a wet slurry; S4. Wet Slurry Buffer: The wet slurry in the mixer enters the buffer tank, where it is sheared at high speed and foamed evenly to form a foamed wet slurry. S5. Booster pumping: The foam wet slurry in the buffer tank is continuously pressurized and pumped to the continuous cooling tank by the paste pump. S6. Continuous cooling: The high-pressure wet slurry flows in the coils in the continuous cooling tank to complete the continuous cooling. S7. Mixed Transport: High-pressure, low-temperature wet slurry enters the main manifold and mixes with the liquid carbon dioxide in the main manifold to continuously form carbon dioxide dry fracturing fluid, which is then transported to the fracturing truck for continuous sand addition.

14. The method according to claim 13, wherein, In step S1, the proppant includes 20-100 mesh fracturing proppant.

15. The method according to claim 13, wherein, In step S1, the proppant is continuously conveyed to the storage tank by a feeding screw.

16. The method according to claim 15, wherein, In step S1, the proppant in the storage tank is delivered to the mixer according to the designed dosage ratio through a high-precision metering conveying screw.

17. The method according to claim 13, wherein, In step S2, the base liquid includes a viscosity enhancer specifically for dry carbon dioxide fracturing with sand.

18. The method according to claim 13, wherein, In step S2, the base liquid is pumped to the mixer in a metered manner according to the designed dosage ratio by adjusting the operating frequency of the cam rotor pump.

19. The method according to claim 13, wherein, In step S4, the wet slurry is sheared at high speed by a rotating mechanism with a rotation speed of 600~1000r / min in the buffer tank, thereby uniformly foaming to form foamed wet slurry.

20. The method according to claim 19, wherein, In step S4, the foaming rate of the wet slurry in the buffer tank is above 280%.

21. The method according to claim 13, 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 0.5~1.5MPa, and the second-stage paste pump pressurizes the foam wet slurry pressurized by the first-stage paste pump to 7~10MPa.

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

23. The method according to claim 13, wherein, In step S6, the continuous cooling tank is filled with a cooling medium, which is liquid carbon dioxide at -15°C to -20°C. The coil is immersed in the cooling medium, and the continuous cooling capacity of the high-pressure wet slurry is 0.8 m³. 3 / min or above.

Images