Hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and method for performing pulsed acid fracturing

Abstract

A hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and a method for performing pulsed acid fracturing. The sliding sleeve includes an outer sleeve body (1) and a rotary valve assembly. The outer sleeve body (1) is provided with a flow-through hole (101). The rotary valve assembly includes a valve core (2) and a valve ball (13), and the valve ball (13) is capable of sealing a bore (203). A flow-guiding channel (206) and a flow-diverting channel (207) are formed between an outer wall of the valve core (2) and an inner wall of the outer sleeve body (1). The outer sleeve body (1) has a first position and a second position in an axial direction thereof. When the valve core (2) is in the first position, the outer wall of the valve core (2) seals the flow-through hole (101). An acid fracturing working fluid flowing through the flow-guiding channel (206) is capable of pushing the valve core (2) to move from the first position to the second position along the outer sleeve body (1), and pushing the valve core (2) to continuously rotate at the second position, such that the flow-diverting channel (207) is intermittently communicated with the flow-through hole (101), and the acid fracturing working fluid is ejected from the flow-through hole in the form of hydraulic pulses. The present application can excite hydraulic pulses of an appropriate frequency downhole, and can reduce energy attenuation and promote the creation of a complex fracture network in a formation.

Description

HYDRAULIC PULSE-TYPE DISSOLVABLE STAGED ACID FRACTURING SLIDING SLEEVE AND METHODfor performing pulsed acid fracturing RELATED APPLICATIONS[1] The present application claims priority to the Chinese Patent Application NO. 202311719439.5, filed on December 14, 2023, which is hereby incorporated by reference in its entirety. TECHNICAL FIELD[2] The present application relates to the technical field of oil and natural gas exploitation, and further, to a downhole tool for acid fracturing in oil and natural gas drilling and production, and in particular, to a hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and a method for performing pulsed acid fracturing. BACKGROUND[3] Acid fracturing is an important measure for increasing production and injection in carbonate rock reservoirs. For acid fracturing in horizontal wells, the vertical well stimulation techniques are often directly applied to perform bullhead acid fracturing, horizontal well coiled tubing fixed-point acidizing, or localized acid fracturing. In recent years, with the breakthroughs in the development of staged completion tools and jetting tools, staged stimulation techniques for horizontal wells have advanced rapidly, and they can generally be divided into five types, namely, limited-entry stimulation, mechanical packer isolation, coiled tubing, hydraulic jetting, and chemical isolation. Among these, mechanical packer isolation staged acid fracturing is currently the mainstream technique for staged acid fracturing in horizontal wells. Since carbonate rock reservoirs are different from sandstone reservoirs in that they have the characteristics such as greater reservoir thickness and stronger heterogeneity, during the stimulation of carbonate rock reservoirs, the acid fluid would preferentially enter the high-permeability layers, resulting in an insufficient utilization of the low-permeability layers. Moreover, the wormholes created during the stimulation of carbonate rock reservoirs would further increase the permeability difference between the high-permeability and low-permeability layers, leading to an ineffective stimulation of the low-permeability layers that are critically important for the production increasing effect of oil wells. Therefore, for acid fracturing stimulation of tight oil and gas resources such as carbonate rocks, the most important thing is to promote the formation of complex fracture networks while ensuring fracture propagation.[4] The combination of the hydraulic pulse effect with the acid fracturing techniques to form a pulse acid fracturing process has obvious results. The hydraulic pulse effect generates continuous pulse stress waves that act on the fracture surfaces where they are continuously reflected and superimposed. The formation rocks undergo fatigue damage under the action of the alternating loads of the hydraulic pulses, which can significantly reduce the strength of the formation rocks. On one hand, this can lower the formation fracture pressure; on the other hand, the pulse effect changes the stress state on the surface of the formation rock, which contributes to the formation of complex fracture networks. Furthermore, the pulse acid fracturing can further dissolve and corrode the created fractures, thereby improving the fracture conductivity and promoting the formation of complex fracture networks.[5] Currently, conventional pulse acid fracturing includes two methods. One is to form a pulse effect by varying the displacement and pump pressure using surface fracturing pumps, which act on the stimulation layers. That is, during acid injection, by controlling the displacement to change alternately, the acid fluid is caused to generate hydraulic shock waves at the wellhead, forcing a water hammer phenomenon to occur in the fluid (that is, the fluid velocity increases sharply or drops sharply within a short period of time). Due to the sudden change in velocity of the acid fluid, the injection pressure is allowed to suddenly rise or fall, creating alternating rising and falling pressures in the tubing. The shock waves propagate and act on the walls of the oil reservoir rocks, performing alternating disturbance and oscillatory shearing, which may produce micro-fractures in the reservoir rocks. Meanwhile, the hydraulic shock pressure can cause the fluid to flow rapidly, playing a role in flushing the pore channels and carrying blockages away from the pore channels, that is, forming a "dynamic unblocking" process, thereby achieving the goal of deep unblocking or pulse acid fracturing.[6] The other method is to run a hydraulic pulse generating tool into the well, which excites hydraulic pulses downhole that act on the formation rocks. One kind of percussive oscillator consists of multiple stages of percussion rupture discs, steel balls, a percussion chamber, and a check valve. During the construction, a pumper truck applies pressure to the tubing at the wellhead. When the wellhead pressure rises to a level at which the sum of it and the pressure generated by the liquid column in the tubing is greater than the bursting pressure of a rupture disc, the rupture disc bursts. At this point, the high-pressure fluid in the wellbore transforms into a high-velocity fluid and enters the percussion chamber, and then flows out of the percussion chamber through the check valve, and in this way a water hammer vibration treatment on the formation is completed. Since the water hammer vibration pressure is greater than the fracture pressure of the formation, multiple irregular fractures would be generated at the instant of the water hammer vibration on the formation. Subsequently, multiple stages of steel balls are successively dropped to perform multiple water hammer vibration treatments on the formation, which can deepen the fractures. After the water hammer vibration treatments of the formation are completed, an acid fluid is injected to complete the acid fracturing of the formation.[7] However, the above two pulse acid fracturing methods each have their own deficiencies. For the method of performing pulse acid fracturing by controlling the construction pressure with surface fracturing pumps, the pulse pressure is excited and generated at the ground surface, and the pressure wave would have experienced significant energy attenuation by the time it reaches the formation rock. Meanwhile, the frequent change in pump displacement also places higher demands on the service life and performance of the fracturing pumps. In addition, researches show that for pulse acid fracturing, the effect is more significant when the pulse frequency is within a certain range (e.g., 18-20 Hz). However, it is very difficult to achieve pressure fluctuations within this frequency range merely by controlling the surface pump unit. For the downhole percussive oscillator, it adopts ball-dropping to excite hydraulic pulses, and the stage difference between the balls limits the number of times of the action of hydraulic pulses. Moreover, since the tool is difficult to retrieve after the construction, the necking portion of the sliding sleeve obstructs the subsequent running of tools into the oil and gas well, causing difficulties for the later production and maintenance of the well.[8] To this end, the applicant, based on years of experiences and practices in the relevant industries, proposes a hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and a pulse acid fracturing operation method to overcome the shortcomings of the prior art. SUMMARY[9] An object of the present application is to provide a hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and a method for performing pulsed acid fracturing, which can ensure the downhole excitation of hydraulic pulses of an appropriate frequency during acid fracturing of carbonate rocks, reduce energy attenuation, increase the proportion of effective energy, and promote the creation of complex fracture networks in the formation, and at the same time can simplify the construction process and shorten the construction period. Moreover, after the acid fracturing operation is completed, a full-bore wellbore environment can be created, which provides favorable wellbore conditions for subsequent downhole operations.

[10] The above object of the present application can be realized by the following technical solutions.

[11] The present application provides a hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve, used for delivering an acid fracturing working fluid in the form of hydraulic pulses, including an outer sleeve body and a rotary valve assembly.

[12] The outer sleeve body is provided with a flow-through hole in communication with its interior.

[13] The rotary valve assembly includes a valve core, a valve ball, and a flow-guiding ring. the valve core is a cylindrical structure open at both ends. The valve core has a bore therein that communicates with its two open ends. The valve core and the flow-guiding ring are both located within the outer sleeve body, and the valve ball is located within the bore and capable of sealing the bore.

[14] The flow-guiding ring is provided with a plurality of flow-guiding holes, and is located upstream of the valve core in a flow direction of the acid fracturing working fluid. A flow-guiding channel and a flow-diverting channel are formed between an outer wall of the valve core and an inner wall of the outer sleeve body. The flow-guiding channel is in a helical shape. The outer sleeve body has at least a first position and a second position in an axial direction thereof. When the valve core is in the first position, the outer wall of the valve core seals the flow-through hole. The flow-guiding holes are used for altering the flow direction of the acid fracturing working fluid introduced into the outer sleeve body and guiding the acid fracturing working fluid into the flow-guiding channel. The acid fracturing working fluid flowing through the flow-guiding channel is capable of pushing the valve core to move from the first position to the second position along the sliding-sleeve outer cylinder, and pushing the valve core to continuously rotate in the second position for a preset duration, such that when the valve core is in the second position, the flow-diverting channel is intermittently communicated with the flow-through hole, and the acid fracturing working fluid flowing from the flow-guiding channel to the flow-diverting channel is ejected from the flow-through hole in the form of hydraulic pulses.

[15] The valve ball is a dissolvable ball body that is wholly or surface-dissolvable in the acid fracturing working fluid, and the valve ball is used for being at least partially dissolved after an acid fracturing operation is completed to open the bore.

[16] In an exemplary embodiment of the present application, a plurality of helical flow-guiding ribs are provided on the outer wall of the valve core, and the plurality of flow-guiding ribs are distributed along a circumferential direction of the valve core, such that a flow-guiding channel is formed between each two adjacent flow-guiding ribs and the inner wall of the outer sleeve body.

[17] In an exemplary embodiment of the present application, a plurality of flow-diverting ribs in a block or strip shape are provided on the outer wall of the valve core, and the plurality of flow-diverting ribs are distributed along the circumferential direction of the valve core, such that a flow-diverting channel is formed between each two adjacent flow-diverting ribs and the inner wall of the outer sleeve body. A width of the flow-diverting rib in the circumferential direction of the valve core is greater than a width of the flow-through hole in a circumferential direction of the outer sleeve body, and a length of the flow-diverting rib in an axial direction of the valve core is greater than a length of the flow-through hole in an axial direction of the outer sleeve body.

[18] In an exemplary embodiment of the present application, the number of the flow-guiding ribs is greater than the number of the flow-diverting ribs.

[19] In an exemplary embodiment of the present application, there is a plurality of flow-through holes, and the plurality of flow-through holes are arranged at intervals in the circumferential direction of the outer sleeve body.

[20] In an exemplary embodiment of the present application, the flow-guiding ring is arranged above the valve core and is movable along the axial direction of the outer sleeve body, and the plurality of flow-guiding holes are distributed along a circumferential direction of the flow-guiding ring.

[21] In an exemplary embodiment of the present application, the flow-guiding holes are inclined holes. A first inflow angle α is formed between a central axis of each of the flow-guiding holes and a radial direction of the outer sleeve body. A second inflow angle β is formed between an extension direction of each of the flow-guiding ribs and the radial direction of the outer sleeve body. The first inflow angle α and / or the second inflow angle β are used for adjusting a driving force of the acid fracturing working fluid on the valve core, so as to change a rotational speed of the valve core.

[22] In an exemplary embodiment of the present application, the flow-guiding ring includes a funnel-shaped flow-guiding section and a cylindrical connecting section. A tapered end of the flow-guiding section is connected to the connecting section, and the plurality of the flow-guiding holes are distributed along a circumferential direction of the flow-guiding section, with connecting ribs separating adjacent flow-guiding holes.

[23] In an exemplary embodiment of the present application, a mounting groove is provided at a bottom of the connecting section in a circumferential direction thereof. An annular first receiving groove is provided on a bottom wall of the mounting groove. A plurality of first rolling balls are rotatably embedded in an end of the valve core close to the flow-guiding ring, and at least a portion of each of the plurality of first rolling balls is rollably embedded in the first receiving groove.

[24] A needle roller assembly is provided in the mounting groove, and the flow-guiding ring is connected to the valve core via the first rolling balls and the needle roller assembly, such that the valve core is rotatable relative to the flow-guiding ring in the circumferential direction of the outer sleeve body.

[25] In an exemplary embodiment of the present application, a conical transition step is provided on an inner wall of the bore, and the valve ball is seated against the transition step.

[26] In an exemplary embodiment of the present application, at least two dynamic sealing assemblies are provided between the outer wall of the valve core and the inner wall of the outer sleeve body. When the valve core is in the first position, the two dynamic sealing assemblies are respectively located on two sides of the flow-through hole in an axial direction of the outer sleeve body.

[27] In an exemplary embodiment of the present application, at least two sealing grooves are provided at intervals along an axial direction of the valve core, the dynamic sealing assemblies are disposed in the corresponding sealing grooves, and the dynamic sealing assemblies are in sealing contact with an outer wall of the outer sleeve body.

[28] In an exemplary embodiment of the present application, when the valve core is in the first position, the outer sleeve body is connected to the valve core via a positioning screw, and the acid fracturing working fluid flowing through the flow-guiding channel is capable of pushing the valve core to shear off the positioning screw and to move from the first position to the second position.

[29] In an exemplary embodiment of the present application, the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve further includes a support ring fixed within the outer sleeve body, an annular second receiving groove is provided on an end of the valve core close to the support ring, and a plurality of second rolling balls are rotatably embedded in an end face of the support ring facing the valve core. When the valve core is in the second position, at least a portion of the second rolling ball is rollably embedded in the second receiving groove, such that the valve core is rotatable relative to the support ring in a circumferential direction of the outer sleeve body.

[30] In an exemplary embodiment of the present application, the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve further includes a first connector and a second connector, and both ends of the outer sleeve body are connected to the first connector and the second connector, respectively, to connect the outer sleeve body to an tubing.

[31] In an exemplary embodiment of the present application, both ends of the outer sleeve body are in threaded connection with the first connector and the second connector, respectively. At least one sealing ring is respectively provided at connection positions between the outer sleeve body and the first connector and between the outer sleeve body and the second connector.

[32] In an exemplary embodiment of the present application, the outer sleeve body, the first connector, and the second connector are all made of a corrosion-resistant, high-strength metal material, and inner walls of the outer sleeve body, the first connector, and / or the second connector are provided with an anti-corrosion layer.

[33] In an exemplary embodiment of the present application, the valve core, the flow-guiding ring, and the support ring are all made of a metal material that is dissolvable or corrodible in the acid fracturing working fluid. A rate at which the valve core, the flow-guiding ring, and the support ring dissolve or are corroded in the acid fracturing working fluid is less than a rate at which the valve ball dissolves in the acid fracturing working fluid.

[34] In an exemplary embodiment of the present application, surfaces of the valve core, the flow-guiding ring, and the support ring are each provided with an anti-corrosion layer.

[35] The present application provides method for performing pulsed acid fracturing, which uses the above-mentioned hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve to fracture an oil and gas reservoir by delivering an acid fracturing working fluid in pulses, the method including:

[36] Step S1: connecting a plurality of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves in series via tubing and running them to a preset position in a wellbore, a packer being installed on the tubing between any two adjacent hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves;

[37] Step S2: dropping the valve ball to seal the internal bore of the valve core in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve;

[38] Step S3: pumping the acid fracturing working fluid into the wellbore and increasing a pump pressure, the acid fracturing working fluid driving the valve core in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve to disconnect from the outer sleeve body, causing the valve core to move from a first position to a second position within the outer sleeve body of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve; and

[39] Step S4: the valve core rotating continuously at the second position for a preset duration, causing the acid fracturing working fluid to be ejected in the form of hydraulic pulses from the flow-through hole on the outer sleeve body into the oil and gas reservoir.

[40] In an exemplary embodiment of the present application, the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves, the plurality of packers, and the tubing are connected to form a tool string. In a direction from a wellhead to a bottom of the wellbore, inner diameters of the bores in the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves sequentially decrease, such that the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves correspond to valve balls of different diameters, respectively.

[41] In an exemplary embodiment of the present application, before the Step S1, the outer sleeve body, the valve core, and the flow-guiding ring in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve are assembled, with the valve core positioned at the first position in the outer sleeve body to seal the flow-through hole.

[42] In an exemplary embodiment of the present application, in the Step S2, if a pressure in the wellbore is detected to be continuously increasing by a pump pressure detection device, it indicates that the valve ball has been sealed in place.

[43] In an exemplary embodiment of the present application, after the Step S4, at least a portion of the valve ball is dissolved, and the transition step within the bore in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve is dissolved, causing the bore to be opened.

[44] From the above, the features and advantages of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve and the pulse acid fracturing operation method of the present application are as follows:

[45] A valve core and a flow-guiding ring are provided in the outer sleeve body, a valve ball is provided in the bore of the valve core, the bore is sealed by the valve ball, and a flow-guiding channel and a flow-diverting channel are formed between an outer wall of the valve core and an inner wall of the outer sleeve body. When the valve core is in the first position in the outer sleeve body, the outer wall of the valve core seals the flow-through hole. During flowing of an acid fracturing working fluid, which is fed into the outer sleeve body, through the flow-guiding channel, the acid fracturing working fluid can push the valve core to move from the first position to the second position in an axial direction of the outer sleeve body, and after the valve core reaches the second position, the acid fracturing working fluid can push the valve core to continuously rotate at the second position for a preset duration. In the state of continuous rotation of the valve core, the flow-diverting channel can be intermittently communicated with the flow-through hole, causing the acid fracturing working fluid to be ejected in the form of hydraulic pulses from the flow-through hole, thereby achieving fracturing of the oil and gas reservoir and promote the creation of a complex fracture network in the formation.

[46] In the flow direction of the acid fracturing working fluid, since the flow-guiding ring is provided upstream of the valve core and a plurality of flow-guiding holes are provided on the flow-guiding ring, when the bore is in a state of being sealed by the valve ball, the flow-guiding holes, the flow-guiding channel, and the flow-diverting channel form the only passage through which the acid fracturing working fluid can flow to the flow-through hole. Therefore, during actual operation, the frequency of the hydraulic pulses can be altered through the flow-guiding ring and / or a fluid pumping pressure on the acid fracturing working fluid, so as to ensure that hydraulic pulses of an appropriate frequency can be excited. Since the hydraulic pulses are excited at the target layer downhole, energy attenuation can be reduced, the proportion of effective energy can be increased, and the fracturing effect can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[47] The following Figures are only intended to illustrate and explain the present application and do not limit the scope of the present application. In the Figures:

[48] FIG. 1 is a schematic structural diagram of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[49] FIG. 2 is a schematic structural diagram of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application in a working state;

[50] FIG. 3 is an axonometric view of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[51] FIG. 4 is a cross-sectional view taken along line A-A in FIG. 1;

[52] FIG. 5 is a cross-sectional view taken along line B-B in FIG. 2;

[53] FIG. 6 is a first schematic structural diagram of the flow-guiding ring in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[54] FIG. 7 is a second schematic structural diagram of the flow-guiding ring in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[55] FIG. 8 is a partial enlarged view of the connection position between the flow-guiding ring and the valve core in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[56] FIG. 9 is an exploded view of the rotary valve assembly in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[57] FIG. 10 is a schematic structural diagram of the protective sleeve in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[58] FIG. 11 is an exploded view of the outer sleeve body, the first connector, and the second connector in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application;

[59] FIG. 12 is an assembly schematic diagram of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application in an operating state.

[60] FIG. 13 is a schematic structural diagram of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application in a completed operating state;

[61] FIG. 14 is a schematic diagram of inflow angles of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application in an operating state; and

[62] FIG. 15 is a schematic diagram showing adjustment of the rotational speed of the rotary valve assembly in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve of the present application.

[63] Reference numerals in the present application:1: outer sleeve body;101: flow-through hole;2: valve core;201: flow-guiding rib;202: flow-diverting rib;203: bore;204: transition step;205: second receiving groove;206: flow-guiding channel;207: flow-diverting channel;208: sealing groove;3: first connector;4: second connector;5: flow-guiding ring;501: flow-guiding hole;502: connecting rib;503: flow-guiding section;504: connecting section;6: positioning screw;7: dynamic sealing assembly;8: second rolling ball;9: support ring;901: second receiving groove;10: protective sleeve;1001: limiting hole;1002: boss;11: set screw;12: dissolvable screw;13: valve ball;14: needle roller assembly;15: limiting sleeve;16: first rolling ball;100: hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve;200: tubing;300: packer;400: oil and gas reservoir. DESCRIPTION OF EMBODIMENTS

[64] For a clearer understanding of the technical features, objectives, and effects of the present application, specific embodiments of the present application will now be described with reference to the accompanying drawings.

[65] In the present application, directional terms such as upper, lower, top, bottom, inner, and outer are determined in accordance with the directions of upper, lower, top, bottom, inner, and outer in FIG. 1, and are intended to illustrate the positional relationships between various structural components, rather than to limit the specific directions thereof, which is hereby explained collectively.

[66] Embodiment 1

[67] As shown in FIGS. 1 to 12, the present application provides a hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve, which is used for delivering an acidic acid fracturing working fluid in the form of hydraulic pulses.

[68] The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve includes a outer sleeve body 1 and a rotary valve assembly. The outer sleeve body 1 is a cylindrical tube (i.e., a straight tube) open at both ends. A flow-through hole 101 in communication with an interior of the outer sleeve body 1 is provided on a cylinder wall of the outer sleeve body 1. The two ends of the outer sleeve body 1 are respectively used to connect to a tubing 200. The rotary valve assembly includes a valve core 2, a valve ball 13, and a flow-guiding ring 5. The valve core 2 is cylindrical (i.e., straight cylindrical) open at both ends, and has a bore 203 therein that communicates with its two open ends. The valve core 2 and the flow-guiding ring 5 are both located within the outer sleeve body 1. The valve ball 13 is located within the bore 203 and capable of sealing the bore 203. The flow-guiding ring 5 is provided with a plurality of flow-guiding holes 501, and is located upstream of the valve core 2 in a flow direction of the acid fracturing working fluid. The acid fracturing working fluid needs to first flow through the flow-guiding holes 501 on the flow-guiding ring 5 before reaching the valve core 2. In an axial direction of the outer sleeve body 1, a flow-guiding channel 206 and a flow-diverting channel 207 are formed between an outer wall of the valve core 2 and an inner wall of the outer sleeve body 1. In the flow direction of the acid fracturing working fluid, the flow-guiding channel 206 is located upstream of the flow-diverting channel 207. The acid fracturing working fluid needs to first flow through the flow-guiding channel 206 before reaching the flow-diverting channel 207. The flow-guiding channel 206 is helical in shape. The outer sleeve body 1 has at least a first position and a second position in an axial direction thereof (in the flow direction of the acid fracturing working fluid, the first position is located upstream of the second position). When the valve core 2 is in the first position, the outer wall of the valve core 2 seals the flow-through hole 101, and the interior of the outer sleeve body 1 is blocked. When the acid fracturing working fluid is pumped into the outer sleeve body 1, the flow-guiding holes 501 can alter the flow direction of the acid fracturing working fluid and divert it into the flow-guiding channel 206. The acid fracturing working fluid flowing through the flow-guiding channel 206 is capable of pushing the valve core 2 to move from the first position to the second position, and pushing the valve core 2 to continuously rotate at the second position for a preset duration, so that when the valve core 2 is in the second position, the flow-diverting channel 207 is intermittently communicated with the flow-through hole 101 (that is, during the rotation of the valve core 2, the flow-diverting channel 207 periodically communicates with the flow-through hole 101, and when the flow-diverting channel 207 is communicated with the flow-through hole 101, the acid fracturing working fluid is ejected from the flow-through hole 101, thereby forming hydraulic pulses). The acid fracturing working fluid flowing from the flow-guiding channel 206 to the flow-diverting channel 207 is ejected, in the form of hydraulic pulses, from the flow-through hole 101. The valve ball 13 is a dissolvable ball body that is wholly or surface-dissolvable in the acid fracturing working fluid. The valve ball 13 is used for being at least partially dissolved after the acid fracturing operation is completed, thereby opening the bore 203, increasing the size of the production channel, and helping to improve the acid fracturing effect.

[69] In the present application, the valve ball 13 is used during acid fracturing. Before acid fracturing starts, the valve ball 13 is dropped into the bore 203 to seal the bore 203, thereby achieving pressure buildup within the bore 203. After the acid fracturing working fluid is pumped in, the pressure pushes the valve core 2 to shear off a positioning screw 6 connecting the valve core 2 to the outer sleeve body 1, causing the valve core 2 to move from the first position to the second position. During this process and the subsequent acid fracturing process, the valve ball 13 remains within the bore 203. After the acid fracturing operation is completed, the valve ball 13dissolves.

[70] In the present application, the preset duration during which the valve core 2 continuously rotates at the second position corresponds to the duration of hydraulic fracturing of the oil and gas reservoir 400 via hydraulic pulses. This duration may be set according to the type of the oil and gas reservoir 400 and the actual fracturing conditions of the oil and gas reservoir 400. The present application gives no specific limitation on the preset duration.

[71] In the present application, any conventional acid fluids capable of dissolving and corroding the fractures in the formations may be used as the acid fracturing working fluid. After pumping is stopped and pressure is released, the dissolved and corroded fractures will not fully close. The present application gives no specific limitation on the specific type of the acid fracturing working fluid.

[72] In the present application, the valve core 2 and the flow-guiding ring 5 are disposed within the outer sleeve body 1, and the valve ball 13 is disposed within the bore 203 of the valve core 2 to seal the bore 203. The flow-guiding channel 206 and the flow-diverting channel 207 are formed between the outer wall of the valve core 2 and the inner wall of the outer sleeve body 1. When the valve core 2 is in the first position in the outer sleeve body 1, the outer wall of the valve core 2 seals the flow-through hole 101. As the acid fracturing working introduced into the outer sleeve body 1 flows through the flow-guiding channel 206, it pushes the valve core 2 to move from the first position to the second position in an axial direction of the outer sleeve body 1. After the valve core 2 reaches the second position, the acid fracturing working fluid drives the valve core 2 to rotate continuously at the second position for a preset duration. While the valve core 2 is rotating, the flow-diverting channel 207 intermittently communicated with the flow-through hole 101, causing the acid fracturing working fluid to be ejected from the flow-through hole 101 in the form of hydraulic pulses, thereby achieving fracturing of the oil and gas reservoir 400 and promoting the creation of a complex fracture network in the formation.

[73] Since the flow-guiding ring 5 is disposed upstream of the valve core 2 in the flow direction of the acid fracturing working fluid, and is provided with the plurality of flow-guiding holes 501, when the bore 203 is sealed by the valve ball 13, the flow-guiding holes 501, the flow-guiding channel 206, and the flow-diverting channel 207 form the only pathway through which the acid fracturing working fluid can flow to the flow-through hole 101. Therefore, during actual operations, the frequency of the hydraulic pulses can be adjusted through the flow-guiding ring 5 and / or the fluid pumping pressure on the acid fracturing working fluid from the ground, ensuring that hydraulic pulses of an appropriate frequency are generated. Since the hydraulic pulses are generated at the target formation within the wellbore, energy attenuation can be reduced, the proportion of effective energy can be increased, and the fracturing effect can be improved.

[74] In an optional embodiment of the present application, as shown in FIGS. 1 to 3 and 11, the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve further includes a first connector 3 and a second connector 4. A top end of the outer sleeve body 1 is connected to the first connector 3, and a bottom end of the outer sleeve body 1 is connected to the second connector 4. The outer sleeve body 1 is connected to the tubing 200 via the first connector 3 and the second connector 4.

[75] Furthermore, as shown in FIGS. 1 and 2, the two ends of the outer sleeve body 1 are in threaded connection with the first connector 3 and the second connector 4, respectively. At least one sealing ring is respectively provided at connection positions between the outer sleeve body 1 and the first connector 3 and between the outer sleeve body 1 and the second connector 4, so as to achieve sealing of the connection surfaces. Specifically, the outer sleeve body 1 as a whole is in an elongated cylindrical shape. A top inner wall and a bottom inner wall of the outer sleeve body 1 are each provided with a short-pitch trapezoidal straight thread and a sealing surface. An inner wall of an upper portion of the first connector 3 is provided with a tapered tubing internal thread for connection with the tubing 200 upstream of the outer sleeve body 1. An outer wall of a lower portion of the first connector 3 is provided with a short-pitch trapezoidal straight thread and two or more sealing grooves. The short-pitch trapezoidal straight thread of the first connector 3 is used to connect to the internal thread at the top of the outer sleeve body 1. A sealing ring is provided in the sealing groove to achieve sealing at the connection surface between the first connector 3 and the outer sleeve body 1. The structure of the second connector 4 is similar to that of the first connector 3. The second connector 4 is in threaded connection with the tubing 200 located downstream of the outer sleeve body 1.

[76] In an optional embodiment of the present application, the outer sleeve body 1, the first connector 3, and the second connector 4 are all made of a corrosion-resistant, high-strength metal material, and the inner walls of the outer sleeve body 1, the first connector 3, and / or the second connector 4, as well as the surfaces that can contact the acid fracturing working fluid, are all provided with an anti-corrosion layer. The anti-corrosion layer can be produced through treatment processes such as chromium plating, tungsten carbide spraying, or carbonitriding, so as to enhance the ability to resist acid corrosion, thereby prolonging the service life of the outer sleeve body 1, the first connector 3, and the second connector 4 during acid fracturing operation, avoiding premature failure or damage thereof due to corrosion by the acid fracturing working fluid, and avoiding affecting the effect of the acid fracturing operation.

[77] Furthermore, the outer sleeve body 1, the first connector 3, and the second connector 4 can be made of alloy steels such as 40CrMnMoA, 42CrMo, or 4330V after quenching and tempering treatment, but are not limited thereto.

[78] In an optional embodiment of the present application, as shown in FIGS. 1 to 3 and 9, a plurality of helical flow-guiding ribs 201 are provided on the outer wall of the valve core 2. The plurality of flow-guiding ribs 201 are distributed along a circumferential direction of the valve core 2, such that a flow-guiding channel 206 is formed between each two adjacent flow-guiding ribs 201 and the inner wall of the outer sleeve body 1. Specifically, the flow-guiding ribs 201 are in a helical shape with a certain angle (clockwise direction). In the flow direction of the acid fracturing working fluid, an angle between a tangential direction at a starting point of the flow-guiding rib 201 and a radial direction of the outer sleeve body 1 (the horizontal direction in FIG. 14) is taken as a helix angle of the flow-guiding rib 201, shown as angle β in FIG. 14. This angle βalso serves as an inflow angle of the flow-guiding channel 206. The degree of this angle β can be adjusted according to actual needs, thereby achieving the purpose of adjusting the driving force and the rotational speed of the valve core 2 driven by the acid fracturing working fluid. The presence of the flow-guiding ribs 201 enables the acid fracturing working fluid to generate a radial force by impacting the flow-guiding ribs 201, thereby driving the valve core 2 to rotate in a circumferential direction of the outer sleeve body 1.

[79] In an optional embodiment of the present application, as shown in FIGS. 3 to 5 and 9, a plurality of flow-diverting ribs 202 in a block or strip shape are provided on the outer wall of the valve core 2. The flow-diverting ribs 202 extend in an axial direction of the valve core 2, and the plurality of flow-diverting ribs 202 are distributed at intervals and uniformly in a circumferential direction of the valve core 2, such that a flow-diverting channel 207 is formed between each two adjacent flow-diverting ribs 202 and the inner wall of the outer sleeve body 1. A width of the flow-diverting rib 202 in the circumferential direction of the valve core 2 needs to be greater than a width of the flow-through hole 101 in a circumferential direction of the outer sleeve body 1, and a length of the flow-diverting rib 202 in an axial direction of the valve core 2 needs to be greater than a length of the flow-through hole 101 in an axial direction of the outer sleeve body 1, so as to ensure that the flow-diverting ribs 202 can effectively and instantaneously seal the flow-through hole 101 on the outer sleeve body 1 during the continuous rotation of the valve core 2.

[80] Furthermore, the number of the flow-guiding ribs 201 is greater than the number of the flow-diverting ribs 202. Exemplarily, the number of the flow-guiding ribs 201 is twice the number of the flow-diverting ribs 202. This helps increase the driving force of the acid fracturing working fluid on the valve core 2 and improve the effect of the pulsed ejection of the acid fracturing working fluid.

[81] In an optional embodiment of the present application, as shown in FIGS. 1, 5 and 11, there is a plurality of flow-through holes 101. The flow-through holes 101 are located in a middle portion of the outer sleeve body 1. The plurality of flow-through holes 101 are arranged at intervals and uniformly in a circumferential direction of the outer sleeve body 1. The flow-through holes 101 are elongated circular through-holes extending in an axial direction of the outer sleeve body 1. The number of the flow-through holes 101 may be, but is not limited to 5 to10. In a specific embodiment of the present application, the number of the flow-through holes 101 is 6, and they are used for ensuring that the sliding sleeve, in a working state, can form the only passage through which the acid fracturing working fluid can flow to the flow-through hole 101, so as to ensure that the acid fluid (acid fracturing working fluid) delivered from the ground surface can enter the wellbore annulus and the oil and gas reservoir 400.

[82] In an optional embodiment of the present application, as shown in FIGS. 1, 2, 6 and 7, the flow-guiding ring 5 is disposed above the valve core 2 and is movable along the axial direction of the outer sleeve body 1, and the plurality of flow-guiding holes 501 are distributed along a circumferential direction of the flow-guiding ring 5.

[83] Furthermore, as shown in FIGS. 7 and 14, the flow-guiding holes 501 may be inclined holes. The number of the flow-guiding holes 501 is the same as the number of the flow-guiding ribs 201. A first inflow angle α is formed between a central axis of each of the flow-guiding holes 501 and a radial direction of the outer sleeve body 1 (the horizontal direction in FIG. 14). A second inflow angle β is formed between an extension direction of each of the flow-guiding ribs 201 and a radial direction of the outer sleeve body 1 (the horizontal direction in FIG. 14). The first inflow angle α and / or the second inflow angle β are used for adjusting a driving force exerted by the acid fracturing working fluid on the valve core 2, thereby altering the driving force on the valve core 2 and consequently changing the rotational speed of the valve core 2.

[84] During actual operations, the rotational characteristics of the valve core 2 can be adjusted by modifying the degree of the first inflow angle α of the flow-guiding holes 501 to regulate the degree of the outflow angle of the fluid flowing out of the flow-guiding ring 5, in conjunction with the different degrees of the second inflow angle β of the flow-guiding ribs 201 on the valve core 2. As shown in FIG. 15, for different operating conditions and formation conditions, the appropriate combination of inflow angle parameters for the rotary valve assembly (i.e., the degree of the first inflow angle α of the flow-guiding holes 501 and the degree of the second inflow angle β of the flow-guiding ribs 201) may be selected according to a pre-obtained rotational characteristic curve of the rotary valve assembly, so as to obtain a rotational speed and hydraulic pulse frequency meeting the requirements of the actual operating requirements. Based on the output rotational speed of the valve core 2 under different displacement and inflow angle conditions, combined with the corresponding theoretical calculations, finite element simulations, and experimental data, it is possible to obtain the relationship curve between the displacement of the fluid, the inflow angle, and the rotational speed of the valve core 2, thereby determining an optimal parameter range. During the operation, the operation displacement of the ground fracturing pumper unit may also be adjusted within an appropriate range to achieve secondary adjustment of the rotational speed of the valve core 2 and the hydraulic pulse frequency, thereby obtaining an optimal hydraulic pulse frequency.

[85] In this embodiment, as shown in FIGS. 6 and 7, the flow-guiding ring 5 includes a flow-guiding section 503 in a funnel shape and a connecting section 504 in a straight cylindrical shape. A tapered end of the flow-guiding section 503 is connected to the connecting section 504. The plurality of flow-guiding holes 501 are distributed along a circumferential direction of the flow-guiding section 503. Adjacent flow-guiding holes 501 are separated by the connecting ribs 502. This structure can both improve the connection strength and corrosion resistance between the flow-guiding section 503 and the connecting section 504 and achieve the change of the first inflow angle α of the fluid after passing through the flow-guiding ring 5 through the angle of the inclined holes, thereby increasing the impact force of the fluid on the flow-guiding ribs 201 on the valve core 2 and improving the hydraulic pulse output capability. The number of the flow-guiding holes 501 and the number of the connecting ribs 502 may each be 3 to 5.

[86] Furthermore, as shown in FIG. 8, an mounting groove is provided on an inner side wall of the bottom of the connecting section 504 in a circumferential direction thereof. A first receiving groove in an annular shape is provided on a bottom wall of the mounting groove in a circumferential direction thereof. A plurality of semi-circular grooves having a semi-circular cross-section are provided on an end of the valve core 2 close to the flow-guiding ring 5 in a circumferential direction of the valve core 2. A first rolling ball 16 is rotatably embedded in each of the plurality of semi-circular grooves, and at least a portion of each of the plurality of first rolling balls 16 is rollably embedded in the first receiving groove. In addition, a needle roller assembly 14 is provided in the mounting groove. The flow-guiding ring 5 is connected to the valve core 2 via the first rolling balls 16 and the needle roller assembly 14. The plurality of first rolling balls 16 and the needle roller assembly 14 play the role of a bearing, so that the valve core 2 is rotatable with relative to the flow-guiding ring 5 in a circumferential direction of the outer sleeve body 1.

[87] Furthermore, as shown in FIG. 8, a limiting sleeve 15 is provided in the mounting groove, and an outer wall of the limiting sleeve 15 is connected to a side wall of the mounting groove. The needle roller assembly 14 in an annular shape is provided between an inner wall of the limiting sleeve 15 and an upper outer wall of the valve core 2, so that the needle roller assembly 14 is limited. The needle roller assembly 14 is formed by a plurality of needle rollers uniformly and circumferentially distributed, and is installed as a whole on a top end of the valve core 2, ensuring that the valve core 2 can rotate smoothly. The needle roller assembly 14 is limited by the limiting sleeve 15, ensuring that during the rotation of the valve core 2, the needle roller assembly 14 does not rotate with the valve core 2 and does not disengage from the valve core 2.

[88] In an optional embodiment of the present application, as shown in FIGS. 1 and 2, a transition step 204 in a tapered shape is provided on an inner wall of the bore 203 in a circumferential direction thereof, so that the bore 203 forms a vertical bore structure with a larger diameter at an upper portion, a smaller diameter at a lower portion, and a transition connection realized by the transition step 204 therebetween. The valve ball 13 is seated against the transition step 204. An outer wall of the valve ball 13 fits and abuts against the wall surface of the transition step 204.

[89] In a specific embodiment of the present application, the transition step 204 and the body of the valve core 2 may be made as separate structures, which are connected after molding. The transition step 204 is made of the same material as the valve ball 13, so that after the acid fracturing operation is completed, both the valve ball 13 and the transition step 204 dissolve, thereby opening the bore 203, while the valve core 2 and other structural components remain undissolved.

[90] Furthermore, each hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 serves as a fracturing tool. In the flow direction of the acid fracturing working fluid, a plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100, a plurality of packers 300, and the tubing 200 are connected to form a tool string. In a direction from a wellhead to a bottom of the wellbore, the inner diameters of the bores 203 of the corresponding valve cores 2 in the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 sequentially decrease, so that the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 correspond to valve balls 13 of different diameters, respectively, thereby achieving staged fracturing of the rocks. The number of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 and the diameters of the corresponding bores 203 may be selected according to the actual staged fracturing working conditions. In general, a diameter difference (stage difference) between the valve balls 13 may be selected as 1 / 4 inch, 1 / 8 inch, etc.

[91] Furthermore, an angle between the wall surface of the transition step 204 and a horizontal direction is exemplarily 30° to 60°, so as to ensure that an effective seal is formed when the valve ball 13 seats against the transition step 204.

[92] In an optional embodiment of the present application, as shown in FIGS. 1 and 2, at least two dynamic sealing assemblies 7 are provided between an outer wall of the valve core 2 and an inner wall of the outer sleeve body 1. When the valve core 2 is in the first position, in an axial direction of the outer sleeve body 1, the two dynamic sealing assemblies 7 are located on two sides of the flow-through hole 101, respectively (that is, a distance between the two dynamic sealing assemblies 7 in the axial direction of the outer sleeve body 1 is greater than a length of the flow-through hole 101 in the axial direction of the outer sleeve body 1), so as to ensure that the flow-through hole 101 can be sealed. When the valve core 2 moves to the second position, the two dynamic sealing assemblies 7 move to the same side of the flow-through hole 101, as shown in FIG. 2.

[93] Specifically, as shown in FIGS. 1, 2 and 9, sealing grooves 208 in one-to-one correspondence with the dynamic sealing assemblies 7 are provided at intervals in an axial direction of the valve core 2. The dynamic sealing assemblies 7 are disposed in the corresponding sealing grooves 208, and are in sealing contact with the outer wall of the outer sleeve body 1. The dynamic sealing assemblies 7 may adopt existing dynamic sealing mechanisms, such as those in which a skeleton and an O-shaped sealing ring on the skeleton are provided in the sealing groove 208, as long as they can ensure sealing between the outer wall of the valve core 2 and the inner wall of the outer sleeve body 1 and do not affect the movement of the valve core 2 during its rotation. The present application gives no limitation on the specific structure of the dynamic sealing assemblies 7.

[94] In an optional embodiment of the present application, as shown in FIGS. 1 and 2, when the valve core 2 is in the first position, the outer sleeve body 1 is connected to the valve core 2 via a positioning screw 6. The acid fracturing working fluid flowing through the flow-guiding channel 206 is capable of pushing the valve core 2 to shear off the positioning screw 6, and pushing the valve core 2 to rotate in a circumferential direction of the outer sleeve body 1.

[95] Specifically, there is a plurality of positioning screws 6. The plurality of positioning screws 6 are arranged at intervals in a circumferential direction of the valve core 2. Each positioning screw 6 connects the cylinder wall of the outer sleeve body 1 to a corresponding flow-diverting rib 202 on the valve core 2, so as to ensure that the valve core 2 and the outer sleeve body 1 are firmly fixed in the initial state.

[96] In an optional embodiment of the present application, as shown in FIGS. 1, 2, 9 and 10, the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 further includes a support ring 9 located within the outer sleeve body 1. The support ring 9 is connected to the outer sleeve body 1 via a dissolvable screw 12. A second receiving groove 205 in an annular shape is provided on an end of the valve core 2 close to the support ring 9. A plurality of second rolling balls 8 are rotatably embedded in an end face of the support ring 9 facing the valve core 2. When the valve core 2 is in the second position, at least a portion of the second rolling ball 8 is rollably embedded in the second receiving groove 205, so that the valve core 2 is rotatable circumferentially relative to the support ring 9along the outer sleeve body 1.

[97] Specifically, as shown in FIGS. 1, 2, 9 and 10, the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 further includes a protective sleeve 10 in an annular shape, located within the outer sleeve body 1. A plurality of semi-circular grooves is provided on the end face of the support ring 9 facing the valve core 2 in a circumferential direction of the support ring 9. The second rolling balls 8 are rotatably provided in the plurality of semi-circular grooves, respectively. A plurality of limiting holes 1001 are provided on the protective sleeve 10 in a circumferential direction thereof. The diameter of the limiting hole 1001 is smaller than the diameter of the second rolling ball 8. The protective sleeve 10 covers the top of the support ring 9 and is connected o it via a set screw 11. The plurality of limiting holes 1001 are in one-to-one correspondence with the plurality of semi-circular grooves. At least a portion of an upper portion of the second rolling ball 8 protrudes from the limiting hole 1001. The second receiving groove 205 is provided on the end of the valve core 2 close to the support ring 9 in a circumferential direction of the valve core 2. The second receiving groove 205 has a semi-circular cross-section. When the valve core 2 is in the second position, the at least a portion of the upper portion of the second rolling ball 8 is rollably embedded in the second receiving groove 205. The protective sleeve 10 limits the second rolling balls 8 while ensuring that the second rolling balls 8 can rotate freely without being restrained.

[98] In the present application, the valve ball 13 is a dissolvable ball body that is wholly or surface-dissolvable in the acid fracturing working fluid, so that after the acid fracturing operation is completed, the valve ball 13 is at least partially dissolved to open the bore 203. The valve ball 13 is in a spherical shape as a whole, and is made of a metal material (which may be, but is not limited to, a magnesium alloy) that is rapidly dissolvable in the acid fracturing working fluid. The diameter of the valve ball 13 depends on the inner diameter of the bore 203 at the position of the transition step 204. Furthermore, the diameter of the valve ball 13 is determined according to the number of stages of the sliding sleeves for staged fracturing. In general, the diameter difference (stage difference) between the valve balls 13 may be selected as 1 / 4 inch, 1 / 8 inch, etc. The dropped valve ball 13 falls into the bore 203 of the valve core 2 under the action of the fluid, and finally seals the bore 203. The valve ball 13 may be a solid ball, a hollow ball, or a ball body coated on the outside with dissolvable rubber. The valve ball 13 is designed solely to ensure temporary (e.g., 3 to 4 hours) sealing of the bore 203 during the acid fracturing operation. After the short-duration acid fracturing operation is completed, the valve ball 13 disintegrates to restore the bore 203 to an open state.

[99] A surface treatment may be performed on the surface of the valve ball 13 (such as using surface treatment processes like electroplating, micro-arc oxidation, and electrostatic powder spraying to form an anti-corrosion layer). Different surface treatments may allow the valve ball 13 to withstand the acid fracturing working fluid for different periods of time. In the actual construction, different surface treatment methods may be selected according to the construction time to achieve the purpose of preventing the dissolvable material of the valve ball 13 from contacting the acid fracturing working fluid, so that the main body (i.e., the portion of the dissolvable material) of the valve ball 13 does not dissolve during the acid fracturing, but can contact the acid fracturing working fluid and rapidly dissolves only when the surface of the valve ball 13 breaks or dissolves in the acid fracturing working fluid after a period of time following the completion of the acid fracturing operation.

[100] In an optional embodiment of the present application, the structural components such as the valve core 2, the flow-guiding ring 5, the support ring 9, the first rolling balls 16, the needle roller assembly 14, the limiting sleeve 15, the protective sleeve 10, the second rolling balls 8, and the dissolvable screw 12 are all made of a metal material (such as a magnesium alloy or aluminum alloy) that is dissolvable in the acid fracturing working fluid or corrodible in a low-concentration acid fluid. Since it is necessary to ensure that the valve ball 13 dissolves first while the rotary valve assembly can still remain and work for a certain period of time within the outer sleeve body 1, it is necessary to ensure that a dissolution or corrosion rate of the structural components such as the valve core 2, the flow-guiding ring 5, the support ring 9, the first rolling balls 16, the needle roller assembly 14, the limiting sleeve 15, the protective sleeve 10, the second rolling balls 8, and the dissolvable screw 12 in the acid fracturing working fluid is less than a dissolution rate of the valve ball 13 in the acid fracturing working fluid.

[101] Furthermore, an anti-corrosion layer may be provided on the surfaces of the structural components such as the valve core 2, the flow-guiding ring 5, the support ring 9, the first rolling balls 16, the needle roller assembly 14, the limiting sleeve 15, the protective sleeve 10, the second rolling balls 8, and the dissolvable screw 12. Specifically, surface treatment processes such as electroplating, micro-arc oxidation, and electrostatic powder spraying may be employed to form the anti-corrosion layers to enhance the ability to resist acid corrosion, thereby ensuring that under a certain temperature and acid fracturing working fluid concentration, the structural components are prevented from premature failure due to corrosion by the acid fracturing working fluid during the acid fracturing operation, which would affect the construction effect. However, after the acid fracturing operation, by adjusting conditions such as the concentration of the acid fracturing working fluid and / or the soaking time, the structural components can be completely dissolved or corroded, thereby restoring the maximum inner diameter of the sliding sleeve. Therefore, the installation thickness and process of the anti-corrosion layers on the surfaces of the rotary valve assembly and its related structural components may be selected in accordance with the working conditions. In general situations, the requirement for the surface acid corrosion resistance of the structural components is: in a 20% acid fluid (e.g., HCl) at 80°C, the effective working time should be greater than or equal to 72 hours. The requirement for the dissolution or corrodibility of the structural components is: in a 1% acid fluid (e.g., HCl) at 80°C, the time for complete dissolution or corrosion should be less than or equal to 720 hours.

[102] In an optional embodiment of the present application, as shown in FIG. 12, a packer 300 is provided on each of the tubing 200 connected upstream and downstream of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100. The packer 300 may be, but is not limited to, an open hole packer.

[103] The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 of the present application can ensure downhole excitation of hydraulic pulses of an appropriate frequency during acid fracturing of carbonate rocks, and can reduce energy attenuation, increase the proportion of effective energy, promote the creation of complex fracture networks in the formation, simplify the operation process, and shorten the operation period. Compared with the pulse acid fracturing which creates a pulse effect by changing the displacement and pump pressure with surface fracturing pumps, and that which uses a percussive oscillator, the present application has the following features and advantages:

[104] 1. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 can generate hydraulic pulses downhole near the target formation interval, thus avoiding the energy loss caused by long-distance propagation of hydraulic pulses;

[105] 2. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve uses the rotation of the valve core 2 to alternately open and close the flow-through hole 101 on the outer sleeve body 1, causing the flow area of the flow-through hole 101 to vary periodically, thereby generating hydraulic pulses. Since the valve core 2 can rotate at a relatively high speed, the present application can generate efficient hydraulic pulses of 18-20 Hz at an appropriate displacement;

[106] 3. In the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve, the outflow angle and inflow angle of the acid fracturing working fluid can be altered by adjusting the flow-guiding holes 501 on the flow-guiding ring 5 and the angle between the helical flow-guiding ribs 201 on the valve core 2 and the horizontal direction. This allows for the adjustment of the rotational characteristics of the valve core 2, thereby enabling the regulation of the hydraulic pulse frequency under different operating conditions, so as to adapt to different working conditions;

[107] 4. In the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve, the rotary valve assembly can continuously rotate and generate hydraulic pulses within the construction displacement range during acid fracturing, with no time limit on the duration of the hydraulic pulses;

[108] 5. In the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve, the structural components constituting the rotary valve assembly are all made of dissolvable materials and can dissolve on their own within a period of time after the fracturing is completed, which increases the size of the production channel and helps improve the acid fracturing effect. 

[109] Embodiment 2

[110] The present application provides a method for performing pulsed acid fracturing. The method adopts the above-described hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 to fracture an oil and gas reservoir 400 by delivering an acid fracturing working fluid in pulses. The method includes:

[111] Step S1: as shown in FIG. 12, connecting a plurality of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 in series via tubing 200 and lowering them to a preset position in a wellbore, a packer 300 being installed on the tubing 200 between any two adjacent hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100;

[112] Step S2: dropping a valve ball 13 to seal a bore 203 of a valve core 2 in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100;

[113] Step S3: pumping an acid fracturing working fluid into the wellbore and increasing a pump pressure, the acid fracturing working fluid driving the valve core 2 in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 to disconnect from an outer sleeve body 1, the valve core 2 moving from a first position to a second position within the outer sleeve body 1 of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100;

[114] Step S4: the valve core 2 rotating continuously at the second position for a preset duration, causing the acid fracturing working fluid to be ejected, in the form of hydraulic pulses, from a flow-through hole 101 on the outer sleeve body 1 into the oil and gas reservoir 400.

[115] In an optional embodiment of the present application, the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100, the plurality of packers 300, and the tubing 200 are connected to form a tool string. In a direction from a wellhead to a bottom of the wellbore, the inner diameters of the bores 203 in the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 sequentially decrease, so that the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 correspond to valve balls 13 of different diameters, respectively. The number of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves 100 and the diameters of the corresponding bores 203 may be selected according to the actual staged fracturing working conditions. In general, a diameter difference (stage difference) between the valve balls 13 may be selected as 1 / 4 inch, 1 / 8 inch, etc.

[116] In an optional embodiment of the present application, before the Step S1, the outer sleeve body 1, the valve core 2, and the flow-guiding ring 5 in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 are assembled, with the valve core 2 positioned at the first position in the outer sleeve body 1 to seal the flow-through hole 101. At this moment, the valve ball 13 is not dropped.

[117] In an optional embodiment of the present application, in the Step S2, if a pressure in the wellbore is detected to be continuously increasing by a pump pressure detection device, it indicates that the valve ball 13 has been sealed in place.

[118] In an optional embodiment of the present application, after the Step S4, at least a portion of the valve ball 13is dissolved, and the transition step 204 within the bore 203 in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 is dissolved, causing the bore 203 to be opened.

[119] The specific construction process of the present application is as follows:

[120] The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 is assembled, with only the valve ball 13 not being dropped. In an initial state, the valve core 2 is fixedly connected to the outer sleeve body 1 via the positioning screw 6, the valve core 2 cannot rotate relative to the outer sleeve body 1, and the flow-through hole 101 on the outer sleeve body 1 is sealed by the valve core 2. During the operation, the two ends of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 are respectively connected to a tubing 200, and a packer 300 is provided on the tubing 200. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 is lowered to a preset position in a wellbore by a wellhead device. The valve ball 13 is then dropped at the wellhead, and a fluid is pumped from the ground surface to push the valve ball 13 into the bore 203 of the valve core 2, thereby sealing the bore 203. Since the dynamic sealing assemblies 7 are provided between the outer wall of the valve core 2 and the inner wall of the outer sleeve body 1, once the valve ball 13 seals the bore 203, a complete seal is established both upstream and downstream of the valve core 2. At this time, if a surface pump pressure detection device shows an increase in pump pressure, it can be determined that the valve ball 13 is already in a sealing position.

[121] When it is detected that the valve ball 13 is in the sealing position, the displacement of the surface pump unit can be increased to drive the fluid pressure inside the tubing 200 to rise. Under the action of the pressure, the positioning screw 6 connecting the valve core 2 and the outer sleeve body 1 is sheared off, causing the valve core 2 to rotate circumferentially away from its initial position while simultaneously moving axially downward to a position where the flow-diverting channel 207 on the valve core 2 communicates with the flow-through hole 101 on the outer sleeve body 1. At the same time, due to the action of the fluid (acid fracturing working fluid), the valve core 2 rotates continuously, during which process the flow-diverting ribs 202 can periodically block the flow-through hole 101 to generate a hydraulic pulse effect. Thus, hydraulic pulses of a certain frequency can be generated downhole during acid fracturing, achieving the purposes of reducing energy attenuation and increasing the proportion of effective energy, and the creation of a complex fracture network in the formation can be promoted.

[122] After the acid fracturing operation, since the components constituting the rotary valve assembly are all made of dissolvable metal materials, as time passes, these components can dissolve on their own. Alternatively, the components constituting the rotary valve assembly are all made of metal materials that can be rapidly corroded in a low-concentration acid fluid, so that after the construction operation, by injecting a low-concentration acid fluid and soaking for a certain period of time, the components constituting the rotary valve assembly can dissolve rapidly. As shown in FIG. 13, after the components constituting the rotary valve assembly are dissolved, the sliding sleeve completely restores its original inner diameter, allowing the sliding sleeve to remain unobstructed, thereby forming a flow passage for the oil, gas, and water at the bottom of the well.

[123] It should be noted that during construction, the frequency of the hydraulic pulses generated by the pulse-type dissolvable staged acid fracturing sliding sleeve can be adjusted by changing multiple parameters such as the first inflow angle α of the flow-guiding holes 501 on the flow-guiding ring 5, the second inflow angle β of the flow-guiding ribs 201, the number of the flow-diverting ribs 202, and the wellhead displacement. During operation, the construction effect of pulse acid fracturing can also be improved by combining the dual effects of the pressure waves excited by a surface pump unit and the hydraulic pulses excited by the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 located in the wellbore.

[124] The method for performing pulsed acid fracturing of the present application has the same technical effects as the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve 100 described above, which will not be repeated here.

[125] The embodiments described above are only schematic specific embodiments of the present application, and are not intended to limit the scope of the present application. Any equivalent changes and modifications made by a person skilled in the art without departing from the concept and principle of the present application shall fall within the protection scope of the present application.  

Claims

1. A hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve for delivering an acid fracturing working fluid in the form of hydraulic pulses, comprising:an outer sleeve body provided with a flow-through hole in communication with its interior; anda rotary valve assembly comprising a valve core, a valve ball, and a flow-guiding ring, wherein the valve core is a cylindrical structure open at both ends and has a bore communicating with its two open ends, the valve core and the flow-guiding ring are both located within the outer sleeve body, and the valve ball is located within the bore and is capable of sealing the bore;wherein the flow-guiding ring is provided with a plurality of flow-guiding holes, and is located upstream of the valve core in a flow direction of the acid fracturing working fluid; a flow-guiding channel and a flow-diverting channel are formed between an outer wall of the valve core and an inner wall of the outer sleeve body; the flow-guiding channel is in a helical shape; the outer sleeve body has at least a first position and a second position in an axial direction thereof, and when the valve core is in the first position, the outer wall of the valve core seals the flow-through hole; the flow-guiding holes are configured to alter the flow direction of the acid fracturing working fluid introduced into the outer sleeve body and to guide the acid fracturing working fluid into the flow-guiding channel; and the acid fracturing working fluid flowing through the flow-guiding channel is capable of pushing the valve core to move from the first position to the second position along the sliding-sleeve outer cylinder, and pushing the valve core to continuously rotate in the second position for a preset duration, such that when the valve core is in the second position, the flow-diverting channel is intermittently communicated with the flow-through hole, and the acid fracturing working fluid flowing from the flow-guiding channel to the flow-diverting channel is ejected from the flow-through hole in the form of hydraulic pulses;the valve ball is a dissolvable ball body that is wholly or surface-dissolvable in the acid fracturing working fluid, and the valve ball is used for being at least partially dissolved after an acid fracturing operation is completed to open the bore.

2. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein a plurality of helical flow-guiding ribs are provided on the outer wall of the valve core, and the plurality of flow-guiding ribs are distributed along a circumferential direction of the valve core, such that a flow-guiding channel is formed between each two adjacent flow-guiding ribs and the inner wall of the outer sleeve body.

3. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 2, wherein a plurality of flow-diverting ribs in a block or strip shape are provided on the outer wall of the valve core, and the plurality of flow-diverting ribs are distributed along the circumferential direction of the valve core, such that a flow-diverting channel is formed between each two adjacent flow-diverting ribs and the inner wall of the outer sleeve body;a width of the flow-diverting rib in the circumferential direction of the valve core is greater than a width of the flow-through hole in a circumferential direction of the outer sleeve body, and a length of the flow-diverting rib in an axial direction of the valve core is greater than a length of the flow-through hole in an axial direction of the outer sleeve body.

4. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 3, wherein the number of the flow-guiding ribs is greater than the number of the flow-diverting ribs.

5. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 3, wherein there is a plurality of flow-through holes, and the plurality of flow-through holes are arranged at intervals in the circumferential direction of the outer sleeve body.

6. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 2, wherein the flow-guiding ring is arranged above the valve core and is movable along the axial direction of the outer sleeve body, and the plurality of flow-guiding holes are distributed along a circumferential direction of the flow-guiding ring. 7. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 6, wherein the flow-guiding holes are inclined holes, and a first inflow angle α is formed between a central axis of each of the flow-guiding holes and a radial direction of the outer sleeve body;a second inflow angle β is formed between an extension direction of each of the flow-guiding ribs and the radial direction of the outer sleeve body; andthe first inflow angle α and / or the second inflow angle β are used for adjusting a driving force of the acid fracturing working fluid on the valve core, so as to change a rotational speed of the valve core.

8. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 6 or 7, wherein the flow-guiding ring comprises a funnel-shaped flow-guiding section and a cylindrical connecting section, a tapered end of the flow-guiding section is connected to the connecting section, and the plurality of the flow-guiding holes are distributed along a circumferential direction of the flow-guiding section, with connecting ribs separating adjacent flow-guiding holes.

9. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 8, wherein a mounting groove is provided at a bottom of the connecting section in a circumferential direction thereof, an annular first receiving groove is provided on a bottom wall of the mounting groove, a plurality of first rolling balls are rotatably embedded in an end of the valve core close to the flow-guiding ring, and at least a portion of each of the plurality of first rolling balls is rollably embedded in the first receiving groove;a needle roller assembly is provided in the mounting groove, and the flow-guiding ring is connected to the valve core via the first rolling balls and the needle roller assembly, such that the valve core is rotatable relative to the flow-guiding ring in the circumferential direction of the outer sleeve body.

10. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein a conical transition step is provided on an inner wall of the bore, and the valve ball is seated against the transition step.

11. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein at least two dynamic sealing assemblies are provided between the outer wall of the valve core and the inner wall of the outer sleeve body; and when the valve core is in the first position, the two dynamic sealing assemblies are respectively located on two sides of the flow-through hole in an axial direction of the outer sleeve body.

12. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 11, wherein at least two sealing grooves are provided at intervals along an axial direction of the valve core, the dynamic sealing assemblies are disposed in the corresponding sealing grooves, and the dynamic sealing assemblies are in sealing contact with an outer wall of the outer sleeve body.

13. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein when the valve core is in the first position, the outer sleeve body is connected to the valve core via a positioning screw, and the acid fracturing working fluid flowing through the flow-guiding channel is capable of pushing the valve core to shear off the positioning screw and to move from the first position to the second position.

14. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve further comprises a support ring fixed within the outer sleeve body, an annular second receiving groove is provided on an end of the valve core close to the support ring, and a plurality of second rolling balls are rotatably embedded in an end face of the support ring facing the valve core; and when the valve core is in the second position, at least a portion of the second rolling ball is rollably embedded in the second receiving groove, such that the valve core is rotatable relative to the support ring in a circumferential direction of the outer sleeve body.

15. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 1, wherein the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve further comprises a first connector and a second connector, and both ends of the outer sleeve body are connected to the first connector and the second connector, respectively, to connect the outer sleeve body to an tubing.

16. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 15, wherein both ends of the outer sleeve body are in threaded connection with the first connector and the second connector, respectively, and at least one sealing ring is respectively provided at connection positions between the outer sleeve body and the first connector and between the outer sleeve body and the second connector.

17. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 15 or 16, wherein the outer sleeve body, the first connector, and the second connector are all made of a corrosion-resistant, high-strength metal material, and inner walls of the outer sleeve body, the first connector, and / or the second connector are provided with an anti-corrosion layer.

18. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 14, wherein the valve core, the flow-guiding ring, and the support ring are all made of a metal material that is dissolvable or corrodible in the acid fracturing working fluid, and a rate at which the valve core, the flow-guiding ring, and the support ring dissolve or are corroded in the acid fracturing working fluid is less than a rate at which the valve ball dissolves in the acid fracturing working fluid.

19. The hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to claim 18, wherein surfaces of the valve core, the flow-guiding ring, and the support ring are each provided with an anti-corrosion layer.

20. A method for performing pulsed acid fracturing, which uses the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve according to any one of claims 1 to 19 to fracture an oil and gas reservoir by delivering an acid fracturing working fluid in pulses, the method comprising:Step S1: connecting a plurality of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves in series via tubing and running them to a preset position in a wellbore, wherein a packer is installed on the tubing between any two adjacent hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves;Step S2: dropping the valve ball to seal the internal bore of the valve core in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve;Step S3: pumping the acid fracturing working fluid into the wellbore and increasing a pump pressure, wherein the acid fracturing working fluid drives the valve core in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve to disconnect from the outer sleeve body, causing the valve core to move from a first position to a second position within the outer sleeve body of the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve; andStep S4: the valve core rotating continuously at the second position for a preset duration, causing the acid fracturing working fluid to be ejected, in the form of hydraulic pulses, from the flow-through hole on the outer sleeve body into the oil and gas reservoir.

21. The method for performing pulsed acid fracturing according to claim 20, wherein the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves, the plurality of packers, and the tubing are connected to form a tool string; and in a direction from a wellhead to a bottom of the wellbore, inner diameters of the bores in the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves sequentially decrease, such that the plurality of hydraulic pulse-type dissolvable staged acid fracturing sliding sleeves correspond to valve balls of different diameters, respectively.

22. The method for performing pulsed acid fracturing according to claim 20, wherein before the Step S1, the outer sleeve body, the valve core, and the flow-guiding ring in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve are assembled, with the valve core positioned at the first position in the outer sleeve body to seal the flow-through hole.

23. The method for performing pulsed acid fracturing according to claim 20, wherein in the Step S2, if a pressure in the wellbore is detected to be continuously increasing by a pump pressure detection device, it indicates that the valve ball has been sealed in place.

24. The method for performing pulsed acid fracturing according to claim 20, wherein after the Step S4, at least a portion of the valve ball is dissolved, and the transition step within the bore in the hydraulic pulse-type dissolvable staged acid fracturing sliding sleeve is dissolved, causing the bore to be opened. 

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