Deep coal seam pulse hydraulic fracturing device and method

Abstract

The present application is a kind of deep coal seam pulse hydraulic fracturing device and method, the device comprises: ground pulse modulation system, including pulse jet generation device for optical casing, for modulating continuous pumping fracturing fluid into pulse fluid and injecting into wellbore on the ground;Pulse fluid can pulse hydraulic fracturing of coal seam;Downhole pulse modulation system, at least including coiled tubing pulse jet generation device, coiled tubing pulse jet generation device is used to generate pulse jet in the set position in well, and pulse jet can jet fracturing to coal seam.The present application proposes an optimization mechanism based on geology-engineering dessert drilling conditions, through flexible selection of operation mode, realizes the depth coupling of pulse generation device and existing mature fracturing process of deep coal seam, applies cyclic alternating load type shock wave to deep coal seam, makes it stress oscillation, fatigue failure, thereby reduces the crack initiation pressure, promotes the formation of crack network, and is expected to become a new technology for deep coal seam reservoir reconstruction.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to a pulsed hydraulic fracturing device and method for deep coal seams. Background Technology

[0002] Deep coalbed methane refers to natural gas resources in coal seams buried at depths exceeding 1500m. Its abundant resources demonstrate broad exploration and development prospects. Numerous field tests have verified the feasibility of developing deep coalbed methane using large-scale hydraulic fracturing technology. However, compared to shallow and medium-depth coal seams, deep coal seams are characterized by "high geostress, medium to high temperatures, extremely low permeability, strong compressibility, and strong heterogeneity," resulting in high fracturing pressure, high extension pressure, and high closure pressure, making the formation of complex fracture networks difficult. Simultaneously, controlled by sedimentary environment and coal facies evolution, deep coal seams exhibit significant vertical heterogeneity, developing four coal types: bright coal, semi-bright coal, semi-dull coal, and dull coal. These different coal types show significant differences in porosity and permeability characteristics, gas content, and reservoir potential for modification. Among them, bright / semi-bright coal, due to its high vitrinite content, well-developed fractures, superior gas content, strong potential for modification, and significant gas production contribution, can be considered a geological-engineering sweet spot for deep coal seam modification. However, current conventional deep coal seam fracturing techniques have poor targeting and indiscriminate reservoir stimulation, making it urgent to explore efficient fracturing methods adapted to the geological characteristics of deep coal seams.

[0003] Pulsed hydraulic fracturing injects fracturing fluid in a pulsed manner at a specific frequency, applying cyclic alternating load-type shock waves to deep coal seams. This causes stress oscillations and fatigue failure, thereby reducing the initiation pressure, promoting fracture network formation, and overcoming the controlling effect of the in-situ stress field to a certain extent. In existing technologies, most disclosed pulse jet generating devices and methods are designed to improve rock-breaking drilling efficiency or are limited to the drilling environment of coal mine roadways. When directly applied to deep coal seam hydraulic fracturing, they face obstacles such as poor integration compatibility with complex downhole tool strings. Therefore, there is an urgent need in the field for a systematic solution for pulsed hydraulic fracturing devices and methods specifically designed for the geological characteristics of deep coal seams, seamlessly integrated with existing mature fracturing processes, and flexibly adjustable according to geological conditions.

[0004] Therefore, based on years of experience and practice in related industries, the inventor proposes a deep coal seam pulse hydraulic fracturing device and method to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a pulsed hydraulic fracturing device and method for deep coal seams, overcoming the problems of poor targeting and indiscriminate reservoir stimulation in conventional deep coal seam fracturing processes in the prior art. This invention proposes an optimization mechanism based on geological-engineering sweet spot drilling conditions. Through flexible selection of operating modes, it achieves deep coupling between the pulse generator and the existing mature fracturing process for deep coal seams, applying cyclic alternating load shock waves to the deep coal seam to induce stress oscillation and fatigue failure, thereby reducing the fracturing initiation pressure and promoting the formation of fracture networks. It is expected to become a new process for deep coal seam reservoir stimulation.

[0006] The objective of this invention is achieved as follows: a deep coal seam pulse hydraulic fracturing device, comprising:

[0007] A surface pulse modulation system includes a smooth casing pulse jet generator connected between the outlet of a surface high-pressure manifold and the wellhead. The smooth casing pulse jet generator is used to modulate continuously pumped fracturing fluid into a pulse fluid on the surface and inject it into the wellbore; the pulse fluid can perform pulse hydraulic fracturing on the coal seam.

[0008] The downhole pulse modulation system includes at least a coiled tubing pulse jet generator installed in the wellbore. The coiled tubing pulse jet generator is used to generate a pulse jet at a set position in the well, and the pulse jet can perform jet fracturing on the coal seam.

[0009] In a preferred embodiment of the present invention, the pulse jet generator for the optical sleeve includes a first outer shell, the top of which is connected to a hollow first connector for connecting to the outlet of the ground high-pressure manifold; a first inner cavity is provided inside the first outer shell, the top of which is connected to a first inlet, the aperture of which is smaller than the inner diameter of the outlet of the ground high-pressure manifold; a first outlet is connected to the bottom of the first inner cavity; a first self-excited oscillation chamber is provided inside the first inner cavity, the cross-section of which gradually expands from top to bottom, the top of which is connected to the first inlet, and the bottom of which is connected to the first outlet; continuously pumped fracturing fluid forms a pulsed fluid through the first self-excited oscillation chamber.

[0010] In a preferred embodiment of the present invention, a partition structure is provided within the first inner cavity, and an attachment channel is formed between the outer wall of the partition structure and the inner wall of the first outer shell, the top end of the attachment channel being connected to the first inlet; a first self-excited oscillation cavity is provided within the partition structure, the top end of the first self-excited oscillation cavity being connected to the first inlet, and the top end of the first outlet being located at the lower part of the first self-excited oscillation cavity; a turning zone is formed between the bottom end of the first self-excited oscillation cavity, the side wall of the first outlet, and the bottom end of the attachment channel, and the first self-excited oscillation cavity, the turning zone, and the attachment channel are connected to form a closed loop that causes the fracturing fluid to generate periodic self-excited oscillation.

[0011] In a preferred embodiment of the present invention, a closed loop is formed on each side of the first self-excited oscillation cavity, which is respectively set as the first closed loop and the second closed loop, and the first closed loop and the second closed loop are symmetrically arranged; a guide block is provided on the side of the first inlet near the second closed loop, and the guide block can make the fracturing fluid enter the first self-excited oscillation cavity eccentrically close to the first closed loop.

[0012] In the initial state, the fracturing fluid is accelerated at the first inlet to generate a high-speed jet and then enters the first self-excited oscillation chamber eccentrically near the first closed loop. At least a portion of the fracturing fluid flows through the first closed loop to the first inlet, impacting the fracturing fluid entering at the first inlet. At least a portion of the fracturing fluid flows through the second closed loop to the first inlet, impacting the fracturing fluid entering at the first inlet. The internal flow field of the first self-excited oscillation chamber undergoes periodic changes, modulating the continuous fracturing fluid flow into a pulsed fluid on the ground.

[0013] In a preferred embodiment of the present invention, the top of the first outer shell is connected to a hollow first connector, which is used to connect to the outlet of the ground high-pressure manifold.

[0014] In a preferred embodiment of the present invention, the pulse jet generator for coiled tubing includes a second outer shell, within which a second inner cavity is provided. A second inlet communicating with the guide channel is located at a first end of the second inner cavity, and a second outlet is connected to the second end of the second inner cavity. The second inlet is eccentrically positioned and narrows from top to bottom. A guide fluid is located at the first end of the second outer shell, within which an eccentric guide channel is provided, constituting the second inlet. An impeller assembly is located below the second inlet in the second inner cavity, and fracturing fluid flowing into the second inlet forms a pulse jet through the impeller assembly. A second self-excited oscillation chamber is located below the impeller assembly, and this chamber has a variable cross-section and gradually narrows from top to bottom. The bottom end of the second self-excited oscillation chamber is connected to the second outlet. The second self-excited oscillation chamber amplifies the pulse pressure generated by the impeller assembly and generates a pulse jet at the second outlet.

[0015] In a preferred embodiment of the present invention, the pulse jet generator for continuous tubing includes a guide fluid disposed at the top of the second housing, and an eccentric guide channel is disposed within the guide fluid, the guide channel constituting the second inlet.

[0016] In a preferred embodiment of the present invention, the impeller assembly includes an impeller seat, an impeller, an impeller shaft, and a bushing. The impeller seat is fixedly connected to the second housing, and the impeller is rotatably connected to the impeller seat via the impeller shaft and the bushing. The central axis of the impeller shaft is perpendicular to the central axis of the second housing.

[0017] In a preferred embodiment of the present invention, the downhole pulse modulation system further includes matching downhole tools, which include, from top to bottom, a safety joint, a rotary sealing sub, a spray gun, a circulation valve, a packer, an eccentric directional device, and a guide shoe; the coiled tubing pulse jet generator is connected in series between the safety joint and the rotary sealing sub, and the safety joint is used to connect the upper coiled tubing.

[0018] The objective of this invention can also be achieved by providing a deep coal seam pulsed hydraulic fracturing method, implemented using the aforementioned deep coal seam pulsed hydraulic fracturing device, wherein the deep coal seam pulsed hydraulic fracturing method includes:

[0019] Based on the situation where the horizontal wellbore trajectory encounters a geological-engineering sweet spot in a deep coal seam, a surface pulse modulation system is used to modulate the continuously pumped fracturing fluid into a high-power pulse fluid on the surface and inject it into the wellbore to complete the smooth casing pumped bridge plug pulse volume fracturing; or, a downhole pulse modulation system is used to generate a high-frequency pulse jet at a set position in the well to complete the coiled tubing bottom seal drag-tight cutting pulse fracturing.

[0020] In a preferred embodiment of the present invention, the tube-pumped bridge plug pulse volume fracturing includes the following steps:

[0021] Install the optical casing pulse jet generator between the high-pressure manifold outlet and the wellhead;

[0022] The surface pumping equipment is started, and the fluid is modulated by the pulse jet generator in the smooth casing to form a periodically changing pulse jet injected into the wellbore to perform pulse hydraulic fracturing on the target section;

[0023] After the target section is fracturing, the section is segmented using a cable pump bridge plug perforation combined operation method. The above steps are repeated until the volumetric fracturing of all sections is completed.

[0024] In a preferred embodiment of the present invention, the coiled tubing bottom seal drag-driven close-cutting pulse fracturing includes the following steps:

[0025] The downhole pulse modulation system is lowered into the well to the set position via coiled tubing; the bottom packer is then set.

[0026] The ground pumping equipment is started, and the fluid drives the pulse jet generator in the coiled tubing to generate a high-frequency pulsating jet, which is then sprayed through the spray gun to fracturing the coal seam.

[0027] After completing the fracturing of this cluster, raise the tubing to the next cluster's designated position, set the bottom packer, and repeat the above steps to perform cluster-by-cluster fine fracturing.

[0028] As described above, the deep coal seam pulse hydraulic fracturing device and method of the present invention have the following beneficial effects:

[0029] Compared with the prior art, the deep coal seam pulse hydraulic fracturing device and method provided by the present invention uses pulse jets to impact coal and rock, causing stress oscillations and fatigue damage to the coal and rock, deteriorating the matrix strength, promoting the connection of micro-fractures and activating natural fractures and bedding planes, reducing fracturing pressure, and forming a complex fracture network with "multiple horizontal and multiple vertical" fractures.

[0030] In this invention, depending on the application scenario, pulsed hydraulic fracturing of deep coal seams can be performed using either a surface pulse modulation system or a downhole pulse modulation system. In field applications, a pulse jet generator for smooth casing is connected to the outlet of the surface high-pressure manifold, or a pulse jet generator for coiled tubing is lowered to a designated position using coiled tubing. Fracturing fluid is injected in a pulsed manner with a specific frequency, applying cyclic alternating load-type shock waves to the deep coal seam, causing stress oscillations and fatigue failure. This reduces the initiation pressure and promotes fracture network formation, potentially becoming a new technology for deep coal seam reservoir stimulation.

[0031] This invention addresses the challenges of "high ground stress and ultra-low porosity and permeability" in deep coal seams. It proposes an optimized mechanism based on drilling conditions in geological-engineering sweet spots (bright / semi-bright coal), achieving deep coupling between the optical pulse generator and existing mature fracturing technology for deep coal seams. The high-power pulses generated by the surface pulse modulation system help overcome high ground stress, initiating and extending the main fractures; the downhole pulse modulation system, targeting geological-engineering sweet spots, effectively activates primary fractures and bedding, forming a complex fracture network, jointly solving the problems of difficult fracture initiation and fracture creation in deep coal seams. Attached Figure Description

[0032] The following figures are intended only to illustrate and explain the present invention and do not limit the scope of the invention. Wherein:

[0033] Figure 1 This is a schematic diagram of the pulse jet generator for optical sleeves according to the present invention.

[0034] Figure 2 This is a schematic diagram of the fluid flow direction inside the pulse jet generator for optical sleeves of the present invention.

[0035] Figure 3 This is a schematic diagram of the pulse jet generator for continuous tubing according to the present invention.

[0036] Figure 4 This is a schematic diagram of the downhole pulse modulation system of the present invention.

[0037] Figure 5 This is a CT scan-fracture reconstruction image of coal and rock after conventional hydraulic fracturing and pulsed hydraulic fracturing in Embodiment 2 of the present invention.

[0038] In the picture:

[0039] 100. Pulse jet generator for optical sheathing; 101. First closed-loop circuit; 102. Second closed-loop circuit; 1. First outer casing; 11. First inlet; 12. First outlet; 13. Guide block; 2. Partition structure; 3. Attached channel; 4. First self-excited oscillation cavity; 5. Turning zone; 6. First connector;

[0040] 200. Pulse jet generator for coiled tubing; 7. Second outer casing; 71. Second inlet; 72. Second outlet; 73. Guide fluid; 8. Impeller assembly; 9. Second self-excited oscillation chamber;

[0041] 300. Matching downhole tools; 301. Safety joint; 302. Rotary sealing sub; 303. Spray gun; 304. Circulation valve; 305. Packer; 306. Eccentric directional device; 307. Guide shoe. Detailed Implementation

[0042] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0043] The specific embodiments of the present invention described herein are for illustrative purposes only and should not be construed as limiting the invention in any way. Under the teachings of this invention, those skilled in the art can conceive of any possible modifications based on the invention, all of which should be considered within the scope of the invention. It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there may be an intervening element. The terms "mounted," "connected," and "linked" should be interpreted broadly; for example, they can refer to mechanical or electrical connections, or internal communication between two elements, and can be direct or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] This invention addresses the significant vertical heterogeneity of deep coal seams by proposing an optimization mechanism based on drilling conditions of geological-engineering sweet spots (bright / semi-bright coal). It also deeply couples this mechanism with the two mainstream fracturing techniques for deep coal seams (smooth casing volume fracturing and coiled tubing close-cut fracturing) to form an integrated pulsed hydraulic fracturing device and method tailored to the geological characteristics of deep coal seams.

[0046] like Figure 1 , Figure 3 , Figure 4 As shown, the present invention provides a deep coal seam pulsed hydraulic fracturing device, comprising:

[0047] The surface pulse modulation system includes a bare casing pulse jet generator 100 connected between the outlet of the surface high-pressure manifold and the wellhead. The bare casing pulse jet generator 100 is used to modulate continuously pumped fracturing fluid into pulse fluid on the surface and inject it into the wellbore; the pulse fluid can perform pulse hydraulic fracturing on the coal seam.

[0048] The downhole pulse modulation system includes at least a coiled tubing pulse jet generator 200 installed in the wellbore. The coiled tubing pulse jet generator 200 is used to generate a pulse jet at a set position in the well, and the pulse jet can perform jet fracturing on the coal seam.

[0049] In this invention, depending on the application scenario, pulsed hydraulic fracturing of deep coal seams can be performed using either a surface pulse modulation system or a downhole pulse modulation system. In field applications, a pulse jet generator 100 for smooth casing is connected to the outlet of the surface high-pressure manifold, or a pulse jet generator 200 for coiled tubing is lowered to a designated position using coiled tubing. Fracturing fluid is injected in a pulsed manner with a certain frequency, applying cyclic alternating load-type shock waves to the deep coal seam, causing stress oscillations and fatigue failure, thereby reducing the fracturing initiation pressure and promoting fracture network formation. This technology is expected to become a new process for deep coal seam reservoir stimulation.

[0050] Furthermore, such as Figure 1 As shown, the pulse jet generator 100 for the optical sleeve includes a first outer shell 1, within which a first inner cavity is provided. A first inlet 11 is connected to the top of the first inner cavity, and the aperture of the first inlet 11 is smaller than the inner diameter of the ground high-pressure manifold outlet. A first outlet 12 is connected to the bottom of the first inner cavity. A first self-excited oscillation chamber 4 is provided within the first inner cavity, and the cross-section of the first self-excited oscillation chamber 4 gradually expands from top to bottom. The top of the first self-excited oscillation chamber 4 is connected to the first inlet 11, and the bottom of the first self-excited oscillation chamber 4 is connected to the first outlet 12. Continuously pumped fracturing fluid forms a pulsed fluid through the first self-excited oscillation chamber 4. The first inlet 11, the first self-excited oscillation chamber 4, and the first outlet 12 are arranged sequentially along the axial direction.

[0051] Furthermore, such as Figure 1 As shown, a partition structure 2 is provided in the first inner cavity. The outer wall of the partition structure 2 and the inner wall of the first outer shell 1 form an attached channel 3. The top end of the attached channel 3 is connected to the first inlet 11. A first self-excited oscillation cavity 4 is provided in the partition structure 2. The top end of the first self-excited oscillation cavity 4 is connected to the first inlet 11. The top end of the first outlet 12 is located at the lower part of the first self-excited oscillation cavity 4. A turning zone 5 is formed between the bottom end of the first self-excited oscillation cavity 4, the side wall of the first outlet 12, and the bottom end of the attached channel 3 (the attached channel 3 connects the turning zone 5 to the first inlet 11). The first self-excited oscillation cavity 4, the turning zone 5, and the attached channel 3 are connected to form a closed loop that causes the fracturing fluid to generate periodic self-excited oscillation.

[0052] In one specific embodiment, such as Figure 1As shown, a closed loop is formed on each side of the first self-excited oscillation chamber 4, which are respectively designated as the first closed loop 101 and the second closed loop 102. The first closed loop 101 and the second closed loop 102 are symmetrically arranged. A guide block 13 is provided in the first inlet 11 on the side near the second closed loop 102. The guide block 13 can cause the fracturing fluid to enter the first self-excited oscillation chamber 4 eccentrically closer to the first closed loop 101. The position of the guide block 13 can be adjusted, or it can be set off to the side of the first closed loop 101, so that the fracturing fluid enters the first self-excited oscillation chamber 4 eccentrically closer to the second closed loop 102.

[0053] like Figure 2 As shown, in the initial state, the fracturing fluid is accelerated at the first inlet 11 to generate a high-speed jet, and then enters the first self-excited oscillation chamber 4 eccentrically near the first closed loop 101. At least a portion of the fracturing fluid passes through the first closed loop 101 ( Figure 1 , Figure 2 The fracturing fluid flows through the closed loop on the right side to the first inlet 11, impacting the fracturing fluid entering at the first inlet 11. Under the action of this impact force, at least part of the fracturing fluid flows through the second closed loop 102 to the first inlet 11, impacting the fracturing fluid entering at the first inlet 11. The internal flow field of the first self-excited oscillation chamber 4 undergoes periodic changes, modulating the continuous fracturing fluid flow into a pulsed fluid on the ground.

[0054] Furthermore, such as Figure 1 As shown, the top of the first outer shell 1 is connected to a hollow first connector 6, which is used to connect to the outlet of the ground high-pressure manifold (existing technology).

[0055] After the fluid (fracturing fluid) flows into the pulse jet generator 100 for the bare casing, the fluid is accelerated at the narrowing point formed by the first inlet 11 to generate a high-speed jet. Under the action of the eccentric guide block 13, the high-speed jet is deflected to one side and enters the first self-excited oscillation chamber 4. Under the effect of the wall adhesion, at least part of the fluid adheres to the side wall of the first self-excited oscillation chamber 4 and flows. After changing its flow direction in the turning zone 5, it further flows upward along the wall adhesion channel 3, that is, along the first closed loop 101 (or the second closed loop 102). When the fluid flows to the first inlet 11, it impacts the fluid that just entered the device, causing it to deflect to the other side, flow along the other side wall, and change direction in the turning zone 5 on the other side. Afterward, the fluid flows upward along the wall adhesion channel 3 on the other side to the first inlet 11, continuing to impact the fluid that just entered the device, causing it to deflect to the other side again. High-speed fluid continuously and alternately impacts the continuous jet at the first inlet 11 through the side-mounted channels 3, causing the jet direction to change periodically. This causes the flow field inside the first self-excited oscillation cavity 4 to change periodically, thus modulating the continuous water flow into a pulsating water flow on the ground.

[0056] Furthermore, such as Figure 3 ,Figure 4 As shown, the pulse jet generator 200 for coiled tubing includes a second outer shell 7, within which a second inner cavity is provided. A second inlet 71 is connected to the first end of the second inner cavity, and a second outlet 72 is connected to the second end of the second inner cavity. The second inlet 71 is eccentric and narrows from top to bottom. An impeller assembly 8 is located below the second inlet 71 in the second inner cavity. The fracturing fluid flowing into the second inlet 71 forms a pulse jet through the impeller assembly 8. A second self-excited oscillation chamber 9 is located below the impeller assembly 8. The second self-excited oscillation chamber 9 has a variable cross-section and gradually narrows from top to bottom. The bottom end of the second self-excited oscillation chamber 9 is connected to the second outlet 72. The second self-excited oscillation chamber 9 amplifies the pulse pressure generated by the impeller assembly 8 and generates a pulse jet at the second outlet 72.

[0057] Furthermore, such as Figure 3 As shown, the pulse jet generator 200 for coiled tubing includes a guide fluid 73, which is disposed at the top of the second housing 7. An eccentric guide channel is provided inside the guide fluid 73, and the guide channel constitutes the second inlet 71. The guide channel is an eccentrically arranged inclined flow channel, and the outlet area is smaller than the inlet area.

[0058] Furthermore, the impeller assembly 8 includes an impeller seat, an impeller, an impeller shaft, and a bushing. The impeller seat is fixedly connected inside the second outer casing 7, and the impeller is rotatably connected to the impeller seat through the impeller shaft and the bushing. The central axis of the impeller shaft is perpendicular to the central axis of the second outer casing 7.

[0059] Furthermore, such as Figure 3 As shown, the second self-excited oscillation cavity 9 can be composed of multiple flow channels with gradually decreasing cross-sectional areas, which are used to amplify the pulse pressure generated by the impeller.

[0060] After the fluid is pumped into the pulse jet generator 200 for coiled tubing, it flows along the guide channel inside the guide fluid 73. Because the outlet area of ​​the guide channel is smaller than the inlet area and is eccentrically positioned, the fluid velocity and flow direction change. After the fluid flows out of the guide channel, it generates a tangential force on the impeller, causing the impeller to rotate continuously at high speed, constantly changing the flow channel area and generating pulse pressure. The second self-excited oscillation chamber 9, located below the impeller, amplifies the pulsating signal, generating a strong pulsating jet at the second outlet 72.

[0061] Furthermore, such as Figure 4 As shown, the downhole pulse modulation system also includes a matching downhole tool 300, which includes a safety joint 301, a rotary sealing sub 302, a spray gun 303, a circulation valve 304, a packer 305, an eccentric orienter 306, and a guide shoe 307 arranged from top to bottom; a pulse jet generator 200 for coiled tubing is connected in series between the safety joint 301 and the rotary sealing sub 302, and the safety joint 301 is used to connect the upper coiled tubing.

[0062] The coiled tubing pulse jet generator 200 and its matching downhole tool 300 are combined to generate and apply high-frequency pulse jet impact at a designated downhole location.

[0063] This invention provides a deep coal seam pulsed hydraulic fracturing method, implemented using the deep coal seam pulsed hydraulic fracturing device of this invention. The deep coal seam pulsed hydraulic fracturing method includes:

[0064] Based on the situation where the horizontal wellbore trajectory encounters a geological-engineering sweet spot in a deep coal seam, a surface pulse modulation system is used to modulate the continuously pumped fracturing fluid into a high-power pulse fluid on the surface and inject it into the wellbore to complete the smooth casing pumped bridge plug pulse volume fracturing; or, a downhole pulse modulation system is used to generate a high-frequency pulse jet at a set position in the well to complete the coiled tubing bottom seal drag-tight cutting pulse fracturing.

[0065] That is, when the deep coal seam pulse hydraulic fracturing device of the present invention is used for construction, the pulse hydraulic fracturing method can be determined according to the coal seam encountered, including two methods: bare casing pump-driven bridge plug pulse volume fracturing and coiled tubing bottom seal dragged close-cutting pulse fracturing. Bare casing pump-driven bridge plug pulse volume fracturing is implemented through a surface pulse modulation system, while coiled tubing bottom seal dragged close-cutting pulse fracturing is implemented through a downhole pulse modulation system.

[0066] Specifically, the appropriate pulse fracturing method is selected based on the geological-engineering sweet spots encountered during drilling in deep coal seams along the horizontal wellbore trajectory.

[0067] When drilling encounters a favorable geological-engineering sweet spot (bright / semi-bright coal), a smooth casing pump-driven bridge plug pulse volumetric fracturing method is adopted. The smooth casing uses a pulse jet generator 100 to generate high-power pulse fluid, which is combined with the pump-driven bridge plug for segmented cluster optimization to perform large-volume, high-displacement volumetric fracturing of the coal seam, thereby achieving full reservoir stimulation.

[0068] When encountering a relatively small proportion of geological-engineering sweet spots (bright / semi-bright coal), a coiled tubing bottom-seal drag-tight pulse fracturing method is adopted. The coiled tubing pulse jet generator 200 and its matching downhole tools 300 are combined. By optimizing the design of the directional direction and the number of arrangement, a high-frequency pulse jet is generated at the target point. Combined with the bottom packer being lifted segment by segment, the geological-engineering sweet spot is finely modified.

[0069] Example 1:

[0070] Horizontal wells are drilled to the target coal seam. Based on the horizontal well trajectory and the coal seam conditions encountered, the pulse hydraulic fracturing method is determined. Furthermore, the pulse hydraulic fracturing pumping scheme for each section is optimized based on the rock mechanical properties and geostress conditions of each coal seam.

[0071] When drilling encounters a favorable geological-engineering sweet spot (bright / semi-bright coal), a smooth casing pump-driven bridge plug pulse volumetric fracturing method is adopted. This method includes the following steps:

[0072] Step S1: Install the optical casing using a pulse jet generator 100 between the high-pressure manifold outlet and the wellhead;

[0073] Specifically, the first section uses coiled tubing or tubing transfer for perforation. Then, a pulse jet generator 100 is installed between the high-pressure manifold outlet and the wellhead using a smooth casing.

[0074] Step S2: Start the surface pumping equipment. After the fluid is modulated by the pulse jet generator 100 through the smooth casing, it forms a periodically changing pulse jet and is injected into the wellbore to perform pulse hydraulic fracturing on the target section.

[0075] Step S3: After completing the fracturing of the target section, the section is segmented using a cable pump bridge plug perforation combined operation method. The above steps are repeated until the volumetric fracturing of all sections is completed.

[0076] When the proportion of geological-engineering sweet spots (bright / semi-bright coal) encountered during drilling is relatively small, the coiled tubing bottom-seal dragged close-cutting pulse fracturing method is adopted. The coiled tubing bottom-seal dragged close-cutting pulse fracturing includes the following steps:

[0077] Step S1: Run the downhole pulse modulation system into the well at the set position through coiled tubing; set the bottom packer;

[0078] Specifically, the first section delivers the coiled tubing pulse jet generator 200 and its matching downhole tools 300 to the designated position via coiled tubing. This includes, in sequence, a guide shoe 307, an eccentric directional device 306, a packer 305, a circulation valve 304, a spray gun 303, a rotary sealing sub 302, the coiled tubing pulse jet generator 200, and a safety joint 301.

[0079] Step S2: Start the ground pumping equipment. The fluid drives the pulse jet generator 200 of the coiled tubing to generate a high-frequency pulsating jet, which is then sprayed onto the coal seam for fracturing through the spray gun.

[0080] Step S3: After completing the fracturing of this cluster, lift the tubing to the next cluster's designated position, set the bottom packer, and repeat the above steps to perform cluster-by-cluster fine fracturing.

[0081] Example 2:

[0082] In order to more intuitively observe the fracturing effect of the deep coal seam pulse hydraulic fracturing method of the present invention, an indoor simulation experiment was conducted on the deep coal seam pulse hydraulic fracturing method, and the rock sample fractures after fracturing were observed.

[0083] The indoor simulation experiment includes the following steps:

[0084] (1) Drilling: Select a cubic coal and rock sample with a side length of 100 mm and drill a 16 mm diameter, 55 mm deep hole along the direction perpendicular to the bedding.

[0085] (2) Cementing: A wellbore with a diameter of 14 mm and a length of 45 mm is inserted into the open hole. The wellbore and the annulus of the open hole are cemented together with epoxy resin.

[0086] (3) Clamping pressure: The coal and rock are placed in the confining pressure vessel of the true triaxial pulse hydraulic fracturing experimental system, and a pressure of 10 MPa is clamped in the vertical direction, and a pressure of 8 MPa and 5 MPa is clamped in the horizontal direction respectively.

[0087] (4) Prefilling with liquid: Inject clean water into the fracturing fluid container, close the pressure relief valve and open the check valve, pump the clean water into the pulse generator, and purge the air in the cylinder and pipeline;

[0088] (5) Start fracturing: When the injection pressure reaches the minimum pressure, the pulse generator is started. The injection pressure rises further and reaches the peak pressure. The pulse generator generates periodically changing pulse loads according to the preset pulse parameters, and the experiment officially begins.

[0089] (6) Termination of the experiment: When the pulse pressure drops or fracturing fluid is observed to overflow from the sample surface, the experiment is stopped and the inflection point of the pressure drop is recorded as the fracturing pressure.

[0090] (7) Reconstructing cracks: The cracks in the specimen after fracturing were scanned and reconstructed using the CT scan-crack reconstruction method.

[0091] like Figure 5 As shown, through indoor true triaxial experiments and CT scan reconstruction comparison, the deep coal seam pulse hydraulic fracturing method of the present invention can form a more complex fracture network and a wider communication range compared with conventional hydraulic fracturing, which intuitively verifies its superiority in improving the effect of deep coal seam stimulation.

[0092] Compared with existing technologies, the deep coal seam pulsed hydraulic fracturing device and method provided by this invention utilizes pulsed jet impact on coal and rock to induce stress oscillations and fatigue damage, thereby deteriorating matrix strength, promoting microfracture connectivity, and activating natural fractures and bedding planes. This reduces fracturing pressure and forms a complex fracture network with multiple horizontal and vertical fractures. It has the following significant beneficial effects:

[0093] Deep coal seams exhibit significant vertical heterogeneity, characterized by diverse coal and rock types with marked differences in porosity and permeability, gas content, and reservoir potential. This invention addresses the core challenges of "high ground stress and extremely low porosity and permeability" in deep coal seams. It proposes an optimization mechanism based on drilling encounters in geological-engineering sweet spots (bright / semi-bright coal) and deeply couples it with the two mainstream fracturing techniques for deep coal seams (smooth casing volumetric fracturing and coiled tubing close-cutting). The high-power pulses generated by the surface pulse modulation system help overcome high ground stress, initiating and extending the main fractures; the downhole pulse modulation system effectively activates primary fractures and bedding in geological-engineering sweet spots, forming complex fracture networks, thus jointly solving the problems of difficult fracture initiation and fracture creation in deep coal seams.

[0094] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A deep coal seam pulse hydraulic fracturing device, characterized in that, include: A surface pulse modulation system includes a smooth casing pulse jet generator connected between the outlet of the surface high-pressure manifold and the wellhead. The smooth casing pulse jet generator is used to modulate continuously pumped fracturing fluid into pulse fluid on the surface and inject it into the wellbore. The pulsed fluid can perform pulsed hydraulic fracturing on the coal seam. The downhole pulse modulation system includes at least a coiled tubing pulse jet generator installed in the wellbore. The coiled tubing pulse jet generator is used to generate a pulse jet at a set position in the well, and the pulse jet can perform jet fracturing on the coal seam.

2. The deep coal seam pulse hydraulic fracturing device as described in claim 1, characterized in that, The pulse jet generator for the optical sleeve includes a first outer shell, the top of which is connected to a hollow first connector for connecting to the outlet of the ground high-pressure manifold; a first inner cavity is provided inside the first outer shell, the top of which is connected to a first inlet, the aperture of which is smaller than the inner diameter of the outlet of the ground high-pressure manifold. The bottom end of the first inner cavity is connected to a first outlet; a first self-excited oscillation cavity is provided inside the first inner cavity, the cross-section of the first self-excited oscillation cavity is gradually expanded from top to bottom, the top end of the first self-excited oscillation cavity is connected to the first inlet, and the bottom end of the first self-excited oscillation cavity is connected to the first outlet. The continuously pumped fracturing fluid forms a pulsed fluid through the first self-excited oscillation chamber.

3. The deep coal seam pulse hydraulic fracturing device as described in claim 2, characterized in that, A partition structure is provided inside the first inner cavity, and an attached wall channel is formed between the outer wall of the partition structure and the inner wall of the first outer shell. The top end of the attached wall channel is connected to the first inlet. A first self-excited oscillation cavity is provided inside the partition structure, and the top end of the first self-excited oscillation cavity is connected to the first inlet. The top end of the first outlet is located at the lower part of the first self-excited oscillation cavity. The bottom end of the first self-excited oscillation chamber, the side wall of the first outlet, and the bottom end of the attached wall channel constitute a turning zone. The first self-excited oscillation chamber, the turning zone, and the attached wall channel are connected to form a closed loop that causes the fracturing fluid to generate periodic self-excited oscillations.

4. The deep coal seam pulse hydraulic fracturing device as described in claim 3, characterized in that, A closed loop is formed on each side of the first self-excited oscillation chamber, which is respectively designated as the first closed loop and the second closed loop. The first closed loop and the second closed loop are symmetrically arranged. A guide block is provided on the side of the first inlet near the second closed loop. The guide block can cause the fracturing fluid to enter the first self-excited oscillation chamber eccentrically closer to the first closed loop. In the initial state, the fracturing fluid is accelerated at the first inlet to generate a high-speed jet and then enters the first self-excited oscillation chamber eccentrically near the first closed loop. At least a portion of the fracturing fluid flows through the first closed loop to the first inlet, impacting the fracturing fluid entering at the first inlet. At least a portion of the fracturing fluid flows through the second closed loop to the first inlet, impacting the fracturing fluid entering at the first inlet. The internal flow field of the first self-excited oscillation chamber undergoes periodic changes, modulating the continuous fracturing fluid flow into a pulsed fluid on the ground.

5. The deep coal seam pulse hydraulic fracturing device as described in claim 1, characterized in that, The pulse jet generator for coiled tubing includes a second outer shell, within which a second inner cavity is provided. A second inlet is connected to a first end of the second inner cavity, and a second outlet is connected to a second inner cavity. The second inlet is eccentrically positioned and narrows from top to bottom. A guide fluid is provided at the first end of the second outer shell, and an eccentric guide channel is provided within the guide fluid, forming the second inlet. An impeller assembly is located below the second inlet in the second inner cavity, and the fracturing fluid flowing into the second inlet forms a pulse jet through the impeller assembly. A second self-excited oscillation chamber is provided below the impeller assembly. The second self-excited oscillation chamber has a variable cross-section and is gradually narrowed from top to bottom. The bottom end of the second self-excited oscillation chamber is connected to the second outlet. The second self-excited oscillation cavity amplifies the pulse pressure generated by the impeller assembly and generates a pulse jet at the second outlet.

6. The deep coal seam pulse hydraulic fracturing device as described in claim 5, characterized in that, The impeller assembly includes an impeller seat, an impeller, an impeller shaft, and a bushing. The impeller seat is fixedly connected to the second housing. The impeller is rotatably connected to the impeller seat via the impeller shaft and the bushing. The central axis of the impeller shaft is perpendicular to the central axis of the second housing.

7. The deep coal seam pulse hydraulic fracturing device as described in claim 5, characterized in that, The downhole pulse modulation system also includes supporting downhole tools, which include, from top to bottom, a safety joint, a rotary sealing sub, a spray gun, a circulation valve, a packer, an eccentric directional device, and a guide shoe; the coiled tubing pulse jet generator is connected in series between the safety joint and the rotary sealing sub, and the safety joint is used to connect the upper coiled tubing.

8. A method for pulsed hydraulic fracturing in deep coal seams, characterized in that, The deep coal seam pulsed hydraulic fracturing device as described in any one of claims 1 to 7 is used for implementation, and the deep coal seam pulsed hydraulic fracturing method includes: Based on the situation where the horizontal wellbore trajectory encounters a geological-engineering sweet spot in a deep coal seam, a surface pulse modulation system is used to modulate the continuously pumped fracturing fluid into a high-power pulse fluid on the surface and inject it into the wellbore to complete the smooth casing pumped bridge plug pulse volume fracturing; or, a downhole pulse modulation system is used to generate a high-frequency pulse jet at a set position in the well to complete the coiled tubing bottom seal drag-tight cutting pulse fracturing.

9. The deep coal seam pulse hydraulic fracturing method as described in claim 8, characterized in that, The pulsed volumetric fracturing of the bridge plug pumped by the sleeve includes the following steps: Install the optical casing pulse jet generator between the high-pressure manifold outlet and the wellhead; The surface pumping equipment is started, and the fluid is modulated by the pulse jet generator in the smooth casing to form a periodically changing pulse jet injected into the wellbore to perform pulse hydraulic fracturing on the target section; After the target section is fracturing, the section is segmented using a cable pump bridge plug perforation combined operation method. The above steps are repeated until the volumetric fracturing of all sections is completed.

10. The deep coal seam pulse hydraulic fracturing method as described in claim 8, characterized in that, The continuous tubing bottom seal drag-driven close-cutting pulse fracturing includes the following steps: The downhole pulse modulation system is lowered into the well to the set position via coiled tubing; the bottom packer is then set. The ground pumping equipment is started, and the fluid drives the pulse jet generator in the coiled tubing to generate a high-frequency pulsating jet, which is then sprayed through the spray gun to fracturing the coal seam. After completing the fracturing of this cluster, raise the tubing to the next cluster's designated position, set the bottom packer, and repeat the above steps to perform cluster-by-cluster fine fracturing.

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