Underground fracturing operation system and underground fracturing process

Abstract

The invention provides an underground fracturing operation system and an underground fracturing process, the system comprises a continuous mixing assembly, a drilling machine and a fracturing rod, a tool string is arranged on the fracturing rod, the continuous mixing assembly is used for preparing slurry for operation, the drilling machine is used for drilling holes in a preset position and driving the fracturing rod to move, and the drilling machine is used for drilling the slurry for operation. The fracturing rod is matched with the tool string to be used for achieving well washing and hole sealing fracturing operation. The embodiment of the invention is suitable for underground operation, can realize various supply functions such as directional drilling, well washing and directional fracturing, and has the advantages of small overall structure size, larger displacement, higher pressure, higher intelligent degree and the like.

Description

Technical Field

[0001] The present disclosure relates to the technical field of downhole fracturing, and in particular, to a downhole fracturing operation system and a downhole fracturing process. Background Art

[0002] Rock burst disasters are also called rock burst disasters (bump disasters), and in coal mines they are called coal bursts. Under the action of high internal stress, the equilibrium state of the ore body or rock mass is destroyed, and a large amount of energy is suddenly released, causing explosion vibrations, and the ore body and rocks on the walls of the shaft and tunnel suddenly erupt, causing disasters.

[0003] Its formation mechanism is: before the excavation of the shaft and tunnel, the rock mass is in a three-dimensional stress state, and a large amount of elastic strain energy accumulates in the high stress area. During the excavation of the shaft and tunnel, when the mining face approaches these areas, the equilibrium state changes due to construction disturbance or blasting vibration, and the elastic strain energy of the rock mass is suddenly released at the weak point, resulting in the sudden eruption of rock and ore body. Rock burst can be divided into general rock burst and severe rock burst: the general rock burst is small in scale, manifested as the vibration of the ore body and rock mass and the generation of dust and cracks; the severe rock burst is large in scale, manifested as the serious crushing of the ore body and rock mass, and the occurrence of strong explosion vibration. Rock burst is mainly affected by multiple factors such as geological structure, ore body and surrounding rock structure properties, mining depth, hydrogeological conditions, etc. In the fold and fault structure zone, the ore body has high elasticity and high strength (hardness), the top and bottom plate rocks are dense, hard, with few cracks and large thickness, the surrounding rock has high water content, and the mine with a large mining depth is prone to rock burst.

[0004] Rock burst often leads to roof accidents, damages shafts and tunnels, causes casualties, destroys equipment, pollutes the working environment, and affects production. Rock burst sometimes leads to strong gas outflows, and sometimes explosions caused by large amounts of dust, causing greater damage. Rock burst is most serious in coal mines, but it also occurs from time to time in other metal and non-metal mines. In addition, rock burst disasters sometimes occur during tunnel and pit construction.

[0005] As an economical, safe and efficient rock burst prevention and control technology, hydraulic fracturing has been verified in some coal mines in my country and has become an effective means of managing rock burst and controlling hard and difficult-to-cross roofs in my country's coal mines. Numerous studies and experiments have shown that high-pressure water pre-fracture of the roof can directionally fracture the roof rock layer and destroy the integrity of the roof rock layer, thereby weakening the strength and integrity of the roof, so that the roof can collapse in time as needed after mining, thereby achieving the purpose of reducing or basically eliminating rock burst and roof disasters.

[0006] However, although surface hydraulic fracturing has the best effect at present, it has problems such as a large number of equipment, high operating costs, large management difficulties, large land area, and difficulty in land acquisition. At the same time, due to the narrow underground tunnels and the relatively small size of the equipment, the fracturing pressure and displacement that can be provided are small, resulting in frequent problems such as large underground construction workload and poor roof management effect. Summary of the invention

[0007] The purpose of the embodiments of the present disclosure is to provide a downhole fracturing operation system and a downhole fracturing process to solve the above-mentioned problems existing in the prior art.

[0008] In order to solve the above technical problems, an embodiment of the present disclosure provides a downhole fracturing operation system, including a continuous mixing assembly, a drilling rig and a fracturing rod, wherein a tool string is arranged on the fracturing rod, the continuous mixing assembly is used to prepare slurry for the operation, the drilling rig is used to drill holes at predetermined positions and drive the fracturing rod to move, and the fracturing rod cooperates with the tool string to realize well washing and sealing fracturing operations.

[0009] In some embodiments, the tool string includes a hydraulic release, a jet short section and a guide head arranged in sequence, the hydraulic release is connected to the pump assembly, at least one pair of plugs is arranged between the hydraulic release and the guide head, each pair of the plugs includes two plugs, and a centralizer is arranged at both ends of each plug.

[0010] In some embodiments, the injection nipple is disposed between the two pluggers of the plugger pair, and at least one nozzle portion is disposed on an outer surface of the injection nipple.

[0011] In some embodiments, the two occluders of the occluder pair are connected by a connecting rod.

[0012] In some embodiments, the continuous mixing component includes a control device and a conveying device, a mixing device, a discharging device and a pumping device connected in sequence; the conveying device is connected to a silo, and is used to convey the materials required for mixing to the mixing device, the mixing device is used to continuously stir the conveyed materials, the discharging device is used to discharge the stirred slurry, and the pumping device is used to pump the slurry to the goaf for filling.

[0013] In some embodiments, the mixing device includes a mixing tank, in which a stirring unit, a stirring drive unit, a circulation pump and a spreading plate are arranged. The spreading plate enables the material before mixing to be evenly spread, and the stirring drive unit is used to drive the stirring unit to rotate to achieve material mixing.

[0014] In some embodiments, the stirring unit adopts a double-impeller structure, and the stirring unit includes an upper impeller and a lower impeller. The upper impeller adopts a downward-pressing structure, and the lower impeller adopts an upward-lifting structure.

[0015] In some embodiments, the discharge device includes a discharge pump, a discharge pump driving unit, and a discharge manifold, and the discharge pump driving unit drives the discharge pump to discharge the slurry through the discharge manifold.

[0016] In some embodiments, an anti-shock pump skid is further included. The anti-shock pump skid is disposed between the continuous mixing assembly and the fracturing rod and is used to transport liquid to the fracturing rod and the tool string.

[0017] Another aspect of the present disclosure provides a downhole fracturing process, comprising:

[0018] The drilling operation is performed at the predetermined position of the key fracturing layer by means of a drilling rig;

[0019] After the drilling operation is completed, the perforating operation is performed through the fracturing rod and tool string to achieve the well cleaning operation;

[0020] After the well washing operation is completed, fracturing operations are carried out using fracturing rods and tool strings.

[0021] The disclosed embodiment is suitable for downhole operations and can realize multiple functions such as directional drilling, well washing, directional fracturing, etc. The overall structure is small in size but has the advantages of larger displacement, higher pressure and higher intelligence. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 A schematic diagram of the structure of the downhole fracturing operation system provided in this embodiment;

[0024] Figure 2 A schematic diagram of the operation flow of the downhole fracturing operation system provided in this embodiment;

[0025] Figure 3 It is a schematic diagram of the structure of a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure;

[0026] Figure 4 It is a structural schematic diagram of a hydraulic release in a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure;

[0027] Figure 5 It is a structural schematic diagram of a plugger in a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure;

[0028] Figure 6 It is a structural schematic diagram of a centralizer in a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure;

[0029] Figure 7 It is a schematic diagram of the structure of a jetting sub in a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure;

[0030] Figure 8 It is a schematic diagram of the structure of a guide head in a tool string in a downhole fracturing operation system provided by an embodiment of the present disclosure.

[0031] Fig. 9 A schematic diagram of the steps of the downhole fracturing process provided in this embodiment;

[0032] Fig.10 A schematic diagram of the process flow of the downhole fracturing process provided in this embodiment.

[0033] Reference numerals:

[0034] 1-Hydraulic release; 11-upper joint, 12-lower joint; 13-core shaft; 14-sealing ball; 2-centralizer; 3-plugging device; 31-main body; 21-sand discharge channel; 4-connecting rod; 5-injection short section; 51-nozzle section; 6-guide head; 100-silo; 101-weighing sensor; 110-continuous mixing assembly; 111-conveying device; 112-mixing device; 1121-mixing tank; 1122-circulating pump; 113-discharge device; 1131-discharge pump; 114-pumping device; 120-drilling rig; 130-anti-impact pump skid; 140-fracturing rod. DETAILED DESCRIPTION

[0035] Various aspects and features of the present disclosure are described herein with reference to the drawings.

[0036] It should be understood that various modifications may be made to the embodiments of the present application. Therefore, the above description should not be considered as limiting, but only as an example of an embodiment. Other modifications within the scope and spirit of the present disclosure will occur to those skilled in the art.

[0037] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the general description of the present disclosure given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.

[0038] These and other characteristics of the present disclosure will become apparent from the following description of a preferred form of embodiment given as a non-limiting example, with reference to the attached drawings.

[0039] It should also be understood that, although the present disclosure has been described with reference to some specific examples, those skilled in the art will be able to realize many other equivalent forms of the present disclosure that have the features described in the claims and are therefore within the scope of protection defined thereby.

[0040] The above and other aspects, features and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0041] Specific embodiments of the present disclosure are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments claimed are merely examples of the present disclosure, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to avoid obscuring the present disclosure with unnecessary or redundant details. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as a basis and representative basis for the claims to teach those skilled in the art to use the present disclosure in a variety of ways with substantially any suitable detailed structure.

[0042] This specification may use the phrases "in one embodiment," "in another embodiment," "in a further embodiment," or "in other embodiments," all of which may refer to one or more of the same or different embodiments according to the present disclosure.

[0043] The first embodiment of the present disclosure provides a downhole fracturing operation system, which is used for downhole fracturing technology, and is mainly used in the control technology of dual-directional rock burst in coal mines. The downhole fracturing process here mainly includes multiple steps such as preparing slurry, directional drilling, peek-and-go washing, sealing and fracturing, and evaluation and detection.

[0044] In order to realize the above process, Figure 1 As shown, the downhole fracturing operation system includes a continuous mixing assembly 110, a drilling rig 120 and a fracturing rod 140, and a tool string is arranged on the fracturing rod 140, wherein the continuous mixing assembly 110 is used to prepare slurry for fracturing and other operations, the drilling rig 120 is used to realize directional drilling at a predetermined position underground, and the fracturing rod 140 cooperates with the tool string to realize hole washing and sealing fracturing operations at a predetermined position.

[0045] Specifically, the continuous mixing component 110 can be used as a pump component, which is connected to the silo 100. The silo 100 preferably has a weighing sensor 101. The material weighed by the weighing sensor 101 is input from the silo 100 to the continuous mixing component 110 for making slurry, wherein the continuous mixing component 110 includes a conveying device 111, a mixing device 112, a discharge device 113, a pumping device 114 and a control device.

[0046] Specifically, the conveying device 111 is used to convey the materials required for mixing to the mixing device 112, specifically, as Figure 2 As shown, the conveying device 111 is linked to the silo 100 , and includes at least a solid conveying unit and a liquid conveying unit. The solid conveyed by the solid conveying unit and the liquid conveyed by the liquid conveying unit are mixed in the mixing device 112 .

[0047] The mixing device 112 is connected to the discharge port of the conveying device 111, and is used for continuously stirring the material conveyed by the conveying device 111. Specifically, the mixing device 112 includes a mixing tank 1121, in which a stirring unit, a stirring drive unit and a circulation pump 1122 are arranged. The stirring unit is driven to rotate by the stirring drive unit, thereby achieving mixing of the slurry.

[0048] Furthermore, the stirring unit adopts a double-impeller structure, and the stirring unit adopting the double-impeller structure includes an upper impeller and a lower impeller. The upper impeller adopts a downward pressure structure, which can press the slurry on the liquid surface into the mixing tank 1121 to prevent the slurry powder from floating on the liquid surface. The lower impeller adopts an upward structure, which can stir the slurry at the bottom of the mixing tank 1121 to the top of the tank. The combined impeller of the stirring unit cooperates with the circulating pump 1121 to enhance the mixing effect.

[0049] Furthermore, a material spreading plate is also provided in the mixing tank 1121, and the material spreading plate enables the materials before mixing to be spread more evenly. Thus, through the coordinated use of the material spreading plate, the stirring unit and the circulating pump 1122, the efficiency of mixing the materials is higher, and the volume of the equipment can be reduced.

[0050] The discharge device 113 is connected to the discharge port of the mixing device 112, and is used to discharge the stirred slurry. Specifically, the discharge device 113 includes a discharge pump 1131, a discharge pump driving unit and a discharge manifold, wherein the discharge pump driving unit drives the discharge pump 1131 to discharge the slurry through the discharge manifold.

[0051] In addition, the pumping device 114 is connected to the discharge port of the discharge device 113, and the pumping device 114 is used to pump the slurry to the goaf for filling through a high-pressure hose.

[0052] Furthermore, the control device in the continuous mixing assembly 110 is respectively connected to the conveying device 111, the mixing device 112, the discharge device 113 and the pumping device 114. For example, the conveying amount of solid and liquid can be controlled by the conveying device 111 to achieve the mixing concentration of the slurry; the feed amount and discharge amount of the mixing device 112 can be controlled to stabilize the stirring liquid level in the mixing tank 1121 to facilitate continuous stirring; in addition, the feed amount and discharge amount of the discharge device 113 can be adjusted according to actual working conditions.

[0053] Furthermore, the role of the drilling rig 120 in downhole fracturing is to perform directional drilling at a predetermined position and drive the fracturing rod 140 and the tool string on the fracturing rod 140 to move.

[0054] In a preferred embodiment, the downhole fracturing operation system also includes an anti-impact pump skid 130, which is arranged between the continuous mixing assembly 110 and the fracturing rod 140, and is used to transport mixed high-pressure and large-flow liquid to the fracturing rod 140 and the tool string on the fracturing rod. The liquid here is, for example, slippery fluid, sand-carrying fluid, fracturing fluid, etc.

[0055] In a preferred embodiment, the continuous mixing assembly 110 and the anti-bumping pump skid 130 may be integrated to form a pump assembly structure, and the pump assembly may realize the functions of the continuous mixing assembly 110 and the anti-bumping pump skid 130 .

[0056] The fracturing rod 140 in this embodiment is used to perform hole washing and hole sealing fracturing operations at a predetermined position after directional drilling through the tool string. The tool string here can particularly perform hole washing and hole sealing fracturing operations simultaneously.

[0057] In a specific embodiment, Figure 3-Figure 8 As shown, the tool string includes a hydraulic release 1, a jet nipple 5 and a guide head 6, at least one plugging device pair is arranged between the hydraulic release 1 and the guide head 6, the hydraulic release 1 is arranged at the first end (or proximal end) of the tool string, the guide head 6 is arranged at the second end (or distal end) of the tool string, the first end of the tool string is connected to the fracturing rod 140, and the second end of the tool string moves to a predetermined position along with the fracturing rod 140.

[0058] Further, the hydraulic release 1 is arranged at the first end of the tool string. The hydraulic release 1 can be a hydraulic double-acting release, and its two ends can be connected to the upper tubular column and / or the lower tubular column. The hydraulic release at least includes an upper joint 11 and a lower joint 12 connected to each other. The upper joint 11 and the lower joint 12 form a cavity, and a core shaft 13 and a sealing ball 14 are arranged in the cavity. When the hydraulic release 1 is stuck during operation, the lower tubular column is disengaged from the fracturing rod by applying an axial load or throwing a ball to pressurize, so that the long string of fracturing rods can be dragged back after the tool string is discarded, thereby reducing losses.

[0059] Furthermore, the guide head 6 here is arranged at the second end of the tool string, and the guide head 6 has the function of guiding and blocking. A thread is arranged on the inner side of the first end of the guide head 1 so that the first end of the guide head 1 can be screwed and arranged on the outer side of the adjacent device, and the second end of the guide head 1 is closed.

[0060] Furthermore, each pair of the pluggers includes two relative pluggers 3, and the packers 3 can expand under pressure to fully contact the open hole wall, thereby realizing repeated sealing and unsealing functions. In each pair of pluggers, the two pairs of pluggers are connected by a connecting rod 4, and the length of the connecting rod 4 can be set according to demand, which can store more liquid. After the tool string is extended into the well, a sealed space is formed between the two pluggers 3.

[0061] Of course, the number of the plugger pairs here can be set to multiple. By setting multiple plugger pairs, effective isolation between layers can be ensured to prevent interlayer interference during fracturing. The lower fractured layer can be effectively isolated, thereby ensuring fine fracturing of the target layer.

[0062] In this embodiment, since the number of the plugging device pairs is at least 1, the number of the packers 3 is an even number greater than or equal to 2. The increase in the number of the packers 3 here is conducive to increasing the contact range with the open hole wall, thereby ensuring the effect of fracturing. In addition, the two packers 3 are connected by the connecting rod 4, which can increase the distance between the two adjacent packers 3, increase the volume space after setting, increase the injection volume, and ensure the development of gaps during fracturing through a larger amount of liquid.

[0063] Furthermore, the packer 3 includes a main body 31, in which a sand discharge channel 32 is arranged. The main body 31 is a high-pressure-resistant and wear-resistant rubber sleeve with high pressure-bearing capacity. The built-in sand discharge channel 32 can reduce the risk of sand jamming.

[0064] Furthermore, a centralizer 2 is provided at both ends of each of the pluggers 3, and the centralizer 2 is used to support the tool string, ensure that the tool string is located at the center of the open hole, and prevent the tool string from being eccentric and causing poor sealing. Here, more pluggers 3 correspond to more centralizers 2.

[0065] In the tool string, more centralizers 2 can reduce the friction between the tool string, especially the packer 3, and the well wall when moving in the well, thereby extending the service life of the tool string. Preferably, the number of centralizers 2 in the tool string is greater than or equal to 4, so as to ensure that the tool string is centered in the open hole to the greatest extent, thereby ensuring the operation effect.

[0066] In this embodiment, the plugging device 3 and the centralizer 2, the centralizer 2 and the hydraulic release 1, and the centralizer 2 and the connecting rod 4 are sleeve-connected with each other.

[0067] Furthermore, a second positioner is provided on the centralizer 2, and the second positioner has an obvious weight change when passing through the casing collar, based on which the depth of the tool string can be accurately calibrated to achieve precise positioning of thin interlayers and fixed-point perforation. In addition, the second positioner can also provide friction, which can assist the packer 3 at the bottom to achieve setting.

[0068] exist Figure 3 In the illustrated embodiment, the number of the plugging device pairs is 2, and for this purpose, the tool string is provided with the hydraulic release 1, the centralizer 2, the plugging device 3, the centralizer 2, the connecting rod 4, the jet short section 5, the centralizer 2, the plugging device 3, the centralizer 2 and the guide head 6 in sequence from the proximal end to the distal end.

[0069] In this embodiment, except for the guide head 6, the hydraulic release 1, the centralizer 2 and the plugging device 3 are all of the structure of a central tube, the first end of which is provided with an internal thread, and the second end of which is provided with an external thread. In this way, based on the structure of the above-mentioned present embodiment, it is convenient for the liquid to pass through the middle after the connection. Specifically, the above-mentioned structure facilitates the second end of the hydraulic release 1 to be arranged on the inner side of the first end of the centralizer 2, the second end of the centralizer 2 to be arranged on the inner side of the first end of the plugging device 3, the second end of the plugging device 3 to be arranged on the inner side of the first end of the centralizer 2, the second end of the centralizer 2 to be arranged on the inner side of the connecting rod 4, etc.

[0070] Furthermore, the injection nipple 5 is arranged between the two plugs 3, especially between the centralizer 2 and the connecting rod 4. The number of the injection nipple 5 here should not be too large, as too large a number will result in a low liquid pressure in the tool string. In addition, too large a number will also result in too much liquid being ejected.

[0071] At least one nozzle portion 51 is provided on the outer surface of the jet sub 5. The jet sub 5 is used to generate a pressure difference by throttling the nozzle 51, converting the pressure energy of the perforating fluid into kinetic energy, thereby opening the casing and the rock formation and finally completing flushing, perforating, fracturing and other operations in the sealed space formed by the plugger 3. In this embodiment, by controlling the flow rate and pressure of the pumped liquid, different processes such as flushing, perforating and fracturing can be achieved in a single trip through the jet sub 5. For this reason, the diameter of the nozzle 51 here is relatively small, for example, a diameter of 7 mm.

[0072] Specifically, when the flow rate and pressure of the pumped liquid are low, the packer 3 does not contact the well wall to achieve sealing, and clean water (fracturing fluid) can continue to flow out of the wellhead, so that the well can be flushed; when the flow rate and pressure of the pumped liquid are low, the water flow ejected by the jet short section 5 has higher energy and can perforate the well wall; when the flow rate and pressure of the pumped liquid are high, the water flow ejected by the jet short section 5 will fracture the rock formations around the well wall along the perforations completed in the early stage, thereby achieving grid-like cracks in a larger area.

[0073] The nozzle 51 of the jet sub 5 here can ensure the outflow of perforating fluid (sand addition) and fracturing fluid. The nozzle 51 here can be multiple, preferably, multiple nozzles 51 are evenly arranged along the circumference on the outer surface of the jet sub 5, and the multiple nozzles 51 are used to make the throttled liquid spray out in different directions, so as to achieve the effect of perforation orientation, and the position and radius of the spraying can be controlled manually.

[0074] In addition, a first positioner is provided on the injection nipple 5, and the position of the tool string, especially the position of the injection nipple 5, can be accurately positioned by the first positioner, so as to perform precise injection operations.

[0075] Based on the structure of the above tool string, its specific usage is as follows:

[0076] The tool string is pushed by the fracturing rod into the open hole drilled by the drilling rig. When the tool string reaches the fracturing position at the bottom layer, the perforating fluid or fracturing fluid flowing out of the fracturing rod enters the tool string. Under the action of the liquid pressure, the packer 3 expands to fully contact the open hole wall. A closed chamber is formed between two packers 3 in each packer pair.

[0077] When performing perforating operations, the jet sub 5 generates a pressure difference by throttling the nozzle 51 thereof, converting the pressure energy of the perforating fluid into kinetic energy to perforate the casing and the rock formation, thereby completing the perforating operation; when performing fracturing operations, the perforations are expanded by adjusting the flow of the nozzle 51 and relying on a large flow rate and high pressure fracturing fluid, thereby creating seams; after completing perforating and fracturing, the hydraulic pressure is reduced to achieve the contraction of the packer 3, and the tool string is moved under the drive of the fracturing rod to enter other positions of the open hole for operations.

[0078] The tool string of this embodiment is used in the dual-directional rock burst control technology in coal mines, which mainly carries out directional long-hole segmented hydraulic directional fracturing and advance pressure relief control on the key layer of the hard roof of the coal seam. On the one hand, it can form a large-scale fracture grid in the coal rock mass and infiltrate the rock strata, and utilize the deterioration effect of water on the rock to reduce the physical and mechanical properties and stress concentration of the coal rock mass, thereby reducing the static load energy of the surrounding rock-coal system; on the other hand, it reduces the hard roof plate size, thereby reducing the dynamic load energy of the surrounding rock-coal system.

[0079] The cooperation between the plugger and the centralizer can ensure that the tool string is centered in the open hole, increase the contact area with the open hole, ensure the sealing effect, and ensure the operating pressure; by using the connecting rod to connect the packers to increase the distance between the packers, the volume space after setting can be increased, and the development of gaps during fracturing can be ensured by increasing the injection volume; by providing the injection nipple with the nozzle, the outflow of perforating fluid (sand) and fracturing fluid can be guaranteed; by the hydraulic release, the long string of fracturing rods can be dragged back after the tool string is discarded to reduce losses; in addition, by equipping with a locator, the position of the tool string can be accurately located for precise operations.

[0080] The downhole fracturing operation system of the disclosed embodiment is suitable for a variety of fracturing processes, achieving multiple uses of one machine. For example, other components can be added to modify the medium to achieve the purpose of reducing friction resistance, improving fracturing effect, temporarily plugging natural gaps, etc., and ultimately maximizing the fracturing effect. Commonly used modified components include: quartz sand, guar gum liquid, drag reducer, etc., and the following functions are achieved based on different modified components:

[0081] (1) Well washing with sand-carrying fluid: its functions are: flushing out the rock cuttings in the open hole to wash the well, ensuring the cleanliness of the open hole wall; and plugging the large cracks in the open hole to prevent fluid leakage during subsequent fracturing work.

[0082] (2) Flushing with drag reducers, which can reduce the resistance of the open hole wall, making it easier to drag the tool string; and can carry fine sand to seal small cracks in the well wall. It should be noted that the role of the traditional sand-carrying fluid in the oil and gas industry is to clamp the carried sand in the rock cracks under high pressure so that the rock cracks do not close. The purpose of adding sand in the rock burst control technology is to seal the cracks in the open hole, ensure that there is no large amount of water leakage, so that pressure can be built up, thereby achieving fracturing of the hard formation.

[0083] (3) Fresh water fracturing: its function is to generate a pressure difference by throttling the nozzle during the perforating operation, convert the pressure energy of the perforating fluid into kinetic energy to perforate the casing and the rock formation to complete the perforation; adjust the flow rate during the fracturing operation, and rely on large flow and high pressure fracturing fluid to expand the perforation and create seams.

[0084] The second embodiment of the present disclosure provides a downhole fracturing process, which can be implemented by the downhole fracturing operation system in the first embodiment. Fig. 9 and Fig.10 As shown, the process includes the following steps:

[0085] S101, drilling operations are performed at predetermined locations of key fracturing layers by using a drilling rig.

[0086] In this step, a drilling operation is performed at a predetermined position of the critical fracturing layer by a drilling rig. Specifically, after the critical fracturing layer is determined, directional drilling is performed at the predetermined position of the critical fracturing layer by, for example, the drilling rig 120 according to the construction requirements.

[0087] S102, after the drilling operation is completed, a perforating operation is performed through a fracturing rod and a tool string to achieve a well cleaning operation.

[0088] After the drilling operation is performed at the predetermined position of the critical fracturing layer by the drilling rig in the above step S101, in this step, a perforating operation is performed by the fracturing rod and the tool string to realize the well washing operation after the drilling operation is completed.

[0089] The well washing and fracturing operations involved in this embodiment are different from the operations in the traditional oil and gas field. The traditional oil and gas industry does not require a well washing step in the fracturing process, because the oil and gas industry needs to run a casing in the fracturing process, and the inner wall of the casing is free of debris, sand and other debris compared to the open hole. In addition, the wells in the oil and gas field are vertically downward, and even if they are cleaned, it is difficult to remove the debris.

[0090] However, in the application of prevention and control technology for rock burst, after the drilling operation is completed, in order to understand the geological structure in the hole, it is necessary to conduct borehole exploration in order to determine the rock structure of the key layer, the distribution of natural fractures, the location of mud / sandstone, whether there is collapse, etc.; at the same time, in order to facilitate the subsequent lowering of the fracturing rod and the tool string, the rock cuttings generated during the drilling process need to be taken out of the borehole, and some natural fractures need to be sealed. At this time, it is necessary to use sand-carrying fluid to wash the well, inject temporary plugging agents, etc. In addition, if the borehole has problems such as collapse, it may be necessary to lower the drill bit again for repair.

[0091] For this reason, considering that downhole fracturing is to save the process of casing installation, if you want to use open hole fracturing directly, you must keep the open hole relatively clean. You need to first use water with no pressure and a small flow rate (for example, water flow less than the flow rate of the packer setting for flushing) to wash the well. Since the holes used for fracturing in the well are drilled obliquely upward, the water flow can carry debris out of the wellhead after washing the holes.

[0092] S103, after the well washing operation is completed, a fracturing operation is performed using a fracturing rod and a tool string.

[0093] After the drilling operation is completed in step S102, the fracturing rod and the tool string are used to perform perforation operations to achieve the well cleaning operation. In this step, the fracturing operation is performed by the fracturing rod and the tool string after the well cleaning operation is completed. Specifically, the orifice of the cleaned borehole is sealed and then the tool string for fracturing is used to enter the fracturing process. The fracturing operation here can, for example, be achieved by dragging the fracturing rod 140 and the tool string through the drill rod of the drilling rig 120 to achieve staged fracturing of the entire horizontal section.

[0094] In the above-mentioned well washing and fracturing operations, the continuous mixing assembly 110 cooperates with the anti-impact pump skid 130, the fracturing rod 140 and the tool string, wherein the liquid output by the continuous mixing assembly 110 is transported to the fracturing rod 140 through the anti-impact pump skid 130, and the liquid passes through the fracturing rod 140 and the tool string to achieve well washing and fracturing.

[0095] Here, the continuous mixing assembly 110 and the anti-impact pump skid 130 can be integrated to form a pump assembly, and the pump assembly can be, for example, a fracturing pump capable of achieving high-pressure and large-displacement operations underground, and the fracturing pump can be a core device for rock burst management. In view of the small underground space and the high difficulty in equipment transportation, the size and weight of the underground supporting equipment are further reduced, and the fracturing pump can meet various downhole methods such as inclined wells and vertical wells.

[0096] Furthermore, under rated operating conditions, the actual displacement of the pump assembly here can be accumulated by connecting multiple pump assemblies in parallel to connect different numbers of anti-collision pump skids. For example, it can be set to 2 pump assemblies, or the pump assembly with higher pressure and flow can be replaced to achieve the corresponding operating effect.

[0097] The downhole fracturing process of this embodiment can realize the dual-directional rock burst control technology, which has great advantages over the traditional fracturing technology in terms of fracturing pressure, operation displacement, fracturing radius, number of working face drilling holes, etc., as shown in the following comparison:

[0098]

[0099] High-pressure construction is beneficial to the net pressure in the fracture and promotes the extension of fracturing. Large displacement is beneficial to improving the fracturing effect and the volume range of the fracture network. Combined with the successful experience of horizontal well volume fracturing construction at home and abroad, when the fracturing pressure is 70MPa and the displacement is 2000L / min, the fracturing radius can reach 80-120m. The operation effect has fully reached the effect required for ground fracturing, but the number of equipment is reduced by more than 90%, and the operation difficulty is reduced by more than 90%.

[0100] The disclosed embodiment has the functions of directional drilling, directional slitting, directional fracturing, intelligent control, complete set of fracturing effect evaluation, etc. Based on the above-mentioned dual directional impact ground pressure control technology adopted in this embodiment, it can replace the effect of ground horizontal well fracturing technology, which can effectively reduce costs and solve the problem of ground construction. Compared with ground fracturing, the number of equipment used in the underground dual directional impact ground pressure control technology is only about 10% of the equipment used in ground fracturing, and the cost of a single device is lower, and the construction difficulty is lower, reducing land acquisition costs, equipment maintenance and maintenance costs, etc. In addition, compared with conventional underground hydraulic fracturing technology, the underground dual directional impact ground pressure control technology has larger parameters such as pressure and displacement, and the fracturing radius is 2.5-3 times that of conventional hydraulic fracturing, and the construction cost is only 30%-40% of that of conventional hydraulic fracturing.

[0101] The disclosed embodiment is suitable for downhole operations and can realize multiple functions such as directional drilling, well washing, directional fracturing, etc. The overall structure is small in size but has the advantages of larger displacement, higher pressure and higher intelligence.

[0102] In addition, the features of the embodiments shown in the drawings of the present application or the various embodiments mentioned in this specification are not necessarily understood as independent embodiments. Instead, each feature described in one example of an embodiment can be combined with one or more other desired features from other embodiments to produce other embodiments not described in words or with reference to the drawings.

[0103] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A downhole fracturing system, characterized in that: It includes a continuous mixing component, a drilling rig and a fracturing rod. A tool string is arranged on the fracturing rod. The continuous mixing component is used to prepare slurry for operation. The drilling rig is used to drill holes at predetermined positions and drive the fracturing rod to move. The fracturing rod cooperates with the tool string to realize well washing and sealing fracturing operations.

2. The downhole fracturing system according to claim 1, characterized in that: The tool string includes a hydraulic release, a jet nipple and a guide head which are arranged in sequence. The hydraulic release is connected to a pump assembly. At least one plugging device pair is arranged between the hydraulic release and the guide head. Each pair of the plugging devices includes two plugging devices, and a centralizer is arranged at both ends of each plugging device.

3. The downhole fracturing system according to claim 2, characterized in that: The injection nipple is disposed between the two plugs of the plugging device pair, and at least one nozzle portion is disposed on an outer surface of the injection nipple.

4. The downhole fracturing system according to claim 2, characterized in that: The two occluders of the occluder pair are connected via a connecting rod.

5. The downhole fracturing system according to claim 1, characterized in that: The continuous mixing assembly includes a control device and a conveying device, a mixing device, a discharging device and a pumping device connected in sequence; the conveying device is connected to the silo, and is used to convey the materials required for mixing to the mixing device, the mixing device is used to continuously stir the conveyed materials, the discharging device is used to discharge the stirred slurry, and the pumping device is used to pump the slurry to the goaf for filling.

6. The downhole fracturing system according to claim 5, characterized in that: The mixing device comprises a mixing tank, in which a stirring unit, a stirring drive unit, a circulation pump and a spreading plate are arranged. The spreading plate enables the material before mixing to be evenly spread, and the stirring drive unit is used to drive the stirring unit to rotate to achieve material mixing.

7. The downhole fracturing system according to claim 6, characterized in that: The stirring unit adopts a double-impeller structure, and the stirring unit comprises an upper impeller and a lower impeller. The upper impeller adopts a downward pressing structure, and the lower impeller adopts an upward lifting structure.

8. The downhole fracturing system according to claim 5, characterized in that: The discharge device includes a discharge pump, a discharge pump driving unit and a discharge manifold. The discharge pump driving unit drives the discharge pump to discharge the slurry through the discharge manifold.

9. The downhole fracturing system according to claim 1, characterized in that: Also included is an anti-bumping pump skid, which is disposed between the continuous mixing assembly and the fracturing rod and is used to transport liquid to the fracturing rod and the tool string.

10. A downhole fracturing process, characterized in that: include: The drilling operation is performed at the predetermined position of the key fracturing layer by means of a drilling rig; After the drilling operation is completed, the perforation operation is performed through the fracturing rod and the tool string to realize the well cleaning operation; after the well cleaning operation is completed, the fracturing operation is performed through the fracturing rod and the tool string.

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