A method for hydraulic fracturing of hot dry rock and a packer self-locking mechanism

Abstract

The present application relates to the technical field of hot dry rock hydraulic fracturing, a hot dry rock hydraulic fracturing heat extraction method and a packer self-locking mechanism, comprising the following steps: step one, evaluating the reservoir of hot dry rock before fracturing; step two, simulating the cracking and expansion of hot dry rock fractures; step three, optimizing hot dry rock perforation parameters and fracturing hot dry rock to form fractures; step four, acid pretreatment of hot dry rock; step five, injecting slickwater into the fractures formed on the hot dry rock; step six, injecting 40-70 mesh low-density proppant into the fractures formed on the hot dry rock; step seven, back flushing; step eight, designing injection pressure and displacement; step nine, simulating shut-in heating time; step ten, extracting hot water through a straight well; step eleven, repeating steps eight to ten to perform heat extraction work after hot dry rock fracturing. The method maximizes the flow conductivity of the fractures through hydraulic fracturing and performs heat extraction work after hot dry rock fracturing.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing technology for hot dry rock, specifically to a method for hydraulic fracturing heat extraction from hot dry rock and a packer self-locking mechanism. Background Technology

[0002] Hot dry rock generally refers to high-temperature rock masses with temperatures exceeding 180℃, buried at depths of several thousand meters, containing little or no internal fluid (dense and impermeable), and in vast quantities. As a new energy source to replace fossil fuels, hot dry rock holds enormous resources in China, with a calorific value exceeding the combined reserves of conventional coal, oil, and natural gas. Furthermore, it is clean, pollution-free, and can be repeatedly recycled. Therefore, vigorously developing hot dry rock resources has significant practical implications. Hot dry rock typically exhibits characteristics such as density, absence of natural fissures, high Young's modulus, and high ground stress, making fracturing extremely difficult. However, without fracturing, effective development and utilization are virtually impossible. Therefore, the fracturing technology for hot dry rock urgently needs to be developed and solved. Summary of the Invention

[0003] The purpose of this invention is to provide a hydraulic fracturing method for thermal recovery from hot dry rock. This method achieves complete fracturing and extension of a single fracture in the hot dry rock through hydraulic fracturing, maximizing the fracture's conductivity and facilitating thermal recovery after fracturing. This invention also proposes a packer self-locking mechanism.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In the first technical solution, a hydraulic fracturing method for thermal recovery from hot dry rock includes the following steps: Step 1, evaluating the hot dry rock reservoir before fracturing; Step 2, simulating the initiation and propagation of fractures in the hot dry rock; Step 3, optimizing the perforation parameters of the hot dry rock and fracturing the hot dry rock; Step 4, acid pretreatment of the hot dry rock; Step 5, injecting slickwater into the fractures created in the hot dry rock; Step 6, injecting 40-70 mesh low-density proppant into the fractures created in the hot dry rock; Step 7, performing backflow; Step 8, designing the injection pressure and flow rate; Step 9, simulating the shut-in heating time; Step 10, extracting hot water through a vertical well; Step 11, repeating steps 8 to 10 to perform thermal recovery work after fracturing the hot dry rock.

[0005] In the first technical solution, preferably, in step three, the vertical well is perforated using a 180-degree phase angle, the perforation hole position is consistent with the direction of the maximum horizontal principal stress, the hole density is 16-20 holes / m, the hole diameter is greater than 12mm, and the penetration depth is greater than 50cm; the horizontal well is perforated along the circumference of the horizontal well casing using hydraulic jetting technology, with 3-6 holes evenly distributed within one circumference of the horizontal well casing; during hydraulic jetting, two jetting tools are connected in series for jetting, and the number of nozzles and the hole diameter of each jetting tool are adjusted to make the hydraulic jetting speed greater than 200m / s.

[0006] In the first technical solution, preferably, in step four, the acid discharge rate is 1.0 m³. 3 / min-1.5m 3 / min, with a section strength of 0.5m 3 / m-1.0m 3 / m.

[0007] In the first technical solution, preferably, in step five, a variable displacement construction strategy is adopted, where the displacement is increased from low to high, and the displacement is increased when the crack half-length reaches 10m-20m.

[0008] In the first technical solution, preferably, in step six, a high-channel fracturing slug-type proppant addition mode is adopted, with an initial proppant-to-fluid ratio of 2%-3%, a maximum proppant-to-fluid ratio of 18%-20%, and a step-by-step increase of 1.9%-2.1%. The volume of each slug with proppant is 0.5-1.5 times the wellbore volume. The low-density proppant includes soluble proppant, which is uniformly mixed with 40-70 mesh proppant at a ratio of 10%-15%.

[0009] In the first technical solution, preferably, in step seven, when the well type of the hot dry rock is a U-shaped well, the horizontal well is fracturing in stages, and the toe of the horizontal well is connected to a vertical well, which is a heat production well. The hot dry rock is flowed back from the vertical well of the U-shaped well. When the pump stop pressure is higher than 30 MPa, it is vented with a 2 mm nozzle; when the pump stop pressure is lower than 20 MPa, it is vented with a 3 mm nozzle; when the pump stop pressure is lower than 10 MPa, it is vented with a 4 mm nozzle; when the pump stop pressure is lower than 5 MPa, it is vented with a 5 mm nozzle; when the pump stop pressure is lower than 2 MPa, it is opened until the wellhead pressure is 0.

[0010] In the second technical solution, a packer self-locking mechanism is used to realize the hydraulic fracturing heat recovery method for hot dry rock as described in any one of the first technical solutions, comprising: an outer locking sleeve; an inner locking tube disposed inside the outer locking sleeve; a locking device disposed between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve; the locking device comprising: a positioning plate fixedly connected to the outer wall of the inner locking tube, wherein a plurality of first locking teeth are fixedly disposed on both sides of the positioning plate, the plurality of first locking teeth being evenly distributed from top to bottom; two limiting components, respectively located below the two sides of the positioning plate, the two limiting components having mirror-symmetrical structures, the limiting components being fixedly connected to the inner wall of the outer locking sleeve, the limiting components comprising a plurality of second locking teeth evenly distributed from top to bottom, the second locking teeth in the two limiting components being arranged opposite to each other; and a driving component disposed between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve, wherein the second locking teeth in the two limiting components can move closer or further apart from each other under the drive of the driving component.

[0011] In the second technical solution, preferably, the first locking tooth includes an inclined first slope and a horizontal first stop surface, the width of the top of the first locking tooth is greater than the width of the bottom, and a notch is provided between the first locking tooth and the positioning plate.

[0012] In the second technical solution, preferably, the limiting component further includes: a limiting box, which is fixedly connected to the inner wall of the outer locking sleeve; the limiting box has a plurality of insertion holes on its side wall facing the positioning plate, the plurality of insertion holes being evenly distributed from top to bottom; and a clearance hole on the top and bottom surfaces of the limiting box; a plurality of insertion rods, respectively disposed in the plurality of insertion holes and slidable along the inner wall of the insertion holes; a second locking tooth fixedly disposed at one end of the insertion rod located outside the limiting box; the second locking tooth including an inclined second slope and a horizontal second stop surface; and a movable plate disposed inside the limiting box and slidable along the inner wall of the limiting box; the end of the insertion rod located inside the limiting box being fixedly connected to the movable plate; and a plurality of placement slots on both ends of the movable plate away from the insertion holes. The placement slots are evenly distributed from top to bottom. Each placement slot contains a spring, one end of which is fixedly connected to the inner wall of the placement slot, and the other end of which is fixedly connected to the inner wall of the limiting box. A stop bar is located inside the limiting box, on the side of the moving plate away from the insertion hole. The stop bar is positioned between the springs on both sides, with its top extending out of the limiting box through the upper clearance hole and its bottom extending out of the limiting box through the lower clearance hole. The driving assembly includes: a support plate, located between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve, and below the limiting box; the bottom of the stop bar is fixedly connected to the top surface of the support plate; and an electric telescopic rod, located above the support plate, fixedly connected to the inner wall of the outer locking sleeve, with its output end facing downwards and fixedly connected to the support plate.

[0013] In the second technical solution, preferably, the middle section of the stop bar is provided with a third slope, the third slope is provided on the side facing the movable plate, the width of the middle section of the stop bar increases from bottom to top, the width of the lower section of the stop bar is the same as the bottom width of the middle section of the stop bar, the width of the upper section of the stop bar is the same as the top width of the middle section of the stop bar, and the bottom of the movable plate facing the stop bar is provided with a groove, and a fourth slope is provided in the groove.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] (i) This method achieves complete fracturing and extension of a single fracture in hot dry rock through hydraulic fracturing, maximizing the conductivity of the fracture and enabling heat recovery operations after fracturing. The unsupported portion within the proppant pile will form a non-uniform proppant placement pattern, which has a greater conductivity than a simple uniform proppant placement pattern.

[0016] (ii) The packer self-locking mechanism proposed in this invention, when the packer is set, the packer center tube moves downward and drives the inner locking tube to move downward. The locking device will restrict the inner locking tube and make the inner locking tube enter the locked state. At this time, the packer center tube is also restricted and enters the locked state, and will not move upward due to the creep of the production tube, thus avoiding packer setting failure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the front view of the packer self-locking mechanism in the present invention when it is not locked;

[0018] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0019] Figure 3 This is a schematic diagram of the main structure of the packer self-locking mechanism after locking in this invention;

[0020] Figure 4 for Figure 3 Enlarged view of point B in the middle;

[0021] Figure 5 This is a schematic diagram of the front view of the packer self-locking mechanism after unlocking in this invention;

[0022] Figure 6 for Figure 5 Enlarged view of point C in the middle;

[0023] Figure 7 This is an isometric sectional view of the outer locking sleeve in this invention;

[0024] Figure 8 This is an isometric view of the inner locking tube in this invention;

[0025] Figure 9 for Figure 8 Enlarged view at point D;

[0026] Figure 10 This is a front sectional view of the inner locking tube in this invention;

[0027] Figure 11 This is an isometric view of the limiting component in this invention;

[0028] Figure 12 This is an isometric sectional view of the limiting component in this invention;

[0029] Figure 13 This is an isometric view of the bearing plate in this invention;

[0030] Figure 14 This is an isometric view of the stop bar in this invention;

[0031] Figure 15 This is an isometric view of the packer self-locking mechanism after it has been installed on the packer in this invention.

[0032] The reference numerals in the figures include:

[0033] 1-Outer locking sleeve, 11-First limiting groove, 12-Second limiting groove, 2-Inner locking tube, 21-Step surface, 3-Positioning plate, 31-First locking tooth, 311-First slope surface, 312-First stop surface, 32-Notch, 4-Limiting component, 41-Limiting box, 411-Insertion hole, 412-Allowing hole, 42-Insertion rod, 43-Second locking tooth, 431-Second slope surface, 432-Second stop surface, 44-Moving plate, 441 - Top block, 442 Placement slot, 443 Groove, 444 Fourth slope, 45 Spring, 46 Stop bar, 461 Third slope, 462 Protruding plate, 463 Horizontal plate, 5 Drive assembly, 51 Bearing plate, 511 Protrusion, 52 Electric telescopic rod, 6 Packer, 61 Upper connector, 62 Rubber sleeve, 63 Cone, 64 Packer center tube, 65 Slipper, 66 Reversing mechanism, 67 Centralizer. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0035] This invention provides a technical solution: a method for hydraulic fracturing and thermal recovery from hot dry rock, comprising the following steps:

[0036] Step 1: Evaluate the reservoir of pre-compression dry hot rock.

[0037] The evaluation of sandstone reservoirs is basically the same as that of conventional sandstone reservoirs. However, the evaluation of hot dry rock reservoirs, especially the evaluation of rock mechanical parameters, should be carried out on the basis of simulating high temperature and high pressure. Other parameters, such as lithology, physical properties, water-bearing properties, triaxial stress and thermodynamics, can be obtained through conventional logging, well logging and core testing, which will not be elaborated here.

[0038] Step 2: Simulate the initiation and propagation of cracks in hot dry rock.

[0039] The GOFHER software, currently well-suited for use in sandstone, can be used as a tool, with the input parameters varying to reflect the characteristics of hot dry rock. Alternatively, outcrop samples of hot dry rock can be used to simulate triaxial stress conditions and conduct physical simulation studies of fracture initiation and propagation. Currently, physical simulation devices and experimental methods for conventional sandstone, carbonate rocks, and shale are largely mature and well-established, including fracture monitoring methods such as CT scanning, which can be applied to the physical simulation of fracture initiation and propagation in hot dry rock. The physical simulation results can be compared and analyzed with the GOFHER software simulation results to find a suitable simulation method for fracture initiation and propagation characteristics of hot dry rock. Based on the above work, the effects of different fracturing fluid properties and proppant particle size and density on fracture geometry and placement morphology can be simulated to optimize the appropriate combination of fracturing operation parameters.

[0040] Step 3: Optimize the perforation parameters of the hot dry rock and perform hydraulic fracturing to create fractures in the hot dry rock.

[0041] For vertical wells, directional perforation with a 180-degree phase angle is used. The perforation hole position should be aligned with the direction of the maximum horizontal principal stress to avoid near-wellbore fracture bending friction effects. Other perforation parameters should ideally be selected for high density, large diameter, and deep penetration; for example, a density of 16-20 holes / m, a diameter of 12mm or more, and a penetration depth of at least 50cm are recommended.

[0042] For staged fracturing of horizontal wells, hydraulic jetting technology should be used to perforate along the circumference of the horizontal wellbore to ensure that all fracturing fluid enters the same main fracture, avoiding the multi-fracture effect caused by the previous spiral perforation. The number of perforations should be evenly distributed within one circumference of the horizontal well casing, such as 3-6 perforations. The perforation diameter and depth are determined by the hydraulic conditions of the hydraulic jetting. The maximum flow rate and the maximum jetting velocity achievable by the hydraulic nozzle under a given wellhead pressure can be simulated using the aforementioned GOFHER software to see if the jetting velocity meets the perforation requirements. The minimum jetting velocity requirement for conventional sandstone is above 131 m / s; considering the high stress characteristics of hot dry rocks, the minimum jetting velocity requirement is raised to above 200 m / s. If there is still room for flow rate, two jetting tools can be connected in series to obtain more hydraulic fractures and increase the fracture modification volume. Since the complexity of a single fracture is difficult to increase, increasing the number of fractures can be considered to increase the fracture modification volume. If the speed of a certain spray tool string is not up to standard, the number of nozzles and the orifice size of each spray tool can be adjusted appropriately.

[0043] During hydraulic fracturing of hot dry rock, the fracturing production string is first run downhole, and then a packer 6 is run into the section to be treated and set. The purpose of setting is to seal off an effective working space. Fracturing fluid is injected downhole from the surface, creating a high pressure within the confined working space. When the pressure exceeds the fracturing pressure at the bottom layer, fractures will form in the hot dry rock.

[0044] In existing technologies, fluctuations in downhole pressure and unstable injection rates can cause creep in the production tubing. This creep can easily cause the packer center tube 64 to move upwards, leading to packer 6 setting failure and packer 6 unsealing. When this happens, the tubing needs to be pulled out and lowered again for setting, and this frequent rework disrupts normal oilfield production.

[0045] Therefore, during hydraulic fracturing in step three, packer 6, equipped with the packer self-locking mechanism described in Example 2, is used in the setting stage. After packer 6 is set, the central tube inside packer 6 can enter a locked state, and the central tube 64 of packer will not move upward, thus preventing packer 6 from failing to set.

[0046] Step 4: Pre-treat the hot dry rock with acid.

[0047] Considering the high stress and relatively high fracturing pressure of hot, dry rocks, although the rock is dense and lacks natural cracks, preventing significant mud leakage and contamination, acid pretreatment can reduce rock strength and thus lower fracturing pressure. Following standard practice, the acid discharge rate is 1.0 m³. 3 / min-1.5m 3 / min, acid dosage is based on the thickness of the hot dry rock, and the section strength is taken as 0.5m. 3 / m-1.0m 3 / m (The injection volume per unit length of the wellbore during the acidizing process is expressed as cubic meters per meter, using segment strength as the unit). The acid formulation generally uses a soil acid system consisting of 10%-15% hydrochloric acid or 10%-15% hydrochloric acid + 3% hydrofluoric acid. The formulation can be adjusted according to the acid dissolution experiments of actual dry hot rock cores.

[0048] Step 5: Inject slippery water into the fissures created in the hot, dry rock.

[0049] Based on the crack parameter sensitivity simulation results from step two, optimize the volume and discharge rate of the slippery water. If there is a need to control the crack height, a variable discharge rate construction strategy can be adopted, starting from low and gradually increasing the discharge rate. However, the timing of the variable discharge rate should be optimized. Generally, the discharge rate should be increased in a timely manner when the crack half-length reaches 10m-20m.

[0050] Step 6: Inject 40-70 mesh low-density proppant into the fissures created in the hot dry rock.

[0051] Considering the improved perforation strategy in step three, the fracture bending friction is significantly reduced, eliminating the need for the conventional multi-stage proppant slug injection procedure using 70-140 mesh proppant. The addition of 40-70 mesh low-density proppant, taking into account the narrow fracture width resulting from the high stress characteristics of hot dry rock, generally adopts a high-channel fracturing slug-type proppant injection mode. The initial proppant-to-fluid ratio is 2%-3%, with a maximum ratio of 18%-20%, and a step-by-step increase of approximately 2%. The volume of each proppant-supported slug is generally designed to be approximately one times the wellbore volume (for horizontal well fracturing, this is the sum of the volumes of the vertical wellbore and the horizontal wellbore at the fracturing location, hereinafter the same), but in the early slug stage, it can be designed to be 0.5-0.75 times the wellbore volume to prevent early sand blockage. The volume of the isolation fluid without proppant is generally designed to be 1.2-1.5 times the wellbore volume, approximately 1.2 times in the early stage and approximately 1.4-1.5 times in the mid-to-late stage. The main purpose is to observe the formation after the upper proppant is inserted into it for a period of time, so as to judge the pressure rise pattern in real time, and make a judgment on whether there are signs of sand blockage, so as to provide a basis for timely adjustment of construction parameters.

[0052] Regarding the addition of soluble proppant (the density and particle size should be the same as the aforementioned 40 / 70 mesh proppant for uniform injection), it can be uniformly mixed with the 40 / 70 mesh proppant at a ratio of 10%-15%. This proppant will dissolve on its own within a period of time (5-10 days) after the fracturing is completed, leaving high-permeability channels. As long as these channels are interconnected to varying degrees, they can play a certain role. Compared to conventional high-channel fracturing technology, the improvement in conductivity is not significant in the early stages of post-fracturing production. However, in the later stages of production, when the original high channels gradually lose their conductivity, the unsupported portions within the proppant pile will form a non-uniform proppant placement pattern, which has a greater conductivity effect than a simple uniform proppant placement pattern. However, if the compressive strength of this low-density proppant is insufficient to meet the specific dry hot rock reservoir conditions, a self-suspended proppant with the same particle size can be considered.

[0053] In traditional high-channel fracturing technology, the proppant stacks do not provide fracture conductivity; they only support the fracture walls. A significant portion of the conductivity is achieved through unsupported channels between the proppant stacks. Therefore, this patented technology, in addition to leveraging the advantages of conventional high-channel fracturing, expands its functionality. It is important to note that the application of the aforementioned soluble proppant requires ensuring that the channels left after dissolution are interconnected and effectively connected to the high channels formed by high-channel fracturing, avoiding situations where the channels left after dissolution are not interconnected.

[0054] Step 7: Perform the reverse sorting.

[0055] Unlike conventional fracturing flowback, hot dry rock wells sometimes employ a U-shaped well configuration. Horizontal wells are fracturing in stages, with a vertical well (the heat extraction well) connecting to the toe of the horizontal well. Therefore, flowback in hot dry rock is not from the original well, but from the vertical well of the U-shaped well. The flowback requirements for the adjacent vertical well are the same as in conventional fracturing: close the fractures as quickly as possible without backflowing proppant. General experience suggests that after the pump shut-off pressure exceeds 30 MPa, use a 2mm nozzle for venting; below 20 MPa, use a 3mm nozzle; below 10 MPa, use a 4mm nozzle; below 5 MPa, use a 5mm nozzle; and below 2 MPa, allow the pressure at the wellhead to reach zero.

[0056] Step 8: Design the injection pressure and displacement.

[0057] After the adjacent vertical well is flushed out, the fracture closes. However, cold water needs to be injected from this fractured well to heat it through the fracture before hot water meeting certain temperature requirements is extracted from the vertical well. The maximum allowable injection pressure at the wellhead should be calculated by using the bottom-hole fracture closure pressure as a boundary. Under this pressure, the flow rate of the injected cold water can be increased as much as possible. However, the adjacent vertical well must be closed during injection.

[0058] Step 9: Simulate the well shut-in heating time.

[0059] Using the mature oil and gas reservoir numerical simulation software ECLIPSE, we can simulate how long it takes for the well to be shut in after a certain amount of cold water is injected in step eight to raise its temperature to the expected level.

[0060] Step 10: Extract hot water through a vertical well.

[0061] After step nine, the vertical well can be started to extract hot water. Care should be taken to prevent the proppant from being carried out until the pressure at the wellhead of the vertical well is 0.

[0062] Step 11: Repeat steps 8 to 10 to carry out heat extraction work after fracturing the dry hot rock. Example

[0063] Please see Figure 1-15A packer self-locking mechanism is disclosed for implementing the hydraulic fracturing heat recovery method for hot dry rock in Embodiment 1. The mechanism includes an outer locking sleeve 1, an inner locking tube 2, and a locking device. The outer locking sleeve 1 is installed at the bottom of a packer 6, which can use the existing Y221 packer. The inner locking tube 2 is located inside the outer locking sleeve 1 and connected to the bottom of the packer's central tube 64. When the packer 6 is set, the downward movement of the packer's central tube 64 causes the inner locking tube 2 to move downward. The locking device then restricts the inner locking tube 2, locking it into a locked state. At this time, the packer's central tube 64 is also restricted and locked, preventing it from moving upwards due to the creep of the production tubing, thus avoiding packer 6 setting failure. When the packer 6 is unsealed, the locking device no longer restricts the inner locking tube 2, allowing it to move freely. At this time, the packer's central tube 64 is also unlocked and can move upwards.

[0064] Please see Figure 15 The packer 6 includes an upper connector 61, a rubber sleeve 62, a cone 63, a packer center tube 64, slips 65, a reversing mechanism 66, and a centralizer 67. During packing, the tubing is lowered to a predetermined depth, the packer center tube 64 descends, and the slips 65 extend under the downward push of the cone 63, engaging with the inner wall of the casing. The upper connector 61 presses downward against the rubber sleeve 62, causing its outer diameter to expand, thus achieving packing. During unpacking, the packer center tube 64 is lifted, the cone 63 moves upward, the slips 65 retract, and the rubber sleeve 62 loses its compressive force, reducing its outer diameter, thus completing unpacking. Please refer to [link to relevant documentation]. Figure 1 , Figure 10 and Figure 15 The outer locking sleeve 1 is connected to the outer tube thread of the centralizer 67 through the internal thread at its upper end. The outer locking sleeve 1 is a split structure, including a sleeve and an end cap that can be detachably connected to the lower end of the sleeve. The inner locking tube 2 is connected to the lower end thread of the packer center tube 64 through the internal thread at its upper end.

[0065] Please see Figure 1-2 , Figure 8-9 and Figure 11-12 The locking device includes a positioning plate 3, a limiting component 4, and a driving component 5. The positioning plate 3 is fixedly connected to the outer wall of the inner locking tube 2, and several first locking teeth 31 are fixedly provided on both sides of the positioning plate 3. There are two limiting components 4, located below the two sides of the positioning plate 3, and each limiting component 4 includes several second locking teeth 43. The driving component 5 is located between the outer wall of the inner locking tube 2 and the inner wall of the outer locking sleeve 1, and the second locking teeth 43 in the two limiting components 4 can move closer or further apart under the drive of the driving component 5.

[0066] Please see Figure 1-2 When the packer 6 has not yet been set, the positioning plate 3 is positioned above the limiting assembly 4, and the first locking tooth 31 is not in contact with the second locking tooth 43. Please refer to [link / reference]. Figure 3-4When the packer 6 is set, the packer center tube 64 drives the inner locking tube 2 downward, which in turn drives the positioning plate 3 downward. The first slope 311 on the first locking tooth 31 contacts the second slope 431 on the second locking tooth 43. Then, the first locking tooth 31 slides downward along the second slope 431. At this time, the first locking tooth 31 undergoes elastic deformation and moves downward to below the second locking tooth 43. At this time, the first stop surface 312 on the first locking tooth 31 abuts against the second stop surface 432 on the second locking tooth 43. The first locking tooth 31 and the second locking tooth 43 interlock and self-lock, completing the one-way locking engagement. At this time, the packer self-locking mechanism is locked, the inner locking tube 2 is restricted from moving upward, and the packer center tube 64 cannot move upward either.

[0067] Please see Figure 4 and 8 -9. The height of the first locking tooth 31 is less than the height of the second locking tooth 43. A notch 32 is provided between the first locking tooth 31 and the positioning plate 3, so that the upper part of the first locking tooth 31 forms a spring arm structure, providing space for the elastic deformation of the first locking tooth 31. Since the first locking teeth 31 on both sides of the positioning plate 3 are respectively restricted by the second locking teeth 43 on both sides, the inner locking tube 2 will neither move upward nor rotate, thus preventing the inner locking tube 2 from disengaging from the packer central tube 64. Please refer to... Figure 10 The inner locking tube 2 includes an upper large-diameter section and a lower small-diameter section. A downward-facing step surface 21 is provided between the large-diameter section and the small-diameter section. That is to say, the width of the step surface 21 is the distance by which the small-diameter section is retracted inward relative to the large-diameter section. Since the positioning plate 3 is fixed on the outer wall of the small-diameter section of the inner locking tube 2, the outer diameter change of the inner locking tube 2 can provide sufficient space for the positioning plate 3.

[0068] Please see Figure 3-4 and Figure 11-12 The limiting assembly 4 also includes a limiting box 41, which is fixed to the inner wall of the outer locking sleeve 1. The side wall of the limiting box 41 has several insertion holes 411, each containing a insertion rod 42. A second locking tooth 43 is located at the end of the insertion rod 42 located outside the limiting box 41, and the end of the insertion rod 42 located inside the limiting box 41 is fixedly connected to the moving plate 44. The top and bottom surfaces of the limiting box 41 each have a clearance hole 412, with the two clearance holes 412 corresponding to each other. The limiting box 41 also contains a stop rod 46, located on the side of the moving plate 44 away from the insertion holes 411. Therefore, when the first locking tooth 31 contacts the second locking tooth 43, the stop rod 46 can prevent the moving plate 44 from moving, and thus the second locking tooth 43 will not move either. The distance between the second locking teeth 43 on both sides remains at its minimum value and does not change.

[0069] Please refer to the figure. Figure 11-12The movable plate 44 has several top blocks 441 at both ends facing the insertion hole 411, and several placement slots 442 at both ends facing away from the insertion hole 411. The placement slots 442 are also located within the top blocks 441, and each placement slot 442 is equipped with a spring 45, providing space for the spring 45. One end of the spring 45 is fixedly connected to the inner wall of the placement slot 442, and the other end of the spring 45 is fixedly connected to the inner wall of the limiting box 41. When the distance between the second locking teeth 43 on both sides is at its minimum, the spring 45 is in a stretched state, storing elastic potential energy.

[0070] Please see Figure 5-6 When the packer 6 is released, the drive assembly 5 operates, causing the stop bar 46 to move downwards. In this embodiment, the width of the top of the stop bar 46 is smaller than the width of the bottom. Therefore, after the stop bar 46 moves downwards, it no longer restricts the moving plate 44. The spring 45 shortens, releasing elastic potential energy and pulling the moving plate 44 away from the insertion hole 411. The moving plate 44 slides along the inner wall of the limiting box 41, causing the insertion rod 42 to slide along the inner wall of the insertion hole 411. The insertion rod 42 causes the second locking tooth 43 to move away from the positioning plate 3. The second locking teeth 43 on both sides move away from each other, and the distance gradually increases to the maximum value. At this time, the distance between the second locking teeth 43 on both sides is greater than the distance between the first locking teeth 31 on both sides, and the first locking teeth 31 are no longer restricted by the second locking teeth 43. At this time, the locking device no longer restricts the inner locking tube 2, and the inner locking tube 2 is unlocked and can move. The packer center tube 64 is also unlocked and can move upwards.

[0071] Please see Figure 1 , Figure 5 , Figure 7 , Figure 8 and Figure 13 The drive assembly 5 includes a support plate 51 and an electric telescopic rod 52. In this embodiment, there are four positioning plates 3, evenly distributed at equal intervals on the outer wall of the inner locking tube 2. There are eight limiting assemblies 4, arranged in pairs on both sides of the positioning plates 3, thereby distributing the pressure on a single positioning plate 3 and increasing the service life of the positioning plates 3. Since each limiting box 41 has a stop bar 46, there are also eight stop bars 46, and the structures of two adjacent stop bars 46 are mirror symmetrical. The support plate 51 is an annular plate, located between the outer wall of the inner locking tube 2 and the inner wall of the outer locking sleeve 1, and below the limiting box 41. The bottom of the stop bar 46 is fixedly connected to the top surface of the support plate 51.

[0072] Please see Figure 3-4When the first locking tooth 31 and the second locking tooth 43 engage, the bottom surface of the positioning plate 3 abuts against the top surface of the bearing plate 51. At this time, the electric telescopic rod 52 is in a shortened state, and the bearing plate 51 cannot move. The positioning plate 3 is also restricted by the bearing plate 51 and cannot continue to move downwards. In other words, the positioning plate 3 cannot move up or down, nor can it rotate. Therefore, the inner locking tube 2 and the packer center tube 64 also cannot move up or down, nor can they rotate. The packer center tube 64 will not rise due to the creep of the production tubing, thus preventing the packer 6 from failing to set.

[0073] There are four electric telescopic rods 52, evenly distributed above the support plate 51. Each electric telescopic rod 52 is fixedly connected to the inner wall of the outer locking sleeve 1. The output end of each electric telescopic rod 52 faces downwards and is fixedly connected to the support plate 51. Please refer to [link / reference]. Figure 3 and 5 When the packer 6 is released, the electric telescopic rod 52 extends, causing the stop rod 46 to move downward. The width of the stop rod 46 at the limit box 41 gradually decreases, allowing the moving plate 44 to move and the spring 45 to shorten.

[0074] Please see Figure 12-14 The stop rod 46 has a third slope 461 in its middle section, which is located on the side facing the moving plate 44. The bottom of the moving plate 44 facing the stop rod 46 has a groove 443, within which a fourth slope 444 is located. During the downward movement of the stop rod 46, the spring 45 shortens, pulling the moving plate 44 closer to the stop rod 46. The bottom end of the moving plate 44 contacts the third slope 461. At this time, the middle section of the stop rod 46 is embedded in the groove 443, and the third slope 461 and the fourth slope 444 are in contact. The stop rod 46 slides along the fourth slope 444. This invention increases the contact area between the stop rod 46 and the moving plate 44 by providing a groove 443 and a fourth slope 444 at the bottom of the moving plate 44. Therefore, the stop rod 46 and the moving plate 44 do not generate excessive pressure when in contact, preventing damage to both.

[0075] Please see Figure 7 and Figure 13 A protrusion 511 is fixedly provided on the outer wall of the support plate 51, and a first limiting groove 11 is provided on the inner wall of the outer locking sleeve 1 to cooperate with the protrusion 511. The protrusion 511 extends into the first limiting groove 11 and can slide along the inner wall of the first limiting groove 11. The first limiting groove 11 can restrict the support plate 51 through the protrusion 511, reducing the shaking of the support plate 51. Please refer to... Figure 7 , Figure 13-14A protruding plate 462 is fixedly provided on the top of the stop bar 46. A second limiting groove 12 that cooperates with the protruding plate 462 is provided on the inner wall of the outer locking sleeve 1. The protruding plate 462 extends into the second limiting groove 12 and can slide along the inner wall of the second limiting groove 12. The second limiting groove 12 can restrict the top of the stop bar 46 through the protruding plate 462, reducing the shaking of the top of the stop bar 46.

[0076] Please see Figure 5-6 and Figure 13-14 A horizontal plate 463 is provided between the tops of two adjacent stop bars 46. The two ends of the horizontal plate 463 are fixedly connected to the protruding plates 462 on both sides. The horizontal plate 463 can strengthen the top of the stop bar 46 and prevent the top of the stop bar 46 from deforming. The horizontal plate 463 is located on the side of the second locking tooth 43 away from the positioning plate 3. Therefore, when the stop bar 46 moves downward, the horizontal plate 463 will not collide with the second locking tooth 43 or the positioning plate 3.

[0077] Please see Figure 5-6 When packer 6 is released, the packer center tube 64 moves upward. That is, after the inner locking tube 2 drives the positioning plate 3 away from the limiting assembly 4, the electric telescopic rod 52 shortens, driving the stop rod 46 to move upward. The width of the stop rod 46 in the limiting box 41 gradually increases, and the stop rod 46 slides along the fourth slope 444, pushing the moving plate 44 closer to the insertion hole 411. At this time, the spring 45 is stretched to store elastic potential energy, and the second locking teeth 43 on both sides move closer to each other, returning to the minimum distance, waiting for the next setting operation. Therefore, when the packer self-locking mechanism is in use, no parts inside the outer locking sleeve 1 will be damaged, regardless of whether the packer 6 is set or released.

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0079] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A packer self-locking mechanism for realizing a hydraulic fracturing and thermal recovery method for hot dry rock, the method comprising the following steps: Step 1: Evaluate the reservoir of pre-compression dry hot rock; Step 2: Simulate the initiation and propagation of cracks in hot dry rock; Step 3: Optimize the perforation parameters of the hot dry rock and perform hydraulic fracturing to create fractures in the hot dry rock; Step 4: Pre-treat the hot dry rock with acid; Step 5: Inject slippery water into the fissures created in the hot, dry rock; Step 6: Inject 40-70 mesh low-density proppant into the fissures created in the hot dry rock; Step 7: Perform the reverse sorting; Step 8: Design the injection pressure and displacement; Step 9: Simulate the well shut-in heating time; Step 10: Extract hot water through a vertical well; Step 11: Repeat steps 8 to 10 to carry out heat recovery work after fracturing the dry hot rock; The packer self-locking mechanism is characterized in that it includes: Outer lock sleeve; The inner locking tube is located inside the outer locking sleeve; A locking device is provided between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve; The locking device includes: A positioning plate is fixedly connected to the outer wall of the inner locking tube. Several first locking teeth are fixedly provided on both sides of the positioning plate, and the several first locking teeth are evenly distributed from top to bottom. The limiting components are two in number, located below the two sides of the positioning plate respectively. The two limiting components are mirror-symmetrical in structure. The limiting components are fixedly connected to the inner wall of the outer locking sleeve. Each limiting component includes a plurality of second locking teeth, which are evenly distributed from top to bottom. The second locking teeth in the two limiting components are arranged opposite to each other. A driving assembly is disposed between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve, wherein the second locking teeth in the two limiting assemblies can move closer or further apart under the drive of the driving assembly.

2. The packer self-locking mechanism according to claim 1, characterized in that, The first locking tooth includes an inclined first slope and a horizontal first stop surface. The width of the top of the first locking tooth is greater than the width of the bottom. A notch is provided between the first locking tooth and the positioning plate.

3. The packer self-locking mechanism according to claim 2, characterized in that, The limiting component also includes: A limiting box is fixedly connected to the inner wall of the outer locking sleeve. The limiting box has several insertion holes on its side wall facing the positioning plate. The insertion holes are evenly distributed from top to bottom. The top and bottom surfaces of the limiting box each have a clearance hole. A plurality of insert rods are respectively disposed in a plurality of said insert holes and can slide along the inner wall of said insert holes. A second locking tooth is fixedly provided at one end of the insert rod located outside the limiting box. The second locking tooth includes an inclined second slope and a horizontal second stop surface. The width of the top of the second locking tooth is smaller than the width of the bottom. A movable plate is disposed inside the limiting box and can slide along the inner wall of the limiting box. One end of the insertion rod located inside the limiting box is fixedly connected to the movable plate. Both ends of the movable plate away from the insertion hole are provided with a plurality of placement slots. The plurality of placement slots are evenly distributed from top to bottom. A spring is provided in the placement slot. One end of the spring is fixedly connected to the inner wall of the placement slot, and the other end of the spring is fixedly connected to the inner wall of the limiting box. A stop bar is provided inside the limiting box and located on the side of the moving plate away from the insertion hole. The stop bar is located between the springs on both sides. The top of the stop bar extends out of the limiting box through the upper clearance hole, and the bottom of the stop bar extends out of the limiting box through the lower clearance hole. The driving component includes: A support plate is disposed between the outer wall of the inner locking tube and the inner wall of the outer locking sleeve, and is located below the limiting box; the bottom of the stop bar is fixedly connected to the top surface of the support plate. An electric telescopic rod is located above the support plate. The electric telescopic rod is fixedly connected to the inner wall of the outer locking sleeve. The output end of the electric telescopic rod faces downward and is fixedly connected to the support plate.

4. The packer self-locking mechanism according to claim 3, characterized in that, The middle section of the stop bar has a third slope, which is located on the side facing the movable plate. The width of the middle section of the stop bar increases from bottom to top. The width of the lower section of the stop bar is the same as the bottom width of the middle section of the stop bar, and the width of the upper section of the stop bar is the same as the top width of the middle section of the stop bar. The bottom of the movable plate on the side facing the stop bar has a groove, and a fourth slope is provided in the groove.

5. The packer self-locking mechanism according to claim 1, characterized in that, In step three, vertical wells are perforated using a 180-degree phase angle, with the perforation holes aligned with the direction of the maximum horizontal principal stress. The perforation density is 16-20 holes / m, the hole diameter is greater than 12mm, and the penetration depth is greater than 50cm. Horizontal wells are perforated along the circumference of the horizontal wellbore using hydraulic jetting technology, with 3-6 holes evenly distributed within one circumference of the horizontal well casing. During hydraulic jetting, two jetting tools are connected in series, and the number of nozzles and the orifice size of each jetting tool are adjusted to ensure that the hydraulic jetting speed is greater than 200m / s.

6. The packer self-locking mechanism according to claim 1, characterized in that, In step four, the acid displacement is 1.0 m³. 3 / min-1.5m 3 / min, with a section strength of 0.5m 3 / m-1.0m 3 / m.

7. The packer self-locking mechanism according to claim 1, characterized in that, In step five, a variable displacement construction strategy is adopted, with the displacement increasing from low to high, and the displacement is increased when the crack half-length reaches 10m-20m.

8. The packer self-locking mechanism according to claim 1, characterized in that, In step six, a high-channel fracturing slug-type proppant addition mode is adopted, with an initial proppant-to-fluid ratio of 2%-3% and a maximum proppant-to-fluid ratio of 18%-20%, with a step-by-step increase of 1.9%-2.1%. The volume of each slug with proppant is 0.5-1.5 times the wellbore volume. The low-density proppant includes soluble proppant, which is uniformly mixed with 40-70 mesh proppant at a ratio of 10%-15%.

9. The packer self-locking mechanism according to claim 1, characterized in that, In step seven, when the well type for the hot dry rock is a U-shaped well, the horizontal well is fracturing in stages, and a vertical well is connected to the toe of the horizontal well. The vertical well is the heat production well, and the hot dry rock is flowed back from the vertical well of the U-shaped well. When the pump stop pressure is higher than 30 MPa, it is vented with a 2 mm nozzle; when the pump stop pressure is lower than 20 MPa, it is vented with a 3 mm nozzle; when the pump stop pressure is lower than 10 MPa, it is vented with a 4 mm nozzle; when the pump stop pressure is lower than 5 MPa, it is vented with a 5 mm nozzle; when the pump stop pressure is lower than 2 MPa, it is opened up to a wellhead pressure of 0.

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