A fracturing method for fracturing tool with oil bottom seal and without back pressure control

Abstract

The present invention provides a fracturing method of a fracturing tool with oil bottom seal dragging without back pressure control, and the specific steps are: step one, tool pipe string connection, step two, drilling; step three, positioning deeper; step four, setting packer; step five, hydraulic sandblasting perforation; step six, fracturing; step seven, unsealing; step eight, layer transfer construction, after the bottom packer is unsealed, continue to lift the continuous oil pipe, adjust the tool pipe string to the next layer construction position, repeat the above steps four and seven, and realize the bottom-to-top layer-by-layer segmented fracturing construction. Compared with the conventional continuous oil pipe with bottom seal dragging fracturing construction, the present invention can meet the working condition construction of the pump stop pressure exceeding 30MPa, does not need to perform back pressure control during the hydraulic sandblasting perforation stage, reduces the oil pressure in the perforation stage, reduces the construction risk, and can better implement the continuous oil pipe with bottom seal dragging fracturing construction in the high pump stop pressure block.

Description

Technical Field

[0001] The invention belongs to the technical field of staged fracturing transformation of low-permeability oil and gas field reservoirs, and particularly relates to a fracturing method of a fracturing tool connected with an oil bottom seal and dragged without back pressure control. Background Art

[0002] The coiled tubing drag fracturing process and tool technology has the characteristics of unlimited-level fine-layered fracturing, full-bore completion, and controllable scale fracturing, and has become the main process technology for staged fracturing transformation of low-permeability oil and gas fields. The current mature application of coiled tubing with bottom seal drag fracturing tool string composition and structure (from top to bottom) are: coiled tubing to wellhead + coiled tubing connector + check valve + safety release + rigid centralizer + hydraulic ejector + Y511 type packer + casing coupling positioner + guide centralizer. After the tool string is connected on the ground, it is transmitted into the wellbore by continuous oil pipe. After it is lowered to a certain depth, the depth position of the pipe string is calibrated by the casing coupling locator, and it continues to go down to the first construction layer section. The pipe string is lifted and released, and mechanical drill pressure is applied to seal the packer. Then the casing and throttling pipeline are slowly opened, and sand-carrying fluid is pumped from the oil pipe. The sand-carrying fluid is ejected from the nozzle outlet of the hydraulic ejector at high speed to erode the casing wall and the cement ring outside the casing to form perforation holes. After perforation is completed, the casing and throttling pipeline are closed to carry out oil and casing simultaneous injection fracturing construction. After fracturing one layer, the pipe string is lifted to unseal the packer and lifted to the upper layer to continue construction.

[0003] Publication number CN104314511B discloses a compression bottom seal packer, which belongs to the technical field of oilfield gas production, and specifically provides a compression bottom seal packer, including a reversing and straightening mechanism, an anchoring mechanism and a sealing mechanism connected in sequence from bottom to top, the reversing and straightening mechanism is composed of a lower joint, a guide center pipe, a guide pin, a guide pin carrier, a straightening block, a straightening block carrier and a spring, the anchoring mechanism is composed of a slip box, slips, slip springs and a cone, and the sealing mechanism is composed of a lower edge ring, an outer rubber tube, a center pipe, an inner rubber tube, an inner center rod and a pressure cap. Compared with conventional fracturing packers, the invention has high construction efficiency, can meet the requirements of dragging the packer down the well for fracturing multiple stages at one time, and overcomes the problem of increasing operation costs and operation risks due to multiple trips.

[0004] However, in the current operation mode, when the next layer is constructed, after the packer is set, due to the influence of the upper opened formation, the formation itself has a certain pressure, which is called pump-off pressure in the industry. This pump-off pressure will generate a certain upward force on the set packer. When hydraulic sandblasting and perforating operations are carried out, the sand-carrying fluid is injected from the tubing, flows downward along the tubing, and when it reaches the hydraulic ejector, it is ejected from the hydraulic ejector nozzle outlet at high speed, and flows out from the casing release throttling pipeline along the oil casing annulus. In this process, the pump-off pressure of the lower annulus formation isolated by the packer will always generate an upward force on the packer. Taking the pump-off pressure of 20MPa in conventional domestic operation blocks as an example, 5 1 / 2″The inner diameter of the wellbore is 124.3mm, and the equivalent uplift load generated is 25t. The mechanical setting load applied to the packer by the coiled tubing can reach up to about 10t under conventional ideal conditions. The equivalent uplift load is much larger than the mechanical drilling pressure applied by the packer. It is difficult to overcome all the uplift effects by the mechanical drilling pressure applied by the coiled tubing. Therefore, when performing perforating operations, this process mode needs to control the back pressure of the throttling pipeline in the casing to generate a certain throttling pressure in the annulus above the packer to balance the uplift effect of the pump-off pressure of the formation in the annulus below the packer on the packer. Calculated based on the pump-off pressure of 20MPa in conventional domestic operating blocks, the reliable mechanical setting load applied by the coiled tubing is 5t, 5 1 / 2″The inner diameter of the wellbore is 124.3mm. The load can balance the upper force of the lower annulus, which is about 4MPa. In order to ensure the reliable sealing of the packer, the back pressure of the upper annulus of the packer needs to be controlled and reach more than 16MPa. In this way, the packer can be reliably sealed during the hydraulic sandblasting perforation stage and reliable fixed-point perforation operation can be achieved. During the hydraulic sandblasting perforation operation, the pumped sand-carrying fluid will produce greater friction resistance in the tubing and generate a certain throttling differential pressure when it leaves the hydraulic ejector nozzle. The superposition of the two will cause the pumping pressure at the tubing injection port to increase. The current operation equipment Under the conditions of equipment and equipment, the injection pressure of the tubing caused by the superposition of the two has reached more than 40MPa. In addition, due to the control of the back pressure of the casing throttling pipeline, the tubing pumping pressure will rise very high during the hydraulic sandblasting perforation stage. At present, due to the pressure limit of the tubing, this kind of continuous tubing with bottom seal dragging fracturing construction process mode that controls back pressure can only meet the construction conditions where the formation stop pump pressure does not exceed 30MPa. However, there are blocks in the southwest, Xinjiang, Changqing, Qinghai and other oil fields in China where the stop pump pressure far exceeds 30MPa, and there is a demand for fine and dense cutting and fracturing of continuous tubing. Summary of the invention

[0005] In order to overcome the pressure limit of the existing oil receiving pipe, the continuous oil pipe with bottom seal dragging fracturing construction process mode that controls back pressure can only meet the construction under the condition that the formation stop pump pressure does not exceed 30MPa. The present invention provides a fracturing method of a continuous oil pipe with bottom seal dragging fracturing tool without back pressure control. The present invention does not need back pressure control during the hydraulic sandblasting perforating stage, reduces the oil pressure in the perforating stage, reduces the construction risk, and can better implement the continuous oil pipe with bottom seal dragging fracturing construction in the high stop pump pressure block.

[0006] The technical solution adopted by the present invention is:

[0007] A fracturing method for a fracturing tool with an oil bottom seal and without back pressure control, comprising the following specific steps:

[0008] Step 1: Connect the tool pipes.

[0009] Step 2: lowering the coiled tubing and the tool string in step 1 into the wellbore until they reach the designed or required position;

[0010] Step 3: For deeper positioning, after the tool string is lowered to the position of the casing short section or the designed perforation section, the coiled tubing depth position is calibrated to ensure that the tool string is accurately positioned relative to the wellbore depth;

[0011] Step 4: Set the packer. After the tool string is lowered to the layer to be constructed and the depth is calibrated, the pipe string is lifted and lowered to switch the bottom packer state. Drilling pressure is applied downward to the bottom packer to set the bottom packer.

[0012] Step 5: hydraulic sandblasting perforation, opening the annulus between the outer wall of the coiled tubing and the inner wall of the casing, injecting sand-carrying fluid from the coiled tubing, and the sand-carrying fluid flows from the coiled tubing to the nozzle of the hydraulic ejector to form a high-speed sand-carrying jet to impact the inner wall of the casing and flow out along the upper annulus and enter the ground storage tank device; during the hydraulic sandblasting perforation process, the wellbore sealed by the rubber cylinder is divided into an upper annulus and a lower annulus;

[0013] Step six, fracturing, closing the upper annulus liquid outflow channel in step five, injecting fluid from the coiled tubing, and injecting sand-carrying fluid from the upper annulus at the same time, the fluid and the sand-carrying fluid enter the formation through the wellbore and formation connection channel formed by hydraulic sandblasting perforation, and realizing fracturing construction;

[0014] Step 7, unblocking, after the fracturing process is completed, stop injecting fluid into the coiled tubing and the upper annulus;

[0015] Step 8: After the bottom packer is unsealed, continue to lift the coiled tubing, adjust the tool string to the next construction position, and repeat the above steps 4 to 7 to achieve staged fracturing construction from bottom to top.

[0016] The tool string includes a continuous tubing, a continuous tubing connector, a one-way valve, a safety release, a rigid centralizer, a hydraulic ejector, a bottom packer, a casing coupling positioner and a guide centralizer which are sequentially connected from top to bottom.

[0017] The bottom packer is arranged in the casing, and the upper joint of the upper end of the bottom packer is connected; the bottom packer comprises a core shaft, a connecting sleeve, a backwash hole, a packing sealing assembly, a packing pressure cap, a balance channel, an anchor claw base, an anchoring mechanism, a rubber cylinder, a lower rubber cylinder seat, a cone and a sitting cava, the balance channel is arranged in the middle and lower part of the connecting sleeve, the connecting sleeve is connected to the anchor claw base through a thread, the core shaft is inserted into the connecting sleeve from the right end of the connecting sleeve, a packing sealing assembly is installed on the right end of the core shaft, a packing pressure cap is arranged on the right end of the packing sealing assembly, and the packing pressure cap is connected to the core shaft through a thread; the core shaft slides left and right in the connecting sleeve; the backwash hole is arranged in the middle and lower part of the core shaft; the lower end of the rubber cylinder is connected to the lower rubber cylinder seat and the cone in sequence and then arranged on the anchor claw base, and the sitting cava is arranged on the outer wall of the lower end of the anchor claw base; the anchoring mechanism is provided on the anchor claw base, the rubber cylinder is arranged on the outer wall of the anchor claw base, and the anchoring mechanism is located at the front end of the rubber cylinder.

[0018] The mandrel slides left and right in the connecting sleeve, and slides to the right limit until the right end face of the mandrel presses against the left end face of the anchor claw base. At this time, the packing seal assembly is inserted into the inner hole at the left end of the anchor claw base. The packing seal assembly is tightly attached to the inner hole at the left end of the anchor claw base to meet the high-pressure sealing.

[0019] When the bottom packer is set, the cone contacts the seated cava and expands and supports the seated cava on the inner wall of the casing. At the same time, the lower rubber tube seat connected to the cone also squeezes the rubber tube to expand and fit the inner wall of the casing, forming a seal for the wellbore, and the upper and lower annuli form an upper annulus and a lower annulus.

[0020] The bottom packer is a Y511 bottom packer.

[0021] In the step three, when positioning and calibrating the depth, the coiled tubing is pulled up, and resistance is generated when the casing coupling locator passes through the casing collar, causing the tension of the coiled tubing to change. The depth data of the tool pipe string in the wellbore is determined by the casing collar depth data and the tension change, and the depth data of the coiled tubing equipment is compared and calibrated.

[0022] In the step 4, a load is applied downward by means of the continuous tubing operating equipment, and the cone of the bottom packer contacts the sitting cava and squeezes the sitting cava to make it open and anchored on the inner wall of the casing; after the load is applied, the lower rubber cylinder seat connected to the cone by a thread squeezes the rubber cylinder, so that the rubber cylinder expands and fits the inner wall of the casing to form a sealed isolation; at the same time, under the action of the applied drilling pressure, the core shaft is inserted into the sealing surface in the anchor claw base, and the packing sealing assembly installed at the front end of the core shaft also forms a seal in the sealing surface in the anchor claw base. The double seal of the rubber cylinder and the packing sealing assembly forms an isolation of the upper and lower annuli after the bottom packer is seated.

[0023] In the step six, during the hydraulic sandblasting perforating process, the annulus below the wellbore sealed by the rubber tube in the bottom packer is at high pressure, and the upper annulus is at low pressure. Under the action of the pressure difference, the anchor claws on the bottom packer extend outward from the anchor claw base and anchor to the inner wall of the casing, preventing the bottom packer from being pushed up or unsealed due to the pressure difference between the lower annulus and the upper annulus, so that the bottom packer can always be reliably sealed.

[0024] In the step seven, the specific process of unsealing is as follows: the coiled tubing is lifted, the core shaft of the bottom packer is pulled upward, the upper annulus and the lower annulus are connected through the balance channel and pressure balance is achieved, the anchor claws lose the pressure difference effect and retract into the anchor claw base, the upward anchoring of the bottom packer is released, the tubing string is continued to be lifted, the rubber cylinder rebounds, the cone is separated from the sitting crotch, the sitting crotch is retracted and no longer supported by the inner wall of the casing, the bottom packer is unsealed, and the upper annulus and the lower annulus are further fully connected.

[0025] Beneficial effects of the present invention:

[0026] In the present invention, the tool pipe string is connected on the ground, and the connecting hook is used for drilling, positioning and depth calibration, setting and sealing the packer, hydraulic sandblasting perforation, annular main fracturing construction, unsealing the packer and layer transfer construction. In the present invention, the bottom packer structure used in the tool pipe string is different, the opening state of the casing pipeline is different when hydraulic sandblasting perforation is performed, and the highest formation pump stop pressure that can be met for construction is different. Compared with the conventional continuous oil pipe with bottom seal dragging fracturing construction, the present invention can meet the working condition construction of pump stop pressure exceeding 30MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Figure 1 Schematic diagram of the structure of the coiled tubing with bottom seal and dragged fracturing tool string without perforation back pressure control.

[0029] Figure 2 Schematic diagram of the fluid flow state and the working state of the anchor claws during the perforating stage after the back-pressure-free bottom sealing tool is set.

[0030] Figure 3Schematic diagram of the fluid flow state and anchor claw retraction state during the main fracturing construction phase after the back-pressure-free bottom sealing tool packer is set.

[0031] Figure 4 Schematic diagram of the bottom packer balance valve being pulled out and in an unsealed state.

[0032] Figure 5 Schematic diagram of the packer status when hydraulic sandblasting perforation is performed after the bottom packer is set.

[0033] In the figure, the reference numerals are:

[0034] 1. Continuous tubing; 2. Continuous tubing connector; 3. Check valve; 4. Safety release; 5. Rigid centralizer; 6. Hydraulic ejector; 7. Bottom packer; 8. Casing coupling locator; 9. Guide centralizer; 10. Casing; 11. Upper joint; 12. Seal ring 1; 13. Mandrel; 14. Connecting sleeve; 15. Backwash hole; 16. Packing seal assembly; 17. Packing pressure cap; 18. Balance channel; 19. Anchor claw base; 20. Pressure plate; 21. Pressure plate screw; 22. Anchor claw; 23. Spring; 24. Seal ring 2; 25. Rubber cylinder; 26. Lower rubber cylinder seat; 27. Cone; 28. Sitting cava. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0037] Embodiment 1:

[0038] In order to overcome the pressure limit of the existing receiving pipe, the back pressure controlled coiled tubing with bottom seal dragging fracturing construction process mode can only meet the construction problem under the condition that the formation pump stop pressure does not exceed 30MPa. Figure 1-Figure 5The fracturing method of a fracturing tool with an oil bottom seal and dragging without back pressure control is shown. The present invention does not require back pressure control during the hydraulic sandblasting perforating stage, reduces the oil pressure in the perforating stage, reduces the construction risk, and can better implement continuous oil pipe with bottom seal dragging fracturing construction in high pump stop pressure blocks.

[0039] A fracturing method for a fracturing tool with an oil bottom seal and without back pressure control, comprising the following specific steps:

[0040] Step 1: Connect the tool pipes.

[0041] Step 2: lowering the coiled tubing 1 and the tool string in step 1 into the wellbore until they reach the designed or required position;

[0042] Step 3: For deeper positioning, after the tool string is lowered to the position of the casing short section or the designed perforation section, the coiled tubing depth position is calibrated to ensure that the tool string is accurately positioned relative to the wellbore depth;

[0043] Step 4: Set the packer. After the tool string is lowered to the layer to be constructed and the depth is adjusted, the pipe string is lifted and lowered to switch the state of the bottom packer 7. The bottom packer 7 is set by applying drilling pressure downwards.

[0044] Step 5: hydraulic sandblasting perforation, opening the annulus between the outer wall of the coiled tubing 1 and the inner wall of the casing 10, injecting sand-carrying fluid from the coiled tubing 1, and the sand-carrying fluid flows from the coiled tubing 1 to the nozzle of the hydraulic ejector 6 to form a high-speed sand-carrying jet to impact the inner wall of the casing 10 and flow out along the upper annulus and enter the ground storage tank device; during the hydraulic sandblasting perforation process, the wellbore sealed by the rubber cylinder 25 is divided into an upper annulus and a lower annulus;

[0045] Step 6: fracturing. The upper annulus liquid outflow channel in step 5 is closed, and fluid is injected from the coiled tubing 1. At the same time, sand-carrying fluid is injected from the upper annulus. The fluid and sand-carrying fluid enter the formation through the wellbore and formation connection channel formed by hydraulic sandblasting perforation to achieve fracturing construction.

[0046] Step 7, unsealing, after the fracturing process is completed, stop injecting fluid into the coiled tubing 1 and the upper annulus;

[0047] Step eight, layer transfer construction, after the bottom packer 7 is unsealed, continue to lift the coiled tubing 1, adjust the tool string to the next layer construction position, repeat the above steps four to seven, and realize the staged fracturing construction from bottom to top layer by layer.

[0048] The tool provided by the present invention is suitable for layered fracturing construction in a casing completion mode in a block where the pump stop pressure is higher than 30 MPa.

[0049] In the present invention, after the tool string is connected in sequence on the ground, it is transmitted to the bottom of the well through the continuous tubing 1. When it reaches the vicinity of the casing short section, the casing coupling locator can be used to find the short casing position and calibrate the depth of the tool string. After calibrating the depth position of the tool string, continue to drill to the vicinity of the layer section to be constructed, calibrate again and accurately locate the construction position of the layer section through the casing coupling locator, lift and release the pipe string to seal the bottom packer 7, and apply a certain mechanical sealing drilling pressure through the continuous tubing 1 to ensure that the bottom packer 7 is reliably sealed.

[0050] For non-first-layer construction, the formation has been opened and formed an oil and gas flow channel with the wellbore, and there is a certain pressure in the wellbore, which is called the formation pump stop pressure in the industry. At this time, the bottom packer 7 needs to be tested by pumping and pressurizing the upper annulus. If there is no obvious pressure drop, it is judged that the bottom packer 7 is sealed and qualified, and the next step of hydraulic sandblasting and perforating can be carried out.

[0051] After the seal is qualified, slowly open the casing throttling pipeline, and start the tubing pumping program to inject a small displacement. The displacement size is determined and adjusted according to the tubing pressure to ensure that the oil pressure will not be too high or exceed the pressure limit threshold. After the casing pipeline is opened, the upper annulus pressure gradually decreases. When it is lower than a certain value of the lower annulus pressure, the anchoring mechanism on the bottom packer 7 starts working under the pressure difference between the upper and lower annuli, extends and anchors to the wall of the casing 10, forming an anti-uplift anchoring effect on the bottom packer 7. The anchoring force can balance the uplift force of the formation pump stop pressure of the bottom packer 7 to isolate the lower annulus, and the bottom packer 7 will not be slipped or unsealed by the uplift.

[0052] The higher the pressure difference between the upper and lower annuli, the better the anchoring effect of the anchor claws 22 on the bottom packer 7, until the upper annular pressure is completely released to zero, achieving true back pressure-free control. At this time, the bottom packer 7 is still reliably anchored at the initial setting position. At this time, sand-carrying fluid is injected from the oil pipe to perform hydraulic sandblasting perforation operations. After the perforation is completed, the casing release pipeline is closed to perform oil and casing simultaneous injection fracturing construction. After the construction is completed, the continuous oil pipe 1 is lifted to unseal the bottom packer 7 and adjust the tool pipe string to the next perforation position, and the above perforation and fracturing construction are repeated to achieve layer-by-layer fracturing from bottom to top.

[0053] Embodiment 2:

[0054] Based on Example 1, in this embodiment, preferably, the tool string includes a continuous tubing 1, a continuous tubing connector 2, a one-way valve 3, a safety release 4, a rigid centralizer 5, a hydraulic ejector 6, a bottom packer 7, a casing coupling positioner 8 and a guide centralizer 9 connected in sequence from top to bottom.

[0055] Preferably, the bottom packer 7 is arranged in the casing 10, and the upper end of the bottom packer 7 is connected to the upper joint 11; the bottom packer 7 includes a core shaft 13, a connecting sleeve 14, a backwash hole 15, a packing seal assembly 16, a packing pressure cap 17, a balance channel 18, an anchor claw base 19, an anchoring mechanism, a rubber cylinder 25, a lower rubber cylinder seat 26, a cone 27 and a sitting card 28, the balance channel 18 is arranged in the middle and lower part of the connecting sleeve 14, the connecting sleeve 14 is connected to the anchor claw base 19 by threads, the core shaft 13 is inserted into the connecting sleeve 14 from the right end of the connecting sleeve 14, and the right end of the core shaft 13 A packing seal assembly 16 is installed, and a packing pressure cap 17 is provided at the right end of the packing seal assembly 16, and the packing pressure cap 17 is connected to the core shaft 13 through a thread; the core shaft 13 slides left and right in the connecting sleeve 14; the backwash hole 15 is arranged in the middle and lower part of the core shaft 13; the lower end of the rubber cylinder 25 is connected with the lower rubber cylinder seat 26 and the cone 27 in sequence and then arranged on the fluke base 19, and the sitting cava 28 is arranged on the outer wall of the lower end of the fluke base 19; an anchoring mechanism is provided on the fluke base 19, and the rubber cylinder 25 is arranged on the outer wall of the fluke base 19, and the anchoring mechanism is located at the front end of the rubber cylinder 25.

[0056] In the present invention, the core shaft 13 and the upper joint 11 are sealed and connected via a sealing ring 12 .

[0057] Preferably, the mandrel 13 slides left and right in the connecting sleeve 14, and slides to the right to the limit of movement until the right end face of the mandrel 13 presses against the left end face of the fluke base 19, at which time the packing seal assembly 16 is inserted into the inner hole at the left end of the fluke base 19, and the packing seal assembly 16 and the inner hole at the left end of the fluke base 19 are tightly attached to meet the high-pressure sealing;

[0058] Preferably, when the bottom packer 7 is set, the cone 27 contacts the seat cava 28 and expands and supports the seat cava 28 on the inner wall of the casing 10. At the same time, the lower rubber tube seat 26 connected to the cone 27 also squeezes the rubber tube 25 so that the rubber tube 25 expands and fits the inner wall of the casing 10, forming a seal for the wellbore, and the upper and lower annuli of the rubber tube 25 are formed.

[0059] Preferably, the bottom packer 7 is a Y511 type bottom packer.

[0060] like Figure 1 As shown, in the present invention, the tool string includes a coiled tubing 1, a coiled tubing connector 2, a one-way valve 3, a safety release 4, a rigid centralizer 5, a hydraulic ejector 6, a bottom packer 7, a casing coupling locator 8 and a guide centralizer 9. The coiled tubing 1 and the coiled tubing connector 2 are connected by the functional characteristics of the connector itself, and can meet the requirements of high pressure sealing and high load connection, and the remaining tools are connected in sequence by threads.

[0061] like Figure 2As shown in the figure, the flow state and the working state of the anchor claw in the perforating stage after the back-pressure-free bottom sealing tool packer is set; in this stage, the sand-carrying fluid is injected from the coiled tubing, flows downward along the channel inside the tubing, and is ejected from the liquid outlet at high speed when reaching the hydraulic ejector, causing erosion and cutting of the casing wall and the cement ring outside the wellbore to form an oil and gas flow channel connecting the formation, and the sand-carrying fluid ejected from the hydraulic ejector hits the casing wall and then returns along the oil and casing annulus.

[0062] like Figure 4 As shown, in the unsealed state, the backwash hole 15 is not connected to the balance channel 18.

[0063] like Figure 5 As shown, when hydraulic sandblasting is performed, the cone 27 contacts the sitting cava 28 and props the sitting cava 28 on the inner wall of the casing 10. At the same time, the lower rubber tube seat 26 connected to the cone 27 also squeezes the rubber tube 25 to make the rubber tube 25 expand and fit the inner wall of the casing 10, forming an isolation for the wellbore. The upper and lower parts of the rubber tube 25 form an upper annulus and a lower annulus, and at the same time, the connecting sleeve 14 moves upward along the core shaft 13, so that the backwash hole 15 is connected with the balance channel 18.

[0064] Preferably, in the step three, when positioning and calibrating the depth, the coiled tubing 1 is lifted up, and resistance is generated when the casing coupling locator 8 passes through the casing collar, causing the tension of the coiled tubing 1 to change. The depth data of the tool pipe string in the wellbore is determined by the casing collar depth data and the tension change, and the depth data of the coiled tubing equipment is compared and calibrated.

[0065] Preferably, in the step 4, a load is applied downward by means of continuous tubing operation equipment, and the cone 27 of the bottom packer 7 contacts the sitting cava 28 and squeezes the sitting cava 28 to make it open and anchored on the inner wall of the casing 10; after the load is applied, the lower rubber cylinder seat 26 connected to the cone 27 by a thread squeezes the rubber cylinder 25, so that the rubber cylinder 25 expands and fits the inner wall of the casing 10 to form a sealed isolation; at the same time, under the action of the applied drilling pressure, the core shaft 13 is inserted into the sealing surface in the anchor claw base 19, and the packing sealing assembly 16 installed at the front end of the core shaft 13 also forms a seal in the sealing surface in the anchor claw base 19, and the double seal of the rubber cylinder 25 and the packing sealing assembly 16 forms an isolation of the upper and lower annuli after the bottom packer 7 is seated.

[0066] Preferably, in the step six, during the hydraulic sandblasting perforating process, the annulus below the wellbore sealed by the rubber tube 25 in the bottom packer 7 is at high pressure, and the upper annulus is at low pressure. Under the action of the pressure difference, the anchor claws 22 on the bottom packer 7 extend outward from the anchor claw base 19 and anchor to the inner wall of the casing 10, preventing the bottom packer 7 from being pushed upward or unsealed due to the pressure difference between the lower annulus and the upper annulus, so that the bottom packer 7 can always be reliably sealed.

[0067] Preferably, in the step seven, the specific process of unsealing is: lifting the coiled tubing 1, the core shaft 13 of the bottom packer 7 is pulled upward, the upper annulus and the lower annulus are connected through the balance channel 18 and pressure balance is achieved, the anchor claw 22 loses the pressure difference effect and retracts into the anchor claw base 19, the upward anchoring of the bottom packer 7 is released, the tubing string is continued to be lifted, the rubber cylinder 25 rebounds, the cone 27 is separated from the sitting crotch 28, the sitting crotch 28 retracts and is no longer supported on the inner wall of the casing 10, the bottom packer 7 is unsealed, and the upper annulus and the lower annulus are further fully connected.

[0068] like Figure 5 As shown, in the Y511 type bottom packer 7, the connecting sleeve 14 is connected to the anchor claw base 19 through threads, the core shaft 13 is inserted into the connecting sleeve 14 from the right end of the connecting sleeve 14, and a packing seal assembly 16 is installed at the right end of the core shaft 13. A packing pressure cap 17 is provided at the right end of the packing seal assembly 16, and the packing pressure cap 17 is connected to the core shaft 13 through threads. The core shaft 13 can slide left and right in the connecting sleeve 14, and can slide to the right to the limit until the right end face of the core shaft 13 presses against the left end face of the anchor claw base 19, at which time the packing seal assembly 16 is inserted into the inner hole at the left end of the anchor claw base 19, and the packing seal assembly 16 and the inner hole at the left end of the anchor claw base 19 are tightly attached to meet the high-pressure sealing. When the bottom packer 7 is set, a certain drilling pressure is applied through the continuous oil pipe ground operation equipment, which can ensure that the cone 27 of the Y511 bottom packer 7 contacts the sitting cava 28 and supports the sitting cava 28 on the inner wall of the casing 10. At the same time, the lower rubber tube seat 26 connected to the cone 27 also squeezes the rubber tube 25 to make the rubber tube 25 expand and fit the inner wall of the casing 10, forming a seal for the wellbore, forming an upper annulus and a lower annulus. After the bottom packer 7 is set, before the upper annulus is opened for hydraulic sandblasting and perforating, the pressure of the upper annulus and the lower annulus are both the formation pump stop pressure after the construction of the upper layer is completed. The size of this pressure is determined by the conditions and characteristics of the formation itself, and the pressure values ​​are different in different oil and gas blocks. At present, the formation pump stop pressure of most common oil and gas blocks in China does not exceed 25MPa, and the formation pump stop pressure of some blocks will be higher than 25MPa, or even as high as 50MPa.

[0069] In the present invention, an anchor mechanism is provided on the anchor claw base 19 in front of the rubber cylinder 25 of the bottom packer 7, and the anchor mechanism is arranged in the corresponding anchor groove; the anchor mechanism includes an anchor claw 22, an anchor claw base 19, a spring 23, a pressure plate 20, a pressure plate screw 21 and a sealing ring 24, and the pressure plate 20 is fixed to the anchor claw base 19 by the pressure plate screw 21; a spring 23 is provided between the anchor claw 22 and the pressure plate 20, and a sealing ring 24 is provided at both the front and rear ends of the anchor claw 22. The continuous tubing connector 2 is connected and fixed to the end of the continuous tubing 1 by means of a seat card 28, screws, etc., and other tool pipe string accessories are sequentially connected together by threads.

[0070] Before the hydraulic sandblasting perforation is prepared, the upper annulus is opened to release the throttling pipeline, and the upper annulus pressure is released until it drops to zero. During the hydraulic sandblasting perforation stage, the upper annulus pressure is zero, and the lower annulus pressure is the pump stop pressure of the upper layer of the completed formation. Under the pressure difference between the lower annulus and the upper annulus, the anchor claw 22 extends from the anchor claw base 19 and anchors to the inner wall of the casing 10.

[0071] For the common 5 1 / 2″ casing, with an inner diameter of 124.3mm, the pump stop pressure of the formation after the construction of the previous layer is calculated to be 25MPa. The pressure of the lower annulus is higher than that of the upper annulus during the hydraulic sandblasting perforation stage. The pressure difference on the packer is calculated to be about 30t. The drilling pressure applied by the continuous tubing ground operation equipment to the packer is usually not more than 10t, and is generally 4-5t. Therefore, in the conventional continuous tubing fracturing construction with bottom seal, the upper annulus will be set to control the throttling of the throttling pipeline to generate back pressure during the hydraulic sandblasting perforation stage to balance the upward force of the lower annulus on the packer. According to the calculation, the balancing force generated by the back pressure must be at least 25t, which is converted into a back pressure of no less than 20.5MPa.

[0072] During conventional continuous tubing hydraulic sandblasting perforation operations, the perforating fluid is injected through the continuous tubing and ejected from the hydraulic ejector nozzle, and then returned to the ground through the casing annulus. During this process, the perforating fluid will produce friction resistance in the continuous tubing, and a throttling pressure difference will be generated at the hydraulic ejector nozzle. Under the combined effect of the two, the pump pressure at the injection end of the continuous tubing generally reaches 40-45MPa. In addition, under the control of back pressure, the three combined causes the pump pressure at the injection end of the continuous tubing to exceed 60MPa, or even as high as 65MPa. The general safe pressure range of continuous tubing is 68-70MPa. Excessive tubing injection pressure is close to the safe pressure limit of the continuous tubing, resulting in extremely high safety risks on the ground part of the continuous tubing, approaching the construction safety limit. Therefore, for formation blocks with a pump stop pressure higher than 30MPa, the conventional continuous tubing with bottom seal operation mode requires back pressure control during the perforation stage, which is difficult to meet construction needs.

[0073] As attached Figure 5As shown, when hydraulic sandblasting perforation is performed, the upper annulus is not back-pressure controlled. Before construction, the bottom packer 7 is set at the designed position. At this time, the upper and lower annular pressures of the bottom packer 7 are both the formation pump stop pressure after the fracturing construction of the upper layer is completed. After the sealing effect of the bottom packer 7 is verified and qualified, the upper annulus casing is opened to release the pipeline, and the upper annular pressure is released until it drops to zero. In this process, the bottom packer 7 relies on the mechanical drilling pressure applied by the continuous oil pipe 1 to complete the setting and isolation. The mandrel 13 of the bottom packer 7 is inserted into the anchor claw base 19, and the packing seal assembly 16 is tightly fitted with the inner hole at the left end of the anchor claw base 19 to form a high-pressure seal. When the upper annular pressure drops to a certain value, and the pressure difference with the lower annular pressure is higher than the starting working pressure of the anchor claw 22, the anchor claw 22 extends outward under the action of the pressure difference and anchors on the inner wall of the casing 10. The pressure difference value of the anchor claw 22 starting operation is generally small, within the range of 2MPa. The higher the pressure difference, the better the anchoring effect of the anchor claw 22 on the inner wall of the casing 10. The outer diameter of the packing seal assembly 16 is relatively small, and the upward force generated under the lower annular high pressure is also relatively small. Calculated with the outer diameter of the packing seal assembly 16 of 30mm and the lower annular high pressure of 50MPa, under the limit state, the upward force of the lower annular high pressure on the core shaft 13 of the bottom packer 7 and the parts above the pipe string is 3.5t. Under normal circumstances, the mechanical sealing drilling pressure applied to the bottom packer 7 by the continuous oil pipe 1 can overcome the upward force of the lower annular high pressure on the core shaft 13 of the bottom packer 7 and the parts above the pipe string. In the hydraulic sandblasting perforation stage, when the annular casing release pipeline is not back-pressure controlled, the bottom packer 7 can achieve downward and upward bidirectional anchoring, and the bottom packer 7 can be effectively sealed after being sealed, and is not limited by the pump stop pressure of the formation sealed by the bottom packer 7, meeting normal construction.

[0074] The main fracturing is self-anchored. After the hydraulic sandblasting and perforating are completed, the casing pipeline gate needs to be closed, and the continuous tubing 1 or the casing annulus is pumped and pressurized to conduct a rupture test on the formation. The pressure is increased to a certain value, and the formation rupture test is completed. The main fracturing pumping channel is formed, and then the main fracturing construction begins. When the main fracturing construction is carried out, the pumping and injection construction can be carried out simultaneously from the continuous tubing 1 and the casing annulus. During the construction process, the upper annulus pressure sealed by the bottom packer 7 will theoretically be higher than the lower annulus pressure, and the anchor claw 22 will be compressed back into the anchor claw base 19 under the action of the reverse pressure difference. After the main fracturing construction is completed, the pump is stopped. The upper annulus pressure sealed by the bottom packer 7 is the formation pump stop pressure after the new layer is constructed, and the lower annulus pressure sealed by the bottom packer 7 is the formation pump stop pressure after the previous layer is constructed.

[0075] Theoretically, the formation pump-off pressure after the construction of a new layer is higher than the formation pump-off pressure after the construction of the previous layer, and the anchor claw 22 will not start to extend, but retract into the anchor claw base 19. Lift the coiled tubing 1, the mandrel 13 of the bottom packer 7 is pulled out from the anchor claw base 19, the packing seal assembly 16 is separated from the inner hole at the left end of the anchor claw base 19, the upper and lower annuli of the bottom packer 7 are connected through the balance channel 18, and the pressure is restored to balance. The anchor claw 22 is still retracted in the anchor claw base 19 under the action of the spring 23, and the coiled tubing 1 is continued to be lifted. The connecting sleeve 14 and the anchor claw base 19 are driven upward through the mandrel 13. The rubber cylinder seat part on the anchor claw base 19 no longer squeezes the rubber cylinder 25, and the rubber cylinder 25 rebounds to release the packing, and the bottom packer 7 is lifted and released. Continue to lift the pipe string to the previous construction layer section for construction.

[0076] The construction steps of the method provided by the present invention are generally similar to the conventional continuous tubing with bottom seal dragging fracturing construction process steps, and mainly include the following steps: ground connection of the tool string - drilling - positioning and depth calibration - sealing the packer - hydraulic sandblasting perforation - annulus main fracturing construction - unsealing the packer - layer transfer construction. The difference of this process method is that the structure of the bottom packer connected and used in the pipe string is different, the opening state of the casing pipeline is different when hydraulic sandblasting perforation is performed, and the highest formation pump-off pressure that can be met for construction is different. Compared with conventional continuous tubing with bottom seal dragging fracturing construction, the method provided by the present invention can meet the construction conditions where the pump-off pressure exceeds 30MPa. The specific implementation steps of the method provided by the present invention are as follows:

[0077] Step 1: Connect the tool pipes: Figure 1 For example, the connection sequence of the tool pipe string involved in the present invention is from top to bottom: continuous tubing 1, continuous tubing connector 2, one-way valve 3, safety release 4, rigid centralizer 5, hydraulic ejector 6, Y511 type bottom packer 7, casing coupling locator 8, guide centralizer 9. The continuous tubing 1 and the continuous tubing connector 2 are connected through the functional characteristics of the connector itself, and can meet the requirements of high pressure sealing and high load-bearing connection. The remaining tools are connected in sequence through threads.

[0078] Step 2, drilling down: relying on the downward thrust provided by the coiled tubing operation equipment, the coiled tubing 1 and the tool string are lowered into the wellbore until they reach the designed or required position.

[0079] Step 3, deeper positioning: After the tool string is lowered to the position of the casing short section or the designed perforation section, the continuous tubing depth position calibration will be performed to ensure that the tool string is accurately positioned relative to the wellbore. When positioning and calibrating the depth, the continuous tubing 1 is lifted up, and the casing collar locator 8 will generate a certain resistance when passing through the casing collar, causing the tension of the continuous tubing 1 to change. The tension acquisition system of the continuous tubing surface equipment can identify the tension change, and the depth data of the tool string in the wellbore is judged by combining the casing collar depth data and the tension change, and the depth data of the continuous tubing equipment is compared and calibrated.

[0080] Step 4, set the packer: After the tool string is lowered to the layer to be constructed and the depth is determined, the pipe string is lifted and lowered to switch the state of the Y511 bottom packer 7, and the drilling pressure is applied downward to the Y511 bottom packer 7 to set the Y511 bottom packer 7. Relying on the continuous tubing operation equipment to apply a certain load downward, the cone 27 of the Y511 bottom packer 7 contacts the seat clasp 28 and squeezes the seat clasp 28 to make it open and anchored on the inner wall of the casing 10. After applying a certain load, the lower rubber cylinder seat 26 connected to the cone 27 by a thread squeezes the rubber cylinder 25, so that the rubber cylinder 25 expands and fits the inner wall of the casing 10 to form a sealed packer. At the same time, under the applied drilling pressure, the core shaft 13 of the Y511 bottom packer 7 is inserted into the sealing surface in the anchor claw base 19, and the packing seal assembly 16 installed at the front end of the core shaft 13 also forms a seal in the sealing surface in the anchor claw base 19. The double seal of the rubber tube 25 and the packing seal assembly 16 forms the isolation of the upper and lower annuli after the Y511 bottom packer 7 is set.

[0081] Step 5, hydraulic sandblasting perforation: open the annulus between the outer wall of the coiled tubing 1 and the inner wall of the casing 10, hereinafter referred to as the upper annulus, inject sand-carrying fluid from the coiled tubing 1, the sand-carrying fluid flows from the coiled tubing 1 to the nozzle of the hydraulic ejector 6, and forms a high-speed sand-carrying jet to impact the inner wall of the casing 10 and flow out along the upper annulus and enter the ground storage tank device. The abrasives such as quartz sand carried by the high-speed sand-carrying jet cut the casing, so as to penetrate the casing, erode the cement ring and the formation, realize the perforation operation, and establish a connecting channel between the wellbore and the formation. During the hydraulic sandblasting perforation process, the annulus below the wellbore sealed by the rubber tube 25 of the Y511 type bottom packer 7 is referred to as the lower annulus as high pressure, and the upper annulus as low pressure. Under the action of the pressure difference, the anchor claws 22 on the Y511 type bottom packer 7 extend outward from the anchor claw base 19 and anchor to the inner wall of the casing 10, preventing the Y511 type bottom packer 7 from being pushed up or unsealed due to the pressure difference between the lower annulus and the upper annulus, so that the Y511 type bottom packer 7 can always be reliably set;

[0082] Step 6, fracturing: close the upper annulus liquid outflow channel, inject fluid from the coiled tubing 1, and inject sand-carrying fluid from the upper annulus at the same time, and the fluid and sand-carrying fluid enter the formation through the wellbore and formation connection channel formed by hydraulic sandblasting perforation to achieve fracturing construction;

[0083] Step 7, unsealing: After the fracturing process is completed, stop injecting fluid into the coiled tubing 1 and the upper annulus. Lift the coiled tubing 1, the core shaft 13 of the Y511 bottom packer 7 is pulled upward, the upper annulus and the lower annulus are connected through the balance channel 18 of the Y511 bottom packer 7 and achieve pressure balance, the anchor claw 22 loses the pressure difference effect and retracts into the anchor claw base 19, and the upward anchoring of the Y511 bottom packer 7 is released. Continue to lift the pipe string, the rubber cylinder 25 of the Y511 bottom packer 7 rebounds, the cone 27 is separated from the sitting crotch 28, and the sitting crotch 28 retracts and is no longer supported on the inner wall of the casing 10, the Y511 bottom packer 7 is unsealed, and the upper annulus and the lower annulus are further fully connected;

[0084] Step 8: Layer transfer construction: After the Y511 bottom packer 7 is unsealed, the coiled tubing 1 is continuously lifted, the tool string is adjusted to the next layer construction position, and the above steps 4 to 7 are repeated to realize the staged fracturing construction from bottom to top layer by layer.

[0085] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0086] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0087] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design that is the same or similar to the present invention belongs to the protection scope of the present invention. The device structures and method steps not described in detail in the present invention are all prior art and will not be further described in the present invention.

Claims

1. A fracturing method for a fracturing tool with oil bottom seal and without back pressure control, characterized in that: The specific steps are: Step 1: Connect the tool pipes. Step 2: lowering the coiled tubing (1) and the tool string in step 1 into the wellbore until they reach the designed or required position; Step 3: For deeper positioning, after the tool string is lowered to the position of the casing short section or the designed perforation section, the coiled tubing depth position is calibrated to ensure that the tool string is accurately positioned relative to the wellbore depth; Step 4, the packer is set. After the tool string is lowered to the layer to be constructed and the depth is calibrated to determine the position of the tool string, the pipe string is lifted and lowered to switch the state of the bottom packer (7), and drilling pressure is applied downward to the bottom packer (7) to set the bottom packer (7). In the step 4, a load is applied downward by means of the continuous tubing operation equipment, and the cone (27) of the bottom packer (7) contacts the seat card slip (28) and squeezes the seat card slip (28) to open and anchor it on the inner wall of the casing (10); after the load is applied, the seat card slip (28) is connected to the cone (27) through a thread. The connected lower rubber cylinder seat (26) squeezes the rubber cylinder (25) so that the rubber cylinder (25) expands and fits the inner wall of the casing (10) to form a sealed isolation; at the same time, under the action of the applied drilling pressure, the core shaft (13) is inserted into the sealing surface in the anchor claw base (19), and the packing seal assembly (16) installed at the front end of the core shaft (13) also forms a seal in the sealing surface in the anchor claw base (19). The double seal of the rubber cylinder (25) and the packing seal assembly (16) forms an isolation of the upper and lower annuli after the bottom packer (7) is set; Step 5: hydraulic sandblasting perforation, opening the annulus between the outer wall of the coiled tubing (1) and the inner wall of the casing (10), injecting sand-carrying fluid from the coiled tubing (1), and the sand-carrying fluid flows from the coiled tubing (1) to the nozzle of the hydraulic ejector (6) to form a high-speed sand-carrying jet that impacts the inner wall of the casing (10) and flows out along the upper annulus and enters the ground storage tank device; during the hydraulic sandblasting perforation process, the wellbore sealed by the rubber cylinder (25) is divided into an upper annulus and a lower annulus; Step 6: fracturing. The upper annulus liquid outflow channel in step 5 is closed, and fluid is injected from the coiled tubing (1). At the same time, sand-carrying fluid is injected from the upper annulus. The fluid and sand-carrying fluid enter the formation through the wellbore and formation connection channel formed by hydraulic sandblasting perforation, thereby realizing fracturing construction. Step 7, unsealing, after the fracturing process is completed, stop injecting fluid into the coiled tubing (1) and the upper annulus; Step 8, layer transfer construction, after the bottom packer (7) is unsealed, continue to lift the coiled tubing (1), adjust the tool string to the next layer construction position, repeat the above steps 4 to 7, and realize the staged fracturing construction from bottom to top layer by layer; The tool string comprises a continuous tubing (1), a continuous tubing connector (2), a one-way valve (3), a safety release (4), a rigid centralizer (5), a hydraulic ejector (6), a bottom packer (7), a casing coupling positioner (8) and a guide centralizer (9) which are connected in sequence from top to bottom; the bottom packer (7) is arranged in the casing (10) and is connected to the upper joint (11) at the upper end of the bottom packer (7); the bottom packer (7) comprises a core shaft (13), a connecting sleeve (14), a backwash hole (15), a packing seal assembly (16), a packing pressure cap (17), a balance channel (18), an anchor claw base (19), an anchor mechanism, a rubber cylinder (25), a lower rubber cylinder seat (26), a cone (27) and a seat cava (28); the balance channel (18) is arranged in the middle and lower part of the connecting sleeve (14); the connecting sleeve (14) ) is connected to the anchor claw base (19) through threads, the core shaft (13) is inserted into the connecting sleeve (14) from the right end of the connecting sleeve (14), a packing seal assembly (16) is installed at the right end of the core shaft (13), and a packing pressure cap (17) is provided at the right end of the packing seal assembly (16), and the packing pressure cap (17) is connected to the core shaft (13) through threads; the core shaft (13) slides left and right in the connecting sleeve (14); the backwash hole (15) is arranged in the middle and lower part of the core shaft (13); the lower end of the rubber cylinder (25) is connected to the lower rubber cylinder seat (26) and the cone (27) in sequence and then arranged on the anchor claw base (19), and the sitting cava (28) is arranged on the outer wall of the lower end of the anchor claw base (19); the anchor mechanism is provided on the anchor claw base (19), the rubber cylinder (25) is arranged on the outer wall of the anchor claw base (19), and the anchor mechanism is located at the front end of the rubber cylinder (25).

2. The fracturing method of a fracturing tool with oil bottom seal and no back pressure control according to claim 1, characterized in that: The core shaft (13) slides left and right in the connecting sleeve (14), and slides to the right to the limit of movement until the right end face of the core shaft (13) presses against the left end face of the anchor claw base (19). At this time, the packing seal assembly (16) is inserted into the inner hole at the left end of the anchor claw base (19). The packing seal assembly (16) and the inner hole at the left end of the anchor claw base (19) are tightly attached to each other to meet the high-pressure sealing requirement.

3. The fracturing method of a fracturing tool with oil bottom seal and no back pressure control according to claim 1, characterized in that: When the bottom packer (7) is set, the cone (27) contacts the seated cava (28) and expands the seated cava (28) to support it on the inner wall of the casing (10). At the same time, the lower rubber tube seat (26) connected to the cone (27) also squeezes the rubber tube (25) so that the rubber tube (25) expands and fits the inner wall of the casing (10), thereby forming a seal for the wellbore. The upper and lower parts of the rubber tube (25) form an upper annulus and a lower annulus.

4. The fracturing method of a fracturing tool with oil bottom seal and no back pressure control according to claim 1, characterized in that: The bottom packer (7) is a Y511 type bottom packer.

5. The fracturing method of claim 1, wherein the fracturing tool is dragged by an oil bottom seal without back pressure control, and the method is characterized in that: In the step 3, when positioning and calibrating the depth, the coiled tubing (1) is lifted up, and the casing collar locator (8) generates resistance when passing through the casing collar, causing the tension of the coiled tubing (1) to change. The depth data of the tool string in the wellbore is determined by the casing collar depth data and the tension change, and the depth data of the coiled tubing equipment is compared and calibrated.

6. The fracturing method of claim 1, wherein the fracturing tool is dragged by an oil bottom seal without back pressure control, and the method is characterized in that: In the sixth step, during the hydraulic sandblasting perforation process, the annulus below the wellbore sealed by the rubber sleeve (25) in the bottom packer (7) is at high pressure, and the upper annulus is at low pressure. Under the action of the pressure difference, the anchor claws (22) on the bottom packer (7) extend outward from the anchor claw base (19) and are anchored on the inner wall of the casing (10), thereby preventing the bottom packer (7) from sliding upward or being unsealed due to the pressure difference between the lower annulus and the upper annulus, so that the bottom packer (7) is always reliably sealed.

7. The fracturing method of claim 1, wherein the fracturing tool is dragged by an oil bottom seal without back pressure control, and the method is characterized in that: In the step 7, the specific process of unsealing is as follows: the coiled tubing (1) is lifted, the core shaft (13) of the bottom packer (7) is pulled upward, the upper annulus and the lower annulus are connected through the balance channel (18) and pressure balance is achieved, the anchor claw (22) loses the pressure difference effect and retracts into the anchor claw base (19), the upward anchoring of the bottom packer (7) is released, the tubing string is continuously lifted, the rubber cylinder (25) rebounds, the cone (27) is separated from the sitting crotch (28), the sitting crotch (28) retracts and is no longer supported on the inner wall of the casing (10), the bottom packer (7) is unsealed, and the upper annulus and the lower annulus are further fully connected.

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