Repeated volume fracturing wellbore reconstruction method for horizontal well

Abstract

The invention relates to the technical field of wellbore reconstruction, and provides a horizontal well repeated volume fracturing wellbore reconstruction method which comprises the following steps: S1, determining production casing working conditions and repeated fracturing requirements of a to-be-constructed repeated fracturing oil and gas well; s2, the placing position of a shaft reconstruction pipe column is determined; s3, the size of a small casing pipe in a shaft reconstruction pipe column is determined, and the construction requirement that the displacement under volume fracturing is larger than or equal to 10 m < 3 > / min is met; s4, the shaft reconstruction pipe column is put into the placing position of the production casing pipe, and a new shaft of a double-layer casing pipe structure is formed; and S5, perforation and fracturing are conducted on the new wellbore, and repeated volume fracturing is achieved. The method has the advantages that the construction technology is simple, well cementation is not needed, friction resistance in fracturing operation is reduced, and therefore it is ensured that construction under the large displacement in horizontal well volume fracturing can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of wellbore reconstruction, and in particular, to a method for reconstructing a wellbore for repeated volume fracturing of horizontal wells. Background Art

[0002] Wellbore reconstruction technology is a necessary condition for oilfields to retrofit and refracture old oil and gas wells in the later stage. In the later stage of oil and gas well production, the production decline rate accelerates, the water content increases significantly, and there are even a large number of sand production, casing corrosion leakage, deformation and casing damage, etc., resulting in a large number of shut-in wells. There are also phenomena such as sliding sleeve failure and screen pipe damage; in addition, the spacing of early staged perforation fracturing is large, the displacement and total volume are insufficient, and the fracturing design is unreasonable, and there is a lot of remaining oil and gas that needs to be re-perforated and fractured.

[0003] The horizontal well volume fracturing technology adopts a large-displacement injection method, which can provide more net pressure to improve the complexity of fractures, fully expand the fractures to increase the extension range, provide sufficient sand-carrying performance to ensure the addition of a large amount of proppant, and can greatly increase the reservoir stimulation volume. Pumping bridge plug and open-hole fracturing is the main construction method in volume fracturing. It reforms the reservoir in a large range by means of pumping cable cluster perforation + composite bridge plug staged volume fracturing. The construction displacement is large, generally at least 10m 3 / min or more.

[0004] At present, there are mainly three technologies for reconstructing and refracturing old wellbores: chemical and physical plugging processes; expandable pipe patch processes; and sleeve-in-sleeve processes. However, the existing processes have the following problems:

[0005] Chemical and physical plugging processes: The through-diameter is large and the construction displacement is high, but all perforation holes are required to be plugged. And with the multi-point leakage effect during repeated fracturing of horizontal wells (the existence of multiple clusters of fractures and the pressure reduction during long-term production after fracturing, which accelerates the leakage effect of the carrying fluid), the random migration of the temporary plugging agent is inevitable, and the plugging reliability is poor.

[0006] Expandable pipe patch process: The through-diameter is large and the upper and lower through-diameters are the same, but the pressure-bearing capacity is limited after patching and cannot meet the continuous construction under large displacement and large pressure.

[0007] Sleeve-in-sleeve process: High requirements for cementing quality. Due to the small annulus gap, the cementing operation becomes more complicated, and the cement sheath has high pressure-bearing capacity requirements. If effective pressure-bearing cannot be achieved, it may lead to packer failure and affect the effect of subsequent operations; the displacement is limited and continuous construction cannot be carried out. The small inner diameter of the casing increases the friction during fracturing, limits the liquid displacement, and cannot support the large-displacement stimulation operations in volume fracturing. And the small-inner-diameter casing cannot perform high-efficiency wellbore reconstruction processes such as pumping bridge plug perforation and coiled tubing operations, further restricting the operation effect.

[0008] Therefore, in view of these problems, it is necessary to develop a new wellbore reconstruction method to improve the poor wellbore stability and restricted displacement after wellbore reconstruction, and meet the requirements of stimulation under volume fracturing. Summary of the Invention

[0009] The purpose of the present invention is to provide a wellbore reconstruction method for repeated volume fracturing of horizontal wells. This method has the advantages of simple construction technology and no need for cementing, reducing the friction in the fracturing operation, so as to ensure that it can meet the construction requirements under large displacement in the volume fracturing of horizontal wells.

[0010] To solve the above technical problems, the technical solution adopted in this application is as follows:

[0011] The embodiments of this application provide a wellbore reconstruction method for repeated volume fracturing of horizontal wells, including the following steps: S1. Determine the production casing conditions and repeated fracturing requirements of the oil and gas wells to be fractured repeatedly; S2. Determine the placement position of the wellbore reconstruction string according to the production casing conditions and repeated fracturing requirements determined in step S1; S3. Determine the size of the small casing in the wellbore reconstruction string based on the inner diameter of the production casing and the wellhead pressure limit. The size of the small casing meets the construction requirement that the displacement ≥ 10m 3 / min under volume fracturing; S4. Lower the wellbore reconstruction string into the placement position of the production casing, and seal it on the inner wall of the production casing through a packer to block the original perforated interval, forming a new wellbore with a double-casing structure, and conduct a pressure test on the new wellbore. The maximum wellhead pressure of the new wellbore is less than the wellhead pressure limit; S5. Perforate and fracture on the new wellbore to achieve repeated volume fracturing.

[0012] In some embodiments of the present invention, the production casing conditions that need to be determined in the above step S1 include: the position and length of the perforated interval in the production casing, the outer diameter and wall thickness of the production casing, the position of the production casing collar and the deformation condition.

[0013] In some embodiments of the present invention, the perforated interval position of the wellbore reconstruction string in the above step S2 corresponds one by one to the perforated interval position of the production casing.

[0014] In some embodiments of the present invention, in the above step S3, the size of the small casing is calculated based on the inner diameter of the production casing, the friction pressure and the wellhead pressure of the new wellbore. Among them, the calculation steps of the friction pressure are as follows: According to the inner diameter of the production casing, the fracturing displacement, the vertical depth of the bottom of the fracturing well, the well depth, the drag reduction coefficient of the slickwater and the density of the fracturing fluid, calculate the fracturing fluid friction pressure △P that needs to be overcome in the whole wellbore under different fracturing displacements. The calculation formula of the liquid friction pressure △P is: △P = 1.385×10 6 ×D -4.8 ×Q 1.8×H×(1 - a), where △P represents the friction of the fracturing fluid, in MPa; D represents the inner diameter of the wellbore, in mm; H represents the wellbore depth, in m; Q represents the displacement of the fracturing fluid, in m 3 / min; a is the drag reduction coefficient of the slickwater, dimensionless.

[0015] In some embodiments of the present invention, by combining the hydrostatic pressure P s , the formation extension pressure P 延 and the liquid friction pressure △P to calculate the wellhead pressure at different fracturing displacements, the calculation formula for the wellhead pressure P 井口 is: P 井口 = P - P s + △P, where P 井口 represents the wellhead pressure, in MPa, P represents the bottom hole pressure, in MPa, and P s represents the hydrostatic pressure, in MPa, where the bottom hole pressure P≈P 延 .

[0016] In some embodiments of the present invention, the calculation formula for the above-mentioned hydrostatic pressure P s is: P s = ρgH, where ρ represents the density of the fracturing fluid, in g / cm 3 ; g is the acceleration due to gravity, in m / s 2 ; H is the vertical depth of the wellbore, in m.

[0017] In some embodiments of the present invention, the calculation formula for the above-mentioned formation extension pressure P 延 is: P 延 = b×H, where b represents the formation extension pressure gradient, in MPa / m; H represents the wellbore depth, in m.

[0018] In some embodiments of the present invention, in the above step S4, the specific steps for pressure testing the new wellbore are: conducting an overall pressure test on the new wellbore, with the test pressure being 3 - 5 MPa higher than the maximum construction pressure of the refracturing, and it is qualified if there is no pressure drop after stabilizing for 15 minutes.

[0019] In some embodiments of the present invention, in the above step S4, the installation position of the packer is selected where the cementing quality is good, avoiding the collar of the production casing, and being within the range of 0.5 m - 1 m above and below the top and bottom of each cluster of perforation sections, and the inner diameter of the packer ≥ the inner diameter of the small casing.

[0020] In some embodiments of the present invention, in the above step S5, the repeated volume fracturing construction selects the pumping bridge plug and perforation combined operation method.

[0021] In some embodiments of the present invention, the specific steps of the above-mentioned pumping bridge plug perforation combined operation method are as follows: In the first stage, the perforation gun is transmitted through the tubing or coiled tubing to complete the perforation. After the tubing is removed from the wellhead, fracturing fluid and proppant are injected into the small casing for the fracturing transformation of the first perforation section. For subsequent intervals, the pumping bridge plug perforation combined operation process is adopted. The soluble bridge plug and multiple clusters of perforation guns are pumped to the designed depth through the wellhead by cable at one time. First, the bridge plug is ignited and set, and then the perforation guns are respectively ignited to shoot open each perforation section. After perforation, the cable is removed and a soluble ball is dropped from the wellhead. After the pumping ball reaches the position, it seals the first layer and the second layer of fracturing starts. After the fracturing is completed, the pumping of the bridge plug and perforation gun for the next layer is repeated, and the above operations are repeated to complete the fracturing construction of the entire well section.

[0022] The embodiment of the present application also provides a wellbore reconstruction string structure for horizontal well repeated volume fracturing, including: the original wellbore casing, on which a plurality of original perforation holes are provided. A small casing is arranged in the original wellbore casing, and the perforation section of the small casing corresponds to the positions of the plurality of original perforation holes. One end of the small casing is connected with a release joint through a tie-back cylinder, and the other end is successively connected with a shear ball seat, a float collar and a float shoe. A drill pipe is inserted on the release joint. An expansion hanger is also sleeved on the small casing, and the expansion hanger abuts against the inner wall of the original wellbore casing to fix the small casing in the original wellbore casing. The small casing is also provided with a plurality of packers, and all the plurality of packers abut against the inner wall of the original wellbore casing, and the plurality of packers are respectively located at positions where the perforation sections can be sealed to seal the perforation sections. Among the plurality of packers, a double-casing structure is formed between any two packers through the small casing and the original wellbore casing of the primary fracturing perforation section, reconstructing a new wellbore that is more stable and effective for repeated fracturing. The inner diameter of the new wellbore is the inner diameter of the small casing.

[0023] In some embodiments of the present invention, the above-mentioned small casing is a non-coupling threaded casing, which has better sealing performance and pressure resistance performance, can effectively improve the structural strength of the wellbore, and reduce the leakage risk between the casings.

[0024] In some embodiments of the present invention, the installation method of the above-mentioned reconstructed string is specifically as follows: Scrape, grind, and wash the original wellbore, select a drift gauge with the same outer diameter as the packer and run it to the bottom of the well. After the treatment is completed, drop a ball from the wellhead. The ball fits with the shear ball seat to block the lower end of the string, ensuring the sealing effect at the lower end. Pressure is applied through the string to set and hang the expansion hanger. The expansion hanger expands and closely contacts the inner wall of the original wellbore casing, and is firmly fixed through the slips, firmly suspending the small casing inside the original wellbore casing. Continue to apply pressure until all packers are set, ensuring that they firmly seal the intervals to be fractured. Subsequently, conduct an overall pressure test on the newly reconstructed wellbore from the wellhead. Only after the pressure test is qualified can the subsequent fracturing construction be carried out. Finally, remove the upper part of the string, lift the string and rotate the drill pipe clockwise to disengage the drill pipe from the expansion hanger, and pull out the drill pipe to complete the wellbore reconstruction, obtaining a new wellbore that meets the requirements for repeated volume fracturing under large displacement. Moreover, the packers seal the perforation intervals that need to be refractured. Throughout the process, cementing is not required, reducing the potential risks brought by cementing quality problems.

[0025] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0026] 1. It is not necessary to use the traditional cementing method, realizing the stable fixation of the wellbore and the sealing of intervals without relying on cementing.

[0027] 2. It improves the operation efficiency and reduces the potential risks brought by cementing quality problems, making the construction process smoother and more controllable.

[0028] 3. The reconstructed wellbore is a large-diameter wellbore, significantly reducing the frictional resistance and enabling the smooth progress of large-displacement volume fracturing operations, providing the basic conditions for realizing efficient and large-scale fracturing transformation.

[0029] 4. Dynamically optimize the size of the small casing to balance the flow efficiency of the fracturing fluid and the pressure-bearing capacity of the wellbore, avoiding problems such as excessive frictional resistance or insufficient fracturing pressure caused by unreasonable sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0031] Figure 1 It is a schematic flow chart of a method for reconstructing a horizontal well repeated volume fracturing wellbore provided by the present invention;

[0032] Figure 2 Schematic diagram of a wellbore reconstruction string structure for repeated volume fracturing in horizontal wells provided by the present invention.

[0033] Icons: 1 - Original wellbore casing; 2 - Drill pipe; 3 - Release joint; 4 - Tie-back cylinder; 5 - Expansion hanger; 6 - Original perforation holes; 7 - Packer; 8 - Small casing; 9 - Shear ball seat; 10 - Float collar; 11 - Float shoe. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0035] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0036] The embodiments of the present application provide a method for reconstructing a wellbore for repeated volume fracturing in horizontal wells, including the following steps:

[0037] S1. Determine the production casing conditions and repeated fracturing requirements of the oil and gas well to be constructed. The oil and gas well to be constructed can be selected according to the reserves of the oil and gas well, the parameter conditions of the oil and gas well itself, etc. The conditions of the production casing include: the position and length of the perforated section in the production casing, the outer diameter and wall thickness of the production casing, the position and deformation of the production casing collar, etc.;

[0038] S2. According to the production casing conditions and repeated fracturing requirements determined in step S1, determine the placement position of the wellbore reconstruction string. The perforated section position of the wellbore reconstruction string corresponds to the perforated section position of the production casing;

[0039] S3. Calculate and select the size of the small casing 8 based on the inner diameter of the production casing, the friction pressure and wellhead pressure of the newly reconstructed wellbore. The size of the small casing 8 meets the construction requirement that the displacement under volume fracturing ≥ 10m 3 / min. Among them, the specific steps for the friction pressure are: According to the inner diameter of the production casing, the fracturing displacement, the vertical depth of the bottom of the fracturing operation well, the well depth, the drag reduction coefficient of slick water, and the density of the fracturing fluid, calculate the friction pressure △P of the fracturing liquid that needs to be overcome in the entire section of the wellbore under different fracturing displacements. The calculation formula for the liquid friction pressure △P is: △P = 1.385×10 6 ×D -4.8 ×Q 1.8 ×H×(1 - a);

[0040] Wherein, △P represents the friction of the fracturing fluid, in MPa; D represents the inner diameter of the wellbore, in mm; H represents the well depth, in m; Q represents the displacement of the fracturing fluid, in m 3 / min; a is the drag reduction coefficient of the slickwater, dimensionless;

[0041] By combining the hydrostatic pressure P s , the formation extension pressure P 延 and the liquid friction pressure △P to calculate the wellhead pressure at different fracturing displacements, the calculation formula for the wellhead pressure P 井口 is: P 井口 = P - P s + △P;

[0042] Wherein, P 井口 represents the wellhead pressure, in MPa, P represents the bottom hole pressure, in MPa, and P s represents the hydrostatic pressure, in MPa, where the bottom hole pressure P≈P 延 ;

[0043] The calculation formula for the hydrostatic pressure P s is: P s = ρgH;

[0044] Wherein, ρ represents the density of the fracturing fluid, in g / cm 3 ; g is the acceleration of gravity, in m / s 2 ; H is the vertical depth of the wellbore, in m;

[0045] The calculation formula for the formation extension pressure P 延 is: P 延 = b×H;

[0046] Wherein, b represents the formation extension pressure gradient, in MPa / m; H represents the well depth, in m;

[0047] According to the above formula, the maximum friction pressure and the maximum pressure of the small casing 8 with different sizes at different fracturing displacements can be calculated, and on the premise of meeting the large displacement and wellhead pressure limit of the volume fracturing bridge plug perforation combination process, select the appropriate size of the small casing 8;

[0048] S4. Lower the wellbore reconstruction string into the placement position of the production casing, and set the packer 7 on the inner wall of the production casing to block the original perforated interval, forming a new wellbore with a double casing structure, and conduct a pressure test on the new wellbore. The maximum wellhead pressure of the new wellbore is less than the wellhead pressure limit. The specific steps for the pressure test of the new wellbore are as follows: conduct an overall pressure test on the new wellbore, the test pressure is 3 - 5 MPa higher than the highest construction pressure of the refracturing, and it is qualified if there is no pressure drop after stabilizing for 15 minutes. The installation position of the packer 7 needs to avoid the collars of the production casing and be within the range of 0.5 m - 1 m above and below the top and bottom of each cluster of perforated intervals;

[0049] S5. Perforate and fracture the new wellbore to achieve repeated volume fracturing. The pumping bridge plug perforation combination method is selected for the repeated volume fracturing construction. Specifically: for the first stage, the perforation gun is transmitted through the tubing or coiled tubing to complete the perforation. After the tubing is removed from the wellhead, fracturing fluid and proppant are injected into the small casing 8 for the fracturing transformation of the first perforation section; for the subsequent intervals, the pumping bridge plug perforation combination process is adopted. The soluble bridge plug and multiple cluster perforation guns are pumped to the designed depth at one time through the wellhead by cable. First, ignite to set the bridge plug, and then ignite the perforation guns respectively to shoot open each perforation section. After perforation, the cable is removed and soluble balls are dropped into the wellhead. After the pumping ball reaches the position, it plugs the first layer and the second layer of fracturing starts; after the fracturing is completed, the pumping of the bridge plug and perforation gun for the next layer is repeated, and the above operations are repeated to complete the fracturing construction of the entire well section.

[0050] The main purpose of this step is to establish an oil flow channel between the oil reservoir and the double-layer casing. By means of segmented fracturing transformation, the degree of reservoir utilization is improved and the single-well production is increased. The same set of fracturing string is used for multiple-stage transformation, which can realize the continuous construction of volume fracturing, reduce the number of trips of the fracturing drill string, avoid the risk of sticking the drill, and reduce the construction cost.

[0051] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0052] Embodiment 1

[0053] Please refer to Figure 1 , Figure 1 which shows the schematic diagram of the reconstructed string structure of the present invention.

[0054] This embodiment provides a horizontal well repeated volume fracturing wellbore reconstructed string structure, which includes the original wellbore casing 1. A plurality of original perforation holes 6 are provided on the original wellbore casing 1. A small casing 8 is arranged in the original wellbore casing 1. The perforation section of the small casing 8 corresponds to the positions of a plurality of original perforation holes 6. One end of the small casing 8 is connected with a releasing joint 3 through a tie-back cylinder 4, and the other end is sequentially connected with a shear ball seat 9, a float collar 10 and a float shoe 11.

[0055] A drill pipe 2 is inserted into the releasing joint 3. An expansion hanger 5 is also sleeved on the small casing 8. The expansion hanger 5 abuts against the inner wall of the original wellbore casing 1 for fixing the small casing 8 in the original wellbore casing 1. The small casing 8 is also provided with a plurality of packers 7. All the plurality of packers 7 abut against the inner wall of the original wellbore casing 1, and the plurality of packers 7 are respectively located at positions where the perforation sections can be sealed for sealing the perforation sections. Among the plurality of packers 7, a double-layer casing structure is formed between any two packers 7 through the small casing 8 and the original wellbore casing 1 of the primary fracturing perforation section, and a new more stable and effective wellbore that can be repeatedly fractured is reconstructed. The inner diameter of the new wellbore is the inner diameter of the small casing 8.

[0056] The above-mentioned small casing 8 is a non-coupling threaded casing, which has better sealing performance and pressure resistance performance, can effectively improve the structural strength of the wellbore, and reduce the leakage risk between casings.

[0057] During use, first perform scraping, grinding, and washing operations on the original wellbore. Select a drift gauge with the same outer diameter as the packer 7 and run it to the bottom of the well. After the treatment work is completed, drop a ball from the wellhead. The ball reaches the shear ball seat 9 and mates with it to block the lower end of the pipe string, ensuring the sealing effect at the lower end. Pressure is applied through the pipe string to set and hang the expansion hanger 5. The expansion hanger 5 expands and comes into close contact with the inner wall of the original wellbore casing 1, and is firmly fixed through the slips, firmly suspending the small casing 8 in the original wellbore casing 1. Continue to apply pressure until all packers 7 are set, ensuring that they firmly seal the interval to be fractured. Subsequently, conduct an overall pressure test on the reconstructed new wellbore from the wellhead. Only after the pressure test is qualified can subsequent fracturing construction be carried out. Finally, remove the upper part of the pipe string, lift the pipe string and rotate the drill pipe 2 clockwise to disengage the drill pipe 2 from the expansion hanger 5, and pull out the drill pipe 2 to complete the wellbore reconstruction, obtaining a new wellbore that meets the requirements for large-displacement repeated volume fracturing. Moreover, the packer 7 seals the perforated intervals that need to be refractured. Throughout the process, no cementing is required, reducing the potential risks brought by cementing quality problems.

[0058] Example 2

[0059] Taking Well Wei 204H47-1 as an example, the well depth of this well is 5423 m, the vertical depth is 2382 m, it is completed with a 139.7 mm casing, the wall thickness is 12.7 mm, the density of the fracturing fluid is 1.2 g / cm 3 , the drag reduction rate > 70%, the extension pressure gradient is 0.023 - 0.026 MPa / m, and the wellhead pressure limit is 120 MPa. During the initial transformation, the displacement is 14 - 16 m 3 / min, the construction pump pressure is 42 - 80 MPa, the total fracturing section length is 2090 m, and there are a total of 24 sections.

[0060] According to the above formula, the maximum friction pressure of the fracturing fluid and the maximum wellhead pressure at different displacements for different small casings 8 are calculated. The sizes of the small casings 8 are 3.5 inches, 4 inches, and 4.5 inches respectively. Among them, the inner diameter of the 3.5-inch casing is 72 mm, the inner diameter of the 4-inch casing is 85 mm, and the inner diameter of the 4.5-inch casing is 98 mm. The calculation results are shown in Tables 1 and 2:

[0061] Table 1 Calculation results of the friction pressure of the fracturing fluid at different displacements

[0062]

[0063] Table 2 Calculation results of the wellhead pressure at different displacements

[0064]

[0065] The maximum wellhead pressure at different displacement rates of 4 m 3 / min, 6 m 3 / min, 8 m 3 / min, 10 m 3 / min, 12 m 3 / min, 14 m 3 / min, 16 m 3 / min and 18 m 3 / min is calculated for small casing 8 of different sizes.

[0066] Under the condition that the maximum pressure limit during on-site construction is 120 MPa, the maximum allowable construction displacement rate during the fracturing process of 4.5-inch small casing 8 is 16 m 3 / min, and the maximum allowable construction displacement rate of 4-inch small casing 8 is 12 m 3 / min. The maximum allowable construction displacement rate of 3.5-inch small casing 8 is 6 m3 / min.

[0067] According to the requirement of large displacement rate in the bridge plug perforation combined operation technology for volumetric fracturing reconstruction (generally

[0068] ≥10 m 3 / min), 3.5-inch small casing 8 cannot meet the volumetric fracturing conditions. Therefore, 4-inch or 4.5-inch non-coupling threaded small casing 8 is selected as the new wellbore after wellbore reconstruction.

[0069] Example 3

[0070] Taking Changning H5-3 horizontal well as an example, the well depth of this well is 4800 m, the vertical depth is 3050 m, it is completed with 139.7 mm casing, the wall thickness is 12.7 mm, the density of the fracturing fluid is 1.18 g / cm 3 , the drag reduction rate > 70%, the average pressure gradient is 0.026 MPa / m, and the wellhead pressure limit is 90 MPa. During the initial reconstruction, the displacement rate is 12 - 14 m 3 / min, the construction pump pressure is 65 - 86 MPa, the average pump pressure is 74.8 MPa, the reconstructed horizontal section is 3229 - 4750 m, the length is 1521 m, it is divided into 22 segments, the single-segment length is 60 - 80 m, and the average segment length is 69.1 m.

[0071] According to the above formula, the maximum frictional resistance pressure and maximum wellhead pressure of the fracturing fluid at different displacement rates for different small casings 8 are calculated. The sizes of small casing 8 are 3.5 inches, 4 inches, and 4.5 inches respectively. Among them, the inner diameter of the 3.5-inch casing is 72 mm, the inner diameter of the 4-inch casing is 85 mm, and the inner diameter of the 4.5-inch casing is 98 mm. The calculation results are shown in Table 3 and Table 4:

[0072] Table 3 Calculation results of frictional resistance pressure of fracturing fluid at different displacement rates

[0073]

[0074] Table 4 Calculation Results of Wellhead Pressure under Different Displacements

[0075]

[0076] By calculation, the maximum wellhead pressures under different sizes of small casing 8 at fracturing displacements of 4 m 3 / min, 6 m 3 / min, 8 m 3 / min, 10 m 3 / min, 12 m 3 / min, 14 m 3 / min, 16 m 3 / min and 18 m 3 / min are obtained.

[0077] Under the condition that the maximum pressure limit during on-site construction is 90 MPa, the maximum construction displacement allowed during the fracturing process of 4.5-inch small casing 8 is 12 m 3 / min, and the maximum construction displacement allowed for 4-inch small casing 8 is 6 m 3 / min, and the maximum construction displacement allowed for 3.5-inch small casing 8 is 4 m 3 / min.

[0078] According to the requirement of large displacement in the bridge plug perforation coiled tubing operation process in volumetric fracturing reconstruction (generally

[0079] ≥10 m 3 / min), 4-inch and 3.5-inch small casings 8 cannot meet the volumetric fracturing conditions. Therefore, 4.5-inch non-coupling threaded small casing 8 is selected as the new wellbore after wellbore reconstruction.

[0080] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A method for reconstructing a wellbore in repeated volume fracturing of a horizontal well, characterized in that, It includes the following steps: S1. Determine the production casing condition and refracturing requirements of the refracturing oil and gas well to be constructed; S2. Determine the placement position of the wellbore reconstruction string according to the determined production casing condition and refracturing requirements; S3. Determine the size of the small casing in the wellbore reconstruction string based on the inner diameter of the production casing and the wellhead pressure limit; S4. Lower the wellbore reconstruction string into the placement position of the production casing, set the packer on the inner wall of the production casing to block the original perforated interval, form a new wellbore with a double-casing structure, and conduct a pressure test on the new wellbore. The maximum wellhead pressure of the new wellbore is less than the wellhead pressure limit; S5. Perforate and fracture on the new wellbore to achieve repeated volume fracturing and complete the wellbore reconstruction of horizontal well repeated volume fracturing.

2. The method according to claim 1, characterized in that, The production casing conditions to be determined in step S1 include: the position and length of the perforated interval in the production casing, the outer diameter and wall thickness of the production casing, the position and deformation condition of the production casing collar.

3. The method according to claim 1, wherein In step S2, the perforated interval position of the wellbore reconstruction string corresponds one by one to the perforated interval position of the production casing.

4. The method according to claim 1, wherein In the step S3, the size of the small casing is calculated based on the inner diameter of the production casing, the friction pressure of the new wellbore, and the wellhead pressure. Among them, the calculation step of the friction pressure is as follows: According to the inner diameter of the production casing, the fracturing displacement, the vertical depth of the bottom of the fracturing operation well, the well depth, the drag reduction coefficient of the slick water, and the density of the fracturing fluid, calculate the fracturing fluid friction pressure △P that needs to be overcome in the whole section of the wellbore under different fracturing displacements. The calculation formula of the liquid friction pressure △P is: △P = 1.385×10 6 ×D -4.8 ×Q 1.8 ×H×(1 - a); Wherein, △P represents the friction of the fracturing fluid, in MPa; D represents the inner diameter of the wellbore, in mm; H represents the well depth, in m; Q represents the displacement of the fracturing fluid, in m 3 / min; a is the drag reduction coefficient of slick water, dimensionless.

5. The method according to claim 4, wherein By combining the hydrostatic pressure P s , the formation extension pressure P 延 and the liquid friction pressure △P to calculate the wellhead pressure at different fracturing displacement rates, the calculation formula for the wellhead pressure P 井口 is: P 井口 = P - P s + △P; Wherein, P 井口 represents the wellhead pressure, in MPa, P represents the bottom-hole pressure, in MPa, and P s represents the static liquid column pressure, in MPa, where the bottom-hole pressure P≈P 延 .

6. The method according to claim 5, characterized in that The hydrostatic pressure P s is calculated by the formula: P s = ρgH; where ρ represents the density of the fracturing fluid, g / cm 3 ; g is the acceleration due to gravity, m / s 2 ; H is the vertical depth of the wellbore, m.

7. The method according to claim 5, characterized in that, The formation extension pressure P 延 is calculated by the formula: P 延 = b × H; In the formula, b represents the formation extension pressure gradient, MPa / m; H represents the wellbore depth, m.

8. The method according to claim 1, characterized in that In step S4, the specific steps for the pressure test of the new wellbore are: conduct an overall pressure test on the new wellbore, and the test pressure is increased by 3 - 5 MPa based on the highest construction pressure value during refracturing. It is qualified if there is no pressure drop after stabilizing for 15 minutes.

9. The method according to claim 1, characterized in that, In step S4, the installation position of the packer needs to avoid the production casing collar and be located 0.5 m - 1 m above and below the top and bottom of each cluster of perforated intervals.

10. The method according to claim 1, characterized in that, In step S5, the repeated volume fracturing construction selects the pumping bridge plug perforating co - operation method.

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