Branch well oil extraction method and pipe column

Abstract

The multilateral well oil extraction method comprises the steps that S1, after a multilateral well is completed, a main well hole oil pipe and at least one multilateral well hole oil pipe are put into a main well hole at the same time; s2, oil pipes of all the branch well holes enter the corresponding branch well holes; s3, a main well hole oil pipe and branch well hole oil pipes are lowered to the designed depth; s4, a multi-pipe wellhead device is installed on the ground; s5, the multi-pipe packer, the branch well hole packer and the main well hole packer are set; s6, an oil extraction pump is arranged in the main well hole oil pipe and each branch well hole oil pipe; and S7, at least one oil extraction pump is opened, and oil extraction is started. The pressure interference problem of the main well hole and the branch well hole in the branch well can be effectively solved, and the oil extraction efficiency of the branch well is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of oil production, and particularly to a method and string for producing oil from multilateral wells. Background Art

[0002] At present, the technology of four-level multilateral wells can reach the highest completion level of TMAL level 5. The single-well production of some multilateral wells implemented in certain oilfield blocks is about 4 to 15 times that of adjacent wells, with a cumulative oil increase of 274,837 tons, a cumulative income increase of 8,082,803,000 yuan, and a cumulative profit of 6,002,112,000 yuan, achieving remarkable economic and social benefits.

[0003] However, in the later oil production of the currently implemented multilateral wells, the pump and tubing are lowered to the upper part of the branch window, and the main wellbore and branch wellbores are simultaneously produced. If the pressure levels of the main wellbore and branch wellbores are the same, this oil production method has a good effect. If the pressures of the main and branch wellbores are inconsistent or the pressure declines of the main and branch wellbores are inconsistent during the oil production process, it will cause a high pressure in one wellbore and a low pressure in the other wellbore. In this way, the wellbore with high pressure will affect the wellbore with low pressure, resulting in the inability to produce oil from the wellbore with low pressure, and the maximum development of the main and branch wellbores of the multilateral well cannot be achieved, affecting the final oil production and recovery rate, and the technical advantages of the multilateral well cannot be fully exerted. At present, there is no mature new oil production method for four-level multilateral wells, which cannot solve the above problems and cannot maximize the technical advantages of four-level multilateral wells. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and string for producing oil from multilateral wells, which can effectively solve the pressure interference problem between the main wellbore and branch wellbores in multilateral wells and effectively improve the oil production efficiency of multilateral wells.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The present invention provides a method for producing oil from multilateral wells, including the following steps: S1. After the completion of the multilateral well, the main wellbore tubing and at least one branch wellbore tubing are simultaneously lowered into the main wellbore; S2. Each branch wellbore tubing is made to enter the corresponding branch wellbore; S3. The main wellbore tubing and each branch wellbore tubing are lowered to the designed depth, so that the multi-tubing packers installed on the main wellbore tubing and each branch wellbore tubing are located above the topmost branch wellbore, the branch wellbore packers installed on each branch wellbore tubing are located in the corresponding branch wellbores, and the main wellbore packer installed at the lower part of the main wellbore tubing is located below the lowermost branch wellbore; S4. A multi-tubing wellhead device is installed on the ground to suspend the main wellbore tubing and each branch wellbore tubing on the casing in the main wellbore; S5. The multi-tubing packers, branch wellbore packers, and main wellbore packer are set; S6. An oil production pump is lowered into the main wellbore tubing and each branch wellbore tubing respectively; S7. At least one oil production pump is opened to start oil production.

[0007] In a preferred embodiment of the present invention, an introducing tool is connected to the bottom end of the branch wellbore tubing. The introducing tool includes a straight section and an inclined section that are connected up and down. The bottom end of the inclined section can be attached to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing.

[0008] In a preferred embodiment of the present invention, the number of branch wellbore tubings and branch wellbores is one each. Step S2 includes: S21. When the branch wellbore tubing is lowered to the branch window of the branch wellbore, rotate the branch wellbore tubing; S22. Continue to lower the main wellbore tubing and the branch wellbore tubing simultaneously, and determine whether the branch wellbore tubing has successfully entered the branch wellbore; S23. If the determination result is no, lift the branch wellbore tubing to a preset distance above the branch window, and repeat steps S21 and S22 until the determination result is yes.

[0009] In a preferred embodiment of the present invention, an annular main wellbore step is provided on the inner wall of the main wellbore and below the branch window, and an annular branch wellbore step is provided on the inner wall of the branch wellbore. The lowering depth corresponding to the branch wellbore step is less than the lowering depth corresponding to the main wellbore step; step S22 includes the following steps: Continue to lower the main wellbore tubing and the branch wellbore tubing simultaneously. When the introducing tool touches the branch wellbore step or the main wellbore step and encounters resistance, causing the drilling pressure at the wellhead to increase, if the current lowering depth of the branch wellbore tubing corresponds to the lowering depth corresponding to the branch wellbore step, the determination result is yes; if the current lowering depth of the branch wellbore tubing corresponds to the lowering depth corresponding to the main wellbore step, the determination result is no.

[0010] In a preferred embodiment of the present invention, the number of branch wellbore tubings and branch wellbores is at least two. The branch wellbore tubings are respectively denoted as the first branch wellbore tubing to the Nth branch wellbore tubing from top to bottom, the branch wellbores are respectively denoted as the first branch wellbore to the Nth branch wellbore from top to bottom, and the branch windows corresponding to the branch wellbores are respectively denoted as the first branch window to the Nth branch window from top to bottom, where N≥2 and is a positive integer; step S2 includes: S21. When the first branch wellbore tubing is lowered to the first branch window of the first branch wellbore, rotate the first branch wellbore tubing; S22. Continue to lower the main wellbore tubing and each branch wellbore tubing simultaneously, and determine whether the first branch wellbore tubing has successfully entered the first branch wellbore; S23. If the determination result is no, lift the first branch wellbore tubing to a preset distance above the first branch window, and repeat steps S21 and S22 until the determination result is yes; S24. In the same manner, enable the second branch wellbore tubing to the Nth branch wellbore tubing to successively enter the second branch wellbore to the Nth branch wellbore.

[0011] In a preferred embodiment of the present invention, annular first to Nth main wellbore steps are provided on the inner wall of the main wellbore and below the first to Nth branch windows, and annular first to Nth branch wellbore steps are respectively provided on the inner walls of the first to Nth branch wellbores; the corresponding setting depths of the first to Nth main wellbore steps gradually increase, the corresponding setting depths of the first to Nth branch wellbore steps gradually increase, and the corresponding setting depths of the first to Nth branch wellbore steps are respectively less than the corresponding setting depths of the first to Nth main wellbore steps; step S22 includes the following steps: continue to simultaneously lower the main wellbore tubing and each branch wellbore tubing. When the guiding tool at the bottom end of the first branch wellbore tubing encounters resistance due to touching the first branch wellbore step or the first main wellbore step, causing an increase in the drilling pressure at the wellhead, if the current setting depth of the first branch wellbore tubing corresponds to the setting depth corresponding to the first branch wellbore step, the judgment result is yes; if the current setting depth of the first branch wellbore tubing corresponds to the setting depth corresponding to the first main wellbore step, the judgment result is no.

[0012] The present invention also provides a production tubing string for a branch well, including a multi-tubing wellhead device, a main wellbore tubing, at least one branch wellbore tubing, a multi-tubing packer, a main wellbore packer, at least one branch wellbore packer, and a plurality of production pumps; the multi-tubing wellhead device is simultaneously installed at the tops of the main wellbore tubing and each branch wellbore tubing, the multi-tubing packer is simultaneously connected to the upper parts of the main wellbore tubing and each branch wellbore tubing, the main wellbore packer is installed at the lower part of the main wellbore tubing, and each branch wellbore packer is installed at the lower part of the corresponding branch wellbore tubing; a production pump is respectively inserted into the main wellbore tubing and each branch wellbore tubing.

[0013] In a preferred embodiment of the present invention, the bottom end of the branch wellbore tubing is connected with a guiding tool, and the guiding tool includes a straight section and an inclined section which are connected up and down. The bottom end of the inclined section can be attached to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing.

[0014] In a preferred embodiment of the present invention, the number of branch wellbore tubings is one.

[0015] In a preferred embodiment of the present invention, both the main wellbore packer and each branch wellbore packer are water- and oil-encountered self-expanding packers.

[0016] As described above, for the oil production method and oil production tubing string of the present invention, after the main wellbore tubing and each branch wellbore tubing are lowered to the designed depth and each packer is set, the isolation of the pressure between the main wellbore and each branch wellbore during the oil production process of the branch well can be achieved, realizing the oil production control of the main wellbore and each branch wellbore in the branch well, avoiding the pressure interference problem between the main wellbore and the branch wellbore in the branch well, and enabling the separate production or combined production of the main wellbore and the branch well in the branch well, maximizing the technical advantages of the branch well, and at the same time improving the oil production efficiency of the branch well, which is an important means for increasing the production of the branch well. Moreover, in the present invention, the main wellbore tubing and each branch wellbore tubing are independent tubing, and each tubing is provided with its own oil pump, resulting in higher oil production efficiency and better production effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following drawings are only intended to illustrate and explain the present invention schematically and do not limit the scope of the present invention.

[0018] Wherein:

[0019] Figure 1 : is a schematic structural diagram of the branch well oil production tubing string provided by the present invention lowered into the branch well.

[0020] Figure 2 : is a schematic structural diagram of the guiding tool provided by the present invention.

[0021] Description of the reference numerals in the drawings:

[0022] 1. Multi-tubing wellhead device;

[0023] 2. Multi-tubing packer;

[0024] 3. Main wellbore tubing; 31. Main wellbore packer

[0025] 4. Branch wellbore tubing; 41. Branch wellbore packer; 42. Guiding tool; 421. Straight section; 422. Inclined section;

[0026] 5. Main wellbore; 51. Vertical section of the main wellbore; 511. Step of the main wellbore; 52. Horizontal section of the main wellbore;

[0027] 6. Branch wellbore; 61. Step of the branch wellbore. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described with reference to the drawings.

[0029] As Figure 1 and Figure 2 shown, the present application provides a branch well oil production method, including the following steps:

[0030] S1. After the completion of the branch well, lower the production tubing 3 in the main wellbore and at least one production tubing 4 in the branch wellbore into the main wellbore 5 simultaneously;

[0031] S2. Ensure that each production tubing 4 in the branch wellbore enters the corresponding branch wellbore 6;

[0032] S3. Lower the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore to the designed depth, so that the multi-tubing packer 2 installed on the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore is located above the topmost branch wellbore 6, the branch wellbore packer 41 installed on each production tubing 4 in the branch wellbore is located in the corresponding branch wellbore 6, and the main wellbore packer 31 installed at the lower part of the production tubing 3 in the main wellbore is located below the lowermost branch wellbore 6;

[0033] S4. Install the multi-tubing wellhead device 1 on the ground to suspend the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore on the casing in the main wellbore 5;

[0034] S5. Set the multi-tubing packer 2, the branch wellbore packer 41 and the main wellbore packer 31;

[0035] S6. Lower a production pump into the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore respectively;

[0036] S7. Open at least one production pump to start oil production.

[0037] Wherein, before lowering each tubing, it is necessary to assemble each packer onto the corresponding tubing. Before oil production after the completion construction of the branch well, lower the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore synchronously. The packers installed on each tubing are lowered into the well together with the corresponding tubing. The production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore need to be lowered simultaneously to avoid the production tubing 3 in the lower part and the production tubing 4 in the branch wellbore getting knotted in the wellbore due to asynchronous lowering depths, which affects the final lowering depths of the production tubing 3 in the main wellbore and the production tubing 4 in the branch wellbore.

[0038] After ensuring that each production tubing 4 in the branch wellbore enters the corresponding branch wellbore 6, continue to lower. After the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore are lowered to the designed depth, install the multi-tubing wellhead device 1 on the ground. Set each packer. The multi-tubing packer 2 can seal the annulus between the production tubing 3 in the main wellbore and each production tubing 4 in the branch wellbore and the main wellbore 5 above the topmost branch wellbore 6. The main wellbore packer 31 can seal the annulus between the production tubing 3 in the main wellbore and the main wellbore 5 below the lowermost branch wellbore 6. Each branch wellbore packer 41 can seal the annulus between the production tubing 4 in the branch wellbore and the corresponding branch wellbore 6 in the corresponding branch wellbore 6. Then lower the production pump, and oil production can be carried out.

[0039] Thus, in the oil production method of the present application, after the main wellbore tubing 3 and each branch wellbore tubing 4 are lowered to the designed depth and each packer is set, the isolation of the pressure between the main wellbore 5 and each branch wellbore 6 during the oil production process of the branch well can be achieved, realizing the oil production control of the main wellbore 5 and each branch wellbore 6 in the branch well, avoiding the pressure interference problem between the main wellbore 5 and the branch wellbore 6 in the branch well, and enabling the separate or combined production of the main wellbore 5 and the branch well in the branch well, maximizing the technical advantages of the branch well, and at the same time improving the oil production efficiency of the branch well, which is an important means to increase the production of the branch well. Moreover, in the present application, the main wellbore tubing 3 and each branch wellbore tubing 4 are independent tubing, and each tubing is provided with its own oil pump, with higher oil production efficiency and better production effect.

[0040] In a specific implementation manner, in order to facilitate the smooth entry of the branch wellbore tubing 4 into the corresponding branch wellbore 6, a guiding tool 42 is connected to the bottom end of the branch wellbore tubing 4. Refer to Figure 2 , the guiding tool 42 includes a straight section 421 and an inclined section 422 that are connected up and down, and the bottom end of the inclined section 422 can be attached to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing 4.

[0041] The straight section 421 and the inclined section 422 in the entire guiding tool 42 can be integrally formed and connected to the lowest end of the branch wellbore tubing 4. When lowering, the end of the inclined section 422 will closely adhere to the inner wall of the casing in the wellbore. The inclination angle of the inclined section 422 compared to the straight section 421 should not be too large, generally 3 - 5°. When the branch wellbore tubing 4 is lowered to the bifurcation window of the corresponding branch wellbore 6, rotate the branch wellbore tubing 4 alone to make the guiding elbow direction of the inclined section 422 in the guiding tool 42 face the branch window as much as possible, so as to facilitate the smooth entry of the branch wellbore tubing 4 into the branch wellbore 6.

[0042] The number of branch wellbores 6 can be determined according to actual needs. The following describes the specific method for making the branch wellbore tubing 4 enter the branch wellbore 6 when the number of branch wellbores 6 is one and at least two, specifically as follows:

[0043] For an embodiment where the number of both the branch wellbore tubing 4 and the branch wellbore 6 is one, step S2 includes:

[0044] S21. When the branch wellbore tubing 4 is lowered to the branch window of the branch wellbore 6, rotate the branch wellbore tubing 4;

[0045] S22. Continue to lower the main wellbore tubing 3 and the branch wellbore tubing 4 simultaneously, and determine whether the branch wellbore tubing 4 has successfully entered the branch wellbore 6;

[0046] S23, if the judgment result is no, then lift the branch wellbore oil pipe 4 to a preset distance above the branch window, and repeat steps S21 and S22 until the judgment result is yes.

[0047] It can be understood that when the main wellbore tubing 3 and the branch wellbore tubing 4 are lowered at the same time, and the branch wellbore tubing 4 is lowered to the branch window, it is necessary to rotate the branch wellbore tubing 4 alone (the main wellbore tubing 3 remains stationary) to adjust the direction of the guide elbow of the introduction tool 42 (that is, the direction of the inclined section 422) so that the guide elbow direction is as close to the branch window as possible, so that the branch wellbore tubing 4 can smoothly enter the branch wellbore 6; but since it is difficult to ensure that the branch window can be aligned with one rotation in actual operation, it is necessary to judge whether the branch wellbore tubing 4 has successfully entered the branch wellbore 6. If the judgment result is yes, that is, the branch wellbore tubing 4 has successfully entered the branch wellbore 6, then step S3 is entered. If the judgment result is no, that is, the branch wellbore tubing 4 has not successfully entered the branch wellbore 6, it is necessary to lift the branch wellbore tubing 4 (the main wellbore tubing 3 remains stationary), and repeat steps S21 and S22 until the judgment result is yes and then step S3 is entered.

[0048] In order to quickly determine whether the branch wellbore oil pipe 4 enters the branch wellbore 6, an annular main wellbore step 511 is provided on the inner wall of the main wellbore 5 and below the branch window, and an annular branch wellbore step 61 is provided on the inner wall of the branch wellbore 6. The descent depth corresponding to the branch wellbore step 61 is less than the descent depth corresponding to the main wellbore step 511.

[0049] Step S22 includes the following steps: continue to lower the main wellbore oil pipe 3 and the branch wellbore oil pipe 4 at the same time, when the introduction tool 42 touches the branch wellbore step 61 or the main wellbore step 511 and encounters resistance so that the wellhead drilling pressure increases, if the current lowering depth of the branch wellbore oil pipe 4 corresponds to the lowering depth corresponding to the branch wellbore step 61, the judgment result is yes; if the current lowering depth of the branch wellbore oil pipe 4 corresponds to the lowering depth corresponding to the main wellbore step 511, the judgment result is no.

[0050] Among them, the main wellbore step 511 is specifically arranged on the inner wall of the inner casing of the main wellbore 5, and the branch wellbore step 61 is specifically arranged on the inner wall of the inner casing of the branch wellbore 6. The axial length of the main wellbore step 511 and the branch wellbore step 61 should be relatively small, generally 3-5 mm, for example, 5 mm is used in this embodiment, to avoid the axial length of the step being too large and causing large resistance, which will affect the smooth continuation of the branch wellbore oil pipe 4 after encountering resistance. Generally, the bottom end of the introduction tool 42 (that is, the end of the inclined section 422) adopts an arc end face to better continue to smoothly enter after encountering resistance. The inner wall shape of the wellbore step can also be designed as needed to facilitate the continued entry of the introduction tool 42 after encountering resistance.

[0051] The tubing running-in depth corresponding to the branch wellbore step 61 is different from the tubing running-in depth corresponding to the main wellbore step 511, and the two should differ by at least 5 m to reduce the judgment error. During running-in, the guiding tool 42 at the bottom end of the branch wellbore tubing 4 runs along the inner wall of the casing. When passing through the branch wellbore step 61 or the main wellbore step 511, it will encounter resistance, and the drill pressure at the wellhead will be displayed. The wellbore into which the branch wellbore tubing 4 enters can be judged through the position where the resistance is encountered.

[0052] If the guiding tool 42 on the branch wellbore tubing 4 does not enter the branch wellbore 6 at one time, that is, the judgment result is negative, then step S23 is entered. The branch wellbore tubing 4 needs to be lifted as a whole by 5 m above the branch window, and then lowered to the branch window. Rotate the entire branch wellbore tubing 4 to adjust the elbow direction of the guiding tool 42 and then continue to lower it. When encountering resistance again, continue to judge, and repeatedly adjust until the branch wellbore tubing 4 successfully enters the branch wellbore 6.

[0053] For the embodiments in which the number of the branch wellbore tubings 4 and the branch wellbores 6 are both at least two, the branch wellbore tubings 4 are respectively denoted as the first branch wellbore tubing to the Nth branch wellbore tubing from top to bottom, the branch wellbores 6 are respectively denoted as the first branch wellbore to the Nth branch wellbore from top to bottom, and the branch windows corresponding to the branch wellbores 6 are respectively denoted as the first branch window to the Nth branch window from top to bottom, where N≥2 and is a positive integer. Step S2 includes:

[0054] S21. When the first branch wellbore tubing is run into the first branch window of the first branch wellbore, rotate the first branch wellbore tubing;

[0055] S22. Continue to simultaneously run in the main wellbore tubing 3 and each branch wellbore tubing 4, and judge whether the first branch wellbore tubing successfully enters the first branch wellbore;

[0056] S23. If the judgment result is negative, lift the first branch wellbore tubing by a preset distance above the first branch window, and repeat steps S21 and S22 until the judgment result is positive;

[0057] S24. In the same way, enable the second branch wellbore tubing to the Nth branch wellbore tubing to successively enter the second branch wellbore to the Nth branch wellbore.

[0058] It can be understood that when the main wellbore tubing 3 and each branch wellbore tubing 4 are simultaneously lowered, and when the first branch wellbore tubing reaches the first branch window, it is necessary to rotate the first branch wellbore tubing alone (the main wellbore tubing 3 and the other branch wellbore tubings 4 remain stationary) to adjust the orientation of the guiding elbow of the guiding tool 42 at the bottom end of the first branch wellbore tubing (i.e., the orientation of the inclined section 422), so that the orientation of the guiding elbow is preferably towards the first branch window, facilitating the smooth entry of the first branch wellbore tubing into the first branch wellbore; however, since it is difficult to ensure that the first branch window can be aligned with a single rotation during actual operation, it is necessary to determine whether the first branch wellbore tubing has successfully entered the first branch wellbore. If the judgment result is negative, the first branch wellbore tubing needs to be lifted (the main wellbore tubing 3 and the other branch wellbore tubings 4 still remain stationary), and steps S21 and S22 are repeated until the judgment result is positive, and then step S24 is entered. If the judgment result is positive, step S24 is directly entered, and the second branch wellbore tubing is continued to be successfully entered into the second branch wellbore in a similar manner, and so on. Until all the branch wellbore tubings 4 have successfully entered the corresponding branch wellbores 6, then step S3 is entered.

[0059] In order to quickly determine whether the branch wellbore tubing 4 has entered the branch wellbore 6, annular first main wellbore steps to Nth main wellbore steps are provided on the inner wall of the main wellbore 5 and below the first branch window to the Nth branch window, and annular first branch wellbore steps to Nth branch wellbore steps are respectively provided on the inner walls of the first branch wellbore to the Nth branch wellbore; the corresponding lowering depths of the first main wellbore steps to the Nth main wellbore steps gradually increase, the corresponding lowering depths of the first branch wellbore steps to the Nth branch wellbore steps gradually increase, and the corresponding lowering depths of the first branch wellbore steps to the Nth branch wellbore steps are respectively less than the corresponding lowering depths of the first main wellbore steps to the Nth main wellbore steps.

[0060] Step S22 includes the following steps: continue to simultaneously lower the main wellbore tubing 3 and each branch wellbore tubing 4. When the guiding tool 42 at the bottom end of the first branch wellbore tubing touches the first branch wellbore step or the first main wellbore step and encounters resistance, causing the drilling pressure at the wellhead to increase, if the current lowering depth of the first branch wellbore tubing corresponds to the lowering depth corresponding to the first branch wellbore step, the judgment result is positive; if the current lowering depth of the first branch wellbore tubing corresponds to the lowering depth corresponding to the first main wellbore step, the judgment result is negative.

[0061] Among them, each main wellbore step is specifically arranged on the inner wall of the casing in the main wellbore 5, and each branch wellbore step 61 is specifically arranged on the inner wall of the casing in the corresponding branch wellbore 6. The axial lengths of each wellbore step and each branch wellbore step 61 should be relatively small, generally 3 - 5 mm, for example, 5 mm is adopted in this embodiment. The tubing running-in depths corresponding to each branch wellbore step 61 are different from those corresponding to each main wellbore step 511, and there should be at least a 5 m difference between each branch wellbore step and the corresponding main wellbore step below the branch window to reduce the judgment error. The specific process of the first judgment on whether the tubing of the first branch wellbore successfully enters the first branch wellbore is the same as the judgment process when the number of branch wellbore tubings 4 is one, which will not be elaborated here.

[0062] It can be understood that the entire branch well has a main wellbore 5 and at least one branch wellbore 6. The main wellbore 5 includes a vertically arranged main wellbore vertical section 51 and a horizontally arranged main wellbore horizontal section 52. After the completion of the branch well, there are corresponding casings in both the main wellbore 5 and each branch wellbore 6. The above-mentioned main wellbore step 511 is specifically arranged in the main wellbore vertical section 51. In step S1, the main wellbore tubing 3 and each branch wellbore tubing 4 are first simultaneously run into the main wellbore vertical section 51 in the main wellbore 5, specifically into the corresponding casings in the main wellbore vertical section 51. In step S2, when the branch wellbore tubing 4 successfully enters the corresponding branch wellbore 6, that is, it successfully enters the corresponding casing in the corresponding branch wellbore 6. In step S3, when reaching the designed depth, according to the geological conditions and actual needs, at this time, all of the main wellbore tubing 3 is in the main wellbore vertical section 51, or the lower part of the main wellbore tubing 3 is located in the main wellbore horizontal section 52. For the embodiment where the lower part of the main wellbore tubing 3 needs to enter the main wellbore horizontal section 52, since the main wellbore horizontal section 52 is connected to the lowest end of the main wellbore vertical section 51, the main wellbore tubing 3 can directly and successfully enter the main wellbore horizontal section 52 during the running-in process without installing an introduction tool 42 and without judging whether it has successfully entered, etc.

[0063] Furthermore, the present application also provides a production tubing string for a branch well, including a multi-tubing wellhead device 1, a main wellbore tubing 3, at least one branch wellbore tubing 4, a multi-tubing packer 2, a main wellbore packer 31, at least one branch wellbore packer 41, and multiple production pumps; the multi-tubing wellhead device 1 is installed at the top of both the main wellbore tubing 3 and each branch wellbore tubing 4 at the same time, the multi-tubing packer 2 is connected to the upper parts of both the main wellbore tubing 3 and each branch wellbore tubing 4 at the same time, the main wellbore packer 31 is installed at the lower part of the main wellbore tubing 3, and each branch wellbore packer 41 is installed at the lower part of the corresponding branch wellbore tubing 4; a production pump is inserted into each of the main wellbore tubing 3 and each branch wellbore tubing 4.

[0064] The specific working principle of this tubing string is the same as the above-mentioned oil production method, and thus has the same effect.

[0065] Furthermore, in order to facilitate the smooth entry of the branch wellbore tubing 4 into the branch wellbore 6 during lowering, an introduction tool 42 is connected to the bottom end of the branch wellbore tubing 4. The introduction tool 42 includes a straight section 421 and an inclined section 422 that are connected up and down. The bottom end of the inclined section 422 can adhere to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing 4.

[0066] The number of the above-mentioned branch wellbore tubings 4 is the same as the number of the branch wellbores 6. In this embodiment, it is more preferable that the number of the branch wellbore tubings 4 is one, which is relatively simple in construction and can fully exert the advantages of the branch well.

[0067] Specifically, the multi-tubing wellhead device 1 is mainly used to suspend the main wellbore tubing 3 and each branch wellbore tubing 4 on the casing. The difference between it and the single-tubing wellhead device is mainly that it can be connected to multiple tubings at the same time. The specific structure can adopt any existing method, and this application does not limit it.

[0068] Both the above-mentioned main wellbore packer 31 and each branch wellbore packer 41 are preferably water- and oil-encountered self-expanding packers. In the above step S5, each packer can be set in the wellbore and seated on the casing wall of the corresponding wellbore after a certain time of encountering water and oil (generally 24-48h) to achieve the corresponding sealing. The specific structure of the packer is the prior art and will not be elaborated here.

[0069] The production tubing string and production method in this embodiment can be applied to any completion-level hierarchical well, especially suitable for oil production after the completion of a four-level branch well. It provides a new oil production method for the four-level branch well, can greatly highlight the technical advantages of the four-level branch well, has a bright application prospect, and has huge economic and social benefits.

[0070] The above is only a schematic specific embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for oil production in a multilateral well, characterized in that, it comprises the following steps: S1. After the multilateral well is completed, the main wellbore tubing and at least one branch wellbore tubing are simultaneously lowered into the main wellbore; S2. Make each of the branch wellbore tubings enter the corresponding branch wellbore; S3. Lower the main wellbore tubing and each of the branch wellbore tubings to the designed depth, so that the multi-tubing packers installed on the main wellbore tubing and each of the branch wellbore tubings are located above the topmost branch wellbore, the branch wellbore packers installed on each of the branch wellbore tubings are located in the corresponding branch wellbores, and the main wellbore packer installed at the lower part of the main wellbore tubing is located below the bottommost branch wellbore; S4. Install a multi-tubing wellhead device on the ground to suspend the main wellbore tubing and each of the branch wellbore tubings on the casing in the main wellbore; S5. Set the multi-tubing packers, the branch wellbore packers and the main wellbore packer; S6. Lower a production pump into the main wellbore tubing and each of the branch wellbore tubings respectively; S7. Open at least one production pump to start oil production.

2. The method for oil production in a multilateral well according to claim 1, characterized in that, the bottom end of the branch wellbore tubing is connected with a guiding tool, the guiding tool comprises a straight section and an inclined section which are connected up and down, and the bottom end of the inclined section can be attached to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing.

3. The method for oil production in a multilateral well according to claim 2, characterized in that, both the number of the branch wellbore tubings and the number of the branch wellbores are one, and step S2 comprises: S21. When the branch wellbore tubing is lowered to the branch window of the branch wellbore, rotate the branch wellbore tubing; S22. Continue to lower the main wellbore tubing and the branch wellbore tubing simultaneously, and judge whether the branch wellbore tubing successfully enters the branch wellbore; S23. If the judgment result is no, lift the branch wellbore tubing to a preset distance above the branch window, and repeat steps S21 and S22 until the judgment result is yes.

4. The method for oil production in a multilateral well according to claim 3, characterized in that, a circular main wellbore step is provided on the inner wall of the main wellbore and below the branch window, and a circular branch wellbore step is provided on the inner wall of the branch wellbore, and the lowering depth corresponding to the branch wellbore step is less than the lowering depth corresponding to the main wellbore step; step S22 comprises the following steps: continue to lower the main wellbore tubing and the branch wellbore tubing simultaneously, when the guiding tool touches the branch wellbore step or the main wellbore step and encounters resistance to increase the drilling pressure at the wellhead, if the current lowering depth of the branch wellbore tubing corresponds to the lowering depth corresponding to the branch wellbore step, the judgment result is yes; if the current lowering depth of the branch wellbore tubing corresponds to the lowering depth corresponding to the main wellbore step, the judgment result is no.

5. The method for oil production in a multilateral well according to claim 2, characterized in that, The number of the branch wellbore tubing and the number of the branch wellbores are both at least two. The branch wellbore tubing is respectively denoted as the first branch wellbore tubing to the Nth branch wellbore tubing from top to bottom, the branch wellbores are respectively denoted as the first branch wellbore to the Nth branch wellbore from top to bottom, and the branch windows corresponding to the branch wellbores are respectively denoted as the first branch window to the Nth branch window from top to bottom, where N≥2 and is a positive integer; Step S2 includes: S21. When the first branch wellbore tubing is lowered into the first branch window of the first branch wellbore, rotate the first branch wellbore tubing. S22. Continue to lower the main wellbore tubing and each branch wellbore tubing simultaneously, and determine whether the first branch wellbore tubing successfully enters the first branch wellbore. S23. If the determination result is no, lift the first branch wellbore tubing to a preset distance above the first branch window, and repeat Step S21 and Step S22 until the determination result is yes. S24. In the same manner, enable the second branch wellbore tubing to the Nth branch wellbore tubing to successively enter the second branch wellbore to the Nth branch wellbore.

6. The branch well oil production method according to claim 5, wherein, annular first main wellbore steps to the Nth main wellbore steps are respectively arranged on the inner wall of the main wellbore and below the first branch window to the Nth branch window, and annular first branch wellbore steps to the Nth branch wellbore steps are respectively arranged on the inner walls of the first branch wellbore to the Nth branch wellbore; the corresponding lowering depths of the first main wellbore steps to the Nth main wellbore steps gradually increase, the corresponding lowering depths of the first branch wellbore steps to the Nth branch wellbore steps gradually increase, and the corresponding lowering depths of the first branch wellbore steps to the Nth branch wellbore steps are respectively less than the corresponding lowering depths of the first main wellbore steps to the Nth main wellbore steps; Step S22 includes the following steps: Continue to lower the main wellbore tubing and each branch wellbore tubing simultaneously. When the guiding tool at the bottom end of the first branch wellbore tubing touches the first branch wellbore step or the first main wellbore step and encounters resistance, causing the drill pressure at the wellhead to increase, if the current lowering depth of the first branch wellbore tubing corresponds to the lowering depth corresponding to the first branch wellbore step, the determination result is yes; if the current lowering depth of the first branch wellbore tubing corresponds to the lowering depth corresponding to the first main wellbore step, the determination result is no.

7. A branch well oil production tubing string, wherein, it includes a multi-tubing wellhead device, a main wellbore tubing, at least one branch wellbore tubing, a multi-tubing packer, a main wellbore packer, at least one branch wellbore packer, and a plurality of oil production pumps; The multi-tubular wellhead device is installed at the tops of the main wellbore tubing and each of the branch wellbore tubings, the multi-tubular packer is connected to the upper parts of the main wellbore tubing and each of the branch wellbore tubings, the main wellbore packer is installed at the lower part of the main wellbore tubing, and each of the branch wellbore packers is installed at the lower part of the corresponding branch wellbore tubing; a production pump is inserted into each of the main wellbore tubing and each of the branch wellbore tubings respectively.

8. The branch well production tubing string according to claim 7, characterized in that a guiding tool is connected to the bottom end of the branch wellbore tubing, the guiding tool includes a straight section and an inclined section which are connected up and down, and the bottom end of the inclined section can be attached to the inner wall of the casing in the corresponding wellbore during the lowering process of the branch wellbore tubing.

9. The branch well production tubing string according to claim 7, characterized in that the number of the branch wellbore tubings is one.

10. The branch well production tubing string according to claim 7, characterized in that both the main wellbore packer and each branch wellbore packer are water- and oil-encountered self-expanding packers.

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