Underground salvage evaluation method based on well repair scrap iron

Abstract

The invention discloses an underground salvage evaluation method based on well repair scrap iron, and belongs to the technical field of petroleum well repair salvage. Comprising the following steps: S1, collecting parameters; s2, the settling velocity of the scrap iron is calculated, and the critical annular return velocity is calculated according to a settling resistance coefficient model; s3, when the critical annulus return speed is larger than the actual annulus return speed, the flowback ratio of the scrap iron at the wellhead is calculated, and otherwise, construction parameters are changed, and the steps S1 to S2 are repeated; the flowback ratio of the scrap iron is the ratio of the actual flowback mass to the theoretical flowback mass of the scrap iron; and S4, when the flowback ratio of the scrap iron reaches a preset threshold value, underground fishing operation can be carried out, otherwise, grinding and milling are continued, and the steps S3-S4 are repeated. According to the method, the thread milling completion condition in the underground milling operation is judged according to the quantity of the scrap iron at the wellhead, and compared with the previous method for determining the thread length through the change of the tripping depth of the pipe column, the judgment result is not influenced by the deformation of the pipe column, so that the precision is high, and scientific guidance can be provided for the underground fishing operation.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum well repair and salvage, and in particular relates to a downhole salvage evaluation method based on well repair iron scraps. Background Art

[0002] With the further development of oil fields, oil and water wells are aging year by year, underground accidents occur frequently, and the frequency of overhaul salvage also increases. The existing methods of salvaging oil pipes are mainly: first milling, then salvaging, milling the threaded hole of the oil pipe and then lowering the salvage cone for salvage. In this process, it is necessary to ensure that the threaded hole is milled, and at the same time, it is necessary to ensure that the salvage cone can be firmly engaged with the milled threaded hole. In order to ensure the smooth progress of the salvage work, it is necessary to ensure that the length of the milled thread can meet the salvage requirements.

[0003] Iron chips are solid iron particles that are carried to the surface by the workover fluid after being cut by the downhole cutting teeth during the workover and salvage process. As the most direct reflection of the downhole status, the shape of the iron chips can be used to determine whether the downhole work is normal at the salvage site. At present, there is little monitoring of the return of iron chips. At present, there is a lack of effective monitoring methods for the threaded hole forming length of the milling well section. Some places believe that the milling thread length can be measured by the descent height of the drill string during the milling process. However, as the milling progresses, the torque received by the drill string will increase, which will cause the complete deformation of the drill string to gradually increase, resulting in the inconsistency between the descent height of the wellhead drill string and the descent height of the bottom hole milling shoe, making it difficult to determine whether the appropriate thread length has been achieved to meet the salvage requirements. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a downhole salvage evaluation method based on well repair iron chips, which is used to accurately measure the thread length in downhole magic milling operations and provide guidance for downhole salvage operations.

[0005] In order to achieve the above object, the solution provided by the present invention is as follows:

[0006] A method for evaluating downhole salvage based on well repair iron scraps comprises the following steps:

[0007] S1. Collect parameters, including basic parameters of iron filings particles in the target area, parameters of workover fluid and construction parameters;

[0008] S2, calculate the settling velocity of iron chips and calculate the critical annular return velocity based on the settling resistance coefficient model;

[0009] S3. When the critical annular return velocity is greater than the actual annular return velocity, the return ratio of the iron chips is calculated. Otherwise, the construction parameters are changed and steps S1 to S2 are repeated. The return ratio of the iron chips is the ratio of the actual return mass of the iron chips to the theoretical return mass.

[0010] S4. When the return ratio of the iron chips reaches a preset threshold, downhole salvage operations can be performed, otherwise, continue grinding and repeating steps S3 to S4.

[0011] As a specific implementation of the present invention, step S2 includes:

[0012] S21, calculate the settling speed of iron chips;

[0013] S211. Take iron chips of different shapes to conduct a milling chip particle sedimentation experiment to obtain their sedimentation velocity, and calculate their resistance coefficient using the following calculation formula:

[0014]

[0015] In the formula, C d is the resistance coefficient of the iron chips, dimensionless; ρ s is the density of iron filings, kg / m 3 ρ f is the density of the workover fluid, kg / m 3 ; g is the acceleration due to gravity, which is 9.8N / kg; d ep is the equivalent volume particle size of iron filings, i.e. its hydraulic radius, mm; v s is the settling velocity of iron filings particles, m / s;

[0016] S212. Calculate the hydraulic radius of the particles in the above iron filings particle sedimentation experiment, use spherical iron filings particles with equal diameter to conduct sedimentation experiments, obtain their sedimentation velocity, and use the following formula to calculate their resistance coefficient:

[0017]

[0018] In the formula, C d-s is the drag coefficient of spherical iron filings, dimensionless; v ss is the settling velocity of spherical iron filings, m / s;

[0019] S213, repeat the above two steps to conduct multiple groups of experiments, and establish C d / C d-s With sphericity φ and S t The relationship is as follows:

[0020]

[0021] Where a, b, c, and d are coefficients obtained by data fitting; Φ is the sphericity; S t is the area influence factor; Re p is the Reynolds number;

[0022] S214. Calculate the sedimentation velocity of iron chips of various sizes by combining the sedimentation resistance coefficient model. The calculation model is as follows:

[0023]

[0024] φ=∑w i φ i

[0025] S t =∑w i S i

[0026]

[0027]

[0028]

[0029] In the formula, w i is the mass content of the i-th type of iron filings; Φ i is the sphericity of the i-th iron filings; S i is the area influence factor of the i-th type of iron filings; d is is the equivalent hydraulic radius of the i-th iron filings; A i is the area of ​​the i-th iron filings; L l is the length of the spiral iron filings, m; s l is the pitch of the spiral iron filings, m; b l is the width of the iron chips, m; D l is the outer diameter of the spiral iron filings, m; R c is the radius of the C-shaped iron filings, m; L p is the length of the flaky iron chips, m; μ AV is the plastic viscosity of the workover fluid, mPa·s;

[0030] S22, calculate the critical annular return speed, the calculation formula is as follows:

[0031]

[0032] Where: C a V is the volume concentration of iron chips in the annulus, dimensionless; rop is the mechanical drilling speed, m / s; V amin is the minimum annular return velocity, i.e. the critical annular return velocity, m / s; k′ is the velocity correction factor; d h is the outer diameter of the annulus, mm; d p is the inner diameter of the annulus, mm;

[0033] As a specific implementation of the present invention, the calculation formula for the theoretical amount of returned iron chips in step S3 is:

[0034]

[0035]

[0036] Where, Q is the displacement of well-repair fluid; v s is the settling velocity of iron chip particles, m / s; A is the radius of the top of the tooth of the grinding and milling equipment; B is the radius of the bottom of the tooth of the grinding and milling equipment; a is the axial length of the top of the tooth of the grinding and milling equipment; b is the axial length of the bottom of the tooth of the grinding and milling equipment; h is the difference between the radius of the top of the tooth of the grinding and milling equipment and the radius of the bottom of the tooth; K is the empirical coefficient, dimensionless; γ is the flow coefficient, which takes a value of 1 when the flow state is laminar flow and a value of 1.2 when the flow state is turbulent.

[0037] As a specific implementation of the present invention, the calculation formula for the actual return mass of iron chips in step S3 is as follows:

[0038]

[0039] In the formula, m s is the actual return mass of iron chips; L is the wellbore length, m; α is the mass content of dry iron chips in the iron chips mud mixture at the wellhead; m s It is the total mass of the iron filings-mud mixture at the wellhead.

[0040] As a specific implementation of the present invention, the threshold value of the flowback ratio is 85%.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention determines the thread length in downhole grinding operations by the amount of iron filings at the wellhead. Compared with the previous method of determining the thread length by the change in the depth of the pipe string, the determination result of the present invention is not affected by the deformation of the pipe string, so it has high accuracy and can provide scientific guidance for downhole salvage operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of the tooth portion of the grinding equipment of the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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.

[0046] Example 1

[0047] In this embodiment, the iron filings particles are produced from the vertical well section or the small-angle well section. Since the well inclination angle is very small, under static conditions, the iron filings particles mainly settle to the bottom of the well. Under dynamic conditions, especially in the case of turbulence and rotation of the inner tube, when the annular return velocity increases to a certain value, the iron filings particles can be smoothly returned to the wellhead. However, if the iron filings are partially deposited in the wellbore to form an iron filing bed, it will affect the measurement of the actual return volume of the iron filings. Therefore, the evaluation method of the present invention is divided into two parts. First, it is determined whether the iron filings particles can be smoothly returned to the wellhead without producing an iron filing bed, that is, whether the actual annular return velocity is greater than the critical annular return velocity of the iron filings returning to the wellhead. Of course, the flow velocity is usually reflected by the flow rate during on-site measurement, so it can also be changed to determine whether the actual annular discharge volume is greater than the critical annular discharge volume. In the case where the actual annular return velocity is greater than the critical annular return velocity, or the actual annular discharge volume is greater than the critical annular discharge volume, the thread length is calculated by the iron filings return volume. Below, the entire step will be described in detail.

[0048] The process of the downhole salvage evaluation method based on well repair iron scraps of the present invention is as follows: Figure 1 As shown, the following steps are included:

[0049] S1. Collect parameters, including basic parameters of iron chips particles in the target area (such as the size of iron chips), parameters of workover fluid and construction parameters;

[0050] S2, calculate the settling velocity of iron chips and calculate the critical annular return velocity based on the settling resistance coefficient model;

[0051] S3. When the critical annular return velocity is greater than the actual annular return velocity, the return ratio of the wellhead iron chips is calculated. Otherwise, the construction parameters are changed and steps S1 to S2 are repeated. The return ratio of the iron chips is the ratio of the actual return mass of the iron chips to the theoretical return mass.

[0052] S4. When the return ratio of iron chips reaches a preset threshold, downhole salvage operations can be performed, otherwise, continue grinding and repeating steps S3 to S4.

[0053] Several major steps are further described below.

[0054] Step S2 is mainly to calculate the critical annular return speed of the iron chips, which includes the following steps:

[0055] S21. Calculate the settling velocity of iron filings;

[0056] S211. Take iron chips of different shapes to conduct a milling chip particle sedimentation experiment to obtain their sedimentation velocity, and calculate their resistance coefficient using the following calculation formula:

[0057]

[0058] In the formula, C dis the resistance coefficient of the iron chips, dimensionless; ρ s is the density of iron filings, kg / m 3 ρ f is the density of the workover fluid, kg / m 3 ; g is the acceleration due to gravity, which is 9.8N / kg; d ep is the equivalent volume particle size of iron filings, i.e. its hydraulic radius, mm; v s is the settling velocity of iron filings particles, m / s;

[0059] S212. Calculate the hydraulic radius of the above iron filings particle settling experiment, use spherical iron filings particles of equal diameter to carry out the settling experiment, obtain the settling velocity, and use the following formula to calculate the resistance coefficient:

[0060]

[0061] In the formula, C d-s is the drag coefficient of spherical iron filings, dimensionless; v ss is the settling velocity of spherical iron filings, m / s; S213, repeat the above two steps, and convert multiple sets of iron filings data C d The sedimentation resistance coefficient C of spherical particles d-s Perform ratio normalization and establish C d / C d-s With sphericity φ and S t The relationship is as follows:

[0062]

[0063] Where a, b, c, and d are coefficients obtained by data fitting; Φ is the sphericity; S t is the area influence factor; Re p is the Reynolds number;

[0064] S214. Calculate the settling velocity by combining the settling resistance coefficient model. The calculation model is as follows:

[0065]

[0066] φ=∑w i φ i

[0067] S t =∑w i S i

[0068]

[0069]

[0070]

[0071] In the formula, w i is the mass content of the i-th type of iron filings; Φ i is the sphericity of the i-th iron filings; S i is the area influence factor of the i-th type of iron filings; d is is the equivalent hydraulic radius of the i-th iron filings; A i is the area of ​​the i-th iron filings; L l is the length of the spiral iron filings, m; s l is the pitch of the spiral iron filings, m; b l is the width of the iron chips, m; D l is the outer diameter of the spiral iron filings, m; R c is the radius of the C-shaped iron filings, m; L p is the length of the flaky iron chips, m; μ AV is the plastic viscosity of the workover fluid, mPa·s;

[0072] S22, calculate the critical annular return speed, the calculation formula is as follows:

[0073]

[0074] Where: C a V is the volume concentration of iron chips in the annulus, dimensionless; rop is the mechanical drilling speed, m / s; V amin is the minimum annular return velocity, i.e. the critical annular return velocity, m / s; k′ is the velocity correction factor (usually around 1.25); d h is the outer diameter of the annulus, mm; d p is the inner diameter of the annulus, mm;

[0075] In actual use, the annular speed is usually determined by the annular displacement at the wellhead. Therefore, in order to facilitate direct observation and comparison, the critical annular displacement is converted into the corresponding annular displacement, called the minimum annular displacement, and its calculation formula is as follows:

[0076]

[0077] Step S3 of the present invention involves calculating the flowback ratio of iron chips, which specifically includes the following steps:

[0078] S31. Calculate the theoretical amount of returned iron chips

[0079]

[0080]

[0081] Where, Q is the displacement of well-repair fluid; v sis the settling velocity of iron chip particles, m / s; A is the radius of the top of the tooth of the grinding and milling equipment; B is the radius of the bottom of the tooth of the grinding and milling equipment; a is the axial length of the top of the tooth of the grinding and milling equipment; b is the axial length of the bottom of the tooth of the grinding and milling equipment; h is the difference between the radius of the top of the tooth of the grinding and milling equipment and the radius of the bottom of the tooth; K is the empirical coefficient, dimensionless; γ is the flow coefficient, which takes a value of 1 when the flow state is laminar flow and a value of 1.2 when the flow state is turbulent.

[0082] S32. The calculation formula for the actual return mass of iron chips is as follows:

[0083]

[0084] In the formula, m s is the actual return mass of iron chips; L is the wellbore length, m; α is the mass content of dry iron chips in the iron chips mud mixture at the wellhead; m s It is the total mass of the iron chips slurry mixture at the wellhead.

[0085] Wherein, obtaining the mass content of dry iron chips in the iron chips slurry mixture comprises the following steps;

[0086] S321, stir the slurry evenly, take a portion of the iron filings slurry mixture and weigh its mass as Δmwet;

[0087] S322, removing the mud from the iron filings-mud mixture, drying and weighing the remaining iron filings to obtain the mass Δmdry of the dry iron filings;

[0088] S323, determine the mass content of dry iron chips in the iron chips slurry mixture, Δmdry / Δmwet

[0089] S33, calculating the iron chip return ratio;

[0090]

[0091] When Rreturn≥β, the threaded hole milling is completed, which can ensure that the salvage cone can successfully salvage the oil pipe. The specific threshold of the return ratio can be obtained based on experience. After many experiments, the inventor believes that the threshold of 85% is better.

[0092] This embodiment is described by taking actual salvage as an example. In step S2, 525 sets of iron filings data C are d The sedimentation resistance coefficient C of spherical particles d-s Perform ratio normalization and establish C d / C d-s With sphericity φ and S t The relationship is as follows:

[0093]

[0094] The sedimentation velocity of iron chips was inverted through the sedimentation resistance coefficient model, and the salvage timing was determined with β=85% as the threshold. The actual thread length after salvage was measured, and the specific data are shown in the following table:

[0095] Number of experimental groups Expected thread length Actual thread length error 1 10 9.12 8.8％ 2 10 9.23 7.7％ 3 10 9.36 6.4％

[0096] It can be seen from the above table that the expected thread milling length is 10.00m. After it was finally salvaged, the actual thread length was measured to be between 9.12 and 9.36, with an error within 10%, which has a good effect.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the embodiments of the present invention should be covered within the protection scope of the present invention.

Claims

1. A downhole salvage evaluation method based on well repair iron scraps, characterized in that: include: S1. Collect parameters, including basic parameters of iron filings particles in the target area, parameters of workover fluid and construction parameters; S2, calculate the settling velocity of iron chips and calculate the critical annular return velocity based on the settling resistance coefficient model; S3. When the critical annular return velocity is greater than the actual annular return velocity, the return ratio of the iron chips is calculated. Otherwise, the construction parameters are changed and steps S1 to S2 are repeated. The return ratio of the iron chips is the ratio of the actual return mass of the iron chips to the theoretical return mass. S4. When the return ratio of iron chips reaches a preset threshold, downhole salvage operations can be performed; otherwise, continue grinding and repeating steps S3 to S4.

2. The method according to claim 1, characterized in that: Step S2 includes: S21, calculate the settling speed of iron chips; S211. Take iron chips of different shapes to conduct a milling chip particle sedimentation experiment to obtain their sedimentation velocity, and calculate their resistance coefficient using the following calculation formula: In the formula, C d is the resistance coefficient of the iron chips, dimensionless; ρ s is the density of iron filings, kg / m 3 ρ f is the density of the workover fluid, kg / m 3 ; g is the acceleration due to gravity, which is 9.8N / kg; d ep is the equivalent volume particle size of iron filings, i.e. its hydraulic radius, mm; v s is the settling velocity of iron filings particles, m / s; S212. Calculate the hydraulic radius of the iron filings in S211, use spherical iron filings of equal diameter to conduct a sedimentation experiment, obtain their sedimentation velocity, and use the following formula to calculate their resistance coefficient: In the formula, C d-s is the drag coefficient of spherical iron filings, dimensionless; v ss is the settling velocity of spherical iron filings, m / s; S213, repeat the above two steps to obtain multiple groups of C d , C d-s Data, build C d / C d-s With sphericity φ and S t The relationship is: Where a, b, c, and d are coefficients obtained by data fitting; Φ is the sphericity; S t is the area influence factor; Re p is the Reynolds number; S213. Calculate the sedimentation velocity of iron chips of various sizes by combining the sedimentation resistance coefficient model. The calculation model is as follows: φ=∑w i f i S t =∑w i S i In the formula, w i is the mass content of the i-th type of iron filings; Φ i is the sphericity of the i-th iron filings; S i is the area influence factor of the i-th type of iron chips; d is is the equivalent hydraulic radius of the i-th iron filings; A i is the area of ​​the i-th iron filings; L l is the length of the spiral iron filings, m; s l is the pitch of the spiral iron filings, m; b l is the width of the iron chips, m; D l is the outer diameter of the spiral iron filings, m; R c is the radius of the C-shaped iron filings, m; L p is the length of the flaky iron chips, m; μ AV is the plastic viscosity of the workover fluid, mPa·s; S22. Calculate the critical annular return speed. The calculation formula is as follows: Where: C a V is the volume concentration of iron chips in the annulus, dimensionless; rop is the mechanical drilling speed, m / s; V amin is the minimum annular return velocity, i.e. the critical annular return velocity, m / s; k′ is the velocity correction factor; d h is the outer diameter of the annulus, mm; d p is the inner diameter of the annulus, mm.

3. The method according to claim 1, characterized in that: The calculation formula of the theoretical return mass of iron chips in step S3 is as follows: Where, Q is the displacement of workover fluid; v s is the settling velocity of iron chip particles, m / s; A is the radius of the top of the tooth of the grinding and milling equipment; B is the radius of the bottom of the tooth of the grinding and milling equipment; a is the axial length of the top of the tooth of the grinding and milling equipment; b is the axial length of the bottom of the tooth of the grinding and milling equipment; h is the difference between the radius of the top of the tooth of the grinding and milling equipment and the radius of the bottom of the tooth; K is the empirical coefficient, dimensionless; γ is the flow coefficient, which takes a value of 1 when the flow state is laminar flow and a value of 1.2 when the flow state is turbulent.

4. The method according to claim 1, characterized in that: The calculation formula for the actual return mass of iron chips in step S3 is as follows: In the formula, m s is the actual return mass of iron chips; L is the wellbore length, m; α is the mass content of dry iron chips in the iron chips mud mixture at the wellhead; m s It is the total mass of the iron filings-mud mixture at the wellhead.

5. The method according to claim 1, characterized in that: The threshold value of the flowback ratio in step S3 is 85%.

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