A downhole fishing evaluation method based on workover iron filings

Abstract

The application discloses a wellbore fishing evaluation method based on well repairing iron filings, and belongs to the technical field of oil well repairing and fishing. The method comprises the following steps: S1, collecting parameters; S2, calculating the settling velocity of the iron filings and the critical annular flowback speed according to a settling resistance coefficient model; S3, when the critical annular flowback speed is greater than the actual annular flowback speed, calculating the flowback ratio of the wellhead iron filings, otherwise, changing the construction parameters and repeating steps S1-S2; the flowback ratio of the iron filings is the ratio of the actual flowback mass of the iron filings to the theoretical flowback mass; and S4, when the flowback ratio of the iron filings reaches a preset threshold, the downhole fishing operation can be performed, otherwise, the grinding and milling are continuously performed and steps S3-S4 are repeated. The application determines the completion condition of the thread grinding and milling in the downhole grinding and milling operation by the wellhead iron filing amount, compared with the previous determination of the thread length by the change of the pipe string depth, the determination result of the application is not affected by the pipe string deformation, and thus the accuracy is high, and the application can provide scientific guidance for the downhole fishing operation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil well repair fishing, and particularly relates to a downhole fishing evaluation method based on well repair iron filings. BACKGROUND

[0002] With further development of oil fields, oil and water wells are aging year by year, downhole accidents occur frequently, and the frequency of overhaul fishing also rises. The existing oil pipe fishing method mainly includes the following steps: first, sleeve milling, and then fishing. After the oil pipe is milled to form a threaded hole, a fishing cone is lowered to fish. 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 fishing cone can be firmly engaged with the milled threaded hole. In order to ensure the smooth progress of fishing work, it is necessary to ensure that the length of the milled thread meets the fishing requirements.

[0003] Iron filings are solid iron particles carried to the ground by well repair fluid after being cut by downhole cutting teeth during well repair and fishing. As the most direct reflection of downhole state, the form of iron filings can be used to judge whether the downhole work is normal at the fishing site. At present, the return monitoring of iron filings is less. At present, there is a lack of effective monitoring means for the forming length of the threaded hole of the milled well section. Some places believe that the length of the milled thread can be measured by the lowering height of the drill string during milling. However, as the milling proceeds, the torque received by the drill string will increase, which leads to the gradual increase of the total deformation of the drill string, thereby causing the inconsistency between the lowering height of the drill string at the wellhead and the lowering height of the milling shoe at the bottom of the well. It is difficult to determine whether the appropriate thread length is reached to meet the fishing requirements. SUMMARY

[0004] In order to solve the above problems, the application provides a downhole fishing evaluation method based on well repair iron filings, which is used to accurately measure the thread length in downhole milling operation and provide guidance for downhole fishing operation.

[0005] In order to achieve the above purpose, the application provides the following scheme:

[0006] A downhole fishing evaluation method based on well repair iron filings, comprising the following steps:

[0007] S1, collecting parameters, including basic parameters of iron filings particles in the target area, parameters of well repair fluid and construction parameters;

[0008] S2, calculating the settling velocity of the iron filings and calculating the critical annular return speed according to the settling resistance coefficient model;

[0009] S3, when the critical annular return speed is greater than the actual annular return speed, the iron filings return and discharge ratio is calculated, otherwise, the construction parameters are changed, and steps S1-S2 are repeated; the return and discharge ratio of the iron filings is the ratio of the actual return and discharge mass of the iron filings to the theoretical return and discharge mass;

[0010] S4, when the flowback ratio of the iron filings reaches a preset threshold, downhole fishing operations can be performed, otherwise, grinding and milling are continued and steps S3-S4 are repeated.

[0011] As a specific embodiment of the present application, step S2 comprises:

[0012] S21, calculating the settling velocity of the iron filings;

[0013] S211, taking iron filings of different shapes to perform a milling particle settling experiment to obtain their settling velocities, and using the following calculation formula to calculate their drag coefficients:

[0014]

[0015] In the formula, C d is the drag coefficient of the iron filings, dimensionless; p s is the density of the iron filings, kg / m 3 ; p f is the density of the workover fluid, kg / m 3 ; g is the acceleration of gravity, taken as 9.8 N / kg; d ep is the equivalent volume particle size of the iron filings, i.e., its hydrodynamic radius, mm; v s is the settling velocity of the iron filings particles, m / s;

[0016] S212, calculating the hydrodynamic radius of the particles in the above iron filings particle settling experiment, using spherical iron filings particles of equal diameter to perform a settling experiment to obtain their settling velocities, and using the following formula to calculate their drag coefficients:

[0017]

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

[0019] S213, repeating the above two steps to perform multiple experiments, and establishing the relationship between C d / C d-s and the sphericity p and S t as follows:

[0020]

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

[0022] S214, combining the settling drag coefficient model to calculate the settling velocities of iron filings of multiple sizes, and the calculation model is as follows:

[0023]

[0024] φ =∑w i φ i

[0025] S t =∑w i S i

[0026]

[0027]

[0028]

[0029] wherein w i is the mass content of the i-th iron filings; Φ i is the sphericity of the i-th iron filings; S i is the area influence factor of the i-th iron filings; d is is the equivalent hydrodynamic 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 filings, 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 sheet iron filings, m; μ AV is the plastic viscosity of the workover fluid, mPa·s;

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

[0031]

[0032] wherein C a is the annular iron filings volume concentration, dimensionless; V rop is the mechanical drilling speed, m / s; V amin is the minimum annular return speed, i.e., the critical annular return speed, m / s; k' is the flow rate correction factor; d h is the annular outer diameter, mm; d p is the annular inner diameter, mm;

[0033] As a specific embodiment of the present application, the calculation formula of the theoretical return iron filings amount in step S3 is as follows:

[0034]

[0035]

[0036] In the formula, Q is the workover fluid displacement; v s is the iron filings particle settling velocity, m / s; A is the radius of the tooth top of the milling device; B is the radius of the tooth bottom of the milling device; a is the length of the tooth top of the milling device in the axial direction; b is the length of the tooth bottom of the milling device in the axial direction; h is the difference between the radius of the tooth top and the radius of the tooth bottom of the milling device; K is an empirical coefficient, dimensionless; and γ is the flow state coefficient, which is 1 when the flow state is laminar flow and 1.2 when the flow state is turbulent flow.

[0037] As a specific embodiment of the present application, the calculation formula of the actual flowback mass of the iron filings in step S3 is as follows:

[0038]

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

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

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

[0042] The present application determines the thread length in the downhole milling operation by the wellhead iron filings amount, which is not affected by the pipe string deformation compared with the previous determination of the thread length by the pipe string running depth change, and thus has high precision and can provide scientific guidance for the downhole fishing operation. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is the flowchart of the embodiment of the present application;

[0044] Figure 2 is the schematic diagram of the tooth part of the milling device. DETAILED DESCRIPTION

[0045] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0046] Embodiment 1

[0047] In the embodiment, the iron filings particles are generated from a straight hole section or a small inclination hole section. 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 internal pipe rotation, when the annular return speed increases to a certain value, the iron filings particles can smoothly return to the wellhead. However, if the iron filings are partially deposited in the wellbore to form an iron filings bed, the actual return flow rate of the iron filings will be affected. Therefore, the evaluation method of the present application is divided into two parts. First, it is determined whether the iron filings particles can smoothly return to the wellhead without forming an iron filings bed, that is, whether the actual annular return speed is greater than the critical annular return speed of the iron filings returning to the wellhead. Of course, when measuring on site, the flow rate is usually reflected by the flow rate, so it can also be changed to determine whether the actual annular discharge capacity is greater than the critical annular discharge capacity. For the case where the actual annular return speed is greater than the critical annular return speed, or the actual annular discharge capacity is greater than the critical annular discharge capacity, the thread length is calculated by the iron filings return flow rate. The following will explain the entire steps in detail.

[0048] The flow of the downhole fishing evaluation method based on the workover iron filings of the present application is shown in Figure 1 as follows:

[0049] S1, collect parameters, including basic parameters of iron filings particles in the target area (size of iron filings, etc.), parameters of workover fluid and construction parameters;

[0050] S2, calculate the settling velocity of the iron filings and calculate the critical annular return speed according to the settling resistance coefficient model;

[0051] S3, when the critical annular return speed is greater than the actual annular return speed, calculate the return and discharge ratio of the wellhead iron filings, otherwise, change the construction parameters and repeat steps S1-S2; the return and discharge ratio of the iron filings is the ratio of the actual return and discharge mass of the iron filings to the theoretical return and discharge mass;

[0052] S4, when the return and discharge ratio of the iron filings reaches a preset threshold, downhole fishing operation can be performed, otherwise, continue to mill and repeat steps S3-S4.

[0053] The following will further explain several main steps.

[0054] Step S2 mainly calculates the critical annular return speed of the iron filings, which includes the following steps:

[0055] S21, calculate the settling velocity of the iron filings;

[0056] S211, take iron filings of different shapes to perform milling and iron filings particle settling experiments to obtain the settling velocity, and calculate the resistance coefficient by using the following calculation formula:

[0057]

[0058] In the formula, C dis the drag coefficient of iron filings, dimensionless; p is the density of iron filings, kg / m s 3 f is the density of iron filings, kg / m 3 ; g is the acceleration of gravity, taking 9.8 N / kg; d ep is the equivalent volume particle size of iron filings, i.e. its hydrodynamic radius, mm; v s is the settling velocity of iron filings particles, m / s;

[0059] S212, calculate the hydrodynamic radius of the above iron filings particle settling experiment, use spherical iron filings particles with equal diameter to carry out the settling experiment, obtain its settling velocity, and use the following formula to calculate its drag coefficient:

[0060]

[0061] In the formula, C d-s is the drag coefficient of spherical iron filings particles, dimensionless; v ss is the settling velocity of spherical iron filings particles, m / s; S213, repeat the above two steps, normalize the drag coefficient C d of the spherical particles to the drag coefficient C d-s of the spherical particles, and establish the relationship between C d / C d-s and the sphericity φ and S t as follows:

[0062]

[0063] In the formula, a, b, c, d are all 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 combined with the settling drag 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] wherein w i is the mass content of the i-th iron filings; Φ i is the sphericity of the i-th iron filings; S i is the area influence factor of the i-th iron filings; d is is the equivalent hydrodynamic 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 filings, 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 sheet-shaped iron filings, m; μ AV is the plastic viscosity of the workover fluid, mPa·s;

[0072] S22, calculating the critical annular flowback speed, the calculation formula of which is as follows:

[0073]

[0074] wherein C a is the annular iron filings volume concentration, dimensionless; V rop is the mechanical drilling speed, m / s; V amin is the minimum annular flowback speed, i.e., the critical annular flowback speed, m / s; k' is a flow rate correction factor (generally about 1.25); d h is the annular outer diameter, mm; d p is the annular inner diameter, mm;

[0075] In actual use, the annular flow rate of the wellhead is usually used to determine the annular rotating speed, therefore, in order to facilitate intuitive comparison, the critical annular flow rate is converted into the corresponding annular flow rate, which is referred to as the minimum annular flow rate, and the calculation formula is as follows:

[0076]

[0077] The step S3 of the present application involves calculating the flowback ratio of the iron filings, and specifically includes the following steps:

[0078] S31, calculating the theoretical returned iron filings amount

[0079]

[0080]

[0081] wherein Q is the workover fluid flow rate; v sis the settling velocity of the iron filings particles, m / s; A is the radius of the tooth top of the milling device; B is the radius of the tooth bottom of the milling device; a is the length of the tooth top of the milling device in the axial direction; b is the length of the tooth bottom of the milling device in the axial direction; h is the difference between the radius of the tooth top and the radius of the tooth bottom of the milling device; K is an empirical coefficient, dimensionless; and γ is a flow state coefficient, which is 1 when the flow state is laminar flow and is 1.2 when the flow state is turbulent flow.

[0082] S32, the actual flowback mass of the iron filings is calculated according to the following formula:

[0083]

[0084] wherein m s is the actual flowback mass of the iron filings; L is the length of the wellbore, m; α is the mass content of dry iron filings in the wellhead iron filings slurry mixture; and m s is the total mass of the wellhead iron filings slurry mixture.

[0085] The mass content of dry iron filings in the iron filings slurry mixture is obtained by the following steps.

[0086] S321, the slurry is stirred uniformly, and a portion of the iron filings slurry mixture is taken and weighed to obtain a mass Δm wet;

[0087] S322, the slurry in the iron filings slurry mixture is removed, and the remaining iron filings is dried and weighed to obtain the mass of dry iron filings Δm dry;

[0088] S323, the mass content of dry iron filings in the iron filings slurry mixture is determined as Δm dry / Δm wet

[0089] S33, the flowback ratio of the iron filings is calculated.

[0090]

[0091] When R flowback ≥β, the threaded hole milling is completed, and it can be ensured that the fishing cone can successfully fish the tubing. The threshold value of the flowback ratio can be obtained according to experience, and the inventors believe that the threshold value of 85% is better after many tests.

[0092] This embodiment is described by taking an actual fishing as an example. In step S2, 525 groups of iron filings data C d and the settling resistance coefficient C d-s of the spherical particles are subjected to ratio normalization processing to establish the relationship between C d / C d-s and the sphericity φ and S t , which is as follows:

[0093]

[0094] The iron filings' sedimentation velocity is inversed by the sedimentation resistance coefficient model, and the fishing opportunity is determined by taking 85% as the threshold value, and the actual thread length after fishing is measured, and the specific data are shown in the following table:

[0095] Number of experiments 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] As shown in the above table, the expected thread milling length is 10.00 m, the actual thread length after fishing is measured to be between 9.12 and 9.36, the error is within 10%, and good effect is achieved.

[0097] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the embodiments of the present application, which should be covered in the protection scope of the present application.

Claims

1. A downhole fishing evaluation method based on well workover scrap, characterized in that, include: S1. Collect parameters, including basic parameters of iron filings in the target area, parameters of the workover fluid, and construction parameters; S2. Calculate the settling velocity of the iron filings 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, calculate the scrap return ratio. Otherwise, change the construction parameters and repeat steps S1 to S2. The scrap return ratio is the ratio of the actual scrap return mass to the theoretical scrap return mass. S4. When the iron filings return ratio reaches the preset threshold, downhole retrieval operation can be carried out; otherwise, continue milling and repeat steps S3 to S4. Step S2 includes: S21. Calculate the settling velocity of the iron filings; S211. Take iron filings of different shapes and conduct milling particle settling experiments to obtain their settling velocities, and calculate their drag coefficients using the following formula: In the formula, C d ρ is the drag coefficient of iron filings, dimensionless; s It is the density of the iron filings, kg / m³ 3 ;ρ f The density of the workover fluid is expressed in kg / m³. 3 g is the acceleration due to gravity, taken as 9.8 N / kg; d ep v represents the volumetric particle size of the iron filings, i.e., their hydraulic radius, in mm; s Let be the settling velocity of the iron filings, in m / s; S212. Calculate the hydraulic radius of the iron filings in S211. A settling experiment was conducted using spherical iron filings of equal diameter to obtain their settling velocity. The drag coefficient was then calculated using the following formula: In the formula, C d-s v is the drag coefficient of spherical iron filings, dimensionless; ss denoted as ρ, the settling velocity of the spherical iron filings, in m / s; S213. Repeat the above two steps to obtain multiple sets of C. d C d-s Data, build C d / C d-s With sphericity φ and S t Relationship: In the formula, a, b, c, and d are coefficients obtained through data fitting; Φ is the sphericity; S t Re is the area influence factor; p It is a Reichstag number; S213. Calculate the settling velocity of multi-sized iron filings using the settling resistance coefficient model. The calculation model is as follows: φ=Σw i f i S t =∑w i S i In the formula, w i Φ represents the mass content of the i-th type of iron filings; i S represents the sphericity of the i-th type of iron filings; i d is the area influence factor of the i-th type of iron filings; is Let A be the equivalent hydraulic radius of the i-th type of iron filings; i Let L be the area of ​​the i-th type of iron filings; l The length of the spiral iron filings is in meters (m) and s is in s. l The pitch of the spiral iron filings is m; b l D represents the width of the iron filings, in meters (m). l R is the outer diameter of the spiral iron filings, in meters (m); c L represents the radius of the C-shaped iron filings, in meters (m). p The length of the sheet-like iron filings is in meters (m); μ AV The plastic viscosity of the workover fluid is given in mPa·s. S22. Calculate the critical annular return velocity, the formula is as follows: In the formula: C a V is the volume concentration of annular iron filings, dimensionless; rop V is the mechanical drilling rate, in m / s; amin The minimum annular return velocity, i.e., the critical annular return velocity, is given in m / s; k′ is the velocity correction factor; d h d is the outer diameter of the annulus, in mm. p The inner diameter of the annulus is in mm; The theoretical return mass of iron filings in step S3 is calculated using the following formula: In the formula, Q is the well workover fluid discharge rate; v s denoted as γ, where γ is the settling velocity of the iron filings (m / s); A is the radius of the tooth crest of the milling machine; B is the radius of the tooth root of the milling machine; a is the axial length of the tooth crest of the milling machine; b is the axial length of the tooth root of the milling machine; h is the difference between the radii of the tooth crest and the tooth root of the milling machine; K is an empirical coefficient, dimensionless; γ is the flow regime coefficient, which takes a value of 1 when the flow regime is laminar and 1.2 when the flow regime is turbulent. The formula for calculating the actual return mass of iron filings in step S3 is as follows: In the formula, m s α represents the actual return mass of iron filings; L is the wellbore length (m); α is the mass content of dry iron filings in the wellhead iron filings mud mixture (m). s This refers to the total mass of the wellhead iron filings and mud mixture.

2. As described in claim 1, characterized in that, The threshold for the return ratio in step S3 is 85%.

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