Method for hydraulic dredging and cleaning in shaft

Abstract

The invention relates to the technical field of oilfield water injection development, in particular to a hydraulic dredging and cleaning method in a shaft. According to the method for hydraulic dredging and cleaning in the shaft, after target well parameters are obtained through well logging work, the water outlet speed of a jet hole is calculated, then dirt types of the inner wall of the shaft are divided, the ultimate strength of the dirt types is calculated, the pressure of a water pump is calculated according to the ultimate strength, and meanwhile the radius of a flushing oil pipe during sand flushing is calculated; and finally, adjusting on-site well washing equipment according to a calculation result. According to the method for hydraulic dredging and cleaning in the shaft, the dirt types are divided and the ultimate strength is calculated after the outlet flow speed of the hydraulic jet hole is calculated, the underground dirt is analyzed, and the equipment parameters for removing the dirt are calculated, so that the success rate of underground treatment work is improved, and meanwhile, the work of lifting a pipe column is not needed; and the working period is shortened, and the working cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of oilfield water injection development technology, and in particular to a method for hydraulic dredging and cleaning inside a wellbore. Background Technology

[0002] During water injection development in oilfields, impurities such as rust, alkaline scale, and polymer cements easily accumulate on the inner wall of the injection well tubing, causing obstruction in the descent of testing instruments. Descaling and unblocking are difficult and have a low success rate. Therefore, it is necessary to dredge the injection well to remove the scale. However, existing methods for adjusting wellbore dredging efficiency are not very effective. Two common adjustment methods exist: the first involves lowering a dredging tool into the well. This tool collides and rubs against the debris on the well wall, mechanically removing the blockage. However, this method requires continuous modification of the tool's parameters, necessitating a repeat wellbore treatment after each modification. This approach lacks specificity, relies heavily on experience for parameter adjustments, and has a low success rate. The second method involves pulling out the tubing when conventional dredging fails, followed by descaling or tubing replacement. This method has a long processing cycle and high costs, impacting water injection efficiency. Therefore, in order to address the above shortcomings, a method for hydraulic dredging and cleaning inside the well is proposed. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a method for hydraulically clearing and cleaning wellbore, which solves the problem of low success rate in downhole operations due to reliance on experience for adjusting downhole tool parameters in existing technologies; it also solves the problem of high construction costs and long construction cycles that affect water injection efficiency when clearing is ineffective and only tubing string operations can be performed.

[0005] (II) Technical Solution

[0006] To solve the above problems, the present invention provides a method for hydraulic dredging and cleaning inside a well, comprising:

[0007] Step 1: Obtain parameter information within the target well through well logging.

[0008] Step 2: Calculate the flow velocity at the outlet of the hydraulic jet orifice;

[0009] Step 3: Classify the types of dirt on the inner wall of the well;

[0010] Step 4: Calculate the ultimate strength of fouling on the inner wall of the rigid wellbore;

[0011] Step 5: Calculate the ultimate strength of the fouling on the inner wall of the viscoelastic wellbore;

[0012] Step 6: Construct the energy balance equation for jet clearing obstruction in the wellbore under hydraulic impact;

[0013] Step 7: Based on the calculation results of Steps 4 to 6, optimize the design of the operating limits for hydraulic jet dredging when encountering obstruction in the well.

[0014] Step 8: Calculate the radius of the flushing tubing inside the well;

[0015] Step 9: Adjust the dredging equipment based on the calculation results of Steps 7 and 8.

[0016] Furthermore, in step two, the calculation can be divided into two cases based on the pressure on the inner wall of the well, depending on the object being pressured: atmospheric pressure connected to the outside and liquid pressure formed by the residual water column.

[0017] Furthermore, the types of fouling on the inner wall of the wellbore in step three are classified into rigid wellbore inner wall fouling and viscoelastic wellbore inner wall fouling.

[0018] Furthermore, step four requires consideration of the mechanical properties of the fouling on the inner wall of the rigid wellbore, where the elastic modulus is approximately infinite.

[0019] Furthermore, in step six, it is necessary to consider that the magnitude of various mechanical forces during the process of water jet dredging the well shaft will change depending on the degree of breakage and deformation of the dirt on the inner wall of the well shaft.

[0020] Furthermore, in step seven, the calculation results from steps four and five are substituted into the energy balance equation in step six.

[0021] Furthermore, the parameter information within the well in step one includes the local atmospheric pressure P. a The injected water density ρ, the distance from the bottom of the injection well to the wellhead Z1, the apparent viscosity μ, and the average thickness of the fouling surface on the inner wall of the wellbore from the well wall.

[0022] Furthermore, the average thickness of the fouling surface on the inner wall of the wellbore from the well wall was obtained by trial contact testing with coiled tubing of different diameters.

[0023] Furthermore, when calculating the radius of the flushing tubing in step eight, it is necessary to first calculate the upward return velocity of the flushing fluid in the well.

[0024] (III) Beneficial Effects

[0025] The method for hydraulic dredging and cleaning inside wells provided by this invention obtains well information through well logging, calculates the outlet flow velocity of the hydraulic jet orifice of the cleaning tool at the target height, classifies the types of fouling, and calculates the ultimate strength of different types of fouling. It can analyze the fouling treatment work in a targeted manner, calculate the equipment parameters required to remove fouling from the well, and no longer rely on experience for adjustments, thereby improving the success rate of downhole treatment work. At the same time, it eliminates the need for tubing string pulling, shortens the work cycle, and reduces work costs. Attached Figure Description

[0026] Figure 1 This is a flowchart of the method for hydraulic dredging and cleaning inside a well shaft according to the present invention;

[0027] Figure 2 Stress diagram of fouling on the inner wall of a rigid well shaft;

[0028] Figure 3 Force diagram of fouling on the inner wall of a viscoelastic well casing. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", "top", and "bottom" are based on the orientation or positional relationship shown in the accompanying drawings. The purpose is only to facilitate the description of this invention and to simplify the description. It is not intended to indicate or imply that the component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0031] like Figure 1 As shown, the present invention provides a method for hydraulic dredging and cleaning inside a well, specifically including:

[0032] Step 1: Obtain parameter information within the target well through well logging.

[0033] Well logging is used to measure and assess various parameters and properties downhole, providing data for subsequent calculations and judgments. Generally, well logging is conducted when the wellhead is put into operation; in actual operation, only the data from the initial well logging session needs to be retrieved.

[0034] The parameters in the well in step one include local atmospheric pressure, injected water density, distance from the bottom of the injection well to the wellhead, apparent viscosity, and the average thickness of the fouling surface on the inner wall of the well.

[0035] It is important to note that the average thickness of the fouling surface on the wellbore inner wall from the well wall is determined by trial insertion with coiled tubing of different diameters. First, the coiled tubing is inserted into the wellbore for trial insertion. If the tubing successfully enters the wellbore, another tubing with a slightly larger diameter is used, and this process is repeated until the tubing encounters fouling on the wellbore inner wall during insertion. The difference between the outer diameter of the tubing and the inner diameter of the wellbore at this point is the average thickness of the fouling surface on the wellbore inner wall from the well wall.

[0036] Step 2: Calculate the flow velocity at the outlet of the hydraulic jet orifice;

[0037] The current method of clearing obstructed wells using hydraulic jetting involves drilling several small-diameter jet holes at the end of the coiled tubing. As the coiled tubing is continuously extended into the water injection well, water is injected into the top of the coiled tubing through a surface flushing pump. Under its own weight, the water will be ejected from the jet holes at the end of the coiled tubing. At this time, the water flow will impact the dirt on the inner wall of the well, breaking it up and dispersing it, thus clearing the dirt accumulated and adhering to the inner wall of the well.

[0038] In this process, the fluid inside the coiled tubing must satisfy the law of energy conservation. According to Bernoulli's energy equation, its equilibrium equation is as follows:

[0039]

[0040] In the formula, Z1 is the distance from the bottom of the injection well to the wellhead, in meters; Z h P represents the distance from the bottom of the well at any well depth; a ρ is the local atmospheric pressure; H is the density of the injected water; P is the head generated by the wellhead driving pump pressure; ρ is the local atmospheric pressure; ρ is the density of the injected water; H is the head generated by the wellhead driving pump pressure; P is the head generated by the wellhead driving pump pressure. h v is the outlet pressure of the jet orifice; h is the outlet velocity of the jet orifice; v is the outlet velocity of the jet orifice; h is the outlet pressure of the jet orifice. f For flow resistance, when the roughness of the inner wall of the coiled tubing is very small, the flow resistance h is... f It can be ignored.

[0041] Based on Bernoulli's energy equation, the relationship between the velocity and pressure of water flowing out of the jet at any depth in the well is obtained as follows:

[0042]

[0043] In step two, the calculation of the pressure on the inner wall of the wellbore can be divided into two cases based on the different objects being pressurized: atmospheric pressure (communicated with the outside) and liquid pressure formed by the residual water column. When the height of the outlet is lower than the residual water column inside the wellbore, the pressure acting on the outlet is the sum of the atmospheric pressure and the pressure of the liquid above the outlet. When the height of the outlet is higher than the height of the residual liquid inside the wellbore, the pressure acting on the outlet is only the atmospheric pressure at the inlet. Based on these two cases, a piecewise function is established to express the pressure at any depth on the inner wall of the wellbore, and its expression is:

[0044]

[0045] In the formula, Z b Z is the distance between the remaining water level in the injection well and the bottom of the well. In practice, this distance can be measured using an infrared distance measuring device installed at the wellhead. b Take measurements.

[0046] Substituting the expression for pressure into the formula for calculating velocity, we obtain the expression for the flow velocity at the outlet of the hydraulic jet orifice at any depth within the wellbore:

[0047]

[0048] In the formula, v is a quantitative representation of flow velocity.

[0049] Step 3: Classify the types of dirt on the inner wall of the well;

[0050] In practical applications, the injected water environment in wells often contains multi-component compounds such as polymers, surfactants, and guar gum. The varying composition of these compounds in different wells leads to diverse chemical compositions of the wellbore wall fouling. Based on their structural mechanical characteristics, wellbore wall fouling can be categorized into two types: rigid fouling, which does not deform under external stress (e.g., carbonate scale, gravel), and viscoelastic fouling, which deforms instantaneously under external stress (e.g., polymer micelles, sludge). Due to their different properties, these two types of fouling exhibit different ultimate strengths upon failure. By calculating their ultimate strengths, the energy intensity required to propel the water jet from the hydraulic jet orifice during downhole treatment operations can be determined.

[0051] Step 4: Calculate the ultimate strength of fouling on the inner wall of the rigid wellbore;

[0052] For fouling on the inner wall of a rigid wellbore, when external forces are applied, the fouling exhibits almost no change in geometry, and its elastic modulus can be considered infinite. As the external pressure on the fouling gradually increases, when the fouling undergoes plastic deformation, it reaches its failure limit. Based on the mechanical structural properties of the fouling, its failure limit strength is:

[0053] σ p =σ b

[0054] In the formula, σ b This represents the yield strength of fouling on the inner wall of a rigid wellbore.

[0055] At this point, the mechanical properties of the near-infinite elastic modulus of the fouling on the inner wall of the rigid well casing need to be considered. When water flows out of the jet and impacts the fouling on the inner wall of the rigid well casing, the fragmentation time of the rigid fouling can be ignored. Assuming that the failure mode is the same at any point on the contact surface between the water flow and the fouling on the inner wall of the rigid well casing, and the fragmentation process is continuous and divisible, we take the jet impact contact surface as the research object and perform mechanical analysis on a cylindrical force-bearing micro-element with a surface area of ​​dA.

[0056] The area of ​​the annular surface of the shear plane is:

[0057]

[0058] In the formula, δ1 is the average thickness of the dirt surface on the inner wall of the rigid wellbore from the well wall; r is the radius of the micro-element; and dA is the surface area of ​​the micro-element.

[0059] When a shear failure occurs on a toroidal surface, the hydraulic jet needs to provide sufficient impact force to break up the fouling on the rigid wellbore's inner wall. The magnitude of this impact force is the product of the toroidal surface area and the ultimate strength of the fouling on the rigid wellbore's inner wall. The expression for the required force is:

[0060]

[0061] In the formula, δ is the vertical distance between the failure point of the micro-element and the inner wall of the wellbore.

[0062] In practical work, considering the mechanical effect of hydraulic jets, the formula for calculating the kinetic energy at the jet outlet can be used. When the scale on the inner wall of a rigid well is sheared and broken at different thicknesses, the required magnitude of the jet impact mechanical force is different. Integrating the jet impact mechanical expression in the above formula over the scale thickness, the expression for the energy required for the scale on the inner wall of the rigid well to shear and break from the jet impact contact surface to the inner wall of the well is:

[0063]

[0064] In this process, the energy density of the fouling on the inner wall of the rigid wellbore, calculated according to the above formula, is exactly at the point of failure. The expression for this is:

[0065]

[0066] In the formula, r is the radius of a circle per unit area.

[0067] Meanwhile, considering the circular impact range formed by the water jet impact on the surface of the fouling on the inner wall of the rigid well, the energy required for the shearing and fracturing of all the stressed micro-elements is superimposed. Combined with the energy expression for the rigid well wall fouling reaching its failure limit state, the form of internal energy generated to resist deformation and fracturing at any depth of the inner wall of the injection well when the mechanical structure of the rigid well wall fouling reaches its failure limit strength can be obtained. Its expression is:

[0068]

[0069] In the formula, W represents the energy form of the ultimate strength of the rigid wellbore inner wall due to fouling.

[0070] Step 5: Calculate the ultimate strength of the fouling on the inner wall of the viscoelastic wellbore;

[0071] Viscoelastic wellbore inner wall fouling possesses a certain elastic modulus and undergoes deformation under hydraulic impact. Therefore, the maximum deformation caused by hydraulic jet impact on the viscoelastic wellbore inner wall fouling can be considered its failure limit state, where the deformation is exactly equal to the thickness of the fouling. At this point, the hydraulic jet can directly contact the wellbore wall surface under hydraulic impact. To describe the elastic and rheological properties of viscoelastic bodies, a VK model consisting of parallel elastic and viscous elements is chosen, with the constitutive equation as follows:

[0072]

[0073] In the formula, G is the modulus of the viscoelastic body when it exhibits pure elasticity; μ is the apparent viscosity of the viscoelastic body when it exhibits pure viscosity; and γ is the strain of the body under stress. denoted as the strain rate under stress.

[0074] Similar to the calculation of fouling on the inner wall of a rigid wellbore, the contact surface between the viscoelastic inner wall fouling and the hydraulic jet impact is taken as the research object. A cylindrical force-bearing micro-element with a surface area of ​​dA is selected for mechanical analysis. Based on the mapping relationship between the cross-sectional area of ​​the water flow at the jet outlet and the descent velocity of the coiled tubing, the hydraulic jet impact contact time that causes deformation on the force-bearing micro-element can be expressed as:

[0075]

[0076] In the formula, r m v0 is the jet orifice outlet radius; v0 is the coiled tubing descent speed.

[0077] Considering that the viscoelastic fouling on the inner wall of the wellbore eventually produces a deformation δ2 within the contact time t under the action of hydraulic impact, and that the water flow velocity decreases to 0 exactly when the hydraulic jet contacts the inner wall of the wellbore, the formulas for calculating the strain and average strain rate during the impact process of the hydraulic jet are as follows:

[0078]

[0079] In the formula, δ2 is the average distance between the fouling surface on the inner wall of the viscoelastic well and the well wall.

[0080] Substituting the strain and average strain rate into the constitutive equation of the VK model, the ultimate strength of viscoelastic wellbore fouling is specifically expressed as:

[0081]

[0082] Since the squeezing surface of the hydraulic impact is the surface area of ​​the stressed micro-element, the magnitude of the mechanical action required from the hydraulic jet when the stressed micro-element just reaches its failure limit can be expressed as:

[0083]

[0084] Similar to the principle in step four, by integrating the jet impact mechanics expression of the hydraulic jet with respect to the fouling thickness, the expression for the energy required for the viscoelastic wellbore inner wall fouling to be squeezed and deformed from the jet impact contact surface to the wellbore inner wall is:

[0085]

[0086] Based on the above energy expression, the energy density of viscoelastic wellbore inner wall fouling reaching the failure limit state is calculated. The obtained energy density is energy divided by the area of ​​force application. The expression for energy density is:

[0087]

[0088] Meanwhile, considering the circular impact range formed by the water jet impact on the viscoelastic wellbore inner wall fouling surface, the energy required for all the stressed micro-elements to undergo compressive deformation is superimposed. By expressing the energy density that just causes the viscoelastic wellbore inner wall fouling to reach its failure limit state, the expression for the internal energy generated to resist deformation and breakage at any depth of the injection wellbore inner wall fouling mechanical structure when it reaches its failure limit strength can be obtained as follows:

[0089]

[0090] Step 6: Construct the energy balance equation for jet clearing obstruction in the wellbore under hydraulic impact;

[0091] During the process of hydraulic jet impacting fouling on the inner wall of a well, taking the jet impact contact surface as the analysis object, it is subjected to the jet impact force brought by the hydraulic jet impact, the internal stress generated by the fouling to resist fragmentation and deformation, the frictional force caused by the jet direction, and the gravity of the fouling structure itself. Then, the mechanical model of the jet clearing obstruction in the well under the action of hydraulic impact can be represented by vectors as follows:

[0092]

[0093] In the formula, For impact force; Internal stress; Friction; It is gravity.

[0094] At this point, it is considered that the magnitude of various mechanical forces during the process of water jet unblocking the well casing will change with the degree of deformation and breakage of the fouling on the inner wall of the well casing. The mechanical model is functionally transformed to construct the energy balance equation for water jet unblocking the well casing under the action of water jet impact. Since there is no displacement in the direction of gravity during the deformation and destruction of the fouling on the inner wall of the well casing, the work done by gravity is zero. Furthermore, after the water jet impact, the water flow velocity is very small, and the energy loss caused by friction can be approximated as negligible. Therefore, the energy equation can be expressed as follows: the kinetic energy of the water jet impact is entirely used to overcome the internal energy generated by the internal stress of the fouling on the inner wall of the well casing.

[0095] W V =E

[0096] In the formula, W V E represents the impact kinetic energy of the hydraulic jet, and E represents the internal energy generated by the internal stress of the fouling on the inner wall of the well.

[0097] In actual operation, the outlet velocity of the coiled tubing jet is very high. During the process of the hydraulic jet impacting the fouling surface of the wellbore inner wall from the coiled tubing, the friction loss and flow time can be ignored. According to the specific expression of the outlet velocity of the hydraulic jet in step (I), the velocity of the hydraulic jet when it reaches the impact contact surface is:

[0098]

[0099] In the formula, v s The velocity of water as it reaches the contact surface with the dirt on the inner wall of the well.

[0100] Based on the relationship between velocity and kinetic energy in Newtonian mechanics, and combined with the contact time of the hydraulic jet impact in step four, a new expression for the hydraulic jet impact is obtained by introducing flow velocity and cross-sectional area into the fluid mass:

[0101]

[0102] Substituting the velocity of the water jet upon reaching the impact contact surface, the kinetic energy of the water jet impact used to overcome the internal energy of the fouling on the well wall can be specifically expressed as:

[0103]

[0104] Therefore, the energy balance equations for jet clearing obstructions in a wellbore under hydraulic impact can be constructed as follows:

[0105]

[0106] This led to the construction of the energy balance equation for jet clearing obstruction in a well under hydraulic impact.

[0107] Step 7: Based on the calculation results of Steps 4 to 6, optimize the operating limits for hydraulic jet unblocking of wellbore obstruction. Considering that the water flow in the coiled tubing is supplied by the flushing pump at the injection wellhead, forming a hydraulic jet with a certain energy to impact and break the dirt on the inner wall of the wellbore, the head of the flushing pump at this time can be used as the operating parameter for hydraulic jet unblocking of wellbore obstruction.

[0108] According to the energy balance equation for clearing obstruction in the wellbore under hydraulic impact in step six, when the work done by the kinetic energy of the hydraulic jet impact equals the maximum internal energy that the fouling on the inner wall of the wellbore can provide, the fouling is at its breaking limit state. If the work done by the kinetic energy of the hydraulic jet impact is further increased, the fouling can be considered to be broken by the jet, achieving the goal of clearing obstruction in the wellbore. Therefore, by analyzing and solving the breaking limit state of the fouling on the inner wall of the wellbore, and substituting the energy forms of the breaking limit strengths of the rigid and viscoelastic fouling on the inner wall of the wellbore from steps four and five into the internal energy of the fouling on the inner wall of the wellbore in the energy balance equation of step six, we obtain the following set of equations concerning the operating limits of hydraulic jet clearing of obstruction in the wellbore under the breaking limit state of the fouling on the inner wall of the wellbore:

[0109] Equations for the head limit of rigid wellbore internal wall fouling wellhead flushing pump:

[0110]

[0111] The equations governing the head limit of viscoelastic wellbore internal wall fouling wellhead flushing pump are as follows:

[0112]

[0113] Furthermore, when the rigid and viscoelastic wellbore inner wall fouling is extracted and reaches the destruction limit, the relationship between the head limit of the injection well flushing pump and the mechanical properties of the wellbore inner wall fouling is as follows:

[0114] Rigid wellbore inner wall fouling wellhead flushing pump head limit:

[0115]

[0116] Viscoelastic wellbore inner wall fouling wellhead flushing pump head limit:

[0117]

[0118] Thus, the optimized design of the operating limits for hydraulic jet dredging wells encountering obstruction was completed.

[0119] Based on the above steps, and according to the geometric shape and mechanical properties of the well wall, a quantitative relationship can be established between the impact kinetic energy of the hydraulic jet and the internal energy of the deformation and breakage of the fouling on the well wall under different water injection well conditions and different water quality environments. Furthermore, by constructing an energy balance equation for the fouling on the well wall, the hydraulic jet unblocking well encounter operation limit that is compatible with the mechanical properties of the fouling on the well wall can be optimized.

[0120] Step 8: Calculate the radius of the flushing tubing inside the well;

[0121] In sand flushing operations, in addition to breaking up the dirt adhering to the inner wall of the tubing, it is also necessary to carry the broken sand particles and impurities to the surface through the flushing fluid. At this time, the upward velocity of the flushing fluid in the well must be greater than the free settling velocity of the largest diameter gravel. The relationship between the two is described by the following formula:

[0122] V s =V L -V d

[0123] In the formula V s —The upward velocity of sand particles during sand flushing, m / s; V L —Upward velocity of the flushing fluid, m / s; V d —The free settling velocity of sand in a static flushing fluid, in m / s.

[0124] A coefficient n is introduced as the ratio of the upward velocity of the flushing fluid to the settling velocity of the sand and gravel. The suspension value of coefficient n is obtained by simulating the downhole environment after sampling. When n is greater than the suspension value, the sand and gravel in the well begin to move upward with the upward flow of the flushing fluid.

[0125] Taking quartz sand as an example, the formula for calculating its n value is:

[0126] n = V L / V dExperiments showed that quartz sand remains suspended when n = 1.6-1.7. Therefore, when n > 1.7, the flushing fluid will carry the quartz sand from the well to the surface. To ensure smooth flushing, the value of n is generally slightly larger than the calculated value to allow for a larger flow. Therefore, for quartz sand, n is generally taken as 2, meaning the minimum upward velocity of the flushing fluid is V. L =2V d .

[0127] The minimum discharge rate required for sand flushing at this time is:

[0128] Q = V L ×A

[0129] Q – Minimum displacement required for sand flushing, in meters. 3 / s;

[0130] V L —The upward velocity of the flushing fluid, m / s, can be calculated to know V L =2V d ;

[0131] A – Cross-sectional area of ​​the backflow of the flushing fluid, in meters. 2 This refers to the cross-sectional area of ​​the downhole tubing for backflow, which can be calculated from the tubing radius.

[0132] Calculate the radius of the flushing oil pipe based on the displacement:

[0133] r = √R 2 -(V L (×π) / Q=√R 2 -(V L ×π) / (V L ×A)

[0134] =√R 2 -(2V d ×π) / (2V d ×A)

[0135] Step Nine: Adjust the dredging equipment based on the calculation results of Steps Seven and Eight. For different injection well casings and different water quality conditions, the correlation boundary between the structural mechanical properties of the fouling on the inner wall of the well casing and the head of the wellhead flushing pump can be clearly defined under this environment. In other words, based on the mechanical characteristic analysis of the fouling sample taken from the inner wall of the injection well casing, and according to the expression of the wellhead flushing pump head boundary for rigid and viscoelastic inner wall fouling in Step Seven, the head parameter boundary of the wellhead flushing pump that just reaches the destructive limit state of the inner wall fouling can be obtained. When the structural mechanical properties of the inner wall fouling are determined to be rigid, the head of the wellhead flushing pump should be adjusted accordingly. When the head reaches the parameter limit, and the mechanical properties of the fouling structure on the inner wall of the well are analyzed to be viscoelastic, the head of the wellhead flushing pump is adjusted accordingly to reach the parameter limit. This ensures the determination of a customized hydraulic dredging scheme for well blockage during water injection well testing, while effectively controlling the damage state of the fouling on the inner wall of the well from a structural mechanics perspective. At the same time, considering that the broken fouling needs to be flushed to the surface after sand flushing, an oil washing pipe with a radius matching the calculation results is selected to flush the fouling to the surface smoothly while breaking the fouling attached to the oil pipe, thus improving the hydraulic dredging efficiency.

[0136] The hydraulic dredging and cleaning method for wellbore provided by this invention can not only achieve good dredging effect in the development of water injection wells, but also achieve good dredging effect in other wells with similar downhole structures, such as rodless oil wells.

[0137] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for hydraulically clearing and cleaning the inside of a well, characterized in that, include: Step 1: Obtain parameter information within the target well through well logging. Step 2: Calculate the flow velocity at the outlet of the hydraulic jet orifice; Step 3: Classify the types of dirt on the inner wall of the well; Step 4: Calculate the ultimate strength of fouling on the inner wall of the rigid wellbore; Step 5: Calculate the ultimate strength of the fouling on the inner wall of the viscoelastic wellbore; Step 6: Construct the energy balance equation for jet clearing obstruction in the wellbore under hydraulic impact; Step 7: Based on the calculation results of Steps 4 to 6, optimize the design of the operating limits for hydraulic jet dredging when encountering obstruction in the well. Step 8: Calculate the radius of the flushing tubing inside the well; Step 9: Adjust and select the dredging equipment based on the calculation results of Steps 7 and 8.

2. The method for hydraulic dredging and cleaning inside a well shaft according to claim 1, characterized in that, In step two, the calculation is based on the pressure inside the wellbore, which can be divided into two cases depending on the object being pressurized: atmospheric pressure connected to the outside and liquid pressure formed by the residual water column.

3. The method for hydraulic dredging and cleaning inside a well shaft according to claim 1, characterized in that, In step three, the types of fouling on the inner wall of the wellbore are classified into rigid wellbore inner wall fouling and viscoelastic wellbore inner wall fouling.

4. The method for hydraulic dredging and cleaning inside a well shaft according to claim 1, characterized in that, Step four requires consideration of the mechanical properties of the near-infinite elastic modulus of the fouling on the inner wall of the rigid wellbore.

5. The method for hydraulic dredging and cleaning inside a well shaft according to claim 1, characterized in that, In step six, it is necessary to consider that the magnitude of various mechanical forces during the process of water jet dredging the well shaft will change depending on the degree of breakage and deformation of the dirt on the inner wall of the well shaft.

6. The method for hydraulic dredging and cleaning inside a well according to claim 1, characterized in that, In step seven, the calculation results from steps four and five are substituted into the energy balance equation in step six.

7. The method for hydraulic dredging and cleaning inside a well shaft according to claim 1, characterized in that, The parameters in the wellbore during step one include the local atmospheric pressure P. a The injected water density ρ, the distance from the bottom of the injection well to the wellhead Z1, the apparent viscosity μ, and the average thickness of the fouling surface on the inner wall of the wellbore from the well wall.

8. The method for hydraulic dredging and cleaning inside a well shaft according to claim 7, characterized in that, The average thickness of the fouling surface on the inner wall of the wellbore from the well wall was obtained by trial contact testing with coiled tubing of different diameters.

9. The method for hydraulically clearing and cleaning the well shaft according to claim 1, characterized in that, When calculating the radius of the flushing tubing in step eight, it is necessary to first calculate the upward return velocity of the flushing fluid in the well.

Images