Method and system for optimizing residual acid flowback time of high-speed water injection oil well

Abstract

The invention is suitable for the field of petroleum engineering, and provides a residual acid flowback time optimization method and system for a high-speed water injection oil well, and the method comprises the steps: testing the critical concentration value of fluorine ions in mud acid; obtaining a rock core test piece, placing the rock core test piece in a test pipeline, and injecting mud acid into the test pipeline; after the acid injection is finished, the mud acid is retained in the test pipeline for a test time length; acquiring the skin factors of the rock core test pieces with different test durations and the fluorine ion concentration of mud acid in the rock core test pieces, acquiring the test duration when the skin factor is minimum and the test duration when the fluorine ion concentration reaches a critical concentration value, and selecting the smaller value of the two as the optimal duration; and after oil well acid injection pump stopping, residual acid flow-back is carried out at the optimal time interval. Therefore, the damage to the reservoir is reduced, the acidification effect is improved, the residual acid flowback time is obtained through the method, and the defect that the flowback time is determined only according to the experience of an engineer at present is overcome.

Description

Technical Field

[0001] The invention belongs to the field of petroleum engineering, and in particular relates to a method and system for optimizing residual acid flowback time of a high-speed water injection oil well. Background Art

[0002] With the continuous exploitation of oil in high-speed water injection oil wells, the reservoir will be blocked to varying degrees due to various reasons, which will lead to a slowdown in the rate of water injection and a decrease in the efficiency of oil production. In conventional technology, acidification technology can be used to remove the blockage. Acidification technology refers to the oil and gas well production increase measure of injecting acid solution into the formation to dissolve certain minerals and restore or increase the permeability of the near-wellbore area. When conducting matrix acidification, if the residual acid in the well is returned too late after the pump is stopped for acid injection, the retained acid will cause damage to the pores and structure of the reservoir, resulting in an increase in the improved skin factor again, reducing the effect of acidification; if the residual acid is returned too early, the acid has not fully dissolved the reservoir rock, and the acid has not become residual acid, the utilization efficiency of the residual acid returned will be reduced, and the ideal acidization effect cannot be achieved. Therefore, it is crucial to determine the time for residual acid return to protect the reservoir and increase the utilization rate of acid during matrix acidification operations on site.

[0003] In the existing technology, the more common practice is for engineers to determine the flowback time after acidification based on experience, which often results in the problem of residual acid flowback being too early or too late. Summary of the invention

[0004] The purpose of the embodiments of the present application is to provide a method for optimizing the residual acid flowback time of a high-speed water injection oil well, aiming to solve the problem in the prior art that engineers determine the residual acid flowback time after acidizing through experience, which easily leads to the problem that the residual acid flowback timing is too early or too late.

[0005] The embodiment of the present application is implemented as follows: a method for optimizing the residual acid flowback time of a high-speed water injection oil well, the method comprising:

[0006] S100: performing a rock powder dissolution experiment to test the critical concentration value of fluoride ions in soil acid, wherein the critical concentration value is the fluoride ion concentration value corresponding to the maximum value of the dissolution rate of the rock powder during the dissolution process of the soil acid on the rock powder;

[0007] S200: obtaining a core specimen, wherein the core specimen is a columnar structure, and both ends of the core specimen have an acid inlet end for soil acid infiltration and an acid outlet end for soil acid infiltration;

[0008] S300: placing the core specimen in a test pipeline and isolating the test pipeline, injecting mud acid into the test pipeline, and allowing the mud acid to permeate through the core specimen from the acid inlet end to the acid outlet end;

[0009] S400: closing the inlet and outlet of the test pipeline, allowing the mud acid to stay in the test pipeline for a test time, obtaining the fluorine ion concentration value at each position in the core specimen, and opening the inlet and outlet of the test pipeline, detecting the liquid pressure of the first pipeline at the acid inlet side and the liquid pressure at the acid outlet side of the core specimen, calculating the pressure difference at both ends of the core specimen, and calculating the skin factor of the core specimen under the test time based on the pressure difference;

[0010] S500: Based on different test durations, repeat steps S200 to S400 to obtain the skin factor of the core specimen and the fluoride ion concentration at each position in the core specimen under different test durations;

[0011] S600: Obtain the test time for obtaining the minimum skin factor to obtain the first time, obtain the test time for the fluoride ion concentration in the core specimen to reach the critical concentration value to obtain the second time, take the smaller value of the first time and the second time as the optimal time, and after stopping the pump during acid injection in the oil well, perform residual acid backflow after the optimal time.

[0012] In a preferred embodiment of the present application, a method for conducting a rock dust dissolution experiment to test the critical concentration value of fluoride ions in soil acid includes:

[0013] Obtaining a core sample, washing the core sample with oil and drying the core sample;

[0014] The dried core sample is crushed and dried again to obtain rock powder;

[0015] The rock powder is placed in prepared soil acid to obtain the corresponding relationship between the fluoride ion concentration of the soil acid and the dissolution rate of the rock powder. The critical fluoride ion concentration value is the fluoride ion concentration value corresponding to the maximum dissolution rate.

[0016] In a preferred embodiment of the present application, the skin factor of the core specimen is calculated based on the following formula:

[0017]

[0018] Among them, S is the skin factor of the core specimen, Pt is the pressure difference at both ends of the core specimen, φ is the porosity of the core specimen, K is the permeability of the core specimen, L is the length of the core specimen, A is the cross-sectional area of ​​the core specimen, and μ is the soil acid viscosity.

[0019] In a preferred embodiment of the present application, the method for obtaining the fluoride ion concentration value at each position in the core specimen includes:

[0020] Perform soil acid sampling at multiple points in the core specimen to obtain a first sample group;

[0021] Detecting the first sample group based on a fluoride ion selective electrode method to obtain fluoride ion concentrations at multiple points in the core specimen;

[0022] Based on the fluorine ion concentrations at multiple points in the core specimen, the distribution of the fluorine ion concentration in the core specimen is obtained to obtain the fluorine ion concentration value at each position in the core specimen.

[0023] In a preferred embodiment of the present application, the residual acid flowback time optimization method further includes:

[0024] The residual acid flowback time optimization method further comprises:

[0025] Obtaining the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration;

[0026] Based on the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration, the distance from the position where the fluoride ion concentration in the core specimen is equal to the critical concentration value to the acid inlet end is obtained to obtain the action radius of the soil acid.

[0027] In a preferred embodiment of the present application, the residual acid flowback time optimization method further includes:

[0028] A displacement medium is injected from the acid outlet end of the core sample, and the displacement medium is used to penetrate into the core sample to drive out the soil acid in the core sample.

[0029] In a preferred embodiment of the present application, acid injection is performed on the core specimen based on a soil acid concentration of 12% HCl+3% HF and a displacement of 10 ml / min.

[0030] In a preferred embodiment of the present application, the particle size of the rock powder is 100 mesh and the drying temperature is 60°C.

[0031] The present application also proposes a system for optimizing the residual acid flowback time of a high-speed water injection oil well, the system comprising:

[0032] A clamp, the clamp comprising an outer tube, a leather sleeve is arranged inside the outer tube, the leather sleeve is used to be sleeved on the outer side of the core specimen, a closed extrusion chamber is formed between the leather sleeve and the outer tube, the extrusion chamber is connected to a confining pressure pump, the two ends of the leather sleeve are respectively an acid inlet and an acid outlet, the acid inlet and the acid outlet are respectively connected to pressure gauges, and the two pressure gauges are respectively used to detect the pressure values ​​of the acid inlet and the acid outlet;

[0033] A soil acid container, the outlet of the soil acid container is connected to the acid inlet, and the soil acid container is used to contain soil acid;

[0034] A constant flow pump connected to the soil acid container, the constant flow pump is used to drive the soil acid in the soil acid container into the core specimen of the holder;

[0035] A liquid collecting component is connected to the acid outlet and is used to recover the residual acid flowing out of the acid outlet.

[0036] In a preferred embodiment of the present application, a plurality of sampling tubes are spaced apart in the length direction of the leather tube, one end of the sampling tube is connected to the inner cavity of the leather tube, and the other end extends to the outside of the outer tube and is connected to a valve.

[0037] The present application provides a method for optimizing the residual acid flowback time of a high-speed water injection oil well, in which acid is injected into a core specimen, and the changes in the skin factor of the core specimen and the changes in the fluoride ion concentration in the soil acid are tested at different test durations, and the test duration for the appearance of the minimum skin factor and the test duration for the fluoride ion concentration to reach the critical concentration value are obtained, and the smaller value of the two is selected as the optimal duration, and the residual acid is flowed back again after the oil well acid is injected and the pump is stopped for the optimal duration. In this way, it is ensured that the reservoir can obtain a smaller skin factor, reducing damage to the reservoir, and it is ensured that no secondary precipitation occurs during the soil acid acidification process to block the gaps in the reservoir again, thereby improving the acidification effect. In addition, by detecting the changes in the skin factor of the core specimen and the changes in the fluoride ion concentration in the soil acid at different durations after the acid injection is completed, the residual acid flowback time is obtained, which overcomes the defect that the existing flowback time is determined solely by the experience of engineers, and improves the acidification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of a method for optimizing the residual acid flowback time of a high-speed water injection oil well in an embodiment of the present application;

[0039] Figure 2 A flow chart of a method for conducting a rock dust dissolution experiment to test the critical concentration value of fluoride ions in soil acid in an embodiment of the present application;

[0040] Figure 3 A flow chart of a method for obtaining fluoride ion concentration values ​​at various locations in a core specimen in an embodiment of the present application;

[0041] Figure 4 This is a flow chart of a method for obtaining the action radius of mud acid in an embodiment of the present application;

[0042] Figure 5 A schematic diagram of the structure of a device for optimizing the residual acid flowback time of a high-speed water injection oil well in an embodiment of the present application;

[0043] Figure 6 The curve showing the change of rock powder dissolution rate over time in the embodiment of the present application;

[0044] Figure 7This is a curve showing the change of the skin factor of the core specimen over time in the embodiment of the present application. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] The specific implementation of the present application is described in detail below in conjunction with specific embodiments.

[0047] It is understandable that after years of development, the oil field has suffered varying degrees of damage to the reservoir, the reservoir pores have been blocked, the oil wells are insufficiently supplied with liquid, and the injection pressure of the water wells has increased, resulting in a slowdown in the rate of water injection, which cannot meet the requirements for high-speed water injection in the oil wells. The embodiment of the present application provides a method for optimizing the residual acid flowback time of a high-speed water injection oil well, which can optimize the residual acid flowback time and improve the blockage removal effect.

[0048] like Figure 1 As shown, a method for optimizing the residual acid flowback time of a high-speed water injection oil well provided in an embodiment of the present application comprises:

[0049] S100: performing a rock powder dissolution experiment to test a critical concentration value of fluoride ions in soil acid, wherein the critical concentration value is a fluoride ion concentration value in the soil acid when precipitates appear during the dissolution process of the rock powder by the soil acid.

[0050] In some embodiments of the present application, a method for conducting a rock dust dissolution experiment to test the critical concentration value of fluoride ions in soil acid includes:

[0051] S110: Obtain a core sample, wash the core sample with oil, and dry it;

[0052] S120: crushing the dried core sample and drying it again to obtain rock powder;

[0053] S130: placing the rock powder into prepared soil acid to obtain the corresponding relationship between the fluoride ion concentration of the soil acid and the dissolution rate of the rock powder, wherein the critical fluoride ion concentration value is the fluoride ion concentration value corresponding to the maximum dissolution rate.

[0054] In this embodiment, by crushing the core sample, the dissolution rate can be increased and the experimental time can be shortened. Drying the rock powder can prevent moisture from interfering with the experiment and improve the accuracy of the experiment. Specifically, in some embodiments of the present application, the core sample is a core, rock cuttings or rock block sample of the reservoir to be transformed. The prepared soil acid concentration is 12% HCl + 3% HF, which is divided into multiple beakers and placed in a water bath. The temperature of the water bath is set to the actual temperature of the reservoir to be transformed, for example, 92°C. The particle size of the rock powder is 100 mesh, and the drying temperature is 60°C, so as to better dissolve the rock powder. In some embodiments, the dissolution rate of the rock powder can be calculated by dividing the mass of the solid in the beaker after the predetermined experimental time of the reaction with the initial mass of the rock powder.

[0055] In one embodiment of the present application, the results of the rock dust dissolution experiment are as follows: Figure 6 As shown in the figure, the rock powder dissolution rate increases with time, but when the time is greater than 3 hours, the dissolution rate no longer increases but decreases, and the dissolution rate has an inflection point, which is due to the formation of precipitation by secondary reaction. The fluoride ion concentration at this moment is 0.32% tested by the fluoride ion selective electrode method, which is the critical concentration value of fluoride ions.

[0056] S200: Obtain a core specimen, wherein the core specimen is a columnar structure, and both ends of the core specimen have an acid inlet end for soil acid infiltration and an acid outlet end for soil acid infiltration.

[0057] In some embodiments, the basic parameters of the core specimen include the length L, diameter d, initial permeability K, porosity φ and initial skin factor S0 of the core. Specifically, in some embodiments, the specific values ​​of the basic parameters are shown in Table 1.

[0058]

[0059] S300: placing the core specimen in a test pipeline and isolating the test pipeline, injecting mud acid into the test pipeline, and allowing the mud acid to penetrate the core specimen from the acid inlet end to the acid outlet end.

[0060] In this embodiment, the soil acid will penetrate into the core specimen and dissolve the carbonate and silicate minerals in the core specimen, thereby increasing the permeability of the core specimen. In some embodiments of the present application, the core specimen is injected with soil acid at a concentration of 12% HCl + 3% HF and a displacement of 10 ml / min.

[0061] S400: Close the inlet and outlet of the test pipeline, allow the mud acid to stay in the test pipeline for a test time, obtain the fluorine ion concentration value at each position in the core specimen and open the inlet and outlet of the test pipeline, detect the liquid pressure of the first pipeline on the acid inlet side and the liquid pressure on the acid outlet side of the core specimen, calculate the pressure difference at both ends of the core specimen, and calculate the skin factor of the core specimen under the test time based on the pressure difference.

[0062] In this embodiment, the core specimen hinders the flow of mud acid in the test pipeline, so that the pressure in the pipe at both ends of the core specimen in the test pipeline is different, so that there is a pressure difference between the acid inlet end and the acid outlet end of the core specimen. After the acid injection is stopped and the test time has passed, the outlet of the test pipeline is opened and the pump is turned on to continue to inject mud acid into the test pipeline, and the pipe pressure at both ends of the core specimen in the test pipeline is measured to obtain the pressure values ​​of the acid inlet end and the acid outlet end. The pressure value of the acid inlet and the pressure value of the acid outlet are subtracted and the absolute value is taken to obtain the pressure difference between the acid inlet and the acid outlet.

[0063] In some embodiments of the present application, the skin factor of the core specimen is calculated based on the following formula:

[0064]

[0065] Where S is the skin factor of the core specimen, P t is the pressure difference at both ends of the core specimen, φ is the porosity of the core specimen, K is the permeability of the core specimen, L is the length of the core specimen, A is the cross-sectional area of ​​the core specimen, and μ is the viscosity of the soil acid.

[0066] The "skin factor" mentioned in this application is a numerical value used to describe the severity of the skin effect, which refers to the change in the permeability of the formation close to the wellbore due to human factors. When the skin factor is greater than zero, it means that the formation has flow resistance or the formation is damaged.

[0067] S500: Based on different test durations, steps S200 to S400 are repeated to obtain the skin factor of the core specimen and the fluoride ion concentration of the soil acid in the core specimen under different test durations.

[0068] For example, in some embodiments, the pressure difference between the acid inlet and the acid outlet at different test durations after the acid injection is completed is shown in Table 2.

[0069]

[0070] Based on the pressure difference, the skin factor of the core specimen under the test time is calculated, and the following can be obtained: Figure 4The relationship between the skin factor and the test time is shown. The minimum skin factor is obtained when the test time is 3 hours, so in this embodiment, the first time length is 3 hours.

[0071] S600: Obtain the test time for obtaining the minimum skin factor, obtain the first time, obtain the test time for the fluoride ion concentration of the soil acid in the core specimen to reach the critical concentration value, obtain the second time, take the smaller value of the first time and the second time as the optimal time, and after the oil well acid injection and pumping are stopped, perform residual acid backflow after the optimal time.

[0072] In this embodiment, the core specimen is injected with acid, and the changes in the skin factor of the core specimen and the changes in the fluoride ion concentration in the soil acid are tested at different test durations, and the test duration for the appearance of the minimum skin factor and the test duration for the fluoride ion concentration to reach the critical concentration value are obtained, and the smaller value of the two is selected as the optimal duration, and the residual acid is returned after the oil well acid injection and the pump is stopped for the optimal duration. In this way, it is ensured that the reservoir can obtain a smaller skin factor, reduce damage to the reservoir, and ensure that no secondary precipitation will occur during the soil acid acidification process to block the gaps in the reservoir again, improve the effect of acidification and unblocking, and then better improve the subsequent water injection rate to meet the requirements of high-speed water injection. In addition, by detecting the changes in the skin factor of the core specimen and the changes in the fluoride ion concentration in the soil acid at different durations after the acid injection is completed, the residual acid return time is obtained, which overcomes the defect that the existing return time is determined only by the experience of engineers, and improves the acidification effect.

[0073] In some embodiments of the present application, the method for detecting the fluoride ion concentration of the mud acid in the core specimen includes:

[0074] S410: performing soil acid sampling at multiple points in the core specimen to obtain a first sample group;

[0075] S420: Detecting the first sample group based on a fluoride ion selective electrode method to obtain fluoride ion concentrations at multiple points in the core specimen;

[0076] S430: Based on the fluorine ion concentrations at multiple points in the core sample, the distribution of the fluorine ion concentration in the core sample is obtained to obtain the fluorine ion concentration value at each position in the core sample.

[0077] In this embodiment, by obtaining the seeping soil acid from the core specimen, a first sample group is obtained, and the fluoride ion concentration of the first sample group is detected, so that the fluoride ion concentration at multiple points in the core specimen can be known. In some embodiments, the fluoride ion concentration value at any point in the core specimen can be obtained by interpolation, and then the distribution of fluoride ion concentration in the core specimen can be obtained. In addition, the fluoride ion selective electrode method can conveniently obtain the concentration value of fluoride ions. The measurement principles involved in the fluoride ion selective electrode method and the required measuring instruments are conventional technologies and will not be repeated here.

[0078] In some embodiments, a plurality of sampling points are provided, such as Figure 5 As shown, there are five sampling points, namely sampling point A, sampling point B, sampling point C, sampling point D, and sampling point E. The five sampling points are evenly spaced from the acid inlet to the acid outlet. The fluoride ion concentration values ​​of the soil acid at multiple points in the core specimen can be detected through multiple sampling points. For example, in some embodiments, the chloride ion concentrations of each sampling point at different test durations after the acid injection is completed are shown in Table 3 below.

[0079]

[0080] It can be seen from the table that 3 hours after the acid injection, the fluorine ion concentration at sampling point E is 0.30%, which is less than the critical concentration of 0.32%. Therefore, the second time length can be taken as 3 hours. From the above, it can be seen that in this embodiment, the test time length corresponding to the minimum skin factor of the core specimen is 3 hours, so the optimal time length in this embodiment is 3 hours. In some other embodiments, when the first time length and the second time length are not equal, the smaller value of the two is taken as the optimal time length.

[0081] In some examples of the present application, the residual acid flowback time optimization method further includes:

[0082] S710: Obtaining the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration;

[0083] S720: Based on the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration, the distance from the position where the fluoride ion concentration in the core specimen is equal to the critical concentration value to the acid inlet end is obtained to obtain the action radius of the soil acid.

[0084] In this embodiment, based on the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration, the distance from the position where the fluoride ion concentration in the core specimen is equal to the critical concentration value to the acid inlet end is obtained, and the effective radius of the mud acid is obtained. This facilitates the subsequent determination of whether the mud acid or the concentration of mud acid is suitable for the reservoir to be optimized.

[0085] In one example of the present application, the residual acid flowback time optimization method further includes: injecting a displacement medium from the acid outlet of the core specimen, wherein the displacement medium is used to penetrate into the core specimen to drive out the soil acid in the core specimen.

[0086] In this embodiment, the core sample is inverted and the soil acid is returned from the core sample by displacement, so that the soil acid can be recovered and environmental pollution can be prevented. Specifically, in some embodiments, the displacement medium can be an inert gas, which penetrates into the core sample and squeezes out the soil acid therein.

[0087] like Figure 5 As shown, an embodiment of the present application also provides a system for optimizing the residual acid flowback time of a high-speed water injection oil well, the system comprising: a constant flow pump 100, a soil acid container 210, a clamp 300 and a liquid collection assembly.

[0088] The clamp 300 includes an outer tube, a leather casing is arranged inside the outer tube, and the leather casing is used to be sleeved on the outside of the core specimen 10. A closed extrusion chamber is formed between the leather casing and the outer tube, and the extrusion chamber is connected to a confining pressure pump 500. The two ends of the leather casing are respectively an acid inlet and an acid outlet, and the acid inlet and the acid outlet are respectively connected to a pressure gauge 700. The two pressure gauges 700 are respectively used to detect the pressure values ​​of the acid inlet and the acid outlet.

[0089] The outlet of the mud acid container 210 is connected to the acid inlet, and the mud acid container 210 is used to contain mud acid.

[0090] The constant flow pump 100 is connected to the mud acid container 210 , and the constant flow pump 100 is used to drive the mud acid in the mud acid container 210 into the core specimen of the clamp 300 .

[0091] The liquid collecting component is connected to the acid outlet, and the liquid collecting component is used to recover the residual acid flowing out of the acid outlet.

[0092] In this embodiment, the core sample 10 is clamped by the clamp 300, and the constant flow pump 100 drives the soil acid in the soil acid container 210 to be injected into the acid inlet of the clamp 300 through the pipeline, and the soil acid penetrates into the core sample 10. Part of the soil acid penetrates through the core sample 10 and flows into the liquid collection component from the acid outlet of the clamp 300 for recovery. In this way, the core sample 10 is subjected to an acidification experiment by the device to determine a better residual acid flowback time.

[0093] In this embodiment, the confining pressure pump 500 injects gas or liquid into the extrusion chamber, so that the leather casing squeezes the core sample 10 to simulate the pressure in the reservoir. In addition, the leather casing is close to the core sample 10 to prevent the core sample 10 and the leather casing from leaking due to a gap, thereby ensuring that the pressure difference between the acid inlet and the acid outlet is accurately measured.

[0094] In one example of the present application, a plurality of sampling tubes 310 are spaced apart in the length direction of the leather tube, one end of the sampling tube 310 is connected to the inner cavity of the leather tube, and the other end extends to the outside of the outer tube and is connected to a valve.

[0095] In this embodiment, a plurality of sampling tubes 310 are provided. By acquiring the distance from each sampling tube 310 to the acid inlet and the fluoride ion concentration of the mud acid sample in each sampling tube 310, the distribution of the fluoride ion concentration of the mud acid in the core specimen can be obtained, and then the distance from the position where the fluoride ion concentration in the core specimen is equal to the critical concentration value to the acid inlet can be obtained, so as to obtain the effective radius of the mud acid and determine whether the mud acid or the mud acid concentration is suitable for the reservoir to be optimized.

[0096] Specifically, Figure 5 As shown, in some embodiments of the present application, the holder 300 is connected to a heating box 600 for heating the holder 300, and the holder is heated by the heating box 600 to simulate the temperature in the real reservoir. The liquid collecting assembly also includes a residual acid container 220, and the residual acid container 220 is connected to the acid outlet of the holder 300 through a pipeline. In some embodiments, a gas container 230 is also provided between the constant flow pump 100 and the holder 300, and the constant flow pump 100 drives the inert gas in the gas container 230 to enter the holder 300 and infiltrate into the core specimen 10, and squeezes out the soil acid in the core specimen 10. In some embodiments of the present application, the inlet ends of the soil acid container 210, the residual acid container 220 and the gas container 230 are connected to different valve ports of a six-way valve 400, and the outlet ends of the three are connected to different valve ports of another six-way valve 400. In this way, by adjusting the working position of the six-way valve 400, different pipelines can be switched to work. For example, the soil acid container 210 or the gas container 230 can be connected to the constant flow pump 100 to inject acid into the clamp 100 or inject inert gas.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for optimizing the residual acid flowback time of a high-speed water injection oil well, characterized in that: The method comprises: S100: performing a rock powder dissolution experiment to test the critical concentration value of fluoride ions in soil acid, wherein the critical concentration value is the fluoride ion concentration value corresponding to the maximum value of the dissolution rate of the rock powder during the dissolution process of the soil acid on the rock powder; S200: obtaining a core specimen, wherein the core specimen is a columnar structure, and both ends of the core specimen have an acid inlet end for soil acid infiltration and an acid outlet end for soil acid infiltration; S300: placing the core specimen in a test pipeline and isolating the test pipeline, injecting mud acid into the test pipeline, and allowing the mud acid to permeate through the core specimen from the acid inlet end to the acid outlet end; S400: closing the inlet and outlet of the test pipeline, allowing the mud acid to stay in the test pipeline for a test time, obtaining the fluorine ion concentration value at each position in the core specimen, and opening the inlet and outlet of the test pipeline, detecting the liquid pressure of the first pipeline at the acid inlet side and the liquid pressure at the acid outlet side of the core specimen, calculating the pressure difference at both ends of the core specimen, and calculating the skin factor of the core specimen under the test time based on the pressure difference; S500: Based on different test durations, repeat steps S200 to S400 to obtain the skin factor of the core specimen and the fluoride ion concentration at each position in the core specimen under different test durations; S600: Obtain the test time for obtaining the minimum skin factor to obtain the first time, obtain the test time for the fluoride ion concentration in the core specimen to reach the critical concentration value to obtain the second time, take the smaller value of the first time and the second time as the optimal time, and after stopping the pump during acid injection in the oil well, perform residual acid backflow after the optimal time.

2. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 1, characterized in that: The method of conducting rock dust dissolution experiment to test the critical concentration value of fluoride ion in soil acid includes: Obtaining a core sample, washing the core sample with oil and drying the core sample; The dried core sample is crushed and dried again to obtain rock powder; The rock powder is placed in prepared soil acid to obtain the corresponding relationship between the fluoride ion concentration of the soil acid and the dissolution rate of the rock powder. The critical fluoride ion concentration value is the fluoride ion concentration value corresponding to the maximum dissolution rate.

3. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 1, characterized in that: The skin factor of the core specimen is calculated based on the following formula: ； Among them, S is the skin factor of the core specimen, Pt is the pressure difference at both ends of the core specimen, φ is the porosity of the core specimen, K is the permeability of the core specimen, L is the length of the core specimen, A is the cross-sectional area of ​​the core specimen, and μ is the soil acid viscosity.

4. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 1, characterized in that: The method for obtaining the fluoride ion concentration value at each position in the core specimen includes: Perform soil acid sampling at multiple points in the core specimen to obtain a first sample group; Detecting the first sample group based on a fluoride ion selective electrode method to obtain fluoride ion concentrations at multiple points in the core specimen; Based on the fluorine ion concentrations at multiple points in the core specimen, the distribution of the fluorine ion concentration in the core specimen is obtained to obtain the fluorine ion concentration value at each position in the core specimen.

5. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 4, characterized in that: The residual acid flowback time optimization method further comprises: Obtaining the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration; Based on the distribution of fluoride ion concentration in the core specimen when the test duration is equal to the optimal duration, the distance from the position where the fluoride ion concentration in the core specimen is equal to the critical concentration value to the acid inlet end is obtained to obtain the action radius of the soil acid.

6. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 1, characterized in that: The residual acid flowback time optimization method further comprises: A displacement medium is injected from the acid outlet end of the core sample, and the displacement medium is used to penetrate into the core sample to drive out the soil acid in the core sample.

7. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 1, characterized in that: Acid injection was performed on the core specimens based on the soil acid concentration of 12% HCl + 3% HF and a displacement of 10 ml / min.

8. The method for optimizing residual acid flowback time of a high-speed water injection oil well according to claim 2, characterized in that: The particle size of the rock powder is 100 mesh, and the drying temperature is 60°C.

9. A system for optimizing the residual acid flowback time of a high-speed water injection oil well, characterized in that: The system comprises: A clamp, the clamp comprising an outer tube, a leather sleeve is arranged inside the outer tube, the leather sleeve is used to be sleeved on the outer side of the core specimen, a closed extrusion chamber is formed between the leather sleeve and the outer tube, the extrusion chamber is connected to a confining pressure pump, the two ends of the leather sleeve are respectively an acid inlet and an acid outlet, the acid inlet and the acid outlet are respectively connected to pressure gauges, and the two pressure gauges are respectively used to detect the pressure values ​​of the acid inlet and the acid outlet; A soil acid container, the outlet of the soil acid container is connected to the acid inlet, and the soil acid container is used to contain soil acid; A constant flow pump connected to the soil acid container, the constant flow pump is used to drive the soil acid in the soil acid container into the core specimen of the holder; A liquid collecting component is connected to the acid outlet and is used to recover the residual acid flowing out of the acid outlet.

10. The system for optimizing the residual acid flowback time of a high-speed water injection oil well according to claim 9, characterized in that: A plurality of sampling tubes are arranged at intervals in the length direction of the leather tube, one end of each sampling tube is connected to the inner cavity of the leather tube, and the other end of each sampling tube extends to the outside of the outer tube and is connected to a valve.

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