A method for removing and maintaining a plug of asphaltene from an oil well

Abstract

The present application belongs to the field of oil well asphaltene precipitation treatment, and particularly relates to a method for removing oil well asphaltene blockage and a maintenance method. After determining the target oil well where the wellbore asphaltene blockage occurs, the present application firstly adopts the single injection of asphaltene dissolving method to obtain the required amount of asphaltene dispersant, and then injects the solution containing the asphaltene dispersant into the target oil well where the wellbore asphaltene blockage occurs according to the smallest injection rate and injection pressure as possible, so as to dissolve the asphaltene and promote the oil well to restore self-flowing on the basis of causing as little additional pressure as possible. In the case that the single injection cannot make the oil well restore self-flowing, the continuous injection method is adopted, the solution containing the asphaltene dispersant is injected into the target oil well according to the daily injection amount according to the initial high and gradually down to stable rule, so as to achieve the effect of quickly dredging to tend to be stable. During the continuous injection process, the wellhead condition is observed in real time, and if the abnormality related to asphaltene blockage occurs, the corresponding measures are taken in time.

Description

Technical Field

[0001] This invention belongs to the field of oil well asphaltene precipitation treatment, specifically relating to a method for relieving and maintaining oil well asphaltene blockage. Background Technology

[0002] At any height within the oil wellbore, changes in conditions such as temperature or pressure can cause crude oil instability, leading to asphaltenes deposition. Factors contributing to asphaltenes deposition primarily include: CO2, gas richness, pH value, organic chemical composition, production enhancement measures, shear capacity, pressure, and temperature.

[0003] The flocculation and deposition of asphaltenes in the wellbore depend on the thermodynamic state of the crude oil colloidal system, namely temperature, pressure, and crude oil composition. Under normal circumstances, asphaltenes remain stable as dispersed colloids in the crude oil, with equal and opposite attractive and repulsive forces acting on the asphaltenes micelles. CO2 primarily causes the crude oil colloidal system to lose equilibrium by lowering the pH value, leading to asphaltenes flocculation and deposition; the smaller the ratio of colloids to asphaltenes, the greater the likelihood of asphaltenes deposition. In light to medium crude oils, if the colloid content is even lower than the asphaltenes content, the likelihood of asphaltenes deposition is sometimes greater than in heavy oils. As crude oil flows upwards in the wellbore, pressure and temperature gradually decrease. When the pressure falls below the bubble point pressure, light hydrocarbon components in the crude oil will separate out as gas, leading to a decrease in the concentration of light hydrocarbon components and ultimately reducing the amount of asphaltenes deposited. However, the bubble point of asphaltenes is difficult to determine because it decomposes when the pressure is below the bubble point pressure.

[0004] For example, a certain oilfield in China has a carbonate fracture-vuggy reservoir at normal temperature and pressure, with low volatility and light oil content. The reservoir is buried at a depth of 7000-8900 meters, classifying it as an ultra-deep oil and gas reservoir. The existing crude oil in this oilfield is mainly light oil, with an asphaltene content of 1.05%. Oil sample analysis shows that the colloid is unstable, indicating a high risk of asphaltene precipitation. Field production and well cleaning results indicate frequent wellbore blockage due to asphaltene. This section of the oilfield has a deep reservoir, a high gas-oil ratio, and a deep shut-off fluid level. Currently, two-thirds of the wells are being extracted using artificial lift methods. With weakening formation energy, changes in wellbore temperature, pressure, and crude oil properties lead to asphaltene precipitation, causing wellbore blockage and a drop in oil pressure, increasing the risk of well operations. This not only affects the effective production rate of the wells but also increases operating costs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing and maintaining asphalt blockage in oil wells, which addresses the problem of frequent asphalt blockage in oil wells with a high risk of asphalt precipitation, thus affecting the effective production of oil wells.

[0006] To achieve the above objectives, the present invention provides a method for removing asphaltene blockage in oil wells, characterized by comprising the following steps:

[0007] Obtain historical asphaltene precipitation data and current oil pressure and production data of the target oil well. If there is an abnormal drop in oil pressure and production of the target oil well, and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has experienced wellbore asphaltene blockage.

[0008] For a target oil well where the wellbore is blocked by asphalt, the depth of the blockage is determined, the volume of the treatment section and the volume of the displacement section are calculated, and the required amount of asphalt dispersant is obtained from the treatment section and the displacement section. The required amount of asphalt dispersant is mixed with thin oil in a set ratio to form a solution with a solubility of a first set value.

[0009] The solution with a solubility of a first set value is injected into the oil well according to a set injection rate and a set initial injection pressure. During the injection process, the injection pressure is adjusted downwards according to the pressure difference.

[0010] If the oil pressure of the target oil well is higher than the reservoir start-up pressure after injection, the oil well will resume self-flowing after injection; otherwise, the oil well will stop flowing and the asphalt blockage of the oil well will continue to be cleared by continuously injecting a solution with a dissolution rate of the second set value according to the set daily injection volume; the reservoir start-up pressure is determined by the opening production pressure difference and the normal production pressure difference of the target oil well.

[0011] The beneficial effects of the above technical solution are as follows: After identifying the target oil well where the wellbore is blocked by asphalt, the asphalt is first dissolved by a single injection. After obtaining the required amount of asphalt dispersant, the solution containing the asphalt dispersant is injected into the target oil well where the wellbore is blocked by asphalt at the lowest possible injection pressure. This dissolves the asphalt in the oil well without causing additional pressure, and promotes the oil well to resume self-flowing.

[0012] Furthermore, the initial injection pressure is set as follows:

[0013]

[0014] Where P is the initial injection pressure, in MPa; P wh The target oil well's oil pressure is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h.

[0015] Furthermore, the method of continuously injecting a solution with a solubility rate of a second set value according to a set daily injection volume is as follows:

[0016] If the asphaltene deposition data of the target oil well can be obtained, then the stable daily injection volume and the initial daily injection volume are determined based on the asphaltene deposition data and the second set value. The initial daily injection volume is greater than the stable daily injection volume. When continuous injection begins, the initial daily injection volume is first used as the set daily injection volume, and the set daily injection volume is gradually reduced during the continuous injection process until the set daily injection volume is reduced to equal the stable daily injection volume.

[0017] If the asphaltene deposition data of the target oil well cannot be obtained, the initial daily injection volume is set as the first injection volume value. When continuous injection begins, the initial daily injection volume is used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection.

[0018] The beneficial effects of the above technical solution are as follows: when a single injection cannot restore the oil well to its self-flowing state, a continuous injection method of chemical dosing (asphalt dispersant) is adopted. The solution containing asphalt dispersant is injected into the target oil well with asphalt blockage in the wellbore according to the daily injection volume, which is initially high and gradually reduced to a stable state, so as to achieve the effect of unblocking the blockage as quickly as possible and making it more stable.

[0019] Furthermore, the set injection displacement is determined based on the minimum displacement of the injection pump that injects a solution with a solubility of a first set value into the oil well.

[0020] The beneficial effects of the above technical solution are as follows: minimizing the set injection displacement to reduce the compaction effect of the reverse flow of fluid in the tubing on the deposited asphalt in the initial stage of injection, thereby injecting the solution containing asphalt dispersant into the target oil well with asphalt blockage in the wellbore at the smallest possible injection displacement, dissolving the asphalt in the oil well without causing additional pressure, and promoting the oil well to resume self-flowing.

[0021] Furthermore, the asphalt dispersant is SDJ-2 type asphalt dispersant.

[0022] The present invention also provides an oil well maintenance method, which acquires historical asphaltene precipitation data and current oil pressure and production data of the target oil well during the oil well production process. If there is an abnormal drop in oil pressure and production of the target oil well and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has been blocked by asphaltene in the wellbore.

[0023] For a target oil well where the wellbore is blocked by asphalt, the depth of the blockage is determined, the volume of the treatment section and the volume of the displacement section are calculated, and the required amount of asphalt dispersant is obtained from the treatment section and the displacement section. The required amount of asphalt dispersant is mixed with thin oil in a set ratio to form a solution with a solubility of a first set value.

[0024] The solution with a solubility of a first set value is injected into the oil well according to a set injection rate and a set initial injection pressure. During the injection process, the injection pressure is adjusted downwards according to the pressure difference.

[0025] If the oil pressure of the target oil well is higher than the reservoir start-up pressure after injection, the oil well will resume self-flowing after injection; otherwise, the oil well will stop flowing, and the asphalt blockage of the oil well will continue to be removed by continuously injecting a solution with a dissolution rate of the second set value according to the set daily injection volume.

[0026] During the continuous injection of a solution with a dissolution rate of the second set value, various parameters at the wellhead are acquired in real time. If the current of the oil well rises or the fluctuation range exceeds the corresponding set change threshold, there is obvious asphalt blockage at the pressure gauge cock sampling port and inspection filter, the polished rod lags, or there is abnormal noise at the wellhead, the set daily injection volume is adjusted accordingly. If the adjustment still cannot alleviate the situation, a large-volume backwash is performed on the target oil well within the set maintenance time.

[0027] The beneficial effects of the above technical solution are as follows: After identifying the target oil well where asphaltene blockage has occurred, a single injection method is first used to dissolve the asphaltene. After obtaining the required amount of asphalt dispersant, the solution containing the asphalt dispersant is injected into the target oil well with the lowest possible injection pressure. This dissolves the asphaltene in the oil well without causing additional pressure, promoting the well to resume self-flowing. Furthermore, during continuous injection, abnormalities related to asphaltene blockage can be observed and detected in a timely manner, and corresponding adjustment measures can be taken to relieve any potential asphaltene blockage, thereby solving the asphalt blockage problem.

[0028] Furthermore, the initial injection pressure is set as follows:

[0029]

[0030] Among them, P wh The target oil well's oil pressure is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h.

[0031] Furthermore, the method of continuously injecting a solution with a solubility rate of a second set value according to a set daily injection volume is as follows:

[0032] If the asphaltene deposition data of the target oil well can be obtained, the stable daily injection volume and the initial daily injection volume are determined based on the asphaltene deposition data and the second set value. The initial daily injection volume is greater than the stable daily injection volume. When continuous injection begins, the initial daily injection volume is first used as the set daily injection volume, and the set daily injection volume is gradually reduced during the continuous injection process until the set daily injection volume is reduced to equal the stable daily injection volume.

[0033] The beneficial effects of the above technical solution are as follows: when a single injection cannot restore the oil well to its self-flowing state, a continuous injection method of chemical dosing (asphalt dispersant) is adopted. The solution containing asphalt dispersant is injected into the target oil well with asphalt blockage in the wellbore according to the daily injection volume, which is initially high and gradually reduced to a stable state, so as to achieve the effect of unblocking the blockage as quickly as possible and making it more stable.

[0034] Furthermore, the set injection displacement is determined based on the minimum displacement of the injection pump that injects a solution with a solubility of a first set value into the oil well.

[0035] The beneficial effects of the above technical solution are as follows: minimizing the set injection displacement to reduce the compaction effect of the reverse flow of fluid in the tubing on the deposited asphalt in the initial stage of injection, thereby injecting the solution containing asphalt dispersant into the target oil well with asphalt blockage in the wellbore at the smallest possible injection displacement, dissolving the asphalt in the oil well without causing additional pressure, and promoting the oil well to resume self-flowing.

[0036] Furthermore, the asphalt dispersant is SDJ-2 type asphalt dispersant. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating the arrangement of injection volume for continuous injection in an embodiment of the method for removing asphalt blockage in oil wells according to the present invention;

[0038] Figure 2 This is a schematic diagram showing the chemical dosing parameters and effects of the oil well in Block A in an embodiment of the method for removing asphalt blockage in oil wells according to the present invention;

[0039] Figure 3 This is a schematic diagram illustrating the effect of periodic well washing in an embodiment of the oil well maintenance method of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Examples of methods for removing asphalt blockage in oil wells

[0042] This embodiment provides a technical solution for removing asphaltene blockage in oil wells, including the following steps:

[0043] Historical asphaltene precipitation data and current oil pressure and production data of the target oil well are obtained. If there is an abnormal drop in oil pressure and production of the target oil well, and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has experienced wellbore asphaltene blockage. Since the blocked section is the key data for subsequent unblocking, but the depth of blockage and the deposition section cannot be predicted by conventional methods, this embodiment uses a test well cleaning method to confirm the blocked depth H, that is, the location of asphaltene precipitation. For example, the SHB5-11H well continued to produce after being switched to pumping in 2020. At the end of February 2021, the fluid level dropped to about 2500m, and 3718m of water was injected at the beginning of March. 3 Then, after injecting asphalt dispersant and simmering the well, water is injected to a depth of 5007m. 3 The well was shut in until April 24th, when it was reopened. After producing a cumulative 444.5 tons of water, it stopped producing fluid on April 30th. The dynamometer card showed a significant change in fluid supply conditions; on April 29th, the dynamometer card indicated a severe shortage of fluid, with a submersion depth of 2690 meters. Analysis suggested a blockage in the well tubing. The well was shut in for workover on May 6th. During the workover, two... 7 / 8 The tailpipe was blocked by a suspected asphalt material in the 3734-6000m section. About 3.8t of asphalt material was removed on site, so it was determined that the SHB5-11H well had an asphalt blockage.

[0044] For target oil wells experiencing asphaltene blockage, the blockage depth is determined, the treatment section volume and displacement section volume are calculated, and the required amount of asphalt dispersant is obtained from these volumes. The required amount of asphalt dispersant is then mixed with thin oil in a set ratio to form a solution with a solubility of a first set value. In this embodiment, all asphalt dispersants used are SDJ-2 type asphalt dispersant (in other embodiments, other dispersants may be used depending on the actual situation, or different asphalt dispersants may be used at different injection stages). The asphalt dispersant is mixed with thin oil in a 1:1 ratio to form a solution with a solubility of approximately 1 g / ml. Considering that the injected fluid should be as minimal as possible in low-pressure wells, and the length of the reagent-soaked section should not exceed 500-1000 m, the treatment section volume X and displacement section volume Y are calculated. Therefore, X / 2 tons of asphalt dispersant and (Y+X / 2) m³ of thin oil are required. 3 Where (Y / 2)m 3 The thin oil is used to further lubricate the tubing after clearing the asphalt blockage, thus mitigating the risk of re-clogging.

[0045] A solution with a solubility of the first set value is injected into the oil well according to a set injection rate and a set initial injection pressure. During injection, a pressure difference generated by the high-density fluid is considered, and the injection pressure is adjusted downwards accordingly based on the pressure difference. Since the fluid in the tubing flows in reverse during the initial injection phase, it has a compacting effect on the deposited asphalt. Therefore, a smaller set injection rate is better. The set injection rate can be determined based on the minimum displacement of the injection pump used to inject the solution with the first set solubility value into the oil well. For example, in this embodiment, the minimum displacement of a 700-type pump truck on site is considered to be 2-4 m³ / h. 3 If the injection rate is around / h, then set the injection displacement to 3m. 3 / h.

[0046] The formula for calculating the initial injection pressure is set as follows:

[0047]

[0048] Where P is the initial injection pressure, in MPa; P wh The target oil well's oil pressure is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h.

[0049] If the oil pressure of the target well is higher than the reservoir start-up pressure after injection, the well can resume self-flowing immediately after injection; otherwise, the well stops flowing, and the asphaltene blockage is cleared by continuously injecting a solution with a dissolution rate of the second set value according to the set daily injection volume. The reservoir start-up pressure is determined by the difference between the well's initial production pressure differential and its normal production pressure differential, specifically the difference between the initial production pressure differential and the normal production pressure differential. The formula for calculating the oil pressure of the target well after injection is as follows:

[0050] P′=P wh -ΔρHg

[0051] Where P' is the oil pressure of the target oil well after injection, in MPa; Δρ is the density difference between the injected fluid and the produced fluid, in kg / m³. 3 H represents the height of the fluid column inside the wellbore, in meters (m).

[0052] In specific applications, the target oil well SHB5-13H experienced a drop in oil pressure from 5.5 MPa to 0 MPa in January 2020. During well testing, blockage occurred at 894m, bringing out asphalt, indicating that the wellbore was clogged with asphalt. The aforementioned unblocking method was successfully applied. After unblocking, well SHB5-13H resumed its flowing flow, restoring daily oil production to 60 tons. Furthermore, the same unblocking method has been successfully applied in wells SHB5 and SHB5-3, resulting in a cumulative increase in production of nearly 4,000 tons.

[0053] In this embodiment, for target oil wells that cannot resume self-flowing, the continuous dosing method of continuously injecting a solution with a dissolution rate of a second set value according to the data acquisition situation of different target oil wells is specifically as follows:

[0054] If the asphaltene deposition data of the target oil well can be obtained, the stable daily injection volume and the initial daily injection volume are determined based on the asphaltene deposition data and the second set value. If the initial daily injection volume is greater than the stable daily injection volume, when continuous injection begins, the initial daily injection volume is initially used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection until it equals the stable daily injection volume. For example, after the target oil well SHB5-11H was switched to pumping, it produced for a cumulative 324 days. The asphaltene deposition data for this well is: 4000 kg of deposited asphaltene, averaging 12.34 kg per day. In this embodiment, the second set value is the same as the first set value, both being 1 g / ml, i.e., a solution with a solubility of 1 g / ml is used. Therefore, the injection volume arrangement for the target oil well SHB5-11H is as follows: Figure 1 As shown, the designed daily dosage is 24L / d based on twice the indoor dosage, with an initial injection dosage of 12L / d. Based on the well blockage and empirical estimation, combined with the solvent efficiency of the agent, the estimated stable daily injection volume is 12L / d based on twice the indoor dosage. The daily injection volume is set to be injected in a manner that is initially high and gradually reduced to a stable level. Specifically, the initial daily injection volume is about twice the designed daily dosage (24L / d) (48L / d), and is gradually reduced until the wellbore stabilizes, that is, the set daily injection volume is reduced to be equal to the stable daily injection volume of 12L / d.

[0055] If the asphaltene deposition data of the target oil well cannot be obtained, the initial daily injection volume is set as the first injection volume value. When continuous injection begins, the initial daily injection volume is used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection. For example, if the first injection volume value is referenced from the daily injection volume of existing block oil wells, the initial daily injection volume is set to 50L / d, and the set daily injection volume is gradually reduced during continuous injection until the wellbore stabilizes.

[0056] Reference Figure 1The well adopted a continuous injection method, injecting a solution with a dissolution rate of the second set value according to the set daily injection volume. The initial injection volume of asphalt dispersant in well SHB5 was 60L / d, and the injection volume was 15L / d after stabilization. The cumulative injection volume of asphalt dispersant is currently 1891L. The well has been effective in receiving water injection from SHB5-3, with the daily oil production increasing from 92.4t to the current 101.6t, and the dynamic fluid level increasing from 1023.8m to 672.7m. The current tends to stabilize after the addition of asphalt dispersant, indicating that asphalt dispersant has played a certain role in improving the fluidity of crude oil.

[0057] In the SHB5-1X well, the initial addition rate of asphalt dispersant was 60 L / d, and after stabilization, the addition rate was 15 L / d. Currently, a total of 2109 L of asphalt dispersant has been added. The well's daily oil production has increased from 102 t to the current 103.3 t, and the dynamic fluid level has decreased from 1379.8 m to 1842.5 m. After the addition of asphalt dispersant, the current tends to stabilize, indicating that asphalt dispersant has played a certain role in improving the fluidity of crude oil.

[0058] In well SHB5-12H, the initial addition rate of asphalt dispersant was 50 L / d, and after stabilization, the addition rate was 12 L / d. Currently, a total of 1003.7 L of asphalt dispersant has been added. The well's daily oil production has stabilized from 18.3 t to the current 17.7 t, and the dynamic fluid level has stabilized from 2102 m to 2353.2 m. The production rate has decreased slowly, and the dynamometer card load has not changed significantly. The role of the asphalt dispersant in improving crude oil fluidity in this well needs to be evaluated.

[0059] After adding 50 L / d of asphalt dispersant to the SHB5-2CH well, the water cut gradually decreased.

[0060] like Figure 2 As shown, for the 12 mechanical pumping wells in Block A, such as TH10403X, TP258X, and TP7-3, which were severely blocked by asphalt, the above-mentioned continuous chemical dosing method was adopted. After the chemical dosing, the average continuous production reached 724 days (the average blockage period was 88 days before the continuous chemical dosing was carried out), and no blockage occurred during the production period.

[0061] Oil well maintenance method examples

[0062] This embodiment provides a technical solution for an oil well maintenance method, as detailed below:

[0063] During oil well production, historical asphaltene precipitation data and current oil pressure and production data of the target oil well are acquired. If there is an abnormal drop in oil pressure and production of the target oil well, and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has experienced wellbore asphaltene blockage. Since the blocked section is the key data for subsequent unblocking, but the depth of blockage and the deposition section cannot be predicted by conventional methods, this embodiment uses a test well cleaning method to confirm the blocked depth H, that is, the location of asphaltene precipitation. For example, the SHB5-11H well continued to produce after being switched to pumping in 2020. At the end of February 2021, the fluid level dropped to about 2500m, and 3718m of water was injected at the beginning of March. 3 Then, after injecting asphalt dispersant and simmering the well, water is injected to a depth of 5007m. 3 The well was shut in until April 24th, when it was reopened. After producing a cumulative 444.5 tons of water, it stopped producing fluid on April 30th. The dynamometer card showed a significant change in fluid supply conditions; on April 29th, the dynamometer card indicated a severe shortage of fluid, with a submersion depth of 2690 meters. Analysis suggested a blockage in the well tubing. The well was shut in for workover on May 6th. During the workover, two... 7 / 8 The tailpipe was blocked by a suspected asphalt material in the 3734-6000m section. About 3.8t of asphalt material was removed on site, so it was determined that the SHB5-11H well had an asphalt blockage.

[0064] For target oil wells experiencing asphaltene blockage, the blockage depth is determined, the treatment section volume and displacement section volume are calculated, and the required amount of asphalt dispersant is obtained from these volumes. The required amount of asphalt dispersant is then mixed with thin oil in a set ratio to form a solution with a solubility of a first set value. In this embodiment, all asphalt dispersants used are SDJ-2 type asphalt dispersant (in other embodiments, other dispersants may be used depending on the actual situation, or different asphalt dispersants may be used at different injection stages). The asphalt dispersant is mixed with thin oil in a 1:1 ratio to form a solution with a solubility of approximately 1 g / ml. Considering that the injected fluid should be as minimal as possible in low-pressure wells, and the length of the reagent-soaked section should not exceed 500-1000 m, the treatment section volume X and displacement section volume Y are calculated. Therefore, X / 2 tons of asphalt dispersant and (Y+X / 2) m³ of thin oil are required. 3 Where (Y / 2)m 3 The thin oil is used to further lubricate the tubing after clearing the asphalt blockage, thus mitigating the risk of re-clogging.

[0065] A solution with a solubility of the first set value is injected into the oil well according to a set injection rate and a set initial injection pressure. During injection, a pressure difference generated by the high-density fluid is considered, and the injection pressure is adjusted downwards accordingly based on the pressure difference. Since the fluid in the tubing flows in reverse during the initial injection phase, it has a compacting effect on the deposited asphalt. Therefore, a smaller set injection rate is better. The set injection rate can be determined based on the minimum displacement of the injection pump used to inject the solution with the first set solubility value into the oil well. For example, in this embodiment, the minimum displacement of a 700-type pump truck on site is considered to be 2-4 m³ / h. 3 If the injection rate is around / h, then set the injection displacement to 3m. 3 / h.

[0066] The formula for calculating the initial injection pressure is set as follows:

[0067]

[0068] Where P is the initial injection pressure, in MPa; P wh The oil pressure of the target well before injection is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h.

[0069] If the oil pressure of the target well is higher than the reservoir start-up pressure after injection, the well can resume self-flowing immediately after injection; otherwise, the well stops flowing, and the asphaltene blockage is cleared by continuously injecting a solution with a dissolution rate of the second set value according to the set daily injection volume. The reservoir start-up pressure is determined by the difference between the well's initial production pressure differential and its normal production pressure differential, specifically the difference between the initial production pressure differential and the normal production pressure differential. The formula for calculating the oil pressure of the target well after injection is as follows:

[0070] P′=P wh -ΔρHg

[0071] Where P' is the oil pressure of the target oil well after injection, in MPa; P wh The target well's oil pressure before injection is expressed in MPa; Δρ is the density difference between the injected fluid and the produced fluid, expressed in kg / m³. 3 H is the height of the liquid column in the injected fluid wellbore, in meters; g is the gravitational acceleration, which is 9.8 m / (s*s).

[0072] In specific applications, the target oil well SHB5-13H experienced a drop in oil pressure from 5.5 MPa to 0 MPa in January 2020. During well testing, blockage occurred at 894m, bringing out asphalt, indicating that the wellbore was clogged with asphalt. The aforementioned unblocking method was successfully applied. After unblocking, well SHB5-13H resumed its flowing flow, restoring daily oil production to 60 tons. Furthermore, the same unblocking method has been successfully applied in wells SHB5 and SHB5-3, resulting in a cumulative increase in production of nearly 4,000 tons.

[0073] In this embodiment, for target oil wells that cannot resume self-flowing, the continuous dosing method of continuously injecting a solution with a dissolution rate of a second set value according to the data acquisition situation of different target oil wells is specifically as follows:

[0074] If the asphaltene deposition data of the target oil well can be obtained, the stable daily injection volume and the initial daily injection volume are determined based on the asphaltene deposition data and the second set value. If the initial daily injection volume is greater than the stable daily injection volume, when continuous injection begins, the initial daily injection volume is first used as the set daily injection volume, and the set daily injection volume is gradually reduced during the continuous injection process until the set daily injection volume is reduced to equal the stable daily injection volume.

[0075] For example, after the target oil well SHB5-11H was switched to pumping, it produced for a total of 324 days. The asphaltene deposition data for this well can be obtained as follows: 4000 kg of asphaltene was deposited, averaging 12.34 kg per day. In this embodiment, the second set value is the same as the first set value, both being 1 g / ml, that is, a solution with a solubility of 1 g / ml is used. Therefore, the injection volume arrangement for the target oil well SHB5-11H is as follows: Figure 1 As shown, the designed daily dosage is 24 L / d based on twice the indoor dosage, with an initial injection dosage of 12 L / d. Based on the well blockage and empirical estimation, combined with the solvent efficiency of the agent, the estimated stable daily injection volume is 12 L / d based on twice the indoor dosage. The daily injection volume is set to be injected in a manner that is initially high and gradually reduced to a stable level. Specifically, the initial daily injection volume is about twice the designed daily dosage (24 L / d) (48 L / d), and is gradually reduced until the wellbore stabilizes, that is, the set daily injection volume is reduced to be equal to the stable daily injection volume of 12 L / d.

[0076] If the asphaltene deposition data of the target oil well cannot be obtained, the initial daily injection volume is set as the first injection volume value. When continuous injection begins, the initial daily injection volume is used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection. For example, if the first injection volume value is referenced from the daily injection volume of existing block oil wells, the initial daily injection volume is set to 50L / d, and the set daily injection volume is gradually reduced during continuous injection until the wellbore stabilizes.

[0077] A continuous dosing method was adopted, injecting a solution with a dissolution rate of the second set value according to the set daily injection volume. The initial addition of asphalt dispersant to well SHB5 was 60L / d, and the addition volume was 15L / d after stabilization. The cumulative addition of asphalt dispersant to this well is currently 1891L. The well has been effective in receiving water injection from SHB5-3, with the daily oil production increasing from 92.4t to the current 101.6t, and the dynamic fluid level increasing from 1023.8m to 672.7m. The current tends to stabilize after the addition of asphalt dispersant, indicating that asphalt dispersant has played a certain role in improving the fluidity of crude oil.

[0078] In the SHB5-1X well, the initial addition rate of asphalt dispersant was 60 L / d, and after stabilization, the addition rate was 15 L / d. Currently, a total of 2109 L of asphalt dispersant has been added. The well's daily oil production has increased from 102 t to the current 103.3 t, and the dynamic fluid level has decreased from 1379.8 m to 1842.5 m. After the addition of asphalt dispersant, the current tends to stabilize, indicating that asphalt dispersant has played a certain role in improving the fluidity of crude oil.

[0079] In well SHB5-12H, the initial addition rate of asphalt dispersant was 50 L / d, and after stabilization, the addition rate was 12 L / d. Currently, a total of 1003.7 L of asphalt dispersant has been added. The well's daily oil production has stabilized from 18.3 t to the current 17.7 t, and the dynamic fluid level has stabilized from 2102 m to 2353.2 m. The production rate has decreased slowly, and the dynamometer card load has not changed significantly. The role of the asphalt dispersant in improving crude oil fluidity in this well needs to be evaluated.

[0080] After adding 50 L / d of asphalt dispersant to the SHB5-2CH well, the water cut gradually decreased.

[0081] For 12 mechanical pumping wells with severe asphalt blockage, such as TH10403X, TP258X, and TP7-3 in a certain block, the above-mentioned continuous chemical dosing method was adopted. After the chemical dosing, the average continuous production reached 724 days (the average blockage period was 88 days before continuous chemical dosing), and no blockage occurred during the production period.

[0082] During the continuous injection of a solution with a solubility of the second set value, the wellhead condition is observed in real time and various wellhead parameters are obtained. If any abnormalities related to asphalt blockage occur, such as an increase or fluctuation in the current corresponding to the oil well exceeding the corresponding set change threshold, obvious asphalt blockage at the pressure gauge cock sampling port and inspection filter, lag in the polished rod, or abnormal noise at the wellhead, the set daily injection volume is adjusted accordingly. If the above abnormalities cannot be alleviated after adjustment, a large-volume backwash is performed on the target oil well within the set maintenance time. In this embodiment, the set maintenance time is 1 day, that is, if the problem cannot be alleviated after adjustment, a large-volume backwash is organized within 1 day (using a thin oil + chemical agent washing method), and the periodic washing pattern is observed and determined.

[0083] For target wells that are expected to resume self-flowing, other self-flowing wells, and some mechanically pumped wells where continuous chemical dosing is not feasible, periodic well washing is used for routine maintenance. This involves periodic hot washing combined with chemical agents to prevent asphalt condensation inside the tubing, thereby resolving the asphalt blockage problem. The effectiveness of this periodic well washing is as follows: Figure 3 As shown.

[0084] The features of this invention are:

[0085] 1) After identifying the target oil well where the wellbore is blocked by asphalt, first use a single injection to dissolve the asphalt to obtain the required amount of asphalt dispersant. Then, inject the solution containing the asphalt dispersant into the target oil well where the wellbore is blocked by asphalt at the smallest possible injection rate and pressure. This will dissolve the asphalt in the oil well without causing additional pressure and promote the oil well to resume self-flowing.

[0086] 2) If a single injection fails to restore the well to its natural flow, a continuous injection method (asphalt dispersant) is adopted. The solution containing asphalt dispersant is injected into the target well with asphalt blockage in the wellbore according to the daily injection volume, which is initially high and gradually reduced to a stable level, in order to achieve a rapid unblocking effect.

[0087] 3) During continuous injection, observe the wellhead condition in real time and obtain various wellhead parameters. If any abnormal situation related to asphalt blockage occurs, adjust the daily injection volume accordingly. If the abnormal situation cannot be alleviated after adjustment, perform a large-volume backwashing of the target oil well within the set maintenance time. For target oil wells that cannot be continuously chemically treated, use periodic well washing for daily maintenance to prevent asphalt from solidifying in the tubing and thus solve the asphalt blockage problem.

[0088] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or explanatory of the principles of the present invention, and do not constitute a limitation thereof.

Claims

1. A method for removing asphalt plugging in oil wells, characterized in that, The steps include the following: Obtain historical asphaltene precipitation data and current oil pressure and production data of the target oil well. If there is an abnormal drop in oil pressure and production of the target oil well, and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has experienced wellbore asphaltene blockage. For a target oil well where the wellbore is blocked by asphalt, the depth of the blockage is determined by well cleaning, and then the volume of the treatment section and the volume of the displacement section are calculated. The required amount of asphalt dispersant is obtained from the volume of the treatment section and the volume of the displacement section. The required amount of asphalt dispersant is mixed with thin oil in a set ratio to form a solution with a solubility of a first set value. The solution with a solubility of the first set value is injected into the oil well according to the set injection rate and the set initial injection pressure. If the pressure suddenly drops during the injection process, it indicates that the asphalt has been unblocked. The injection pressure is then lowered accordingly to ensure stable injection and further dilute the asphalt to ensure unblocking. The initial injection pressure is set as follows: Where P is the initial injection pressure, in MPa; P wh The target oil well's oil pressure is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h If the oil pressure of the target well is higher than the reservoir start-up pressure after injection, the well will resume self-flowing after injection; otherwise, the well will stop flowing, and the asphaltene blockage will continue to be cleared by continuously injecting a solution with a dissolution rate of the second set value according to the set daily injection volume. If the asphaltene deposition data of the target well can be obtained, the stable daily injection volume and the initial daily injection volume will be determined according to the asphaltene deposition data and the second set value. If the initial daily injection volume is greater than the stable daily injection volume, when continuous injection begins, the initial daily injection volume will be used as the set daily injection volume, and the set daily injection volume will be gradually reduced during the continuous injection process until the set daily injection volume is reduced to equal the stable daily injection volume. If the asphaltene deposition data of the target oil well cannot be obtained, the initial daily injection volume is set as the first injection volume value. When continuous injection begins, the initial daily injection volume is used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection. The reservoir start-up pressure is determined by the well start-up production pressure differential and the normal production pressure differential of the target well.

2. The method for relieving asphaltene blockage in oil wells according to claim 1, characterized in that, The reservoir start-up pressure is determined by the difference between the well start-up production pressure differential and the normal production pressure differential of the target well, and is the difference between the well start-up production pressure differential and the normal production pressure differential.

3. The method for removing asphaltene blockage in oil wells according to claim 1 or 2, characterized in that, The oil pressure of the target oil well after injection is calculated using the following formula: Where P' is the oil pressure of the target well after injection, in MPa; Δρ is the density difference between the injected fluid and the produced fluid, in kg / m³. 3 H represents the height of the fluid column inside the wellbore, in meters (m).

4. The method for relieving asphaltene blockage in oil wells according to claim 1, characterized in that, The set injection displacement is determined based on the minimum displacement of the injection pump that injects a solution with a solubility of a first set value into the oil well.

5. The method for relieving asphalt plugging in oil wells according to claim 1, characterized in that, The asphalt dispersant is SDJ-2 type asphalt dispersant.

6. A method for maintaining oil wells, characterized in that, During the oil well production process, historical asphaltene precipitation data and current oil pressure and production data of the target oil well are obtained. If there is an abnormal drop in oil pressure and production of the target oil well, and the historical asphaltene precipitation data meets the set conditions, it is determined that the target oil well has experienced wellbore asphaltene blockage. For a target oil well where the wellbore is blocked by asphalt, the depth of the blockage is determined, the volume of the treatment section and the volume of the displacement section are calculated, and the required amount of asphalt dispersant is obtained from the treatment section and the displacement section. The required amount of asphalt dispersant is mixed with thin oil in a set ratio to form a solution with a solubility of a first set value. The solution with a solubility of a first set value is injected into the oil well according to a set injection rate and a set initial injection pressure. During the injection process, the injection pressure is adjusted downwards according to changes in the pressure difference. The set initial injection pressure is: Among them, P wh The target oil well's oil pressure is expressed in MPa; Pe is the formation static pressure, expressed in MPa; P wf Formation flowing pressure, in MPa; Q is daily liquid production, in m³. 3 / d; q represents the injection displacement, in meters. 3 / h; If the oil pressure of the target well is higher than the reservoir start-up pressure after injection, the well resumes self-flowing after injection; otherwise, the well stops flowing, and the asphaltene blockage is cleared by continuously injecting a solution with a dissolution rate of a second set value according to a set daily injection volume. If asphaltene deposition data of the target well can be obtained, a stable daily injection volume and an initial daily injection volume are determined based on the asphaltene deposition data and the second set value. The initial daily injection volume is greater than the stable daily injection volume. When continuous injection begins, the initial daily injection volume is first used as the set daily injection volume, and the set daily injection volume is gradually reduced during continuous injection until it is equal to the stable daily injection volume. During the continuous injection of a solution with a dissolution rate of the second set value, various parameters at the wellhead are acquired in real time. If the current of the electric pump well corresponding to the oil well rises or the fluctuation range exceeds the corresponding set change threshold, there is obvious asphalt blockage at the pressure gauge cock sampling port and inspection filter, the polished rod lags, or there is abnormal noise at the wellhead, the set daily injection volume is adjusted upward accordingly. If the adjustment still cannot alleviate the situation, a large-volume backwash is performed on the target oil well within the set maintenance time.

7. The oil well maintenance method according to claim 6, characterized in that, The reservoir start-up pressure is determined by the difference between the well start-up production pressure differential and the normal production pressure differential of the target well, and is the difference between the well start-up production pressure differential and the normal production pressure differential.

8. The oil well maintenance method according to claim 6 or 7, characterized in that, The oil pressure of the target oil well after injection is calculated using the following formula: Where P' is the oil pressure of the target well after injection, in MPa; Δρ is the density difference between the injected fluid and the produced fluid, in kg / m³. 3 H represents the height of the fluid column inside the wellbore, in meters (m).

9. The oil well maintenance method according to claim 6 or 7, characterized in that, The set injection displacement is determined based on the minimum displacement of the injection pump that injects a solution with a solubility of a first set value into the oil well.

10. The oil well maintenance method according to claim 6 or 7, characterized in that, The asphalt dispersant is SDJ-2 type asphalt dispersant.

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