Oil casing corrosion protection method based on cathode protection

Abstract

The invention relates to the field of oil casing corrosion protection, and discloses an oil casing corrosion protection method based on cathode protection, which comprises the following steps: in the production increasing operation and production process, putting a soluble sliding sleeve into a shaft along with an oil pipe, and throwing a ball to open the soluble sliding sleeve; the internal ball seat part of the soluble sliding sleeve comprises a ball seat upper part, a ball seat lower part and a ball; the metal activity of the material of the upper part of the ball seat is higher than that of the material of the oil casing; and the metal activity of the ball seat lower part and the ball material is higher than that of the ball seat upper part. The method is long in protection validity period, capable of achieving integrity protection of the oil and gas well in the whole life cycle, wide in application range and low in operation cost and has great industrial application prospects.

Description

Technical Field

[0001] The invention relates to the field of oil casing corrosion protection, and in particular to an oil casing corrosion protection method based on cathodic protection. Background Art

[0002] Waterflooding is a common pressure-maintaining measure in oil reservoir development. During the middle and late stages of waterflood development, tubing and casing corrosion is a common issue, hindering the increase or stability of oilfield production. This is particularly true in areas with high salinity of injected or produced water, such as Iraq's carbonate reservoirs and China's Northwest Oilfield. Tubing and casing integrity issues caused by electrochemical corrosion are common during the middle and late stages of oilfield development.

[0003] To address the electrochemical corrosion problem of oil casing, the industry's current primary approach is to use corrosion inhibitors. Guangli Oilfield uses corrosion-resistant alloy steel pipes, adds chemical agents, and employs other protective technologies such as coated tubing. CNOOC Zhanjiang Branch has conducted research on corrosion, perforation, and breakage of tubing during service. During subsequent use, they use corrosion and scale inhibitors to protect the tubing, thereby reducing scale-induced corrosion on the tubing wall and extending its service life. Research from Southwest Petroleum University suggests that downhole injection of water-based corrosion inhibitors for pre-filming is a relatively advanced and low-cost method. However, these methods generally have high operating costs and a short shelf life. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for corrosion protection of oil casing based on cathodic protection. This method has a long protection period, can achieve integrity protection of oil and gas wells throughout their entire life cycle, has a wide range of applications, low operating costs, and great industrial application prospects.

[0005] The present invention provides a method for corrosion protection of oil casing based on cathodic protection, the method comprising: during a production stimulation operation and production process, lowering a soluble sliding sleeve into a wellbore along with the oil pipe, and dropping a ball to open the soluble sliding sleeve; the internal ball seat component of the soluble sliding sleeve comprises a ball seat upper part, a ball seat lower part and a ball; the metal activity of the material of the ball seat upper part is higher than that of the oil casing; the metal activity of the material of the ball seat lower part and the ball is higher than that of the material of the ball seat upper part.

[0006] The protection method described in the present invention is based on the principle of cathodic protection. A sliding sleeve with soluble internal components is used during production stimulation operations or production processes. By sacrificing the soluble internal components in the sliding sleeve, the corrosion of the oil casing is greatly alleviated, the integrity of the oil casing is protected throughout the life cycle of the oil and gas well, and the service life of the oil casing is greatly increased. The protection method described in the present invention is simple to operate, has low operating costs, and has a wide range of applications. It can be applied to oil casing corrosion protection in a variety of different scenarios, has a long protection period, and can achieve integrity protection of the oil and gas well throughout its life cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a diagram of the internal structure of a soluble sleeve with a circulation hole, where the dotted line represents the soluble part; Figure 2 This is a diagram of the internal structure of a soluble sleeve without circulation holes, with the dotted line representing the soluble part; Figure 3 This is a schematic diagram of the operation scene of Example 1; Figure 4 This is a schematic diagram of the operation scene of Example 2; Figure 5 This is a schematic diagram of the operation scene of Example 3; Figure 6 This is a schematic diagram of the operation scene of Example 4.

[0008] Description of Reference Numerals 1 Upper part of the ball seat; 2 Lower part of the ball seat; 3 Ball; 4 Fracturing acid; 5 Pickling acid; 6 Injection water direction; 7 Oil tubing; 8 Soluble sleeve without circulation holes; 9 Packer; 10 Produced fluid direction. DETAILED DESCRIPTION

[0009] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0010] The present invention provides a method for corrosion protection of oil casing based on cathodic protection, the method comprising: during a production increase operation and production process, lowering a soluble sliding sleeve into a wellbore along with an oil pipe, and dropping a ball to open the soluble sliding sleeve; the internal ball seat component of the soluble sliding sleeve comprises a ball seat upper part, a ball seat lower part and a ball; the metal activity of the material of the ball seat upper part is higher than that of the oil casing; the metal activity of the material of the ball seat lower part and the ball is higher than that of the material of the ball seat upper part.

[0011] In the present invention, the specific operations of lowering the soluble sleeve into the wellbore along with the oil pipe and dropping the ball to open the soluble sleeve to achieve full bore inside the oil pipe are well known to those skilled in the art and will not be described in detail here.

[0012] In the present invention, there is no special requirement for the material of the oil casing, which is generally carbon steel.

[0013] In the present invention, the metal activity of the material of the lower part of the ball seat is higher than that of the material of the upper part of the ball seat. There is no special limitation on the specific type of the material of the lower part of the ball seat. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the material of the lower part of the ball seat is selected from magnesium alloy.

[0014] In the present invention, the metal activity of the ball material is higher than that of the material on the upper part of the ball seat. There is no special limitation on the specific type of the ball material. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the material of the ball is selected from magnesium alloy.

[0015] According to a preferred embodiment of the present invention, the composition of the magnesium alloy comprises 88-92% magnesium, 7-10% aluminum, 0.5-2% zinc, and the remainder is impurities. In the present invention, there is no special requirement for the pressure difference tolerance of the material on the upper part of the ball seat. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the material on the upper part of the ball seat can withstand a pressure of 50-90MPa, preferably 60-80MPa.

[0016] According to a preferred embodiment of the present invention, the weight loss of the material of the upper portion of the ball seat after acid fracturing is no more than 5wt%, preferably 1-3wt%. The above technical solution can ensure that the upper portion of the ball seat will not be rapidly eroded during the acid fracturing operation.

[0017] In the present invention, the acid concentration of the acid pressing is not particularly limited. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the acid concentration of the acid pressing is 8-20 vol%.

[0018] In the present invention, there is no particular limitation on the specific type of the acid solution for acid fracturing, and it can be, for example, hydrochloric acid.

[0019] In the present invention, the material of the upper part of the ball seat only needs to meet the above requirements, and there is no special limitation on the specific type of the material of the upper part of the ball seat. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the material of the upper part of the ball seat is selected from aluminum alloy.

[0020] According to a preferred embodiment of the present invention, the composition of the aluminum alloy comprises, by weight percentage, 95-98% aluminum, 1-4% magnesium, 0.5-1% copper, 0.5-1% manganese, and the remainder being impurities.

[0021] In the present invention, there is no special requirement on whether the soluble sleeve is provided with circulation holes. It can be provided according to specific working conditions, which is well known to those skilled in the art. The soluble sleeve of the present invention optionally includes 2-4 circulation holes.

[0022] The method of the present invention can be applied to a variety of oil well operation scenarios, and can achieve anti-corrosion protection for oil casing. There is no special limitation on the specific operation scenario. For example, it can be horizontal well acid fracturing (there is no special requirement for the acid concentration of acid fracturing, for example, 8-20 vol%), horizontal well fracturing / pickling (there is no special requirement for the acid concentration of pickling, for example, 8-20 vol%), oil production wells or water injection wells. In oil production wells and water injection wells, although there is no acid fracturing or pickling, the dissolution of the upper part of the ball seat during acidification during the water injection process or the production process must still be considered.

[0023] In the present invention, using a packer to seal the casing annulus in oil production wells and water injection wells is a conventional operation well known to those skilled in the art and will not be described in detail here.

[0024] According to the method of the present invention, the soluble spheres can be controlled to completely dissolve within 5-7 days of operation.

[0025] According to the method of the present invention, the lower portion of the ball seat can be controlled to completely dissolve within 5-7 days of operation, thereby achieving full bore inside the oil pipe.

[0026] According to the method of the present invention, the upper portion of the ball seat can be completely dissolved within 9-10 years of operation, thereby protecting the integrity of the casing and tubing throughout the entire life cycle of the oil and gas well (generally about 10 years), significantly extending the service life of the casing and tubing.

[0027] The present invention will be described in detail below through examples.

[0028] In the following examples, The integrity of the oil casing is tested by casing pressure test, and the integrity of the oil casing is judged according to the test pressure; The casing annulus pressure is monitored by the wellhead casing pressure gauge; The oil wells involved in the embodiments of the present invention are all oil wells in the carbonate reservoir development area of ​​an oil field in the Middle East.

[0029] [Example 1] Operation scenario: horizontal well acid fracturing; Figure 3 This is a schematic diagram of the operation scene of this embodiment.

[0030] Select five horizontal wells in tight reservoirs, with daily oil production of 200-500 barrels per day; Soluble sleeve (set up 2 circulation holes, internal structure as Figure 1As shown, the dotted line indicates the soluble part, the material of the upper portion 1 of the ball seat is an aluminum alloy (aluminum 96wt%, magnesium 2wt%, copper 0.6wt%, manganese 0.9wt%, and the rest are inevitable impurities; the bearing pressure is 75MPa, and the weight loss under 10vol% hydrochloric acid acid pressing is 2wt%), and the material of the lower portion 2 of the ball seat and the ball 3 is a magnesium alloy (magnesium 90wt%, aluminum 8.5wt%, zinc 0.9wt%, and the rest are inevitable impurities); The soluble sleeve is lowered into the wellbore along with the oil pipe, and the ball 3 is dropped to open the soluble sleeve and connect the oil casing annulus to carry out the operation; then the acid 4 is injected for fracturing, and the acid 4 is hydrochloric acid with a concentration of 10 vol%.

[0031] The tubing and casing were subjected to integrity tests and well tests. The tubing and casing integrity tests of the five horizontal wells all showed that the lower part of the ball seat and the ball were completely dissolved on the 7th day to form a full diameter, and the upper part of the ball seat was completely dissolved on the 10th year. From the 1st year to the 10th year, the tubing and casing had good integrity and no corrosion occurred.

[0032] [Example 2] Operation scenario: horizontal well pickling; Figure 4 This is a schematic diagram of the operation scenario of this embodiment; Five horizontal wells in tight reservoirs were selected, with a daily oil production of 200-500 barrels per day.

[0033] Soluble sleeve (set up 4 circulation holes, internal structure as Figure 1 As shown, the dotted line indicates the soluble part, and the material of the upper portion 1 of the ball seat is an aluminum alloy (aluminum 95wt%, magnesium 3wt%, copper 0.5wt%, manganese 0.5wt%, and the rest are unavoidable impurities; the bearing pressure is 68MPa), and the material of the lower portion 2 of the ball seat and the ball 3 is a magnesium alloy (magnesium 91wt%, aluminum 7.8wt%, zinc 0.7wt%, and the rest are unavoidable impurities); The soluble sleeve is lowered into the wellbore along with the oil pipe, and the ball 3 is dropped to open the soluble sleeve and connect the oil casing annulus to implement the operation; the well is pickled once a year to increase production, and the acid solution 5 is hydrochloric acid with a concentration of 20wt%.

[0034] The tubing and casing were subjected to integrity tests and well tests. The tubing and casing integrity tests of the five horizontal wells all showed that the lower part of the ball seat and the ball were completely dissolved on the sixth day to form a full bore, and the upper part of the ball seat was completely dissolved in the 9th year and 10th month. The tubing and casing had good integrity and no corrosion occurred.

[0035] [Example 3] Operation scenario: water injection well; Figure 5 This is a schematic diagram of the operation scenario of this embodiment; Select 5 water injection wells, injecting 5,000-20,000 barrels of water per day; Soluble sleeve (no circulation hole, internal structure as Figure 2 As shown, the dotted line is the soluble part) and the material of the ball seat upper part 1 is aluminum alloy (aluminum 96wt%, magnesium 2wt%, copper 0.6wt%, manganese 0.9wt%, the rest are unavoidable impurities, and the bearing pressure is 75MPa), and the material of the ball seat lower part 2 and the ball 3 is magnesium alloy (magnesium 90wt%, aluminum 8.5wt%, zinc 0.9wt%, the rest are unavoidable impurities); The soluble sliding sleeve 8 is lowered into the wellbore along the oil pipe 7, and the ball 3 is dropped to seal the packer 9 to achieve independent water injection into the oil reservoir; water injection operations are carried out in the water injection well with a daily water injection rate of 5,000-20,000 barrels / day, and the oil casing annulus is sealed with a packer in the water injection layer.

[0036] Integrity tests were conducted on the tubing and casing. The tests on the tubing and casing integrity of the five water injection wells showed that the lower part of the ball seat and the ball were completely dissolved on the 7th day, forming a full diameter, and the upper part of the ball seat was completely dissolved on the 10th year. From the 1st year to the 10th year, the tubing and casing had good integrity and no corrosion occurred. In addition, according to the tubing and casing annulus pressure monitoring, it was found that the pressure did not change, which also proved that the tubing and casing were effectively protected.

[0037] [Example 4] Operation scenario: oil well; Figure 6 This is a schematic diagram of the operation scenario of this embodiment; Select 5 water-breaking oil wells with a daily oil production of 2,000-3,500 barrels per day; Soluble sleeve 8 (without circulation hole, internal structure as Figure 2 As shown, the dotted line indicates the soluble part) the material of the upper portion 1 of the ball seat is an aluminum alloy (aluminum 95wt%, magnesium 3wt%, copper 0.5wt%, manganese 0.5wt%, the rest are unavoidable impurities, and the bearing pressure is 68MPa), the material of the lower portion 2 of the ball seat and the ball 3 is a magnesium alloy (magnesium 91wt%, aluminum 7.8wt%, zinc 0.7wt%, the rest are unavoidable impurities); A soluble sliding sleeve 8 is connected to the end of the oil pipe 7, and a ball 3 is dropped to seal the packer 9, thereby realizing independent development of the oil reservoir.

[0038] The casing and tubing were subjected to integrity tests and well tests. The integrity tests of the casing and tubing in 5 oil production wells showed that the lower part of the ball seat and the ball were completely dissolved on the 7th day to form a full diameter, and the upper part of the ball seat was completely dissolved in 9 years and 11 months. The casing and tubing had good integrity and no corrosion occurred. In addition, according to the casing and tubing annulus pressure monitoring, it was found that the pressure did not change, which also proved that the casing and tubing were effectively protected.

[0039] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for corrosion protection of oil casing based on cathodic protection, characterized in that: The method comprises: during the production stimulation operation and production process, lowering the soluble sliding sleeve into the wellbore along with the oil pipe, and dropping a ball to open the soluble sliding sleeve; the internal ball seat component of the soluble sliding sleeve comprises a ball seat upper part, a ball seat lower part and a ball; The metal activity of the material of the upper portion of the ball seat is higher than that of the material of the oil casing; The metal activity of the material of the lower portion of the ball seat and the ball is higher than that of the material of the upper portion of the ball seat.

2. The method according to claim 1, characterized in that The material of the lower part of the ball seat is selected from magnesium alloy; and / or The material of the ball is selected from magnesium alloy.

3. The method according to claim 2, characterized in that In terms of weight percentage, the magnesium alloy comprises 88-92% magnesium, 7-10% aluminum, 0.5-2% zinc, and the remainder is impurities.

4. The method according to claim 1, wherein The material of the upper portion of the ball seat can withstand a pressure of 50-90 MPa; and / or The weight loss of the material on the upper part of the ball seat after acid pressing is not more than 5wt%.

5. The method according to claim 1, characterized in that The material of the upper portion of the ball seat can withstand a pressure of 60-80 MPa; and / or The material on the upper portion of the ball seat loses 1-3 wt % of its weight after acid pressing.

6. The method according to claim 4 or 5, characterized in that The acid concentration of the acid pressing is 8-20 vol%; and / or The acid solution for acid pressing is selected from hydrochloric acid.

7. The method according to claim 1 or 2, characterized in that The material of the upper portion of the ball seat is selected from aluminum alloy.

8. The method according to claim 7, characterized in that In terms of weight percentage, the aluminum alloy comprises 95-98% aluminum, 1-4% magnesium, 0.5-1% copper, 0.5-1% manganese, and the remainder is impurities.

9. The method according to claim 1 or 2, characterized in that The soluble sleeve optionally includes 2-4 circulation holes.

10. The method according to claim 1 or 2, characterized in that The operation scenarios include horizontal well acid fracturing, horizontal well fracturing / acid washing, oil production wells or water injection wells.

11. The method according to claim 1 or 2, characterized in that The spheres completely dissolve within 5-7 days of operation.

12. The method according to claim 1 or 2, characterized in that The lower part of the ball seat is completely dissolved within 5-7 days of operation.

13. The method according to claim 1 or 2, characterized in that The upper portion of the ball seat will completely dissolve within 9-10 years of operation.

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