Flow-limiting screen pipe suitable for corrosive environment and design method of flow-limiting screen pipe

Abstract

The invention provides a flow-limiting screen pipe suitable for a corrosive environment and a design method thereof, the flow-limiting screen pipe comprises at least one flow-limiting unit, the flow-limiting unit comprises a blind pipe and a screen pipe, the blind pipe and the screen pipe are arranged at an interval, and the screen pipe is provided with at least one hole. Through combined application of different anti-corrosion materials or coatings / plating layers, the long-term service working requirement of the current-limiting screen pipe in a high-corrosion environment is met, and meanwhile, conditions are created for secondary well completion (such as plugging after water is discharged from a certain layer section) possibly occurring in the later stage of oil well production.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas exploitation, and relates to a limited-entry liner applicable to a corrosive environment and a design method thereof. Background Art

[0002] A limited-entry liner (LEL) is a downhole tool widely used for the completion of long horizontal wells in the Middle East. Its function is to make up for the difference in acid fluid flow friction in the long horizontal well section during the acidification process through the differential design of the number of perforations in each section of the liner, and at the same time actively limit the flow in high-permeability layers or fracture-developed layers, and finally achieve uniform acid distribution in the entire horizontal well section. The limited-entry liner can be used in production wells or injection wells.

[0003] However, when the limited-entry liner is used in a corrosive environment: for example, the crude oil in the production well has a high content of hydrogen sulfide or carbon dioxide, or the salinity of the injected water in the injection well is high. During service, the limited-entry liner is easily corroded and damaged. Since the limited-entry liner is used in cooperation with a permanent packer, the corroded and damaged liner is difficult to remove and replace, resulting in the inability to perform the flow-limiting function during subsequent secondary acidification, tertiary acidification, etc.; at the same time, the non-uniform corrosion damage surface will also hinder the lowering of downhole operation tools such as coiled tubing, affecting subsequent downhole operations.

[0004] Therefore, it is very important to control the corrosion of the limited-entry liner during service. Using corrosion-resistant alloys (such as Alloy028) can well control corrosion, but the cost of corrosion-resistant alloys is much higher (for example, the price of Alloy 028 is 10 times that of carbon steel). Using coating / plating technology can also control corrosion, but since the limited-entry liner needs to be perforated: if coated / plated first and then perforated, the coating / plating at the perforation will be damaged, becoming a breakthrough point for corrosion failure, and even exacerbating the corrosion damage of the liner; if perforated first and then coated / plated, the coating / plating effect at the perforations is very poor, and the processing cost increases significantly. Using anti-corrosion materials, such as glass fiber reinforced epoxy resin (GRE), to replace steel to manufacture the limited-entry liner is also a solution, but since the limited-entry liner needs to be perforated, and glass fiber reinforced epoxy resin has strong brittleness, cracks are easily generated during the perforation process, damaging the liner. Therefore, it is crucial to find a limited-entry liner that can well control corrosion and is economical at the same time. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a limited-entry liner applicable to a corrosive environment and a design method thereof. By the combined use of different anti-corrosion materials or coatings / platings, the long-term service requirements of the limited-entry liner in a highly corrosive environment are met, and at the same time, conditions are created for possible secondary well completion (such as plugging after water production in a certain layer) in the later stage of oil well production.

[0006] To achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] One of the objectives of the present invention is to provide a current-limiting screen pipe applicable to a corrosive environment. The current-limiting screen pipe includes at least 1 current-limiting unit. The current-limiting unit includes at least 1 blind pipe and at least 1 screen pipe. The blind pipes and the screen pipes are arranged at intervals, and the screen pipe is provided with at least 1 hole.

[0008] Among them, the number of current-limiting units in the current-limiting screen pipe can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; the number of blind pipes can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; the number of screen pipes can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; the number of holes provided in the screen pipe can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., but is not limited to the listed values. Other unlisted values within the above numerical ranges are equally applicable.

[0009] As a preferred technical solution of the present invention, the material of the screen pipe is an anti-corrosion material.

[0010] As a preferred technical solution of the present invention, the anti-corrosion material includes Alloy 028 corrosion-resistant alloy.

[0011] In the present invention, the "anti-corrosion material" means that the screen pipe processed from this material can continuously serve for more than 20 years in an actual corrosive environment. For example, for injection wells with high salinity of injected water (chloride ion greater than 10000 ppm) or oil production wells with high hydrogen sulfide content (hydrogen sulfide content greater than 5%), Alloy 028 corrosion-resistant alloy can be used. Specifically, it is necessary to experimentally test the uniform corrosion rate of the "anti-corrosion material", and then calculate the service life that can be continuously served. More than 20 years meets the requirements.

[0012] As a preferred technical solution of the present invention, the material of the blind pipe is carbon steel with an anti-corrosion coating or anti-corrosion plating.

[0013] As a preferred technical solution of the present invention, the anti-corrosion coating includes an FBE coating, and the anti-corrosion plating includes a tungsten alloy plating.

[0014] In the present invention, the "anti-corrosion coating or anti-corrosion plating" means a coating or plating that can resist corrosive media, including but not limited to: FBE (FUSION BOND EPOXY) coating (used in a strong electrochemical corrosion environment); tungsten alloy plating (used in a high hydrogen sulfide environment), etc.

[0015] In the present invention, the material of the blind pipe can also be a low-cost anti-corrosion material. The "low-cost anti-corrosion material" refers to a material with a cost comparable to that of carbon steel but having good anti-corrosion ability under actual well conditions, such as glass fiber reinforced epoxy resin (GRE).

[0016] As a preferred technical solution of the present invention, the length of the flow-limiting unit is not less than 50% of the length of the flow-limiting unit, such as 50%, 55%, 60%, 65%, 70% or 75%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] As a preferred technical solution of the present invention, the length of a single blind pipe in the flow-limiting unit is ≥ 30 m, such as 30 m, 35 m, 40 m, 45 m, 50 m, 55 m or 60 m, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] The second object of the present invention is to provide a design method for a flow-limiting screen pipe applicable to a corrosive environment, characterized in that the design method includes:

[0019] (1) Segment the horizontal section of the oil well according to the requirement of uniform acid distribution during acidification, and design the number of holes configured for each segment;

[0020] (2) Determine the number of blind pipes and flow-limiting screen pipes to be configured for each segment;

[0021] (3) Select a flow-limiting screen pipe according to the number of holes configured for each segment;

[0022] (4) Select a blind pipe according to the remaining length.

[0023] As a preferred technical solution of the present invention, a special design software is used to design the number of holes configured for each segment.

[0024] In the present invention, the special design software used can be Microsoft Visual Basic.

[0025] As a preferred technical solution of the present invention, the formula for determining the matching lengths of the blind pipe and the flow-limiting screen pipe is:

[0026]

[0027] In the formula, l si is the matching length of the flow-limiting screen pipe in each flow-limiting unit of the i-th segment, n i is the number of designed holes in the i-th segment; a is the length of each blind pipe / screen pipe, l b is the length of the blind pipe in each flow-limiting unit, m is the number of holes on each flow-limiting screen pipe; l i is the total length of the i-th segment.

[0028] In the present invention, the number of holes on a single restricted flow screen pipe is minimized as much as possible, so that the holes are as scattered as possible, which is conducive to the uniform distribution of acid fluid; at the same time, economy should also be taken into account (because the restricted flow screen pipe uses relatively expensive corrosion-resistant alloy materials). Generally, first design with one hole on a single screen pipe, calculate whether it meets the economy, and if not, gradually increase the number of holes on a single screen pipe one by one.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] The present invention provides a restricted flow screen pipe applicable to a corrosive environment and its design method. By using a combination of different corrosion-resistant materials or coatings / platings, the long-term service requirements of the restricted flow screen pipe in a highly corrosive environment are met, and at the same time, conditions are created for possible secondary well completion in the later stage of oil well production (such as plugging after water production in a certain interval). BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the cross arrangement of the blind pipe and the screen pipe in the restricted flow screen pipe provided by the present invention for a corrosive environment.

[0032] The present invention will be further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention is subject to the claims. DETAILED DESCRIPTION OF THE INVENTION

[0033] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the typical but non-limiting embodiments of the present invention are as follows:

[0034] Embodiment

[0035] Taking a water injection well in the Middle East as an example, the length of its horizontal well section is 8000 feet. The salinity of the injected water is 220,000 ppm, and the chloride ion is 125,000 ppm. Data of other wells in the same block show that the completion string is prone to electrochemical corrosion and failure. It is planned to divide the horizontal section into 8 segments on average with a bare hole packer and complete the well with a 6" restricted flow screen pipe. The budget for the lower completion string is 600,000 US dollars. According to the design of special software, the number of holes of these 8 segments of restricted flow screen pipes is respectively (from the heel end to the toe end): 15 (the first segment), 17 (the second segment), 18 (the third segment), 19 (the fourth segment), 22 (the fifth segment), 26 (the sixth segment), 27 (the seventh segment), 30 (the eighth segment). The completion string of this well is designed and selected according to the following steps:

[0036] (1) Determine the combination of the blind pipe and the screen pipe for each segment: The length of each blind pipe / screen pipe is calculated according to a = 30 feet, and the length of the blind pipe in each restricted flow unit is taken as l b = 150 feet. From the above conditions, it can be known that n i = 15, li = 1000 feet. First, start the design from m = 1 for each hole position on each restricted flow screen pipe. Then, calculate the length of the restricted flow screen pipe in the restricted flow unit according to Equation (1) as follows: feet. The design result for the first section is: blind pipe + screen pipe = 150 feet + 123 feet;

[0037] Use the same method to determine the lengths of the blind pipes and screen pipes for the restricted flow units in other sections, as shown in Table 1:

[0038] Table 1

[0039]

[0040]

[0041] (2) Determine the material of the blind pipe: This well is an injection well with a high salinity of the injected water. Select fiberglass-reinforced epoxy resin (GRE) as the material of the blind pipe;

[0042] (3) Determine the material of the restricted flow screen pipe: Select Alloy 028 corrosion-resistant alloy as the material of the restricted flow screen pipe;

[0043] (4) Calculate the pipe material cost according to the above length design results and material selection results, as shown in Table 2:

[0044] Table 2

[0045]

[0046] (5) According to the above length design, the cost of $819,000 exceeds the cost budget of the lower completion string. Therefore, adjust the number of openings of each single screen pipe in the section near the toe end of the horizontal section until the total cost obtained is lower than $600,000. The final design results are shown in Tables 3 and 4:

[0047] Table 3

[0048]

[0049]

[0050] Table 4

[0051]

[0052] (6) Assemble and install the lower completion string according to the above pipe string configuration plan, and perform normal acidizing and water injection operations;

[0053] Secondary completion: For example, after 10 years of production, if severe water breakthrough is found in a certain section through PLT testing and plugging is required, a smaller-sized packer and a blank pipe are run into the 6" string. For example, a 4-1 / 2" packer + 4-1 / 2" tubing + 4-1 / 2" packer are used to block the water-producing section. The two 4-1 / 2" packers are seated in the 6" blank pipe, and the 4-1 / 2" tubing plugs the 6" restricted flow screen between the two 4-1 / 2" packers to achieve water shutoff.

[0054] The applicant declares that the detailed structural features of the present invention are illustrated by the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0055] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0056] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable way without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0057] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A flow limiting screen suitable for a corrosive environment, characterized in that: The flow-limiting screen tube comprises at least one flow-limiting unit, and the flow-limiting unit comprises at least one blind tube and at least one screen tube. The blind tube and the screen tube are arranged at intervals, and the screen tube is provided with at least one hole.

2. The flow limiting screen according to claim 1, characterized in that: The screen tube is made of corrosion-resistant material.

3. The flow limiting screen according to claim 2, characterized in that: The anti-corrosion material includes Alloy 028 corrosion-resistant alloy.

4. The flow limiting screen according to claim 1, characterized in that: The blind pipe is made of carbon steel with an anti-corrosion coating or an anti-corrosion plating.

5. The flow limiting screen according to claim 4, characterized in that: The anti-corrosion coating includes a FBE coating, and the anti-corrosion plating includes a tungsten alloy plating.

6. The flow limiting screen according to claim 1, characterized in that: The length of the current limiting unit is not less than 50% of the length of the current limiting unit.

7. The flow limiting screen according to claim 1, characterized in that: The length of a single blind pipe in the current limiting unit is ≥30m.

8. A design method for a flow-limiting screen suitable for a corrosive environment, characterized in that: The design method comprises: (1) According to the requirement of uniform acid distribution, the horizontal section of the oil well is divided into sections, and the number of holes configured in each section is designed; (2) Determine the number of blind pipes and flow-limiting screens that should be configured in each section; (3) Select the flow-limiting screen according to the number of holes configured in each section; (4) Select the blind tube according to the remaining length.

9. The design method according to claim 8, characterized in that: The number of holes in each section is designed using dedicated design software.

10. The design method according to claim 8, characterized in that: The formula for determining the length of the blind leg and the flow limiting screen is: In the formula, l si The length of the flow-limiting screen pipe in each flow-limiting unit in the i-th section, n i is the number of holes designed for the i-th section; a is the length of each blind tube / screen tube, l b is the length of the blind pipe in each flow limiting unit, m is the number of holes on each flow limiting screen tube; l i is the total length of the i-th segment.

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