Submarine pipeline with porous medium shield

Abstract

The present application relates to the field of submarine pipeline construction and operation, and relates to a submarine pipeline with a porous medium protective layer, the submarine pipeline with the porous medium protective layer comprises three layers, from inside to outside, the three layers are: a steel pipe, a protective layer, and a porous medium protective layer, the porous medium protective layer is a porous medium wrapping layer with water permeability, wherein, the permeability coefficient of the porous medium protective layer is 2-60 times the permeability coefficient of the seabed soil under the pipeline, and the thickness of the porous medium protective layer is 0.05-0.25 times the outer diameter of the pipeline without the porous medium protective layer. Compared with the prior art, the present application has the advantages of low protection cost, convenient construction, low environmental impact, etc.

Description

Technical Field

[0001] This invention relates to the field of submarine pipeline construction and operation, and in particular to a submarine pipeline with a porous media protective layer. Background Technology

[0002] Subsea pipelines are crucial facilities in offshore oil and gas production systems, and their safe operation is a key guarantee for marine energy development. Pipelines laid directly on the seabed surface experience pressure differences between the two sides under ocean wave and current conditions, leading to seepage in the seabed beneath the pipeline. When the seepage intensity is too high, seepage damage occurs in the seabed soil beneath the pipeline, resulting in localized scouring. With the continued action of ocean waves and currents, the scour pit extends along the pipeline's length, causing the pipeline to enter a suspended state. If the length of the suspended section exceeds a critical value, it will cause vortex-induced vibration, leading to fatigue damage and failure. Subsea pipeline failure not only affects the normal production of oil and gas platforms, causing huge economic losses, but also causes oil and gas leaks, resulting in damage to the marine ecological environment. Therefore, implementing localized scour protection measures for pipelines laid directly on the seabed is imperative.

[0003] Currently, local protection measures for subsea pipelines can be mainly divided into two technical approaches. The first is to reduce the intensity of seepage in the seabed beneath the pipeline, preventing seepage damage to the soil and resulting in localized scouring. This mainly includes methods such as rock dumping, soft drainage systems, rigid protective plates, deflector buoys, and artificial grass. The second is to promote the development of scour pits beneath the pipeline, causing it to fall into these pits and be naturally buried within them in a short period. This mainly includes methods such as spoilers and flexible protective plates. However, these methods currently have some shortcomings, primarily in the following aspects:

[0004] 1. High protection costs: Submarine pipelines are slender structures, while most protective devices such as rock dumps, soft rafts, and artificial turf can be several times the diameter of the pipeline. If protective devices need to be installed along the entire length of the pipeline, the manufacturing and construction costs of the devices are very high.

[0005] 2. Poor construction convenience: Most of the above-mentioned protective methods require additional installation after the pipeline is laid, which not only causes inconvenience in construction, but also leads to a window period of unprotected pipeline, increasing the risk of local scouring of the pipeline.

[0006] 3. High environmental impact: Rock dumping and soft riprap protection devices require continuous replenishment of washed-away sand and gravel throughout their life cycle, and long-term extraction of natural sand and gravel will seriously affect the ecological environment. In addition, the large-scale installation of soft riprap protection devices will isolate the exchange of matter and energy between the seabed soil and the water flow, destroy the living environment of marine benthic organisms, and may cause ecological imbalance.

[0007] 4. Poor Applicability: Submarine pipeline burial is an economical and efficient method for localized pipeline scour protection, and some projects have already implemented it. However, this type of protection typically requires relatively consistent water flow and soil conditions along the pipeline's route. Otherwise, inconsistent scour rate development can lead to long-distance pipeline suspension, ultimately jeopardizing pipeline safety. Many sea areas in my country do not meet this requirement.

[0008] Chinese patent CN210770654U discloses a subsea pipeline with a honeycomb structure. This pipeline comprises five layers: from the inside out, a steel pipe, an anti-corrosion insulation layer, a thermal insulation layer, a casing, and a concrete protective layer. The outer surface of the concrete protective layer is uniformly covered with a honeycomb structure, consisting of circular concave holes. The design optimizes four indicators using two parameters: depth ratio (DR) and area ratio (AR). The optimal combination of these four indicators determines the drag reduction effect of the subsea pipeline. However, this technical solution only reduces pipeline resistance by adjusting the flow field around the suspended pipeline, thus only addressing the flow field around the pipeline and neglecting the seepage field and scour issues within the seabed soil. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-cost, easy-to-construct, environmentally friendly, and widely applicable subsea pipeline with a porous media protective layer for local scour protection, which effectively suppresses the formation of scour pits under the pipeline and provides technical support for the safe operation of subsea pipelines.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] A subsea pipeline with a porous media protective layer comprises three layers, from the inside out: a steel pipe, a protective layer, and a porous media protective layer.

[0012] The porous media protective layer is a porous media wrapping layer with water permeability. The permeability coefficient of the porous media protective layer is 2-60 times that of the permeability coefficient of the seabed soil beneath the pipeline, and the thickness of the porous media protective layer is 0.05-0.25 times the outer diameter of the pipeline after removing the porous media protective layer.

[0013] Furthermore, a concrete counterweight layer may be provided between the porous media protective layer and the protective layer.

[0014] Furthermore, the porous media protective layer is selected from one or more of permeable cement concrete, recycled aggregate permeable concrete, and permeable asphalt.

[0015] Furthermore, the porous media protective layer is recycled aggregate permeable concrete.

[0016] Furthermore, the thickness of the porous media protective layer remains constant in the circumferential direction of the steel pipe.

[0017] Furthermore, the thickness of the porous media protective layer is 0.11 times the outer diameter of the pipe after removing the porous media protective layer.

[0018] Furthermore, the permeability coefficient of the porous media protective layer is 30 times that of the permeability coefficient of the seabed soil beneath the pipeline.

[0019] Furthermore, the protective layer is one or more layers and is installed on the outside of the steel pipe.

[0020] Furthermore, the protective layer is provided by a sleeve or a coating applied to the outside of the steel pipe.

[0021] Furthermore, the subsea pipeline with a porous media protective layer is laid on the seabed.

[0022] Furthermore, the porous media protective layer includes two technical indicators: the permeability coefficient k and the thickness d of the porous media protective layer. Based on the outer diameter of the subsea pipeline after removing the porous media protective layer, the properties of the actual seabed soil, and the actual marine hydrodynamic conditions, the above two technical indicators are comprehensively determined through optimization methods. The optimized combination of the two technical indicators can determine the protective effect against local scour of the subsea pipeline, specifically including the following steps:

[0023] 1. By using two parameters—the relative thickness d0 of the porous media protective layer and the relative permeability coefficient k0 of the porous media protective layer—two technical indicators of the subsea pipeline are normalized:

[0024]

[0025]

[0026] Where: d is the thickness of the porous media protective layer, in meters (m); D is the outer diameter of the subsea pipeline after removing the porous media protective layer, in meters (m); d0 is the relative thickness of the porous media protective layer, which is the ratio of the thickness d to the outer diameter D of the subsea pipeline after removing the porous media protective layer. It is dimensionless and represents the relative size of the permeable and impermeable parts of the pipeline cross-section; k is the permeability coefficient of the porous media protective layer, in meters per second (m / s); k s K0 is the permeability coefficient of the seabed soil beneath the pipeline, in m / s; k0 is the relative permeability coefficient of the porous media protective layer, which is the ratio of the permeability coefficient k0 of the porous media protective layer to the permeability coefficient k0 of the seabed soil beneath the pipeline. s The ratio is a dimensionless number, representing the degree to which the permeability of the porous media protective layer is improved compared to the seabed soil below the pipeline.

[0027] 2. Through seabed geological surveys, sampling, and corresponding indoor tests, the physical and mechanical properties of the seabed soil along the pipeline route are determined.

[0028] 3. Determine the marine hydrodynamic properties of the sea area through marine hydrological surveys and the collation of relevant marine hydrological and meteorological data.

[0029] 4. Input the physical and mechanical properties of the seabed soil and the hydrodynamic properties of the ocean into numerical simulation software based on computational fluid dynamics (CFD) to simulate the flow field near the subsea pipeline and the seepage field in the seabed soil below the pipeline under the action of ocean hydrodynamics, and analyze the variation law of seepage intensity in the seabed soil.

[0030] 5. The accuracy and reliability of the simulation of the flow field near the subsea pipeline and the seepage field below the pipeline were verified by indoor physical model tests (wave flow flume test).

[0031] 6. Using the two parameters of the relative thickness d0 and the relative permeability coefficient k0 of the porous media protective layer, combined with the simulation results of the seepage field of the seabed soil below the pipeline, and taking the seepage head gradient in the seabed soil as the objective function, the two technical indicators of the porous media protective layer, namely the permeability coefficient k and the thickness d, are quantitatively optimized to obtain the optimized technical indicators.

[0032] This invention provides a subsea pipeline with a porous media protective layer. The protection mechanism is as follows: by introducing a permeable porous media protective layer between the pipeline and the seabed soil, the seepage below the pipeline is guided to primarily pass through the more permeable porous media protective layer. This alters the seepage field in the seabed soil below the pipeline, reduces the seepage intensity, and inhibits seepage damage and localized scour below the pipeline, thus protecting the subsea pipeline. Furthermore, the permeability coefficient of the porous media protective layer is less than 60 times that of the seabed soil, preventing contact scour between the porous media protective layer and the seabed soil, effectively ensuring the stability of the seabed soil below the pipeline.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1. Low protection cost. Compared with existing subsea pipelines, the subsea pipeline of this invention only adds a protective layer with a thickness of less than 0.25 times the pipe diameter to the outer surface of the pipeline. Compared with the protective materials required by methods such as rock dumping, soft drainage, and "artificial grass" which require several times the pipe diameter, the material consumption is significantly reduced, resulting in lower protection costs. In addition, in the technical solution of this invention, the material of the porous media protective layer can preferably be permeable cement concrete or recycled aggregate permeable concrete. In this case, the porous media protective layer can simultaneously achieve the functions of counterweight and suppression of local scour of the pipeline, eliminating the need for a separate concrete counterweight layer, further reducing the cost of local scour protection for subsea pipelines.

[0035] 2. Convenient construction. The technical solution of this invention involves directly installing the porous media protective layer onto the surface of the submarine pipeline during prefabrication. This layer is then laid along with the pipeline during installation, eliminating the need for secondary installation and avoiding any unprotected window period for the submarine pipeline. Using this technical solution, the physical and mechanical properties of the submarine pipeline remain unchanged, and existing submarine pipeline laying methods are applicable.

[0036] 3. Low environmental impact. The porous media protective layer used in this invention has virtually no impact on the living environment of benthic organisms in the marine area after the pipeline is laid, and its impact on the marine ecological environment is minimal. If recycled aggregate permeable concrete is used to make the porous media protective layer, the concrete counterweight layer can be eliminated, and the environmental impact of the protective device will be further reduced throughout its entire life cycle.

[0037] 4. Good applicability. This invention starts from the mechanism of local scour of subsea pipelines, directly weakens the seepage intensity in the seabed below the pipeline, thereby inhibiting seepage damage and the occurrence of local scour. It achieves protection against local scour below the pipeline in principle. The effectiveness of the protection does not depend on the water flow and soil properties of the sea area where the pipeline is located. Therefore, it is applicable to subsea pipelines in different sea areas. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a subsea pipeline with a porous media protective layer.

[0039] Figure 2 This is a schematic cross-sectional view of a subsea pipeline with a porous media protective layer.

[0040] Figure 3 This is a schematic diagram illustrating the working principle of a subsea pipeline with a porous media protective layer.

[0041] Figure 4 This is a schematic diagram of the cross-section of a subsea pipeline with a concrete counterweight layer.

[0042] The attached figures are labeled as follows: 1. Steel pipe; 2. Protective layer; 3. Porous media protective layer; 4. Concrete counterweight layer; d. Thickness of porous media protective layer; A. Seepage through the porous media protective layer; B. Seepage through the seabed soil after being weakened by the porous media protective layer. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] The following embodiments are implemented based on the above-described technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0045] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0046] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0047] Example

[0048] This embodiment provides a subsea pipeline with a porous media protective layer, such as Figure 1 As shown, it includes a steel pipe 1, a protective layer 2, and a porous media protective layer 3;

[0049] In this embodiment, steel pipe 1 is the innermost layer of the submarine pipeline, used to transport various oil and gas products, water and other fluid media.

[0050] The protective layer 2 is a sleeve covering the outside of the steel pipe 1, which can play the roles of corrosion prevention, insulation, heat insulation, protection and fixation. It generally includes a heat insulation layer made of polyurethane foam, a corrosion prevention and insulation layer made of polyethylene, and a protective and fixing layer made of steel sleeve.

[0051] In this embodiment, the porous media protective layer 3 can simultaneously achieve the functions of counterweight and suppression of local scour of the pipeline. The porous media protective layer 3 covers the outer layer 2, increasing pipeline stability and protecting against external impact damage; it also suppresses local scour of the subsea pipeline. The porous media protective layer 3 includes two technical indicators: the permeability coefficient k and the thickness d of the porous media layer. Based on the outer diameter of the protective layer 2, the properties of the actual seabed soil, and the actual marine hydrodynamic conditions, the above two technical indicators are comprehensively determined through optimization methods. The optimized combination of these two technical indicators determines the protective effect against local scour of the subsea pipeline.

[0052] In this embodiment, the porous media protective layer 3 is made of recycled aggregate permeable concrete material. Its manufacturing process should meet the requirements of the industry standard "Technical Specification for Application of Recycled Aggregate Permeable Concrete" (CJJ / T 253-2016).

[0053] The subsea pipeline with a porous media protective layer provided in this embodiment is designed based on the engineering route selection scheme and the hydrological and geological data of the sea area to determine the marine hydrodynamic conditions and the physical and mechanical properties of the seabed soil. Through numerical simulation based on computational fluid dynamics (CFD) methods, combined with indoor physical model tests, the permeability coefficient k and thickness d of the porous media protective layer 3 are quantitatively optimized using the seepage head gradient in the seabed seepage field as the objective function. Finally, when the optimized pipeline is manufactured on land, the production process is basically the same as existing pipeline manufacturing processes. Existing subsea pipeline laying methods are applicable during pipeline laying. The optimization process specifically includes the following steps:

[0054] 1. By using two parameters, namely the relative thickness d0 and the relative permeability coefficient k0 of the porous media protective layer 3, the two technical indicators of the subsea pipeline are normalized:

[0055]

[0056]

[0057] Where: d is the thickness of the porous media protective layer, in meters (m); D is the outer diameter of the subsea pipeline after removing the porous media protective layer, in meters (m); d0 is the relative thickness of the porous media protective layer, which is the ratio of the thickness d to the outer diameter D of the subsea pipeline after removing the porous media protective layer. It is dimensionless and represents the relative size of the permeable and impermeable parts of the pipeline cross-section; k is the permeability coefficient of the porous media protective layer, in meters per second (m / s); k s K0 is the permeability coefficient of the seabed soil beneath the pipeline, in m / s; k0 is the relative permeability coefficient of the porous media protective layer, which is the ratio of the permeability coefficient k0 of the porous media protective layer to the permeability coefficient k0 of the seabed soil beneath the pipeline. s The ratio is a dimensionless number, representing the degree to which the permeability of the porous media protective layer is improved compared to the seabed soil below the pipeline.

[0058] 2. Through seabed geological surveys, sampling, and corresponding indoor tests, the physical and mechanical properties of the seabed soil along the pipeline route are determined.

[0059] 3. Determine the marine hydrodynamic properties of the sea area through marine hydrological surveys and the collation of relevant marine hydrological and meteorological data.

[0060] 4. Input the physical and mechanical properties of the seabed soil and the hydrodynamic properties of the ocean into numerical simulation software based on computational fluid dynamics (CFD) to simulate the flow field near the subsea pipeline and the seepage field in the seabed soil below the pipeline under the action of ocean hydrodynamics, and analyze the variation law of seepage intensity in the seabed soil.

[0061] 5. The accuracy and reliability of the simulation of the flow field near the subsea pipeline and the seepage field below the pipeline were verified by indoor physical model tests (wave flow flume test).

[0062] 6. Using the two parameters of the relative thickness d0 and the relative permeability coefficient k0 of the porous media protective layer, combined with the simulation results of the seepage field of the seabed soil below the pipeline, and taking the seepage head gradient in the seabed soil as the objective function, the two technical indicators of the porous media protective layer, namely the permeability coefficient k1 and the thickness d1, are quantitatively optimized to obtain the optimized technical indicators.

[0063] The technical specifications of a porous media protective layer for submarine pipelines were determined using the above methods, such as: Figure 2 As shown, the outer diameter of the subsea pipeline protective layer 2 is 559 mm, the near-bottom current velocity in the area is 0.452 m / s, and the permeability coefficient of the seabed soil beneath the pipeline is 2.80 × 10⁻⁶. -5 The permeability of the porous media protective layer 3 is 60 mm, which is 0.11 times the pipe diameter. The material of the porous media protective layer 3 is recycled aggregate permeable concrete. According to the method specified in Appendix A of the industry standard "Technical Specification for Permeable Cement Concrete Pavement" (CJJ / T 135-2009), the permeability coefficient of the porous media protective layer is measured to be 8.40 × 10⁻⁶ m / s. -4 The flow rate is m / s, which is 30 times the permeability coefficient of the seabed soil beneath the pipeline. According to CFD-based numerical simulation results, compared with traditional subsea pipelines, this type of subsea pipeline with a porous media protective layer reduces the seepage head gradient in the seabed soil beneath the pipeline by 30%, ensuring the safety and stability of the soil beneath the pipeline.

[0064] This embodiment employs a porous media protective layer made of recycled aggregate permeable concrete to suppress localized scouring of the subsea pipeline, making full use of waste concrete resources. The porous media protective layer also serves as a concrete weight-bearing layer for the pipeline. Installation of the porous media protective layer is completed onshore and then laid in place along with the pipeline. It has the advantages of low cost, convenient construction, low environmental impact, and widespread applicability. Furthermore, as... Figure 3 As shown, starting from the mechanism of local scour of subsea pipelines, the intensity of seepage in the seabed below the pipeline is directly weakened, thereby inhibiting seepage damage and the occurrence of local scour. In principle, this method can protect against local scour below the pipeline. The effectiveness of the protection does not depend on the water flow and soil properties of the sea area where the pipeline is located, so it is applicable to subsea pipelines in different sea areas.

[0065] In other embodiments, such as Figure 4As shown, to prevent the simple porous media protective layer 3 from failing to meet the counterweight requirements, a concrete counterweight layer 4 can be added between the porous media protective layer 3 and the protective layer 2. The design and fabrication of the concrete counterweight layer should meet the requirements of Section 12.3 of the oil and gas industry standard "Submarine Pipeline System" (SY / T 10037-2018).

[0066] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A subsea pipeline with a porous media protective layer, characterized in that, The submarine pipeline with a porous media protective layer comprises three layers, from the inside out: a steel pipe (1), a protective layer (2), and a porous media protective layer (3). The porous media protective layer (3) is a porous media wrapping layer with water permeability. The permeability coefficient of the porous media protective layer (3) is 2-60 times that of the permeability coefficient of the seabed soil under the pipeline, and the thickness of the porous media protective layer (3) is 0.05-0.25 times the outer diameter of the pipeline after removing the porous media protective layer. The porous media protective layer (3) is selected from one or more of permeable cement concrete, recycled aggregate permeable concrete, and permeable asphalt, which simultaneously achieves the functions of counterweight and inhibiting local scouring of the pipeline. The submarine pipeline with a porous media protective layer is laid on the seabed. The porous media protective layer (3) guides the seepage below the submarine pipeline through the porous media protective layer (3), changes the seepage field in the seabed soil below the submarine pipeline, reduces the seepage intensity in the seabed soil, and inhibits the occurrence of seepage damage and local scouring below the submarine pipeline, thereby achieving protection for the submarine pipeline.

2. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, A concrete counterweight layer (4) is also provided between the porous media protective layer (3) and the protective layer (2).

3. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The porous media protective layer (3) is made of recycled aggregate permeable concrete.

4. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The thickness of the porous media protective layer (3) remains constant in the circumferential direction of the steel pipe (1).

5. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The thickness of the porous media protective layer (3) is 0.11 times the outer diameter of the pipe after removing the porous media protective layer.

6. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The permeability coefficient of the porous media protective layer (3) is 30 times that of the permeability coefficient of the seabed soil beneath the pipeline.

7. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The protective layer (2) is one or more layers and is installed on the outside of the steel pipe (1).

8. The subsea pipeline with a porous media protective layer according to claim 1, characterized in that, The protective layer (2) is provided by sleeve or coated on the outside of the steel pipe (1).

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