Deepwater Pipeline Research Articles

Based on PVM image gray level data to analysis the effect of N-vinyl caprolactam on hydrate growth

The usage of hydrate inhibitors is an effective method to solve the problem of flow assurance in deep-water pipelines. However, the mechanism of hydrate formation and transformation in inhibitor-containing systems is not well understood, and the research methodology needs to be innovated. In this study, a possible mechanism of wearing away during hydrate particle transformation was proposed for the first time, based on the hydrate growth process in the system containing the kinetic inhibitor N-vinyl caprolactam monomer. A method to analysed the hydrate growth and transformation dynamics through the change of gray level in the image was proposed. And the hydrate growth process was divided into three different stages based on the trend analysis of the gray level data of the images,trends in the dynamics of hydrate particle growth within the bulk phase corresponding to changes in gray level were verified. On this basis, the effects of stirring rate, subcooling and the monomer concentration of the NVCap on the growth of hydrates were discussed, and it was suggested that there might be differences in the mechanisms exhibited by the inhibitor at different growth stages of hydrates. In this study, the process of analysing the internal growth dynamics of hydrate systems through image gray levels was reported for the first time, and its trend changes corresponding to hydrate growth dynamics were verified, which proved the feasibility of this method, and this study provides an innovative research methodology and idea for the study of the dynamics of hydrate generation and transformation.

Establishment of constitutive model and simulation study on sealing performance of special-shaped rubber cylinder for inner packer in deepwater pipeline

It’s important to improve the sealing performance of the inner packer in deepwater pipelines, which is an emergency sealing and oil control equipment. The deformation characteristics and sealing stress conditions of the packer’s sealant cylinder are analyzed, and the hyperelastic constitutive model is determined based on uniaxial tensile experiments. The effective contact stress and effective contact range between the rubber cylinder and the pipe wall are the main parameters for evaluating the sealing performance. Through simulation, it was found that the rubber cylinder on the force application side plays a major sealing role, and severe stress can lead to shoulder protrusions. The location of fatigue damage on the rubber cylinder’s shoulder is consistent with the sea trial. Therefore, special-shaped rubber cylinders with different structures are designed to address the shoulder protrusion. The simulation shows that the sealing performance of the right-angled trapezoidal double-layer rubber cylinder with force applied on the slope side(S-RARC) is significantly better than the original rubber cylinder(ORC), and it does not produce shoulder protrusions.

Effect of wax on hydrate formation and aggregation characteristics of water-in-oil emulsion

In recent years, the formation and aggregation of wax and hydrate under the condition of coexistence has become a hot spot in the safety assurance of deep-water pipeline flow. In order to clarify the influence mechanism of wax and hydrate in deep-sea crude oil under coexistence conditions, the effects of different wax-containing conditions on the nucleation, growth and aggregation characteristics of hydrate in oil–water emulsion were studied by macroscopic and microscopic experimental equipment. The results show that low wax content (0–3.wt%) provides nucleation sites for hydrate formation and thus promotes hydrate formation. High wax content (>3.wt%) inhibits hydrate formation by preventing water droplets from contacting gas molecules. Low wax content (0–3.wt%) significantly reduces hydrate interparticle aggregation. High wax content (>3.wt%) promotes hydrate interparticle aggregation, which changes the flow characteristics of the hydrate slurry. In addition, through further analysis by PVM and high-speed camera, a wax-containing hydrate aggregation mechanism model was established.

Friction Performance of Rubber Sealing Disc Inside Pipe Robots for the Production of High-Paraffin Oil

The in-pipe robot is the most commonly used technique in offshore pipelines. The use of rubber sealing discs is important for in-pipe robots to ensure that the robots are moved by fluid pressures inside offshore pipelines. This paper focuses on the measuring and modeling of the wax–oil gel-breaking process at the soft frictional area between sealing discs and the pipe wall. In this study, a detailed characterization of the gel-scraping process and in situ probing portable microscopy are performed. Two contributions are made in this study. First, a direct observation of wax–oil deposition breaking is employed to detect the minute changes at the in-pipe robot. Second, we find that a simple function is possible to describe the relationship between the wax contents and dewaxing efficiency, in which the debris material removal ratio (DRR) is discussed. Thus, the gel deposition-breaking phenomena are quite different under the influence of rubber sealing discs. This result is further confirmed by the real contact ratio measurements. It is important to research the sealing disc further and apply it more in the petroleum industry, especially in in-pipe robots for deepwater pipeline systems.

Heat transfer characteristics of subsea long-distance pipeline subject to direct electrical heating

For deep-water pipelines with long tie-back distances, high external pressure, and low ambient temperature, it is a key issue to ensure flow safety by controlling the generation of hydrates and waxes through electric heating technology. In-detail analysis of the heat transfer performance of electric heating pipelines is of great engineering significance for developing the safety of pipeline flow in offshore oil-gas fields. This paper proposed an electrical heating analytical method applicable to long-distance submarine pipelines. Based on the thermal equilibrium theory and the differential equation of heat conduction, a mathematical model of heat-fluid coupling for electric heating pipes is established, involving the theoretical model of the steady-state distribution of the electric heating in the axial and radial directions. Then, the definition of the average temperature of the pipeline is introduced and combined with the two-point Hermite approximation interpolation method, and an improved lumped parameter model of the transient heat transfer of the electric heating pipeline is established. Meanwhile, the finite difference method is applied to solve the ordinary differential equation of the pipeline and the energy equation of the internal fluid. The steady-state calculation result is utilized as the initial value of the transient heat transfer process, and the model is applied to analyze the influence variation on the transient temperature response characteristics of the pipeline under different working conditions, finally determining the prediction formula of the average temperature of the fluid under normal transportation and shutdown conditions.

Design and characterization of subsea pipeline rehabilitation connectors

This paper examined the technology for repairing deep water pipelines and designed a new type of subsea pipeline repair connector for a depth of 1500 m with a diameter of 12 inches. The technical specifications of subsea pipeline repair connectors and the characteristics of deepwater environments were used to propose an overall design plan. Static analysis, elastic mechanics theory, and finite element simulation were used to analyze contact stress distribution on the main rubber sealing ring surface. A mathematical relationship was evident between the axial driving force and positive anchoring pressure. A mechanical model was established for the free and constrained deformation stages of the rubber sealing ring and the relationship between the sealing driving force and contact stress. The structure was optimized using the contact stress distribution law. The anchoring and sealing performance of the designed connector were analyzed and optimized.

Development of Predictive Model for Wax Formation in Deep-water Pipeline Using Machine learning

Wax deposition in deep sea pipelines can affect oil and gas production. It happens when the pipeline temperature drops below the wax appearance temperature, causing the wax to solidify and stick to the pipeline walls. This paper discusses the limitations of current models in predicting wax deposition in pipelines and proposes the development of more complex, intelligent models that are accurate, resilient, and adaptable to novel input-output scenarios. It also highlights various methods for preventing wax deposition, including the use of chemical inhibitors and thermal remediation techniques. The paper aims to develop a neural network modeling approach for predicting wax deposition potential in producing reservoirs to prevent accumulation before removal. The parameters that were used are wax molecule concentration gradient at pipe wall, temperature gradient at pipe wall, reported wax deposition rate, the pipe wall shear stress, and crude oil viscosity. The radial basis function neural network (RBFNN), is based on the machine learning technique. RBFNN is a good choice for building a predictive wax deposition rate model because it is highly accurate, robust to noise and outliers, computationally efficient, can model complex nonlinear relationships, suitable for real-time applications and requires less training data. The RBF neural network is constructed using MATLAB. The outcomes and experimental data are consistent with a 1.5 percent relative inaccuracy when compared to prior studies. The R^2 value was 0.9906, R value was 0.9953 and the RMSE value was 0.8598. The RBF neural network-based approach for predicting wax deposition rate was successful.

Stress Analysis of Pipe-In-Pipe Systems under Free Span for Deep Water Pipeline Applications

This study examined the phenomena of free span for a pipe -in- pipe (PIP) system for pipeline application. Two different span length of 8 and 30 meters are modelled and simulated using nonlinear stress analysis. The effect of pressure, temperature and gravity on the PIP system are determined and compared with conventional single pipeline. From the results obtained, it is clear that the finite element analysis (FEA) results correlated very well with those calculated using analytical methods. Percentage differences were generally less than 10%, with some discrepancies which were due to assumption of thin-walled theory which assumes a radial stress equals to zero, whereas the FEA calculates a non- zero radial stress. The key finding in this study demonstrated the strong potentials of PIP system in terms of structural reliability for deepwater pipeline application. Specifically, the 30m single pipe in free span (with pressure and temperature) deflected 205.1mm, more than double the corresponding PIP. This knowledge can be beneficial to selection and design considerations for pipeline system responses to both the gravity, thermal and pressure loading as well as the potential failure modes that may results in a typical scenario. Various theoretical calculations of stresses are used to validate the finding in this study of the single pipe and PIP models for flat seabed and free span.

Investigation of the process of pipeline penetration at a shallow embedment in clay with large-deformation analysis

Pipe-soil interaction is an essential aspect of a deep-water pipeline system. It may significantly influence both the structural behavior and integrity of the pipeline during installation and operation. The pipe embedment is an important factor influencing the pipe-soil interaction for an exposed pipeline. The embedment will determine the boundary conditions around the pipe for the subsequent loading scenarios. In this paper, based on the assumption of plane strain, the “Remeshing and Interpolation Technique with Small Strain” (RITSS) method was used to establish the large deformation finite-element model of vertical penetration of pipelines in clay. Compared with the previous literature, the robustness of the model was verified. Based on this model, the development mechanism of the soil shear band has been discussed during pipeline penetration; the effect of pipeline roughness on the undrained shear strength degradation mechanism and enhancement mechanism has been further explored. Finally, the effects of soil buoyancy, soil strength gradient, strain softening, and strain rate on the penetration resistance were discussed through parametric analysis. According to the influence sensitivity of each parameter, the evaluation framework of the penetration resistance has been developed. Compared with the previous literature, the validity of the framework was verified. The framework could provide guidance and reference for designing vertical penetration of pipelines in deep-water engineering.

Numerical study of microwave impact on gas hydrate plugs in a pipeline

Purpose. Development of a technique for the numerical study on the decomposition of gas hydrate plugs in deep-water pipelines under microwave radiation using a coaxial source. Theoretical efficiency evaluation of using such an impact to unblock the pipelines. Methodology. Mathematical modeling and computational experiment. Findings. An original mathematical model is proposed to describe heat transfer processes during the decomposition of gas hydrates in a pipeline under the action of heat sources distributed over the volume. The non-stationary problem of heat transfer was considered in a one-dimensional formulation. An algorithm for numerical computation is proposed. A mathematical expression is obtained for distributed heat sources generated by the microwave radiation from a coaxially located SHF antenna. Parametric numerical studies on temperature fields and decomposition dynamics of a gas hydrate plug are performed for specified parameters of pipe and microwave radiation power. The boundaries of the decomposition area and the dynamics of change in this area are determined. The decomposition time of a gas hydrate plug with a diameter of 0.3 m was determined using a 300 W microwave source. The complete decomposition took approximately 40 hours. Originality. The task of thermal decomposition of a cylindrical gas hydrate plug in a pipeline due to microwave heating using a coaxial microwave power source has been considered for the first time. The process is viewed as a sequence of several stages: heating, heating and decomposition, decomposition after complete heating of the gas hydrate layer. To model the volumetric dissociation of gas hydrate, it was proposed to use special functions that characterize the amount of decomposed gas hydrate. The introduction of such functions makes it possible to construct an efficient computational algorithm taking into account the action of volumetric sources in the decomposition area. The known models mainly consider only surface thermal effect or microwave impact on gas hydrate in porous mediums. The presented model allows describing the decomposition during volumetric heating of a solid hydrate adequately. Practical value. Blocking plugs may occur due to hydrate formation when transporting gas through deep-water pipelines or through pipelines in cold environments. The elimination of such complications is a complex technical task. In particular, a special source of microwave radiation, which was proposed by the authors in previous works, can be used to unblock the pipeline. The device that makes the microwave radiation is located along the pipe axis. The results of this work allow us to evaluate the effectiveness of the microwave method for eliminating the gas hydrate plug. The mathematical model and computational method can be used in the development of appropriate technologies using a coaxial microwave heating source.

Pressure prediction in deep-water pipeline considering formation of natural gas hydrate

Pressure in the deep-water pipeline is an important parameter that should be carefully predicted to control the natural gas transport in petroleum industry. However the present methods to predict pressure along the deep-water pipeline are complex and time-consuming. Some methods even ignore the formation of natural gas hydrate leading to the inaccurate pressure prediction. In this work, we proposed a model to predict the pressure along the deep-water pipeline considering the reduction of pipeline radius induced by the formation of natural gas hydrate. The model was validated by experimental data and was applied to the real deep-water pipeline in China. Results indicate that the decline of pressure in the pipeline is mainly caused by the reduction of pipeline radius due to the formation of natural gas hydrate compared with the flow resistance caused by viscous flow. The decline of pressure becomes faster against time with the 40% pressure loss at the fifth year of natural gas transport. This model enables to obtain the pressure values in the deep-water pipeline with high accuracy and good convenience.

The influence of underwater work on the functions of attention, thinking, fine muscle coordination and subjective assessment of the state of the body of divers

Introduction. Currently, there is an increasing need for the study and development of the World Ocean, including for the purpose of laying deep-water pipelines, searching for new sources of minerals, etc. The performance of special tasks by divers at great depths has its own characteristics. The high cost of error, harmful working conditions - all this dictate the need for continuous receipt and analysis of scientific material on the preservation and promotion of health, ensuring their longevity, as well as the adaptation of divers to the nature and conditions of professional activity in order to prevent the occurrence of errors. The study aims to explore the functions of attention and thinking of a person, his fine muscular coordination and subjective assessment of the state of the body of divers, as elements of the functional state of the body, when working underwater. Materials and methods. We examined 18 divers, divided into two groups: the first - ten people made daily descents to a depth of 18 m, the second group - eight people dived to a depth of 56 m. Before and after diving, the divers underwent a psychophysiological examination to assess the function of attention (the method of the correction test with Landolt rings), the function of thinking (the method of the arithmetic test "addition in mind"), fine muscle coordination (the method of macrography) and subjective assessment of the state (the SAN questionnaire (state of health - activity-mood)). Results. During diving operations, there was a decrease in subjective self-assessment of the state of the body (SAN test), an increase in the number of errors (correction test with Landolt rings - attention function) and the values of the height index of numbers (macrography technique - fine muscle coordination), a decrease in the speed of thinking depending on the depth, the multiplicity of diving descents, as well as the dive itself (regardless from depth and multiplicity) on the functional state of divers. There were most pronounced changes during prolonged work (3-5 days or more) and when diving to a depth of 56 m. Conclusion. The dynamics of objective indicators and subjective assessment of the state of the body indicates that with an increase in the depth of immersion (from 18 to 56 m), the multiplicity of diving descents (daily immersion for 5 days) and the dive itself, the self-esteem of the state, the speed of thinking, attention, fine muscle coordination decreases. Ethics. The study was conducted in compliance with the Ethical principles of conducting medical research with human participation as a subject, set out in the Helsinki Declaration of the World Medical Association.

Ductile Fracture Prediction of X80 Pipeline Steel Using Void Growth Model

In this study, the Void Growth Model (VGM) is employed to predict the ductile fracture of X80 pipeline steel. The X80 pipeline tends to be applied in challenging scenarios, such as extremely deep water and long-distance pipelines, which might cause a ductile fracture; however, the study of ductile fractures for pipeline steel is rare, especially for X80 pipeline steel. To understand ductile fractures of X80 pipeline steel, a hybrid numerical–experimental calibration method is used to determine the fracture parameter for the VGM model. The toughness capacity defined by the critical void growth index (VGI) in this study is determined to be 4.304. A shear-tension specimen is applied to verify the calibrated VGM. The results show that the calibrated VGM can predict the fracture initiation of the shear-tension specimen. In addition, the fracture of the shear-tension specimen initiates at the center of the section and propagates to the edge of the groove of the specimen. The initiation of fracture is identical to the testing observation.

Feasibility of Middle East-to-India Pipeline Examined in Study

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202396, “Middle East to India Pipeline,” by Ian Nash and Matthew Rawlings, SPE, Peritus International. The paper has not been peer reviewed. The complete paper addresses the conceptualization and planning of a Middle East-to-India deepwater pipeline (MEIDP), which is planned to reach a record water depth of 3450 m and cross two continental slopes, an earthquake subduction zone [the Owen Fracture Zone (OFZ)], and outfall debris of the Indus River Fan in 2500-m-deep water. The authors examine the techniques, analysis, and technology development available at the time of writing to make such challenging routes increasingly feasible. Introduction India relies on regasification of liquefied natural gas (LNG) with terminals at major port locations. The Middle East has ready supplies of gas; however, significant challenges exist for a long-distance, ultradeepwater pipeline. South Asia Gas Enterprise (SAGE) has been developing the MEIDP as a transnational gas infrastructure project to deliver 1.1 billion scf/D from Oman to the Gujarat coast of India by a deepwater route across the Arabian Sea (Fig. 1). The pipeline will be laid as a common carrier pipeline wherein SAGE would be the gas transporter and pay a tariff for pipeline use. Gas buyers and gas sellers will negotiate long-term gas-supply contracts in a tripartite framework agreement. The current work builds on the extensive study of a potential deepwater route of the Oman-to-India pipeline performed in the early 1990s. Economic and political drivers for the project, including project economics, are detailed in the complete paper.

Безопасность морских газопроводов

Due to the nature of the development of gas transmission network, the problem of ensuring reliability and safety of the underwater gas pipelines was practically exhausted by the calculation of underwater crossings through the rivers, lakes, and other water barriers. However, in recent years in connection with the development of oil and gas fields on the shelf, and the globalization of the gas transmission network, the question came up related to designing, building, and subsequently ensuring the stable operation of the offshore deep-water pipelines. Individual information about the accident rate of the offshore pipelines is given. They mainly concern the coastal pipelines transporting raw materials from the offshore production platforms to the onshore terminal. The largest number of accidents is typical for the pipelines of small diameters (2–6 inches) — 59 % of their total number. A group of medium-diameter pipelines (8–16 inches) accounts for 32 % of accidents. Pipelines of large diameter (18–36 inches) are the least susceptible to damage — about 3 % of accidents. In recent decades, the offshore main gas pipelines were widely used and are considered as the most promising way of transporting gas due to higher reliability, safety, and environmental friendliness, as well as the advantages of direct Analysis is presented in the article concerning the accident rate and features of failures of the offshore gas pipelines. The criteria of limit states and the algorithm for calculating the stress-strain state of the offshore pipeline, which are the main part of the safety assessment, are given. Methodology for the safety of the offshore gas pipelines was developed, based on which the example of the safety assessment of the Blue Stream gas pipeline is given. The materials of the article were used in the development of the projects for the offshore gas pipelines and are also included in the industry regulatory document.

Numerical simulation of deepwater S-lay and J-lay pipeline using vector form intrinsic finite element method

S-lay and J-lay systems are progressively utilized for deepwater pipeline installation. The paper presents a simple and feasible model for the static and dynamic analysis of S-lay and J-lay pipelines. This mechanical model of the laying pipeline is established by the combination of the vector mechanics principle with the numerical technique based upon the vector form intrinsic finite element (VFIFE) method. The internal forces resulted from element deformations and node rotations as well as the external forces due to hydrodynamic loads and the boundary interactions are fully taken into account. The movement governing equation of pipeline particles is solved by the explicit central difference approach using program coding. Two numerical models of a 12-inch pipeline being laid to 1000 m water depth are created in order to illustrate in detail the modeling process of S-laying and J-laying pipeline, respectively, and also verify the feasibility of the VFIFE model with a reasonable accuracy for deepwater pipeline installation. The effects of wave height and sloping seabed on the pipeline responses are identified and the noticeable differences of the pipeline behaviors between the S-lay and J-lay operation are observed. The results offer a significant reference for the installation design of the offshore pipeline.

Sealing reliability assessment of deep-water oil and nature gas pipeline connector considering thermo-mechanical coupling

The deep-water pipeline connector (DPC) is a key piece of equipment for the connection of multiple facilities located in different positions of the subsea production system. Its sealing reliability affects the safety of the production system directly during oil and gas exploration. Although the reliability assessment methods of the DPC have been investigated, previous studies have mostly been carried out under a single mechanical field. To determine the DPC reliability considering thermo-mechanical coupling, this paper establishes random load models of working pressure and temperature by using the Gaussian function, and the stochastic finite element model of the DPC is constructed to obtain the sealing performance under coupling conditions. A Kriging–Sobol sensitivity analysis method is developed to obtain the main variables influencing the sealing performance for the purpose of decreasing the computational cost of the ordinary sensitivity analysis. A reliability assessment approach based on the cross entropy-importance sampling-Kriging method is introduced to analyze the DPC reliability, and a sealing reliability assessment method of DPC under thermo-mechanical coupling conditions is finally formed. An engineering case is taken to verify the effectiveness of the proposed method. The results show that the reliability analysis accuracy of the proposed method is almost agreed with the Monte Carlo method, but the computational cost can be reduced 85.61%, which indicates that the proposed method provides designers with a fast method with an acceptable computational cost to assess the reliability of the DPC connector under coupling conditions.

BUCKLING ANALYSIS OF DEEPWATER PIPELINES BY VECTOR FORM INTRINSIC FINITE ELEMENT METHOD

Local buckling damage is one of the biggest safety issues during the operation of deepwater pipelines. The innovative vector form intrinsic finite element method (VFIFE) is used to analyze the buckling behavior of deepwater pipelines. After deriving the calculation formula of VFIFE space shell elements considering the nonlinear elastoplastic material, we developed a Fortran calculation program and a MATLAB post-processing program to simulate the collapse and buckling propagation process. The collapse pressure and the buckling propagation pressure were calculated. A full-scale pressure chamber test was conducted to analyze the buckling load and buckling morphology. The VFIFE results were compared with those of the test, traditional finite element method (FEM) and DNV method. The VEIFE can directly simulate the pipeline collapse, the buckling propagation, the collapse pressure, and the buckling propagation pressure. The VFIFE results are in line with the actual situation and in good agreement with those of the other methods. The VFIFE has the advantages of not requiring special calculation processing and tracking of the entire behavior, thus providing a new and universal analytic strategy for buckling simulation of deepwater pipelines.

Viscosity investigation on metastable hydrate suspension in oil-dominated systems

Predicting the viscosity of hydrate slurries is essential in evaluating the transport performance of oil and gas in deep-water pipelines and the risk of blockage. In this work, based on the Camargo–Palermo model and the bimodal suspension model, a new viscosity model was developed for hydrate slurries. In this model, the viscosity of slurry is determined jointly by small hydrate particles and larger hydrate aggregates, in which the maximum critical diameter of the aggregate is controlled by shear force and cohesion force, while amount of hydrate particles and aggregates can be described by a dimensionless parameter proposed. In addition, rheological measurements of methane hydrate slurry formed from water-in-oil emulsion were conducted with a high-pressure rheometer to validate the developed model. The predictions of the model agree well with the experimental data for metastable hydrate suspension in oil-dominated systems with either different initial water cuts or different water conversion rates.

Assessment of the Acoustic Reflectometry Technique to Detect Pipe Blockages

Abstract Flow assurance is an important aspect of deepwater pipeline design and operation since one of the critical issues is the eventual initiation and growth of hydrate or paraffin blockages under certain conditions. Another relevant problem is the incidence of inorganic scale deposition in oil well production tubes during operation. Offshore operators can obtain enormous benefits if information regarding the position and extent of an eventual blockage is available since mitigation measures can be optimized. This work deals with experimental and numerical simulations of an acoustic system to identify and measure blockages. The technique uses a short duration acoustic pulse that is injected into the pipe. When the pulse encounters an impedance discontinuity, a portion is reflected toward the acoustic source. The analysis of the measured signal reflections can provide valuable data related to the location and size of the blockages. An experimental setup with a steel pipe of 4 in. internal diameter and length of 100 m was developed to evaluate the suitability of the technique for gas pipelines. In parallel, finite element analyses were performed using the commercial software abaqus to simulate the same physical parameters. The experiments were numerically reproduced with good correlation proving the potential of the technique. Subsequently, a parametric study was carried out to examine the acoustic detection capability using different blockage types. Finally, a prototype of the acoustic reflectometry detection system was developed and tested in a full-scale onshore water-filled pipeline to show the feasibility of the method for detecting blockages.