In view of the CO2/H2S corrosion of buried oil pipelines, the corrosion mechanisms of pipelines are investigated and some related influencing factors are analyzed. Taking Q235 steel for the buried oil pipelines of an oilfield as the case, the CO2/H2S corrosion behavior of Q235 steel is tested by using corrosion testing device and SEM; and the influence of different factors, such as temperature, Cl ion concentration, CO2 partial pressure, H2S partial pressure, and pH value, is studied in the simulated buried pipeline environment by using orthogonal experimental design method. On this basis, the corresponding CO2/H2S corrosion rate prediction model of pipelines is established by using Grey-Neural Network Theory, which has high prediction accuracy and credibility by an example of verification. According to the results, the protective measures are presented by adopting the Cathodic Protection Technology and Chemical Anti-corrosion Technology etc, which has certain guidance for the extension of pipeline-life and improving the economic benefits of pipelines.
Based on the free sliding phenomenon of the monopterus albus in the cave, an oil-tolerant and easy-wetting viscoelastic system (A3B4C3E5F2) was selected and compounded as a possible lubricant to enable the transportation of heavy crude oil. In the viscoelastic system, the final floating equilibrium velocity of LD1 crude oil droplets with a diameter of about 5 mm is 0.01853 mm/s, and the floating resistance coefficient (CD) is 11067862, which shows favorable oil suspension performance. When the shear rate is approximately zero, the viscosity of the viscoelastic system is about 7000 mPa·s. However, when the shear rate is up to100 1/s, the viscosity is only about 32 mPa·s. A high viscoelastic film is formed at shutdown or low flow rates. Conversely, a low viscosity liquid ring formed at high flow rate. After being wet by easy-wetting viscoelastic system, the contact angle between LD1 crude oil and common pipe materials is wider than 160° at 30 min. The incubation time (t0) and the wettability composite index (WCI) are shorter than 1800 s and higher than 4800, respectively. Upon stability evaluation, the system can maintain good viscoelasticity and wettability in the range of temperature (5 ∼ 90 °C), oil content (0 ∼ 15 wt.%), and shear rate (0 ∼ 1000 1/s), respectively.
The Ar-Sai waxy crude oils were taken as the research objects, and the viscosity reduction rates and the condensation point reduction rates were regarded as the evaluation indexes, the impacts of components content of the crude oils and carbon number distribution of waxes on the modification effect of EVA-type pour point depressant (PPD) were analyzed by using gray correlation analysis method. The oil wax was acquired by applying the extraction and separation techniques initially, then the structures and the lattice parameters of wax crystals before and after adding the PPD were studied by polarized light microscopy observation and x-ray diffraction techniques, the mechanism of pour point depression was discussed at last. The results indicate that wax content and the low carbon number wax have significant influences on the modification effect of PPD, while the impact of high carbon number wax is relatively small. Co-crystallization is the main mechanism of pour point depression, nevertheless, the impacts of the asphaltenes, resins, solid particles, and light components of the crude oils on the modification effect of the PPD cannot be ignored.
With the depletion of conventional light crude oil, heavy crude oil will occupy an increasing share of the energy structure in the 21st century. Heavy crude oil is characterized by an API gravity of 10 to 22.3 or a viscosity of 0.09 to 10 Pa·s. The flow of heavy crude oil in the pipeline is laminar in the higher viscosity range and turbulent in the lower viscosity range, and its flow resistance comes from the viscous force between the oil and the wall or the additional stress of turbulent flow. Hence, pipeline transportation of heavy crude oil is faced with a huge loss of frictional resistance, which means a reduction of the transportation efficiency. To decrease pump power consumption, improving the transportation efficiency of heavy crude oil pipelines is a key factor. In recent years, some biomimetic technologies that reduce the flow resistance of viscous oils have made new progress in improving their fluidity and have not yet been put into use in commercial pipelines. Therefore, it is important and appropriate to discuss the breakthrough achievements and progress made by researchers in the drag reduction (DR) of heavy crude oil and to summarize its advantages, disadvantages, and potential problems. This review discusses boundary layer control methods for heavy crude oil drag reduction. First, conventional DR technologies, such as polymers, surfactants, fiber suspensions, oil–water core annular flow (CAF) and oil–aqueous foam CAF, and potential DR technologies, including oleophobic surfaces, flexible walls, biomimetic microgrooves, and ferrofluid annular DR under magnetic confinement, are presented. Second, the mechanism of DR is investigated and summarized; the highlights and progress of the technology are reviewed, and new ideas to improve the existing DR technology are proposed. Finally, the challenges and prospects of DR are presented.
Water-lubricated oil–water flow is an effective low-energy consumption method for pipeline transportation. This study proposes a novel wellbore lubrication fitting (WLF) for developing a core-swirling flow to reduce flow resistance and enhance lubrication efficiency. The pressure drop across the lubricating fitting, the maximum oil volume fraction at the overflow outlet and the drag reduction percentage of core-swirling flow were taken as the indicators, and the fluid calculation software Ansys Fluent was applied to optimize the structural parameters of the WLF with orthogonal and single-factor methods. The experimental study was carried out with mineral oil and tap water. The results indicate that the swirl generator can develop a stable and low-viscosity liquid annulus to isolate the oil from the pipe wall and reduce the flow resistance of viscous oil. The optimized WLF demonstrates the clear core-swirling flow with input velocity between 0.48 and 0.62 m/s. The experimental pressure drops deviate from the simulated data within ±25%. The drag reduction percentage of the core-swirling flow is above 90% with the input velocity above 0.51 m/s. The results of this study have important engineering value for efficient application of WLFs.
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