Transport Of Hydrocarbons Research Articles

Microstructural and mechanical characterization of HSLA X70 Welded joints using eddy current testing (ECT)

This paper proposes an approach for measuring the mechanical properties by non-destructive testing techniques using eddy current testing (ECT), for a welded and heat-treated microalloyed material (X70) dedicated to hydrocarbon transport. This study offers a new measurement method based on linear approach, to expect mechanical property in microstructures by using Non-destructive testing (ECT) that can apply to mechanical systems, materials, weldments, etc. The result show that hardness measurements are in broad have the same trend with impedance function which depend of heat treatment variable applied to weld joint.

The self-diffusivity of natural gas in the organic nanopores of source rocks

Natural gas stored in source rocks has become a significant contributor to supply the energy demand. Source rocks are a special subclass of sedimentary rocks where the matrix serves as both the source and the reservoir at the same time. Attributed to their complex mineralogy and multi-scale pore systems, source rocks exhibit transport and storage processes that are not within the continuum framework. Significant portion of source rocks pores is of few nanometers in size. These nanopores offer large surface area to host hydrocarbons in the free and sorbed forms. Our ability to model the mechanisms by which hydrocarbons are stored and transported is, however, at infancy stages. In this paper, representative organic nanopores were formed from kerogen at different thermal maturation states. Free molecular diffusion was found to be the dominant mechanisms based on the calculated Knudsen number. Furthermore, diffusivity analysis was performed using molecular dynamics for some range of pressure that is typically encountered during the production span. The results revealed some deviation of the diffusivity coefficient from the value calculated theoretically. The deviation was even more pronounced for the post-mature case. The gap between the theoretically calculated and molecularly simulated diffusivity coefficients was found to reduce with increasing the pressure and the pore size. The sorption and diffusion data were coupled to redefine the mean free path for gas transport in organic nanopores. The reported values can serve as input for better description of the hydrocarbons transport in source rocks.

NORTHERN SEA ROUTE: CLASSIFICATION OF EMERGENCY SITUATIONS

The purpose of the work is to study the theoretical problem concerning the completeness of the classification of emergency situations in relation to maritime spaces in the Arctic zone, and to develop on this basis scientific proposals for improving Russian legislation. The relevance of the chosen topic is predetermined by the increasing importance of the Northern Sea Route as a global transport communication in the face of the possibility of occurrence in the Arctic as a result of climate change and anthropogenic impact of events that entail catastrophic environmental consequences, the formation of global risks for the economy, population, environment and state security. The relevance of the proposed materials is due to the implementation of large-scale economic and environmental projects by Russia, the provision of defense and security, the sea transportation of hydrocarbons, and potential terrorist threats. The classification of situations serves as the basis for management decisions on rescuing people at sea, protecting the environment and eliminating oil spills in difficult environmental conditions. Classification as a method of scientific knowledge correlates with the goals of its application, which determines its scientific and practical significance in this work. As a result of the analysis of regulatory legal acts and scientific publications, the author identified a gap in the classification of emergencies at sea and substantiated the conclusion that it is necessary to develop a proposal to fill it by improving legislation.

ON THE ANALYSİS OF OPERATİNG PRACTİCES OF LİQUEFİED GAS PİPELİNES

ON THE ANALYSİS OF OPERATİNG PRACTİCES OF LİQUEFİED GAS PİPELİNES

Molecular dynamics study of fluid-fluid and solid-fluid interactions in mixed-wet shale pores

Mixed wet pores are abundant in shales, yet there is little to no information on the behavior of fluids confined within pores characterized by one hydrophilic and one hydrophobic surface. This mixed wettability can impact fluid storage, distribution, capillary pressures and transport. In this study, we use molecular dynamics simulations to describe the initial distribution of reservoir fluids, such as multicomponent hydrocarbon mixtures and water, in mixed-wet pores. This is an essential pre-requisite to additional studies documenting fluid transport in such pores. The molecular model of the mixed wet pore used consists of kerogen separated by some distance from two clay surfaces. We evaluate spatial distribution of water and individual hydrocarbon species, at varying values of water concentration. Throughout the entire study, the results from the equilibrated system indicate a high affinity between the heavy components, such as the asphaltene/resin fraction and the kerogen surfaces. The more surprising result is the hydrogen bonding observed between the polar constituents in the asphaltene/resin fraction and water. This creates a situation where the asphaltene/resin fraction shows an affinity towards water. When this happens, the hydrophilic clay surface effectively becomes hydrophobic. A pore bounded by an asphaltene layer on one side and kerogen on the other is more oil-wetting than mixed-wet. The presence of asphaltenes can therefore expect to create conditions of modified wettability that will impact oil recovery, oil transport and distribution. Another surprising result in this work is that water forms structures that bridge between opposing surfaces of the model. These water bridges are seen to happen for water concentration values larger than 20%. In other words, water is not merely just adsorbed on to the clay surfaces, but also forms these bridge-like structures. Nevertheless, we still observe a strong affinity between the asphaltene/resin fraction and water leading to a lesser degree of mixed wettability. This study is the first, to the best of our knowledge, that considers water and multicomponent hydrocarbon mixtures in mixed-wet pores with realistic surface chemistry and constitutes a necessary first step towards additional studies related to water and hydrocarbon transport and EOR processes in shale nanopores.

Alcohols for hydrate inhibition – Different alcohols and different mechanisms

Methanol has been used to prevent hydrate formation in industrial handling of hydrate forming mixtures containing water for many decades. Ethanol is also used for the same purpose in countries that have easy access to low price ethanol, like for instance Brasil. Common to these small alcohols is that they also have surfactant properties that will promote hydrate formation, but when added to water in sufficient amounts, the hydrate prevention characteristics will dominate. These alcohols will primarily prevent heterogeneous hydrate formation on the interface between water and a separate hydrate phase. The effect of “alcohol” on both of these routes to hydrate formation are investigated and compared to experimental data. In particular we also investigate the effects of these small alcohols on Gibbs free energy for the hydrate formed on the new, shifted, stability conditions. Gibbs free energy is generally higher than hydrate formed from pure water. Enthalpies of hydrate formation are also higher for hydrate formed from water containing alcohols. These are negative numbers, so in absolute values released formation enthalpy is lower. The presence of these alcohols in water will also prevent homogeneous hydrate formation from dissolved hydrate formers in water. Glycols have more important roles in other routes to hydrate nucleation. Heterogeneous hydrate nucleation towards mineral surfaces is feasible in different ways. Polar hydrate formers like H2S and CO2 can adsorb directly on rust, and as discussed here, are able to form hydrate from adsorbed state on rust surface. Non-polar hydrocarbons like, for instance methane might get trapped in structured water and then nucleate to hydrate. Some research on this is published and further research is in progress. Glycols have very strong attraction to rust and corresponding chemical potentials for adsorbed glycols on rust are favourable enough to facilitate phase transition from glycols dissolved in water over to adsorption. Injection of glycol in gas processing plants has been used by industry for many years and in many cases it might even be economically and technically feasible compared to expensive drying units. Exceptions are situations that will lead to water/glycol freezing. But even in multiphase transport of hydrocarbons with various water cuts, mixtures of alcohols might be a technically efficient solution in which the small alcohols may be very efficient as discussed above and glycols may go through adsorption phase transition from water solution over to glycol film on rust and prevent hydrate nucleation towards rust surface. This possible strategy requires more theoretical work as well as experimental investigation. On the basis of thermodynamic analysis and calculations of hydrate formation from different routes, it is argued that real natural and industrial systems are unable to reach thermodynamic equilibrium. It is therefore a need for a consistent thermodynamic platform with a uniform reference system for all phases. We propose and demonstrate a residual thermodynamic model system for all phases.

In Situ Passive Sampling to Monitor Long Term Cap Effectiveness at a Tidally Influenced Shoreline.

Polydimethylsiloxane solid-phase microextraction passive samplers were used to evaluate long-term performance of a sand/gravel cap placed in 2005 in a tidally influenced shoreline in Puget Sound to reduce polycyclic aromatic hydrocarbon (PAH) transport into overlying surface water. Sampling in both 2010 and 2018 measured porewater concentrations of <1 ng/L total PAHs in the cap layer. d-PAH performance reference compounds were used to evaluate the extent of equilibration of the contaminants onto the samplers and to estimate net upwelling velocities through a mass-transfer model. The upwelling velocities were used to predict long-term migration of selected PAHs through the cap, showing that the cap is expected to continue being effective at limiting exposure of contaminants at the cap–water interface.

Features of assessing the level of fire and explosion safety of tanks before hot works

Introduction. One of the most important stages in the development of fire and explosion safety requirements applicable to the process of design and operation of oil and petroleum products storage facilities is the correct examination of the facts of fires and explosions. Unfortunately, electronic resources don’t always correctly disclose the causes of fires and don’t allow for the correct assessments of the fire safety level. Goals and objectives. The goal of the study is to improve the quality of evaluation of statistical data on fires arising in reservoirs, based on the use of data from various information sources. The compilation of qualification attributes of causes of fires will simplify the fire examination procedure.Methods. Research methods include the analysis of statistical data on fires at hydrocarbon storage, transportation and processing facilities. The work encompasses the computational and analytical assessment of the possibility of formation of combustible concentrations in the gas space of tanks and formation of explosive zones outside technological devices.Results and their discussion. The article addresses features of assessing the fire and explosion safety of tanks by classifying causes of fires at the stage of pre-repair preparation of tanks and hot works. Three principal classification features have been identified: fires that occur during the pre-repair preparation; fires that occur after the fulfillment of regulatory requirements for the pre-repair preparation, and fires caused by major violations of fire safety requirements.Conclusions. To prevent fires, the issue of tank farm design should be elaborated in detail, fire safety measures should be taken during the operation of hydrocarbon storage facilities, maintenance of equipment should be carried out, preventive maintenance should be executed, as well.

Impact of the oil and gas production process on the environment and human health

Technologies for oil and gas production and transportation of hydrocarbons pose a potential threat to the environment and human health. The aim of this work is to consider the consequences caused by the proximity of oil fields on the health of the population living nearby using the north of the Irkutsk Region as an example. The incidence of the population was analyzed for the Katanga and Ust-Kut oilfield areas of Irkutsk Region based on statistical information from the annual reports of the Ministry of Health of the Irkutsk Region for the period 2015-2019. We analyzed information on general morbidity, eye diseases, diseases of the skin and subcutaneous tissue, diseases of the musculoskeletal system and malignant neoplasms as well as perinatal and infant mortality and stillbirth. The results obtained indicate the negative impact of oil fields on the health of the population in the immediate vicinity. It is shown that the Katanga Municipality, where the oil field is practically the only type of economic activity, is leading in all the considered indicators of the population morbidity, as well as in perinatal and infant mortality, and stillbirths. It is noted that babies are the most vulnerable group, the infant mortality rate in the area adjacent to the oil field is more than 2 times higher than in the region as a whole, and the stillbirth rate is almost 6 times higher than the corresponding indicators for the region. The obtained data are interpreted by the authors as preliminary and requiring additional research.

Simulating the Efficiency of Electromagnetic Pigging in Pipelines and Production Tubing Aided by Nanopaint

SummaryWax and hydrates deposition is a major concern for hydrocarbon transport in pipelines, production tubing, and other pipes in cold environments. Traditionally, chemical, mechanical, and thermal methods are used to mitigate the deposition at the expense of production interruption, complex maintenance, costs, and environmental hazards, and many of these methods are not feasible in deep water environments.This paper studies the potential of nanopaint-aided electromagnetic pigging. This process has potentially low production impact, simple maintenance, low energy cost, and no chemical expense or hazards. The electromagnetic pig contains an induction coil that emits an alternating magnetic field. The alternating magnetic field induces heat in the nanopaint coating (i.e., coating with embedded paramagnetic nanoparticles) on the pipeline’s inner wall and in the pipeline wall itself. The heat then melts and peels off the wax and hydrates adhering to the pipeline, allowing the hydrocarbon to carry them away. Without loss of generality, we focus on wax remediation in this paper.We analyze the heating effectiveness and efficiency of electromagnetic pigging. The heating effectiveness is measured by the maximum pigging speed that allows deposit removal. The heating efficiency is measured by the ratio of the heat received by the wax over the total emitted electromagnetic energy, which we define as the pig induction factor (PIF).An axisymmetric transient model is built to study the heat transfer without considering phase change. Based on our numerical model, we compare the PIF for different coil designs, different hydrocarbon flow rates, and different pig traveling speeds. We reevaluate the maximum pig speed defined by the static pig model from our previous work and found the electromagnetic pigging system is much more effective than previously estimated, while we confirm that a solenoid with larger radius allows higher pig speed. We find that faster pig speed generally improves the efficiency but decreases effectiveness and that shorter solenoids with larger radius have higher efficiency. The hydrocarbon flow rate does not impact the heating process if the wax is thicker than the threshold wax thickness. Based on the simulation results, the field application is discussed.

Non-equilibrium influence on G/P partitioning of PAHs: Evidence from the diurnal and nocturnal variation

Gas/particle (G/P) partitioning is an important behavior for the atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). In this study, paired daytime and nighttime air samples were collected for one year in order to study the diurnal and nocturnal variations of concentration and G/P partitioning of PAHs. Higher PAHs concentrations in total phase were observed in nighttime. The geomean (GM) concentrations of Σ15PAHs in total phase were 69.6 and 52.8 ng/m3 in nighttime and daytime, respectively. More obviously diurnal and nocturnal variations were observed in non-heating season, with the GM ratios of Σ15PAHs in nighttime to daytime of 1.65 and 1.06 in non-heating season and heating season, respectively. The results could be attributed to emission sources and meteorological conditions. The values of particulate phase fraction (ϕP) and G/P partitioning quotient (log KP) were used to quantify the phase distribution of PAHs. For most high molecular weight PAHs, the values of ϕP and log KP in nighttime were higher than those in daytime, which could be mainly attributed to the lower temperature in nighttime. However, for the three light molecular weight PAHs (Acy, Ace and Flu), higher values of ϕP and log KP were observed in daytime. The regression of log KP against log KOA for the three PAHs in daytime differed from those in nighttime. The chemical losses of PAHs in different phases might be responsible for the result. These findings suggested that the chemical loss of PAHs in gas phase should be considered for the G/P partitioning process.

Numerical and Experimental Analysis of Fire Resistance for Steel Structures of Ships and Offshore Platforms

The requirements for the fire resistance of steel structures of oil and gas facilities for transportation and production of hydrocarbons are considered (structures of tankers and offshore platforms). It is found that the requirements for the values of fire resistance of structures under hydrocarbon rather than standard fire conditions are given only for offshore stationary platforms. Experimental studies on the loss of integrity (E) and thermal insulating capacity (I) of steel bulkheads and deck with mineral wool under standard and hydrocarbon fire regimes are presented. Simulation of structure heating was performed, which showed a good correlation with the experimental results (convective heat transfer coefficients for bulkheads of class H: 50 W/m2·K; for bulkheads of class A: 25 W/m2·K). The consumption of mineral slabs and endothermic mat for the H-0 bulkhead is predicted. It is calculated that under a standard fire regime, mineral wool with a density of 80–100 kg/m2 and a thickness of 40 to 85 mm should be used; under a hydrocarbon fire regime, mineral wool with a density above 100 kg/m2 and a thickness of 60–150 mm is required. It is shown that to protect the structures of decks and bulkheads in a hydrocarbon fire regime, it is necessary to use 30–40% more thermal insulation and apply the highest density of fire-retardant material compared to the standard fire regime. Parameters of thermal conductivity and heat capacity of the applied flame retardant in the temperature range from 0 to 1000 °C were clarified.

Reservoir Forming Conditions and Enrichment Law of Tight Sandstone Gas in Upper Paleozoic in Ordos Basin

With the popularization of natural gas and the requirement of environmental protection, the development and utilization of natural gas are particularly important. The status of natural gas in China’s oil and gas exploration and development is constantly improving, and the country pays more and more attention to the exploitation and utilization of natural gas. The tight sandstone of Upper Paleozoic in Ordos Basin has the characteristics of low porosity, low permeability, and large area of concealed gas reservoirs. With the increasing demand for natural gas in China, systematic analysis and research on the geological conditions and enrichment law of large area gas reservoirs of tight sandstone of Upper Paleozoic in Ordos Basin to guide exploration and production also pose a great challenge to the current level of natural gas exploration and development in China. In order to solve this problem, this paper takes the Upper Paleozoic tight sandstone in Hangjinqi area in the north of Ordos Basin as the research object, summarizes the natural gas accumulation conditions of tight sandstone according to the geological characteristics of Ordos Basin, determines the main control factors of gas accumulation by superposition method in combination with the distribution characteristics of natural gas, simulates the dynamic process of gas accumulation, establishes the gas accumulation model, analyzes the conditions of gas accumulation and enrichment by statistical methods, summarizes the accumulation and enrichment rules of natural gas, and predicts the favorable exploration areas for natural gas. The results show that the relationship between hydrocarbon source rocks, traps, migration and transportation, and other reservoir-forming conditions and the distribution characteristics of natural gas is summarized, and the main controlling factors of reservoir-forming are determined by superposition method. We simulate the evolution process of faults, strata, oil, gas, and water flows in the study area and establish the dynamic reservoir-forming process of natural gas. By combining the reserve data with the reservoir source distance, reservoir facies type, and gas filling times, the reservoir-forming and enrichment conditions are studied by statistical analysis method, and the reservoir-forming and enrichment rules are summarized by combining the main controlling factors. The enrichment of natural gas is controlled by the development degree of source rocks, favorable tight sandstone combination, confluence channel, and local structure. According to the law of accumulation and enrichment, the division standards of favorable areas in different horizons are established, and the favorable exploration areas in the study area are predicted. The results provide theoretical data support for natural gas exploration in the study area.

Automated non-destructive integrity assessment of metal structures

Offshore windmills and pipeline networks are examples of strategic infrastructures used for the production of clean energy and for the storage and long-distance transportation of hydrocarbons, hydrogen and water. The relevant structural elements are mainly made of welded portions of steel pipes, which often interact with aggressive fluids and hostile environments. Material aging is thus accelerated and localized damage processes are promoted, harming the design safety factors. The structural health of such components can be monitored in operation, throughout their lifetime, by non-destructive testing performed by portable devices. The equipment at present available on the market permits to develop fully automated testing campaigns, overcoming the difficulties associated to large extension and difficult accessibility. The data collected on site can be transferred through virtual networks, to be evaluated and processed in order to permit the quantitative evaluations required by the optimization and the planning of repair and retrofit operations. This contribution discusses the potential offered by the current practice and illustrates the methodological adaptations that produce effective diagnostic tools in the outlined context.

A Differential Pressure Technique for Void Fraction Measurement in Gas-Liquid Flow

Two-phase Gas-liquid flows have many industrial uses, such as hydrocarbon transportation and energy production. The knowledge and an accurate determination of the gas phase's proportion rate in the two-phase mixture known as the gas void fraction is necessary for optimal and secure sizing of the installations where this kind of flow takes place. This paper focuses on the possibility of using a cost-effective differential pressure transmitter to measure the void fraction parameter. It is obtained using a mathematical model derived from the energy balance equation and the measured pressure drop from the vertical upward gas-liquid flow. Results on flow void fraction obtained through the use of the conductance probe method, are used to validate those derived from the pressure drop that is evaluated by employing the differential pressure transmitter. The measurement accuracy of the void fraction measured using the pressure drop technique, is found to be principally affected by the flow pattern. Moreover, the slip ratio between the phases was the primary factor influencing the void fraction measurement by the differential pressure technique.

Development of KPI’s for Ageing Export Pipelines in the UK North Sea

Abstract: Export pipelines are of inestimable value to the oil and gas industry, as they have continuously provided a path and means for hydrocarbon transportation. The most recent report from the UK HSE shows that there are about 1372 pipelines installed in the UK North-sea and about 442 of them are ageing export pipelines. The most unique function of these pipelines is to convey fluids from HC wells to the available processing facility; which are applicable for both onshore and offshore applications. During the useful life of these pipelines, they encounter various degradations that range from fatigue, corrosion, thermal expansion, spans, erosion and many other associated third-party challenges. It is the responsibility of duty holders to ensure that these degradations do not propagate into triggering hazardous and catastrophic incidents, to this effect, it is necessary for operators to protect the state of these pipelines by the application of an efficient management structure known as Pipeline Integrity Management System (PIMS). Keywords: Pipeline, Export, Ageing, Key Performance Indicators, PARLOC, OGP, Management, Integrity, Degradation Mechanism, Mitigation, PIMS.

Predictive control of the starting pressure of the main oil pipeline

The article calculates the starting pressures and the time of safe shutdown of the pipeline during the transportation of high-viscosity and high pour point oils, the rheological properties of which depend on temperature. When the oil temperature decreases, its viscosity increases and paraffins are released, forming a strong structure, for which additional stress is necessary to shift. To start a stopped oil pipeline transporting oil with such characteristics, the pressure developed by the pumps may not be enough. In this regard, it is necessary to determine the safe time of stopping the oil pipeline. The relevance increases with an increase in the share of high-viscosity and high pour point oil in the total production volume. Predictive control, based on the analysis of data on the characteristics of the transported product and forecasting the nature of their changes, is an intelligent tool for managing the efficiency of technological transport enterprises. Predictive control allows you to choose the optimal way to ensure reliable and trouble-free operation of the main equipment of hydrocarbon transport systems.A numerical experiment was carried out for the effect of seasonal cooling devices to protect permafrost soils from thawing, at the time of a safe shutdown of the oil pipeline. The values of starting pressures have been determined. Dependence of the pressures on the duration of the safe shutdown of the pipeline has been established. It was revealed that due to the operation of seasonally operating cooling devices, the difference between the temperature soil and oil increases during cooling, and the cooling rate increases. More pressure will be required to launch such an oil pipeline.

Formation mechanism and structural characteristic of pore-networks in shale kerogen during in-situ conversion process

In-situ conversion process (ICP) appears to be a promising approach to enhance hydrocarbon recovery of shale reservoirs. During the ICP, the pore-networks gradually generate underground and serve as the conduits for the storage and transport of hydrocarbon, which finally decides the recovery ability of the reservoir. Reactive molecular dynamics simulations are used to study the pyrolysis behavior of kerogen under the reservoir conditions. The pyrolysis proceeds in four stages: energy accumulation, oil window, gas window, and steady stage. And during this process, the kerogen pyrolytic pore-networks form under the combined actions of chemical bond breaking and physical deformation. Further analysis demonstrates that the structural characteristic is dependent on the maturities of kerogen and pyrolysis temperature. Low-maturity kerogen creates high-quality pore-networks (∼15% porosity), while the pores in medium- and high-maturity kerogen are scarce and isolated (∼1% porosity). In the simulation, the optimal pyrolysis temperature of pyrolysis is about 2300 K to develop high-quality pore-networks. In addition, a conversion relationship between the simulation temperatures and ICP engineering temperatures is established using Arrhenius equations, and the optimal temperature for ICP engineering is suggested to be ∼730 K.

Experimental Approach to Monitoring the Degradation Status of Pipelines Transporting Hydrocarbons

Improve the reliability of the gas and oil transportation process is a primary objective of the pipeline designers because it interests the safety of the goods and the people, the availability and the performance of pipelines as well as the economy of the hydrocarbon transport. Corrosion is a present phenomenon that occurs inside and outside of buried pipes, causing the pipeline to be pierced, leading to gas and oil leaks and causes consequences of the major economic losses. In this context, our study focused on the corrosion monitoring of metals used in the transport of hydrocarbons by two approaches based on electrochemical techniques. Monitoring the evolution of the corrosion potential using an elaborated reference instead of a commercial reference electrode, and by electrochemical impedance spectroscopy (EIS) coupled with the gravimetric method. The obtained results showed the efficiency of our approach for the realization of a corrosion sensor intended for the monitoring of corrosion in pipelines.

Comparative analyses of changes in the ice cover of the Tatar Strait in relation to 1961-1990 and 1991-2020 climate normals

Current warming in the Northern Hemisphere has encompassed not only the surface atmosphere, but also manifested itself in a change in the state of the sea ice cover, as an integral part of the climate system. One of the indicators of the warming was a reduction in ice cover observed in the water area of the Far Eastern seas since the late 1980s. The prospective areas of hydrocarbon deposits discovered in the Tatar Strait, as well as the existing needs for the transportation of hydrocarbons along the shipping routes in the strait, led to the emerging interest in researching the ice regime of the Sea of Japan in the modern climatic era. The proposed paper analyses the changes in ice cover of the Tatar Strait in relation to 1961–1990 and 1991–2020 climate normals. The regularities of the long-term variability of ice cover within non-overlapping 30-year periods were revealed. The analysis of the dynamics of ice cover anomalies, calculated for each normal separately, was carried out. An assessment of the distribution of winter types in the periods under study was carried out. The characteristic features of variations in the intra-seasonal course of ice cover and the dates of the onset of ice phases in different types of winters were identified.