Analysis of sensitivity to hydrate blockage risk in natural gas gathering pipeline

During the operational process of natural gas gathering and transmission pipelines,the formation of hydrates is highly probable,leading to uncontrolled movement and aggregation of hydrates.The continuous migration and accumulation of hydrates further contribute to the obstruction of natural gas pipelines,resulting in production reduction,shutdowns,and pressure build-ups.Consequently,a cascade of risks is prone to occur.To address this issue,this study focuses on the operational process of natural gas gathering and transmission pipelines,where a comprehensive framework is established.This framework includes theoretical models for pipeline temperature distribution,pipeline pressure distribution,multiphase flow within the pipeline,hydrate blockage,and numerical solution methods.By analyzing the influence of inlet temperature,inlet pressure,and terminal pressure on hydrate formation within the pipeline,the sensitivity patterns of hydrate blockage risks are derived.The research indicates that reducing inlet pressure and terminal pressure could lead to a decreased maximum hydrate formation rate,potentially mitigating pipeline blockage during natural gas transportation.Furthermore,an increase in inlet temperature and terminal pressure,and a decrease in inlet pressure,results in a displacement of the most probable location for hydrate blockage towards the terminal station.However,it is crucial to note that operating under low-pressure conditions significantly elevates energy consumption within the gathering system,contradicting the operational goal of energy efficiency and reduction of energy consumption.Consequently,for high-pressure gathering pipelines,measures such as raising the inlet temperature or employing inhibitors,electrical heat tracing,and thermal insulation should be adopted to prevent hydrate formation during natural gas transportation.Moreover,considering abnormal conditions such as gas well production and pipeline network shutdowns,which could potentially trigger hydrate formation,the installation of methanol injection connectors remains necessary to ensure production safety.

Development of a least squares support vector machine model for prediction of natural gas hydrate formation temperature

Hydrates always are considered as a threat to petroleum industry due to the operational problems it can cause.These problems could result in reducing production performance or even production stoppage for a long time.In this paper, we were intended to develop a LSSVM algorithm for prognosticating hydrate formation temperature(HFT) in a wide range of natural gas mixtures. A total number of 279 experimental data points were extracted from open literature to develop the LSSVM. The input parameters were chosen based on the hydrate structure that each gas species form. The modeling resulted in a robust algorithm with the squared correlation coefficients(R^2) of 0.9918. Aside from the excellent statistical parameters of the model, comparing proposed LSSVM with some of conventional correlations showed its supremacy, particularly in the case of sour gases with high H_2S concentrations, where the model surpasses all correlations and existing thermodynamic models. For detection of the probable doubtful experimental data, and applicability of the model, the Leverage statistical approach was performed on the data sets. This algorithm showed that the proposed LSSVM model is statistically valid for HFT prediction and almost all the data points are in the applicability domain of the model.

Initial estimation of hydrate formation temperature of sweet natural gases based on new empirical correlation

Production,processing and transportation of natural gases can be significantly affected by clathrate hydrates.Knowing the gas analysis is crucial to predict the right conditions for hydrate formation.Nevertheless,Katz gas gravity method can be used for initial estimation of hydrate formation temperature （HFT） under the circumstances of indeterminate gas composition.So far several correlations have been proposed for gas gravity method,in which the most accurate and reliable one has belonged to Bahadori and Vuthaluru.The main objective of this study is to present a simple and yet accurate correlation for fast prediction of sweet natural gases HFT based on the fit to Katz gravity chart.By reviewing the error analysis results,one can discover that the new proposed correlation has the best estimation capability among the widely accepted existing correlations within the investigated range.

Resistivity in Formation and Decomposition of Natural Gas Hydrate in Porous Medium

A new one-dimensional system for resistivity measurement for natural gas hydrate(NGH)exploitation is designed,which is used to study the formation and decomposition processes of NGH.The experimental results verify the feasibility of the measurement method,especially in monitoring the nucleation and growth of the NGH. Isovolumetric formation experiment of NGH is performed at 2°C and 7.8 MPa.Before the NGH formation,the initial resistivity is measured to be 4-7Ω·m,which declines to the minimum value of 2-3Ω·m when NGH begins to nucleate after the pressure is reduced to 3.3 MPa.As the NGH grows,the resistivity increases to a great extent,and finally it keeps at 11-13Ω·m,indicating the completion of the formation process.The NGH decomposition experiment is then performed.When the outlet pressure decreases,NGH begins to decompose,accordingly,the resistivity declines gradually,and is at 5-9Ω·m when the decomposition process ends,which is slightly higher than the resistivity value before the formation of NGH.The occurrence and distribution uniformity of NGH are determined by the distribution and magnitude of the resistivity measured on an one-dimensional sand-packed model.This study tackles the accurate estimation for the distribution of NGH in porous medium,and provides an experimental basis for further study on NGH exploitation in the future.

Calorimetric Determination of Enthalpy of Formation of Natural Gas Hydrates

This paper reports the measurements of enthalpies of natural gas hydrates in typical natural gas mixture containing methane, ethane, propane and iso-butane at pressure in the vicinity of 2000 kPa (300 psi) and 6900 kPa(1000psi). The measurements were made in a multi-cell differential scanning calorimeter using modified high pressure cells. The enthalpy of water and the enthalpy of dissociation of the gas hydrate were determined from the calorimeter response during slow temperature scanning at constant pressure. The amount of gas released from the dissociation of hydrate was determined from the pumped volume of the high pressure pump. The occupation ratio (mole ratio) of the water to gas and the enthalpy of hydrate formation are subject to uncertainty of 1.5%.The results show that the enthalpy of hydrate formation and the occupation ratio are essentially independent of pressure.

Mechanical Modeling and Analysis of Stability Deterioration of Production Well During Marine Hydrate Depressurization Production

Different from oil and gas production,hydrate reservoirs are shallow and unconsolidated,whose mechanical properties deteriorate with hydrate decomposition.Therefore,the formations will undergo significant subsidence during depressurization,which will destroy the original force state of the production well.However,existing research on the stability of oil and gas production wells assumes the formation to be stable,and lacks consideration of the force exerted on the hydrate production well by formation subsidence caused by hydrate decomposition during production.To fill this gap,this paper proposes an analytical method for the dynamic evolution of the stability of hydrate production well considering the effects of hydrate decomposition.Based on the mechanical model of the production well,the basis for stability analysis has been proposed.A multi-field coupling model of the force state of the production well considering the effect of hydrate decomposition and formation subsidence is established,and a solver is developed.The analytical approach is verified by its good agreement with the results from the numerical method.A case study found that the decomposition of hydrate will increase the pulling-down force and reduce the supporting force,which is the main reason for the stability deterioration.The higher the initial hydrate saturation,the larger the reservoir thickness,and the lower the production pressure,the worse the stability or even instability.This work can provide a theoretical reference for the stability maintaining of the production well.

Numerical Simulation on Production Trials by Using Depressurization for Typical Marine Hydrate Reservoirs:Well Type and Formation Dip

Natural gas hydrate has huge reserves and is widely distributed in marine environment.Its commercial development is of great significance for alleviating the contradiction between energy supply and demand.As an efficient research method,numerical simulation can provide valuable insights for the design and optimization of hydrate development.However,most of the current production models simplify the reservoir as a two-dimensional(2D)horizontal layered model,often ignoring the impact of formation dip angle.To improve the accuracy of production prediction and provide theoretical support for the optimization of production well design,two three-dimensional(3D)geological models with different dip angles based on the geological data from two typical sites are constructed.The vertical well,horizontal well and multilateral wells are deployed in these reservoirs with different permeabilities to perform production trial,and the sensitivity analysis of dip angles is also carried out.The short-term production behaviors in high and low permeability reservoirs with different dip angles are exhibited.The simulation results show that 1)the gas and water production behaviors for different well types in the two typical reservoirs show obviously different variation laws when the short-term depressurization is conducted in the inclined formation;2)the inclined formation will reduce the gas production and increase the water extraction,and the phenomena becomes pronounced as the dip angle increases,particularly in the low-permeability reservoirs;3)and the impact of formation dip on hydrate recovery does not change significantly with the variation of well type.

Experimental Study on Preparation of Natural Gas Hydrate by Crystallization

In this paper, the saturated solution crystallization method is proposed to promote the formation of hydrate by means of the known similarities between the hydrate formation process and the crystallization process. In this method,adding the second phase crystals was used to replace the spontaneous formation of hydrate crystal nuclei to form hydrate.The effects of saturated Na_2SO_4, MgSO_4, NH_4HCO_3 and CuSO_4 solutions on the formation rates of natural gas hydrate and gas storage capacity were investigated. The results showed that the saturated solution had an influence on the hydrate formation process. Under the given experimental conditions, the saturated Na_2SO_4 solution showed a highest increase in the hydrate formation rate, and the average hydrate formation rate in its presence was 11.8 times higher than that obtained in the deionized water. Moreover, the largest formation rate of gas hydrates observed in the saturated Na_2SO_4 solution was 386 times bigger than that in the deionized water, and the gas storage capacity increased by 10 times. In addition, the average hydrate formation rate in the saturated Mg SO_4 solution was faster than that in water by 20 times. The largest formation rate of gas hydrates in the saturated MgSO_4 solution was 165 times faster than that obtained in the deionized water, and the gas storage capacity increased by 6.2 times. The saturated NH_4HCO_3 and saturated CuSO_4 solutions also influenced the formation process of hydrate. Therefore, the crystallization method of saturated solution can be used to achieve a highefficiency preparation of natural gas hydrates, which provides theoretical guidance for the storage of natural gas in the form of hydrate.

Research and application of thermal insulation effect of natural gas hydrate freezing corer based on the wireline-coring principle

Natural gas hydrate(NGH)holds great promise as a source of clean energy.It is critical for acquiring the largest possible in situ NGH core for NGH eigen features and resource assessment.However,the existing NGH coring technology has limitations,such as temperature increments,limited coring diameters,low coring rates,and complex coring structures.Therefore,this study designs and proposes an NGH freezing coring(NGHFC)method and verifies the freezing and coring capacities of the NGHFC method in laboratories and experimental wells.Results suggest that NGHFC shows good freezing and heat-retention properties.A freezing core heat transfer model is developed.According to the actual air temperature and operating time,the optimum initial temperature of the cold source can be determined using this model.The average coring rate of NGHFC can reach 77.86%.The research results will provide a new idea of coring gas hydrates.

Evaluation on the natural gas hydrate formation process

Gas hydrates have endowed with great potential in gas storage,and rapid formation of gas hydrates is critical to use this novel technology.This work evaluated the natural gas hydrate formation process,which was compared from six parameters,including conversion of water to hydrate,storage capacity,the rate of hydrate formation,space velocity(SV)of hydrate reaction,energy consumption and hydrate removal.The literature was selected by analyzing and comparing these six parameters mentioned above,meanwhile placing emphasis on the three parameters of storage capacity,the rate of hydrate formation and space velocity of hydrate reaction.Through analysis and comparison,four conclusions could be obtained as follows.Firstly,the overall performance of the stirring process and the spraying process were better than other processes after analyzing the six parameters.Secondly,the additive types,the reactor structure and the reactor size had influence on the natural gas hydrate formation process.Thirdly,the energy consumption via reciprocating impact in the hydrate formation process was higher than that via stirring,spraying and static higee.Finally,it was one key for hydrate removal to realize the hydrate industrial production.

Nuclear magnetic resonance study of the formation and dissociation process of nature gas hydrate in sandstone

In this work,the authors monitored the formation and dissociation process of methane hydrate in four different rock core samples through nuclear magnetic resonance(NMR)relaxation time(T_(2))and 2D imaging measurement.The result shows that the intensity of T_(2) spectra and magnetic resonance imaging(MRI)signals gradually decreases in the hydrate formation process,and at the same time,the T_(2) spectra move toward the left domain as the growth of hydrate in the pores of the sample accelerates the decay rate.The hydrate grows and dissociates preferentially in the purer sandstone samples with larger pore size and higher porosity.Significantly,for the sample with lower porosity and higher argillaceous content,the intensity of the T_(2) spectra also shows a trend of a great decrease in the hydrate formation process,which means that high-saturation gas hydrate can also be formed in the sample with higher argillaceous content.The changes in MRI of the sample in the process show that the formation and dissociation of methane hydrate can reshape the distribution of water in the pores.

Molecular simulation studies on natural gas hydrates nucleation and growth:A review

How natural gas hydrates nucleate and grow is a crucial scientific question.The research on it will help solve practical problems encountered in hydrate accumulation,development,and utilization of hydrate related technology.Due to its limitations on both spatial and temporal dimensions,experiment cannot fully explain this issue on a micro-scale.With the development of computer technology,molecular simulation has been widely used in the study of hydrate formation because it can observe the nucleation and growth process of hydrates at the molecular level.This review will assess the recent progresses in molecular dynamics simulation of hydrate nucleation and growth,as well as the enlightening significance of these developments in hydrate applications.At the same time,combined with the problems encountered in recent hydrate trial mining and applications,some potential directions for molecular simulation in the research of hydrate nucleation and growth are proposed,and the future of molecular simulation research on hydrate nucleation and growth is prospected.

STUDY FOR NATURAL GAS HYDRATE CONVERSED FROM ICE

Natural gas hydrates are crystalline clathrate compounds composed of water and gases of small molecular diameters that can be used for storage and transport of natural gas as a novel method. In the paper a series of experiments of aspects and kinetics for hydrate formed from natural gas and ice were carried out on the industrial small scale production apparatus. The experimental results show that formation conditions of hydrate conversed from ice are independent of induction time, and bigger degrees of supersaturation and supercooling improved the driving force and advanced the hydrate formation.Superpressure is also favorable for ice particle conversion to hydrate. In addition, it was found there have an optimal reaction time during hydrate formation.

Wellbore temperature distribution during drilling of natural gas hydrate formation in South China sea

The natural gas hydrate resources in the South China Sea alone are about 85 trillion cubic meters.In the drilling process of marine gas hydrate,the natural gas hydrate will decompose and produce gas,as the rising of temperature and dropping of the pressure in the annulus.This process will have a significant impact on drilling safety.Therefore,it is necessary to study the wellbore temperature distribution during the drilling of marine hydrate layer.In this paper,the wellbore temperature distribution of safe drilling in hydrated formation is taken as the research goal,and the research status of relevant domestic and international wellbore temperatures was investigated.According to the characteristics of the marine environment and reservoir-forming characteristics of hydrate reservoirs in the South China Sea,the wellbore temperature distribution model of offshore drilling wellbore under the condition of hydrate decomposition was established.The temperature distribution curve of drilling straight wellbore in hydrate layer of South China Sea was obtained.When drilling the hydrate reservoir,the distribution regularity of the wellbore temperature is similar to that of the conventional offshore drilling wellbore.However,the temperature of the wellbore annulus near the hydrate decomposition site is lower than the ambient temperature,mainly due to the hydrate decomposition endothermic.In this paper,the sensitivity analysis of several main parameters of the wellbore temperature distribution of drilling straight wellbore in hydrate layer of South China Sea was carried out.Through the conduction of experiment and numerical simulation,we have get some new findings:(1)The hydrate saturation has little effect on the wellbore temperature;(2)As the drilling fluid displacement increases,the annulus temperature of the wellbore above the mudline increases,and the temperature of the wellbore below the mudline decreases continuously;(3)As the density of the drilling fluid increases,the temperature at the wellhead decreases,and the temperature at the bottom of the well increases slightly;(4)The greater the rate of penetration of the well,the temperature at the upper part of the wellbore decreases,and the temperature at the bottom of the wellbore increases;Among them,the penetration rate has the most obvious effect on the annular temperature.The results are expected to be helpful to guide the drilling process of marine gas hydrate and offer some references.

Developing a robust correlation for prediction of sweet and sour gas hydrate formation temperature

There are numerous correlations and thermodynamic models for predicting the natural gas hydrate formation condition but still the lack of a simple and unifying general model that addresses a broad ranges of gas mixture.This study was aimed to develop a user-friendly universal correlation based on hybrid group method of data handling(GMDH)for prediction of hydrate formation temperature of a wide range of natural gas mixtures including sweet and sour gas.To establish the hybrid GMDH,the total experimental data of 343 were obtained from open articles.The selection of input variables was based on the hydrate structure formed by each gas species.The modeling resulted in a strong algorithm since the squared correlation coefficient(R2)and root mean square error(RMSE)were 0.9721 and 1.2152,respectively.In comparison to some conventional correlation,this model represented not only the outstanding statistical parameters but also its absolute superiority over others.In particular,the result was encouraging for sour gases concentrated at H2S to the extent that the model outstrips all available thermodynamic models and correlations.Leverage statistical approach was applied on datasets to the discovery of the defected and doubtful experimental data and suitability of the model.According to this algorithm,approximately all the data points were in the proper range of the model and the proposed hybrid GMDH model was statistically reliable.

Influences of different types of magnetic fields on HCFC-141b gas hydrate formation processes

In this study, visualizations and experiments are carried out on the influence of static and rotating magnetic fields on the characteristics of HCFC-141b gas hydrate formation, such as crystallization form, formation temperature and induction time. It has been found that a proper rotating magnetic field can considerably improve the low-pressure gas hydrate formation process, especially in increasing the formation temperature and shortening the induction time. The mor- phology of the gas hydrate formation appears rather complex and compact. However, a proper static magnetic field can make the gas hydrate crystal more organized, which will be benefit to heat transfer.

Research progress in hydrate-based technologies and processes in China:A review

Natural gas hydrate(NGH) is considered as an alternative energy resource in the future as it is proven to contain about 2 times carbon resources of those contained in the fossil energy on Earth. Gas hydrate technology is a new technology which can be extensively used in methane production from NGH, gas separation and purification, gas transportation, sea–water desalination, pipeline safety and phase change energy storage, etc. Since the 1980s, the gas hydrate technology has become a research hotspot worldwide because of its relatively economic and environmental friendly characteristics. China is a big energy consuming country with coal as a dominant energy.With the development of the society, energy shortage and environmental pollution are becoming great obstacles to the progress of the country. Therefore, in order to ensure the sustainable development of the society, it is of great significance to develop and utilize NGH and vigorously develop the gas hydrate technology. In this paper,the research advances in hydrate-based processes in China are comprehensively reviewed from different aspects,mainly including gas separation and purification, hydrate formation inhibition, sea–water desalination and methane exploitation from NGH by CH4–CO2 replacement. We are trying to show the relevant research in China, and at the same time, summarize the characteristics of the research and put forward the corresponding problems in a technical way.

Analysis of factors affecting microwave heating of natural gas hydrate combined with numerical simulation method

As a clean and abundant unconventional natural gas resource,natural gas hydrate(NGH)holds the characteristics of safety,high efficiency and sustainable exploitation,which helps to alleviate the energy shortage of China,reduce the foreign-trade dependence of oil and gas,and ensure the national energy security.Microwave heating is a significant method that has been used in natural gas hydrate exploration.By using the microwave heating,the NGH in the reservoir formations would be heated,decomposed and stimulated thanks to taking advantage of microwave heating's unique characters:efficiency,high speed,clean and pollution-free.This paper established the temperature under microwave heating gas hydrate distribution theory model,and by using the finite element method for simulating temperature field of microwave heating gas hydrate,this paper analyzed the natural gas hydrate in the microwave field temperature distribution in the influencing factors.Microwave has a significant heating effect on the hydrate reservoir in the immediate vicinity of wellbore,and it is not affected by the initial conditions of reservoir.The temperature can rise to above 50℃ within 1 h which is higher than the phase equilibrium temperature at the time of hydrate decomposition and is helpful to improve the decomposition rate of hydrate.The frequency is set at 915 MHz,and the feed port has a spiral arrangement with a length of 10 mm,which greatly expands the microwave heating range.

Application of statistical learning theory for thermodynamic modeling of natural gas hydrates

The gas hydrate formation in pipelines of industries and chemical plants can cause various operational damages and can increase economic risks.Hence,the knowledge of hydrate formation conditions has become a critical research study to overcome the problems arising from the formation of hydrates.In this study,we applied an algorithm to develop an LSSVM model to predict the formation temperature of natural gas hydrate for a comprehensive range of data points.Total 188 experimental data points were applied from the literature for the development of the LSSVM model.The input parameter was finalized based on the structure of hydrates by each gas species.The results obtained by the LSSVM model have good accuracy as compared with empirical correlations available in the literature.This model gave the squared correlation coefficient(R2),and root mean square error of 0.9901 and 0.59974,respectively.The composition of gases may affect the phase equilibrium condition of gas hydrates.The applied algorithm revealed that the developed LSSVM model could become a good alternative for calculating the formation temperature of hydrate for the range of all data sets.The results showed that the proposed LSSVM model could be applicable for the prediction of hydrate formation temperature for all data points.

天然气水合物钻探近井地层与井筒热量传递规律研究

在天然气水合物钻探中,井筒温度变化易导致储层水合物分解,产生大量以甲烷为主的气体侵入环空。侵入气体随环空流体上返过程中,当环空温度压力等环境符合水合物二次生成条件时,水合物会在环空大量生成并附着井壁,堵塞环空引发井壁失稳、井喷等事故。文章研究了水合物钻探过程中井筒地层段的温度分布和热量传递规律,研究发现,环空流体温度降低易导致水合物生成,温度过高则会增大水合物储层的分解速率;钻井液入口温度越高,热量由环空传入地层的井段越长,反之越短;相较于低密度钻井液,高密度钻井液对井底温度影响更大;排量变化也会对井筒温度分布产生较大影响。因此,在水合物钻探过程中,通过对入口流体温度、排量和密度参数进行合理调节,避免发生储层水合物失控分解,对于保障水合物钻探过程井筒稳定,实现水合物安全钻采具有重要意义。文章阐明了热流量在井筒中的变化规律,通过计算井筒地层段中各区域换热速率和换热量的大小,为水合物钻探井筒温度监测提供理论支撑。同时也为后续的水合物得到井筒温度变化研究提供参考。