Study And Application Of Analytical Methods For Water And Gas Components Of Natural Gas Hydrate

As one of the hottest clean energy sources,natural gas hydrate plays an important role in resource distribution and economic development.In this paper,a method for the analysis and test of water components in natural gas hydrate and a method for the test and analysis of its gas molecules are established.And through the simulation experiment on the synthesis of natural gas hydrate,the analytical method was applied to the test of hydrate samples to study the component changes during its synthesis and decomposition.The main research contents are as follows:(1)The determination conditions of main ions in the solution(including Cl-,Br-,I-,Na+,K+,Ca2+,etc.)were analyzed,including ion regulator,pH range,stirring speed,response time,etc.Standard linear relationship experiment,sensitivity experiment and precision and accuracy experiment were carried out for each ion.The correlation coefficient(R2)of each ion standard curve was basically between 0.9964-1.The detection limit meets the requirements of the operation instructions and has high sensitivity.The relative standard deviation of each ion was 0.37%?1.268%.The test results are good under optimized conditions.(2)The analysis of mutual interference between ions shows that the mutual interference between ions of halogen elements is strong,and ions with strong oxidation ability are relatively weak in oxidation ability.The measurement results change the linear range of ions with weak oxidation ability,and the greater the concentration difference between the two,the more deviated the measurement results are from the standard linear curve;Compared with the ions with strong oxidation,the ion with weak oxidation will have a certain chemical reaction on the surface of the electrode membrane,which will lead to the poisoning of the ion electrode with high oxidation.In both experiments,the regression equation under interference ion can be obtained by regression experiment,and the correlation coefficient is good(3)By means of single injection,the content of hydrocarbon gas such as CH4,C2H6,C3H8,C4H10 and C5H12 and other conventional gas components such as CO2 and O2 can be simultaneously determined by gas chromatography with hydrogen flame ion detector and thermal conductivity detector in parallel.The chromatographic column and column box temperature,column flow rate,injection port temperature,detector temperature,as well as tail gas and reference gas flow conditions were optimized.The standard gas retention time experiment,calibration curve experiment,precision and accuracy experiment were evaluated,and the correlation coefficient(R2)was basically between 0.9972 and 1,indicating that the concentration of each gas component had a good linear relationship with its corresponding peak area.The relative standard deviation is within 0.5%?3%,which can well meet the requirements for the determination of various components in natural gas.(4)The synthesis and decomposition process of hydrate in glacial sand environment was simulated.And the changes of multi-component gas components and ion concentration in solution during the synthesis and decomposition of natural gas hydrate were analyzed.Conclusion:in the process of hydrate formation,salt drainage effect will occur.The concentration of main ions in the residual solution that is not involved in hydrate synthesis,such as Na+,K+,Ca2+,Cl-and SO42-,increases obviously.During the process of hydrate synthesis,the pure water in the solution is absorbed,resulting in higher concentration of surrounding ions.The main hydrocarbon gas components are differentiated in the process of hydrate synthesis,and the remaining free gas and hydrate decomposition gas components that are not involved in hydrate synthesis are differentiated to different degrees.The content of methane increased obviously in free gas and decreased obviously in decomposed gas.The components of ethane,propane and butane decreased in the residual free gas and increased in the decomposed gas.This conclusion can provide a good proof for the phenomenon that"the ion concentration in the pore water around the formation where the gas hydrate exists is abnormal".At the same time,the differentiation of gas components provides a method for judging the gas source.