| Offshore shallow gas usually refers to gas accumulated in sediments near the coastal seabed,and there are layers of shallow gas,cluster(block)shallow gas,high pressure airbags,and the like.Shallow gas is widely distributed in the Yangtze River Delta and Hangzhou Bay,while the shallow gas is in a dynamic equilibrium state of continuous production and migration within the sediment;however,it is very unstable in marine construction projects.The balance,if this unstable balance is broken by the on-site drilling construction,it will easily cause the shallow gas to directly release and erupt,and even more,it will burn and explode.It has serious consequences for the equipment and construction personnel used in the exploration.At present,the detection of shallow gas in China is based on manual on-site sampling,laboratory instrument analysis,low degree of automation,no real-time,and continuous continuous long-term monitoring.Based on the method of membrane interface detection,the author designs and An instrument capable of real-time in-situ on-line monitoring of methane concentration in shallow gas in offshore water was realized and tested in actual field.It has a wide measuring range and can realize long-term continuous monitoring.The specific research and design contents are as follows:(1)By consulting relevant domestic and foreign materials,the main techniques of existing shallow gas detection are studied,and the characteristics of various technologies are analyzed.The research objectives and key technologies of this topic are proposed.(2)The overall and various parts of the instrument are described,including the introduction of the mechanical structure of the instrument and the electronic circuit.The mechanical structure includes the selection and protection of the film material,the separation structure of the deposit,and the methane gas collection and detection structure.The electronic circuit part includes the selection of the methane detection sensor,the circuit design of the sensor signal acquisition node,and the circuit design of the signal collection node.(3)The software of each part of the instrument system is designed,including the data acquisition and transmission software design of the sensor signal acquisition node,the software design of the signal collection node,the software design of the upper computer and the real-time data and curve display,and the software design of the real-time query of the mobile phone mobile data.(4)The data fitting and simulation experiments were carried out,including water-proof and resist compression test of the instrument and methane detection experiments in simulated sediments.The waterproof and compression resistance of the instrument is verified by the waterproof and compression test.It is an important basis for the instrument to be used in the actual field.A series of methane gases with different standard concentrations were used to calibrate the selected sensors,and the output data of the sensors were analyzed and fitted,which were transformed into the standard gas concentration output.The methane detection experiments in simulated sediments were carried out using the barrel device designed by the laboratory.(5)Actual field test use and analysis of results.A detailed analysis of the results of the shallow gas detection data in the actual site provides a valuable reference for re-optimizing the structure of the instrument in the future.The real-time monitoring instrument designed by this subject can realize one-time penetration into the seabed,regionalized long-term in-situ online effective monitoring of methane concentration in shallow gas,and real-time acquisition of measurement data.It can effectively avoid and prevent the damage caused by shallow gas in marine construction projects,and can help to explore other aspects of shallow gas in sediments. |
PDF Full Text Request