OBEM Development And For Gas-hydrate Prospecting

Marine controlled source electromagnetic method has been proved to be an effective geophysical prospecting method for natural gas hydrate exploration in the bottom of the sea.China's marine reserves are predicted to be huge,in the area of limited seismic methods,the electromagnetic method is needed as the main detection means,so the detection of underwater gas hydrate in China needs the high technical support of electromagnetic methods.Marine controlled source electromagnetic method is composed of the method theory,marine equipment,data processing and interpretation,and so on.Which is a key component of the marine equipment,uand its overall performance directly determines the quality of the data,which determines the success or failure of the sea operations.In the face of the special needs of the natural gas hydrate detection,the existing submarine electromagnetic receiver has some shortcomings in the background noise,the continuous operation time,the time drift error,the offshore operation efficiency and so on.According to some typical areas in the sea areas of gas hydrate reservoir characteristics,the establishment of stratigraphic model;numerical simulation according to the stratigraphic model;and on the basis of forward calculation results to determine the parameters of the apparatus;and the hardware and software of marine electromagnetic receiver development;through a series of laboratory tests,field tests and land sea test index the receiver will eventually develop;batch production and used for actual hydrate investigation work.This paper mainly studied four aspects: 1)controlled source electromagnetic specific formation under the conditions of the forward calculation;2)developed hardware and software receiver;3),indoor land and sea test;4)Natural Gas Hydrate Offshore Exploration application.Receiver intended target:Channels: 5(Ex,Ey,Ez,Hx,Hy);Bandwidth: 0.001Hz?100Hz;Noise floor: 0.1n V/m/rt(Hz)@1Hz,0.1p T/rt(Hz)@1Hz: magnetic field;Dynamic range: E: 110 d B,H: more than 100 d B;Maximum working depth: 4000m;Storage space: 16GB;Continuous working time: 30 days;Clock error: less than 5ms/day;In order to meet the technical specifications,the technical problems such as low noise,low time drift,low power consumption and so on are overcome,and the important progress is made in many aspects such as the release mechanism and the efficient operation of the sea.Indoor,terrestrial and marine tests have verified the effectiveness and the advanced nature of the receiver,and successfully applied to the investigation and production of the marine gas hydrate.