The Development Of Ocean Bottom Electromagnetic And Seismic Receiver

Marine electromagnetic method and offshore seismic method are important marine oil and gas exploration technologies.Joint marine electromagnetic(EM)and seismic inversion is widely used in offshore gas hydrate and petroleum exploration,further improve the retrieval accuracy,better estimate hydrocarbon reservoir,and reduce the risk of low gas saturation well.The wide application of the joint inversion method of ocean electromagnetic and seismic data also drives the data acquisition system to develop the joint acquisition technology of electromagnetic and seismic data.Currently marine electromagnetic data acquisition mainly employ the ocean bottom electromagnetic receiver(OBEM),offshore seismic exploration mainly employ the ocean bottom seismometer(OBS).Joint marine electromagnetic(EM)and seismic data acquisition can decrease costs and improve efficiency.Traditional receiver has high costs,large size,position errors.Developed ocean bottom electromagnetic and seismic receiver,achieve the integrated observation of controlled source electromagnetic(CSEM),magnetotelluric(MT)and seismic signals,reduce the cost of offshore operation and improve the efficiency of offshore operation.Based on the research foundation of Ocean Bottom Electrometer(OBE),the overall research scheme of ocean bottom electromagnetic and seismic receivers was designed,carried out the following work:1)newly increased magnetic and seismic signal observation functions;2)developed the singlechip control circuit,achieved the functions of state query(reading pressure,temperature,voltage and time parameters,Wi-Fi communication,GPS timing,etc);2)developed the preamplifier circuit of Geophone,achieved the functions of amplification,impedance matching and low-pass filtering,etc.Developed the Multiparameter Multicomponent Receiver with User Interaction Software,achieved state parameter inquiry,switch control,etc.Developed the micro Ag/AgCl electrodes,the size was reduced from 320mm(L)×56mm(D)to100mm(L)×25mm(D),which is one sixth of the current electrode size.Attitude acquisition module was integrated to achieve attitude data acquisition.The mechanical structure of the ocean bottom electromagnetic and seismic receiver was designed,the hardware circuits are placed in a glass sphere,The size of the receiver was reduced from100cm(L)×100cm(W)×120cm(H)to 103cm(L)×52cm(W)×65cm(H)(without measuring arm),which is one fourth of the size of the existing OBEM receiver.Equipped the Ultra Short Baseline Positioning System(USBL)responder and mechanical releaser for underwater positioning and mechanical release.9)Circuit performance test,flume test and marine test were completed,twice marine electromagnetic exploration were completed.The test results show that:effective ocean bottom magnetotelluric,controlled source electromagnetic and seismic data have been obtained,the noise level of electric field is 4E-16V/Am~2@8Hz,the noise level of magnetic field is 4E-10nT/Am@8Hz,effective electrical parameters of formation in target area of hydrate were obtained,verified the reliability,effectiveness and advancement of the receiver.