Study Of 3-D Anisotropy Forward Modeling Of Marine Controlled-source Electromagnetic Method Using Finite Element Method

Marine controlled-source electromagnetic(CSEM) surveying has been in commercial use for predrill reservoir appraisal and hydrocarbon exploration for 10 years. The method has become firmly established as an important geophysical tool in the offshore environment. The marine CSEM method involves towing a transmitter that is routed through power circuits onboard a sea going vessel. Receivers on the seafloor collect total electric and magnetic fields which are produced as a result of interaction of the transmitter generated primary fields with the seawater and subsurface. The distribution of underground geological structure’s electrical resistance can be obtained by processing and analyzing received electromagnetic signals, so as to whether the reservoir contains oil and gas can be judged.In this paper MCSEM 3-D forward modeling is achieved by the finite element method, we obtain the law that electromagnetic waves propagate in a homogeneous marine environment, and analyze the influence of several key forward parameters on the electromagnetic response characteristics. The objective of the present study is to model the changes in electromagnetic response for a resistive disk and an anticlinal oil and gas reservoir, which are rough approximations of hydrocarbon reservoirs. The main contents of this paper can be summarized as followings:(1) Based on Maxwell’s equations for the theoretical foundation, Marine CSEM in domestic and international situation and development trend has been analyzed, and has an in-depth understanding of the principle of marine controlled source electromagnetic method. According to Maxwell’s equations, we obtain the analytical solution of air, sea and underwater formation of three different media. Come to any point in the seabed at frequency domain electromagnetic field equation. According to the electromagnetic field formula, simulate models’ electromagnetic response. We abtain a Anisotropy By giving unequal conductivity to the adjacent sub-unit.(2) The modeling of three-dimensional marine controlled source electromagnetic forward has been achieved.(3) By establishing homogeneous marine geology geoelectric model, the law of electromagnetic waves propagation in a homogeneous marine environment is achieved under the circumstance of electric and magnetic dipole source being transmitters. The influence of several key forward parameters(water depth, the transmit mode, the transmission frequencies) on the electromagnetic response characteristics has been discussed.(4) The reservoir is simulated by establishing the resistive disk and the anticlinal models using different transmission modes. The identify effects of target electromagnetic field components have been compared by analyzing the changes of electromagnetic responses. The results show that each component has a vary ability in identifying reservoirs, while VED achieves the better result and the vertical electric field component Ez has the best identifying ability.