Study On Forward Modeling Of Three Dimensional Marine Controlled-source Electromagnetic Method

Study of marine controlled-source electromagnetic methods began in the1970s,andthe rapid development began in the late1990s, instrument design, continuousimprovement in data processing, and data interpretation, in academic research andindustrial applications proved to be an effective geophysical method for offshoreresource exploration and constructing investigation,and it has gradually become animportant marine geophysics exploration tool. At present, the marinecontrolled-source electromagnetic methods widely used in offshore oil and gasresources before drilling a secondary assessment, and in other areas of explorationplays an increasingly important role.In this paper we present a method based on staggered-grid finite differencemethod for marine controlled source of three-dimension forward modeling method,proceed from the fundamental equations and deduced primary fields and secondaryfields satisfied Maxwell equations. The horizontal electric dipole source in theuniform layer media is used for computing primary fields, staggered-grid finitedifference method for computing secondary fields which using Jacobi preconditioning,and adopt the Quasi-Minimal Residual (QMR) method for solving large equationsystems,which gives accurate and reliable results. Setting up three dimensionalmodels, we calculate electromagnetic response through the forward program and drawMagnitude Value Offset(MVO) curve and Normalized Magnitude Value Offset(N-MVO) curve studying changes of frequency, changes of offset, changes ofabnormal body burial depth and different towing device heights effect for differentelectric field response. Based on changes of frequency, changes of offset, changes ofabnormal body burial depth and different towing device heights effect of thesedifferent factors, we give recommendations for the setting of the actual constructionparameters, provide a theoretical basis for actual construction.We introduce the fundamentals of the polarization ellipse, through comparativeanalysis, we can see thatPM AXnormalized amplitude curve reflected anomalousbodies better than the Ex, when transmit dipole with the uncertainty relative positions of the receiver, observations of polarization ellipse valuePM AXcan provide a morestable information. The angleα Ncan be used to estimat e azimuth angles of thereceiver and disturbances appear inthe boundary of anomalous bodies...