An improved interpolation scheme at receiver positions for 2.5D frequency‐domain marine controlled‐source electromagnetic forward modelling

Abstract

An improved interpolation scheme is presented for 2.5‐dimensional marine controlled‐source electromagnetic forward modelling. For the marine controlled‐source electromagnetic method, due to the resistivity contrast between the seawater and seafloor sedimentary layers, it is difficult to compute the electromagnetic fields accurately at receivers, which are usually located at the seafloor. In this study, the 2.5‐dimensional controlled‐source electromagnetic responses are simulated by the staggered finite‐difference method. The secondary‐field approach is used to avoid the source singularities, and the one‐dimensional layered background model is used for calculating the primary fields excited by the source quasi‐analytically. The interpolation of electromagnetic fields at the cell nodes for the whole computational domain to the receiver locations is discussed in detail. Numerical tests indicate that the improved interpolation developed is more accurate for simulating the electromagnetic responses at receivers located at the seafloor, compared with the linear or rigorous interpolation.

Improved Detectivity for Detecting Gas Hydrates Using the Weighted Differential Fields of the Marine Controlled-Source Electromagnetic Data

“…The 2D model (Figure 4) is modified after the 1D case (Figure 2), except that its hydrate deposit is of finite horizontal length of 8000 m. The transmitter-receiver layout is the same as in the 1D test. The receivers are along the inline direction y from 500 m to 5500 m with an even interval 100 m. The code given by Li and Han [30] and Li et al [37] is used to perform the frequency-domain 2D marine CSEM field simulation. Figure 5 shows the results for the original electric field, the weighted differential field (Figure 5a) and their corresponding detectivity (Figure 5b).…”

“…The marine electromagnetic (EM) method, especially the marine controlled-source EM (CSEM) technique, is widely used for investigating the gas hydrate [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. The presence of methane or free gas increase the resistivity of the gas hydrate zone significantly [21,39,40], thus the EM method is useful for detecting the space distribution of hydrate in natural sediments, estimating its saturation [41][42][43][44] and monitoring the formation and dissociation of hydrates with the help of the borehole data [45][46][47][48].…”