MARINE MAGNETOTELLURICS FOR PETROLEUM-EXPLORATION, PART II - NUMERICAL-ANALYSIS OF SUBSALT RESOLUTION

Citation
Gm. Hoversten et al., MARINE MAGNETOTELLURICS FOR PETROLEUM-EXPLORATION, PART II - NUMERICAL-ANALYSIS OF SUBSALT RESOLUTION, Geophysics, 63(3), 1998, pp. 826-840
Citations number
20
Categorie Soggetti
Geochemitry & Geophysics
Journal title
ISSN journal
00168033
Volume
63
Issue
3
Year of publication
1998
Pages
826 - 840
Database
ISI
SICI code
0016-8033(1998)63:3<826:MMFPPI>2.0.ZU;2-I
Abstract
In areas where seismic imaging of the base of salt structures is diffi cult, seaborne electromagnetic techniques offer complementary as well as independent structural information. Numerical models of 2-D and 3-D salt structures demonstrate the capability of the marine magnetotellu ric (MT) technique to map the base of the salt structures with an aver age depth accuracy of better than 10%. The mapping of the base of the salt with marine MT is virtually unaffected by internal variation with in the salt. Three-dimensional anticlinal structures with a horizontal aspect ratio greater than two can be interpreted adequately via two-d imensional inversions. Marine MT can distinguish between salt structur es which possess deep vertical roots and those which do not. One measu re of the relative accuracy of MT acid seismic methods can be made by considering the vertical and lateral position errors in the locations of interfaces caused by neglecting velocity anisotropy in migration. F or the shallow part of the section where two-way travel times are on t he order of 1 s, the vertical and lateral position errors in the locat ions of salt-sediment interfaces from 2-D MT inversion is more than tw ice the expected migration error in reflectors in transversely isotrop ic sediments, such as those in the Gulf of Mexico. Deeper in the secti on where two-way times are on the order of 4 s, lateral position error s in migration become comparable to those of the MT inverse, whereas s eismic vertical position errors remain more than a factor of two small er than MT errors. This analysis shows that structural mapping accurac y would be improved using MT and seismic together.