Changes

==Applications==

==Applications==

Since sedimentary rocks have little magnetism, the classic use of magnetic surveys in petroleum exploration has been to map basement rocks, as well as any intrusives or volcanics within the sediments. Basement depths are determined and faults are interpreted from disruptions in the magnetic patterns. Such applications are most common in the early stages of exploring a basin, and thus, magnetic data have been little used in development programs. However, the high sensitivity of modern instruments has allowed detection and mapping of weak magnetic anomalies arising from within the sediments. The sources of these intrasedimentary anomalies vary from one region to another and include salt structures, faulting, and diagenetic formation of magnetite from seeping hydrocarbons, as suggested by Donovan et al.<ref name=pt07r10>Donovan, T. J., Forgey, R. L., Roberts, A. A., 1979, [http://archives.datapages.com/data/bulletns/1977-79/data/pg/0063/0002/0200/0245.htm Aeromagnetic detection of diagenetic magnetite over oil fields]: AAPG Bulletin, v. 63, p. 245–248.</ref> It has been difficult to establish the sources with certainty, especially in the presence of magnetic anomalies introduced by human activities, such as the use of steel in oilfield development. Reynolds et al.<ref name=pt07r49>Reynolds, R. L., Webring, M., Grauch, V. J. S., Tuttle, M., 1990, Magnetic forward models of Cement oil field, Oklahoma, based on rock magnetic, geochemical, and petrologic constraints: Geophysics, v 55, p. 344–353., 10., 1190/1., 1442842</ref> have recently studied this problem over the Cement oil field.

Since sedimentary rocks have little magnetism, the classic use of magnetic surveys in petroleum exploration has been to map [[basement]] rocks, as well as any [[intrusives]] or [[volcanics]] within the sediments. Basement depths are determined and [[fault]]s are interpreted from disruptions in the magnetic patterns. Such applications are most common in the early stages of exploring a basin, and thus, magnetic data have been little used in development programs. However, the high sensitivity of modern instruments has allowed detection and mapping of weak magnetic anomalies arising from within the sediments. The sources of these intrasedimentary anomalies vary from one region to another and include [[salt structure]]s, faulting, and [[Diagenesis|diagenetic]] formation of [[magnetite]] from seeping hydrocarbons, as suggested by Donovan et al.<ref name=pt07r10>Donovan, T. J., Forgey, R. L., Roberts, A. A., 1979, [http://archives.datapages.com/data/bulletns/1977-79/data/pg/0063/0002/0200/0245.htm Aeromagnetic detection of diagenetic magnetite over oil fields]: AAPG Bulletin, v. 63, p. 245–248.</ref> It has been difficult to establish the sources with certainty, especially in the presence of magnetic anomalies introduced by human activities, such as the use of steel in oilfield development. Reynolds et al.<ref name=pt07r49>Reynolds, R. L., Webring, M., Grauch, V. J. S., Tuttle, M., 1990, Magnetic forward models of Cement oil field, Oklahoma, based on rock magnetic, geochemical, and petrologic constraints: Geophysics, v 55, p. 344–353., 10., 1190/1., 1442842</ref> have recently studied this problem over the [[Cement oil field]].

The application of magnetics to development geology is unlikely to be important except in two special circumstances. The first situation is when the field is related to basement structure and both regional and local magnetic features are involved. The second case is when intrasedimentary magnetic anomalies have been detected and may provide a key to local boundaries.

The application of magnetics to development geology is unlikely to be important except in two special circumstances. The first situation is when the field is related to basement structure and both regional and local magnetic features are involved. The second case is when intrasedimentary magnetic anomalies have been detected and may provide a key to local boundaries.