Changes

* Carrier beds for migrating fluids and gases.

* Carrier beds for migrating fluids and gases.

In AAPG Memoir 8, Diapirs and Diapirism, Musgrave and Hicks<ref name=Musgraveandhicks_1988>Musgrave, A. W., and W. G. Hicks, 1968, [http://archives.datapages.com/data/specpubs/structu1/data/a153/a153/0001/0100/0122.htm Outlining shale masses by geophysical methods], ''in'' E. Braunstein and G. D. O'Brien, eds., Diapirism and diapirs: AAPG Memoir 8, p. 122–136.</ref> provided a set of characteristics for what appear to be displaced shale masses in the Gulf of Mexico: (1) low-velocity sound transmission, in the range of 6500–8500 ft/s (1981.2–2590.8 m/s) with very little increase in velocity with depth; (2) low density, estimated to be in the range of 2.1–2.3 g/cm³; (3) low resistivity, approximately 0.5 ohm m; and (4) high fluid pressure, about 90% of the overburden pressure. Other authors (Henry et al.<ref name=Henryetal_2010 />) have documented sonic velocities in near surface (~0–3500 ft [~0–1070 m] below surface) mobile muds of onshore Trinidad to be lower than that of water! Authors from a range of disciplines have attributed these behaviors to high fluid pressure within the shales. At times, these densities are reduced to the point that the shales will rise as a mass in a diapiric fashion that is similar to that of salt. However, such behavior is not widely documented.

In AAPG Memoir 8, Diapirs and Diapirism, Musgrave and Hicks<ref name=Musgraveandhicks_1988>Musgrave, A. W., and W. G. Hicks, 1968, [http://archives.datapages.com/data/specpubs/structu1/data/a153/a153/0001/0100/0122.htm Outlining shale masses by geophysical methods], ''in'' E. Braunstein and G. D. O'Brien, eds., Diapirism and diapirs: AAPG Memoir 8, p. 122–136.</ref> provided a set of characteristics for what appear to be displaced shale masses in the [[Gulf of Mexico]]: (1) low-velocity sound transmission, in the range of 6500–8500 ft/s (1981.2–2590.8 m/s) with very little increase in velocity with depth; (2) low density, estimated to be in the range of 2.1–2.3 g/cm³; (3) low resistivity, approximately 0.5 ohm m; and (4) high fluid pressure, about 90% of the overburden pressure. Other authors (Henry et al.<ref name=Henryetal_2010 />) have documented sonic velocities in near surface (~0–3500 ft [~0–1070 m] below surface) mobile muds of onshore Trinidad to be lower than that of water! Authors from a range of disciplines have attributed these behaviors to high fluid pressure within the shales. At times, these densities are reduced to the point that the shales will rise as a mass in a diapiric fashion that is similar to that of salt. However, such behavior is not widely documented.

Improved seismic technologies have allowed a step change forward in the interpretation of shale tectonics in the subsurface with many previously interpreted mobile masses now much better defined. In some instances, improved imaging techniques have shown features previously interpreted as shale diapirs to be tightly folded anticlinal cores (Elsley and Tieman<ref name=Elsleyandtieman_2010 />). However, other instances exist in which shale substrates do appear to show inflation and upward mobility (Wiener et al.<ref name=Wieneretal_2010 />). Because criteria for interpreting mobile shales are not well documented in literature, many of the characteristics that were developed for interpreting mobile salts have been applied to shale basins, albeit with mixed success. In addition, in basins where both salt and shale occur, geoscientists commonly fail to differentiate mobile shales from mobile salts in seismic images. To rectify this deficiency, the following criteria for differentiating salt and shale are provided.

Improved seismic technologies have allowed a step change forward in the interpretation of shale tectonics in the subsurface with many previously interpreted mobile masses now much better defined. In some instances, improved imaging techniques have shown features previously interpreted as shale diapirs to be tightly folded anticlinal cores (Elsley and Tieman<ref name=Elsleyandtieman_2010 />). However, other instances exist in which shale substrates do appear to show inflation and upward mobility (Wiener et al.<ref name=Wieneretal_2010 />). Because criteria for interpreting mobile shales are not well documented in literature, many of the characteristics that were developed for interpreting mobile salts have been applied to shale basins, albeit with mixed success. In addition, in basins where both salt and shale occur, geoscientists commonly fail to differentiate mobile shales from mobile salts in seismic images. To rectify this deficiency, the following criteria for differentiating salt and shale are provided.