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Types of energy shielding effect, formation mechanism and countermeasures
YANG Qing dao1, WANG Wei feng1, YIN Yi dong2, ZHAO Yu sheng2, LI Ji bai2, HU Jian hui2
(1.School of Geosciences in China University of Petroleum, Qingdao 266555, China;2.Yunnan Geophysical Company of Southwest Petroleum Bureau, SINOPEC, Kumming 650233, China)
Abstract:
By analyzing the seismic wave transmission conditions for different areas, three types of formation mechanism of energy shielding effect were proposed. Besides the energy shielding effect caused from strong reflection interface which is named as reflecting shielding, there are two mechanisms which greatly reduce the transmission energy and greatly degrade the seismic data quality. One is named as dissipation shielding where there are one or more strong viscous dissipation layers absorbing most of seismic energy rapidly. The other is named as dispersion shielding where there are one or more strong scattering belts scattering most of seismic energy to different directions. In some cases there are intense reflection interfaces as well as dissipation layers or dispersion belts which give rise to dual shielding effect. On the basis of the mechanism of the energy shielding effect, the following countermeasures were proposed to deal with the energy shielding effect:① optimizing the line deployment to avoid the energy shielding belt as far as possible, ② increasing the transmission energy from shooting and receiving, ③ selecting reasonable ways of observation on the basis of forward modeling of shielding interfaces or belts, ④ introducing the high density seismic survey with small group intervals to increase the effective channels of receiving, ⑤ eliminating noises such as multiples, ground roll waves derived from strong interfaces or other dispersion belts by means of seismic processing, ⑥ increasing the maximum transmission windows of strong reflection interfaces by means of converted wave seismic exploration prospecting, ⑦ introducing crooking lines seismic survey to reduce the dissipation or reflection shielding in Loess areas.
Key words:  energy shielding  formation mechanism  seismic wave  reflection  transmission  dissipation  dispersion