Research On Reverse Time Migration Method Of Prism Waves In Viscoacoustic Media

At present,the key target areas of our country’s oil and gas field exploration have shifted from simple structural oil and gas reservoir areas to areas with complex lithological oil and gas reservoirs.In order to comply with the strategic guidelines of oil and gas field exploration,geophysical technology,as an important means of oil and gas field exploration,must develop seismic migration imaging methods that can adapt to the target area according to the structural characteristics of complex lithological oil and gas reservoirs.Complex structural areas have brought great challenges to seismic imaging technology.High-steep structures are a kind of special underground structures.Traditional reverse-time migration imaging methods are difficult to accurately restore underground high-steep structures.Prismatic waves are used as a special kind of seismic wave is different from primary wave,it often carries information about the high-steep structures.At the same time,in areas with complex lithological oil and gas reservoirs,the absorption and attenuation of seismic waves in underground propagation is more serious.Because prismatic waves have three reflection paths,unlike a single reflection wave,it is more difficult to perform attenuation compensation along the three reflection paths of prismatic waves.Based on the above background,it is urgent to develop a seismic imaging method that can accurately image high-steep structures in complex structural areas and effectively compensate for attenuation.Mainly carried out the following work:(1)The characteristics and propagation paths of prismatic waves are studied.According to the acoustic wave equation,the forward extension operator of the prismatic wave source wave field,the reverse extension operator of the geophone wave field and the extension operator of the reflection wave field are derived,to realize the prismatic wave reverse time migration imaging method;(2)The basic theory of visco-acoustic medium is studied.By citing memory variables,the solution of time convolution is transformed into the solution of differential equations,the operation of time convolution on memory is reduced,and the visco-acoustic wave equation based on standard linear solids is derived.At the same time,in order to eliminate the problem of instability of high-frequency components caused by the viscoacoustic wave equation in the back propagation process,a low-pass filter is added to filter the high-frequency components during the reverse extension process to achieve a stable viscoacoustic wavefield extension;(3)The prismatic wave reverse time migration is extended to visco-acoustic media,and the forward attenuation compensation extension operator of the prismatic wave source wave field,the reverse attenuation compensation extension operator of the geophone wave field and the attenuation compensation reflection wave field are derived,to realize the reverse time migration imaging method of viscoacoustic medium prism wave attenuation compensation.Based on the above theoretical foundation,a trial calculation of the model was carried out,and compared with the traditional reverse time migration technology,it was verified that the proposed viscoacoustic medium prismatic wave reverse time migration method can restore the high-steep structures well and is effective compensate the absorption and attenuation of seismic waves by visco-acoustic media.