Application Of Unfolded Phase Spectrum In The Boundary Of Discontinuity Of Superimposed Sand Bodies

Due to the diversion and migration of channels,the layers of fluvial facies show the feature of sand-shale thin interbed multi-interbeded at the vertical direction.In addition,the geological forms of fluvial facies are complex and diverse with very fast lithological changes in the lateral dierction.Besides the interbeds caused by sedimentation,there are other factors,such as diagnesis and tectonic movement,leading to the development of various discontinuous boundaries in fluvial sand bodies.These discontinuity boundaries include large scale geological feaure,such as channel boundary,faults,large cracks;medium scale geolocial feature,such as overlapping area of channel sand body,point bar edge;and mirco scale geologic unit,such as micro-cracks,internal texture of sand body,bedding,and so on.Study of these discontinuity boundaries can analyze remaining oil distribution charateristics,plan well trajectory while drilling,and analyze injection flow charateristics,so as to optimize adjustment of well position and improve implementation effect while drilling and optimize injection effect.At present,the main methods for studying the prediction methods of discontinuity boundaries are forward modeling,well-seismic interaction,90 degree phase shift,coherence volume,curvature and other seismic attributes,three-dimensional visualization technology,ant algorithm and other algorithms.These methods can identify some discontinuity boundaries.However,they are mainly aimed at the channel boundary,large faults,cracks and other boundaries.There is still an urgent need for the boundary identification methods of sand overlay.The seismic signal will be affected by the underground media(such as lithology,structure,location,rock physical parameters,etc.)in the process of transmission in the underground media.These influences can change the amplitude and frequency of the signal,as well as the phase of the signal.These geological information carried by amplitude,frequency and phase can be used to understand the feature of underground reservoirs.It provide the theoretical support for the study of overlapping discontinuity of fluvial facies sand body by phase in this paper.First,some two-dimensional and three-dimensional sand body superimposition models are established based on the classification of channel facies reservoir configuration types and the actual situation of the project area.Then,seismic records are obtained by convolution and wave equation forward modeling.Second,the unwrapped phase spectrum is obtained from seismic records.Through the analysis of the unwrapped phase spectrum,it is found that the abnormal jump at the overlapping area of sand body.Baed on this discovery,one can predict the overlapping area of sand body.Due to the "non-intuitionism" of phase spectrum expansion,two methods,i.e.integral phase spectrum and principal frequency phase spectrum,are proposed.The results of model tests show that these two phase spectra can not only predict the overlapping area of sand body,but also characterize the thickness of sand body.Compared with integral phase spectrum,principal frequency phase spectrum expansion is better used to the compact sand body.Next,the unwrapped phase spectrum,the integral unwrapped phase spectrum and the main frequency unwrapped phase spectrum are tested at the case of different frequencies and noises.At low frequencies,these three phase spectra can still predict the overlapping area of sand bodies.In the end,the proposed method is applied to a target area in Bohai Bay.The feasibility is verified through geologic and well log data.Then,the proposed method is further confirmed with high accuracy by the profile result.