PREDICTION FOR THE ELASTIC PROPERTIES OF THIN HOMOGENEOUS LAYERS, BASED ON SEISMIC DATA
P.A. Alekseeva^{1,2}, I.N. Kerusov^{2}
^{1}Lomonosov Moscow State University, Leninskie Gory 1/1, Moscow, 119234, Russia ^{2}LUKOILEngineering LLC, Pokrovskii bul’v. 3/1, Moscow, 109028, Russia
Keywords: Spectral decomposition, thin layer, Middle Jurassic deposits
Abstract
Many attributes and inversion transformations solving the problem of extracting information on the elastic properties of a medium are based on the Zoeppritz equation or its approximations calculated for a boundary between two halfspaces. In a real medium, a seismic signal is in interference as a result of reflection from the top and bottom of individual thin layers or units whose elastic properties differ from those of the adjacent rocks. In such media, there is a discrepancy between experimental and theoretical dependences of the reflection coefficient amplitude developed for halfspaces. For a homogeneous thin layer, the change in the frequency response of the reflection coefficient is associated with the reflection coefficients of the layer top and bottom interfaces and the wave traveltime within the layer at the same time. A detailed analysis of the reflection coefficient amplitude of a homogeneous thin layer using the spectral decomposition technology allows us to isolate only the change in the reflection coefficients, regardless of the thickness. The proposed method for predicting the elastic properties of thin layers is based on the analytical derivation of the reflection coefficient of a homogeneous thin layer, according to which there is a parabolic relation between the squared reflection coefficient amplitude and the squared frequency. The approximation coefficient at the zero degree of the argument mainly characterizes the properties of a medium, unlike the first and seconddegree coefficients, which depend both on the properties and on the thickness of the layer. Therefore, it makes sense to use the approximation coefficient at the zero degree of the argument as an attribute of the wavefield to predict the elastic properties of thin layers in the interwell space. A good example of a relatively homogeneous thin layer is a narrow riverbed. Determining the properties of the rock filling the channel feature helps identify more sandy areas promising for further development of the field.
