Acoustic zoom high-resolution seismic beamforming for imaging specular and non-specular energy of deep oil and gas bearing geological formations

An unconventional oil and gas exploration technology for 3D/4D seismic imaging called Acoustic Zoom (AZ) is described which offers high resolution and direct focusing of specular and non-specular backscatter energy returns in land and marine environments. A dense configurable source-receiver array (with beam steering via phased array methods) is employed, with vertical stacking to suppress incoherent noise and adaptive classification filters to detect and image the diffuse character of formations. By design, the rich content of the non-specular backscatter energy is accentuated by directly probing underlying geophysical properties of the earth (through appropriate choice of scattering Green function and corresponding true amplitude weights). Each beamformed image is formed by the totality of the energy backscattered in the direction and range of the corresponding beam. The methods described add value to existing 3D seismic surveys by reconstructing the complementary components of recorded energy that 3D seismic rejects as incoherent noise. The application of the method in a proof-of-concept pilot study of the Eagle Ford formation is introduced. This paper introduces in detail the Acoustic Zoom seismic beamforming method as applied to the imaging of diffuse non-spectral returns corresponding to subtle features in the earth's subsurface. Imaging of non-specular seismic returns requires significant attenuation ( > 30 dB) of coherent background interference (e.g. ground roll, specular reverberation) achieved by combining the narrow beam-width of the receiver array with adaptive classification and filtering of specular energy using singular value decomposition (SVD) and eigenstructure methods. This approach replaces conventional filters that could introduce imaging artifacts greater than the non-specular signals being sought. Acoustic P-wave imaging of the earth's subsurface using the Acoustic Zoom's fixed position sensor array and beam steering results in higher lateral and vertical resolutions than conventional 3D seismic surveys. The energy returns along the symmetry axis of the underlying geology at zero offset over the Eagle Ford formation analyzed are true backscatter returns that have interesting interpretative value in their own right. When these specular returns are analyzed as "non-specular" backscatter, only the returns along a "virtual well bore" for the zero-offset ray are imaged. Theoretical issues arising from the beamforming method are discussed and observations regarding the resulting Acoustic Zoom data acquired and processed are presented. (C) 2014 The Authors. Published by Elsevier B.V.