Seismic field data displaying azimuthal anisotropy, 1986–2020

Abstract

The azimuthal (az’l) processing of 3D full-azimuth full-offset P-P reflection seismic data can enable better imaging, thus yielding improved estimates of structure, lithology, porosity, pore fluids, in situ stress, and aligned porosity that flows fluids (macrofracture porosity). In the past 34 years, the oil and gas industry has significantly advanced in the use of seismic azimuthal anisotropy, in particular, to gain information concerning unequal horizontal stresses and/or vertically aligned fractures, and possibly more importantly, to improve the prestack imaging especially in complex structure. The important development stages during the past 40 years were enabled by industry advancements in acquisition, processing, theory, and interpretation. The typical important techniques became evident in PP amplitude variation with angle and azimuth (AVAaz) and orthorhombic imaging. These techniques addressed the complications due to wave propagation in birefringent media. PP AVAaz, now industry standard for vertically aligned fracture characterization, is accompanied by a near-angle azimuthal amplitude variation when aligned connected porosity that flows fluids is present. Birefringence is present with unequal horizontal stresses and/or vertically aligned fractures that flow fluids. I have focused on the field-data documentation of the relationships among azimuthal P-P reflection data, S-wave birefringence, and hydrocarbon production. With increases and improvements in acquisition and processing, plus today’s powerful versatile interpretation platforms, continual advances beyond orthorhombic (ORT) into monoclinic and triclinic symmetries are to be expected. The use of 3D azimuthal seismic for time-lapse changes of the in situ stress field, fracture populations, and pore fluids, as rocks undergo production processes (oil and gas reservoir production processes, wastewater disposal, etc.) and at plate boundaries where stresses change, offers great potential to benefit not just the oil and gas industry but all of humanity.