Anisotropy is an intrinsic rock property that is important for the understanding of rock mechanics and seismic wave propagation. Unfortunately, this property is often poorly understood for lack of calibration. Typically, it is measured at a mega scale for seismic processing or at a micro scale on core samples. The seismic measurement is made during seismic processing and typically has a very course resolution of many hundreds to thousands of meters. The core measurement is highly sensitive to experimental technique (complexities include sample quality and representing in-situ conditions) and is limited to a very minute stratal range of the rock (inches) and only in locations and sections where expensive core is taken.
Since true calibration is almost always limited, anisotropy is often ignored or estimated in an arbitrary fashion in applications. Examples include: 1) Geomechanical models, which historically use vertical sonic properties as input, require some means to allow horizontally-derived rock property data to be used alongside vertical log data. 2) Downhole microseismic raypaths from fracture loci to wellbore receivers have a dominantly horizontal component but are usually calibrated with sonic velocities from vertical wells.
Quantico leveraged its experience with a wide variety of geological settings and its vast library of well data – with more horizontal logging and drilling data than possessed by virtually any single oil and gas company – to develop a workflow for anisotropy calculation at the sonic scale. This workflow has been utilized to develop calibrated estimates for anisotropy in various basins. This workflow is based on geologically specific comparison of vertical and horizontal sonic data. This calibration fills the scale gap between seismic and core scale measurements.
Quantico customers can benefit from this workflow as a means of calibrating rock properties and developing Earth models utilizing both horizontal and vertical input. A more thorough understanding anisotropy provides a more complete understanding of the geomechanical properties of the rock. Calibrated anisotropy can also provide a more constrained velocity model for microseismic evaluation.