Anisotropy analysis of multicomponent data can map polarization and time delay information associated with velocity anisotropy. These can be related to stress, crack-like pore structure and fractures in the subsurface. In this figure, orientation is indicated by the individual vector segments and the magnitude of time delay between 'fast' and 'slow' polarization is shown in colour. The information being mapped is cumulative anisotropy through a thick carbonate section. The rose plot in the lower left illustrates the distribution of fast shear polarizations.

Knowledge of fractures is important for understanding the fluid pathways and fluid flow within a reservoir.

Fracture analysis is often tackled using P-wave data alone, by examining velocity or amplitude variation with azimuth. This requires a good distribution of offsets for each azimuth.

However, when multicomponent data are available, they offer a robust, direct approach to fracture analysis.

Anisotropy & Fractures

It can be very useful to understand the anisotropy orientation (which indicates fracture orientation and potentially directions of preferred permeability) and the anisotropy intensity (which indicates fracture density and potentially porosity). These anisotropy properties can be predicted and mapped using S-wave splitting.

Once measured, anisotropic effects can be compensated for during seismic processing, leading to an improvement in image quality.

Multicomponent & Tight Gas

Tight gas reservoirs can be found around the world, including the USA and the Middle East. Modern techniques now make these viable production targets.

A typical tight gas reservoir has very low permeability. Here, natural and induced fractures are essential for economic gas production.

Conventional seismic allows the interpretation of large-displacement faults, however most fractures are well below seismic resolution. Instead, we depend on macro effects of fracturing on seismic attributes to highlight fracture orientation and density. This provides valuable insight into key reservoir properties that are essential for optimizing well placement and production.

COMPARE: isotropic vs. anisotropic

What is Shear-Wave Splitting?

Unlike P waves, S waves come in two types – characterized by orthogonal polarizations.

For the isotropic case, polarization is determined by the source-receiver geometry. For the azimuthally anisotropic case, polarization is determined by the fracture orientation.

It may be that there is more than one anisotropic layer, in which case the imprint corresponds to the shallowest layer, and layer stripping compensation is required for deeper layers.