Use of Post-Stack Seismic in Fractured Reservoir Characterization

Gary C. Robinson, Ahmed Ouenes, Udo Araktingi, and Abdel Zellou
Prism Seismic, Centennial, CO

Fractured reservoirs are notoriously difficult to develop efficiently. In order to optimally develop these reservoirs, the location of the fractures within the reservoir must be known – and therein lies the problem. Modern logging tools allow us to precisely locate fractures within wellbores, but this information is of limited use in the inter-well region. Seismic data covers the inter-well region and could be used to map the fractures.

There is currently much interest and research in the use of azimuthal anisotropy in the detection of fractures. Although this technology shows much promise, there are numerous accompanying caveats and problems. An alternative to using pre-stack seismic data for mapping fractures is to use post-stack seismic attributes.

In the post-stack seismic method, we identify the geologic “drivers” that localize the presence of fractures. These drivers are typically factors such as lithology, porosity, and distance to faults. Seismic attributes can provide information on these drivers. By combining the seismic information with a fracture indicator in the wells using a neural network, we can produce models of fracture intensity, which can be then be used both in locating development wells and in reservoir simulation.

The key to this method is the synergistic combination of seismic data, containing the interwell information, with geologic and engineering data at the wells to develop a fracture model that honors the various datasets. This method has been successfully applied to fractured reservoirs around the world, and has produced results similar to the more expensive and time-consuming pre-stack azimuthal anisotropy method.