Quantitative Reservoir Description from 3-D Surveys

Catherine Lewis

3-D seismic surveys are being used routinely to define the structure and compartmentalization of reservoirs by faults. In many cases more detail can be obtained about reservoir properties, such as sand percent or porosity, from the seismic amplitudes. Quantitative estimates of sand percent and hydrocarbon volumes can be obtained using seismic attributes when the seismic impedance depends on the reservoir properties. Well logs and cores can be used to evaluate what the seismic response to changing reservoir properties should be. Once the seismic response is understood, maps of the reservoir properties with quantitative values can be made from the seismic attributes.

Examples of this technique include 3-D surveys of a deep-water channel and levee complex and of a fluvial channel complex. In the case of a single deep-water channel, the event of the seismic data is a half cycle in duration. A well-known attribute is composite amplitude, which has been assumed to be linear in relationship to hydrocarbon pore thickness. For deep-water sands, it is in fact nonlinear and better fit by a cubic relationship. In contrast, an attribute we call IAA, which is the integrated absolute value of the amplitudes in the interval, can be used to make a map of the hydrocarbon pore volumes using a simple linear regression. In the case of stacked fluvial channels, the reservoir sands occur over a two-cycle interval. Two attributes, Ian and Iap, which are the areas of th troughs and the peaks, can be used to map sand content versus shale content. For a model test case, the sand percent of a 3-D volume can be recovered to 97% accuracy.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995