Use of Seismic Attributes in Porosity and Lithology Prediction, Gyda Field, Norwegian Offshore Continental Shelf

BURRELL, J., BP Exploration, Aberdeen, Scotland, M. LUHESHI,* and A. MACKENZIE, BP Norway, Stavanger, Norway, and A. WALDEN, BP Exploration, London, England

Gyda field (operated by BP) is located in Block 2/1 of the Norwegian outer continental shelf. The reservoir comprises a thin, wedge-shaped Upper Jurassic sand, overlain by Lower Cretaceous mudstones. For field development, it is necessary to accurately map a laterally discontinuous high-porosity zone and thus to help site well locations. To this end, it was decided to invert the 3-D seismic data set over the field to the seismic attribute of absolute acoustic impedance (AAI). This was based on the observation that there is a good correlation between porosity and AAI derived from well logs. Comparisons of core porosity, log-derived porosity, and seismic-derived porosity at several well locations showed this technique to be generally satisfactory.

An additional problem in Gyda is the detection of the truncation edge of the reservoir along the southeastern part of the field. Deterministic methods based on AAI and on forward seismic modeling were not able to unambiguously define the edge of the reservoir. The truncation of the reservoir is not clear on normal seismic amplitude displays. In order to investigate the zone where the reservoir interval changes from sand to shale, certain special seismic attributes were computed over a gate of seismic data covering the top reservoir reflection. These attributes represented the energy, phase, and frequency content of the gate of seismic data. The area investigated was between wells where the reservoir sand was known to pinch out. These attributes were clustered using the statistical tec nique of projection pursuit. The cluster map correlates with the observations from the wells in this area of the field and appears to show the edge of the effective reservoir in the field.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)