Mapping Lower Zubair Channel Sands Using 3-D Seismic Data: A Case Study
Raghav Prasad*, Saifullah Khan Tanoli, and Mohammed Dawwas Al-Ajmi
The Lower Cretaceous Zubair Formation is a 1,300–1,400 ft thick clastic unit consisting of alternating sand-shale sequences. At the base of the formation thin sands were encountered in many wells in Sabiriyah field. The sands are discontinuous and not mappable from 2-D seismic data due to limits in seismic resolution, lateral facies changes and the complexity of fault system at the Zubair level. Mapping of the sands from 3-D seismic data was accomplished when a thick reservoir fluvial sand (of about 54 ft) was encountered in a single deep exploratory well in Sabiriyah field. To map the areal distribution of the sand we used a 3-D seismic data set (bin size of 25 m x 25 m) together with borehole data and a structural map at the top of sand. Horizon flattening and seismic amplitude, at the level of interest, were used to delineate the configuration of the sand channels. Illumination of reservoir sand by spectral decomposition brought-out differences in sand thickness. Subsequent drilling of the play confirmed the channel geometry of the reservoir. The study, for the first time, upgraded the prospectivity of the Zubair Formation in the field and highlighted potential sweet spots for further exploration and development.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain