The Use of Spectral Decomposition and Seismic Attribute Volumes in Mapping of Truncating Carbonate Units

Hussain Najwani*, Mahmood Mahrooqi, and Janine Jones
PDO
*[email protected]

The mid-Cretaceous Natih Formation produces oil and gas in northern and central Oman. It consists of seven main carbonate members intercalated with shales of variable seal quality. The carbonate and shale sequence forms a total thickness of about 500 m. Previous and ongoing work suggested that conventional structural plays are creamed and that the future of Natih exploration lies in identifying stratigraphic sub-plays. The Natih truncation play consists of carbonate units truncating against the base Tertiary unconformity. Mapping of the truncating carbonate units is critical in verifying existing leads and identifying new ones. Various seismic volumes were examined out of which spectral decomposition slices volume (frequency slices), seismic envelope volume (instantaneous amplitude) and a coloured impedance volume (seismic inversion) proved useful for mapping the lateral extent of Natih truncations. These volumes yielded two comparable sets of truncating Natih unit trends. Most of the trends are compliant with well data and modelling results. Furthermore, a new well drilled to target a deeper objective confirmed a Natih trend. Despite this confidence, imprints of seismic data quality were noted and a seismic re-processing project was initiated to overcome observed seismic artefacts. Combining available well results with the seismic data and associated attribute volumes resulted in refining current Natih interpretation that allowed for an improved understanding of some Natih prospects.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain