The application of high resolution seismic processing to low relief structures - Harriet oil accumulation*

Abstract

The Harriet structure is located within the offshore permit WA-192-P on the north-west shelf of Western Australia, near Barrow Island. The structure is a low-relief feature controlled by late faulting. An oil-bearing sand of Lower Cretaceous age forms the reservoir which has excellent porosity and permeability. The reservoir has a low seismic acoustic impedance contrast with the overlying deep marine shales. This low acoustic impedance contrast, combined with penetration problems due to near surface carbonates, results in a generally weak reflector at the top of the reservoir sands at a two-way time of approximately 1.5 s. Four recent vintages of seismic surveys using different recording parameters have been shot over the structure with a resultant grid spacing of 250 m. After the Harriet No. 1 discovery well, all the data over the structure were reprocessed using 'state-of-the-art' processing techniques to improve the resolution of the reflecting event at the top of the reservoir sand. The reprocessing was also carried out to minimize mis-ties between the various vintages of seismic data, and to improve the match between the surface seismic data and the vertical seismic profile at the wells. The above three aims were achieved by replacing standard pre-stack predictive deconvolution by deterministic deconvolution, i.e. instrument phase compensation and spectral equalization and by statistical wavelet extraction and shaping to 'zero phase'. Also a pre-stack FK filter was applied to suppress noise on the data. Additionally, the application of spectral equalization to the suppression of low frequency short period multiples is demonstrated.