Optimizing 3-D seismic technologies to accelerate field development in the Berkine Basin, Algeria

Abstract

A radical approach to 3-D acquisition in country with large sand dunes was developed to improve seismic data quality. A methodology was devised which allowed accurate removal of near-surface statics and transmission effects giving enhanced depth prognosis. An adaptive noise-attenuation technique, based upon an image-processing procedure, was developed to improve the signal-to-noise ratio of 3-D data that were contaminated with ‘acquisition footprint’. Finally, parallel survey geometries were devised that reduced the noise contamination of the next generation of 3-D surveys in the Berkine Basin. Most of the 3-D surveys acquired in the Berkine Basin are now designed with parallel templates rather than cross-spreads. This survey technique has been shown to provide better spatially sampled data, despite the interference caused by the huge sand dunes, which, in turn, respond more positively to standard pre-stack noise-attenuation processing. Attribute and coherency analysis, as well as stratigraphic interpretation, is now possible on these datasets with a much greater degree of confidence.

Map compilations and synthesis of Africa’s petroleum basins and systems

“…Hydrocarbons were generated from Silurian and Devonian source rocks predominantly during Mesozoic reburial, pre-Hercynian generation having been largely ineffective, although the Ahnet Basin gas reserves could, as Coward & Ries (2003) point out, be exceptions to this general rule. The impact of the secondary Devonian source rocks has been significant for the most recent discoveries and these are described in this volume by Liming et al (2003) Technologies that are contributing and will continue to contribute to the discovery of more petroleum in these Palaeozoic systems include improved seismic imaging in areas of unfavourable surface conditions, such as shifting sand dunes (Drummond et al 2003)), and shallow carbonate occurrences. Improved petrophysical and engineering practices in some of the tighter reservoirs, particularly the Ordovician fluvioglacial sands, will undoubtedly contribute to increased recovery of in situ hydrocarbons.…”

“…There are also major reserves at this level in the Sirt Basin, sourced stratigraphically downward from Cretaceous source rocks (Burwood et al 2003). Imaging of undrilled traps below shifting sand dunes and salt is a critical-technology technique that has led to considerable recent success (Drummond et al 2003).…”

Seismic Ground Roll Absorption and Reemission by Sand Dunes

“…When surface sources are used in the acquisition of land seismic data, as in vibroseis and weight drop surveys, approximately two thirds of the energy delivered by the source propagates along the Earth's surface in the form of such waves (Miller & Pursey, ; Richart et al, ), which are reflected or refracted where topography or seismic velocity at the surface varies (Hudson & Knopoff, ; Levander, ). Since desert sand dunes are associated with topographical variation of tens or hundreds of meters and with considerably lower seismic velocities than surrounding bedrock (Almalki & Alkhalifah, ; Zhou, ), these dunes will reflect seismic signals on arrival and absorb seismic energy that is subsequently reemitted over time (Combee, ; Drummond et al, ; Ling et al, ). This scattered energy will propagate to the seismic receiver spread as seismic noise, with again the preponderance of energy transmitted by surface waves.…”