Seismic attributes, well correlation and geostatistical analysis for sequence variability prediction in the Sleipner area

Abstract

The upper Cenozoic stratigraphy in the northern North Sea (Sleipner area) have been investigated, using high quality 3D seismic data and five exploration wells. Interpretation of the seismic data, have indicated six distinct sequences (S1-S6). These sequences have been classified according to reflection configuration, and well log characteristics. Based on the seismic data, a simple model have been constructed for the upper Cenozoic succession. The model form the basis for co-kriging interpolation, which have been used to interpolate the petrophysical data from the well logs in each sequence. This gives the possibility to predicate how the petrophysical properties change laterally within the study area. The upper most sequences (S1 – S3) is deposited from Pliocene to Holocene. These sequences have continuous reflections, with a parallel to subparallel reflection geometry. This configuration is often seen in sediments derived from glacio-marine processes. The well logs indicate that these sequences consist of shale, and the co-kriging interpolation, indicate that this lithology is dominant in the entire Sleipner area. Sequence S4 correspond to the Utsira formation, which is currently used as a 𝐶���𝑜���2storage. The Utsira formation consist of well-sorted sands, from Upper Miocene to Lower Pliocene. The seismic response, is characterized by low amplitudes, discontinuous reflections. This reflection configuration can be seen in relation to the shelf dominated, shallow marine environment, which the sequence was deposited in. The well logs clearly indicate a sand interval, and can be strongly correlated between the five wells. The co-kriging interpolation technique, indicated that the Utsira formation is present in the whole study area. Sequence S5 was deposited during Middle Miocene. The sequence comprises several discontinuous reflections, with a disrupted configuration. Numerous anticlinal features have been observed at the base of the sequence, possibly caused by mobilized sediments, injecting into the sequence. The reflection configuration is highly affected by these features. The well logs indicate a shale dominated interval, with a few thin-layers of sand. The co-kriging interpolation, confirms a shale dominated lithology with localized sands in the study area. Sequence S6 is deposited during Lower Miocene, and show a shale dominated lithology. The sequence comprise several high amplitude, discontinuous reflections. This configuration is related to extensive polygonal faulting of the sequence. The co-kriging results, suggest that sequence S6 consist of shale in major parts of the study area.