Abstract
The Lapa field is situated in block BM-S-09 of the Santos Basin, with production having started some years ago. Here the pre-salt reservoir rocks are formed by the Aptian microbial carbonates of Itapema and Barra Velha Formations. More precisely, the target lays in a marginal high in a mantle-decoupled domain under extension constraint with transfer zone and local inversion. The hydrocarbon bearing reservoirs are oil-bearing showing a 4-way dip closure with one main porous sequence and a tight zone underneath. With the northeast part of the field already well developed, the context of a re-processing, imaging and inversion program is that of a planned increase in activity in the southwest part of the field. The southwest part of the field is complicated by rapidly changing thickness of overburden salt, that can have an impact on seismic products. The objective of the study is to get a seismic image more suitable for the interpretation of this structurally complex field, with reliable amplitude information for lithology and porosity characterization of Lapa reservoirs.
Amplitudes on seismic images can reveal important information regarding Petro-Elastic (PE) properties of geological formations. "Amplitude preservation" during seismic data processing and imaging is key for many exploration and development projects. Though in data processing steps (pre-migration) this is assured by direct evaluation of input and output data amplitudes, in the imaging process, amplitude preservation is a more effortful task. This is mainly due to the complications concerning imaging algorithms (e.g. the approximations for wave propagation regime) and geological complexity of the subsurface. For example, in complex media, such as deep salt structures, imaging algorithms based on asymptotic approximation of wave propagation (e.g. Kirchhoff and Beam migration) may not deliver very accurate images (from structural and amplitude perspectives). Therefore, for subsurface imaging of complex zones, industry tends toward more accurate algorithms such as Reverse Time Migration (RTM) and Least Squares (LS) imaging. Moreover, for elastic inversion based on or AVO/AVA principles (Amplitude Variation with respect to Offset/Angle) one needs to create offset/angle gathers in an amplitude friendly manner. In this study, we present our workflow to produce an amplitude friendly image with a high SNR (signal to noise ratio) suitable for elastic inversion.
