Conceptual Geological Models (CGM) serve as a robust tool for 3D reservoir model building, since they allow the representation of geological knowledge in the subsurface, guiding the depiction of fault and fracture distribution, providing insights into their local occurrences, densities, orientations, and aperture. The Brazilian pre-salt carbonate reservoirs are characterized by complex fault systems and natural fractures, with variations related to structural geology, paleotopography, and stratigraphy. This study aims to integrate a CGM into 3D reservoir modeling, focusing on faults and fractures below seismic resolution for an area within an oilfield in the Santos Basin (Santos Outer High), centered on the Barra Velha Formation (BVE), where a PSDM seismic volume, wells (with conventional and special logs), and core samples and thin sections were available. Data analysis resulted in the interpretation of the main horizons in the area and the preferential distribution of fracture families (P10, P20, and P21). Findings from a CGM of fracture distribution were incorporated into reservoir modeling through the Discrete Fracture Network (DFN) methodology, in particular, that the fractures in the BVE are generally correlated with silica-rich zones of the formation. From this, maps of silica distribution were elaborated for the different stratigraphic units of the BVE and used as a constraint for the creation of the fracture networks and the DFN model. Preliminary results show that the use of a CGM proved to be advantageous in the DFN model creation process.
Tag: Pre-salt
Paleokarst features in the Aptian carbonates of the Barra Velha Formation, Santos Basin, Brazil
Seismic data, borehole image logs, and conventional well logs were used to investigate the distribution and characteristics of paleokarst features in the Aptian carbonates of the Barra Velha Formation in a pilot area of the Santos Basin, Brazil. Multiple seismic attributes were used to enhance details on the seismic data and highlight key seismic parameters including strata deformation and geometry, continuity of seismic events, and fault patterns. The study found that karst structures are controlled by faults and fractures along structural highs, which served as a conduit for the flow of dynamic fluids that dissolved the carbonate materials. Several closed, circular depressions and bright spots identified in the northeastern portion of the study area represent possible sinkhole structures. Epigenic and hypogenic processes due to the action of meteoric water, hydrothermal activity, and intra-formation acidity along regional unconformities in the Barremian-Aptian may have been responsible for the dissolution. Limitations of this study are related to the difficulty of integrating multiple datasets with various scales. However, the higher confidence for the occurrence of the karst features is provided by borehole images at the sub-seismic scale. The findings of this study hold significant relevance for the strategic planning of energy development and carbon sequestration initiatives in the Brazilian continental margins, thereby aiding in informed decision-making.
Impact of seismic data conditioning on the identification of structural elements: A case of study from the pre-salt reservoir, Santos Basin, Brazil
Three-dimensional seismic data provides valuable insights into structural interpretation when dealing with naturally fractured reservoirs. The faults or fractures may control the direction of fluid flow in the reservoirs, especially during the sensitive analysis in projects of carbon sequestration and reservoir development, since these features may impact the rock-fluid interaction and oil field production. However, characterizing faults and fractures in pre-salt reservoirs using conventional approaches is challenging due to a complex and heterogeneous overlying evaporitic unit which reduces the seismic-to-noise ratio. Therefore, seismic data conditioning targeted at improving the seismic image is necessary for quality subsurface investigations. This work provides a systematic series of filters to enhance and detect discontinuities in post-stack seismic volume, primarily by reducing migration artifacts and salt multiples, thereby maintaining the true geological characteristics of the data. We emphasize the delineation of the fault and potential fracture zones by computing seismic attributes in a post-stack time-migrated 3D seismic in the Santos Basin’s deep waters. Initially, the seismic signal-to-noise ratio was analyzed, and a sequence of structural-oriented filters and spectral balancing was applied to generate vertically refined images with enhanced seismic amplitudes. To assess the quality of the conditioned data, we employed the Similarity and Curvature attributes to identify the distribution of discontinuities and compare the before-and-after denoising approach. The data conditioning and analysis of seismic attributes improved our understanding of the distribution and compartmentalization of the reservoirs, highlighting predominantly NE-trending discontinuities. The systematic processing significantly improved the signal-to-noise ratio, allowing us to identify the relative direction of structural elements and insights into potential fractured zones over the reservoir.