Otimização da interpretação sísmica via aumento de banda espectral e inversão acústica. Aplicação em caracterização de reservatórios não convencionais de hidrocarbonetos

Abstract

This study discuss several methodologies widely used in the oil industry for conventional reservoirs characterization. On this dissertation, those methodologies were tested and applied in an integrated workflow for an unconventional reservoirs characterization, where the source rock is also the reservoir rock. A case study at the Brejo Grande field, located at an onshore portion of the Sergipe Basin is presented here. Within this region it’s believed that the generating shales of the Coqueiro Seco Formation are buried at a depth within the hydrocarbon generation window. For the development of this dissertation a 3D seismic volume of the Brejo Grande area and logs of four wells provided by ANP (Agência Nacional de Petróleo) were used. To the seismic data a workflow that consists of three main stages were applied: precon- ditioning, enhancement of spectral bandwidth and data inversion. The preconditioning stage consists basically on the inspection, uploading and filtering application to the seismic data in order to attenuate the random noise effects. A filter that uses information of dip and azimuth of the seismic reflection was used as a guide to the filtering process. As a result, an enhancement on the signal/noise ratio of the seismic data was obtained. On the second stage a technique called Seismic Spectral Blueing (SSB) was applied to the filtered data with the objective to enhance the spectral bandwidth of the seismic data, making it blue, it means higher amplitude higher frequencies. The high frequencies are necessary to enhance the resolution of the seismic and define thinner layers and structural features such as faults and fractures. At the last stage, the seismic data was inverted to obtain relative acoustic impedance, which represents the contrast impedance between subsequent layers. The seismic inversion was performed using the Seismic Coloured Inversion (SCI) technique. The main goal is to analyze the impact of these methodologies in subsequent seismic interpretation stage and on the unconventional reservoirs characterization. The result of these methodologies applications showed the reduction of noise content into the seismic data, a better event definition, mainly in thin layers, and a greater lateral continuity of events. These enhancements lead to a volume with a higher precision and better resolution to the interpretation stage. The results obtained were corroborated through wells log profiles. Due to the Seismic resolution enhancement, it was possible to map into Coqueiro Seco Formation alternate layers of arkoses and shales, validated through wells logs profiles, mainly of the Gamma Ray log. The fracture and faults study is highly important to the characterization of unconventional reservoirs, the detailed mapping of those structures is extremely necessary. Several techniques used for unconventional reservoirs production such as fracturing and mud injection expels the hydrocarbon out of the pores, and if those structures are not mapped, it may occur scape through these structures in unwanted locals. During the seismic interpretation was observed the presence of a NW-SE faulting on the Coqueiro Seco Formation that divide the block into two parts. The shale of the NE portion is more shallow and more fractured, while the SW shale is more homogeneous and non-fractured.