Análise espectral de ruído sísmico ambiental de bacias sedimentares do nordeste do Brasil

Abstract

An increasing number of low-frequency seismic research in oil and gas producing fields has shown the presence of anomalies between 1 – 6 Hz. These signals are known as hydrocarbon microtremors (HM), and the method of analysis of these records has stood out among geoscientists as a Direct Hydrocarbon Indicator (IDH). This method, which is completely passive, that is, does not require sources of artificial excitation, is useful for optimizing the distribution of wells during exploration, as well as the development and monitoring of oil and gas fields. In this work, the Passive Seismic method was applied in the NE region of Brazil using an arrangement of 28 short-period seismographic stations, distributed along a linear profile that crossed the sedimentar basins of Potiguar, Jatobá and Tucano. Using the seismic data from the 28 stations, the spectral attributes of vertical-horizontal ratio (V/H), vertical component power spectral density (PSD-Z) and polarization were analyzed. Through the results it was possible to identify the spectral anomaly (3 Hz) which serves as a direct hydrocarbon indicator (DHI). A prior analysis of the data was performed using spectra and spectrograms to identify and correct possible errors in the sensors. Then, spectral attributes were applied for each station and the results were analyzed and compared. From these results, it was noticed the absence of anomaly generated by in areas outside the sedimentar basins and, for the seasons on the Potiguar and Jatobá basins the attributes indicated respectively a médium and low hydrocarbon potential. For the stations on the Tucano Basin, the Passive Seismic method identified there is a variation in the oil potentical in the área, ranging from médium to low, however, stations A037 and 9FFC indicated high hydrocarbon potential. Everything leads to believe that this observation in the hydrocarbon indicator may be the thickness of the reservoir.