Preliminary model of hydrocarbon reservoir related microtremors and recent application in the Potiguar Basin
Published in
11th International Congress of the Brazilian Geophysical Society held in Salvador, Brazil
Date of publication
25 August 2009
Abstract
Passive seismic low-frequency (between about 1 Hz and 6 Hz) data has been acquired at several locations around the world. Spectra calculated from this data, acquired over fields with known hydrocarbon accumulations, show common spectral anomalies. A preliminary model is presented which can explain the source mechanism of those microtremors. Poroelastic effects due to wave induced fluid flow and oscillations of different fluid phases are significant processes in the low-frequency range which can modify the earth’s omnipresent seismic background spectrum. These processes only occur in partially saturated rocks. We assume that hydrocarbon reservoirs are partially saturated whereas the surrounding rocks are fully saturated. Real data observations are consistent with this conceptual model.
This paper also discusses a recent application of the technology in the Potiguar Basin, onshore Brasil. Although this project included acquisition, processing and some interpretation, only the main points of the project are highlighted, as follows: out of the five project areas, one area shows the highest potential, two medium and two low/no potential. Both PSD-IZ and V/H attributes are calculated for all areas, but given the high environmental and anthropogenic noise conditions in most areas, the V/H attribute proves to be the most reliable one, which correlates well with operator field knowledge of hydrocarbon locations. Also, a mini-survey conducted over the previous 2004 Mossoro I project location shows good repeatability of results in an area which has not been produced and utilizing new tools that do not require surface correction. Finally, we learned that 24hour measurements, longer synchronized lines and greater aperture are essential for this area, adding them into our requirement base for new projects in similar locations.
This paper also discusses a recent application of the technology in the Potiguar Basin, onshore Brasil. Although this project included acquisition, processing and some interpretation, only the main points of the project are highlighted, as follows: out of the five project areas, one area shows the highest potential, two medium and two low/no potential. Both PSD-IZ and V/H attributes are calculated for all areas, but given the high environmental and anthropogenic noise conditions in most areas, the V/H attribute proves to be the most reliable one, which correlates well with operator field knowledge of hydrocarbon locations. Also, a mini-survey conducted over the previous 2004 Mossoro I project location shows good repeatability of results in an area which has not been produced and utilizing new tools that do not require surface correction. Finally, we learned that 24hour measurements, longer synchronized lines and greater aperture are essential for this area, adding them into our requirement base for new projects in similar locations.
