CHARACTERIZATION OF GAS CHIMNEYS IN THE PARNAÍBA BASIN: A NEW EXPLORATORY TOOL
Gas chimney; oil exploration; special seismic processing; frequency spectrum; Parnaiba Basin.
This study aims to apply a special processing in the investigation of gas chimneys in the Parnaíba Basin and, to use this knowledge, as an exploratory tool in hydrocarbon research. The new processing methodology aims to facilitate the visualization process in seismic of the gas chimneys by frequency spectrum enhancement of the seismic signal in the Hilbert domain. Allowing for an amplification of the information concerning the petroleum system, this research methodology diminishes the high exploratory risks inherent to the frontier basins with high territorial extension such as the Parnaíba Basin. Other basins that were also visited in this dissertation using this technology were the Paraná and Tacutu basins. Often the seismic response of gas chimneys is treated as noise or even their presence is not even perceived in conventional PSTM seismic processing. This work shows a processing methodology that seeks to highlight the gas chimneys and make their interpretation in the seismic profiles unequivocal. Its sismofacies consists of chaotic and low-frequency disturbances that interrupts the lateral continuity of good reflectors and its origin is related to migration of fluids or free gas in its path between the source rock and the reservoir rock. In addition, this research, by observing the rooting of the gas chimneys in the basin grabens, strongly indicates a new petroleum system associated with the deposits present in the pre-silurian grabens. To prove that these seismic features enhanced by the new processing are actually gas chimneys, a validation work was carried out to identify topographic, seismic and geochemical features that occur in other sedimentary basins associated with the presence of gas chimneys. To facilitate the management of future exploratory process by directing the new seismic programs to be acquired, a table was elaborated with the different types of traps associated to gas chimneys found in this basin and their respective probabilities of success considering the results obtained in this basin and in other parts of the world. Those most likely to succeed should be those chosen for further seismic detailing. Considering the quantity of gas chimneys encountered with this special processing, the significant area of the structures found and the other direct hydrocarbons indicators revealed in the work, it can be affirmed that one faces a high potential basin for commercial discoveries of hydrocarbons and with relatively low risk.