Implicações do magmatismo nageração e migração de hidrocarbonetos na Bacia do Parnaíba, Brasil, a partir da Modelagem 1D de sistemas petrolíferos

Abstract

The Parnaíba Basin is considered an exploratory frontier basin, with a recent exploratory success story, but it already represents the fourth place among the basins with the highest production of natural gas per day. The petroleum system established for the main gas accumulations is framed in the so-called atypical systems that is still meanly understood due to the influence of sills in the thermal maturation of the source rock, in the generation and migration of hydrocarbons, in addition to forming the seal and the trap for the accumulations. The main source rock and focus of the study is the Pimenteiras Formation, which was characterized by Rodrigues (1995), with three source intervals A, B and C being recognized, also counting with the D interval, which is less characterized. Using geochemical analyzes and data from wells, located in the center-north portion of the basin, and with the 1D modeling program, Silli 1D, the quality, distribution and thermal maturation of these source intervals were initially evaluated and then defined three wells for 1D modeling. Each well represents a scenario of thermal maturation for the source intervals and integrated with the oil and gas records in the wells, the thermal effects caused by multiple intrusions in the Pimenteiras Formation and the result of the oil, gas generation, retention and expulsion framework were evaluated. The thickness maps and residual TOC of the source intervals show enough thickness to be considered intervals with excellent source rock potential also with a good distribution in the basin. Thermal maturation maps seen through the reflectance of the vitrinite indicate that in the central region, where the largest amounts of sills are concentrated in the Pimenteiras Formation, there is a predominant maturation for gas generation, with greater degradation of the COT. As it continues towards the north-northwest, there is less thermal maturation and greater potential for oil generation, in addition to a higher residual TOC content. The best fit between the well data and thermal modeling results was assuming that the intrusions occurred at intervals of 30,000 years, from the entry of the first sill at 201.25 Ma, and this first sill was the deeper in the stratigraphic stacking. The most advanced stage of thermal maturation is achieved mainly in areas where there is interaction of the thermal effects of multiple sills and in simulations in which the intrusions are simultaneous or with a time interval between the intrusions equal to or less than 10,000 years. The main factors that influenced the thermal evolution history of the source intervals were the thickness and quantity of the intrusions, the relative distances from the sills, the thermal pre-conditioning of the host rock and the chronological order of the intrusions. The implications of these factors are observed in the volumes of generation, retention and the capacity of expulsion of oil and gas from the source rock, presenting in most models, a significant increase in the volume of oil cracked for gas, through secondary cracking, where most of this volume of gas is expelled from the rock. The source intervals in areas more distant from the sills, present less secondary cracking and a larger portion of the oil generated, is retained in the source rock.