Thermal history of potential gas reservoir rocks in the eastern Parnaíba Basin, Brazil

Abstract

The Parnaíba Basin is a major intracratonic sedimentary basin in Brazil with unconventional petroleum systems as a potential natural resource formed by the influence of igneous intrusions. To constrain the thermal history of unexplored potential reservoir rocks in the eastern part of the Parnaíba Basin, sedimentary rocks near intrusions were analyzed by petrography and thermochronology (apatite fission-track [AFT] and zircon fission-track [ZFT] dating). Petrography shows grain dissolution and carbonate pore filling generated by thermal destabilization of feldspars. The AFT results indicate partial annealing by the last magmatic event in the basin, and ZFT results show ages of maximum paleotemperature compatible with the Sardinha magmatic event (120–130 Ma). In thermal history models, rocks close to intrusions experienced maximum paleotemperatures above 300°C, which is higher than what is considered favorable for reservoir rocks. Hydrothermal fluids modified the diagenetic evolution of the succession by dissolving and precipitating carbonate cement in pore spaces. In the studied area, at distances greater than 50m(>164 ft) from the intrusion, the rocks were not substantially altered, and in terms of paleotemperature, they can be considered potentially viable reservoirs. The thermal history analysis of potential tight gas sandstone reservoirs affected by intrusive bodies is valuable for characterizing the thermal enhancement or destruction of the reservoir’s qualities.