Atypical igneous-sedimentary petroleum systems of the Parnaíba Basin, Brazil: seismic, well logs and cores

Abstract

The Paleozoic Parnaíba Basin has proven to be one of the most successful onshore gas basins in Brazil. Since 2010, seven gas fields have been declared as commercial. Conventional gas accumulations occur in the Devonian Cabeças Formation sandstone, Upper Devonian/Lower Carboniferous heterolitic sandstones of the Longá Formation, Carboniferous Poti Formation arkosic-sandstones and in the Upper Carboniferous Piauí Formation sandstones. The stacked geometry of an extensive Mesozoic igneous complex is responsible for the creation of several four-way structures and compartmentalization of both source rock and reservoirs. The dolerite sills intrude the organic-rich intervals of the Devonian Pimenteiras shale, triggering maturity and hydrocarbon generation, thus creating an atypical igneous–sedimentary petroleum system. Major seismic concerns are the complexity of imaging subigneous plays, the large areal extent of the basin, strong velocity heterogeneity and the difficulty of imaging high-angle or vertical sealing structures, critical to prospect success. The recognition and understanding of this atypical igneous–sedimentary petroleum system could be used to unlock the potential of analogue basins worldwide and also to expand the exploration successful cases in the Parnaíba Basin itself.

Cratonic basin formation: a case study of the Parnaíba Basin of Brazil

“…The paradox of a shallow basin, low heat flow and commercial quantities of thermogenic gas has been solved by heating and maturation due to a large magmatic sill intrusion event, invading, surrounding and thermally maturing to gas the source intervals. The same sills also act as closed structures, traps and seals for gas (Abelha et al 2018;Miranda et al 2018;Trosdtorf et al 2018).…”

“…This recent and widespread success in thermogenically-generated gas is paradoxical for such a shallow basin (maximum depth 3.5 km) on thick lithosphere, with the associated very low geothermal gradient of the order of c. 20°± 7°C km −1 (Zambruscki & Campos 1988). Miranda et al (2018) describe the atypical but conventional gas accumulations of the Parnaíba Basin petroleum system reservoired in three Devonian and Carboniferous sandstone intervals. They explain the paradox alluded to above through the seismic and well log mapping of extensive and thick Mesozoic dolerite sills.…”

Volcanic reservoirs: historic and current context

“…However, productivity declined, even though it stabilized, for some decades, in a production of approximately 2,000 BOPD (Guardado et al, 1990;Bruhn et al, 2003). The Brazilian fields case has two highlights: the first is that igneous rocks and their thermal influence have a secondary importance, as it happens in other countries, even though they are quite common in sedimentary basins (Thomaz Filho et al, 2008;Costa et al, 2016;Miranda et al, 2018;Penna et al, 2018;Cioccari & Mizusaki, 2019;Fornero et al, 2019;Correia et al, 2019;Avellar & Pereira, 2019); and second is about the complexity in offshore regions added to the presence of the pre-salt, especially in prospects of microbial carbonates and coquinas, as noted by De Luca et al (2015). In other words, better understanding the igneous rock can improve the characterization of reservoirs (sometimes in a complex geology site) as a whole, in the oil system in general, since its presence is recurrent in many prospects.…”

Palynology and geochemistry of the Frasnian global transgression in the Parnaíba Basin, Brazil

“…Dry composition is normally indicating a generation at high maturation stage. However, in Parnaíba Basin, this condition is not reached by burial, suggesting an atypical process of generation related to the heat effect of dolerite intrusions (Rodrigues, 1995;Rodrigues et al, 1995Rodrigues et al, , 2012Zambrano et al, 2017;Miranda et al, 2018;Cioccari and Mizusaki, 2019).…”