Facies, petrophysical and geochemical properties in analogues to heterogeneous reservoirs of the Itararé Group, Paraná Basin

Studies on reservoir analogs have been widely used aiming to better understand the spatial distribution of reservoir properties, since many reservoirs do not allow direct observation due to their depth and difficulty of sampling. The Paraná Basin has two known petroleum systems with potential for the generation and accumulation of hydrocarbons. The Itararé Group, due to the exploration history, is the best exploratory target in the basin because it has thick intervals of sandstones with moderate to good reservoir quality and also because it often lies directly on gas-prone source rocks of the Devonian Ponta Grossa Formation. In order to increase knowledge about Itararé Group reservoirs, as well as to better understand its heterogeneities, this study aims to integrate petrophysical data with facies and facies associations using both outcrop and cores from shallow wells in the region of Mafra and Doutor Pedrinho, Santa Catarina. By doing this it is expected to fill a gap of quantitative data in previous studies on reservoir analogs in the Itararé Group. Cores and outcrops were analyzed in sedimentary facies in order to integrate surface and subsurface data, and to understand the lateral continuity according to stratigraphic correlations. Equipment such as gamma-ray spectrometer, portable x-ray fluorescence, and a minipermeameter were used for the acquisition of quantitative data. Sedimentological description of cores and outcrops as well as thin section description were also carried out. As a result, 15 facies were described, in which massive and normally graded sandstones showed the highest porosity (9 to 32%) and permeability (68 to 222 mD). The API values have wide variation in facies with normally graded due to composition variation (63 to 152 °API). In relation to the massive facies, the API variation is lower (61-103 °API). The analyzed geochemical values are related to the elements SiO₂, AI₂O₃, Fe₂O₃ and TiO₂, to evaluate the relation of the clay minerals in the composition of the samples. In samples of higher clast size, iron and titanium oxides are associated with clay minerals. In fine sands, the iron oxides are associated with cementation and clay minerals. Both facies are interpreted as the deposits of turbidity currents. These turbidites are spatially associated with deformed facies remobilized by mass transport which porosity and permeability and lateral continuity of sand bodies are lower. We conclude that the best reservoir facies in the Itararé Group will be associated with sites located basinward from the slope region and the influence of mass-transport processes. (author)