Caracterização estratigráfica, petrográfica e qualidade de rochas reservatório dos arenitos do Membro Siderópolis na região carbonífera de Santa Catarina

Abstract

The primary goal of this research is the petrographic, petrophysic and sedimentological characterization of Siderópolis Member arenites of the Rio Bonito Formation, set in Santa Catarina Coalfield. To guarantee an accurate characterization, several methods were utilized that consisted of: burial history model, stratigraphic profiles, geologic sections, as well as structural and paleogeographics maps. A structural graben was identified on the structural map of the base of the Barro Branco coal seam. The graben is located in the center of the study area and is limited by two principle fault systems (NW-SE and NE-SW). Thirteen faciologies were determined from core descriptions, which were then assembled into six facies associations interpreted to have been deposited in a coastal environment related to a lagoon-barrier island. Chronostratigraphic sections assisted in the characterization of the Siderópolis Member s depositional evolution, which was identified one complete transgressive-regressive cycle. During the transgressive event, barrier deposits developed and advanced over lagoon deposits. Whereas the regressive event shows sedimentary progradational stacking that is characterized by lagoon deposits (registered in all wells) and formation of the main coal seams in the study region. The Siderópolis Member arenites diagenetic evolution has three diagenetic stages: the early diagenesis (infiltrated clay, kaolinite, quartz outgrowth, siderite and calcite cementation as principal constituents), the late diagenesis (poiklotopic calcite, feldspar and quartz outgrowth, illite, chlorite and albite), and the telodiagenesis (iron oxides/ hydroxides). Linking diagenesis with burial and thermal history models (which was realized based on backstripping), it is observed that the stratigraphy unit stayed inside the early diagenesis window during the majority of its depositional time. Combining this burial history and the meteoric water percolation through the coal seams, enhancing the early diagenesis processes such as kaolinitization and dissolution. Moreover, the relative shallow and cooler precipitation of albite (about 1450m and 100°C), as well as, pervasive chlorite, illite and quartz outgrowth in study area, indicates an influence from hot fluid of the Serra Geral magmatism. Four petrofacies were defined for the study member using petrophysics and petrographics data. Petrofacies A has the best reservoir potential. However, the database used in this study indicates the need to be cautious when characterizing these arenites as a reservoir. This is due to the facies variation, the existence of zones with predominant carbonate cementation, levels with intense concentration of authigenic clays, and pervasive quartz and feldspar outgrowth, which lead to big reservoir heterogeneities and compartmentation and results in porosity and permeability anisotropy.