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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Fluid inclusions in calcite filled opening fractures of the Serra Alta Formation reveal paleotemperatures and composition of diagenetic fluids percolating Permian shales of the Parana Basin

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Teixeira, C. A. S. [1] ; Sawakuchi, A. O. [1] ; Bello, R. M. S. [1] ; Nomura, S. F. [2] ; Bertassoli, D. J. [1] ; Chamani, M. A. C. [1]
Total Authors: 6
[1] Univ Sao Paulo, Dept Geol Sedimentar & Ambiental, Inst Geociencias, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil
[2] Petroleo Brasileiro SA Petrobras, Unidade Operacoes E&P Bacia Santos, Rua Marques Herval 90, Santos, SP - Brazil
Total Affiliations: 2
Document type: Journal article
Source: Journal of South American Earth Sciences; v. 84, p. 242-254, JUL 2018.
Web of Science Citations: 2

The thermal and diagenetic evolution of shale units has received renewed focus because of their emergence as unconventional hydrocarbon reservoirs. The Serra Alta Formation (SAF) is a Permian shale unit of the Parana Basin, which is the largest South American cratonic basin. The SAF stands out as a pathway for aqueous fluids and hydrocarbon migration from the Irati organic-rich shales to the Piramboia fluvial-eolian sandstone reservoirs. Vertical NNW and NNE opening fractures would be the main pathways for the migration of buried pore waters and aqueous fluids, besides the input of meteoric water. These fractures would be associated to the reactivation of basement discontinuities such as the Jacutinga (NE) and Guapiara (NW) faults. Thus, vertical NNE and NNW associated fractures would represent the main pathways for fluid migration in the studied area. The vertical calcite filled opening fractures from SAF record moderately low salinity (0-4.5 wt % of NaCl eq.) aqueous fluids, suggesting the input of meteoric water in the buried fracture system. Eutectic melting temperatures at -52 +/- 5 degrees C indicate an H2O + NaCl + CaCl2 system with CaCl2 or MgCl2 in solution. Homogenization temperatures recorded in fluid inclusion assemblages (FIAs) of calcite filled opening fractures indicate that the SAF in the studied area reached temperatures above 200 degrees C, suitable for generation of gaseous hydrocarbons. The recorded paleotemperatures point to a thermal peak associated with Serra Geral volcanic event during the Early Cretaceous, with the thermal effect of volcanic rock cap possibly overcoming the effect of intrusive igneous bodies. The detection of methane in SAF shale pores indicates conditions for hydrocarbon generation. However, additionally studies are necessary to confirm the thermogenic and/or biogenic origin of the methane within the SAF. (AU)