--> The Silurian of Dornes and Mação (Central Iberian Zone, Portugal) and its shale gas potential: preliminary results

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The Silurian of Dornes and Mação (Central Iberian Zone, Portugal) and its shale gas potential: preliminary results


The Silurian units of the Central Iberian Zone, specifically in the area of Dornes and Mação, are relatively unknown regarding its potential for oil generation/accumulation. The recent geological map of Mação (28-A), and literature on the age of the outcropping formations, based on the available biostratigraphic record, as well as some recent maturation values, palynological studies and stable isotopes data, are the only relevant works developed in the region from the hydrocarbon exploration point of view. However, more work needs to be done in order to assess the potential interest in hydrocarbon exploration of these shale units.

The lithostratigraphic units of the Dornes and Mação region displaying potential interest in unconventional hydrocarbons exploration are Vale da Ursa Formation, Foz da Sertã Formation, Aboboreira Formation and Chão Lopes Formation, all Silurian in age, and with 30 to 200 meters thick. Such thickness range, potentially generating/accumulating, in addition to other factors, respects one of the main premise in unconventional hydrocarbons exploration, which also requires significant lateral continuity of the formations, or at least little or no fracturation.

As for the maturation values in the literature, the vitrinite reflectance values are in the order of 1.9%, pointing to the gas window, which is a good indicator.

Given its potential for the industry of non-conventional hydrocarbons several preliminary studies were developed at the Dornes and Mação region in order to understand the origin, deposition and subsequent deformation of the Silurian units, as well as to identify the factors that may have originated hydrocarbons. They include stratigraphic logs, gamma-ray spectrometry, total organic carbon (TOC) analysis, rock-eval and illite crystallinity.

Despite being in an early stage, the obtained results so far are comparable to other areas with potential for the exploitation of shale gas around the world. Further studies will enable a deeper knowledge on the unconventional petroleum system in the above mentioned formations, and a more accurate assessment of their shale gas potential.