--> Looking for a New Player in Old Terranes – is there any shale gas potential in Southern Portugal?

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Looking for a New Player in Old Terranes – is there any shale gas potential in Southern Portugal?


In the last few years several authors worked to prove the hydrocarbon potential outside the Portuguese Mesozoic-Cenozoic basins. The majority of the field work focused on late Paleozoic, Carboniferous tectonostratigraphic units of Baixo Alentejo Flysch Group (BAFG), one of the most representative domains of South Portuguese Zone (SPZ). SPZ is associated to an ancient terrane/lithospheric plate subducted beneath northern Ossa-Morena Zone during Hercynian orogeny; overlying a volcano-sedimentary complex, the BAFG represents the distal sector, away from the accretionary prism and is now the main outcropping group, which nowadays preserves a low grade regional metamorphic trend decreasing southwestwards.

The amount and distribution of available geochemical data increased over the past years, at least for some sectors of Brejeira, Mira and Mértola Formations (BAFG). Recent works testify previous observations using traditional analytical methods. Gamma radiation has proven useful especially in relation to the organic maturation estimation, as well as on hydrocarbon radiometric anomalies identification.

Although some of the TOC data recently acquired show reasonable values, several questions may still stand and need further investigation. Part of those samples present vitrinite reflectance values under 2,5% Ro and consequently the potential for an unconventional shale play remains an open possibility. Should those lower than average values be considered valid? If so, it is possible that some potential might still be present in any preserved structures. Due to the high complexity observed at the surface, regional structural and thermal models need to be adjusted to explain the above observations.

Furthermore, gas shows observed onshore Mesozoic Lusitanian Basin were described as probably being sourced from late Paleozoic units. This assumption suggests a model where BAFG can be considered as an analogue source for the southern Meso-cenozoic basins. Late Paleozoic organic maturity in SPZ is now fairly representative and apparently mostly post-mature, but what happens to the Carboniferous black shales away from main metamorphic zones or in the offshore?

Unconventional reservoir exploration worldwide already proved that recipes are often different from play to play. Despite some promising geochemical results, many other parameters are crucial to prove play feasibility in this region and a long way to go is still ahead. Furthermore, the American Model for unconventional resources development hardly fits European standards. Can the Old Continent aspire to keep in the race?