Spain Factsheet 

Figure 1: Generalised stratigraphy within main area of geographical focus. Black spots are potential/proven reservoir horizons and red flags are potential/proven source rocks.

Deposited during the Variscan orogeny, Carboniferous shales, analogous to those in the Fore Sudetic Monocline of Poland, have shown significant shale gas potential. Often reaching several thousand meters in thickness and with coals, high total organic carbon (TOC) shale and type II/III kerogen, the interval commonly lies within the gas generating window indeed it is these Carboniferous shales and coals provided the hydrocarbon source for the Gaviota field.

Liassic (Jurassic) shales within the hydrocarbon generating window, reportedly the source for the Ayeluengo field, attain thicknesses of several 100 meters and show TOC’s upwards of 8%. Asphalts linked to Jurassic shales have been actively mined in Northern Spain, and Jurassic oil is also known to have been the reducing agent for Cantabrian lead/zinc deposits in Lower Cretaceous limestones.

The Upper Cretaceous (Albian/Cenomanian) is the source for the proven gas in the Castillo field. In the 1960s the Valmaseda Fm. proved to be a viable exploration target with vertical wells capable of initial rates of several million standard cubic feet per day. Decline curves were steep however, suggesting relatively low permeability. Modern drilling, completion and stimulation techniques provide encouragement that this unit can deliver sustained high production rates. In apparent support of that, the most recent discovery (Viura - 2010) was put on production in March 2015 at an initial rate of 10.5MMSCFD ramping up to 17.5MMSCFD by year end.

Eocene flysch shales, deposited in the fore-land of the Pyrenean mountains and with TOC values of around 1-1.5%, have proven to be the source for the Eocene Serrablo field, as well as the Riudaura discovery.



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