Over the last century, oil and gas (hydrocarbons) have come to form one of the principal energy sources supporting human economic development and welfare. Hydrocarbons currently account for 56.79% of the world's consumption of primary energy (BP, 2016). This trend is forecast to continue over coming decades, in both developed western nations and in emerging economies (International Energy Agency, OECD/ IEA, 2012a, b).

Hydrocarbons were already being produced in the Basque-Cantabrian Basin (BCB) from as early as the eighteenth century. In the Maeztu area of Alava, oil was extracted from the pores of various surface reservoir rocks.

Once the value of oil as a basic energy source came to be understood, these traces of oil on the surface attracted further surveying.

Indeed, since the early twentieth century, the basin has been one of the leading targets of onshore and offshore exploration on the Iberian peninsula.


2007 – present

Current stage

During this period, SHESA has participated in the drilling of several wells:

  • 2009 Estella-1 (Operator SHESA): Negative result.
  • 2009 -2010: Viura-1 (Operator UFG): Discovery of a conventional natural gas deposit.
  • 2013 Viura-3 (Operator UFG): Excellent traces of gas.
  • 2017–2018: Viura-1 (Operator UFG)


VIURA is an oil and gas exploration project led by UFG E&P (Unión Fenosa Gas Exploración y Producción, S.A.) on conjunction with SHESA (Sociedad de Hidrocarburos de Euskadi, S.A.) and OGS (Oil and Gas Skills, S.A.). The project is being carried out in the province of La Rioja and was originally associated with the Cameros-2 and Ebro-A exploration licences.

When the Viura-1 well (2009 – 2010) was drilled in the municipal area of Sotés, conventional natural gas was discovered. Following initial drilling, tests were run which showed sufficient production flows to allow the project to continue.

In 2013 the Viura-3 well was drilled in the municipal area of Hornos de Moncalvillo. The well had excellent gas traces.

The first natural gas from the well was introduced into the national network in February 2015, and in early March it began to be commercialised on a continuous basis.

The Royal Decree awarding the VIURA hydrocarbon deposit operating concession was published in the Official State Gazette (BOE) on 25 July 2017.

In October 2017, the Ministry granted authorisation to drill Viura-1 ST3, a sidetrack well from Viura-1. Drilling concluded in February 2018.


Very few seismic lines have been acquired during this phase. However, there has been a spectacular advance in geological understanding of both the surface and subsurface, and this new information has been added to our knowledge of the dynamics of the different oil and gas-bearing systems.

Our understanding of the subsurface has been further increased by reprocessing and re-interpretation of a large number of seismic lines acquired in the past throughout different sectors of the BCB and surroundings. Since it was first set up, Sociedad de Hidrocarburos de Euskadi has played a very important part in this work.

By integrating this geological information with knowledge of the dynamics of oil and gas-bearing systems in the BCB, it has been possible to:

  • discover new oil and gas-bearing systems, generally local within the basin.
  • extend our knowledge of the oil and gas-bearing systems.
  • locate geological structures in different oil and gas-bearing systems with the potential to host accumulations of hydrocarbons.

This substantial boost to our understanding of the dynamics of the different oil and gas-bearing systems in the Basque-Cantabrian Basin should form the basis for future discoveries.


1973 – 2007

Systematic onshore and offshore exploration

During this phase, intense acquisition of onshore and offshore seismic lines and the drilling of wells continued, albeit at a slightly slower pace than in the previous stage.

Information began to emerge on offshore Oil and gas-bearing systems, entirely unconnected to those previously explored and exploited onshore. As had already happened onshore, the real oil and gas potential of underwater resources and an increase in information led to the first positive discoveries.

  • 68 wells drilled, 21 of which were offshore
  • 1982 – 1983 Navajo-1: Traces of gas
  • 1983 – 1984 Cadialso-1: Non-commercial accumulation of gas
  • 2000 – 2001 El Coto-1: Traces of gas
  • Castillo gas field (Valmaseda formation): Drilling of Marinda-1 (1974), San Antonio-1 (1982 – 1984), Armentia-1 (1997). In long-term production tests, Armentia-1 supplied more than 0.5 bcf of dry gas.
  • Gaviota gas field and its satellite, the Albatros gas field: In production from 1986 to 1994

1959 – 1973

Consolidation of systematic onshore exploration

This stage was marked by intense exploratory activity, with 118 wells drilled, numerous seismic lines acquired (primarily onshore but the first offshore lines were also run) and the first commercial oil and gas discoveries.

  • 1959 – 1961 Castillo-1: Castillo gas field in production from 1962 to 1981. Gas was found in all wells running through what would later be called the Valmaseda formation.
  • 1964 Ayoluengo-1: Ayoluengo oil field. In production until February 2017.
  • 1965 Hontomin-1: Non-commercial oil accumulation.
  • 1973 Golfo de Vizcaya-1: First offshore well.

1941 – 1958

Beginnings of systematic exploration

Exploration programmes during this period were based on technical criteria. However, the data used were scarce and of dubious quality. No information was as yet available on the subsurface (seismic lines), a basic tool for investigation.

  • 28 wells (recorded). No commercial discovery but the results of some wells augured well for future discoveries
  • 1949 Peña Ortun-1: Traces of oil and gas
  • 1954 Zuñiga-1: Traces of gas
  • 1956 Alda-1: Traces of gas
  • 1957 Leva-1: Traces of oil
  • 1958 Retuerta-1: Good traces of oil and gas


1915 – 1941

First wells

Etapa en la que no se conocía ninguna herramienta de investigación indirecta que permitiese obtener datos geológicos de subsuelo. Los pozos exploratorios se emplazaban sobre indicios de hidrocarburos existentes en superficie, sobre núcleos anticlinales o en la proximidad de diapiros.

  • 1915 Salvatierra-1: First (recorded) well drilled to explore for oil and gas. Negative result.
  • 1922 Uzuguiano-1: Negative result
  • 1923 Elorrio-1 and Jaizquibel-1: Negative result
  • 1940 Zumaya-1: Negative result


    • • 1960: Castillo-1 drilling (Operator CIEPSA)
    • • 1961: Castillo-2 drilling (Operator CIEPSA)
    • • Castillo-1 and Castillo-2 production start-up (until 1981). Produced dry gas, practically pure methane. Accumulated production 33 MNm3
    • • 1997: Armentia-1 drilling (Operator SHESA)
    • • Armentia-1 long-term test until 2003
    • • Accumulated production Castillo-1 + Castillo-2 + Armentia-1 = 52.8 MNm3

    Source rock: Black shale from the Albo-Cenomanian
    Reservoir rock: Fractured limestones and sandstones from the Cretaceous (upper Albian – Turonian)


    • • 1964: Discovered with drilling of Ayoluengo-1 well (Amospain-Campsa)
    • • 1966 – February 2017: In production
    • • 53 wells drilled
    • • From 1986 on, the gas produced was used for power generation
    • • Accumulated oil production 2.30 Mt

    Source rock: Marls and black shale from the marine Jurassic megasequence
    Reservoir rock: Sandstone and canaliform conglomerate levels from the Purbeck Complex


    • • 1980: Discovered with drilling of the Vizcaya B-1 well (Operator Eniepsa)
    • • 1986 – 1994: In production
    • • Accumulated Gas production: 7,242 MNm3
    • • Accumulated condensate production: 536,982.4 t

    Source rock: Black shale and coal levels (carboniferous)
    Reservoir rock: Upper cretaceous limestones



    The Gaviota gas field is one of three underground natural gas stores currently active in Spain

    • • 1994: Start-up year
    • • 2010: Enagas acquires Gaviota
    • • Available capacity 980 MNm3

More Information


    • • 1981: Discovered with drilling of the Vizcaya B-2 well (Albatros)
    • • 1989: Albatros W-1 drilling (Albatros West)
    • • 1995 – 1997: In production
    • • Accumulated Gas production: 729 MNm3
    • • Accumulated condensate production: 8,052.3 t

    Source rock: Black shale and coal levels (carboniferous)
    Reservoir rock: Calcareous sandstones, limestones and marls (Upper Albian – lower Cenomanian)


    • • 2009 - 2010: Viura-1 drilling (Operator UFG)
    • • 2010: Tests in Viura-1 -> discovery of a conventional natural gas deposit.
    • • 2012 - 2013: 3D subsurface study (232 km2)
    • • 2013: Viura-3 drilling (Operator UFG). Excellent gas traces
    • • 2015: Long-term test, Viura-1 and Viura-3
    • • March 2015: First continuous natural gas injection into the national network
    • • July 2017: Award of VIURA Operating Concession
    • • Gas reserves: 3 BCM (proven)

    Source rock: Black carbonaceous shale and coals contained in the Escucha (Aptian- mid-Albian) and Utrillas (upper Albian - lower Cenomanian) formations
    Reservoir rock: Sandstones and conglomerates from the Utrillas formation