EXPLORATION COUNTRY FOCUS
Spain
by Elvira Álvarez de Buergo and Anunciación Pérez García, Repsol-YPF, Madrid, Spain
In parallel to Spain’s dramatic economic growth in the last years, one of the largest in Europe, gas and oil consumption have also increased following the growth trend, while hydrocarbon production has decreased in a nearly opposite trend (Graph 1). Under these circumstances, the question is if the country is doing an aggressive effort to increase the barrels that are being lost.
Historical perspective
To answer this question let us first investigate the discoveries under a historical perspective. Spain has a diversity of basins and sub-basins and in fact the Hydrocarbon Department (Ministry of Economy) divides the prospective acreage into more than 10 different areas. However, most of the exploration wells are concentrated in just a few basins: the Cantabrian (offshore and onshore) in the north, Gulf of Valencia (Mediterranean Sea) in the East and Gulf of Cadiz/Guadalquivir Basins in southern Spain (see map). Repsol, Chevron and Shell account for nearly half of the total number of exploration wells drilled.
According to the Spanish Hydrocarbon Department Well Files (2006), exploration commenced in the 1940’s. The first successes were onshore Northern Spain, in the Cantabrian Basin: the Castillo small gas discovery (33 MMSCM) in Vitoria in 1959 and the Ayoluengo oil & gas discovery (17 MBO & 430 MMSCM) in Burgos in 1964 (see map). To the shame of explorationists no other oil field has been found onshore since.
During the 1970s most of the fields were found:
- in the Gulf of Valencia, Amposta (61 MBO), Dorada (18 MBO), Casablanca-Montanazo (144 MBO) & Tarraco (14 MBO);
- in the Cantabrian Sea, Gaviota (7100 MNm3 of gas & 4 MBO of condensate);
- in the Gulf of of Cadiz the gas fields of the same name (2000 MNm3) and Jaca-Serrablo in the Pyrenean foothills (0.3 MMSCM) (see map).
In the 1980s the onshore extension of the Gulf of Cadiz gas fields trend was proven with several gas discoveries in the Guadalquivir Basin (Marismas, El Romeral, El Ruedo & Las Barreras, around 1300 MNm3). The Ayoluengo gas field was put on production and two minor oil discoveries were tested in the Mediterranean Sea: Salmonete & Angula.
The 1990s brought most of the satellites to the major fields: Albatros in the Cantabrian Sea and Rodaballo, Chipirón, Boquerón & Barracuda in the Mediterranean Sea (see map).
After that, less than 10 exploration wells have been drilled in the 21st century, none successful and only one with gas and oil shows.
Exploratory rate
How many wells were needed to achieve those successes? The Hydrocarbon Department Well Files account for 762 wells historically drilled. Among these, the number of exploration wells is less than 600. Spain has an extension of 504.750 km2; with the net exploration acreage or potentially prospective sedimentary basins being around 70%. This statistically represents just over 1 exploration well drilled per 1000 km2 of net exploration area. Of these exploration wells, 407 are located onshore and 189 offshore. In addition to the low exploratory rate analogs to the found discoveries were extensively searched for.
At present the exploration rate is amazingly low, with many basins having only a few wells drilled by small independents, 30 years ago and with no “modern” technology, even in the cases where active petroleum systems had been proved.
In contrast, the exploratory rate in nearby countries with similar potential like France and Italy, has been much higher. In France, only in the Paris Basin 700 wells have been drilled and 1,200 in the Aquitanian Basin. In Italy by the end of year 2004, 2000 wells had been drilled, 700 of which located offshore (Wood Mackenzie, 2004).
Future exploratory trends
Exploration results could be very different if today’s improvements in seismic technology and a more refined geological thinking were applied on a systematic basis. Some examples of the many areas with remaining high potential are:
- the middle Cretaceous of the Basque Cantabrian Basin, in particular the Urgonian Carbonate Platforms and fluvial-shallow marine siliciclastic systems (with both stratigraphic and structural traps);
- the Carboniferous Triassic gas plays, explored by only three wells so far, all with gas shows;
- the lower Cretaceous clastics of the Ebro Rioja Basin, with oil proven in two wells.
Recently, encouraged by the high oil prices, some newcomers are slowly taking positions and also the “majors” seem to be changing attitude as proven by the steadily increasing award of new exploration acreage.
References
Estadística de Hidrocarburos (2003). Ministerio de Economía: Subdirección General de Hidrocarburos.
Estadística de Hidrocarburos (2004, 2005 & 2006). Ministerio de Industria, Turismo y Comercio. Secretaría General de Energía. Dirección General de Política Energética y Minas.
Wood Mackenzie (2004). Country Analysis Reports for France, Italy & Spain.