Amposta Oil Field (Spanish Mediterranean Offshore)

U. Seeman

The Amposta oil field lies some 20 km off the Mediterranean coast of Spain directly south of the Ebro delta in 70 m of water. The field is operated by Shell in association with Repsol Exploracion (the Spanish national oil company) and Coparex. The field was discovered in 1970 and came on stream in 1972, reaching a maximum production of 40,000 bbl/day. The current cumulative production of 55.7 million bbl is just 300,000 bbl short of the field's expected ultimate primary recovery. Original production was established via a single-buoy mooring system (SBM) with a permanently moored tanker acting as a floating storage vessel.

Oil is produced from a fractured, karstified Lower Cretaceous limestone reservoir in a tilted fault-block structure (areal closure is 900 ha), sealed by overlying Miocene clastics. The top of the reservoir is at 1,746 m; the original oil column was 194 m. Designing the optimal production/drainage scheme for a complex reservoir such as the Amposta field with its intricate pore geometry (channels, caves, and fractures) formed an interesting challenge. The field has produced from 7 wells so far. Until recently pressure could be maintained and dry oil produced. Enhanced recovery tests (gas injection) are presently being undertaken.

The heavy, undersaturated, high-sulfur crude (17° API, gas-oil ratio of 380 scf/bbl, and 5.5% sulfur) is an early expulsion product generated from a marly/chalky type II source rock sequence of latest Jurassic-earliest Cretaceous age, underlying the field.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.