Diagenetic processes in the Tarragona Basin Oil Fields, Valencia Trough, offshore Spain

Elisabet Playa, Anna Travé, Noélia Rodríguez, Adrià Guerrero, Vinyet Baqués, Miguel Ángel Caja, and Ramon Salas

The Valencia Trough is a Neogene oil-producing basin where accumulations are in Jurassic-Lower Cretaceous and Neogene rocks. Reservoir rocks are fractured and karstified limestones and dolostones located at the top of tilted fault blocks overlain by Miocene sediments. Samples from Amposta, Casablanca, Montanazo, Angula and Salmonete oil fields have been investigated to understand the origin of fractures and porosity and to reconstruct the fluid flow history prior, during and after oil emplacement.

The earliest fractures, identified only in the Amposta limestones, developed prior to the Alpine compression and are totally filled by calcite cement.

Mesozoic carbonates were uplifted and subaerially exposed between the Paleogene compression and the Neogene extension resulting in the karstification of the host rock, creating significant vug porosity, and enhancing fracture porosity, that was partially filled by reddish and greenish microspar calcite sediment, clays, pyrite, barite, quartz, Kfeldspar, ilmenite, Ti and Fe oxides, derived from the weathering of the oucropping rocks. Following the Neogene extension, the host rocks and the karst infillings in the Casablanca and Montanazo fields were dolomitized during progressive burial.

After this dolomitization event, the erosion of these dolomites from the structural highs originated dolomitic conglomerates and carbonated sandstones (Angula and Salmonete fields). A second dolomitization event occurred at increasing burial conditions in a more evolved stage of the Neogene extension.

Prior (or during) the oil emplacement in the Pliocene, calcite cementation and associated calcitization of dolomite took place. Simultaneously, there was a precipitation of anhydrite, pyrite, kaolinite and barite. Oil circulated through partially cemented fractures, open stylolites, intercrystalline porosity and in the cleavage planes of the latest calcite cements. Comparison with more detailed studies in the surrounding onshore outcrops allows to better constrain the relationships between this diagenetic events with tectonic evolution of the Valencia through.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013