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Three Different Exploration Plays in the Marine Guadalquivir Foreland Basin in the Context of the Late Miocene Closure of the Tethys Ocean (South of Spain)

Kilian Motis and Wenceslao Martínez del Olmo

During the Burdigalian Alpine tectonic phase, the marine Guadalquivir foreland basin was established in the South of Spain between the passive Spanish Shield at the North and the uplifting Betic Chain at the South. In the Tortonian, the SW-NE marine North Betic Strait that connected the Atlantic and the Mediterranean was closed due to the last compressive events of the Betic Cordillera uplifting. So, the Atlantic and Mediterranean only remained connected by the Gibraltar Strait and some short and isolated N-S canyons communicating the Alboran Sea and the Guadalquivir Basin.

In the Guadalquivir foreland basin the seismic lines allow to distinguish three different exploration plays: 1) Upper Miocene sandy turbidites. 2) Hanging wall anticlines. 3) Stephanian-Permian sub-basins.

In the Upper Miocene turbidites (Guadalquivir sandstones Formation) more than 20 biogenic gas fields have been found presenting individual reserves from 2 to 6 BCF. The historic exploration success (> ½) in part due to the AVO analysis use, the gas price (10$ MBTU), the prospects deepness (from 600 to 2,300 ft.) and the big area that still remain underexplored make interesting their exploration.

Hanging wall anticlines are a new prospect play identified in the seismic images in an area with an excellent shale and salt seal (the Miocene Olistostrome) above thick Mesozoic series in four-way-closure fault propagation anticlines. Source rocks are present in Miocene marls (biogenic, out of structure) and especially in the Neocomian, Kimmeridgian and Liassic shales in structure. Mesozoic shales have kerogene type III-II.

Stephanian-Permian sub-basins are also an unexplored play seen in seismic lines with improved definition below the basal Miocene unconformity (3,000-4,000 ft. deep). These Late Hercynian sub-basins can be correlated with the coalbearing NW-SE trending sub-basins present in the Southern Spanish Shield. Their sedimentary infill opens a new opportunity for the coal bed methane exploration.

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