AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Middle Miocene hydrocarbon plays in the North Eastern Carpathian foreland

Abstract

The foreland of the Eastern Carpathians fold and thrust belt is developed mainly over the East-European Platform, except for the southern tip (e.g. Benz Zone), at the transition to Southern Carpathians, where it is overlying the Scythian Platform and North Dobrogea Promontory. Several trans-crustal faults separating different tectonic blocks are defining the structural grain of the platform. This inherited geometry played an important role over the structural style of the Eastern Carpathians fold and thrust belt and its foreland, during its east-ward tectonic transport and subsequent Miocene collision with the platform. The rigid behavior of the old and cold East European Platform reassemble in the formation of wide and shallow flexural foreland. The Eastern Carpathian is a well know hydrocarbon province, with the early production since the 18th century mainly from the fold and thrust belt, related with the Oligo-Miocene hydrocarbon system (Maykop series in the Paratethys Basins). Another hydrocarbon system, Middle Miocene biogenic gas, has been identified in the foreland or the Eastern Carpathians, since the late 50’s, in the search for oil in the deeper structures. The recent changes in gas market trigger a new era for the gas exploration in the foreland, which brought a significant uplift in the seismic data and a number of new discoveries. Our study focus on the elements of the Middle Miocene hydrocarbon system and define the hydrocarbon plays based on the structural-stratigraphic interpretation seismic lines calibrated by the exploration wells. Sequence stratigraphy interpretation was used to constrain the facies distribution along the foreland basin. The biogenic gas is trap into the Sarmatian sandstone reservoirs, in mixed structural and litho-stratigraphic traps. The structural component is usually given by the flexural normal faults formed during Miocene loading of the platform with the Carpathian Orogen. The faults localization is influenced by the inherited structural grain as proven by the variable faults offsets. The reservoirs range from shallow to deep water turbiditic siliciclastic deposited in canyons, channel and lobe facies. The sands have two sedimentary sources, the older ones form E and NE from the uplifted and eroded East European platform and the younger ones from the West from the uplifting Carpathians as proven by the large scale progradation wedges observed on the seismic lines. The seal is usually intraformational. The gas geochemical analysis is a clear prove for the biogenic origin of the gas system since most of migration is in situ with interbedded reservoir and sources. However most of the discoveries have a structural component suggesting that lateral and vertical gas migration have been focused by the existing normal faults toward the footwall. During the study we have identified another possible plays for the Middle Miocene foreland of the Eastern Carpahtians. The first one is related with the truncated and rotated Badenian-Sarmatian strata against the Subcarpathian thrust front. The second one is stratigraphic and is related with topsets of the large progradational features during the Sarmatian times. The third play is more risky and related with deep water isolated turbiditic lobes. However the risk that the lobes are connected with the canyons is high, hence a detailed evaluation of stratigraphic trap components has to be performed using seismic attributes.