AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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3D or/and 3R (Reprocessing, Re-dating, Re-interpretation) strategy for exploration in mature hydrocarbon province, South Carpathian Foreland

Abstract

The South and South-Eastern Carpathian foreland basin, with its classical provinces Diapiric Fold Zone and Getic Depression, it is the most prolific hydrocarbon province in Romania, with official production dated back in the 1847. After 1.5 century most of the production is still coming from shallow fields (above 2500 m) with only a few deep field, such as the recent Totea discovery in the Getic Depression. One of the problem face by exploration is the huge data base of seismic and wells acquired in the las 100 years of E&P activities, which have a large anisotropy with significant impact over the interpretation. One of the option for tackle these technical and geological challenges is to acquire 3D cubes that in theory is more suitable for complex tectonic settings with lateral and vertical velocity variations. However the disadvantages of the 3D in onshore settings are related with high cost, difficulty to have a uniform acquisition due to land access limitations, reduce offsets, and reduce coverage area with most of the 3D acquired over the existing shallow fields. One option for homogenize and improve the seismic image is to re-process using new algorithms. The existing key wells should be re-dated and correlated with the current understanding of stratigraphy of the area and with this avoiding the generation’s inconstancies. Following the describe strategy one of the first step was to re-date and correlate the key wells, with the identification of key markers like the volcanic tuf levels and the large transgressive event at the Oligocene-Aquitanian boundary which can be trace across the entire foreland. Significant stratigraphic changes have been brought by the identification of large scale re-worked Cretaceous and Eocene fauna into the Lower Miocene strata. In the last 2 years more than 3000 km of 2D lines have been reprocessed using state of the art technologies like, 6D interpolation and wave equation migration (WEM), an approach that led to large increase of data quality and uniformity across the entire basin. Focused in-house PSDM processing have been performed for better illumination of complex duplex structures on a series of 2D seismic lines. The classical tomographic velocity update is limited in such area, therefore a structural based migration was necessary implying a join effort between processor and interpreters, incorporating the geological knowledge in the processing flux. In-house re-processing of the Moreni-Runcu and Rpesti-Babeni 3D cubes brought significant image improvements, mostly for the shallow level, with deep structure illumination still challenging. The combine 3D and 3R strategy have improve the quality and reduced the anisotropy of the data giving to G&G team the tools to reinterpret the South Carpathians foreland as a coherent fold and thrust belt with similar structural styles, defined by thin skinned deformation, across the Diapiric Fold Zone and the Getic Depression, with the key role played by low-angle detachments at multiple levels and salt diapirism. The switch from thick skinned and stike-slip related deformation model to the thin skinned one led to the identification of new leads and prospects in this mature hydrocarbon province.