GNGTS 2019 - Atti del 38° Convegno Nazionale

582 GNGTS 2019 S essione 3.1 SEISMIC PRE STACK DEPTH IMAGING WITH LARGE VINTAGE SEISMIC DATA IN A MATURE HYDROCARBONS PROVINCE: THE NORTHERN ADRIATIC SEA CASE HISTORY D.Scalise, M. Bertarini, B. Webb, R. Vannuccini, N. Pajola, M. Antonelli, R. Fantoni Eni S.p.A. - Upstream & Technical Services Introduction . This paper illustrates a 2 years seismic reprocessing program intended to assess deep gas potential in a mature producing province. The area of interest is characterized by very complex over-thrusted geology,accordingly the project was focused on the application of high end Pre-Stack Depth Imaging algorithms to properly address the imaging complexity. The goal was to asses and de-risk the HC potential by preserving the seismic amplitude response in the context of a challenging structural setting. Legacy or vintage datasets are amenable to re-examination using new pre-stack imaging tools. The available seismic dataset, called Adria 3D, covers an area of 11,000 km 2 ; it consists of a merge of ten different surveys, acquired during the last 25 years from Ancona to Caorle. Over the past two decades, 3D pre- stack depth migration (PSDM) has changed industry perspective on how to approach seismic data in areas of complex geology; moreover, the improvement of seismic velocity analysis and seismic imaging technologies is allowing to extract new information and value from legacy data, providing opportunities to better investigate these difficult areas without acquiring new data. Leveraging on modern HPC capabilities, the project delivered a first PreSDM volume by using an accurate well-constrained velocity model to better characterize the geometries and the correct positioning of new and still producing fields. Then, a fully integrated multi-disciplinary approach, with a strong integration between geologists, geophysicists and explorationists, was mandatory for the success of the project, exploiting the huge technical know-how built up by Eni during decades of exploration in this area. In this regard, a series of tailored G&G integrated studies have been carried out to validate the good quality of preprocessed data and for the economic assessment of the new assets. The Geological Setting . The geological framework of the Adriatic foreland is the result of the overlay of two distinct tectonic events: Mesozoic extensional cycles and the compressional Cenozoic stages. The former is characterized by the deposition of prevalent evaporitic units while the latter by the deposition of prevalent terrigenous layers (Fantoni and Franciosi, 2010). In this regional geological setting, several effective petroleum systems are present, making Italy one of the most endowed hydrocarbon provinces in Southern Europe (Bertello et al. , 2010). In particular, the northern sector of the Adriatic Sea is characterized by a massive presence of biogenic gas bearing levels hosted by different types of structural and stratigraphic traps: the complex faulted anticlines of the of the Apennines compressional structures of the foredeep region and the stratigraphic onlaps pinching over the foreland ramp monocline within the Plio-pleistocene terrigenous succession. These mineralized levels are normally associated with evident seismic gas indicators or DHI (Direct Hydrocarbon Indicator) mapping on the seismic signal as amplitude and phase anomalies, structures pull-downs and flat spot reflection representing the water-gas interface (Cazzini et al. , 2015). Velocity Model Building and Pre-stack depth migration. Kirchhoff pre-stack depth migration (KPSDM) and well-oriented velocity model building were selected for this project, based on two main criteria: 1. The complexity of geology and the severe structural distortions caused by the thrusts area 2. The presence of rapid lateral velocity variations related to localized gas accumulations Furthermore, since good quality preprocessed data are mandatory in order to both preserve important HC indicators for the delineation of new potential discoveries and for an effective PSDM processing, a robust noise attenuating and amplitude preserving data processing flow was developed. Particular emphasis was put on multiples attenuation and offsets regularization