Spontaneous fluid emissions in the Northern Apennines: geochemistry, structures and implications for the petroleum system
Rossella Capozzi, Vincenzo Picotti, 2010. "Spontaneous fluid emissions in the Northern Apennines: geochemistry, structures and implications for the petroleum system", Hydrocarbons in Contractional Belts, G. P. Goffey, J. Craig, T. Needham, R. Scott
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Natural seeps in the Northern Apennines document a variability of fluids and reservoirs in terms of origin, age and evolution. Their spatial distribution appears controlled by the presence or absence of the tectonic overburden provided by the Ligurian nappe. The general trend of deepening of the Mesozoic basement toward the internal part of the thrust belt is reflected by the nature of the seeps, characterized by thermogenic methane and oil at the foothills, whereas the innermost seeps show occurrence of dry thermogenic gas suggesting overcooking of the residual oil. At the front of the Ligurian nappe, or in places never covered by it, the seepages are associated with biogenic methane related to bacterial degradation of the organic-rich intervals occurring in the Pliocene and Pleistocene marine succession. The coupling of geochemical and structural analysis allows reconstructing the tectono-thermal evolution of the belt, improving our knowledge on the processes acting within the reservoir and controlling important parameters of the petroleum system, such as the reservoir porosity and its modifications, and the migration patterns.
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Onshore fold–thrust belts are commonly perceived as ‘difficult’ places to explore for hydrocarbons and are therefore often avoided. However, these belts host large oil and gas fields and so these barriers to effective exploration mean that substantial unexploited resources may remain. Over time, evaluation techniques have improved. It is possible in certain circumstances to achieve good 3D seismic data. Structural restoration techniques have moved into the 3D domain and increasingly sophisticated palaeo-thermal indicators allow better modelling of burial and uplift evolution of source and reservoirs. Awareness of the influence of pre-thrust structure and stratigraphy and of hybrid thick and thin-skinned deformation styles is augmenting the simplistic geometric models employed in earlier exploration. But progress is a slow, expensive and iterative process. Industry and academia need to collaborate in order to develop and continually improve the necessary understanding of subsurface geometries, reservoir and charge evolution and timing; this publication offers papers on specific techniques, outcrop and field case studies.