Structural analysis and 3D modeling of a potential analogue of hydrocarbon reservoir: The Jurassic synsedimentary structure of Monte Testo (Southern Alps, Italy)

Structural traps created by synsedimentary extensional tectonics events can hold very interesting hydrocarbon accumulation and for this reason, they are a main target for the hydrocarbon exploration. Furthermore, the faults generated during extensional events can favour the circulation of dolomitaizing fluids, leading to the formation of fault related dolomitized bodies that can strongly improve the porosity framework. In the last few years, this type of bodies received particularly attention by the hydrocarbon industry, due to the decrease of conventional reservoir discoveries. However, structural network, porosity distribution, shape and geometry of the fault related dolomitized bodies and the porosity evolution of these types of reservoirs are difficult to predict only on the bases of well-logs and seismic information. The study of outcrop analogues can help to solve these issues. In this work I focused my attention to the carbonate platform of the Calcari Grigi group (formed by Monte Zugna, Loppio and Rotzo Formations), located on the Trento platform in the Southern Alps, which was extensively affected by synsedymentary extensional tectonic during the Early Jurassic. This tectonic event led to the tilting of the Loppio Formation and caused abruptly change of thickness in the Rotzo Formation. The extension ceased during the deposition of the upper part of the Rotzo Formation, which seals the Jurassic faults. During the late Paleocene-early Eocene, the Alpine tectonics reactivated, with a strike slip movement, the Jurassic faults allowing the circulation of dolomitizing fluids and leading to the formation of secondary fault-related dolomitized bodies. A Jurassic synsedimenatry structure affected by secondary dolomitization is spectacularly exposed near the Monte Testo on the Asiago Plateau. In this work a geological map, structural studies, porosity analysis, 3D photogrammetric model and 3D geomodel were realized in order to reconstruct the tectonic evolution, porosity distribution and reservoir potential of M.Testo structure and better understand geometry, shape and porosity of the fault-related dolomititized bodies. Moreover, this multi-approaching analysis allows to reconstruct the complex porosity evolution of the potential reservoirs. The final results have shown that during the Jurassic, the early cemented tilted and high porous (8%) blocks of the Loppio Formation were put in contact laterally and above with the low porous (0%) Rotzo Formation, creating important potential hydrocarbon traps on the upper part of the tilted blocks. At that time the Zugna Formation likely had a porosity given only by fracturing (1%), hence fluids might have circulated from depth up to potential Loppio reservoir following the extensional fault network. Starting from this moment onwards the porosity of the Loppio Formation began to decrease due to cementation. During Late Paleocene-Early Eocene, the formation of the fault-related dolomitized bodies within reactivated fault zones gave a new chance to the reservoir potential of the M. Testo structure. Indeed, these bodies have a porosity ranging from 0% to 10,6% with a mean of 4,7%. The higher porosity values are concentrated along the breccia fault zones enclosed within low porous and low permeable formations, confirming the strong relationship between late dolomitization and the structural network as well as the great potential of these bodies for hydrocarbon accumulation.