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Characterizing Fracture Networks in Tight Carbonates of the Tethyan Realm: Lessons Learned and Insights for Handling Fractured Reservoirs of the Eastern Mediterranean

Abstract

The understanding and characterization of fracture networks in tight carbonate reservoirs of the Tethyan realm is a complex task because involves the use of different dataset and a mindset able to approach issues at different scale and build concepts and models using missing information. It is also particularly important for correctly assessing the hydrocarbon potentials and productivity of the HC discoveries as well as to design an appraisal and a field development plan. Characterizing fractured reservoirs also means to build a reasonable static picture of the fault and fracture network at different scales that is then validated by dynamic data trying to predict the movement of fluids within the reservoir. The initial structural and fault and fracture (F&F) conceptual models built during the exploration phases are based on the integration of different data (seismic, outcrop and regional information). They offer a raw first-hand picture about the organization of the fault and fracture network. The subsequent drilling of the exploration well and the data acquisition can be used to update and tune the initial models by taking into account: i) the subsurface conditions, ii) the local stress field, iii) the mechanical properties of the different lithological units and iv) the type and characteristics of hydrocarbons. The new updated F&F network model allows to better plan the next appraisal phase and to find out which would be the most efficient design for the wells. Ultimately, the new geological and dynamic data can be then used to understand the effective productivity of the discovery and to better perceive the main risks and uncertainties associated to the following development phase. This iterative approach to the characterization of fractured carbonate reservoirs requires the immediate integration of newly acquired information that is fundamental to avoid any further delay on the development of the discovery. The use and integration of data acquired from drilling, logging, coring and testing is the key for envisage where are located the complexities and the uncertainties, which are a prerogative of fractured carbonate reservoirs. In this contribution, we present two case studies of fracture network characterization of tight carbonate reservoirs belonging to the Tethyan realm. The first case is selected from the external fold zone of the Zagros Thrust Belt in Northern Iraq (Kurdistan region) in which modern subsurface data were available and integrated with other data to properly reconstruct the static picture of the F&F network following the iterative approach. The second case comes from an old oil discovery made in the Southern Apennines of Italy in which there was a limited dataset composed of three wells with cores and vintage well-logs, 2D seismic lines, drilling and test data. Here, an alternative approach was adopted for reconstructing the F&F conceptual model by integrating strain-modelling simulations compared with information from surface and subsurface analogues in the region. The cases here presented suggest how to approach and characterize fracture networks in tight carbonate reservoirs of the Tethyan realm with both vintage and modern datasets. The lessons learned may provide insights for handling similar fractured reservoirs of the Tethyan realm (e.g., Eastern Mediterranean).