Journal of Conference Abstracts

Matrix and Fracture Porosity in Carbonate Turbidites from the Ionian Zone of Albania

Rudy Swennen (Rudy.Swennen@geo.kuleuven.ac.be)¹, Maarten Van Geet, Cerciz Durmishi², Francois Roure³ & Philippe Muchez¹

¹ Fysico Chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium

² Laboratory of Sedimentology, University of Tirana, Tirana, Albania

³ Institut Francais du Pétrole, av. de Bois-Préau, F-92852 Rueil-Malmaison, Cedex, France

Within fold and thrust belts, reservoir characteristics are dependent on the preservation of matrix porosity and on the development of fracture porosity. Reconstruction of the diagenetic processes through the footwall evolution and deformation history of potential reservoir lithologies, as the Cretaceous to Eocene carbonates of the Ionian zone in Albania, are one of the most challenging tasks in present-day exploration oriented diagenetic research. Within the studied deep marine carbonates south of the oil producing centre of Fier-Ballsh (central Albania), a detailed reconstruction of potential reservoir controlling processes revealed that:- sedimentary and early diagenetic framework stabilising cementation processes control the development and preservation of important matrix porosities in the basal parts of turbidity induced fining upward sequences;- several fracturation episodes alternate with cementation of the fractures. A detailed reconstruction of this history is based on the crosscutting relationships of fractures and their relationships with respect to compactional and layer parallel shortening stylolites. In the studied area their evolution through time fits the results of stress evolution modelling in thrust front zones reported in literature. Fluid flow characteristics are initially i.e. during the footwall stage, rock buffered. Once a topographic relief is created in the hinterland, gravity induced meteoric water flow systems intervene. According to the isotope and fluid inclusion signature of hydraulic calcite veins a mixed marine - meteoric fluid is indicated which is periodically released by tectonic activity. From then onwards the influx of non-marine fluids is assumed. This evolution becomes even more developed in the compressional fold and faulted thrust front stage, where large-scale fluid fluxes are recorded;- an important open joint system developed during or at the last stage of the faulting and folding period and is explained by the high palaeo-topographic position of the studied area. Here an extension stress regime is predicted by sandbox modelling reported in literature;- a sediment-filled karst cavity network may develop during the following emergence period. The latter can contribute to the matrix porosity of the host rock. It clearly has another distribution pattern as the sedimentary controlled matrix porosity. This research also showed that in geologically complex areas such as fold and thrust belts it is extremely helpful to study reservoir outcrop analogues. Many of the complex relationships between diagenetic phases (e.g. matrix porosity, veins, stylolites, karst cavities, ...) could never be studied in such detail in core material simply due to the size limitation of the cores.

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