Title: Study of reservoir analogues in foreland fold and thrust belts: Sedimentology, diagenesis, deformation and fracturation of Cretaceous-Paleocene carbonate turbidite systems of the Ionian Basin (Southern Albania).
Other Titles: Study of reservoir analogues in foreland fold and thrust belts: Sedimentology, diagenesis, deformation and fracturation of Cretaceous-Paleocene carbonate turbidite systems of the Ionian Basin (Southern Albania).
Authors: Vilasi, Nadège; S0165842
Issue Date: 6-Nov-2009
Abstract: Although Albania constitutes a relatively small country, it displays a unique petroliferous foreland fold-and-thrust belt (FTB) system. The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary record helps to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios. Since the mid-90's, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools aswell as the application of new analytical methods for the study of petroleum systems in tectonically complex areas. The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The main results of this collaborative study involving scientists from various European countries outline the benefits that any Earth Science project could gain in integrating various techniques and expertise, especially when dealing with sedimentary basins where both deep and shallow processes are involved.The objective of this PhD is to give a better understanding of the mechanisms and timing of fracturing and fluid flow during the Albanides evolution. Results from structural analyses and petrographic investigations in three selected case studies, which are considered as reservoir analogues for neighboring reservoirs situated in the Ionian Zone, are presented. Their study allows to work out a three dimensional picture of the reservoir features and processes that control porosity and permeability. These analyses have been performed on cemented fractures in the Upper Cretaceous to Eocene deep water carbonates, considered as the best carbonatereservoir intervals in the Mediterranean zone. The results are subsequently replaced into the deformation history of the area in order to placethe different fluid migrations into their geological context.Albania represents a part of the widen Circum-Mediterranean Peri-Tethyan thrustbelts and constitutes a key area for the study of petroleum systems in foothills and thrust front domains (Van Geet et al., 2002). The Ionian tectonic zone corresponds to a foreland fold-and-thrust belt, characterised by a west verging thrusting over the Adriatic foreland. It corresponds to a complex tectonic assemblage, made up of thin-skinned allochthonous units, progressively emplaced during the Neogene deformations. The major décollement level consists of the Triassic evaporites and the major structural fault zones possess a NNW-SSE alignment.The tectonic evolution of the Albanides included a Middle Liassic–Late Cretaceous phase of oceanic rifting accompanied by a passive margin formation and is divided into two major divisions: the internal and externalAlbanides. The external zone consists of two platform areas (Sazani andKruja), which are separated by the Ionian Basin, i.e. the area studied.This basin can be split into three belts: the Berati, the Kurveleshi and the Cika belts. It consists of Triassic evaporite-carbonate and Jurassic to Eocene carbonate sequences in a syn-rift and post-rift setting, covered by Lower Tertiary flysch and/or Neogene clastic deposits. The northern part of the Ionian Zone is marked by the Vlora-Elbasan transfer zone, along which most of the oil and gas fields occur in both carbonate and clastic reservoirs. Their storage is largely improved by the presence of a dual matrix/fracture porosity system. At this place, the Ionian Zone plunges below the Peri-Adriatic Depression (Roure et al., 1995).The first area studied is located near the hanging-wall of the Berati belt and is made up of Paleocene to Eocene pelagic carbonates. The fracturing of the reservoir interval has a pre-folding origin and relates to the regional flexuring in the foreland. The first recorded cement, postdating the burial stylolites development, has a meteoric signature, implying downward migration and the development of an earlier forebulge in theIonian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium with values up to 6960 ppm, attesting for important fluid-rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal veins. The tectonic burial increased up to 6 km due to the overthrusting that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, upward migration of SO42-, Ba2+ and Mg2+-rich fluids, which migrated probably along the décollement level, allow a precipitation in thermal disequilibrium. This period corresponds to the out-of-sequence development of the Berati belt from the Upper Miocene onward, implying the onset of its uplift. From shallower depth to the subsurface, the circulation of meteoric fluid likely develops a selective karstification.The second area studied is situated in the most western belt, i.e. the Cika belt, and consists of the Saranda anticline, characterised by a NNW-SSE oriented fold hinge. The core of the anticline is made up of Jurassic to Lower Cretaceous carbonates and the flanks consist of Upper Cretaceous to Eocene highly fractured deep marine carbonates. The fracturing of the reservoir interval in the Cika belt has also a pre-folding origin,associated to the flexuring of the foreland during the Lower to Middle Oligocene (Nieuwland et al., 2001). The next fracturing stages are associated to the folding of the area and the subsequent cementations record its progressive burial, indicated by an increase of the O-isotopic signatures from -1 to -13‰ V-PDB, which is directly related to the increase of the precipitation temperature. This period is also characterised by the development of a conjugated system of tectonic stylolites. From the Serravalian onward, the thrusting phase implies the uplift of the anticline towards the subsurface and the erosion of the Oligocene flysch and theNeogene molasse. The last stage corresponds to the emersion of the anticline and the migration of meteoric fluid into the carbonate system through re-opened fractures. A last tectonic reactivation implies the overthrusting of the western flank on the eastern side. During the Albanide FTB development, no overpressuring period has been recorded in the Sarandaarea. Moreover some fluids, which migrated during the folding, contain non-euhedral barite, likely originated from the Neogene molasse. This likely suggests downward migration.The Kremenara anticline, located in the northern part of the Kurveleshibelt at the vicinity of the Vlora-Elbasan transfer zone, has the particularity to demonstrate oil seeps in a dual matrix-fracture porosity system. This anticline is characterised by a NNE-SSW oriented fold hinge, which does not describe the specific NNW-SSE orientation of the main structural features occurring in the Ionian Basin. Here, the main fracturing stages have a post-folding origin and the fractures relate mainly to twomain principal stresses 1, oriented N110° and N70°. This area studied is characterised by an early folding and the migration of meteoric fluid, which precipitated non-luminescent calcite cement. The post-folding stage is characterised by a second burial stage, caused by an increase of the sedimentary overburden, and the development of two main overpressuring regimes. The latter compressions are pointed out by the occurrence of crack-seal and brecciated veins, which respectively relate to N110°- and N70°-oriented compressions. An interaction with an evaporitic interval has also been suggested by the positive O-isotopic signature of the crack-seal veins. From the Serravalian, the N70°-oriented compression developed NNW-SSE transversal faults, which compartmentalise the anticline. Then, an E-W compression generated an overthrusting of the anticline towards the south-west. This period is likely associated to the out-of-sequence development of the Berati belt. The reorientation of thecompression during the last stage may be associated to the vicinity of the Vlora-Elbasan transfer zone (Swennen et al., 1998). The Kremenara anticline was not buried deeply, since the Kurveleshi belt has been upliftearly in the Albanide development. This is in agreement with the O-isotopic signatures, which plot down to -5‰ V-PDB, and is close to the signature of the Upper Cretaceous to Eocene host-rocks.The fluid flow modelling allowed to reconstruct the hydrocarbon generation and migration but also to trace the changes in the water flow through time (origin, migration pathways and velocity). The third utility consists of determining the evolution of the overpressuring periods through time and space and then to correlate them to the overpressuring periods determined by studying the fracture-fillings. This will help to place the diagenetic evolution in the tectonic evolution of the FTB. The main results of the hydrocarbon fluid flow modelling show that the Upper Cretaceous-Eocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flowbarriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur. The results of the modelling demonstrate that the water migrations are dominantly vertical during the flexure of the foreland. Then the increase of the sedimentary overburden and the thrusting of the units imply upward water migration under high pore fluid pressure. The development of a high topographicrelief caused large downward and lateral meteoric flow migration, whichare characterised by higher velocities. From the thrusting phase onward, the faults act as flow barriers, due to the occurrence of evaporites along the décollement levels and compartmentalise the reservoir interval.
ISBN: 978-90-8649-292-3
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division of Geology

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