Search

The petroleum system in Central Italy and the Adriatic Sea is of great interest for future hydrocarbon exploration. However, major uncertainties remain about key risk elements such as source rock spatial distribution and maturation history, the timing of hydrocarbon migration, and the nature of migration pathways. This paper presents a new regional‐scale petroleum systems model based on an integrated inter‐disciplinary study which includes public‐domain subsurface data on key petroleum systems elements, heat‐flow and petroleum geochemical data, and an extensive set of 1D basin models. Results show the importance of the Mesozoic palaeogeographic and stratigraphic setting which was characterized by the presence of platform and basinal domains. Thermal data highlight an overall higher basal heat flow in platform domains which persist at the present‐day. Considering the geochemical and thermal characteristics of possible source rocks in the study area, the Upper Triassic Burano Formation appears to be the most likely active source rock but only in those geological domains where it has been deeply buried. In particular, source rocks reached maturity only during the most recent Apennine deformation phase in the late Pliocene/early Pleistocene, i.e. after the deposition of regional seals such as the Messinian Gessoso‐Solfifera Formation. Lateral migration is suggested to have occurred to explain most of the known oil accumulations. The margin of the Apulia Platform could have acted as a migration pathway for hydrocarbons, connecting basinal kitchens to the carbonate reservoir units at the top of the platform succession within which oil and gas accumulations have been proven. Heavy oils could represent early expulsion products from the source rock, but may also locally be a result of biodegradation due to recent partial exhumation of the traps and the loss of lighter components. The results of this study may support ongoing and future exploration efforts over other carbonate platforms in the study area, and more widely on carbonate targets elsewhere in the Mediterranean region. [ABSTRACT FROM AUTHOR]

Empirical scaling relationships between fault or slip dimensions and earthquake magnitudes are often used to assess the maximum possible earthquake magnitude of a territory. Upon the assumption of the reactivability of any fault, the earthquake magnitudes derived from the surface fault length (FLEM) are compared at the national scale in Italy against catalogued magnitudes. FLEMs are obtained by considering a comprehensive fault dataset regardless of fault age, stress field orientation, strain rate, etc. In particular, (1) a comprehensive catalogue of all known faults is compiled by merging the most complete databases available; (2) FLEM is then derived from fault length; and (3) the resulting FLEMs are compared (i.e. the mathematical difference) with catalogued earthquake magnitudes. Results show that the largest FLEMs as well as the largest differences between FLEMs and catalogued magnitudes are observed for poorly constrained faults, mainly inferred from subsurface data. It is suggested that these areas have to be further characterized to better estimate fault dimension and segmentation and hence properly assess the FLEM. Where, in contrast, the knowledge of faults is geologically well constrained, the calculated FLEM is often consistent with the catalogued seismicity, with the 2 σ value of the distribution of differences being 1.47 and reducing to 0.53 when considering only the Mw≥6.5 earthquakes. Our work highlights areas, in Italy, where further detailed studies on faults are required. [ABSTRACT FROM AUTHOR]

Seismic imaging is the most common tool to detect subsurface structures in continental and marine settings. Despite technological advancement, seismic analysis of carbonates is still challenging because they are strongly influenced by petrophysical heterogeneities, being this even more difficult when further heterogeneities are added by the presence of faults. In this work, unmigrated forward-seismic models are developed to understand the seismic response changes related to carbonate-bearing fault systems and their deformation behaviour. We focus on the carbonate ramp of the Majella Massif (central Italy), that is characterised by the presence of porous and faulted carbonate lithologies. This carbonate system represents an analogue of carbonate reservoirs worldwide. Field and laboratory data of fault rocks sampled at increasing distances from the slip planes highlight a damage zone/fault core architecture with a decreasing porosity approaching fault planes. This observation is also confirmed by the thin sections analysis and the calculation of the shear modulus. Seismic images of fault rocks presenting lower porosity than the host rock show weak diffraction hyperbolas while diffraction hyperbolas are more evident in the forward-seismic models of fault rocks with greater porosity than the host rock. Moreover, factors such as the variation in the dip angle of the fault or the thickness of the damage zone can enhance or reduce the hyperbolas. Performing the migration process to stacked sections would not provide evidence of increased porosity in the damage zone due to the suppression of the diffractive component. The presence of weak hyperbolas in unmigrated seismic images is thus interpreted as evidence of a lower porosity damage zone with respect to the host rock. This can be related to deformation mechanisms leading to porosity loss in the damage zone for porous rocks as observed in the study area. However, this could also be related to the confining stress or fracture filling that counteract the fracture-related porosity increase when faults are hosted by tight rocks. • We integrated field and laboratory data to carry out 2D forward modelling. • We developed a workflow linking geocellular model and forward seismic modelling. • The deformation behaviour of carbonate fault rocks can generate compaction bands. • Modification of petrophysics in the damage zone leads to different seismic images. • Diffractions analysis can lead to new insights on buried carbonate fault zone. [ABSTRACT FROM AUTHOR]

Forward modeling is a fundamental support to study the seismic response of reservoirs structure and subsurface architectures. Carbonate reservoirs result in non-univocal seismic response caused by the facies heterogeneity and due to the possible presence of infilling fluids. The carbonate ramp outcropping in the Majella Massif (Central Italy) is an excellent surface analogue of buried heterogeneous structures. It offers the opportunity to directly analyze a carbonate reservoir which clearly shows facies variations and natural hydrocarbon-impregnations allowing to quantify the induced petrophysical changes. In this study, we integrated original field and laboratory measurements with 3D facies modeling to carry out 1D and 2D forward seismic models of a carbonate reservoir following a structured workflow. A careful petrophysical characterization measuring density porosity and seismic wave velocities has been performed in all the sampled facies and then used as input for the 3D velocity model. The "Sequential Gaussian Simulation Co-Kriging" (SGS-CK) results to be the best algorithm to build the seismic velocity model, consequently a low-frequency (40 Hz) synthetic 1D seismogram was carried out simulating facies and hydrocarbon-saturation variations. Thus, a 9 km long synthetic profile from the platform top to the basin, SE-NW oriented, was carried out simulating the outcropping architecture and spatial distribution of the facies. The obtained synthetic seismic outputs are closer to real geophysical surveys with respect to classical forward modeling. Perturbations of the seismic signal derived from the modeled facies heterogeneity without introducing artificial noises made the synthetic results more realistic preserving the horizons architecture. We also quantitatively show that variations in the signal related to the hydrocarbon saturation can result in an increase or decrease in reflectivity depending on the seismic properties of the surrounding layers. The presented results give new insights about reservoir architectures and can be useful to better process as well as to interpret the field seismic data and the resulting seismic sections acquired in carbonate realms. • We integrated field and laboratory data to carry out 2D forward modeling. • We developed a workflow linking geocellular model and forward seismic modeling. • Reservoir heterogeneity results in signal disturbance related to reservoir features. • Hydrocarbons change signals depending on the properties of the surrounding layers. • Signal process can result in a loss of information about the reservoir architecture. [ABSTRACT FROM AUTHOR]

Despite data coming from fully developed oil fields are fundamental to validate reservoir models, they are rarely publishable because of confidentiality. In this work, we benefit from an exceptionally dense public dataset represented by 43 wells logs drilled in a carbonate-heavy oil-rich reservoir of the Majella Mountain (Central Italy) over a grid of 200 m × 200 m, with depths in the range of 90–200 m. We tested different modelling solutions, to assess the best modelling approach that fits the available data on hydrocarbon distribution. Both deterministic (using Kriging) and stochastic simulations (using Sequential Gaussian Simulation- SGS) were tested. The role of the variogram resulted as a fundamental parameter for both simulation methods. Wells-derived variogram agrees with the size and orientation of carbonate dunes that drive the hydrocarbon distribution highlighting the importance of an accurate depositional model. Kriging was faster in terms of computation time and better in maintaining the lateral continuity of the layers, however, it excessively smoothed the results. SGS gave a better distribution of computed values but the lateral continuity was not preserved. By adding a main vertical trend derived from the upscaled logs to the SGS, results become more accurate. We then applied the best model to estimate the total volume of hydrocarbon in place in an already exploited area starting from just one well. The computed reserves show a good fit with historical production data demonstrating the reliability of the model. • We benefit from a public dense well dataset to test carbonate-reservoir models. • Deterministic solutions are faster but mostly inaccurate. • Stochastic simulation with vertical trend improves simulations of single well profile. • Variogram shape is crucial to improve the 3D stochastic simulation results. • Wells-derived variogram agrees with size and shape of carbonate dunes. [ABSTRACT FROM AUTHOR]

Within inversion tectonic contexts, the reactivation of pre-existing discontinuities depends upon many structural, stratigraphic and mechanical factors. Among these, a fundamental aspect is represented by the orientation and attitude of pre-existing discontinuities with respect to the new stress field. The aim of this work is to evaluate the stress regimes and the mechanical conditions that controlled the reactivation of segmented pre-thrusting normal faults in the Central-Northern Apennines of Italy. These faults were involved both in positive and negative inversion tectonic events during Tertiary-Quaternary times. Mechanical (slip tendency analysis) and numerical (using COULOMB 3.3 software) models allowed us to reconstruct a 3D stress field for both inversion events and to evaluate the effect of many parameters (orientation of faults, fault dip-angle and mechanical parameters) on fault reactivation. Our results highlighted that the orientation of pre-existing faults with respect to the stress axes represents the main factor controlling inversion tectonic phenomena, where other mechanical and geometric variables exert a subordinate role. The models well reproduce the Neogene-Quaternary deformation history reconstructed from detailed geological and structural analyses for the Central-Northern Apennines of Italy and could be applied to other regions that have experienced inversion tectonic processes. [ABSTRACT FROM AUTHOR]

Abstract: Complex fault patterns, i.e. faults which exhibit a diverse range of strikes, may develop under conditions where a regional tectonic stress field is weak or absent (e.g. polygonal faults). The present paper considers a complex system of synsedimentary faults in the Umbria-Marche Apennines (Italy), geometrically similar to polygonal fault systems, developed during an early Jurassic extensional episode. This particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate “Andersonian” geometry. A conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in Triassic Evaporites due to dehydration processes (anhydritisation) during burial. The lithological architecture of the Triassic Evaporites, comprising interbedded Ca-sulphate layers and dolostones, played a fundamental role in controlling the deformation processes. Cyclic fluid overpressure build-up/release and the coexistence of brittle and brittle-ductile flow processes led to horizontal isotropic and non-plane extensional strain fields within the dehydrating rock mass, which favoured the development of complex deformation patterns. The mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane. The data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics. The findings are relevant to many other areas where complex faulting patterns—including polygonal faults—occur in association with evaporite or clay-rich sedimentary sequences. [Copyright &y& Elsevier]

The Mw 6.1 (6 April 2009) L'Aquila (Italy) earthquake occurred in one of the most seismically active areas of central Italy and was preceded by a three-month-long foreshock period. Thanks to recordings by a regional permanent network, we derive for the first time P- and S-wave velocity tomographic models of a major fault prone to an imminent main shock. Close to the Mw 6.1 hypocenter, we observe high Vp (>6.8 km/s) and high Vp/Vs (>1.9) consistent with thick dolomitic volumes filled with fluids sealed by impermeable anhydritic layers. Significant changes in velocities defined by time-lapse imaging during the foreshock period suggest rapid fluid migration through the locked fault zone. The complex positive feedback between fluid pressure buildup and hydrofracturing of the dolomitic reservoir, testified by foreshock production, eventually provoked the catastrophic coseismic breaching of the fault seal. Our results show that foreshock time-lapse tomography provides clues on the preparatory phase of a large normal-faulting earthquake. [ABSTRACT FROM AUTHOR]

Basin modelling represents an important approach for the prediction of hydrocarbon generation/migration, identifying possible prospects and reducing the risk in exploration areas. This modelling can be also used to study the structural evolution of an area. Main input are the thermal/burial history of the sedimentary basin (key parameters for source rock maturity) and the adopted crustal model. We applied a basin modelling approach to the study of a portion of the Central Apennine orogen (Central Italy), where both thick-vs thin-skin interpretation models were historically proposed, and to the adjoining Central Adriatic foredeep/foreland system, to contribute reducing the tectonic and petroleum system uncertainties of this structurally complex area. We started from the available dataset obtained from the past hydrocarbon exploration activities, that resulted in several small/medium oil discoveries (evidence of an active petroleum system), making a structural review of the different crustal models proposed by the literature. We built two balanced 2D regional sections using MOVE software: one across the off-shore Central Adriatic foreland; and one from the front of the Central Apennine through the Central Adriatic foredeep/foreland system. This last section was modelled testing both a thick and a thin-skin structural scenario, implementing a structural restoration step using Dynel2D software. Using PetroMod2D we then compared the obtained petroleum system results to verify which structural scenario better fit with the present-day known distribution of hydrocarbon occurrences, both on-shore/off-shore. A 3D model was then implemented over key sectors to better understand the main hydrocarbon generation trends. Results suggest the thick-skin model as most suitable to justify the known hydrocarbon occurrences in the area. In addition, modelling indicates a lateral hydrocarbon migration as a key process for known hydrocarbon accumulation, active from the Upper Miocene (in the Central Apennine foredeep) and Upper Pliocene (in the Central Adriatic foreland) to present-day. • The Central Apennine Thick-Skin model can justify the known hydrocarbon occurrence. • The excessive hydrocarbon generation of the thin-skin model is not compatible with the on-shore/off-shore oil&gas occurrence. • The Lateral hydrocarbon migration is the key process to explain known oil accumulations. • The structuring of the Central Apennine is a key factor for the petroleum system activation. [ABSTRACT FROM AUTHOR]