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This work focuses on the nature, relative timing, and multi-scale dimensional properties of both background and fault-related fracture networks that crosscut the Lower Cretaceous shallow-water carbonates exposed at the Monte Alpi, southern Italy. Away from the major fault zones, fractures mainly consist of stratabound and non-stratabound joints and sheared joints, which form two main bed-perpendicular cross-orthogonal sets. Both sets are characterized by a Poissonian spacing distribution, they do not form well-defined clusters, and formed during either burial diagenesis or subsequent Upper Miocene foreland flexure of the Inner Apulian Platform. In contrast, the study fault damage zone is mainly crosscut by non-stratabound fractures and through-going slip surfaces, which form clustered conjugate systems characterized by power law spacing distributions. Results of Discrete Fracture Network modelling of geocellular volumes representative of the surveyed outcrops show that the fractured carbonates of the study fault damage zone form the main storage volume for underground fluids. There, non-stratabound fractures act as the main control on fracture porosity and contribute towards determining isotropic horizontal fluid flow properties. These isotropic conditions are interpreted as a factor of the profound control exerted by the pre-existing cross-orthogonal fracture sets, which underwent to an extreme uplift during the Plio-Quaternary tectonic evolution of the area. Data presented in this work also highlight the importance of scan area methods for the quantitative analysis of stratabound fracture sets.

Discrete Fracture Network (DFN) modelling is a useful tool to assess both fluid storage and migration properties of naturally fractured carbonate rocks. This work presents the results of multiple DFN models, which represent the structural network associated with a ca. 100 m–offset, oblique-slip, normal fault zone crosscutting Miocene ramp carbonates of the Majella Mountain, Italy. Specifically, by taking advantage of a previously published conceptual model of fault nucleation and growth, the DFN models are aimed at computing the amount of fracture porosity and equivalent permeability of representative portions of the evolving fault damage zone. In fact, by first considering only background structural elements, those pre-dating the fault nucleation stage, all fault-related structural elements such as joints, small and medium faults are added, one by one, according to their relative time of formation. Small faults are characterized by several cm-offset, whereas the latter ones have several 10's of cm-offset. The following fracture parameters are inputted for each structural element: (i) length; (ii) aspect ratio; (iii) mechanical and hydraulic aperture; (iv) fracture intensity and (v) orientation. A sensitivity analysis is carried out in order to test the seeding procedure of the software, and the input fracture aperture values. Results of DFN modelling are consistent with the small faults forming the main repository for underground geofluids. Differently, the fluid migration paths through the fault damage zone are mainly controlled by opening-mode-related fractures, which mainly form clusters at the extensional quadrants of sheared structural elements. Due to their attitude and distribution, these features mainly enhance fault-parallel fluid migration paths. In fact, the computed values of horizontal equivalent permeability obtained along this direction are about one order of magnitude higher than those along the orthogonal direction. The approach and methodologies applied in this work, together with the results of the multiple DFN model configurations show the relative influence and role of the different structural elements on fluid storage and migration properties of limestone-hosted, fault damage zones.

A multidisciplinary study of the dolomitized bodies present in the Lower Cretaceous platform carbonates of Mt. Faito (Southern Apennines – Italy) was carried out in order to explore the connection between early dolomite formation and fluctuating climate conditions. The Berriasian-Aptian investigated succession is 466 m thick and mainly consists of shallow-water lagoonal limestones with frequent dolomite caps. The dolomitization intensity varies along the succession and reaches its peak in the upper Hauterivian-lower Barremian interval, where it is present a completely dolomitized interval about 100-m-thick. Field relations, petrography, mineralogy, and geochemistry of the analyzed dolomite bodies allowed identifying two populations of early dolomites, a fine-medium crystalline (FMdol) and a coarse crystalline dolomite (Cdol), both interpreted as the product of mesohaline water reflux. According to our interpretation, FMdol precipitated from concentrated brines in the very early stage of the reflux process, producing typical sedimentary features as dolomite caps. In the successive step of the process, the basin-ward ‘latent’ reflux precipitated Cdol from less concentrated brines. A peculiar feature of the studied succession is the great consistency between stratigraphic distribution of dolomite bodies and their geochemical signature. The completely dolomitized Hauterivian-Barremian interval, in fact, is characterized by geochemical values suggesting an origin from distinctly saltier brines. Considering that the observed near-surface dolomitization process is controlled by physical and chemical parameters reflecting the paleoenvironmental and paleoclimatic conditions during dolomite formation, we propose that the stratigraphically controlled dolomitization intensity reflects periodic fluctuations in the salinity of dolomitizing fluid, in turn controlled by long-term climate oscillations. The present work highlights that the stratigraphic distribution of early diagenetic dolomite may be used as proxy to define the climatic fluctuations that have influenced the sedimentary dynamics in the Early Cretaceous. Moreover, considering that a comparable early dolomite distribution is present also in the Dinaric Platform, we suggest that a regional scale climate control acted on early dolomite formation and distribution. Refining the knowledge of such a key control may have a significative impact on hydrocarbon reservoir characterization and exploration in the Periadriatic area.

Fracture networks in porous carbonates can control, assist, or even contribute negatively to reservoir quality. In scenarios where fractures and matrix pore systems are of similar importance, a dual-porosity/permeability (DP/P) modeling approach is necessary or at least recommendable for the reservoir characterization. These workflows are well established at the reservoir scale, however at the microscale, the interaction between fractures and porous matrix needs to be further investigated. The aim of this work is to assess the contribution of meter-scale fractures (macrofractures) to the porosity and permeability in a porous carbonate reservoir analogue at the microscale. To reach this objective, we created DP/P models at the microscale through the integration of two different methods of 3D imaging such as, high-resolution synchrotron X-ray microtomography (SR micro-CT) and Structure from Motion (SfM) photogrammetry. Quantitative analyses of pristine rock and DP/P models were performed to evaluate the contribution of macrofracture segments to the porosity and connectivity of the pore network. These results were integrated with single-phase flow simulations for calculating permeability values. Different scenarios were modeled in order to systematically evaluate the control exerted by fracture roughness parameters (i.e., asperity height distribution and fractal dimension) on porosity and permeability in various lithofacies. The key analyzed samples come from the Roman Valley quarry located at the Majella Mountain (central Italy), which has been widely investigated due to the presence of consistent bitumen impregnations distributed in pervious medium-to-coarse grainstones and along two main fault zones. The results of this study demonstrate the utility of obtaining DP/P microscale models as complementary approach to explain the hydrocarbon distribution in fractured multi-facies porous carbonates. We document the potential of macrofracture segments to provide neo-connected porosity by linking up adjacent isolated or partially isolated matrix pore networks in impervious carbonate rocks. In pervious carbonate lithofacies, fault-related macrofractures can enhance permeability and contribute to bitumen migration and distribution, whereas the increment of storage capacity is limited since these rocks are already fully connected. In the case of impervious carbonate lithofacies, results indicate that the actual contribution of neo-connected pores to fluid transport is limited, which agrees with outcrop observations.

Fluid flow through a single fracture is traditionally described by the cubic law, which is derived from the Navier-Stokes equation for the flow of an incompressible fluid between two smooth-parallel plates. Thus, the permeability of a single fracture depends only on the so-called hydraulic aperture which differs from the mechanical aperture (separation between the two fracture wall surfaces). This difference is mainly related to the roughness of the fracture walls, which has been evaluated in previous works by including a friction factor in the permeability equation or directly deriving the hydraulic aperture. However, these methodologies may lack adequate precision to provide valid results. This work presents a complete protocol for fracture surface mapping, roughness evaluation, fracture modeling, fluid flow simulation, and permeability estimation of individual fracture (open or sheared joint/pressure solution seam). The methodology includes laboratory-based high-resolution structure from motion (SfM) photogrammetry of fracture surfaces, power spectral density (PSD) surface evaluation, synthetic fracture modeling, and fluid flow simulation using the Lattice-Boltzmann method. This work evaluates the respective controls on permeability exerted by the fracture displacement (perpendicular and parallel to the fracture walls), surface roughness, and surface pair mismatch. The results may contribute to defining a more accurate equation of hydraulic aperture and permeability of single fractures, which represents a pillar for the modeling and upscaling of the hydraulic properties of a geofluid reservoir.

Recent geological and structural analyses of the Monte Alpi carbonate massif focused on the dimensional properties and growth mechanisms of large-scale, high-angle fault zones. In this work, we focus on the role played by primary heterogeneities on the vertical growth of high-angle structural elements such as joints, sheared joints, persistent fracture zones, and small faults. By combining traditional field structural analyses with 3D photogrammetric analysis, we are able to document the attitude and height distribution of individual structural elements. Data are statistically elaborated in order to assess their multi-scale dimensional properties, which are discussed in light of the abutting and crosscutting relationships with respect to the primary heterogeneities. Results of this work fill the gap that exists between the in situ and seismic resolution analyses, and provide new insights into the mechanical stratigraphy of tight, platform-related carbonates of the Inner Apulian Platform.

This work assesses the impact of the stratigraphic and structural heterogeneities on the fluid distribution and migration within a deformed carbonate reservoir analogue. The study was carried out in the abandoned Roman Valley quarry (Majella Mountain, central Italy), well-known for its historical bitumen extraction. The studied rocks consist of ramp carbonates of the lower member of the Bolognano Formation (Oligocene-Miocene in age) mainly composed of grainstones, and secondary packstones and wackestones. In the quarry, the exposed rocks are crosscut by two high-angle oblique-slip faults striking WNW-ESE with up to 40 m of throw. With the aim of deciphering the contribution of both matrix and fracture pore space on the fluid storage and migration, both laboratory measurements and field-based Discrete Fracture Network (DFN) models (cubes with 4-m per side) have been carried out. The obtained dual-porosity/permeability model, which includes the lithological and the structural heterogeneities observed at the location, was used to run flow simulations under different scenarios of well locations. The fluid distribution in the matrix, resulting from these flow simulations, is consistent with field observations where bitumen localizes within the most permeable lithofacies (grainstones). In the fault zones, the fracture network causes an important fluid flow anisotropy, enhancing the flow in a direction subparallel to the faults. The flow orthogonal to the fault zones is controlled by type and lateral continuity of fault rocks, where fault breccias represent conduits and cataclasites localized barriers.

Petrographic, petrophysical and fracture analyses were carried out on middle Cretaceous platform carbonates of the southern Apennines (Italy) that represent an outcrop analogue of the Val d’Agri and Tempa Rossa reservoirs of the Basilicata region. The studied outcrops, which are made of interlayered limestones and dolomites of inner platform environment, were selected to study the impact of dolomitization on reservoir properties and the control of dolomite texture on fracture development. Two types of dolomites – both formed during very early diagenesis – were found interlayered, at a metre scale, with micrite-rich limestones (mainly mudstones and wackestones). Dolomite A is fine-to medium crystalline and makes non-planar mosaics. Dolomite B is coarse-crystalline and makes planar-s and planar-e mosaics. The intercrystalline space of the planar-e subtype of dolomite B is either open or filled by un-replaced micrite or by late calcite or saddle dolomite cement. Dolomite A and dolomite B have similar average porosities of 3.7 and 3.1% respectively, which are significantly higher than the average porosity of limestones (1.4%). Their poro-perm relationships are similar, with the notable exception of planar-e type B dolomites, which generally display higher permeability values. The intensity of top bounded fractures is distinctly lower in coarse-crystalline dolomites than in fine-crystalline dolomites and limestones, both at the macro- and the micro-scale. On the other hand neither lithology (i.e. limestone vs. dolomite) nor dolomite crystal size control the intensity of perfect bed-bounded fractures, which is strictly controlled by the fracture layer thickness. Our results provide information that could be used as guidance for the characterization and modelling of fractured carbonate reservoirs made of interlayered limestones and dolomites.

Fault breccia present along strike-slip faults was studied by mean of an integrated field and laboratory investigation. In particular, samples of sheared pre-existing, syn-sedimentary gravitative breccia were detailed studied in order to decipher the deformation mechanisms associated to strike-slip faulting. The sheared gravitative breccia is made up of matrix-supported, monomictic, unsorted intraformational fragments embedded within a reddish hematite rich, clayish matrix. Microsparry calcite cement is also present around the limestone fragments. In contrast, tectonic breccia consists of comminuted limestone fragments embedded in a calcite-rich matrix also including small amounts of reddish matrix. Particle shape analysis of representative images of the study hand specimens shows a variability of the box-counting dimension (D-0-value) between the two different types of breccias, which can be explained in terms of peculiar strain localization within a threefold aggregate that characterizes the gravitative breccia, which is made up of calcite fragments, clayish matrix and very minute oxides.

An approach is presented for fracture porosity, fracture aperture and permeability evaluation through extracting conductive image features from FMITM borehole image logs. The methodology of image feature and in particular fracture recognition, extraction and characterisation is based on the borehole image tool button response simulation model originally developed by Luthi (1990) for the water-based mud system and the principle of 2D fracture intensity (P32) to 3D fracture intensity/volume (P33) transformation. The extracted conductive image features allow us to distinguish open fractures and karst features. Fracture aperture is calculated as a function of the button resistivity, tool current & voltage, mud resistivity and background rock resistivity. Fracture porosity is computed with consideration of fracture type, well type and condition. Fracture permeability is estimated by taking fracture aperture, type and intensity into account. The results for naturally fractured tight carbonate reservoirs are demonstrated. Various types of conductive features are successfully recognised and characterised using the new approach. Sedimentary features like bedding and shale boundaries are identified too. Drilling induced or borehole breakout features have been distinguished and excluded from true nature formation features. The robustness of the fracture characterisation can be demonstrated through various field examples and reservoir model implementation. The new approach provided independent fracture characterisation inputs for discrete fracture network (DFN) and dynamic models of the fractured reservoir examples shown.

Through-going joints cutting across beds are often invoked to match large-scale permeability patterns in tight carbonate reservoirs. However, despite the importance of these structures for fluid flow, only few field studies focused on the understanding and estimation of through-going joint dimensional parameters, including spacing and vertical extent in relation to stratigraphy. Recent improvements in the construction of digital models of outcrops can greatly help to overcome many logistic issues, favouring the evaluation of relationships between jointing and stratigraphy at the reservoir scale. In this study, we present the results obtained from integrating field measurements with a digital outcrop model of a carbonate platform reservoir analogue in the Sorrento peninsula (Italy). The outcrop consists of a nearly vertical cliff exposing a monocline of alternating gently-dipping shallow-water limestones and dolostones, crossed by several vertical joints of different size. This study allowed us to define how major through-going joints pass across thick beds (bed thickness > 30 cm), while they arrest against packages made of thinly stratified layers. In essence, through-going joints arrest on “weak” levels, consisting of thinly bedded layers interposed between packages made of thick beds, in the same manner as bed-confined joints arrest on less competent interlayers.

In the Agri Valley, high-angle faults crosscut platform carbonates that are analogues of the lithological units that host the deep seated largest onshore oil reservoir in Europe. The main faults are W-NW oriented with a left-lateral strike-slip kinematics; additionally, three sets of related secondary faults are present: ( i ) N-NE oriented with right-lateral/transtensional kinematics; ( ii ) E-W trending left-lateral transtensional and ( iii ) N-NW trending left-lateral transpressional. Two of the secondary N-NE striking faults, strike-slip and transtensional, together with the adjacent host rock, were selected to build a Discrete Fracture Network model eventually used to evaluate the hydraulic properties and permeability anisotropy of these faults. The outcomes of this modelling show that the total permeability of the fault zones is higher than that one of the host rock. Moreover, the results are consistent with the transtensional fault having higher permeability values relative to the strike-slip one. The permeability anisotropy within the fault damage zone as well as in the host rock is mainly related to the fracture orientation.

This work focuses on the spacing and height distributions of bed-perpendicular fracture sets present within a carbonate multilayer, and on their effect on the volumetric (P32 and fracture porosity) and hydraulic (correspondent permeability) properties of the rock mass computed after DFN modelling. Results of integrated field and laboratory analyses are consistent with an uneven spacing distribution of Strata-Bound (SB) fractures. The oldest SB fractures formed within individual limestone beds bounded by bed interfaces, which likely acted as mechanical interfaces. Differently, the youngest SB fractures formed within smaller rock volumes bounded by the pre-existing fractures. Non Strata-Bound (NSB) fractures consist on sheared bed-perpendicular fractures, originally compartmentalized within individual beds, which now form incipient strike-slip faults. DFN modelling of representative rock volumes show that both volumetric and hydraulic properties are strongly affected by the two main sets of NSB fractures, which form a conjugate system of faults producing the principal structural anisotropy in the fractured carbonate multi-layer.

The Upper Jurassic to Lower Cretaceous platform-slope to basinal carbonate strata cropping out in Gargano Promontory (southern Italy) are partly dolomitized. Fieldwork and laboratory analyses (petrographic, petrophysical and geochemical) allowed the characterization of the dolomite bodies with respect to their distribution within the carbonate succession, their dimensions, geometries, textural variability, chemical stability, age, porosity, genetic mechanisms and relation with tectonics. The dolomite bodies range from metres to kilometres in size, are fault-related and fracture-related, and probably formed during the Early Cretaceous at

We present the results of in situ permeability measurements performed, using a portable field permeameter, on normal and strike-slip fault zones that crosscut high-porosity carbonate grainstones. The measurement sites expose in the Cretaceous Orfento Formation of the Majella Mountain (Abruzzo, Italy), and the Lower Pleistocene deposits of the Favignana Island (Sicily, Italy). Nine small-displacement, compactive shear banding-based fault zones have been tested in the field. The fault offset ranges between 10 and 200 centimeters. The acquired permeability data indicate a two orders of magnitude decrease of porosity and permeability from the host rock to the cataclastic fault cores. A clear dependence of the fluid circulation paths through porous carbonates is therefore inferred at depth due to orientation, density and connectivity of the fault zones. Moreover, this study indicates the key role played by the pore network characteristics (pore dimensions above all) of undeformed host rocks on determining extremely different permeability values of the faulted porous carbonate grainstones. Accordingly, the results presented in this study may be helpful in applications such as geofluids management for improving the forecasting of carbonate reservoir quality and understanding the extent of reservoir compartmentalization.

The modelling of natural fracture in reservoirs requires, as input data, the results of previous detailed and accurate analysis of the 3D fracture network. These data could be derived from well logs and production tests (which however limit our understanding of the fracture geometry, intensity and distribution) and outcrop analogues. Data obtained applying scanline and scanarea methodologies on rocks exposed at the surface, in fact, allow the construction of more representative numerical models of natural fractured reservoirs. This paper focuses on with the (DFN) modelling of natural fractures associated to strike-slip faults crosscutting tight carbonates, which are exposed along vertical walls and pavements of an inactive quarry of the Murge area, southern Italy. The studied outcrops expose the inner structure of two conjugate fault zones striking WNW-ESE and NNW-SSE, respectively. DFN models were built according to the spatial and dimensional properties computed for the natural fracture network. The results of these models show that the overall fault permeability is 3-to-4 orders of magnitude higher than the host rock permeability. The fault damage zones form the main fluid conduits, with the highest permeability values computed for fault-parallel fluid flow. Such a pronounced permeability anisotropy obtained for the fault damage zone is mainly related to the fracture dimension, both lengths and heights, and their aperture values.

The work tackles the control exerted by a sub-seismic fracture network on both secondary porosity and correspondent permeability of outcropping tight carbonates. Taking advantage of excellent 3D exposures, located in the Murge Plateau of southern Italy, the fracture network is investigated at different scales of observation. The rock multi-layer is made up of 10's of cm-thick, sub-horizontal, laterally continuous limestone beds crosscut by stratabound fractures, non-stratabound fractures, and small faults named as persistent fracture zones with low amounts of offset. Stratabound fractures consist of bed-perpendicular joints and sheared joints, non-stratabound fractures of incipient, cm-offset, sub-vertical faults, whereas the 10's of cm-offset persistent fracture zones are made up of 10's of m-high, m-thick fractured damage zones. The aforementioned structural elements localize within discrete carbonate units bounded by primary features such as bed surfaces, prominent surfaces and sedimentary breccia horizons. Such interfaces therefore affected the fracture stratigraphy of the limestone rock, and thus impact the fluid flow properties of the carbonate multilayer by compartmentalizing deformation. In the field, the fracture network is investigated by means of scanline and scan area methodologies to document the orientation, intensity, height distribution, mechanical aperture and roughness of individual fractures exposed along vertical outcrops and pavements of abandoned quarries. Then, Discrete Fracture Network (DFN) models of representative geocellular volumes are built, according to the different scales of analysis, to compute both fracture porosity and correspondent permeability (K xx , K yy , K zz ). Results of such a work show that the most prominent non-stratabound fracture set forms the major control on fluid storage and migration at the scales of single beds and bed-packages. At a larger scale, we document that fluid migration mainly occurs along the persistent fracture zones, which enhance the fault-parallel flow. As a whole, the persistent fracture zones form localized fluid conduits embedded within carbonate matrices that show isotropic fluid flow properties.

Hauterivian-Barremian dolomitized carbonates of the Monte Faito ridge (Sorrento peninsula, Italy) rep-resent a good analogue for the Lower to middle Cretaceous portion of the reservoir units of the Southern Italy oilfields. In order to gain a better understanding of the distribution of reservoir-scale, flow-controlling ‘fracture corridors’ and of the nature of the mechanical boundaries con-trolling their vertical propagation, an integrated sedimentological, petrographic and structural study has been performed on a 200 m-thick succession of alternating dolostones and limestones. The fracture analysis, performed on a 3D model generated from photogrammetry with the help of an Unmanned Aer-ial Vehicle, identified a clear mechanical stratigraphy for large-scale fracture corridors and fault damage zones. The following stratigraphic survey established that the position of the main mechanical interfaces is controlled by: (i) tens of meters-thick bed packages dominated by fine- to medium-grained dolomite abutting a package of thick calcareous or calcareous-dolomitic beds; and (ii) packages of thin laminated dolomitic beds, representing thinning upward cycles deposited during the late highstand of lower order cycles. The rather regular stacking pattern resulting from the superposition of several orders of shallow-ing-upward cyclicity may be used to obtain a predictive tool for fracture distribution and impedance.

In order to better understand the relative contribution of background and localized deformation on the petrophysical properties of fractured tight carbonates, Discrete Fracture Network (DFN) models of representative outcrops were build up by using a stochastic approach. The study carbonates, which crop out along the vertical walls and pavements of an abandoned quarry of southern Italy, represent a surface analogue of the hydrocarbon reservoirs currently developed in nearby areas of Italy. The outcrops expose a well-layered, tight, Cretaceous limestone crosscut by both background (diffuse) and fault-related (localized) deformation. Fractures show a high variability of their spatial and dimensional properties (length, intensity, aspect ratio and aperture), according to the different structural domains (fractured host rock, fault damage zone and fault core) in which they were surveyed. Such variability highlights the different scales at which the structural domains affect the tight carbonates, and can be considered a key challenge to construct a realistic reservoir model. DFN modelling of representative rock volumes of the fractured host rock showed that both volumetric (P32 and porosity) and hydraulic properties (correspondent permeability) are mainly affected by the two main sets of Non-StrataBound fractures (NSB). Equivalent porous media modelling, which include both fractured host rock and fault zones, showed that the overall permeability of the Fault Damage Zones (FDZ) is 2-to-4 orders of magnitude higher than the fractured host rock permeability. The FDZ can be therefore interpreted as fluid conduits that enhance fluid flow, which is controlled by both the dimensional properties of the fractures and by their aperture values.

In this study we performed a fracture analysis on a Cretaceous bedded carbonate succession well exposed in the Sorrento Peninsula. The studied succession includes stratigraphic units that are very similar to the productive units of the buried Apulian Platform reservoir rocks in southern Italy. We analyzed eight carbonate beds, including both limestones and dolomites. The basic technique used in this study consisted of measuring fractures along bedding-parallel scan lines. For one limestone bed, a microscale scan line, about 15 cm long, was also analyzed using a digital microcamera. Provided the cumulative distribution of fracture apertures is well described by a power law, our analysis shows how the uncertainty in the estimate of fracture aperture cumulative frequencies grows for large aperture values. This feature results in a large uncertainty in the estimate of the slope of the least-squares line (in a bi-logarithmic diagram) approximating the data distribution, which is the exponent of the power law. As the latter represents a fundamental parameter characterizing a fracture set and fracture distribution over different scales, reducing the uncertainty in the estimate of the slope of the curve represents an important objective of quantitative fracture analysis. This is obtained in this study by the application of multi-scale analysis, and by integrating micro-scan line data with classic outcrop-based scan line analysis. The quantification of uncertainties in the cumulative distribution estimates of fracture apertures is performed by analyzing in detail the spacing distribution – and consequently fracture-density distribution – for each aperture value. Our results suggests that a meaningful statistical analysis of fracture attributes such as aperture (or opening displacement) may be effectively carried out by using properly determined confidence intervals and by the integration of outcrop-based and micro-scan line data sets.

Fracture analysis, carried out on two reservoir analogues cropping out at Faito and Chianello Mts. (southern Italy) allowed us to unravel the role of stratabound joint networks for oil migration and storage within well-bedded carbonate successions. The fracture regression analysis pointed out that stratabound fracture aperture increases as a function of bed thickness according to a linear law, independently by the lithological characteristics of the analyzed rock. Furthermore, statistical results suggest that fracture aperture and spacing exhibit, for each bed thickness value, a lognormal probability distribution. The estimation of the stratabound fracture porosity allowed us to identify, in well-bedded sedimentary successions, three classes of multilayer packages: ( i ) thin beds, characterized by a dual role of permeable pathways and oil storage systems; ( ii ) medium sized beds, showing limited permeability and porosity values and ( iii ) thick beds, acting as highly permeable pathways and showing a negligible storage capacity. Our results permit a full characterization and modeling of stratabound fracture networks. In particular, they provide a powerful tool for predicting preferential fluid pathways and major oil storage systems based on bed thickness data, within the framework of an analysis that may be further enhanced by the integration of petrophysics data.

This article addresses the controls exerted by sedimentologic and diagenetic factors on the preservation and modification of pore-network characteristics (porosity, pore types, sizes, shapes, and distribution) of carbonates belonging to the Bolognano Formation. This formation, exposed at the Majella Mountain, Italy, is composed of Oligocene–Miocene carbonates deposited in middle- to outer-ramp settings. The carbonates consist of (1) grainstones predominantly composed of either larger benthic foraminifera, especially Lepidocyclina, or bryozoans; (2) grainstones to packstones with abundant echinoid plates and spines; and (3) marly wackestones to mudstones with planktonic foraminifera. The results of this field- and laboratory-based study are consistent with skeletal grain assemblages, grain sizes, sorting, and shapes, all representing the sedimentologic factors responsible for high values of connected primary macroporosity in grainstones deposited on the high-energy, middle to proximal outer ramp. Cementation, responsible for porosity reduction and overall macropore shape and distribution in grainstones to packstones deposited on the intermediate outer ramp, was mainly dependent on the following factors: (1) amount of echinoid plates and spines, (2) grain size, (3) grain sorting and shapes, and (4) clay amount. Differently, in the wackestones to mudstones, laid down on the low-energy, distal outer ramp, matrix is the key sedimentologic factor responsible for low values of scattered macroporosity and dominance of microporosity. The aforementioned results may be useful to improve the prediction of reservoir quality by means of mapping, simulating, and assessing individual carbonate facies with peculiar pore-network characteristics.

Fractures can play an important role in the fluid storage–migration properties of fault damage zones. In this present contribution, we document the role exerted by fractures on fluid flow in carbonate damage zones of hydrocarbon-bearing, km-long, oblique-slip normal faults with 10's of m-throw. The carbonate fault damage zones were analysed by mean of scan line surveys conducted in both tar-free and tar-rich outcrops. In this way, the relationships among the individual fracture characteristics (length, spacing, aperture, orientation, connectivity and distance from slip surfaces pertaining to small faults of the fault damage zones) and hydrocarbons have been established. Data obtained by scan line surveys were also used to compute the amount of fracture porosity, the degree of fracture connectivity and, based upon simple assumptions, the orientation of the local σhmax at times of faulting. Additionally, scan line surveys were also carried out along outcrops exposing unfaulted carbonate host rocks. The results of our computation are consistent with a carbonate host rock made up of a quite isotropic fracture array comprised of isolated and coupled fractures, in which individual fracture sets have negative exponential spacing distributions. In terms of fluid flow, the fracture array of the carbonate host rock enhances the fluid storage. Conversely, the fracture array of the fault damage zones is characterized by a pronounced anisotropy due to interconnected fractures, which enhance the fluid migration. Fractures in the fault damage zones include those inherited from background deformation and others related to the faulting processes. The latter fracture sets are characterized by power law spacing distributions. In conclusion, counter-intuitively, both fracture length and fracture spacing do not have any correlation with hydrocarbons in the fault damage zones. On the contrary, fracture anisotropy, fracture spread and fracture orientation are positively correlated with hydrocarbons.

Radioactive chemical logging sources have been used in the E&P industry for many years to help operators obtain valuable information about their reservoirs. Until recently, much of the information obtained using these sources could not be obtained with any other method. While the potential risks involved with the use of such sources have always been known, more awareness in the industry has led to increased efforts towards the reduction or even elimination of the use of chemical sources where possible. A new Logging-While-Drilling (LWD) tool has been developed, using innovative technology to provide a complete suite of formation evaluation measurements without having to use a chemical radioactive logging source. The use of a non-chemical radioactive source significantly reduces the environmental and operational risks normally involved with traditional LWD tools. The data delivered by this service include not only the traditional measurements such as gamma ray, resistivity, density, and neutron porosity, but also measurements not previously available in LWD such as formation capture cross section (sigma) and elemental analysis from neutron capture spectroscopy used to compute formation mineralogy. An entirely new LWD measurement has also been introduced with the tool, making it possible for the first time to determine formation density without the use of a chemical logging source. A case study is presented of a well situated in a field in southern Italy, inside an environmentally sensitive national park. Because of the location of the well, it has not been possible to use radioactive logging sources for formation evaluation. As a result, fully evaluating the reserves has been an ongoing challenge for the operator. In addition, because of the move towards high angle and horizontal wells, wireline formation evaluation acquisition has been, at times, replaced by LWD. The new LWD tool allowed the operator to not only improve efficiency, but also brought with it the possibility of more completely evaluating the diagenetically complex tight carbonate reservoir through the use of the new measurements. The favourable environmental conditions (low temperature and low mud salinity) made it possible to obtain additional spectral data, which was used to correct the neutron porosity measurement for lithology effects, despite the presence of dolomite. The results of the formation evaluation studies are presented, together with an analysis of the impact on operational efficiency and environmental and operational safety as a result of not having to use a chemical logging source.

[1] We have analyzed a 1500 m section at 3.9 to 5.4 km depth in a well of the southern Apennines, in order to better characterize the local active stress field and its correlation with tectonic structures. In this paper we present and discuss the results obtained from the comparison between breakouts and structural analysis from dipmeter data. We have found that the mean breakout direction is in agreement with the regional stress field that in this area is characterized by normal faulting (σ1 = σv) with NE-SW trending extension (horizontal σ3). Since the regional stress field is relatively well known in this region, we could detect and study some anomalous horizontal stress directions along the well, which we interpret as due to faults crosscutting the borehole. A detailed comparison between the breakout-inferred stress variations along depth and the faults identified by the dipmeter analysis reveals that some of these faults are associated with stress rotations, whereas others do not show any variation. The former can be interpreted either as “open” fractures or as faults that slipped recently with a near-complete stress drop, and the latter can be interpreted as “sealed” faults. In particular, we found that the main thrust faults of the area, mainly active in Pliocene times, appear to be sealed, whereas ∼E-W trending high-angle (normal?) faults determine strong stress rotations, suggesting that they are the main active structures of the region. This suggests that the study area is located in a transfer zone between the two main “Apenninic” (NW-SE trending) fault systems which ruptured in the last 150 years. This study has shown that a detailed analysis of the structural and geometrical characteristics of deep wells can be used for the reconnaissance of active structures. This approach can contribute to seismic hazard studies and, if carried out in an oil-bearing section, can help to maximize the hydrocarbon production.

The fault cores of extensional faults in Mesozoic limestones and dolostones are examined by mean of combined microstructural, ultrasonic and petrophysical analyses. Grain-supported fault rocks commonly localize in the outer fault cores, whereas matrix-supported fault rocks in their inner portions. Cemented fault rocks, if present, surround the main slip surfaces. All dolomite-rich fault rocks, include elongated pores that show a preferential orientation only in the inner fault core. On the contrary, the pore network of calcite-rich fault rocks is made up of elongated pores in the outer fault core, and of sub-spherical pores in the inner fault core. Despite their different pore network characteristics, the petrophysical values of both grain-supported and matrix-supported fault rocks are quite similar one another, with effective porosity up to 10–12%, and permeability up to 2–5 mD. Differently, these values drop down to host rock values, porosity ~5% and permeability ~10−3 mD, in the cemented fault rocks. Experimental data are discussed to establish, for the first time, the relative control exerted by individual cataclastic and diagenetic processes on the present day pore characteristics, and to decipher the fault core permeability structure at depth.