Irina Korneva

Bedding-parallel stylolites in shallow-water limestone successions of the Apulian Carbonate Platform (central-southern Italy)

Bedding-parallel stylolites typically represent the product of chemical compaction (overburden weight-induced pressure solution) experienced by carbonate successions during their burial history, when bedding is still horizontal. Due to their common occurrence in carbonate rocks, with lateral extents that can exceed 1 km, bedding-parallel stylolites are of special interest for the hydrocarbon industry because they may affect the regional fluid flow in the subsurface. Aimed at assessing the development and distribution of bedding-parallel stylolites in shallow-water, platform limestone successions, field and laboratory studies were carried out on Cretaceous limestones originally pertaining to the Apulian Carbonate Platform realm and now exposed in three distinct Italian locations: Maiella Mountain, Gargano Promontory and Murge Plateau. Results point to a prominent role played by the geological characteristics of limestones on development and localization of bedding-parallel stylolites within shallow-water, platform limestone successions. In particular, bedding-parallel lamination and fine rock grain size, co-occurring in stromatolitic limestones, determined there laterally more extensive and closely spaced stylolites than in the associated calcilutites and calcarenites. Large fenestral pores, which are ubiquitous in stromatolitic limestones, represent rock heterogeneities able to influence the roughness of individual stylolites. Laboratory measurements revealed that the permeability of the studied Cretaceous limestones is very low (<10 μD). Pilot tests suggest that bedding-parallel stylolites in stromatolitic layers are not barrier to fluid flow but may represent pathways through low-permeability, platform limestone successions in the subsurface.

Fracture properties analysis and discrete fracture network modelling of faulted tight limestones, Murge Plateau, Italy

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.

Characterisation of the permeability anisotropy of Cretaceous platform carbonates by using 3D fracture modeling: the case study of Agri Valley fault zones (southern Italy)

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.

Mass-transport deposits within basinal carbonates from southern Italy

A detailed characterisation of submarine mass-transport deposits (MTDs), in terms of both emplacement processes and internal architecture of depositional products, is crucial to define the hydraulic properties of slope-to-basinal deposits.The Late Jurassic-Early Cretaceous basinal Maiolica Formation exposed in the Gargano Promontory (southern Italy) represents an ideal natural laboratory to study the complex stratigraphic architecture of ancient MTDs. This formation consists of undisturbed intervals of flat-lying, thin-bedded, cherty micritic limestone inter-bedded with intervals of lithologically similar, but chaotic strata that are characterized by significant internal distortion. The stratigraphic thickness of these deformed units, which are interpreted to represent several types of mass movements (e.g., slumps and, to a lesser extent, slides and debris flows), varies from several decimetres to tens of metres. The internal deformation features comprise down-slope verging folds, together with both normal and reverse faults. In several places, the studied MTDs exhibit signs of reworking, as demonstrated by reactivation of the slump-related faults resulting in deformation of beds directly overlying the MTDs. Structural features within MTDs, provide information about the direction of the mass movement, and hence the orientation of the paleoslope. Measurements in the eastern and north-eastern part of Gargano Promontory suggest flow is directed towards the E and N respectively. The internal architecture of studied MTDs is discussed in the context of triggering mechanisms related to the characteristics of the Cretaceous paleoslope of the Apulian Platform.