FAULT ZONE PROPERTIES IN THE ROMAN VALLEY QUARRY RESERVOIR ANALOGUE: INSIGHT FOR WELL LOGS, CORE AND FIELD DATA

Carbonate rocks represent important natural reservoirs of geofluids (e.g. mineral and hydrothermal waters, geothermic fluids, oil and gas) in which containment and migration are strongly influenced by the “fracturing” state of the rocky masses. According to several field-based research papers, fault zones exert a first order control on fluid flow and accumulation in the subsurface. In order to implement this information into predictive modeling tools, helpful to optimize the exploitation of oil reservoirs, it should be useful to integrate field-based data together with wells-based data (generally consisting of core and well logs analyses), usually employed by oil company workers for the formation evaluation. The present work aims at filling this cognitive gap by integrating field, core and well log data collected on a fault zone cropping out in a reservoir-analogue, located in the Roman Valley Quarry (Majella Mountain, Italy). The characterization of cores and geophysical data (from well logs) aims to: (i) perform a detailed structural analysis from well cores and optical scanner images data; (ii) calculate both matrix and fracture porosities of the collected cores; (iii) find the relationships among the measured porosities values and the geophysical logs; (iv) develop a method to discriminate, from well log data, the matrix porosity from fracture porosity. The comparison of well log, core and outcrop data of a fault zone crosscutting an analogue carbonate reservoir allow us to correlate the fracture characteristics with the geophysical properties. We also define some issues, and propose practical solutions, to compute the petrophysical parameters characterizing both matrix and fracture net pore volume in a carbonate rock

Natural and laboratory compaction band in porous carbonates: a 3D characterization using synchrotron X-ray microtomography

Porous carbonates form important reservoirs for water and hydrocarbons. Post-depositional processes (e.g. mechanical) are important to quantify because they may affect the fluid flow properties of reservoirs. Field-based studies (Tondi et al., 2006; Rustichelli et al., 2012) described bed-parallel compaction bands (CBs) within carbonates with a wide range of porosities. These CBs are burial-related structures, which accommodate volumetric strain by grain rotation, grain translation, pore collapse and pressure solution. Cilona et al. (2012) performed triaxial compression experiments, under dry conditions on the porous cretaceous grainstones (the Orfento Formation, in Majella Mountain, Abruzzi), reproducing for the first time CBs in laboratory. In this work, the authors defined the pressure conditions at which natural CBs form and documented the role of Hertzian cracks for grain size and porosity reduction within the CBs. Here we use a new methodology to characterize the pore networks of natural and laboratory CBs and compare them with the host rock one. Data were collected using the synchrotron X-ray microtomography technique at the SYRMEP beamline of the Elettra-Sincrotrone Trieste Laboratory (Basovizza (Trieste), Italy). Quantitative analyses of the samples were carried out using the Pore3D software library (Brun et al., 2010). The porosity was calculated from segmented 3D images of deformed and pristine rocks. The process of skeletonization, which provides the number of connected pores within a rock volume, was applied. By analyzing the skeletons we were able to highlight the differences between natural and laboratory CBs, and to investigate how pore connectivity evolves as a function of the deformation. Preliminary results show that within compaction bands both pore volume and connectivity are reduced in comparison with the undeformed host rock. Natural CB has a lower porosity with respect to the laboratory one. In natural CBs, the contact among granules seem be welded, whereas in the laboratory CBs it shows pores with irregular shape

Fault zone properties in carbonate rocks: insights for well logs, core and field data

In the last few years, numerous works addressed the deformation processes in carbonate rocks. These studies, generally sponsored by the oil industry, aimed to a better understanding of the structural and hydraulic properties of fault zones as well as of the subsurface fluid pathways in deformed carbonate rocks. This effort was mainly driven by the economic significance that carbonate rocks have for the oil industry, since they represent important natural reservoirs of hydrocarbons. According to the many field-based research scientific articles published in the recent past, both structural and hydraulic properties of fault zones, and their evolution trough time, exert a first order control on subsurface fluid flow and accumulation in fractured carbonate reservoirs. In order to convert this knowledge into predictive modeling tools that would help to optimize their exploitation, it should be useful to integrate the field-based data together with the subsurface data, which generally consist of core and well log (resistivity, acoustic, gamma ray etc.) analyses usually gathered to assess the formation evaluation of carbonate reservoir. The presented work aims at filling this cognitive gap by the acquisition and elaboration of subsurface geophysical properties of a hydrocarbon-bearing oblique normal fault zone characterized by 10’s of m offset, and cropping out in an exposed analogue of fractured carbonate reservoir (Maiella Mountain, Italy). The deformation mechanisms associated to the processes of fault nucleation and development within the Oligo-Miocene shallow-water carbonate rocks were documented in the recent past by our research group. In this present contribution, we present the results of our elaboration of the geophysical data, obtained from well logs oriented perpendicular to the study fault zone. These results are consistent with the following statements: a) there is a meaningful correlations between cores and digital images; b) a detailed structural analysis of the deformed carbonates can be performed by using well cores and digital image data; c) both matrix (primary) and fracture (secondary) porosities can be obtained from subsurface data; d) some possible relationships exist between secondary porosity and the measured log geophysical properties (P- and S-wave velocities, Resistivity). In conclusion, the results of this multi-disciplinary study, which involved the analyses of well logs, core and outcrop data of an hydrocarbon-bearing fault zone permitted us, therefore, to obtain useful correlation between fracture porosity and geophysical properties. We propose some practical solutions to compute the petrophysical parameters in order to assess both primary and secondary porosity in fractured carbonate reservoirs

Structural and statistical characterization of joints and multi-scale faults in an alternating sandstone and shale turbidite sequence at the Santa Susana Field Laboratory: Implications for their effects on groundwater flow and contaminant transport

This paper describes the properties of faults and fractures in the Upper Cretaceous Chatsworth Formation exposed at Santa Susana Field Laboratory and its surroundings (Simi Hills, California), where groundwater flow and contamination have been studied for over three decades. The complex depositional architecture of this turbidite consisting of alternating sandstones and shales, interacting with formative stress conditions are responsible for multi-scale fault hierarchies and permeable fractures in which nearly all groundwater flow occurs. Intensity and distribution of background fractures and their relation to bedding thickness are established for sandstones, the dominant lithology. The architecture of faults with increasing displacement is described, and relationships among fault dimensional parameters captured. Data from ∼400 boreholes and piezometers reveal the effect of faults and fractures on groundwater flow. Large hydraulic head differences, observed across fault zones with shale-rich cores, indicate these structures as cross-flow barriers. Moreover, hydraulic head profiles under ambient conditions, and pumping tests suggest strong hydraulic connectivity in all directions to depth of hundreds of meters. This outcrop-based structural characterization relates the horizontal hydraulic conductivity to the observed well-connected fracture network, and explains the strong vertical connectivity across low-hydraulic conductivity shales as faults and sheared fractures provide flow pathways.Fil: Cilona, Antonino. University Of Stanford; Estados UnidosFil: Aydin, Atilla. University Of Stanford; Estados UnidosFil: Likerman, Jeremias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos; ArgentinaFil: Parker, Beth. University of Guelph; CanadáFil: Cherry, John. University of Guelph; Canad

Spatial and dimensional variations of the faults and fractures attributes, and their influence on the permeability of the Cretaceous platform carbonates in Val d'Agri, southern Italy

In the Agri Valley, high-angle faults crosscut platform carbonates that are analogues of the lithological units that host the deep-seated Val d’Agri field, which is among the largest onshore oil reservoirs in Western Europe. The main faults are W-NW oriented with a left-lateral strike-slip kinematic; 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

Deformation bands in porous carbonate grainstones: Field and laboratory observations

International audienc

Modelling a strike-slip fault system affecting porous carbonates in Favignana Island (Sicily, southern Italy)

Understanding the deformation processes in carbonates is fundamental for geo-fluid exploitation. Indeed, in these rocks fluid containment and migration are influenced by fault zones and fractures. This contribution integrates structural analysis and numerical modelling approaches aimed at testing a new workflow for creating a 3D Discrete Fracture Network (DFN) model of a reservoir from outcrop data. In Favignana Island (Italy), several quarries provide 3D exposures of Lower- Pleistocene grainstones crosscut by a strike-slip fault system. This fault system is comprised of three types of structures: compactive shear bands (CSB); zones of bands (ZB); and, faults. The DFN model was built using the Fracture Modelling module within the Move software package from Midland Valley©. Analysis of an aerial photo was performed to identify the major faults. The intensity of CSBs and ZBs, was calculated from the lineament analysis tool of Move. We used the variation in intensity to build a DFN that reflects an intensity of deformation similar to the natural structural framework. Both CSBs and ZBs reduce permeability whilst slip surfaces enhance fault-parallel fluid flow. The DFN was then used to model the effect of deformation on the permeability of the host rock by imposing a reduced permeability in CSBs and ZBs relative to the host rock and the slip surfaces. This semi-automated process of lineament analysis, followed by the use of power law distributions to model sub-seismic scale features is proposed as a workflow for reservoir-scale assessment of the structural control on permeability in porous carbonate reservoirs