Juliette Lamarche

The Elbe Fault System in North Central Europe—a basement controlled zone of crustal weakness

Abstract The Elbe Fault System (EFS) is a WNW-striking zone extending from the southeastern North Sea to southwestern Poland along the present southern margin of the North German Basin and the northern margin of the Sudetes Mountains. Although details are still under debate, geological and geophysical data reveal that upper crustal deformation along the Elbe Fault System has taken place repeatedly since Late Carboniferous times with changing kinematic activity in response to variation in the stress regime. In Late Carboniferous to early Permian times, the Elbe Fault System was part of a post-Variscan wrench fault system and acted as the southern boundary fault during the formation of the Permian Basins along the Trans-European Suture Zone (sensu [Geol. Mag. 134 (5) (1997) 585]). The Teisseyre–Tornquist Zone (TTZ) most probably provided the northern counterpart in a pull-apart scenario at that time. Further strain localisation took place during late Mesozoic transtension, when local shear within the Elbe Fault System caused subsidence and basin formation along and parallel to the fault system. The most intense deformation took place along the system during late Cretaceous–early Cenozoic time, when the Elbe Fault System responded to regional compression with up to 4 km of uplift and formation of internal flexural highs. Compressional deformation continued during early Cenozoic time and actually may be ongoing. The upper crust of the Elbe Fault System, which itself reacted in a more or less ductile fashion, is underlain by a lower crust characterised by low P-wave velocities, low densities and a weak rheology. Structural, seismic and gravimetric data as well as rheology models support the assumption that a weak, stress-sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the Elbe Fault System.

Tectonic versus diagenetic origin of fractures in a naturally fractured carbonate reservoir analog (Nerthe anticline, southeastern France)

Field analogs allow a better characterization of fracture networks to constrain naturally fractured reservoir models. In analogs, the origin, nature, geometry, and other attributes of fracture networks can be determined and can be related to the reservoir through the geodynamic history. In this article, we aim to determine the sedimentary and diagenetic controls on fracture patterns and the genetic correlation of fracture and diagenesis with tectonic and burial history. We targeted two outcrops of Barremian carbonates located on both limbs of the Nerthe anticline (southeastern France). We analyzed fracture patterns and rock facies as well as the tectonic, diagenetic, and burial history of both sites. Fracture patterns are determined from geometric, kinematic, and diagenetic criteria based on field and lab measurements. Fracture sequences are defined based on crosscutting and abutting relationships and compared with geodynamic history and subsidence curves. This analysis shows that fractures are organized in two close-to-perpendicular joint sets (i.e., mode I). Fracture average spacing is 50 cm (20 in.). Fracture size neither depends on fracture orientation nor is controlled by bed thickness. Neither mechanical stratigraphy nor fracture stratigraphy is observed at outcrop scale. Comparing fracture sequences and subsidence curves shows that fractures existed prior to folding and formed during early burial. Consequently, the Nerthe fold induced by the Pyrenean compression did not result in any new fracture initiation on the limbs of this fold. We assume that the studied Urgonian carbonates underwent early diagenesis, which conferred early brittle properties to the host rock.

Three‐dimensional structural modeling of an active fault zone based on complex outcrop and subsurface data: The Middle Durance Fault Zone inherited from polyphase Meso‐Cenozoic tectonics (southeastern France)

The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7 km to 8 km around the main segment of the fault zone.

Reconstruction of the Provence Chain evolution, southeastern France

The Provence fold-and-thrust belt forms the eastern limit of the Pyrenean orogenic system in southeastern France. This belt developed during the Late Cretaceous-Eocene Pyrenean-Provence compression and was then deformed by Oligocene-Miocene Ligurian rifting events and Neogene to present-day Alpine compression. In this study, surface structural data, seismic profiles, and crustal-to-lithospheric-scale sequentially balanced cross sections contribute to the understanding of the dynamics of the Provence Chain and its long-term history of deformation. Balanced cross sections show that the thrust system is characterized by various structural styles, including deep-seated basement faults that affect the entire crust, tectonic inversions of Paleozoic-Mesozoic basins, shallower decollements within the sedimentary cover, accommodation zones, and salt tectonics. This study shows the prime control of the structural inheritance over a long period of time on the tectonic evolution of a geological system. This includes mechanical heterogeneities, such as Variscan shear zones, reactivated during Middle Cretaceous Pyrenean rifting between Eurasia and Sardinia. In domains where Mesozoic rifting is well marked, inherited basement normal faults and the thermally weak crust favored the formation of an inner thick-skinned thrust belt during Late Cretaceous-Eocene contraction. Here 155 km (similar to 35%) of shortening was accommodated by inversion of north verging crustal faults, north directed subduction of the Sardinia mantle lithosphere, and ductile thickening of the Provence mantle lithosphere. During the Oligocene, these domains were still predisposed for the localized faulting of the Ligurian basin rifting and the seafloor spreading.

Background fractures in carbonates: inference on control of sedimentary facies, diagenesis and petrophysics on rock mechanical behavior. Example of the Murge Plateau (southern Italy)

Characterizing fracture networks in Naturally Fractured Reservoirs (NFR) is a major challenge for hydrocarbon exploration and production. The fracture organization is: i) a key parameter for fluid flow understanding in carbonates (in a general sense) and ii) the key parameter in tight, non-porous carbonates. However, at present-day, the fracture parameters from subsurface data are not sufficient to define the 3D distribution of a fracture network. Moreover, in carbonate reservoirs, fracture occurrence strongly depends on the mechanical properties of the host rock such that characterizing fractures is only possible through the close study of the host rock heterogeneities. Studying fractures in outcrop analogues allows accessing to 3D fracture patterns, determining the host rock mechanical properties and their impact on fracture distribution. In this paper, we trace the conditions for the fracturing process through the geodynamic history of the reservoir. We aim at determining the sedimentary and diagenetic controls on fracture patterns and the genetic correlation with tectonic and burial history.To this purpose, we have targeted two formations made of platform carbonates from the Murge Plateau. We analyzed the fracture patterns and sedimentary facies as well as the tectonic, diagenetic and burial history for each studied site. Fracture patterns are characterized from geometrical, kinematic and diagenetic criteria based on field and laboratory measurements. Fracture sequences are defined based on cross-cutting and abutting relationships and compared with geodynamic history.Fractures are bed-perpendicular joints and veins, and numerous bed-parallel stylolites. We observe a stage of fracturing synchronous with shallow burial and prior to major tectonic events. Carbonates have undergone early diagenesis during fast and shallow burial, conferring early brittle behavior. Fracture development, mechanical and petrophysical properties are acquired during early burial.

Three-dimensional structural model of composite dolomite bodies in folded area (Upper Jurassic of the Etoile massif, southeastern France)

The three-dimensional (3-D) geometry of fractures and fault-related dolomite is difficult to access with classical subsurface prospection tools. Therefore, we have investigated an outcrop to improve the subsurface prediction for complex dolomite bodies. This outcrop is located in the Etoile massif (southeastern France) within a fault-bend anticline. The sedimentary units are of Upper Triassic to lower Barremian age. The fold results from the Pyreneo-Provencal shortening during the Late Cretaceous to the Eocene. The anticline hosts three types of dolomite bodies: (1a) massive dolomite of middle to late Oxfordian age, (1b) syndepositional stratabound dolomite of Tithonian age, and (2) isolated dolomite bodies associated with fractures and faults. Large-scale geometries of fault-related dolomite bodies have been modeled in 3-D. The 3-D geometries of these bodies show diapir-, finger- and wall-like structures. These bodies are located close to the main thrusts, in strata of middle Oxfordian to early Barremian age and are linked to the compressive fold-bending phase during the Late Cretaceous. Fault-related dolomitization occurred because of magnesium removal from the hydraulic brecciation and the pressure solution of type 1 dolomite with overpressured fluids. These fluids flushed upward along the main thrust and laterally by following the reservoir property contrasts in the host rocks. Fault-related dolomite bodies are either spread far apart from faults in grainy limestones with good initial reservoir properties or are restricted to fault vicinity in muddy limestones with poor initial reservoir properties. The study of the structural and stratigraphic framework was essential in the understanding of the dolomitization process.

Summary of the AAPG–SPE–SEG Hedberg Research Conference on “Fundamental Controls on Flow in Carbonates”

A joint AAPG–Society of Petroleum Engineers–Society of Exploration Geophysicists Hedberg Research Conference was held in Saint-Cyr sur Mer, France, on July 8 to 13, 2012, to review current research and explore future research directions related to improved production from carbonate reservoirs. Eighty-seven scientists from academia and industry (split roughly equally) attended for five days. A primary objective for the conference was to explore novel connections among different disciplines (primarily within geoscience and reservoir engineering) as a way to define new research opportunities. Research areas represented included carbonate sedimentology and stratigraphy, structural geology, geomechanics, hydrology, reactive transport modeling, seismic imaging (including four-dimensional seismic, tomography, and seismic forward modeling), geologic modeling and forward modeling of geologic processes, petrophysics, statistical methods, numerical methods for simulation, reservoir engineering, pore-scale processes, in-situ flow experiments (e.g., x-ray computed tomography), visualization, and methods for data interaction. The conference was organized into four thematic sessions on the first two days (fundamentals, measurement and detection of flow on laboratory to field scales, uncertainty and prediction, and novel modeling and simulation techniques); a field trip on the third day was preceded by a dedicated poster session that introduced the geology of the area, whereas the ice breaker featured guest lectures on innovation and complex adaptive leadership, as well as a panel discussion. Given the challenge of cross-disciplinary communication, delegates were encouraged to adopt a beginners mind, challenging the status quo and exploring basic questions that the establishment might have overlooked. Stepping back and slowing down to promote effective conversations among different disciplines was emphasized upfront. Several delegates noted that technical jargon was a significant barrier to novel thinking in the way that it impeded effective communication among disciplines during the meeting. Cross-disciplinary interactions were encouraged by several further mechanisms, representing a shift from more common Hedberg Conference formats. Overall, the …