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Hard rocks or crystalline rocks (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, and are particularly exposed at the surface in the large shields of Africa, India, North and South America, Australia and Europe. They were, and are still in some cases, exposed to deep weathering processes. The storativity and hydraulic conductivity of hard rocks, and thus their groundwater resources, are controlled by these weathering processes, which created weathering profiles. Hard-rock aquifers then develop mainly within the first 100 m below ground surface, within these weathering profiles. Where partially or noneroded, these weathering profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) the permeable stratiform fractured layer (SFL). The development of the SFL’s fracture network is the consequence of the stress induced by the swelling of some minerals, notably biotite. To a much lesser extent, further weathering, and thus hydraulic conductivity, also develops deeper below the SFL, at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). The demonstration and recognition of this conceptual model have enabled understanding of the functioning of such aquifers. Moreover, this conceptual model has facilitated a comprehensive corpus of applied methodologies in hydrogeology and geology, which are described in this review paper such as water-well siting, mapping hydrogeological potentialities from local to country scale, quantitative management, hydrodynamical modeling, protection of hard-rock groundwater resources (even in thermal and mineral aquifers), computing the drainage discharge of tunnels, quarrying, etc.

This article discusses an inscribed bronze lamina, fractured on both sides, that was found in the horrea Agrippiana, located between the vicus Tuscus and the north-western slopes of the Palatine hill. The preserved portion of the text seems to contain a topographical indication, at stabulum (scil. factionis) Venetae, which would identify the stabulum that the factio Veneta (blue) had in Campus Martius to house horses, charioteers and staff. The function of the lamina remains uncertain. However, the typological characteristics, the shape and the tight layout of the letters, the linguistic aspects and the topographical indication itself have suggested identifying it with a narrow ribbon-like slave collar and proposing a possible reconstruction of the lost part of the text thanks to a comparison with the recurring formulary on this class of artefacts.

Modeling of fluid flow in porous media is a pillar in geoscience applications. Previous studies have revealed that heterogeneity and fracture distribution have considerable influence on fluid flow. In this work, a numerical investigation of two-phase flow in heterogeneous fractured reservoir is presented. First, the discrete fracture model is implemented based on a hybrid-dimensional modeling approach, and an equivalent continuum approach is integrated in the model to reduce computational cost. A multilevel adaptive strategy is devised to improve the numerical robustness and efficiency. It allows up to 4-levels adaption, where the adaptive factors can be modified flexibly. Then, numerical tests are conducted to verify the the proposed method and to evaluate its performance. Different adaptive strategies with 3-levels, 4-levels and fixed time schemes are analyzed to evaluate the computational cost and convergence history. These evaluations demonstrate the merits of this method compared to the classical method. Later, the heterogeneity in permeability field, as well as initial saturation, is modeled in a layer model, where the effect of layer angle and permeability on fluid flow is investigated. A porous medium containing multiple length fractures with different distributions is simulated. The fine-scale fractures are upscaled based on the equivalent approach, while the large-scale fractures are retained. The conductivity of the rock matrix is enhanced by the upscaled fine-scale fractures. The difference of hydraulic property between homogeneous and heterogeneous situations is analyzed. It reveals that the heterogeneity may influence fluid flow and production, while these impacts are also related to fracture distribution and permeability. Article highlights A multilevel adaptive implicit scheme up to 4-levels adaption is presented for two-phase ow in heterogeneous fractured reservoir. Discrete fracture model is combined with an equivalent continuum approach to reduce the complexity of fracture networks. The effects of permeability, orientation, size and number of fractures on hydraulic properties are studied. A comparison study of fluid flow and numerical performance between homogeneous and heterogeneous media is conducted.

Floor‐Fractured Craters (FFCs) are a class of lunar craters characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures; additional interior features are moats, ridges, and patches of mare material. Two formation mechanisms have been hypothesized—floor uplift in response to shallow magmatic intrusion and sill formation, and floor shallowing in response to thermally driven viscous relaxation. This study combines new Lunar Orbiter Laser Altimeter (LOLA) and Lunar Reconnaissance Orbiter Camera (LROC) data to characterize and categorize the population of FFCs and map their distribution on the Moon, and uses variations in floor‐fractured crater morphology and regional distribution to investigate the proposed formation mechanisms. The population of FFCs was categorized according to the classes outlined by Schultz (1976). The distribution of these FFC categories shows an evolution of crater morphology from areas adjacent to lunar impact basins to areas in the lunar highlands. We propose that this trend is supportive of formation by shallow magmatic intrusion and sill formation—crustal thickness determines the magnitude of magmatic driving pressure, and thus either piston‐like floor uplift for high magnitude, or a convex floor profile for low magnitude. Predictions from previous studies modeling viscous relaxation are inconsistent with the observed altimetric profiles of FFCs. Hence our analysis favors FFC formation by shallow magmatic intrusion, with the variety of FFC morphologies being intimately linked with location and crustal thickness, and the driving pressure of the intrusion. Data from the GRAIL (Gravity Recovery and Interior Laboratory) mission will help to test these conclusions. Key Points Areal distribution of floor‐fractured craters Morphology consistent with magmatic intrusion Intrusion governs crater morphology

Strong interference has been observed due to small well spacing in the well pad of gas reservoirs, and the fracture properties significantly impact the interference degree. However, current well-test model hardly considers the interference among different multi-fractured horizontal wells (MFHWs) in the well pad and the fracture conductivity are assumed to be the same for different fractures. It would cause erroneous interpretation results for well interference and fracture properties using previous models. Thus, this paper presents a semi-analytical well interference model to better describe flow and mass transfer in fractured porous media by incorporating non-uniform fracture conductivity and interference from adjacent wells. The fractures contain two segments which covers difference values of half-length, production and conductivity. Eight flow regimes can be seen on the interference type curves, and interference can be observed obviously on pressure and its derivative curves during multi-well interference flow. Sensitivity analysis is conducted to analyze the effect of well spacing, fracture conductivity and production distribution on the pressure response. Finally, field application indicates that the proposed model can be used to analyze the well interference among MFHWs in fractured reservoirs, which further demonstrate the accuracy and advantages of the established interference-test model.

Enhanced oil recovery (EOR) from heavy oil reservoirs is challenging. High oil viscosity, high mobility ratio, inadequate sweep, and reservoir heterogeneity adds more challenges and severe difficulties during any EOR method. Foam injection showed potential as an EOR method for challenging and heterogeneous reservoirs containing light oil. However, the foams and especially polymer enhanced foams (PEF) for heavy oil recovery have been less studied. This study aims to evaluate the performance of CO2 foam and CO2 PEF for heavy oil recovery and CO2 storage by analyzing flow through porous media pressure profile, oil recovery, and CO2 gas production. Foam bulk stability tests showed higher stability of PEF compared to that of surfactant-based foam both in the absence and presence of heavy crude oil. The addition of polymer to surfactant-based foam significantly improved its dynamic stability during foam flow experiments. CO2 PEF propagated faster with higher apparent viscosity and resulted in more oil recovery compared to that of CO2 foam injection. The visual observation of glass column demonstrated stable frontal displacement and higher sweep efficiency of PEF compared to that of conventional foam. In the fractured rock sample, additional heavy oil recovery was obtained by liquid diversion into the matrix area rather than gas diversion. Aside from oil production, the higher stability of PEF resulted in more gas storage compared to conventional foam. This study shows that CO2 PEF could significantly improve heavy oil recovery and CO2 storage.

The largest ultra-deep (>6000 m) strike-slip fault-controlled oilfield in the world is found in the Tarim Basin of Northwestern China. The localized fractured reservoirs are the major production targets along the strike-slip fault zones. Different from its use in the primary porous-type reservoirs, however, the conventional technology is not favorable for use in oil/gas development in Ordovician carbonate reservoirs. For this reason, high-density seismic acquisition and high-resolution seismic processing were carried out to provide high-precision data for fault and fractured reservoir identification. In addition, the multi-filtering process and the maximum likelihood method are typically used to identify small faults and fault segments along a strike-slip fault zone. Further, seismic facies-constrained inversion and amplitude attributes are favorable for large fracture-cave reservoir description. With the advancements in seismic technology, the high and stable production well ratio has been doubled in the “sweet spots” of fractured reservoir optimization, and the first ultra-deep strike-slip fault-controlled oilfield with an annual oil production of over 1 million tons has been realized, achieving economic development in the ultra-deep fractured reservoirs. However, unstable production and high rates of production decline are still significant challenges in the economic exploitation of the ultra-deep fractured reservoirs. Seismic technology requires further improvement for the description of small fractured reservoirs and matrix reservoirs, as well as reservoir connectivity prediction and hydrocarbon detection in the deep subsurface.

Increasing the field development efficiency of fractured reservoirs is a contemporary issue. This paper presents fundamental and exploratory research results in this field using modern high-tech experimental equipment from the “Arctic” Scientific Centre at the Saint Petersburg Mining University. Oil reserves in fractured reservoirs are enormous; however, they are classified as hard-to-recover. The before-mentioned reservoirs require a specific approach when selecting technologies to improve the efficiency of their development. In this paper, as a solution to the problem under discussion, we propose the use of a physicochemical method of developing fractured reservoirs based on the injection of a water shut-off agent to exclude highly permeable water-conducting fractures from the drainage process. This technology makes it possible to effectively include and develop previously undrained reservoir areas by directly controlling their filtration properties with the use of new highly efficient and ecologically safe chemical reagents and process fluids.

Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energy applications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrock to gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displacements, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sections were tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fracture and a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experiments confirmed the generation of new fractures. Accurate positioning of measurement tools was ensured through gamma log profiling and an innovative FFEC-based method for detecting flowing fractures. The tests revealed several transitional pressure values associated with mechanical events, with intact rock requiring the highest pressure to induce fracturing, followed by the nonconductive fracture section and the initially conductive fracture section. Following fluid injection, transient pressure decays were observed that were associated with leakage from newly generated fractures, providing insights into fracture behaviour under stimulation. Vertical displacements were predominant across the different tests, with measured displacements typically ranging from 10 to 100 µm. Fracture activation modes primarily involved the normal opening of subhorizontal fractures that were parallel to the metamorphic foliation, with some irreversible slip at higher pressures. However, a more complex scenario was observed in the test interval with previously nonconductive fractures, involving competition between the opening of subhorizontal fractures and reverse shearing of a steeply dipping fracture.