This study presents an approximate analytical solution for predicting drawdown temperature transient behaviors of a fully penetrating vertical well in a two-zone radial composite reservoir system. ...The inner zone may represent a damaged (skin) zone, and the outer (non-skin) zone represents an infinitely extended reservoir. The analytical solution is obtained by solving the decoupled isothermal pressure diffusivity equation and temperature equation for the inner and outer zones with the Boltzmann transformation. The convection, transient adiabatic expansion and Joule–Thomson heating effects are all accounted for in the solution. The developed solution compares well with the results of a thermal numerical simulator. The analytical solution is used as a forward model for estimating the parameters of interest by nonlinear regression built on a gradient-based maximum likelihood estimation (MLE) method. A methodology, based on semilog analyses of pressure and temperature data as well as log–log diagnostic plots of pressure- and temperature-derivative data, is proposed to obtain good initial guesses of parameters, which derive the MLE objective function to have reliable optimized estimates. The statistical measures such as estimated standard deviation of noise in pressure and temperature data, confidence intervals for parameters and correlation coefficients between parameter pairs are used to evaluate the goodness of fit and reliability of the estimated parameters from history matching pressure and/or temperature data sets. The results show that the rock, fluid and thermal properties of the skin zone and non-skin zone can be reliably estimated by regressing on temperature transient data jointly with pressure transient data in the presence of noise.
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The Monte Piano — Blsmantova sequence (Middle Eocene — Late Miocene) in the Northern Apenmnes represents a new sedimentary cycle after the tectonic phase of the Early—Middle Eocene. This phase ...principally affected the structural Units of Ligurian domain. This sedimentary sequence (the postorogenic Ligurian Sequence), shows evidence of the progression of the Apennine orogenesis mainly through the development of unconformities of regional extension. In fact, this new sedimentary cycle began after the definitive closure of the Ligurian ocean (Oceanic stage) and sedimentation continued durIng the subsequent development of a collisional margin (Ensialic stage) between the European and African Adriatic plates.
The stratigraphic and structural features of the Apenmne margin between Tresinaro Valley and Lavino Valley are described brteflv in this paper. Moreover, the contact between the Ranzano Formation and the Antognola Formation, parts of the postorogenic Ligurian Sequence, is discussed in terms of the micropaleontologica data obtained from three stratigraphical sections situated In the lower valley of the Secchia River. The contact coincides with an unconformity that is marked by a biostratigraphical hiatus.
In fact, foraminifera associations indicate that the top of the Ranzano Formation is attributable to Zone PI 8 (Lower Oligocene) and that the base of the Antognola Formation is already attributable to Zone P 21 (Upper Oligocene). There was no evidence of the presence of Zone PI 9/20. The chronological range of the hiatus is estimated as 2.4 to 1 0 Ma, depending upon the chronological scale adopted and the exact position of the "top" of the Ranzano Formation and the base of the Antognola Formation.
On the basis of the stratigraphic relations existing among the various units of the postorogenic Ligurian Sequence outcropping in the studied area and on the basis of the data collected on the contact between the Ranzano Formation and Antognola Formation, it is clear that the hiatus is attributable to submarine erosion of a part of the turbiditic deposits of the Ranzano Formation, which are affected by pronounced tectono—sedimentary phenomena. The tectonic movements developed in the Ligurian domain in a per10d preceding the deposition of the Antognola Formation. They are thus contemporary with the beginning of the deposition of the Macigno in the Tuscan paleogeographical domain.
Underground Hydrogen Storage (UHS) provides a large-scale and safe solution to balance the fluctuations in energy production from renewable sources and energy consumption but requires a proper and ...detailed characterization of the candidate reservoirs. The scope of this study was to estimate the hydrogen diffusion coefficient for real caprock samples from two natural gas storage reservoirs that are candidates for underground hydrogen storage. A significant number of adsorption/desorption tests were carried out using a Dynamic Gravimetric Vapor/Gas Sorption System. A total of 15 samples were tested at the reservoir temperature of 45 °C and using both hydrogen and methane. For each sample, two tests were performed with the same gas. Each test included four partial pressure steps of sorption alternated with desorption. After applying overshooting and buoyancy corrections, the data were then interpreted using the early time approximation of the solution to the diffusion equation. Each interpretable partial pressure step provided a value of the diffusion coefficient. In total, more than 90 estimations of the diffusion coefficient out of 120 partial pressure steps were available, allowing a thorough comparison between the diffusion of hydrogen and methane: hydrogen in the range of 1 × 10−10 m2/s to 6 × 10−8 m2/s and methane in the range of 9 × 10−10 m2/s to 2 × 10−8 m2/s. The diffusion coefficients measured on wet samples are 2 times lower compared to those measured on dry samples. Hysteresis in hydrogen adsorption/desorption was also observed.
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Underground porous media are complex multiphase systems, where the behavior at the macro-scale is affected by physical phenomena occurring at the pore(micro)-scale. The understanding of pore-scale ...fluid flow, transport properties, and chemical reactions is fundamental to reducing the uncertainties associated with the dynamic behavior, volume capacity, and injection/withdrawal efficiency of reservoirs and groundwater systems. Lately, laboratory technologies were found to be growing along with new computational tools, for the analysis and characterization of porous media. In this context, a significant contribution is given by microfluidics, which provides synthetic tools, often referred to as micromodels or microfluidic devices, able to mimic porous media networks and offer direct visualization of fluid dynamics. This work aimed to provide a review of the design, materials, and fabrication techniques of 2D micromodels applied to the investigation of multiphase flow in underground porous media. The first part of the article describes the main aspects related to the geometrical characterization of the porous media that lead to the design of micromodels. Materials and fabrication processes to manufacture microfluidic devices are then described, and relevant applications in the field are presented. In conclusion, the strengths and limitations of this approach are discussed, and future perspectives are suggested.
The understanding of multiphase flow phenomena occurring in porous media at the pore scale is fundamental in a significant number of fields, from life science to geo and environmental engineering. ...However, because of the optical opacity and the geometrical complexity of natural porous media, detailed visual characterization is not possible or is limited and requires powerful and expensive imaging techniques. As a consequence, the understanding of micro-scale behavior is based on the interpretation of macro-scale parameters and indirect measurements. Microfluidic devices are transparent and synthetic tools that reproduce the porous network on a 2D plane, enabling the direct visualization of the fluid dynamics. Moreover, microfluidic patterns (also called micromodels) can be specifically designed according to research interests by tuning their geometrical features and surface properties. In this work we design, fabricate and test two different micromodels for the visualization and analysis of the gas-brine fluid flow, occurring during gas injection and withdrawal in underground storage systems. In particular, we compare two different designs: a regular grid and a real rock-like pattern reconstructed from a thin section of a sample of Hostun rock. We characterize the two media in terms of porosity, tortuosity and pore size distribution using the A* algorithm and CFD simulation. We fabricate PDMS-glass devices via soft lithography, and we perform preliminary air-water displacement tests at different capillary numbers to observe the impact of the design on the fluid dynamics. This preliminary work serves as a validation of design and fabrication procedures and opens the way to further investigations.
We map the High Sillaro Valley, in the Northern Apennines of Italy. Here the Ligurian wedge overthrust the foredeep deposits of the Marnoso Arenacea formation - MA. The overthrusting occurred through ...a shear zone with components derived from the frontal part of the Ligurian wedge and interpreted as a tectonic mélange (Sestola-Vidiciatico Tectonic unit - SVU) here subdivided into two different subunits structurally independent one from the other. In the area, the Visignano chaotic body (VIS) constitutes an intercalation within the Serravallian-Tortonian MA and derives, as the SVU, from the frontal part of the Ligurian wedge. We performed a detailed investigation of the components of the VIS that helps to better define the architecture of the frontal part of the Ligurian wedge and to constrain the timing of the deformation phases affecting this portion of the Northern Apennines during the middle-late Miocene.
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Carbonate deposits related to active seeps are documented along most continental margins and are characterized by peculiar seep-related facies and by chemical (isotope signature), paleontological and ...mineralogical markers. Their fossil analogues are recognized all over the world by the same features and occurred since the beginning of Phanerozoic. In this paper, we present a new seep outcrop (Castagneto village, Reggio Emilia, northern Italy) belonging to the late Eocene Loiano Formation which, to our knowledge, is in Italy the most ancient seep deposit with not-reworked chemosymbiotic fauna The outcrop can be roughly divided into two portions, a northern part showing abundant presence of macrofossils in silty carbonate matrix and subhorizontal subdivisions, and a southern part, where macrofossils are almost absent, characterized by sub-vertical internal subdivisions and a clear vertical structure consisting of the rhythmic alternation of light and dark mineralization. Detailed analysis of samples from the southern portion showed the occurrence of authigenic calcite and pyrite, the latter with a peculiar framboidal texture. This feature, together with the occurrence of chemosymbiotic species and
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C isotope depletion, suggests possible hydrocarbon-rich fluid-related genesis and provides useful criteria for identifying hydrocarbon-rich fluid-related deposits in geologic units.
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Thorough comprehension of flow behavior in underground porous media is fundamental for several applications such as oil and gas production, Underground Gas Storage, CO2 storage, and Enhanced ...Geothermal Systems. Macroscale petrophysical parameters, as well as hydraulic parameters, are strongly linked to the microstructure of the rock.
In this paper, we present a methodology for the geometric analysis and characterization of the pore structure of 3D binary images of rocks. The geometric analysis is based on the A∗ pathfinding algorithm extended to 3D domains and on the measurement of the pore radius along the identified paths. The analysis is carried out for the main flow directions to obtain a tensorial representation of tortuosity, effective porosity, and representative pore radius, to provide permeability estimation and effective characterization of anisotropy. Moreover, the approach provides the analysis of pore size distribution and constriction.
The methodology was applied to synthetic but realistic rock samples, generated through the QSGS algorithm. Two case studies, representative of an isotropic and an anisotropic porous media, are presented. Validation was carried out through comparison with FVM hydrodynamic modeling. Analysis of the results shows that the presented geometric approach can provide thorough and reliable characterization of the porous media.
•Interdisciplinary approach for microstructure and transport properties characterization.•Pore structure analysis through path-finding technique derived from graph theory.•Determination of tortuosity, permeability and effective porosity in tensor form.•Anisotropy estimation from geometrical analysis.•Application to 3D realistic rock images generated with QSGS.
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Pore-scale analysis and characterization of reservoir rocks provide valuable information for the definition and management of underground hydrogen storage and CO2 storage or sequestration.
This ...article presents an optimized implementation of the A* algorithm, the most popular pathfinding method in the presence of obstacles. In this context, the algorithm is applied to recognize the minimum length connected paths through each flow direction of 3D images of a porous medium representative of a reservoir rock. The identification of the main paths allows the characterization of the pore space and the calculation of fundamental petrophysical properties such as tortuosity and effective porosity, which can be used for permeability estimation. Compared to other algorithms available for pore-scale characterization, such as the pore centroid, A* provides a better approximation of the pore space available for the flow and, therefore, a reliable characterization of the petrophysical properties. On the other hand, path identification is significantly consuming in terms of time and memory. In this paper, an efficient and optimized implementation based on C++/OpenMP programming language is presented.
The proposed implementation aims to the analysis of large-scale models profiting from parallelization, memory optimization, and enhanced managing of dead paths. Three test cases of increasing sizes are presented, to analyze the advantages and the disadvantages of the algorithm as the number of explored points increases. The 3D binary images analyzed are related to a synthetic domain (1 million voxels) and two actual sandstone samples (about 4 and 64 million voxels respectively). The code is validated against a Matlab serial implementation, showing a significant improvement in efficiency. Remarkable test cases of several millions of voxels were afforded, overcoming the memory and execution slowness issues. Moreover, the proposed implementation is suitable for large pore-scale models run in HPC environments.
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•Computer-aided geometric characterization of porous media images.•Pathfinding algorithm implementation applied to Digital Rocks Physics.•Parallel computing optimization for native serial algorithms.•Validation on real sample binary representations.•Geometrical properties computation for underground storage.
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Tortuosity (
τ
) is one of the key parameters controlling flow and transport in porous media. Although the concept of tortuosity is straightforward, its estimation in porous media has yet been ...challenging. Most models proposed in the literature are either empirical or semiempirical including some parameters whose values and their estimations are in prior unknown. In this study, we modified a previously presented geometric tortuosity (
τ
g
) model based on percolation theory and validated it against a methodology based on the pathfinding A* algorithm. For this purpose, we selected 12 different porous materials including four sandstones, three carbonates, one salt, and four synthetic media. For all samples, five sub-volumes at different lengths with fifty iterations were randomly selected except one carbonate sample for which three sub-volumes were extracted. Pore space properties, such as pore radius, throat radius, throat length, and coordination number distributions were determined by extracting the pore network of each sub-volume. The average and maximum coordination numbers and minimum throat length were used to estimate the
τ
g
. Comparison with the A* algorithm results showed that the modified model estimated the
τ
g
accurately with absolute relative errors less than 28%. We also estimated the
τ
g
using two other models presented in the literature as well as the original percolation-based tortuosity model. We found that our proposed model showed a significantly higher accuracy. Results also indicated more precise estimations at the larger length scales demonstrating the effect of uncertainties at the smaller scales.
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