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The greater Paris area has some 12 million inhabitants and 48 heating network production units that exploit the heat capacity of a 1.5 km deep aquifer, the Bathonian limestone. This is one of the most productive aquifers in the world for district heating, with an annual output of about 1.7 TWh of energy. The current challenge for Paris is to triple the number of heating networks using geothermal energy so as to reduce dependence on fossil fuels (40% in 2020 in France). As no detailed geothermal reservoir model is available, drilling involves geological risk. A recent well, drilled at Grigny (20 km south of Paris), turned out to be a failure in transmissibility because the bed of permeable limestones it tapped into was very thin (meter-scale). The main aim of this study is to create a digital database and a 3D geological model of this aquifer to minimize geological risks and optimize the location of future geothermal operations around Paris. By compiling data from 168 wells, a high-resolution 3D geological model of 360 km3 size is constructed (about 40 km x 50 km x 0.2 km), made up of 12.2 million cells and displaying sedimentary facies, sequence stratigraphy, porosity (Φ) and permeability (k). About 20% of the oolitic and bioclastic facies are of good reservoir quality (Φ > 13% and k > 350 mD), especially in two targeted, high-quality reservoir sequences. These facies of interest probably correspond to giant dunes and a shoal/barrier prograding from east to west. In these facies, permeable zones are generally 4 m thick and form patches of 1600 m x 1100 m, on average, elongated perpendicular to the depositional slope. 2D and 3D maps of temperature, salinity, porosity, transmissivity, and permeability allow us to understand the areas of interest for geothermal exploration, as demonstrated around Grigny. This model helps us to apprehend better the heterogeneous character of the reservoir for geothermal prospection and to reduce the risk of future doublets during well implantation. Detailed local models may be extracted to anticipate better the implantation of new doublets in areas with already densely spaced existing wells.

It is widely acknowledged that CO2, a greenhouse gas, is largely responsible for climatic changes that can lead to warming or cooling in various places. This disturbs natural processes, creating instability and fragility of natural and social ecosystems. To combat climate change, without compromising technology advancements and maintaining production costs at acceptable levels, carbon capture and storage (CCS) technologies can be deployed to advance a non-disruptive energy transition. Capturing CO2 from industrial processes such as thermoelectric power stations, refineries, and cement factories and storing it in geological mediums is becoming a mature technology. Part of the Mesohellenic Basin, situated in Greek territory, is proposed as a potential area for CO2 storage in saline aquifers. This follows work previously done in the StrategyCCUS project, funded by the EU. The current investigation includes geomechanical and petrophysical methods to characterise sedimentary formations for their potential to hold CO2 underground. The work is progressing under the Pilot Strategy, funded by the EU.

We study the circles of the Apollonian band circle super-packing, which are also the images of the real projective line by all linear fractional transformations of the group PLS (2 ,Z [ i ]) . This super-packing takes place on the torus rather than on the plane. We focus first on the connection between these circles and lattices in the ring of Gaussian integers. Then we explore the group structure of the set of such circles with given curvature. The end of this paper is more geometrically-minded and describes first a test to determine whether a Gaussian circle is Apollonian or not, then a process which yields quickly all Gaussian circles with curvature smaller than a given integer. We develop algorithms for each of the computational problems we encounter. MSC Classification: 11E25 , 11G99 , 20K01 , 52C26

The water supply in drylands mainly relies on groundwater, making it a crucial resource. Springs in southern Africa are often underutilized, and are neither protected nor monitored. Thus, the aim of this study was to evaluate their quality in a sample area in northwestern Namibia and to propose solutions for the sustainable use of springs. In total, 35 springs and hot springs were evaluated in the study area located in the drier part of Namibia (Pmean = 150–400 mm/year), an area highly impacted by ongoing climate change with longer and more frequent drought seasons. The springs there are mostly uncaptured and the discharge is in the form of surface runoff, which is mainly lost to the atmosphere by evaporation. Most of the studied springs were perennial, despite a severe drought period. Local communities rely on the springs mainly for livestock and human consumption, as well as for irrigation. However, 71% of the springs do not have any protective measures. The temperature, pH, conductivity and alkalinity were tested in situ. In total, 20 samples were collected and analyzed for major ions (boron, fluoride, silica and strontium) and total dissolved solids (TDS). The physical and inorganic results mostly indicated good and excellent quality water for human consumption, while the hot springs tended to have poor water quality in terms of Namibian standards, indicating that the water was not fit for human consumption.

International audience; Applied to Enhanced Oil Recovery, microemulsions are valuable systems for extracting the crude oil trapped by capillary forces in the porous reservoir rocks. The performances of the injected formulations are often assessed by quantifying oil composition in model systems that contain relatively high amount of surfactant/co-surfactant. Recently, the question of representativity of such systems was raised because kinetics aspects and complexity of crude were neglected in model systems and are likely to impact the process efficiency. The current quantification techniques limit the characterization of representative model systems as they are destructive, time consuming and not often applicable to dark or opaque systems. In the original aim to provide a quantitative kinetic study of such microemulsions, we propose a high resolution T1-weighted imaging technique to have access to 1D-composition profiles of co-surfactant, oil and brine in Winsor I, Winsor III and Winsor II microemulsions. The analysis is carried out on model systems at equilibrium for proof of concept. Results are correlated with X-Ray Micro-CT experiments to provide better interpretations and assess the method accuracy. We provide conditions of validity of the developed NMR method and discuss its potential limitations. To a larger extent, the method could be of interest to other applications that use similar systems.

Time varying media can dramatically modify the emission of embedded sources by producing time reversed waves refocusing on the source. Here we show that such a back action can create an angular momentum by setting the source in a spontaneous spin state. We experimentally implement this coupling using self-propelled bouncing droplets sources coupled to the surface waves they emit on a parametrically excited bath. The spin state dynamics result from a self-organized interplay between the source motion and the time reversed waves. The discrete stability analysis agrees with the experimental observations. In addition, we show that these spin states provide a unique opportunity for an experimental access to parameters enabling comparison and calibration of the various existing models.

A silica gel was applied in a porous gas reservoir, with the purpose of testing mitigation and remediation of CO 2 leakage from geological storage reservoirs. The gel has a high strength and a very low water-like viscosity, that extends its applicability to small pore diameters and low permeability media. The gel was prepared and applied on-site with oilfield equipment. Mixing was upscaled from laboratory- to field-scale, including one unsuccessful attempt. Environmental concerns and additional health and safety requirements were modest as the formulation was composed only of the non-toxic commercial silica-based product Betol K28 T, acetic acid and fresh water. A well was selected and prepared in the Becej natural CO 2 field in Serbia, the well and reservoir were prepared and the gel was placed into a 600 m deep CO 2 - and CH 4 -bearing sandstone layer. The reservoir was selectively sealed to the gas cap through a fast, CO 2 -selective gelation, while the hydraulic pathways of the liquid-filled part of the reservoir remained open. In the regions where no CO 2 was present the gelation reaction was slower and the kinetic was temperature-accelerated. A numerical model was used to simulate the impact of the pre-injection operational procedures and to quantify the impact on the temperature-dependent gelation time. The workflow aligns the needs of a research project with the interests and practical priorities of an operating company. A© 2019 Elsevier Ltd

International audience; We present a general novel technique to monitor saturation changes on small rock samples of only 15 mm in diameter and 20 mm in length for the purpose of assessing the kinetics of spontaneous imbibition processes. With a fully-3D imbibition configuration involving counter-current flows through all faces of the sample, the method is based on a NMR technique in which the sole oil phase present within the sample is monitored. The experimental method is fast for two reasons that are i) the possibility to perform accurate measurements on tiny samples, ii) the adoption of a 3D flow geometry. The kinetics of oil desaturation during spontaneous imbibition is analyzed with the help of an analytical 3D diffusion model, according to which the kinetics is proportional to the value of a "capillary" diffusion coefficient. For the purpose of demonstrating our methodology, we used this technique to compare the spontaneous imbibition of restored sandstone miniplugs from a sandstone reservoir, with and without alkali in the imbibing brine. The imbibition kinetics was quantified as capillary diffusion coefficient values. The studied case results revealed mixed impacts of alkali on the spontaneous imbibition kinetics, involving both a brine-oil interfacial tension change and a wettability alteration of the rock, the latter requiring further investigation beyond the scope of this article. List of symbols EOR Enhanced oil recovery IFT Interfacial tension [N/m] NMR Nuclear magnetic resonance D, 2r Diameter of the core (r: radius) [m] D c Capillary diffusion coefficient [m 2 /s] D e Effective molecular diffusion coefficient [m 2 /s] D m Molecular diffusion coefficient [m 2 /s] K Single-phase permeability [m²] k rw , k ro Relative permeabilities to water (w) and oil (o) L, 2l Length of the core (l: half length) [m]  w,  o Relative mobility for water (w) and oil (o) [Pa-1 .s-1 ]  w ,  o Viscosities of water (w) and oil (o) [Pa.s] Pc Capillary pressure [Pa]  Porosity of the core S w , S o Water (w) and oil (o) saturation S w *, S o * Scaled water (w) and oil (o) saturation (cf eq (3)) S wi , S oi Initial water (w) and oil (o) saturation S of Final oil saturation T 2 Transverse relaxation time [s] V Bulk volume of the sample [m 3 ] V p Porous volume [m 3 ] V o Oil volume in the core [m 3 ] V oi Initial oil volume in the core [m 3 ] ACKNOWLEDGEMENTS We thank OMV for allowing us to publish the results. Wolfgang Hujer is also acknowledged for providing laboratory data and rock description.

Applied to Enhanced Oil Recovery, microemulsions are valuable systems for extracting the crude oil trapped by capillary forces in the porous reservoir rocks. The performances of the injected formulations are often assessed by quantifying oil composition in model systems that contain relatively high amount of surfactant/co-surfactant. Recently, the question of representativity of such systems was raised because kinetics aspects and complexity of crude were neglected in model systems and are likely to impact the process efficiency. The current quantification techniques limit the characterization of representative model systems as they are destructive, time consuming and not often applicable to dark or opaque systems. In the original aim to provide a quantitative kinetic study of such microemulsions, we propose a high resolution T

International audience; The main motivation of this work is to determine quantitatively the pore occupancy of water and oil in some source rocks. The pore occupancy might be imposed by differences in chemical composition, wettability behavior and sorption of fluids in organic and inorganic porosities and will dramatically affect the hydrocarbons flow through the porous medium. We address this issue using NMR cryoporometry in two phase situations complemented by other NMR measurements. Using oil-wet samples originating from the Vaca Muerta formation, oil saturation as large as 70% were obtained by simply immersing fully water saturated samples into decane. At 100% water saturation, the measured pore size distributions indicate two main peaks around 2 and 80 nm. After immersion into oil, the pores occupied by water in the presence of decane are mostly around 2 nm and less. The pore sizes occupied by decane in the presence of water can then be deduced by subtracting the distributions obtained at 100% water saturation and after spontaneous drainage. Oil is mainly located in pores around 80 nm. These measurements are confirmed by high resolution SEM images showing the presence of porosity in the organic matter (sponge-like structure). Most of the oil can be associated with the porous organic matter network. These observations are complemented by the determination of the porosity below 2 nm and the water connectivity. From D2O diffusion experiments at 100% water saturation, we observed that about 19% of the total porosity is non-exchangeable with D2O. From the measurements of the liquid signal at −29 °C, we observed that on average 58% of the total porosity is located in pores smaller than 2 nm.

In a previous project, a silicate based sealant was developed and applied to the case of a clayey sandstone formation with the objectives of plugging the surroundings of a well typically within a radius of 1 m. Here, we report experiments conducted at the Mont Terri Underground Research Laboratory (MT-URL) focusing on the mitigation of pressure leakages associated with CO2 containment in near wellbore injection well systems. This work was performed under the auspices of the CO2 Capture Project (CCP), a three-company collaboration comprising Chevron, BP and Petrobras. The CCP effort is directed to develop more cost effective and efficient processes for CO2 concentration, capture and sequestration applied to the energy, refining, chemical and power generation industries in order to reduce greenhouse gas emissions. The experimental set-up installed at the underground test site mimics an injection well with the objectives of testing various sealants able to contain losses associated with delaminations that may occur at various well boundaries such as cement to casing and cement to caprock. Cement and caprock may also be micro-fractured. The tested sealant takes advantage of the properties of alkaline silicate solutions forming a gel after addition of an acid in appropriate strength and quantity. With a viscosity close to water, it can easily be injected in a liquid state and does not need to be activated after injection. The gelation time can be adjusted and is mostly sensitive to temperature. We tested two formulations of the sealant in a 1 m interval of the well system. The sealing capacity is evaluated by comparing flowrates at constant imposed pressure before and after injection of the sealant. Typically, a decrease by a factor of 10 of these flowrates is an indication of a good sealing performance. The first formulation proved to be efficient only for a limited time smaller than 1 month. The second improved formulation proved to be efficient for a period larger than one month.

International audience; With a NMR based fast diffusion measurement technique we performed a comprehensive experimental program on 30 samples to measure the pore diffusion coefficient in two series of cement pastes, mortar and concrete made with an ordinary Portland cement (CEM I) and a composite cement (CEM V). In addition, measurements were also possible in the presence of fibers and their effect could be evaluated. The principle is to monitor a deuterium-water exchange in a well-defined cylindrical geometry. The NMR technique allows the measurement of 1H concentration inside the sample as a function of time, while ignoring 1H outside the sample. Using well known analytical formulations, the diffusion curve can be fitted to obtain the pore diffusion coefficient of the material.The results are first presented in terms of the measured pore diffusion coefficients at 30 °C characterizing the porous network independently of porosity. For CEM I based materials, the measured values are Dp = 7.6 ± 1.4x10−12 m2/s for pastes, 40 ± 20x10−12 m2/s for pastes with fibers, 9.5 ± 0.6x10−12 m2/s for mortars, 4.4 ± 0.2x10−12 m2/s for concretes and 28 ± 7x10−12 m2/s for concretes with fibers. For CEM V based materials, the measured values are Dp = 1.1 ± 0.4x10−12 m2/s for pastes, 9.3 ± 2.7x10−12 m2/s for pastes with fibers, 0.8 ± 0.1x10−12 m2/s for mortars, 5.9 ± 2.2x10−12 m2/s for concretes and 5.3 ± 0.8x10−12 m2/s for concretes with fibers. In all cases, the fibers produce an increase of Dp together with a sample dependent result within a set of 3. When expressed in terms of effective diffusion by taking into account the porosity that can be exchanged by D2O estimated during the diffusion experiments, the results were found in agreement with a few existing values measured with HTO through diffusion techniques (Dp = 2.1 ± 0.4×10−12 m2/s for the CEMI paste, 1.1 ± 0.06×10−12 m2/s for the CEMI mortar, 0.12 ± 0.02×10−12 m2/s for the CEMV concrete with fibers).

Investigations on geochemical processes involved in H2 generation in natural reservoirs are important for the present energy transition from fossil fuels. Most studies related to native H2 focus on the serpentinisation of ultra-mafic rocks, in which the source of H2 is linked to oxidation of Fe2+-bearing minerals and a reduction of H2O. In this study, we investigate abiotic H2 generation from a biotite-rich granite using an approach based on a study case of the Soultz-sous-Forêts geothermal site in France. Using a geochemical and reactive transport model and an existing database, we simulated the hydrothermal alteration of the granite at 130–200 °C with a redox potential from −100 mV to −300 mV. The simulations show that generation of native H2 is possible in an open system by hydrothermal alteration of biotite as a source of Fe2+, which oxidises to Fe3+ leading to precipitation of Fe3+ minerals and reduction of H+. The amount of H2 produced depends on the type of Fe2+/3+ minerals which precipitate. The optimal conditions for H2 generation are related to magnetite precipitation as in the serpentinisation process. We assessed that the upper bound for H2 production for this site is 102 kt per km3 of granite. This is in case of complete oxidation of all the ferrous iron contained in the biotite of the geothermal reservoir. In practice, only part of this potential may be attained owing to the limited current exploitation methods which are unlikely to result in a complete disequilibrium of the whole biotite. Future research needs to focus on how to reach most of the H2 potential. Simulations with increasing CO2 pressures suggest that CO2 injection can stimulate the H2 production. This study has implications for possible coupling of heat extraction and future exploitation with H2 production. Fil: Murray, Jesica María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina. Université de Strasbourg; Francia. Centre National de la Recherche Scientifique; Francia Fil: Clément, Alain. Université de Strasbourg; Francia. Centre National de la Recherche Scientifique; Francia Fil: Fritz, Bertrand. Université de Strasbourg; Francia. Centre National de la Recherche Scientifique; Francia Fil: Schmittbuhl, Jean. Université de Strasbourg; Francia. Centre National de la Recherche Scientifique; Francia Fil: Bordmann, Vincent. TotalEnergies SE; Francia Fil: Fleury, Jean Marc. TotalEnergies SE; Francia

International audience; The mechanism behind the 1H nuclear magnetic resonance (NMR) frequency dependence of T1 and the viscosity dependence of T2 for polydisperse polymers and bitumen remains elusive. We elucidate the matter through NMR relaxation measurements of polydisperse polymers over an extended range of frequencies (f0 = 0.01–400 MHz) and viscosities (η = 385–102 000 cP) using T1 and T2 in static fields, T1 field-cycling relaxometry, and T1ρ in the rotating frame. We account for the anomalous behavior of the log-mean relaxation times T1LM ∝ f0 and T2LM ∝ (η/T)−1/2 with a phenomenological model of 1H–1H dipole–dipole relaxation, which includes a distribution in molecular correlation times and internal motions of the nonrigid polymer branches. We show that the model also accounts for the anomalous T1LM and T2LM in previously reported bitumen measurements. We find that molecular dynamics (MD) simulations of the T1 ∝ f0 dispersion and T2 of similar polymers simulated over a range of viscosities (η = 1–1000 cP) are in good agreement with measurements and the model. The T1 ∝ f0 dispersion at high viscosities agrees with previously reported MD simulations of heptane confined in a polymer matrix, which suggests a common NMR relaxation mechanism between viscous polydisperse fluids and fluids under nanoconfinement, without the need to invoke paramagnetism.

The mechanism behind the

As part of the MiReCOL three-year European project ( www.mirecol-co2.eu ) on storage remediation technologies, we studied in the laboratory the capacity of foams to reduce gas flow for CO2-brine systems in rock core sample with common surfactants, as a function of interstitial velocity and gas to water fraction. Two different types of experimental set-up are used. They both allow local measurement of the water saturation for low and high pressure/temperature condition. A small MRI core-flood set-up is used to perform experiments at 35 °C and 10 bars pore pressure, in CO2 non-dense condition. In order to work under reservoir condition, at 40 °C and 130 bars, with dense super-critical CO2 we used a classical core-flood system coupled to an X-ray detection set-up. All experiments were carried out in similar Clashach sandstones with permeability between 220 and 1500 mD, and porosity in the range 10-20%. The gas and the surfactant-brine solution were co-injected at the core inlet face with a gas fraction around 0.7. We vary the interstitial velocity within two decades from about 3 ft/day up to 100 ft/day. The performance of the generated foams was evaluated from the relative foam viscosity, the ratio of the measured pressure drop in the presence of foam to the pressure drop in single phase condition for the same interstitial velocity. Whatever the pressure and permeability/porosity, the relative foam viscosity can be described as a power law vs. the shear rate evaluated from the interstitial velocity, permeability and porosity. The exponent is close to -1 describing the shear-thinning behavior.

A method for treating the surrounding of a well using a reactive suspension is studied, using silicate based solutions. They present the following key qualities: high performance, long term chemical stability, good injectivity, little environmental impact. We present an experimental investigation of the precipitation of commercial low-cost potassium silicate solutions, using a weak acid to lower the pH. Experiments were performed between 20 °C and 60 °C, by adding a non-hazardous acidic compound to the silica based solution. Bulk gelation times were estimated between a few minutes to 4 days. A coreflood injection experiment was then performed on an analog sandstone sample, representative of CO 2 formation, by using an optimum mixture with viscosity close to water. After a few days, a breakthrough experiment was performed by increasing gradually the differential pressure across the sample. Preliminary results indicate a very large strength of the order of 600 bar/m.

In the unlikely case of CO 2 leakage from a storage reservoir, it is desirable to close the leak efficiently and permanently. This could be done by injecting a reactive solution into the leak path, thereby immobilizing migrating CO 2 by consuming the gas and forming solid reactants. With regard to permanent closure, it is important to consider materials that are stable in the long-term, ensuring permanent CO 2 containment. Numerical modelling was applied to assess the feasibility of injecting calcium-rich water as a CO 2 -reactive solution to form calcite. A scenarios analyses of key parameters showed that the success of leakage remediation can be up to 95% when carefully balancing the injection rate and distance versus the permeability and leakage rate.

International audience; In this work, we studied experimentally and numerically the pressure–flow rate relationship for yield stress fluids in porous media. We developed and validated 3D numerical simulations of the velocity field via a lattice Boltzmann method based on the TRT scheme, and a specific experimental setup allowing yield stress fluids to flow in a closed-loop system to obtain stable rheological properties over a wide range of flow rates (4 decades). The porous medium studied experimentally is a sandstone. The flow properties were also simulated on a regular sphere packing and a random sphere packing as well as on a 3D geometry of a sandstone obtained by x-ray tomography. These different geometries allow highlighting the role of the heterogeneity of the pore structure on the flow properties. All results are expressed as the flow rate ˜Q versus the difference of the pressure gradient to the critical pressure (Δ˜P−Δ˜Pc); Pc defines the pressure below which there is no flow. We observed both numerically and experimentally three specific scaling regimes, already identified by Talon and Bauer [Eur. Phys. J. E 36, 139 (2013)] for a Bingham fluid in 2D porous media. We also evidenced the existence of two critical pressures: the “true” critical pressure ˜Pc defined as the pressure below which there is no flow and the “pseudo” critical pressure threshold ˜P∞c determined by fitting the data in the high-flow-rate regime. We show that the “true” critical pressure is always lower than the “pseudo” one in heterogeneous porous media and can be equal only in the case of regular porous structures. We explain these observations using an energy minimization principle.

Numerous circular depressions have been observed in the Saint-Magne area of South Gironde, France. To understand if the formation of the depressions is linked to hydrogen generation as noted elsewhere, surface gas measurements were made in the vicinities of these depressions by drilling a 12 mm-diameter hole to 1 m depth and inserting a thin perforated tube, which was used to pump and analyse the soil gases on site via a portable gas analyser. Hydrogen concentrations reached 3.5%, prompting the installation of a permanent monitoring system to verify the hydrogen flux. After more than 1 year of continuous monitoring, including measurements of dissolved hydrogen concentrations in the surface aquifer, no hydrogen flux was detected in the soil or the surface aquifer. Additionally, soil thermal desorption experiments did not release any hydrogen, indicating that no stock of hydrogen was present in the soil. Two different protocols used to make the holes were compared: one using a drill and the other using a tube and hammer, which was less destructive. Comparisons of gases sampled using both techniques indicate that drilling the 1 m hole led to in situ gas generation. Additional soil crushing experiments indicated that drilling could provide enough energy to crack the organic matter naturally present in the soil by a milling action or excessive heating. Hydrogen and alkenes were artificially produced when the rock was crushed, both of which are indicators of drill bit metamorphism. Therefore, hydrogen was artificially generated in the soil during drilling. A robust method that can assure the repeatability of these measurements is paramount to guarantee that hydrogen concentrations obtained from organic-rich soils are not biased by an artefact, as observed here. This paper is the first to discuss this technique commonly used in native hydrogen studies and warns against drill usage when measuring subsurface hydrogen concentrations.

Nuclear Magnetic Resonance (NMR) relaxation methods are key techniques for evaluating shales, from both cores and logging data. First, very small pore sizes, down to nano-meter length scales, can be detected and quantified if the NMR tool has the ability to measure relaxation times in the range [0.1–1 ms], and second the different proton populations (water, oil, gas, and kerogen) can be distinguished using 2D T1–T2 maps. We use a NMR instrument working at a higher frequency (23 MHz) that yields a much higher sensitivity than standard plug-size benchtop apparatus. In this work, we show the position of each proton population in this map: hydroxyls from the clay (T2

We propose a deuterium diffusion tracer approach to measure diffusion coefficient in the case of very short NMR relaxation times, too short for NMR pulsed field gradient sequences (T1 or T2 below 1 ms). We also treat the case of porous media containing metallic fibers (such as reinforced concrete) strongly disturbing the magnetic field, and the case of inhomogeneous porous media containing large non porous granulates. For the latter, we propose a hollow geometry maximizing the investigated volume and minimizing the experimental time. The method is a 3D diffusion technique in which samples are immersed in deuterium and the water content inside the sample is monitored as a function of time. Water diffusing outside the sample with very long relaxation times can be subtracted either from T2 relaxation time distribution or not polarizing these components using a short repeat delay. Using analytical formulations describing the concentration of a tracer diffusing out of a cylinder or a hollow cylinder, we can calculate the corresponding pore diffusion coefficient.

The south sub-Andean zone of Bolivia is characterized by east-verging thrusts, detaching within Silurian and Devonian series, and associated to a series of north-south to north-north-east-south-southwest regional anticlines and synclines holding large gas accumulations. This chapter is a case history of the multi-TCF (trillion cubic feet) Incahuasi discovery and how an integrated, multidisciplinary approach allows a progressive improvement in the understanding of the trap geometry, reducing the uncertainty during exploration and field appraisal. While-drilling structural interpretation and biostratigraphic analyses suggested that the discovery well, prognosed mainly by surface geology and targeting the top of the Huamam-pampa Formation as a bright discontinuous seismic reflector on a 2-D seismic test line, was drilling the overturned limb of the surface anticline instead of penetrating the core of the structure. The top reservoir was found deeper by a side track well. The appraisal wells all contributed to progressively constrain the complex geometry of the trap while leaving several possible geometric interpretations of the reservoir structure. The Huamampampa Formation is repeated and overturned by a series of thrusts that increase the internal complexity of the field. These results also confirmed that the shales of the Icla Formation behave as an effective detachment below the reservoir, contributing to the structural complexity of the field. A calibrated/constrained inversion of 3-D magnetotelluric acquisition performed over the structure shows the near-top Huamampampa Formation resistivity anomaly plunging to the north, which helps to identify the possible structural spills. In map view, the variation of orientation provides information on local bends of the target and hence is an important element to be considered for optimizing future appraisal wells. The Incahuasi discovery provided the opportunity to test the validity and efficiency of many geological and geophysical tools while noting their limitations in a context where only a few hundred meters of horizontal error can lead to missing the reservoir and trap.

We consider the motion of a droplet bouncing on a vibrating bath of the same fluid in the presence of a central potential. We formulate a rotation symmetry-reduced description of this system, which allows for the straightforward application of dynamical systems theory tools. As an illustration of the utility of the symmetry reduction, we apply it to a model of the pilot-wave system with a central harmonic force. We begin our analysis by identifying local bifurcations and the onset of chaos. We then describe the emergence of chaotic regions and their merging bifurcations, which lead to the formation of a global attractor. In this final regime, the droplet's angular momentum spontaneously changes its sign as observed in the experiments of Perrard et al. (Phys. Rev. Lett., 113(10):104101, 2014)., Comment: Accepted for publication in Chaos: An Interdisciplinary Journal of Nonlinear Science

We present a general model (SMIM) specifically designed for the interpretation of NMR velocimetry data. Extending the well-known concept of Mobile/Immobile tracer particles applied in dispersion theory, we reproduce two mechanisms responsible for non-Gaussian behavior: immobile molecules trapped in non-flowing zones, and unexpectedly long but rare displacements. From the derived analytical expressions of the NMR signals fitted to the recorded data, we can determine a generalized dispersion coefficient in the case of super dispersion. Using NMR velocimetry data collected in a homogeneous 30 μm grain pack and 10

International audience; The Vaca Muerta Formation is currently regarded as the most prolific source rock interval for unconventional petroleum exploration in Argentina. In this study, we integrate recent CT-scanner, nuclear magnetic resonance (NMR) T1-T2 and Rock-Eval Shale Play® analytical techniques, combined with classical geochemical, petrological and petrophysical methods to characterize Vaca Muerta source rocks along a vertical profile. The proposed analytical workflow was tested here on 4 samples derived from one core: the LJE-1010 borehole drilled in the lowermost Jurassic Vaca Muerta member (Neuquén Basin – Argentina), to evaluate the unconventional hydrocarbon potential and pore network attributes. First, entire rock samples were analyzed by dual energy CT scanner to evaluate possible heterogeneities; this also helped in the selection of representative samples. Then the organic matter properties were investigated by open-system pyrolysis techniques, organic petrography and biomarker analyses as a function of the core depth. A comparative approach between open-system pyrolysis methods (e.g. Rock-Eval Basic/Bulk-Rock & Shale Play® methods vs. Source Rock Analyzer) is also illustrated in this work. Finally, petrophysical characteristics and pore network attributes in shale were estimated by gas permeability (steady-state method corrected for Klinkenberg effect), porosity and NMR methods. The investigated samples have oil-window maturity and are characterized by a network of solid bitumen. Based on new Rock-Eval Shale Play® data, the potentially producible oil present in the rock samples was estimated using the modified oil saturation index (OSI = Sh0 + Sh1 peaks × 100/TOC). Results indicate that the oil crossover effect and potential productive oils occur within intervals showing higher TOC values (~ 3 to 8 wt%). We also illustrated here that, for unconventional shale play perspectives, Rock-Eval Shale Play® parameters (Sh0 & Sh1) allow to obtain both a better quantification of free and retained hydrocarbons in source-reservoir rock samples and correct original oil in place (OOIP) estimations in early exploration campaign for shale oil and shale gas assessment. For Vaca Muerta rock samples, OOIP estimations range from 60 to 160 bbl oil/acre-ft, approximately. We also demonstrated that the solid bitumen, oil and organic matter are clearly distinguished in the studied samples using advanced NMR T1-T2 maps obtained at different temperatures. The solid bitumen was clearly evidenced as a peak with T1/T2 ratio ~ 14 on NMR T1-T2 maps. Concerning the matrix bulk rock permeability, the obtained results showed that the most deep sample is characterized by a permeability of about 140 nanoDarcy (nD) whereas the shallower sample containing also higher amounts of organic matter is more permeable (~ 213 nD), indicating that TOC values play a main control on Vaca Muerta poromechanical characteristics. The maximum total porosity values range between 6.5 and 21.8% and were calculated in this work integrating NMR and helium porosity values. Finally, global interpretations of these obtained results suggest that the Vaca Muerta Formation could be considered as a prolific shale play interval for unconventional petroleum exploration in the near future.

International audience; The interfacial area between two immiscible phases in porous media is an important parameter for describing and predicting 2 phase flow. Although present in several models, experimental investigations are sparse due to the lack of appropriate measurement techniques. We propose two NMR techniques for the measurement of oil-water interfacial area: (i) a time dependent NMR diffusion technique applicable in static conditions, similar to those used for the measurement of the solid specific surface of a porous media, and (ii) a fast relaxation technique applicable in dynamic conditions while flowing, based on an interfacial relaxation mechanism induced by the inclusion of paramagnetic salts in the water phase. For dodecane relaxing on doped water, we found an oil interfacial relaxivity of 1.8 μm/s, large enough to permit the measurement of specific interfacial surface as small as 1000 cm2/cm3. We demonstrate both NMR techniques in drainage followed by imbibition, in a model porous media with a narrow pore size distribution. While flowing, we observe that the interfacial area is larger in imbibition than in drainage, implying a different organization of the oil phase. In a carbonate sample with a wide pore size distribution, we evidence the gradual invasion of the smallest pores as the oil-water pressure difference is increased.

We observed the arrangement of water molecules when confined in the interlayer space of smectites using low field nutation experiments. Despite the presence of paramagnetic impurities that prevent such observation at high field, we can determine the amount of water in strong interaction with the clay surface, i.e., water molecules which are partially oriented within each platelet. The experiments do not require the orientation of the clay platelets relative to the magnetic field. We present the NMR theory, the signal processing, and the results on a series of 4 homoionic smectites (Na, Ca, Mg, and K) at different relative humidities in order to vary the water content and the basal spacing. In these systems, we found that between 0.5 and 2.5 water molecules per ion are oriented.

International audience; Spontaneous imbibition processes can play an important role in oil production. It can be enhanced or influenced by wettability changes generated by properly designed chemicals or by the natural surfactants resulting from reactive crude oils in the presence of alkaline solutions. The reaction of basic salts with some components of oil can, indeed, lead to the formation of natural soaps that reduces the interfacial tension between oil and brine. The latter scenario is studied herein on samples and oil from the St Ulrich oil field in the Vienna basin. To that end, spontaneous imbibition experiments were performed with two brines differing by the absence or presence of alkali. We first present a general novel technique to monitor saturation changes on small rock samples for the purpose of assessing the efficiency of a given recovery process. Samples of only 15 mm in diameter and 20 mm in length and set at irreducible saturation were fully immersed in the solution of interest, and the evolution of the samples' saturation with time was monitored thanks to a dedicated NMR technique involving the quantification of the sole oil phase present within the sample. A fully-3D imbibition configuration was adopted, involving counter-current flows through all faces of the sample. The experimental method is fast for two reasons: (i) the kinetics of capillary imbibition process is proportional to the square of sample size, i.e. very rapid if accurate measurements can be acquired on tiny samples, (ii) the present 3D situation also involves faster kinetics than the 1D configuration often used. The NMR technique was crucial to achieve such conditions that cannot be satisfied with conventional volumetric methods. The kinetics of oil desaturation during spontaneous imbibition is interpreted with the help of an analytical 3D diffusion model. For the alkaline solution, the diffusion coefficient is reduced by a factor of only two compared to the non-alkaline brine, although the interfacial tension between the oil and the imbibing solution is reduced by a factor of 10. Hence, a wettability change to a more water wet state has to be assumed when the alkaline solution replaces the non-alkaline solution in the imbibition process. However, no significant impact on the final saturation was observed.

We show that simple low-field nuclear magnetic resonance (NMR) can provide quantitative measurements of water content in clays providing appropriate instrumentation and protocols. In particular, NMR is a good tool to study the swelling of smectites and the interlayer water content despite pore sizes of the order of or less than 1 nm and the presence of paramagnetic impurities yielding short T1 and T2 relaxation times. The NMR measurements performed at a magnetic field of 0.5 T were: (i) the standard CPMG sequence to deduce a distribution of transverse relaxation times T2, (ii) the 2D T1–T2 sequence to analyze the mobility of protons, and (iii) a free induction decay (FID) sequence to detect very short relaxation time and evaluate the total amount of protons present in the system, including structural hydroxyls. We complemented the NMR data with small angle X-ray scattering (SAXS) to obtain the basal spacing d001. On powder clays, the total interlayer water content is obtained from FID measurements after c...

Foams are among the most promising and cost effective means to alleviate the drawbacks associated with gas-based EOR-processes. The objective of this work is to probe the impact of residual oil saturation on CO2-foam generation and on their flow behavior in porous mediaDesigning a foam-EOR process requires its evaluation and optimisation at laboratory scale using coreflood tests. However, such coreflood tests are usually performed on relatively long core sample, this lead to long time-consuming experiments. In this study are presented results using both long and short coreflood systems. Short coreflood systems (allowing short-duration test) are coupled to a NMR apparatus and to an CT-scanner that allow live and non-invasive measurements of the fluids saturation.In a first part of this work, the efficiencies of two proprietary formulations to generate stable foam in porous media under reservoir conditions and in absence of oil have been compared. We used a coreflood set-up equipped with X-Ray detection to monitor gas propagation inside relatively long core samples. Then, their ability to resist the oil (Dodecane) have been evaluated and compared. The results evidenced two largely different behaviors. One of the two formulations resists the presence of oil up to an oil saturation of 35-40% while the second is destabilized as soon as the oil saturation exceeds 20%. Both formulations were insensitive to oil bellow an oil saturation of 15%. Depending on the application targeted, this laboratory evaluation should be coupled with a detailed economic evaluation to select the formulation to be used.In a second part, we performed co-injection tests using NMR small coreflood set-up and IRM-scanner in absence of oil. They brought more detailed information regarding fluid saturations that help interpreting foam characteristics and flow behavior in porous media.

International audience; Dispersion of a passive tracer in a tube has been extensively studied in the case of Newtonian fluids since the pioneer work of Taylor (1953). However, the influence of more complex rheological behavior on the transport has only be scarcely investigated. Non-Newtonian fluids are increasingly used in the industry and transport in this type of fluid merits therefore thorough investigations. An example of industrial application is Enhanced Oil Recovery, that is based on the injection of non-Newtonian fluids as polymers or surfactant solutions in porous media, which are then submitted to dispersion phenomena.This work deals with transport of a passive tracer in shear thinning fluids with and without yield stress whose constitutive behaviors are representative of a large number of industrial fluids. We focus on transport in capillary tubes, essential for the understanding of dispersion in porous media. Transport is investigated at different time scales by solving the advection–diffusion equation using a Two-Relaxation-Time Lattice–Boltzmann method. We also derived an analytical expression of the Taylor dispersion coefficient for a large range of fluid rheologies. Dispersion coefficients of all fluids described by the Herschel–Bulkley model can now be determined. Analytical and numerical results are compared and very good accordance is obtained.We discuss the characteristic time scales of the transport before reaching steady state as a function of fluid rheology and Péclet number. We show that the time to reach the dispersive regime is nearly independent of the fluid rheology whereas the effective dispersion coefficient is a function of the rheological parameters.We also present the displacement distribution of the tracer molecules (propagators) as a function of time and show that they are strongly conditioned by the fluid rheology. Indeed, propagators give valuable information on the temporal evolution of the concentration profile towards the stationary Taylor regime.

Carbon Capture and Storage (CCS) is one of the solutions studied to reduce greenhouse gas accumulation in the atmosphere. Depleted oil and gas reservoirs have been studied for potential storage sites but also saline aquifers that have the advantages of much larger pore volume. In this latter case, injection of large volume of anhydrous carbon dioxide will lead to a strong water desaturation of the near wellbore region because of evaporation mechanisms. Even the capillary trapped water can be removed by thermodynamical transfer of water vapor in the CO2 phase. The extension in time and space of the dry zone will be controlled by the drying rate induced by the gas flow. Consequences of drying may induce alteration of the injectivity by salt precipitation and/or alteration of the rock fabric itself, especially for shaly sandstones in the case of clay drying. The context of CCS has raised new interests in the understanding of drying kinetic where the water vapor is evacuated by gas convection. In this study, we investigated experimentally the drying rate evolution with time on a shaly sandstone sample in two conditions of drying: convective and diffusive. In convective conditions, air is injected at different flow rates through the porous media in conditions of drying representative of a CO2 injection site at one million ton per year. In diffusive conditions, no flow is imposed and the water vapor escape by diffusion. Drying rates dynamics in both conditions were measured by Nuclear Magnetic Resonance (NMR) and compared. We varied the temperature and the salinity in diffusive-driven drying and the gas flow rate in convective-driven drying. The water distribution in the pore network and the water saturation profiles were monitored continuously using T2 relaxation and 1D imaging NMR techniques. For the range of temperature and air flow rate used, we show that drying rates in the two drying conditions are similar but not identical. They both present different periods characteristic of the main mechanisms for water mass transfer. Drying rate has a power law dependence on the temperature, as predicted by thermodynamic, and drying rate was found proportional to the flow rate in convective drying. Presence of salt has a complex effect: an increase of the drying rate at early stage of drying followed by a strong decrease for the remaining time of drying.

Low field NMR T(2) distribution is an efficient tool for characterizing pore size distribution in porous media. In NMR relaxation experiments, we measure the magnetization decay characterized by the so-called T(2) relaxation time, resulting essentially from liquid-solid interactions of the spins carried by molecules and exploring the pore space by diffusion. For multimodal systems, a new technique called T(2)-store-T(2) allows the analysis of diffusional pore to pore exchange that is extremely useful for the characterization of connectivity. This technique uses 2D inverse Laplace techniques and produces T(2)-T(2) maps. Qualitatively, a system is coupled when off-diagonal peaks are observed. Based on an analytical solution describing diffusional coupling between two pore populations, we propose defining a coupling factor that quantify the degree of coupling between the two populations, providing an easy understanding of the complex analytical solution. This analysis allows understanding 1D T(2) experiments as well, and indicates some limitations of the T(2) characterization when interpreted as a pore size distribution. We provide examples of bimodal pore structures in which we applied our methodology: a clay gel system, a shaly sandstone and two double porosity carbonates. These systems are also described by conventional techniques (mercury injection, SEM visualization) and illustrate weak, intermediate and strong coupling. Despite the presence of distribution of pore sizes, the two pore system exchange model gives satisfactory results for the quantitative analysis of the coupling and T(2)-store-T(2) experiments. In carbonates, more complex exchanges can occur between micro-, meso- and macropores.

With the perspective of long term CO2 storage, thermodynamic data are necessary for the simulations of CO2 injection in aquifers of depleted oil reservoirs. We focus here on the determination of the resistivity and viscosi ty of aqueous NaCl solutions with dissolved CO2. It is well known that dissolved CO2 increases slightly the water density. Recently, Bando et al. (2004) measured the viscosity of CO2 saturated brines and found an increase of viscosity with increasing amoun t of dissolved CO2. For resistivity, no data is available to our knowledge. We evaluated the effect of dissolved CO2 simultaneously on the resistivity and viscosity of three NaCl solutions covering the range of salinity usually encountered in potential CO2 storage geological formations. At a constant temperature of 35 ∘C, we show that the variation of resistivity and viscosity are proportional to the amount of dissolved CO2. For viscosity, our data are in agreement with previous observations. The observed variations are small, at maximum of the order of 10%. The increase of viscosity is well correlated with the variation of conductivity because ions are moving in a more viscous solvent and th erefore conductivity decreases. For the temperature dependence, w e used the Arps model to describe the measured variation of conductivity as a function of temperature. We propose a simple model to take into account the small modifications of conductivity and viscosity as a function of the dissolved CO2 fraction and temperature. Finally, we examine two potential impact s of these findings.

Water diffusivity D measured by using NMR techniques in Na-smectite suspensions decreases with increasing smectite fraction (up to 50 wt%), but increases with increasing salinity (NaCl or CaCl2 aqueous solutions) at a fixed clay fraction. The increase, larger for CaCl2 solutions, is explained by aggregation of clay particles when high salinities are reached. Macroscopic organisation of dense mixtures of clay and aqueous solutions can be inferred by T 2 transverse NMR relaxation times which are sensitive to the volume to surface ratio. Dispersed suspensions exhibit mono-modal T 2 distributions, whereas bimodal T 2 distributions are observed for flocculated systems. The bimodal T 2 distributions are interpreted as a measurement of the spacing between clay particles within aggregates and between aggregates. Finally, the diffusion data can be gathered in an unique curve using the Debye length and the measured spacing between particles. When the thickness of the electro-diffuse layer (Debye length) is of the same order as the spacing between clay particles, the water diffusivity decreases. Otherwise it is constant at about 2.22 ± 0.25 × 10 −9 m 2 / s . This last result illustrates clearly the effect of electro-chemical properties of smectite on water diffusivity.

The effect of dissolved CO2 on the electrical conductivity and viscosity of three NaCl solutions covering the range of salinity usually encountered in potential CO2 storage geological formations has been studied. At a constant temperature of 35 °C, the variations of conductivity and viscosity are proportional to the mole fraction of dissolved CO2. For viscosity, our data are in agreement with previous observations. The observed variations are small and are at maximum on the order of 10 %. The variations of conductivity and viscosity as a function of temperature up to 100 °C are not modified by the presence of CO2, and we suggest using the empirical Arps model. A simple model is proposed to take into account the small modifications of conductivity and viscosity as a function of the dissolved CO2 mole fraction and temperature.

In certain situations, such as in viscous liquids or nano-porous media, the transversal relaxation time T 2 may become so short that the pulse duration or the detector dead time is no longer negligible. These cases raise fundamental questions about relaxation during the radio-frequency pulses used in classical CPMG or Inversion-Recovery sequences. For an ideal system having a single relaxation time, we examine the effect of the finite pulse duration on the magnetization decay after the pulses occurring in FID, CPMG and Inversion-Recovery sequences. We solved analytically the Bloch equations during and after the pulses and compared the theoretical predictions with experimental data. Finally, we propose approximate simple expressions to correct the sequences for the magnetization attenuation during the pulses. IR curves are affected by transversal relaxation during the pulses, yielding asymmetric curves even if T 1 is very large. The magnetization decay obtained during a CPMG sequence is not affected by relaxation during the pulses. This is valid provided the time origin is chosen in the middle of the first pulse.

Canadian oil sands represent a huge oil resource. Stable water-in-oil (W/O) emulsions, which persist in Athabasca oil sands from surface mining, are problematic, because of clay solids. This article focuses on the characterization of water-in-diluted-bitumen emulsions by nuclear magnetic resonance (NMR) measurement and the transient behavior of emulsions undergoing phase separation. An NMR restricted diffusion experiment (pulsed gradient spin-echo (PGSE)) can be used to measure the emulsion drop-size distribution. Experimental data from PGSE measurements show that the emulsion drop size does not change much with time, which suggests that the water-in-diluted-bitumen emulsion is very stable without an added coalescer. The sedimentation rate of emulsion and water droplet sedimentation velocity can be obtained from NMR one-dimensional (1-D) T 1 weighted profile measurement. Emulsion flocculation can be deduced by comparing the sedimentation velocity from experimental data with a modified Stokes' Law prediction. PR 5 (a polyoxyethylene (EO)/polyoxypropylene (PO) alkylphenol formaldehyde resin) is an optimal coalescer at room temperature. For the sample without fine clay solids, complete separation can be obtained; for the sample with solids, a rag layer that contains solids and has intermediate density forms between the clean-oil and free-water layers. Once formed, this rag layer prevents further coalescence and water separation.