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Formation dry‐out in fracture‐dominated geological reservoirs may alter the fracture space, impair rock absolute permeability, and cause a significant decrease in well injectivity. In this study, we numerically model the dry‐out processes occurring during supercritical CO2 (scCO2) injection into single brine‐filled fractures and evaluate the potential for salt precipitation under increasing effective normal stresses in the evaporative regime. We use an open‐source, parallel finite‐element framework to numerically model two‐phase flow through 2‐D fracture planes with aperture fields taken from naturally fractured granite cores at the Grimsel Test Site in Switzerland. Our results reveal a displacement front and a subsequent dry‐out front in all simulated scenarios, where higher effective stresses caused more flow channeling, higher rates of water evaporation, and larger volumes of salt precipitates. However, despite the larger salt volumes, the permeability impairment was lower at higher effective normal stresses. We conclude that the spatial distribution of the salt, precipitated in fractures with heterogeneous aperture fields, strongly affects the absolute permeability impairment caused by formation dry‐out. The numerical simulations assist in understanding the behavior of the injectivity in fractures and fracture networks during subsurface applications that involve scCO2 injection into brine. Key Points: We numerically model formation dry‐out due to supercritical CO2 injection into a single natural fractureVolume of precipitated salt is not a direct indicator for the absolute permeability reduction of a single fractureSalt precipitation patterns in the fracture space vary significantly with the applied effective normal stress [ABSTRACT FROM AUTHOR]

When water is injected into a fracture-dominated reservoir that is cooler or hotter than the injected water, the reservoir permeability is expected to be altered by the injection-induced thermo-mechanical effects, resulting in the redistribution of fluid flow in the reservoir. These effects are important to be taken into account when evaluating the performance and lifetime particularly of Enhanced Geothermal Systems (EGS). In this paper, we compare the results from two dye tracer tests, conducted before (at ambient temperature of 13 ∘ C ) and during the injection of 45 ∘ C hot water into a fractured crystalline rock at the Grimsel Test Site in Switzerland. Conducting a moment analysis on the recovered tracer residence time distribution (RTD) curves, we observe, after hot water injection, a significant decrease in the total tracer recovery. This recovery decrease strongly suggests that fluid flow was redistributed in the studied rock volume and that the majority of the injected water was lost to the far-field. Furthermore, using temperature measurements, obtained from the same locations as the tracer RTD curves, we conceptualize an approach to estimate the fracture surface area contributing to the heat exchange between the host rock and the circulating fluid. Our moment analysis and simplified estimation of fracture surface area provide insights into the hydraulic properties of the hydraulically active fracture system and the changes in fluid flow. Such insights are important to assess the heat exchange performance of a geothermal formation during fluid circulation and to estimate the lifetime of the geothermal formation, particularly in EGS. [ABSTRACT FROM AUTHOR]

Temperature variations often trigger coupled thermal, hydrological, mechanical, and chemical (THMC) processes that can significantly alter the permeability/impedance of fracture-dominated deep geological reservoirs. It is thus necessary to quantitatively explore the associated phenomena during fracture opening and closure as a result of temperature change. In this work, we report near-field experimental results of the effect of temperature on the hydraulic properties of natural fractures under stressed conditions (effective normal stresses of 5–25 MPa). Two specimens of naturally fractured granodiorite cores from the Grimsel Test Site in Switzerland were subjected to flow-through experiments with a temperature variation of 25–140 °C to characterize the evolution of fracture aperture/permeability. The fracture surfaces of the studied specimens were morphologically characterized using photogrammetry scanning. Periodic measurements of the efflux of dissolved minerals yield the net removal mass, which is correlated to the inferred rates of fracture closure. Changes measured in hydraulic aperture are significant, exhibiting reductions of 20–75% over the heating/cooling cycles. Under higher confining stresses, the effects in fracture permeability are irreversible and notably time-dependent. Thermally driven fracture aperture variation was more pronounced in the specimen with the largest mean aperture width and spatial correlation length. Gradual fracture compaction is likely controlled by thermal dilation, mechanical grinding, and pressure dissolution due to increased thermal stresses exerted over the contacting asperities, as confirmed by the analyses of hydraulic properties and efflux mass. [ABSTRACT FROM AUTHOR]

The mechanical behavior of many types of rocks is anisotropic due to their complex micro-structure. For example, rock types such as granite and gneiss exhibit anisotropy due to foliation. Enhanced geothermal systems are normally placed in crystalline basement, where these types of anisotropic rocks are likely to be present. A few methods have been proposed to determine the elastic constants of anisotropic rocks. However, these methods often determine the shear moduli indirectly, or use the Saint-Venant assumption to approximate the transverse shear modulus. In this paper, we present a methodology to determine the shear moduli directly from a simple uniaxial compression test.We developed explicit formulae that allow the calculation of the orientation of the isotropy plane, and static and dynamic values of the shear moduli from one cylindrical sample. In order to examine this development, we performed uniaxial compression tests on cylindrical specimens of granite, extracted from the underground rock laboratory in the Grimsel Test Site (GTS), Switzerland. These rock samples exhibit a clear foliation that induces anisotropy. In order to allow lateral displacement at the top of the samples, we used a modified uniaxial test configuration, where a ball-bearing plate is placed on top of the sample. Normal and shear strains were measured at different polar angles around the circumference. In addition, the lateral displacement of the ball-bearing plate was measured in two directions, allowing the determination of the isotropy plane orientation. Apart from the uniaxial test, ultrasonic measurements were conducted in order to obtain the orientation of the isotropy plane and the dynamic elastic constants. The main outcomes of our experiments are as follows: 1) strain variations around the circumference are shown to follow the variations in the analytical formulae that are obtained for a transverse isotropy model. This indicates that transverse isotropy is a suitable model to predict the elastic response of this type of granite. 2) The orientation of the isotropy plane, determined from two independent methods, shows that the assumption of coinciding foliation plane and isotropy plane is a very good approximation. 3) The developed method proves to be accurate and efficient for determining the shear moduli directly. This method is based on only one sample, and prevents introducing errors due to heterogeneity when multiple samples are used to obtain the shear moduli. Overall, this research is considered to be an important step towards designing a standard method for the determination of the elastic constants in anisotropic rocks. [ABSTRACT FROM AUTHOR]

The mechanical behavior of fractures in rocks has strong implications for reservoir engineering applications. Deformations, and the corresponding change in contact area and aperture field, impact rock fracture stiffness and permeability, thus altering the reservoir properties significantly. Simulating contact between fractures is numerically difficult as the non-penetration constraints lead to a nonlinear problem and the surface meshes of the solid bodies on the opposing fracture sides may be non-matching. Furthermore, due to the complex geometry, the non-penetration constraints must be updated throughout the solution procedure. Here we present a novel implementation of a dual mortar method for contact. It uses a non-smooth sequential quadratic programming method as solver, and is suitable for parallel computing. We apply it to a two body contact problem consisting of realistic rock fracture geometries from the Grimsel underground laboratory in Switzerland. The contributions of this article are: (1) a novel, parallel implementation of a dual mortar method with a non-smooth sequential quadratic programming method, (2) realistic rock geometries with rough surfaces, and (3) numerical examples, which prove that the dual mortar method is capable of replicating the nonlinear closure behavior of fractures observed in laboratory experiments. [ABSTRACT FROM AUTHOR]

This study presents the first field validation of using DNA-labeled silica nanoparticles as tracers to image subsurface reservoirs by travel time based tomography. During a field campaign in Switzerland, we performed short-pulse tracer tests under a forced hydraulic head gradient to conduct a multisource-multireceiver tracer test and tomographic inversion, determining the two-dimensional hydraulic conductivity field between two vertical wells. Together with three traditional solute dye tracers, we injected spherical silica nanotracers, encoded with synthetic DNA molecules, which are protected by a silica layer against damage due to chemicals, microorganisms, and enzymes. Temporal moment analyses of the recorded tracer concentration breakthrough curves (BTCs) indicate higher mass recovery, less mean residence time, and smaller dispersion of the DNA-labeled nanotracers, compared to solute dye tracers. Importantly, travel time based tomography, using nanotracer BTCs, yields a satisfactory hydraulic conductivity tomogram, validated by the dye tracer results and previous field investigations. These advantages of DNA-labeled nanotracers, in comparison to traditional solute dye tracers, make them well-suited for tomographic reservoir characterizations in fields such as hydrogeology, petroleum engineering, and geothermal energy, particularly with respect to resolving preferential flow paths or the heterogeneity of contact surfaces or by enabling source zone characterizations of dense nonaqueous phase liquids.

Background: Practice guidelines for examining febrile patients presenting upon returning from the tropics were developed to assist primary care physicians in decision making. Because of the low level of evidence available in this field, there was a need to validate them and assess their feasibility in the context they have been designed for., Objectives: The objectives of the study were to (1) evaluate physicians' adherence to recommendations; (2) investigate reasons for non-adherence; and (3) ensure good clinical outcome of patients, the ultimate goal being to improve the quality of the guidelines, in particular to tailor them for the needs of the target audience and population., Methods: Physicians consulting the guidelines on the Internet (www.fevertravel.ch) were invited to participate in the study. Navigation through the decision chart was automatically recorded, including diagnostic tests performed, initial and final diagnoses, and clinical outcomes. The reasons for non-adherence were investigated and qualitative feedback was collected., Results: A total of 539 physician/patient pairs were included in this study. Full adherence to guidelines was observed in 29% of the cases. Figure-specific adherence rate was 54.8%. The main reasons for non-adherence were as follows: no repetition of malaria tests (111/352) and no presumptive antibiotic treatment for febrile diarrhea (64/153) or abdominal pain without leukocytosis (46/101). Overall, 20% of diversions from guidelines were considered reasonable because there was an alternative presumptive diagnosis or the symptoms were mild, which means that the corrected adherence rate per case was 40.6% and corrected adherence per figure was 61.7%. No death was recorded and all complications could be attributed to the underlying illness rather than to adherence to guidelines., Conclusions: These guidelines proved to be feasible, useful, and leading to good clinical outcomes. Almost one third of physicians strictly adhered to the guidelines. Other physicians used the guidelines not to forget specific diagnoses but finally diverged from the proposed attitudes. These diversions should be scrutinized for further refinement of the guidelines to better fit to physician and patient needs., (© 2014 International Society of Travel Medicine.)

Inherited platelet defects are a rare and heterogeneous group of disorders. The majority of affected patients present with mild to moderate bleeding tendencies. However, in trauma and surgery, bleeding may be difficult to control. Laboratory tests for diagnosis are necessary for the prevention and treatment of critical bleeding. The aim of the THROMKID study was to obtain information on the means of investigating platelet function employed by clinical centres in German-speaking countries. For this purpose a patterns-of-practice survey was conducted from 2005 to 2007, the results of which are reported here. A total of 37 out of 41 identified clinical centers serving 98 million people completed the survey questionnaire. The number of tests offered for assessment of platelet function varied between 1 and 11, median 4. Aggregometry continued to be the most popular and helpful technique for evaluation of suspected platelet function disorders (100%). The PFA-100(R) CT (76%) and in vivo bleeding time (54%) were used to screen patients with suspected platelet function disorders. Selection of tests was based on a case-by-case decision at most centres (82%). The majority of centres performed specific platelet function tests less than 50 times per month. This survey illustrates the preferences of clinical centres in the selection, performance and interpretation of platelet function tests. These practices may considerably influence the detection and diagnosis of platelet function disorders. There is an urgent need for existing tests to be improved and new, fast and reliable tests of platelet function to be developed.

Sexual conflict can elevate mating costs via male inflicted damage to females. Possible selective advantages to males include decreasing the likelihood that females remate and/or increasing females' current reproductive investment in a manner analogous to terminal reproductive investment. We investigated female mating behaviour relative to their number of previous copulations in the fly Sepsis cynipsea, and whether males accepted as first mates were more likely to be accepted again. Females were more likely to remate with new rather than original males, although there was no associated fitness benefit, and in contrast to theoretical predictions, females became less reluctant to remate as the number of previous copulations increased. Additionally, females did not increase reproductive investment as would be expected if they were ensuring their final reproductive efforts were maximized by remating. This suggests that damaging females is a pleiotropic effect which inadvertently leads to increased, not decreased, polyandry.