Geomechanical Characterization of Sandstones Cliffs of Segou (Senegal, West Africa) in the Madina Kouta Basin

AbstractDengue virus is a major and rapidly growing public health concern in tropic and subtropic regions across the globe. In late 2018, Senegal experienced its largest dengue virus outbreak to date, covering several regions. However, little is known about the genetic diversity of dengue virus (DENV) in Senegal. Here we report complete viral genomes from 17 previously undetected DENV cases from the city of Thiès. In total we identified 19 cases of DENV in a cohort of 198 individuals with fever collected in October and November 2018. We detected 3 co-circulating serotypes; DENV 3 was the most frequent accounting for 11/17 sequences (65%), 4 (23%) were DENV2 and 2 (12%) were DENV1. Sequences were most similar to recent sequences from West Africa, suggesting ongoing local circulation of viral populations; however, detailed inference is limited by the scarcity of available genomic data. We did not find clear associations with reported clinical signs or symptoms, highlighting the importance of testing for diagnosing febrile diseases. Overall, these findings expand the known range of DENV in Senegal, and underscore the need for better genomic characterization of DENV in West Africa.

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Surface and Underground Geomechanical Characterization of an Area Affected by Instability Phenomena in Zaruma Mining Zone (Ecuador)

Sustainability ◽

10.3390/su13063272 ◽

2021 ◽

Vol 13 (6) ◽

pp. 3272

Author(s):

Paúl Carrión-Mero ◽

Maribel Aguilar-Aguilar ◽

Fernando Morante-Carballo ◽

María José Domínguez-Cuesta ◽

Cristhian Sánchez-Padilla ◽

...

Keyword(s):

Mass Movement ◽

Mining Activity ◽

Mining District ◽

Mean Values ◽

Surface Areas ◽

Definition Of ◽

Action Measures ◽

Geomechanical Characterization ◽

The City

In the last decade, in the mining district of Zaruma-Portovelo, there has been significant land subsidence related to uncontrolled mining activity. The purpose of this work was to carry out a surface and underground geomechanical characterization of a mining sector north of the city of Zaruma that allows the definition of potentially unstable areas susceptible to the mass movement. The methodology used consists of the following stages: (i) compilation of previous studies; (ii) surface and underground characterization of rocky material to establish its susceptibility to mass movement; (iii) interpretation of results; and (iv) proposal of action measures. Among the most relevant results, it stands out that 26.1% of the 23 stations characterized on the surface present conditions that vary from potentially unstable to unstable. In underground galleries, the studied mean values of the 17 stations indicate that the rock has a medium to good quality, representing a medium susceptibility to gallery destabilization. The results obtained for the surface areas (depths up to 50 m, where altered materials predominate) and the underground areas (depths > 50 m, where the alterations are specific) can be used to identify the areas with a more significant potential for instability. For both cases, it has been possible to define specific monitoring, control, and planning actions for sensitive areas.

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Hydrologic and geomechanical characterization of deep sedimentary rocks and basement for safe carbon sequestration in the Cook Inlet Basin, Alaska

International Journal of Greenhouse Gas Control ◽

10.1016/j.ijggc.2020.103243 ◽

2021 ◽

Vol 106 ◽

pp. 103243

Author(s):

Scott Pantaleone ◽

Shuvajit Bhattacharya

Keyword(s):

Carbon Sequestration ◽

Sedimentary Rocks ◽

Cook Inlet ◽

Cook Inlet Basin ◽

Geomechanical Characterization

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Geomechanical aspects of induced microseismicity during CO2 injection in Illinois Basin

The Leading Edge ◽

10.1190/tle40110823.1 ◽

2021 ◽

Vol 40 (11) ◽

pp. 823-830

Author(s):

Nikita Bondarenko ◽

Sherilyn Williams-Stroud ◽

Jared Freiburg ◽

Roman Makhnenko

Keyword(s):

Oil Field ◽

Co2 Injection ◽

Low Permeability ◽

Illinois Basin ◽

Petrographic Analysis ◽

Flow Properties ◽

Geomechanical Characterization ◽

Fluid Penetration ◽

Geophysical Log

Carbon sequestration activities are increasing in a global effort to mitigate the effects of greenhouse gas emissions on the climate. Injection of wastewater and oil-field fluids is known to induce seismic activity. This makes it important to understand how that risk relates to CO2 injection. Injection of supercritical CO2 into the Cambrian Mt. Simon sandstone in Illinois Basin induced microseismicity that was observed below the reservoir, primarily in the Precambrian crystalline basement. Geomechanical and flow properties of rock samples from the involved formations were measured in the laboratory and compared with geophysical log data and petrographic analysis. The controlling factors for induced microseismicity in the basement seem to be the hydraulic connection between the reservoir and basement rock and reactivation of pre-existing faults or fractures in the basement. Additionally, the presence of a laterally continuous low-permeability layer between reservoir and basement may have prevented downward migration of pore pressure and reactivation of critically stressed planes of weakness in the basement. Results of the geomechanical characterization of this intermediate layer indicate that it may act as an effective barrier for fluid penetration into the basement and that induced microseismicity is likely to be controlled by the pre-existing system of faults. This is because the intact material is not expected to fail under the reservoir stress conditions.

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2D quantitative analysis of fractures from high-resolution photos for the geomechanical characterization of rock masses

10.5194/egusphere-egu21-2589 ◽

2021 ◽

Author(s):

Emmanuel Wyser ◽

Lidia Loiotine ◽

Charlotte Wolff ◽

Gioacchino Francesco Andriani ◽

Michel Jaboyedoff ◽

...

Keyword(s):

High Resolution ◽

Point Clouds ◽

Mitigation Measures ◽

Future Perspective ◽

Rock Masses ◽

Sampling Errors ◽

Discontinuity Sets ◽

Adverse Weather ◽

Geomechanical Characterization

The identification of discontinuity sets and their properties is among the key factors for the geomechanical characterization of rock masses, which is fundamental for performing stability analyses, and for planning prevention and mitigation measures as well. In practice, discontinuity data are collected throughout difficult and time-consuming field surveys, especially when dealing with areas of wide extension, difficult accessibility, covered by dense vegetation, or with adverse weather conditions. Consequently, even experienced operators may introduce sampling errors or misinterpretations, leading to biased geomechanical models for the investigated rock mass. In the last decades, new remote techniques such as photogrammetry, Light Detection and Ranging (LiDAR), Unmanned Aerial Vehicle (UAV) and InfraRed Thermography (IRT) have been introduced to overcome the limits of conventional surveys. We propose here a new tool for extracting information on the fracture pattern in rock masses, based on remote sensing methods, with particular reference to the analysis of high-resolution georeferenced photos. The first step consists in applying the Structure from Motion (SfM) technique on photos acquired by means of digital cameras and UAV techniques. Once aligned and georeferenced, the orthophotos are exported in a GIS software, to draw the fracture traces at an appropriate scale. We developed a MATLAB routine to extract information on the geostructural setting of rock masses by performing a quantitative 2D analysis of the fracture traces, based on formulas reported in the literature. The code was written by testing few experimental and simple traces and was successively validated on an orthophoto from a real case study. Currently, the script plots the fracture traces as polylines and calculates their orientation (strike) and length. Subsequently, it detects the main discontinuity sets by fitting an experimental composite Gaussian curve on histograms showing the number of discontinuities according to their orientation, and splitting the curve in simpler Gaussian curves, with peaks corresponding to the main discontinuity sets. Then, for each set, a linear scanline intersecting the highest number of traces is plotted, and the apparent and real spacing are calculated. In a second step, a grid of circular scanlines covering the whole area where the traces are located is plotted, and the mean trace intensity, trace density and trace length estimators are calculated. It is expected to test the presented tools on other case studies, in order to optimize them and calculate additional metrics, such as persistence and block sizes, useful to the geomechanical characterization of rock masses. As a future perspective, a similar approach could be investigated for 3D analyses from point clouds.

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