Overpressure preventing quartz cementation? - A reply

Chemical compaction and the relative importance of the pressure dissolution and illite-mica induced dissolution (IMID) models have remained a contentious issue, as is the role played by stress in chemical compaction. This paper offers further support and evidence as discussed in Stricker et al. (2016b), focusing on the reservoir quality of the Triassic Skagerrak Formation sandstones in the high pressure high temperature (HPHT) Central Graben, North Sea. The reply discusses alterative reservoir quality interpretations and comments as raised by Maast (2016). A series of theoretical and experimental studies, as well as field based evidence is presented providing strong support to the important role of stress (e.g. vertical effective stress) during chemical compaction. The evidence leads to the conclusion that the process of chemical compaction is stress and temperature driven and significantly enhanced by clay minerals, playing a catalytic role by increasing the width of diffusion pathway or by modifying the kinetics of the dissolution process

Final Report of FORGE WP4.1.2: verification of critical stress theory applied to repository concepts

This report describes an experimental study of 48 separate experiments examining the validity of critical stress theory. Two main types of experiment were conducted: 1). Loading-unloading tests, where fracture flow was monitored at constant injection pressure as normal load was increased in steps to a given level and then reduced back to the starting stress state; 2). Gas breakthrough experiments, where gas injection pressure was increased in a pressure ramp at constant vertical load. These were conducted with and without active shear. It was found that critical stress theory is valid in predicting the preferential flow of gas in relation to the orientation of the fracture plane with respect to the maximum horizontal stress direction. However, loading unloading experiments showed that understanding the stress history of the rocks is of paramount importance and a mere knowledge of the current stress state is insufficient in accurately predicting the nature of fluid flow. A total of 17 loading-unloading experiments were conducted, all on a 30° slip-plane. The main conclusions of this part of the study were; a). During a loading (vertical stress) and unloading cycle considerable hysteresis in flow was observed signifying the importance of stress history on fracture flow; b). For the case of gas injection the change in flow is chaotic at low normal loads, whereas for water injection the flow reduces smoothly with increased normal load; c). Hysteresis in horizontal stress observed during unloading demonstrates the importance of the ratio between horizontal stress and vertical stress and its control on flow; d). Differences have been observed between injection fluids (water and helium), especially the hysteresis observed in flow. For water injection flow is only partially recovered during unloading, whereas for gas enhanced flow is seen at low normal loads. A total of 26 gas breakthrough experiments were conducted on 0°, 15°, 30°, and 45° discontinuities; both with and without active shear. All tests were conducted in an identical manner. The main conclusions of this part of the study were; a). During gas breakthrough experiments episodic flow/fault valve behaviour was seen with a decrease in subsequent peak pressures and the form of the pressure response was different during subsequent breakthrough events; b). Repeat gas injection testing had shown a consistent gas entry pressure but considerably different, non-repeatable, gas peak pressures; c). Differences in gas entry pressure were seen dependent on the orientation of the fracture; d). Shear can be seen to reduce the gas entry pressure, suggesting that shearing in kaolinite has the opposite effect of self-sealing to gas. Other general observations of gas flow along fractures included; a). The flow of fluids through clay filled fractures is non-uniform and occurs via localised preferential pathways; b). The pressure recorded within the slip-plane showed a negligible fracture pressure and did not vary much in all tests

Summary Report of FORGE WP4.1.2: verification of critical stress theory applied to repository concepts

This report outlines the major conclusions from an experimental study of 48 separate experiments with the primary aim to verify critical stress theory. Two main types of experiment were conducted: 1). Loading-unloading tests, where fracture flow was monitored at constant injection pressure as normal load was increased in steps to a given level and then reduced back to the starting stress state; 2). Gas breakthrough experiments, where gas injection pressure was increased in a pressure ramp at constant vertical load. These were conducted with and without active shear. It was found that critical stress theory is valid in predicting the preferential flow of gas in relation to the orientation of the fracture plane with respect to the maximum horizontal stress direction. However, loading unloading experiments showed that understanding the stress history of the rocks is of paramount importance and a mere knowledge of the current stress state is insufficient in accurately predicting the nature of fluid flow

Bayes estimation of Lorenz curve and Gini-index for power function distribution

In this article, we estimate the shape parameter, Lorenz curve and Gini-index for 3power function distributions using a Bayesian method. Bayes estimators have been developed under squared error loss function as well as under weighted squared error loss function. We demonstrate the use of the proposed estimation procedure with the U. S. average income data for the period 1913-2010. Our proposed Bayesian estimators are compared using a Monte Carlo simulation study with the ML estimators proposed by Belzunce, Candel and Ruiz (1998)

Prevalence of multidrug resistant uropathogens isolated from different age groups in South-India: a cross-sectional study

Background: Urinary tract infections (UTIs) continue to be one of the most common infections encountered by clinicians. The purpose of this study is to identify relevant multidrug resistance (MDR) patterns in South India.Methods: 401 urine culture samples with significant bacteriuria were collected from labs in South India between January 2019 and December 2020. Routine biochemical tests were conducted for primary identification of uropathogens. Antibiotic susceptibility testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Statistical package for the social sciences (SPSS) 16 and Microsoft excel were used to analyse data and determine MDR patterns.Results: The results showed that 54% of cultures with significant bacteriuria exhibited an organism with multidrug resistance. Of these, extended-spectrum beta-lactamases (ESBL) resistance was confirmed in 34.9%. Furthermore, over half (54%) of significant cultures were from outpatients. The incidence of UTIs was highest during the summer and at the lowest in the second phase of the monsoon season.Conclusions: Although the sample collection was limited to a few centres in South India, the results of our study justifies the rationale behind stringent regulation of antibiotic use and careful monitoring of antimicrobial resistance

An in vitro study of probiotic activity exhibited by Lactobacillus acidophilus and Lactobacillus rhamnosus on oral isolates of Streptococcus mutans and Candida albicans

Background: Oral infections caused by microorganisms have led to increased risk of oral health problems like dental caries (DC). Streptococcus mutans and Candida albicans are the organisms responsible for DC. The goal of the presented study was to investigate the potential of probiotics to prevent and treat DC. An in vitro assay was developed to investigate several probiotic strains for their ability to inhibit the aforementioned oral pathogens. Methods: 40 oral isolates of Streptococcus mutans and 51 oral isolates of Candida albicans were tested for probiotic activity against Lactobacillus acidophilus and Lactobacillus rhamnosus using agar overlay interference technique as prescribed by Fleming et al. Results: The zone of inhibition shown by L. acidophilus was higher than L. rhamnosus against Streptococcus mutans and Candida albicans. Conclusions: In conclusion the two probiotic strains L. acidophilus and L. rhamnosus exhibited inhibitory activity on S. mutans and C. albicans respectively in vitro

Assessment of minimum inhibitory concentration to vancomycin, tigecycline, linezolid, daptomycin, ceftaroline and mupirocin against methicillin resistant Staphylococcus aureus clinical isolates by antibiotic gradient strips

Background: Staphylococcus aureus infections are one of the most common and serious hospital-acquired infections seen in developing countries. Methicillin resistant Staphylococcus aureus (MRSA) is an important human pathogen and normally colonized in body parts including skin, nose, perineum and throat. MRSA is resistant not only to all β-lactam groups but also other antibiotics including aminoglycosides, tetracycline and macrolides. In the present study the efficacy of agents used in the management of MRSA infections was determined by antibiotic gradient testing. Methods: A total of 60 clinical isolates of MRSA strains were collected from various diagnostic labs in central Kerala. Clinical isolates were reconfirmed as MRSA by gram staining, yellow-coloured colonies on mannitol salt Agar (MSA). Antibiotic susceptibility testing was done by disc diffusion method as recommended by CLSI guidelines. S. aureus isolates resistant to cefoxitin (30 µg) was identified as MRSA. Antibiotic gradient testing was performed to determine the MIC of vancomycin, tigecycline, linezolid, daptomycin, ceftaroline and mupirocin against MRSA isolates. Results: All the 60 MRSA isolates tested were sensitive to vancomycin, tigecycline, linezolid, daptomycin, ceftaroline and mupirocin (100%) and none of the MRSA isolates show resistance.  Conclusions: Results of present study indicates that these agents may be used alongside vancomycin in management of infection caused by MRSA