Immunity to Sda1 Protects against Infection by Sda1+ and Sda1− Serotypes of Group A Streptococcus

Group A Streptococcus (GAS) causes a variety of diseases globally. The DNases in GAS promote GAS evasion of neutrophil killing by degrading neutrophil extracellular traps (NETs). Sda1 is a prophage-encoded DNase associated with virulent GAS strains. However, protective immunity against Sda1 has not been determined. In this study, we explored the potential of Sda1 as a vaccine candidate. Sda1 was used as a vaccine to immunize mice intranasally. The effect of anti-Sda1 IgG in neutralizing degradation of NETs was determined and the protective role of Sda1 was investigated with intranasal and systemic challenge models. Antigen-specific antibodies were induced in the sera and pharyngeal mucosal site after Sda1 immunization. The anti-Sda1 IgG efficiently prevented degradation of NETs by supernatant samples from different GAS serotypes with or without Sda1. Sda1 immunization promoted clearance of GAS from the nasopharynx independent of GAS serotypes but did not reduce lethality after systemic GAS challenge. Anti-Sda1 antibody can neutralize degradation of NETs by Sda1 and other phage-encoded DNases and decrease GAS colonization at the nasopharynx across serotypes. These results indicate that Sda1 can be a potential vaccine candidate for reduction in GAS reservoir and GAS tonsillitis-associated diseases.

Investigation of the Enrichment and Accumulation of Normal Pressure Shale Gas in Anchang Syncline Outside of Sichuan Basin

Gas shales from the Wufeng-Longmaxi Formation in Anchang syncline in northern Guizhou area of Sichuan Basin are stable in distribution and can be classified as type I shale gas reservoir with great resource potential. The exploration and development of shale gas in Anchang syncline have achieved great progress. However, the enrichment rule and accumulation pattern of shale gas in Anchang syncline are still not clear at the present. Gas pressure in the Wufeng-Longmaxi Formations shales in Anchang syncline is normal. The maximum tested gas production in the field ranges from 18,000 to 58,000 m3/d. However, gas production of shale wells varies greatly even in the same platform. In order to understand the shale gas enrichment and accumulation and improve the effective development of shale gas in this area, comparative analyses on the geological characteristics and preservation conditions of gas reservoirs in several typical wells were carried out from the perspective of geology, petrophysics, geophysics, and well logging. Results show that shale gas in Anchang syncline has the characteristics of accumulating in both deep central position and gently wings. Tectonic preservation condition is the key factor to high gas production in Anchang area. The hydrological conditions, syncline structure, fault distribution, and cap rock quality comprehensively control the gas pressure and gas bearing capacity of shale reservoir. According to these factors, an accumulation model of shales with normal gas pressure is established: syncline controls the distribution of gas reservoir; fault controls the boundary of the reservoir; preservation conditions controls gas capacity. The results are benefit for the rolling exploration and development of shale gas in Anchang area, and are important for the development of normal pressure shale gas in northern Guizhou area.

The accumulation model of organic matters for the Niutitang Formation shale and its control on the pore structure: a case study from Northern Guizhou

Shale gas reservoir is a fine-grained sedimentary rock with component of clastic particles and organic matters, and the accumulation of the organic matters would determine the effective development of shale gas. The paleoclimate, detrital influx, redox of the water and paleoproductivity are effective geochemical indicators that could help to find the favorable shale gas reservoir stratum. In this study, the shale samples collected from Niutitang Formation (Northern Guizhou, China) were launched the measurements of the content of major elements and trace elements, and the characteristics of geochemical indicators were analyzed, which can be used to discuss the accumulation model of organic matters. Besides, the pore structure of shale sample controlled by the enrichment of organic matters is also discussed. The paleoclimate is dominant cold and dry, and it changes to warm and humid at the later Niutitang period, and the detrital influx also increased at the later Niutitang period; the water environment of Niutitang Formation shale presents as reductive, and the paleoproductivity of the Niutitang Formation shale is commonly high. The enrichment of organic matters in the Niutitang Formation is dominantly controlled by the redox of the water, while the hydrothermal activity and the paleoproductivity lead to the difference enrichment of organic matters in the Niutitang Formation shale. The accumulation model of organic matters also influences the characteristics of pore structure from the Niutitang Formation shale, and the pore structure could be divided into two types. The shale with high content of organic matters also features high content of quartz and pyrite, and these minerals contribute to the preservation of pore space in the shale, while that of the clay minerals is contrary. The high content of organic matters and preferable pore characteristics indicate the Niutitang Formation favors the development of shale gas, especially that for the lower Niutitang Formation.

A Hydrofracturing-Triggered Earthquake Occurred Three Years after the Stimulation

Hydrofracturing, used for shale gas exploitation, may induce felt, even damaging earthquakes. On 15 June 2019, an Mw2.8 earthquake occurred, spatially correlated with the location of earlier exploratory hydrofracturing operations for shale gas in Wysin in Poland. However, this earthquake was atypical. Hydrofracturing-triggered seismicity mainly occurs during stimulation; occasionally, it continues a few months after completion of the stimulation. In Wysin, there were only two weaker events during two-month hydrofracturing and then 35 months of seismic silence until the mentioned earthquake occurred. The Wysin site is in Gdańsk Pomerania broader region, located on the very weakly seismically active Precambrian Platform. The historical documents, covering 1000 years, report no natural earthquakes in Gdańsk Pomerania. We conclude, therefore, that despite the never observed before that long lag time after stimulation, the Mw2.8 earthquake was triggered by hydrofracturing. It is possible that its unusually late occurrence in relation to the time of its triggering technological activity was caused by changes in stresses due to time-dependent deformation of reservoir shales. The Wysin earthquake determines a new time horizon for the effect of HF on the stress state, which can lead to triggering earthquakes. Time-dependent deformation and its induced stress changes should be considered in shall gas reservoir exploitation plans.

An Optimization-Based Method for the Explicit Production Data Analysis of Gas Wells

This work aims at the exploration of production data analysis (PDA) methods without iterations. It can overcome limitations of the advanced type curve analysis relying on the iterative calculation of material-balance pseudotime and current explicit methods reckoning on specific production schedule assumptions. The dynamic material balance equation (DMBE) is strictly proved by the integral variable substitution based on the gas flow equation under the boundary dominated flow (BDF) condition and the static material balance equation (SMBE) of a gas reservoir. We introduce the pseudopressure level function γ(p) and the recovery factor function R(p) to rewrite the DMBE in terms of observed variable Y and estimated variable Ye; then the PDA can be transformed into an optimization problem of minimizing the error between Y and Ye. An optimization-based method for the explicit production data analysis of gas wells (OBM-EPDA), therefore, is developed in the paper, capable of determining the BDF constant and gas reserves explicitly and accurately for variable rate and/or variable flowing pressure systems. Three stimulated cases demonstrate the applicability and validity of OBM-EPDA with small errors less than 1% for estimated values of both reserves and Y. Not second to previous studies, the field case analysis further proves its practicability. It is shown that the nonlinear relation of γ to R can be represented by a polynomial function merely dependent on the inherent properties of the gas production system even before sorting out the production data. The errors of observed variable Y provided by OBM-EPDA facilitate the data quality control, and the elimination of outliers not subject to the BDF condition improves the reliability of the analysis. For various gas systems producing whether at a constant rate, a constant bottomhole pressure (BHP), or under variable rate and variable BHP conditions, the proposed method gives insights into the well-controlled volume and production capacity of the gas well whether in a low-pressure or high-pressure gas reservoir, where the compressibilities of rock and bound water are considered.