Treatment and recycling of acidic fracturing flowback fluid.

Acidic fracturing flowback fluid (AFFF) has the characteristics of low pH value, high chemical oxygen demand (COD), high corrosiveness and complex components. Surface discharge without treatment may contaminate the environment. However, wastewater treatment after centralized transportation has potential safety risks and requires high costs. In this study, we confirmed that calcium and magnesium could affect cross-linking property of fracturing fluid prepared by flowback fluid, and conducted a three-step process, two-stage filtration, chemical precipitation, and flocculation precipitation, on AFFF. After treatment, we made new hydraulic fracturing fluid using the treated acidic flowback fluid as base fluid and compared the quality of the new hydraulic fracturing fluid to the ones used freshwater as base fluid. The results showed when concentration of sodium carbonate, polyaluminium chloride (PAC), polyacrylamide (PAM) were 145, 1000, and 20 mg/L respectively, the treatment result was optimal. After treatment, the oil content of AFFF decreased from 7400 to 26.53 mg/L and suspended solids (SS) from 650 to 18.24 mg/L, and the removal rate of high-valence metal ions was more than 99%. The rheological properties and viscoelasticity of new fracturing fluid prepared by the treated AFFF were similar to the ones prepared by freshwater, which met the requirements of high temperature and shear resistance for ultra-deep wells.

Selective Enrichment of Clostridium Spp. by Nutrition Control from Sihe Coal Geological Microbial Communities.

In the coal biogasification, butyric acid is an important intermediate product. The enrichment of butyric acid-producing bacteria in coal geological methanogens is critical to confirm this assertion. Therefore, to study a method for enrichment of butyric acid-producing bacteria and to explore characteristic factors for evaluating the enrichment effect would be the basis for further strain isolation and metabolomics research. In this study, the nutrition control method was used for the butyric acid-producing bacteria enrichment from concentrated bacteria solution in Sihe coal seam. The characteristic factors' changes in gas production, gas composition, butyric acid concentration, and pH were observed and analyzed in the experiment. High-throughput sequencing was used as a verification method to validate the medium and genera enrichment effect that can be used for the butyric acid-producing bacteria. Through experimental research and analysis, it was identified that the glucose-sucrose-maltose medium was the beneficial medium to the enrichment of butyric acid-producing bacteria, and the high-throughput sequencing determined that the enriched genera were Clostridium spp. Glucose-sucrose-maltose medium experimental data confirmed that the decrease of CO2 and H2 daily yield, the increase of butyric acid concentration, and the decrease of pH value had a significant positive correlation with the enrichment of Clostridium spp.