Summary: To solve the problem of poor salt resistance of conventional drag reducers, a hydrophobic associative polymer drag reducer was prepared by inverse emulsion polymerization with acrylamide (AM), methacrylic acid (MAA), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), and hexadecyl dimethyl allyl ammonium chloride (C16DMAAC) as the main monomers. The synthetic product was confirmed as the target product by infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS). The viscosity-average molecular weight of the prepared drag reducer is 1100×104 g/mol. The pipeline friction results show that the drag reducer has good friction reduction and salt resistance. When the concentration in clean water is 0.06%, the maximum friction reduction rate is 71.1%. When the salinity is 5×104 mg/L, the calcium ion concentration is 2000 mg/L, and the suspended solid content is 500 mg/L, the maximum friction reduction rate is 68.9% when the concentration of the drag reducer is 0.06%. Salt water will not significantly lower the friction reduction rate. If the concentration of the drag reducer is increased to 0.08%, the maximum drag reduction rate will reach 73.8%. The microrheological test results of the friction reducer solution show that, at 0.2% concentration, there is no network structure between friction reducer molecules, which is consistent with Newtonian fluids possessing a certain viscosity. The elasticity index (EI) of the drag reducer solution is basically unchanged over time, maintaining good friction reduction and sand-carrying performance during the shearing process of large displacement pumping.

To address critical limitations of ultra-low viscosity supercritical CO₂ fracturing fluids, including excessive fluid loss and inadequate proppant transport capacity, a series of thickeners designed to significantly enhance CO₂ viscosity were synthesized. Initially, FT-IR and ¹H NMR characterization confirmed successful chemical reactions and incorporation of both solvation-enhancing and -thickening functional groups. Subsequently, dissolution and thickening performance were evaluated using a custom-designed high-pressure vessel featuring visual observation capability, in-line viscosity monitoring, and high-temperature operation. All thickener systems exhibited excellent solubility, with 5 wt% loading elevating CO₂ viscosity to 3.68 mPa·s. Ultimately, molecular simulations performed in Materials Studio elucidated the mechanistic basis, electrostatic potential (ESP) mapping, cohesive energy density analysis, intermolecular interaction energy, and radial distribution function comparisons. These computational approaches revealed dissolution and thickening mechanisms of polymeric thickeners in CO₂.

In this paper, a dithiocarbamate-type flocculant DTC-TETA was prepared by using triethylenetetramine as the material and combination of DTC-TETA and polyacrylamide was used for the coagulation-flocculation of flowback water from shale gas hydraulic fracturing (FWSG). The coagulation-flocculation process was optimized by using turbidity as index and the recommended process was as follows: DTC-TETA dosage 200 mg/L, anionic polyacrylamide AN905 dosage 1 mg/L, flocculation stirring speed 200 rpm, flocculation stirring time 3 min and settlement time 5 min. The turbidity of FWSG can be reduced to be 13 NTU from the initial turbidity of more than 2000 NTU under the recommended process. The performance of DTC-TETA was much better than that of polyaluminum chloride and the Fe²⁺ in FWSG also can be removed. The function mechanism of DTC-TETA was investigated through the studies of zeta potential change of suspended solids and structural characteristics of flocs. The results confirmed that the flocs were developed by the network formed by the coordination reaction between DTC-TETA and Fe²⁺, which can filter out suspended solids. This study signifies that both suspended solids and Fe²⁺ ion can be removed by using DTC-TETA as flocculant, which is a new choice for the FWSG treatment.

To investigate the corrosion failure of a reducing tee at a shale gas station, a failure analysis was carried out. The failed tee was made of L245N steel, with a large-diameter branch of DN 80 and a small-diameter branch of DN 25. The DN 80 branch conveyed shale gas, while the DN 25 branch served as a vent and remained closed. The tee was after approximately 20 months of service. By means of macroscopic observation, transported medium analysis, chemical composition testing of the pipe fitting, hardness testing, metallographic structure examination, and analysis of the composition and morphology of corrosion products, the corrosion failure mechanism was identified. The chemical composition and mechanical properties of the tee met the standard requirements, the inclusion content was low, and the microstructure was normal. A substantial quantity of loose, lamellar and block-like corrosion products had formed at and around the perforation. The corrosion pit regions were mainly composed of Fe, C, O, and a small amount of S. The corroded areas exhibited pitting, ring-like corrosion, and mesa attack. The corrosion products were predominantly FeCO₃, with a small amount of FeS. Comprehensive analysis indicates that the synergistic corrosion effect of carbon dioxide (CO₂) and sulfate-reducing bacteria (SRB) is the root cause of the corrosion perforation of the tee.

In this study, we attempted to use the response surface methodology with temperature, pH and thiourea concentration as control variables by systematically varying the experimental parameters in order to find the optimal preparation process for electroless deposition of Ni-B coatings. A mathematical model of the effect of different experimental parameters on the impedance of Ni-B coating was constructed by selecting the Box–Behnken Design (BBD) design, and the optimum plating solution temperature, pH and thiourea concentration for electroless deposition of Ni-B coating were discussed through optimization analysis. The surface microstructure of the Ni-B coating was characterized by SEM. The chemical composition of the Ni-B coating was analyzed by XRD and EDS, and the corrosion resistance of the coating was characterized by EIS and potentiodynamic polarization techniques. The results showed that the best morphology and the best corrosion resistance of the coatings were achieved when the plating solution temperature was 69.31 °C, the plating solution pH was 6.06, and the concentration of thiourea was 0.0015 g/L. The predicted impedance value was 5828.77 Ω, while the impedance value of the prepared coating based on the experimental setup parameters was 6041 Ω.