Storm-driven runoff scours accumulated sediments within stormwater drainage systems, transporting multi-source pollutants (including pathogens) into surface water through stormwater overflows, thereby elevating contamination risks in the recipient. Chlorine-based disinfection of overflowed stormwater applied in related storage tanks mitigates these risks before release. This study reveals that chlorophenylacetonitriles (CPANs), which are formed during the disinfection process, exhibit toxicity levels higher than conventional trihalomethanes and haloacetonitriles. Laboratory analyses conducted in this work demonstrated that sewer sediments — not runoff or stormwater — are the dominant precursor source for CPAN formation during overflow disinfection. Source apportionment further identified a robust linear correlation (R² = 0.95) between sediment indole concentrations (0.093–0.91 μg/g) and CPAN formation, experimentally confirming for the first time that indole is a critical precursor. Laboratory experiments also uncovered the presence of monochloroindoles in indole chlorination, a novel class of aromatic nitrogenous disinfection byproducts (DBPs). In addition, density functional theory calculations demonstrated that monochloroindole formation has lower activation energy barriers compared to CPAN pathways, resulting in new molecular-level insights into their preferential transformation. Given that indole serves as a shared precursor for both highly toxic CPANs and even more ecotoxic monochloroindoles, this study emphasizes the urgent need for sewer sediment management to mitigate the ecological and human health risks associated with these highly toxic nitrogenous DBPs.

In the process of the exploitation of deep oil and gas resources, shale wellbore stability control faces great challenges under complex temperature and pressure conditions. It is difficult to reflect the micro mechanism and process of the action of inorganic salt on shale hydration with the traditional experimental evaluation technology on the macro effect of restraining shale hydration. Aiming at the characteristics of clay minerals of deep shale, the molecular dynamics models of four typical cations (K⁺, NH₄⁺, Cs⁺ and Ca²⁺) inhibiting the hydration of clay minerals have been established by the use of the molecular dynamics simulation method. Moreover, the micro dynamics mechanism of typical inorganic cations inhibiting the hydration of clay minerals has been systematically evaluated, as has the law of cation hydration inhibition performance in response to temperature, pressure and ion type. The research indicates that the cations can promote the contraction of interlayer spacing, compress fluid intrusion channels, reduce the intrusion ability of water molecules, increase the negative charge balance ability and reduce the interlayer electrostatic repulsion force. With the increase in temperature, the inhibition of the cations on montmorillonite hydration is weakened, while the effect of pressure is opposite. Through the molecular dynamics simulation under different temperatures and pressures, we can systematically understand the microcosmic dynamics mechanism of restraining the hydration of clay in deep shale and provide theoretical guidance for the microcosmic control of clay hydration.

Recently, a multiwell-pad-production (MWPP) scheme has been the center of attention as a promising technology to improve shale-gas (SG) recovery. However, the increasing possibility of multiwell pressure interference (MWPI) in the MWPP scheme severely distorts flow regimes, which strongly challenges the traditional pressure-transient analysis methods that focus on single multifractured horizontal wells (SMFHWs) without MWPI. Therefore, a methodology to identify pressure-transient response of the MWPP scheme with and without MWPI is urgent. To fill this gap, a new semianalytical pressure-transient model of the MWPP scheme is established by use of superposition theory, Gauss elimination, and the Stehfest numerical algorithm. Type curves are generated, and flow regimes are identified by considering MWPI. Finally, a sensitivity analysis is conducted. Our results show that there are good agreements between our proposed model and numerical simulation; moreover, our semianalytical approach also demonstrates a promising calculation speed compared with numerical simulation. Some expected flow regimes are significantly distorted by MWPI. In addition, well rate determines the distortion of pressure curves, whereas fracture length, well spacing, and fracture spacing determine when the MWPI occurs. The smaller the gas rate, the more severely flow regimes are distorted. As the well spacing increases, fracture length decreases, fracture spacing decreases, and the occurrence of MWPI occurs later. The stress-sensitivity coefficient has little to no influence on the occurrence of MWPI. Similar to the concept of the dual-porosity model, three new flow regimes—the single-well flow regime, MWPI flow regime, and MWPP flow regime—are artificially defined to systematically characterize the flow regimes of the MWPP scheme. This work offers some additional insights on pressure-transient response for the MWPP scheme in the SG reservoir, which can provide considerable guidance for fracture-properties estimation and well-pattern optimization for the MWPP scheme.