Numerical study on the stimulation effect of boundary sealing and hot water injection in marine challenging gas hydrate extraction.

This study proposed a novel development mode combining boundary sealing and hot water injection to address the challenges of gas leakage, limited reservoir sensible heat, boundary water intrusion, and low productivity faced by challenging hydrate extraction, and the stimulation effect was numerically investigated with Shenhu hydrates as the geological background. The results showed that lower boundary permeability facilitated pressure propagation and achieved volumetric dissociation of hydrates, whereas insufficient formation energy resulted in substantial gas retention. Hot water injection was effective for stimulation, but open boundaries could not maintain the high injection pressure, leading to massive hot water losses and gas escapes. However, their combination achieved a synergistic stimulation like "1 + 1 > 2" because a piston water drive similar to secondary recovery in oil and gas development was formed. Relative to three-spot well patterns, the five-spot shortened the extraction cycle by 680 days and enhanced the gas-to-water ratio by 17%. Increasing injection pressure enhanced water yield more significantly while the improvement of gas yield was more significant by increasing hot water temperature. Overall, high-pressure and high-temperature injection was suggested for gas enhancement and water control. These findings provide important guidance for advancing the commercial development of challenging hydrates.

[Concentration levels and spatial distribution of heavy metals in soil surrounding a municipal solid waste incineration plant (Shenzhen)].

The municipal solid waste (MSW) incineration has been well known among key sources of heavy metal (HM) emission. To investigate the multivariate relationships and spatial distribution of HMs from this source, 9 HMs (Hg, As, Cd, Cr, Cu, Ni, Pb, Se and Zn) were analysed by multivariate statistical analysis in 80 representative soil samples including surface soils and subsurface soils around the Shenzhen Qingshuihe MSW Incineration Plant (MSWIP). Results show that, the concentrations of Hg, As, Cd, Cr, Cu, Ni, Pb, Se and Zn range 0.012-0.136, 0.23-75.89, not detected (ND)-1.17, 21.7-116.0, ND-61.1, ND-47.0, ND-133.0, ND-16.4 and 8.6-246.9 mg x kg(-1), respectively. No significant elevation of concentrations of HMs in soils is observed, compared with the natural background. Based on the hierarchical cluster and historical analysis, the spatial correlations of HMs have been changed by the impact of MSWIP. According to the similarity of concentration, the HMs can be divided into 3 categories: (1) Cu, Ni, Cr, Se, Zn, Pb; (2) As, Cd; (3) Hg. Factors analysis was also performed and shows that the HM distribution patterns are dominantly affected by 3 principal components: local biogeochemical characteristics (48.6% of variance), impact of the MSWIP (16.6% of variance) as well as topographical characteristics (13.2% of variance). Subsequently the 3 maps of factor scores are calculated and exhibited. This study favors to estimate the long-term effects of HM emission from MSWIP on surrounding soil environment and facilitate the local health risk assessment.

[Mercury pollution investigation in predominant plants surrounding Shenzhen Qingshuihe municipal solid waste incineration plant].

In order to investigate the effects of mercury emission from municipal solid waste incineration (MSWI) on the surrounding plants and soils, the mercury concentrations were examined in the plant samples including leaves and stems and the soil samples around Shenzhen Qingshuihe MSWI Plant. Results show that, these plants are significantly polluted by mercury, the mercury concentrations of the plant leaves are 0.030 9-0.246 7 mg x kg(-1), with the mean value 0.094 8 mg x kg(-1), among the local prominent plants, the mercury concentrations in the leaves are in the order of: Acacia confuse > Litsea rotundifolia > Acacia mangium > Acacia auriculaeformis > Schima superb > Ilex asprella. The mercury concentrations of the plant stems are 0.007 4-0.119 6 mg x kg(-1), with the mean value 0.041 7 mg x kg(-1). For the same plant, the mercury concentration in its leaf correlates positively with that in its stem, but presents little correlation with that in the soil where it grows. Under the direction of the dominant wind, the concentration of smoke diffusion is often influenced by the distance from the stack and the difference of terrain. The mercury concentrations of the plant leaves and stems vary almost in accordance with spatial heterogeneity patterns of smoke diffusion. These results demonstrate that the interaction of the smoke and plant leaves play the leading role in the mercury exchange between plants and environment.