Prediction Model for Tight Gas Wells with Time-Dependent Mechanism and Stress Sensitivity Effect.

In the production process of tight gas wells, reservoir fluid distribution and gas-water relative permeability vary with time. However, traditional models fail to handle the time-dependent mechanism and stress sensitivity effect in the reservoir, leading to significant errors in the dynamic analysis results. To address this issue, this article presents a prediction model for fractured well production in tight gas reservoirs. It is based on a three-dimensional embedded discrete fracture model (EDFM), which considers the influences of the time-dependent mechanism and stress-dependent reservoir permeability. Transient flow equations are treated by using the finite volume method to obtain the solution of the model. The accuracy and reliability of the model are verified by comparison with the results of the commercial simulator Eclipse and the field application. Based on the model's solution, this study emphasizes the analysis of the impact of the time-dependent mechanism and reservoir stress sensitivity on gas well productivity. Simulation results show that the time-dependent relative permeability curve can decrease the level of irreducible water saturation and promote the migration of irreducible water, resulting in an increase in water permeability and a decrease in gas permeability. This effect will reduce the period of stable gas production and increase the level of water production. Besides, reservoir stress sensitivity will reduce daily water production and accelerate gas well decline. It is necessary to control the production pressure difference reasonably during the production process to effectively reduce the negative impact of stress sensitivity effects. The results indicate that when the relative permeability curve and the reservoir permeability are constant, the real gas production capacity of the reservoir will be strengthened. The application of field case studies shows that the theoretical model exhibits stronger adaptability, achieves better fitting results, and can guide the compilation and adjustment of development plans for water-bearing tight gas reservoirs. These findings provide insights into understanding the effects of the time-dependent mechanism on gas production rates in tight gas reservoirs. Furthermore, this study offers useful guidance for the prediction of field-scale gas production.

[Simultaneous nitrification and denitrification by catching bed biofilm reactor].

Catching bed biofilm reactor combined with traditional biofilm process as a novel treatment was developed. The performance of the reactor for nitrogen removal was investigated. Steady removal effect with 81.7% of average COD removal rate was achieved in various hydraulic retention time (HRT). Even when hydraulic retention time (HRT) was only at 3.90 h with average NH4(+) -N volumetric loading of 0.47 kg/(m3 x d) and TN of 0.59 kg/(m3 x d), 92.7% of average NH4(+) -N removal rate and 67.5% of average TN removal rate were achieved. In the experiment dissolved oxygen (DO) was the most crucial factor for removal rates of TN and pH was a crucial factor for removal rates of NH4(+) -N, TN. The optimal condition was with DO 0.1-2.0 mg/L and pH of 7.0-7.5. Mechanisms of TN removal via simultaneous nitrification and denitrification in the experiment were analyzed.

Investigation of natural VOC emitted from tropical vegetations in China.

Twenty-three kinds of typical plants in Xishuangbanna, the tropical area of southwestern China, were screened to estimate the emission rates of isoprene and monoterpenes by adopting bag-enclosure and curette sampling methods followed by a GC-FID analysis. It was found that the Ficus species were mainly emitting isoprene and most tropical vegetations were mainly releasing monoterpenes. The results also showed that the emissions of isoprene were affected by both temperature and PAR(Photosynthetic Active Radiation), while monoterpene emissions were mainly temperature-dependent.