Simulation study of hydrogen sulfide removal in underground gas storage converted from the multilayered sour gas field

A simulation study was carried out to investigate the temporal evolution of H_(2)S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H_(2)S (27.2 g/m^(3)), and the lower layer Jia-1 contains a low concentration of H_(2)S (14.0 mg/m^(3)). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H_(2)S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H_(2)S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H_(2)S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H_(2)S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H_(2)S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H_(2)S removal. After nine cycles, the produced gas’s H_(2)S concentration can be lowered to 20 mg/m^(3). Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H_(2)S concentration of the produced gas to 20 mg/m^(3), thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H_(2)S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.

Nanostructured Bi2S3 encapsulated within three- dimensional N-doped graphene as active and flexible anodes for sodium-ion batteries

Sodium-ion batteries （SIBs） have been increasingly attracting attention as a sustainable alternative to lithium-ion batteries for scalable energy storage. The key to advanced SIBs relies heavily upon the development of reliable anodes. In this respect, Bi2S3 has been extensively investigated because of its high capacity, tailorable morpholog, and low cost However, the common practices of incorporating carbon species to enhance the electrical conductivity and accommodate the volume change of Bi2S3 anodes so as to boost their durability for Na storage have met with limited success. Herein, we report a simple method to realize the encapsulation of Bi2S3 nanorods within three-dimensional, nitrogen-doped graphene （3DNG） frameworks, targeting flexible and active composite anodes for SIBs. The Bi2S3/ 3DNG composites displayed outstanding Na storage behavior with a high reversible capacity （649 mAh·g^-1 at 62.5 mA·g^-1） and favorable durability （307 and 200 mAh·g^-1 after 100 cycles at 125 and 312.5 mA·g^-1, respectively）. In-depth characterization by in situ X-ray diffraction revealed that the intriguing Na storage process of Bi2Sa was based upon a reversible reaction. Furthermore, a full, flexible SIB cell with Na0.4MnO2 cathode and as-prepared composite anode was successfully assembled, and holds a great promise for next-generation, wearable energy storage applications.