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Chitin biomass is the second largest biomass resource on Earth but under-utilized. In this study, pretreated shrimp shells were converted into value-added platform chemical 5-hydroxymethylfurfural (HMF) using microwave hydrothermal treatment. Under the combined pretreatment of acid decalcification at room temperature and microwave-assisted alkali deacetylation, the HMF yield could reach 1.8 wt%. The key process parameters, including the holding temperature, holding time, and pH value, were evaluated and optimised. The highest HMF yield of 6.5 wt% was obtained at 202.6°C at a holding time of 5.8 min and a pH value of 1.5. This result demonstrates the potential of synchronously treating waste and recycling it, thereby offering a highly promising valorisation strategy for chitin-biomass utilisation. [ABSTRACT FROM AUTHOR]

The eastern Ordos Basin plays an important role in China's coalbed methane (CBM) industry, boasting considerable CBM resources and pronounced reservoir heterogeneity, making it an ideal site for comparative research on deep and shallow CBM geology. In order to dissect the fundamental reasons for significant differences in production capacity between blocks and promote mutual learning from successful development experiences, this paper conducts a systematical study on the distribution characteristics of in-situ geological conditions of CBM reservoirs based on extensive well-testing data. Additionally, through coal permeability sensitivity experiments on coal samples with various Ro max values, burial depths, and initial permeabilities, this study explores the change law of permeability during the process of CBM extraction. The results indicate that as the burial depth of coal seam increases, so do the temperature, pressure, and stress. Moreover, the distribution of geothermal gradient, reservoir pressure gradient, horizontal stress gradient, and lateral pressure coefficient tends to converge with increasing burial depth, with a turning depth typically between 1,000 and 1,500 m. Coal seams below 1,500 m generally exhibit a normal-fault type stress field with normal-overpressure. In-situ permeability decreases with depth, but the permeability in deep stress relief zones can be maintained at a relatively high level. A lower initial permeability corresponds to a smaller stress sensitivity coefficient and reduced temperature sensitivity effects, resulting in slower permeability damage during CBM extraction. However, when the reservoir pressure drops to depletion pressure, the maximum damage rate of permeability increases significantly, underscoring the importance of reservoir reconstruction in deep CBM development. This study provides a theoretical basis for selecting favorable areas for CBM exploration and development, as well as for designing efficient development plans in practice. [ABSTRACT FROM AUTHOR]

China is rich in high-grade coalbed methane resources, accounting for one-third of the total amount of coalbed methane resources. Qinshui Basin is the main high ranking coalbed methane mining basin in China. In the early stage of CBM development, low-production and low-efficiency wells were formed in the process of block development because of an insufficient understanding of reservoir geological conditions. The existence of low-yield and low-efficiency wells with low output and a poor development benefit seriously restricts the efficient development of coalbed methane. In order to improve the overall development efficiency of coalbed methane fields, how to revitalize low-yield and low-efficiency wells is the main problem facing the development process of coalbed methane. With the deepening understanding of the study area geology, the formation of low-yield and low-efficiency wells has been basically identified. With the advancement of development technology, developers have the ability to retrofit some low-producing and inefficient wells. Low-production and low-efficiency wells are widely distributed. It is difficult to find the criteria for classifying low-producing and low-efficiency wells because of the great differences in geological conditions and reservoir physical properties in different blocks. In addition, the causes of a low-production and low-efficiency well are complex, as the same well is often caused by many reasons, and how to identify the causes of low-production and low-efficiency wells is difficult. In recent decades, developers have studied many methods to retrofit low-production wells, but the retrofit results are not satisfactory. How to choose an economical and efficient reservoir reconstruction method to revitalize low-production and low-efficiency wells is particularly important. This paper starts with the definition of low-production and low-efficiency wells in different blocks, combining an economic evaluation and productivity characteristics to judge whether they are low-production and low-efficiency wells, and defines the distribution of low-production and low-efficiency wells in blocks. The reasons for the formation of low-production and low-efficiency wells are analyzed with the geological characteristics, production dynamic performance, and engineering reconstruction effects. This paper makes a comparative analysis of the current relatively mature low-production and low-efficiency well treatment measures, clearly identifies the advantages and disadvantages of different treatment measures, and takes corresponding stimulation measures for different causes of low-production and low-efficiency wells. The research shows that there are 687 low-production and low-efficiency wells in block A, accounting for 69.4% of the total number of wells, and the low-production and low-efficiency wells account for a relatively large proportion; so, it is necessary to treat them. The main causes of low-production and low-efficiency wells are geology, engineering and drainage systems. The geological reason mainly refers to the low gas production of coalbed methane wells influenced by three factors: resource abundance, faults, and collapse columns. According to the different causes, three treatment measures of large-scale secondary fracturing, temporary plugging, and diversion fracturing and foam fracturing are put forward. The research method in this paper is targeted at different geological conditions so it can be used to guide the treatment of low-yield and low-efficiency wells in other CBM blocks, and it has very important significance for revitalizing the existing low-efficiency CBM assets and improving the development efficiency of CBM. [ABSTRACT FROM AUTHOR]

To more accurately study the adsorption characteristics of coalbed methane in deep coal reservoirs, and to understand the effects of different factors such as temperature, pressure and water on adsorption of CH4 in coal seams, we accurately described the isothermal adsorption curves of CH4 in four different rank coals under different temperature and pressure conditions, before and after different fluids. In this paper, we adopted simplified Ono-Kondo lattice model fitting method. The results show that pressure has a positive effect on adsorption of CH4, and temperature has a negative effect on adsorption of CH4. The higher the pressure is, the greater the influence of adsorption on temperature. Moisture will reduce the maximum adsorption capacity of coal to CH4, which is not conducive to adsorption of CH4. Supercritical CO2 extraction can increase the micropore surface area and pore volume of coal to increase the maximum adsorption capacity of CH4 in coal seam. The maximum adsorption amount shows a “U” type relationship with the change of coal rank.

The investigation of micropore structure changes by H2O2-coal reactions can provide an understanding of macroscopic effects of oxidant stimulation on coalbed methane (CBM) diffusion and seepage behavior. In this study, we prepared H2O2 to oxidize coals with three different ranks, and scanning electron microscopy (SEM), high-pressure mercury intrusion (HPMI), low-temperature N2 adsorption (LT-N2A), low field nuclear magnetic resonance (LF-NMR) tests were conducted to characterize variations in micropore structures of the coals treated with H2O2. The results showed that H2O2 treatment can change, to varying degrees, the pore structure characteristics of coals with different rank. The SEM results showed that coal surface structures were destroyed by oxidation and dissolution, and pores and fissures became more developed after H2O2 treatment. The HPMI and LT-N2A tests revealed that the porosity, total pore volume, maximum pore throat diameter and average pore diameter of coals with different rank generally increased after H2O2 treatment. The HPMI-derived fractal dimensions of seepage pores decreased after oxidation, indicating that the heterogeneity of pore structure was weakened and the connectivity was improved. The fractal dimensions of adsorption pores derived from LT-N2A generally showed a downward trend, indicating that oxidation can reduce the roughness and complexity of adsorption pores, and improve the pore connectivity. The results of LF-NMR tests also corroborated the above findings. The mechanism of coal permeability enhancement by H2O2 treatment is reflected mainly in the oxidation and dissolution of organics and inorganic minerals. Thus, H2O2 treatment can lead to more significant oxidation effects on low- and medium-rank coals. This study suggests that H2O2 can be used for fracturing addition fluid in low- to medium-rank coals to improve coal permeability, thereby remove plugging and enhancing CBM recovery effectively. [ABSTRACT FROM AUTHOR]