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Coalbed methane reservoirs exhibit a low strength and high heterogeneity, rendering them susceptible to coal fines generation during hydraulic fracturing operations. The detrimental impact of coal fines on the conductivity of the propped fracture has been overlooked, leading to a substantial negative effect on the later-stage recovery of coalbed methane reservoirs. Moreover, the particle size distribution of the composite proppant also affects the conductivity of the propped fracture. To mitigate the damage caused by coal fines to the conductivity of the proppant pack in CBM reservoirs, this study conducted conductivity tests on actual coal rock fractures. The aim was to assess the effect of various particle size ratios in composite proppant blends on the conductivity of complex fractures in CBM reservoirs. The ultimate goal was to identify an optimized proppant blending approach that is suitable for hydraulic fracturing in coal seams. The results indicated that, in terms of the short-term conductivity of coalbed methane reservoirs, the conductivity of composite proppants is primarily influenced by the proportion of large or small particles. A higher proportion of large particles corresponds to a stronger conductivity (e.g., the conductivity is highest at a particle ratio of 5:1:1 for large, medium, and small particles). On the other hand, a higher proportion of small particles leads to a poorer conductivity (the conductivity is lowest when the particle ratio is 1:1:5). In the long-term conductivity of coalbed methane reservoirs, the fluid flushing of the fracture surfaces generates coal fines, and small particles can fill the gaps between larger particles, hindering the infiltration of coal fines. Therefore, it is important to control the particle size ratio of composite proppants, with a predominant proportion of larger particles. This approach can maintain long-term conductivity and prevent the excessive infiltration of coal fines, thereby avoiding fracture blockage (e.g., the conductivity is highest at a particle ratio of 5:1:5, followed by a ratio of 3:1:3). Furthermore, considering the influence of proppant placement methods and the support effect on near-wellbore opening fractures and far-end sliding fractures, segmented placement is utilized to fully fill the fractures for short-term conductivity, whereas mixed placement is employed for long-term conductivity to achieve a balance in particle gaps and hinder the infiltration of coal fines. The findings of this study contribute to the understanding of proppant selection and placement strategies for efficient hydraulic fracturing in coalbed methane reservoirs. [ABSTRACT FROM AUTHOR]

This paper proposes a continuous-rate clock-data-recovery (CDR) circuit that covers a data rate range of 500Mbps to 1.7Gbps. The proposed CDR is based on the phase interpolation principle and implemented in 130nm CMOS. The design utilizes digital voter and phase control logic instead of analog charge pump and filter, which facilitates migration among different technologies. To avoid the phase interpolator (PI) getting into the nonlinear region, multiple modes are selected to limit the frequency range of the sampling clock within 500MHz to 1GHz. A 5mm2 test chip is fabricated, where the CDR core occupies 0.359mm2 of silicon area. The PI achieves a resolution of 7 bits and a good linearity of 0.9955. The proposed CDR also achieves a BER less than 10 and has a frequency tracking range of ppm. The power consumed by the proposed CDR is 32.6mW/Gbps. [ABSTRACT FROM AUTHOR]

With the improvement of environmental protection requirements in offshore oil and gas exploration, there is a great demand to find environmentally friendly surfactants for cementing preflush fluids. In the present paper, the application potential of three biosurfactants of rhamnolipid, lipopeptide, and sophorolipid in the preflush fluid was evaluated through a series of experiments. The experiments studied the interfacial tension (IFT) of the biosurfactants, resistance to temperature, salt resistance (sodium chloride and sea salt), and the influences of the studied biosurfactants on the rheological compatibility and capabilities to convert the wettability of the formation from oil-wet to water-wet, mud cake removal efficiency, and to improve the interfacial bonding properties of the preflush fluid. The results showed that rhamnolipid, lipopeptide, and sophorolipid exhibited excellent surface activities in high-temperature and sodium chloride (NaCl) environments. When exposed to sea salt, lipopeptides lost their function due to agglomeration, while rhamnolipids and sophorolipids maintained structural stabilities and high surface activities. When rhamnolipid was mixed with sophorolipid in a ratio of 2:1 at the same concentration, the combined biosurfactant had the best surface activity among the studied surfactants. The combined biosurfactant not only had good rheological compatibility with the drilling fluid and cement slurry but also showed excellent properties in the removal of mud cake. In addition, the effect of the removal of the mud cake was verified by the gas channeling experiment. The experimental results show that the presence of mud cake can reduce the bonding strength. When rhamnolipid was mixed with sophorolipid in a ratio of 2:1 at the same concentration, the removal efficiency of mud cake was the highest, and the interfacial bonding property of the cement sheath can be improved., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)