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The Influence of Nozzles on Bottomhole Flow Field of Dual-diameter PDC Bit
Yan Yan,Zhichuan Guan,Cai Yang,Han Yan 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.1
In order to improve cleaning efficiency of dual-diameter PDC bit, the total flow area, inclination angle and azimuth angle of bit’s pilot and reaming nozzles were analyzed. By numerical simulation, the velocity, pressure and particle distribution of bottomhole are obtained. The results show that low pressure area of pilot downhole decreases while low pressure of reamer downhole increases with the increase of total flow area. The mud velocity of central bottomhole has the negative relationship with inclination angle and positive relationship with azimuth angle. Best cleaning efficiency can be achieved when total flow area is 12 ㎠, inclination angles of pilot and reamer are respectively 15° and 25°, and azimuth angles of pilot and reamer are respectively 60° and 30°.
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Modeling of micro-annulus propagation along cementing interface in stimulated horizontal wellbore
Yan Yan,Guan Zhichuan,Yan Weijun 한국자원공학회 2021 Geosystem engineering Vol.24 No.5
Once there are micro-annulus at cementing interfaces in the process of reservoir stimulation, it is easy to form fluid channeling in the later development. Fluid channeling reduces the efficiency of reservoir development and even the service life of oil and gas wells. Based on the characteristics of ‘multi-stage’ in stimulated reservoir volume, a mathematical model was set up to calculate the interface debonding length driven by hydraulic pressure. The propagation process of microannulus in stimulated reservoir volume was also analyzed. The results show that the propagation speed of the micro-annulus gradually slows down with the progress of fracturing. Meanwhile, the debonding azimuth of the micro-annulus and the cement elastic modulus have dominant effects on the propagation length. It is recommended that the setting position of the packer be outranged from the debonding area of the cementing interface in the design of the stimulated reservoir volume scheme to avoid fluid channeling between the stages. This study can predict the unsealing length of cement sheath during hydraulic fracturing as a reference for the optimization of fracturing parameters.
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Zhai, Cong,Chou, Xiujian,He, Jian,Song, Linlin,Zhang, Zengxing,Wen, Tao,Tian, Zhumei,Chen, Xi,Zhang, Wendong,Niu, Zhichuan,Xue, Chenyang Elsevier 2018 APPLIED ENERGY Vol.231 No.-
<P><B>Abstract</B></P> <P>There is plenty of exploitable energy in the ambient environments. Triboelectric nanogenerator is an innovative electricity generation technology to convert the wasted mechanical energy into electrical energy. However, the output of conventional triboelectric nanogenerators cannot be employed efficiently because their tremendous internal resistance limits the current of electrons. Inspired by the principle of lightning rods, for the first time we propose the utilization of electrostatic discharge to improve the performance of triboelectric nanogenerators, which is realized by an opposite needles structure enclosed in an inert atmosphere. When this structure is connected in series with a vertical contact-separation triboelectric nanogenerator, the strong electric field near tips of two needles ionizes the gas around them, forming a conductive plasma channel between the tips, and releasing a mass of free charges. As a result, some exciting performances are obtained in triboelectric nanogenerator. The output peak-to-peak voltage is increased from 300 V to 1300 V, and the equivalent impedance of energy harvesting circuit is reduced from 100 MΩ to 10 kΩ. Especially in the optimal conditions, the maximum continuous power can even be significantly improved by 330.76%. Therefore, this work provides a new strategy for the energy conversion technology, which is significant for the advancement and application of triboelectric nanogenerators.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A strategy is proposed to improve the performance of triboelectric nanogenerators. </LI> <LI> The maximum continuous power can be boosted dramatically by electrostatic discharge. </LI> <LI> This design reduces the optimal impedance that is important for circuit matching. </LI> <LI> With this design triboelectric nanogenerators can directly drive low-power devices. </LI> <LI> This work is also significant for macro-energy conversion, such as ocean energy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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