基于振动实测的非均质地层钻头失效分析与对策

四川盆地作为国内页岩气开发的重点区域,通过近几年的不断攻关和实践,机械钻速得到了提高,但由于受地层复杂、可钻性差、非均质性强等地质因素的影响,导致井下钻柱系统不良振动剧烈,容易出现钻头损坏严重、钻速较低等问题,严重影响了钻井时效。为了解决上述难题,以该盆地涪陵工区上二叠统龙潭组—中二叠统茅口组为例,采用井下振动高频测量工具的实测手段,测量了钻头—钻柱系统的动态振动加速度参数,结合地层的岩性和矿物组分分析,研究钻头失效原因与对策,并开展了现场试验。研究结果表明:①在非均质地层中钻进的钻头—钻柱系统产生了大于40 m/s~2的高幅值瞬时冲击振动,高幅值的瞬时冲击是导致钻头先期失效的主要原因;②提出了抑制高幅值的瞬时冲击振动采用"减振+增压"工具组合和避免井下工具共振的钻井参数;③采用钻井新参数的试验井比邻井的高幅值瞬时振动降低了17%,单只钻头进尺增加24%,钻头工作环境得到了较大的改善,钻头使用数量减少。结论认为,该研究成果能够有效地改善钻头—钻柱系统的振动状态,有利于达成延长钻头使用寿命的目标。     

Combined hardware–software multi-parallel prefiltering on the Convey HC-1 for fast homology detection

Protein databases used in research are huge and still grow at a fast pace. Many comparisons need to be done when searching similar (homologous) sequences for a given query sequence in these databases. Comparing a query sequence against all sequences of a huge database using the well-known Smith–Waterman algorithm is very time-consuming. Hidden Markov Models pose an opportunity for reducing the number of entries of a database and also enable to find distantly homologous sequences. Fewer entries are achieved by clustering similar sequences in a Hidden Markov Model. Such an approach is used by the bioinformatics tool HHblits. To further reduce the runtime, HHblits uses two-level prefiltering to reduce the number of time-consuming Viterbi comparisons. Still, prefiltering is very time-consuming. Highly parallel architectures and huge bandwidth are required for processing and transferring the massive amounts of data. In this article, we present an approach exploiting the reconfigurable, hybrid computer architecture Convey HC-1 for migrating the most time-consuming part. The Convey HC-1 with four FPGAs and high memory bandwidth of up to 76.8 GB/s serves as the platform of choice. Other bioinformatics applications have already been successfully supported by the HC-1. Limited by FPGA size only, we present a design that calculates four first-level prefiltering scores per FPGA concurrently, i.e. 16 calculations in total. This score calculation for the query profile against database sequences is done by a modified Smith–Waterman scheme that is internally parallelized 128 times in contrast to the original Streaming ‘Single Instruction Multiple Data (SIMD)’ Extensions (SSE)-supported implementation where only 16-fold parallelism can be exploited and where memory bandwidth poses the limiting factor. Preloading the query profile, we are able to transform the memory-bound implementation to a compute- and resource-bound FPGA design. We tightly integrated the FPGA-based coprocessor into the hybrid computing system by employing task-parallelism for the two-level prefiltering. Despite much lower clock rates, the FPGAs outperform SSE-based execution for the calculation of the prefiltering scores by a factor of 7.9.     

Characterization of spectral responses of humic substances upon UV irradiation using two-dimensional correlation spectroscopy

The spectral responses of a leaf litter derived humic substance (LLHS) and Suwannee River fulvic acid (SRFA) upon ultraviolet (UV) A irradiation were characterized using two-dimensional correlation spectroscopy (2D-COS) based on the absorption and the synchronous fluorescence spectra at different irradiation times. A 12 day irradiation on the humic substances (HS) resulted in higher reduction of the absorbance relative to the dissolved organic carbon concentration, suggesting that aromatic chromophores were preferentially oxidized and/or non UV-absorbing compounds were generated by the photobleaching. Synchronous fluorescence spectra revealed the preferential removal of fulvic-like and humic-like fluorophores and delayed response of protein-like fluorescence upon the irradiation. The spectral features at long wavelengths (>430 nm) appear to be affected by intra-molecular interactions of the individual chromophores associated with shorter wavelengths. Absorption-based 2D-COS demonstrated that there are three types of absorption bands for the two HS, which changed sequentially in the order of 290-400 nm → 200-250 nm → 250-290 nm. In addition, two or three distinctive fluorescence bands in response to the irradiation were identified from 2D-COS. The sequential orders and the associated wavelength bands were possibly explained by the irradiation wavelengths and the differences between direct and indirect photochemical reactions. The interpretation of the 2D-COS results was very consistent with the kinetic rate constants individually calculated at several discrete wavelengths. Our study demonstrated that 2D-COS could be used as a powerful tool in identifying distinctive bands of HS that have dissimilar behavior and the associated sequential orders by visualizing the spectral changes at continuous wavelengths.     

Numerical investigation for the suitable choice of bubble diameter correlation for EMMS/bubbling drag model

Mesoscale bubbles exist inherently in bubbling fluidized beds and hence should be considered in the constitutive modeling of the drag force. The energy minimization multiscale bubbling (EMMS/bubbling) drag model takes the effects of mesoscale structures (i.e., bubbles) into the modeling of drag coefficient and thus improves the coarse-grid simulation of bubbling and turbulent fluidized beds. However, its dependence on the bubble diameter correlation has not been thoroughly investigated. The hydrodynamic disparity between homogeneous and heterogeneous fluidization is accounted for by the heterogeneity index,H_d, which can be affected by choice of bubble diameter correlation. How this choice of bubble diameter correlation influences the model prediction calls for further fundamental research. This article incorporated seven different bubble diameter correlations into EMMS/bubbling drag model and studied their effects onH_d. The performance of these correlations has been compared with the correlation used previously by EMMS/bubbling drag model. We found that some of the correlations predicted lower H_d by order of a magnitude than the correlation used by the original EMMS/bubbling drag. Based on such analysis, we proposed a modification in the EMMS drag model for bubbling and turbulent fluidized beds. A computational fluid dynamics (CFD) simulation using two-fluid model with the modified EMMS/bubbling drag model was performed for two bubbling and one turbulent fluidized beds. Voidage distribution, time averaged solid concentration and axial solid concentration profiles were studied and compared with the previous version of the EMMS/bubbling drag model and experimental data. We found that the right choice of bubble diameter correlations can significantly improve the results for CFD simulations.     

A three-dimensional heterogeneity analysis of electrochemical energy conversion in SOFC anodes using electron nanotomography and mathematical modeling

In this paper a fully three dimensional, multiphase, micro-scale solid oxide fuel cell anode transport phenomena numerical model is proposed and verified. The Butler-Volmer model was combined with empirical relations for conductivity and diffusivity - notably the Fuller-Shetler-Giddings equation, and the Fickian model for transport of gas reagents. FIB-SEM tomography of a commercial SOFC stack anode was performed and the resulting images were processed to acquire input data. A novel method for estimating local values of Triple Phase Boundary length density for use in a three-phase, three-dimensional numerical mesh was proposed. The model equations are solved using an in-house code and the results were verified by comparison to an analytical solution within the range of its applicability. A limited parametric study was performed to qualitatively assess simulation performance and impact of heterogeneity. Despite the high dependence of the SOFC anode performance on the geometry of its anisotropic, three-phase microstructure there are very few micro-scale numerical models simulating transport phenomena within these electrodes.     

NBTI alleviation on FinFET-made GPUs by utilizing device heterogeneity

Recent experimental studies reveal that FinFET devices commercialized in recent years tend to suffer from more severe NBTI degradation compared to planar transistors, necessitating effective techniques on processors built with FinFET for endurable operations. We propose to address this problem by exploiting the device heterogeneity and leveraging the slower NBTI aging rate manifested on the planar devices. We focus on modern graphics processing units in this study due to their wide usage in the current community. We validate the effectiveness of the technique by applying it to the warp scheduler and L2 cache, and demonstrate that NBTI degradation is considerably alleviated with slight performance overhead.     

3D analytical solution for a functionally graded transversely isotropic piezoelectric circular plate under tension and bending

A three-dimensional (3D) analysis of a functionally graded piezoelectric circular plate under tension and bending is carried out. A direct displacement method is developed, with analytical solutions obtained for plate with either free or simply-supported edge conditions. The material properties of the plate can vary arbitrarily along the thickness except that the strain-energy function should be positive definite as required for stable materials and certain integrable conditions are assumed valid during the derivation. The validity of the present solutions is discussed both analytically and numerically. Numerical analyses are made for a specific functionally graded material to show the influence of material heterogeneity on the piezoelastic field.     

静载荷作用下磷矿石多颗粒的破裂过程数值试验

为了研究静载荷作用下磷矿石多颗粒的破碎规律,用岩石破裂过程分析系统RFPA2D建立了在静载荷作用下多颗粒磷矿石在破碎腔内破坏的数值模型,分析探讨了静载荷和破碎腔的约束作用对磷矿石多颗粒试样的破碎效果和能量消耗的影响。数值模拟结果表明,静载荷破碎多颗粒磷矿石时,在破碎腔中间的磷矿石颗粒的破坏单元数相对较多;破碎腔内磷矿石在一定的压缩变形范围内破碎单元消耗的能量相对较少。因此,为了获得较好的破碎效率和节能效果,在设计破碎机时应考虑颗粒的破碎行为。     

变形介质低渗透气藏水平井产能分析

大量实验研究证实低渗透气藏中气体渗流需要克服启动压力梯度,同时气体渗流还要受应力敏感效应影响。针对变形介质低渗透气藏,利用保角变换等方法,考虑非均质性、压力敏感效应、启动压力梯度以及表皮效应等影响因素,推导出了水平井产量计算模型。研究表明,各种考虑影响因素对低渗透气藏水平井的产量影响呈近似线性变化关系;非均质性的影响程度最大,其垂向渗透率高将有利于水平井产量的提高。通过实例计算说明该模型产能预测结果的相对误差小。     

Structural characterization of poly(ε-caprolactone)-grafted cellulose acetate and butyrate by solid-state C NMR, dynamic mechanical, and dielectric relaxation analyses

Investigations were made into the molecular dynamics and intercomponent mixing state in solid films of two series of cellulosic graft copolymers, cellulose acetate-g-poly(ε-caprolactone) (CA-g-PCL) and cellulose butyrate-g-PCL (CB-g-PCL), both series being prepared over a wide range of compositions with CAs or CBs of acyl DS ≈ 2.1, 2.5, and 2.95. It was shown by T_1ρ^H measurements in solid-state ¹³C NMR spectroscopy that all the copolymer samples, except ones using CA of DS = 2.98, formed an amorphous monophase in which the trunk and graft components were mixed homogeneously at least in a scale of a few nanometers. However, those copolymer samples gave, more or less, a response of dynamic heterogeneity, when examined under mechanical oscillation. Through dielectric relaxation measurements, a clear comparison was made between the CA-g-PCL and CB-g-PCL series, regarding the cooperativeness in segmental motions of the trunk and graft chains, directly associated with the extent of the dynamic heterogeneity. The cooperativeness was generally higher in the CB-based copolymer series, probably due to working of the butyryl substituent as an internal compatibilizer.