Water imbibition of shale and its potential influence on shale gas recovery-a comparative study of marine and continental shale formations

A large volume of fracturing fluid is pumped into a well to stimulate shale formation. The water is imbibed into the reservoir during this procedure. The effect of the imbibed water on gas recovery is still in debate. In this work, we study the spontaneous imbibition of water into marine shale samples from the Sichuan Basin and continental shale samples from Erdos Basin to explore the fluid imbibition characteristics and permeability change during water imbibition. Comparison of imbibition experiments shows that shale has stronger water imbibition and diffusion capacity than relatively higher permeability sandstone. Once the imbibition stops, water in shale has stronger ability to diffuse into deeper matrix, the water content in the main flow path decreases. Experiments in this study show that marine shale has stronger water imbibition capacity than continental shale. The permeability of continental shale decreases significantly with increasing imbibition water volume; however, the permeability of marine shale decreases at first and increases after a certain imbibition time. The induced fracture is obvious in the marine shale. SEM analysis shows that the relationship between the clay mineral and organic matter of continental shale is much more complex than that of marine shale, which may be the key factor restricting the water imbibition because the flow path is trapped by swelled clay minerals. Through this study, we concluded that whether gas recovery benefits from water imbibition depends on three aspects: 1) the diffusion ability of liquid into matrix; 2) the new cracks introduced by imbibed water; and 3) the formation sensibility. This study is useful for optimizing fracture fluids and determining the best flow-back method. (C) 2016 Elsevier B.V. All rights reserved

Insight into the compatibility behaviors between various rejuvenators and aged bitumen: Molecular dynamics simulation and experimental validation

The compatibility potential of rejuvenators plays an important role in improving the blending degree of rejuvenated bitumen. This study aims at estimating the efficiency of molecular dynamics (MD) simulation in predicting the compatibility between rejuvenators and aged binders, and exploring the influence of rejuvenator type, aging degree of bitumen, and temperature on the compatibility potential. The thermal stability of rejuvenated binders is evaluated to validate the compatibility prediction, and the underlying mechanism for the thermal stability difference between rejuvenators and aged bitumen is explained with the atomic‐scale parameters. The results revealed that the ranking on predicted compatibility and experimentally measured thermal stability for four rejuvenators is the same as AO > BO > NO > EO. The thermodynamic parameters of solubility parameter difference Δδ, Flory‐ Huggins parameter χ, and mixing free energy ΔGm are efficient to estimate the compatibility potential of various rejuvenators with aged bitumen. Moreover, the separation index (SI) parameters based on rheological and chemical indices are available to assess the thermal stability of rejuvenated bitumen. At the molecular scale, the compatibility and thermal stability issues between rejuvenators and aged bitumen are complicated and related to different aspects of the intermolecular interaction, dispersion degree, and molecular mobility.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement Engineerin

Accelerating DNA Variant Calling Algorithms on High Performance Computing Systems

Next generation sequencing (NGS) technologies have transformed the landscape of genomic research. With the significant advances in NGS technologies, DNA sequencing is more affordable and accessible than ever before. Meanwhile, many DNA sequence analysis tools have been developed to derive useful information from the raw sequencing data produced by NGS platforms. However, the massive amount of generated sequencing data poses a great computational challenge, thereby shifting the bottleneck towards the efficiency of the DNA sequence analysis tools. Due to the high computational needs, high performance systems are playing an important role for DNA sequence analysis. Moreover, dedicated hardware, including graphics processing units (GPUs) and field programmable gate arrays (FPGAs), have become important computational resources in many high performance systems.In this thesis, we use GPUs and FPGAs to accelerate a number of important bioinformatics algorithms. These represent the most computationally intensive algorithms of the GATK HaplotypeCaller (HC), which we use to improve its performance. GATK HC is a widely used DNA sequence analysis tool. By investigating GATK HC, three computationally intensive algorithms are selected, including the de Buijn graph (DBG) construction algorithm for micro-assembly, the pair-HMMs forward algorithm and the semi-global pairwise alignment algorithm. We first propose a novel GPU-based implementation of the DBG construction algorithm for micro-assembly. Compared with the software-only implementation, it achieves a speedup of up to 3x using synthetic datasets and a speedup of up to 2.66x using human genome datasets. We then propose a systolic array design to accelerate the pair-HMMs forward algorithm on FPGAs. Experimental results show that the FPGA-based implementation is up to 67x faster than the software-only implementation. In order to fully utilize the computing resources on FPGAs, we present a model to describe the performance characteristics of the systolic array design. Based on the analysis, we propose a novel architecture to better utilize the computing resources on FPGAs. The implementation achieves up to 90\% of the theoretical throughput for a real dataset. Next, we propose several GPU-based implementations of the pair-HMMs forward algorithm. Experimental results show that the GPU-based implementations of the pair-HMMs forward algorithm achieve a speedup of up to 5.47x over existing GPU-based implementations. Finally, we propose to accelerate the semi-global pairwise sequence alignment algorithm with traceback to obtain the optimal alignment on GPUs. Experimental results show that the GPU-based implementation is up to 14.14x faster than the software-only implementation. After accelerating these algorithms on GPUs and FPGAs, we integrate two GPU-based implementations into GATK HC. We first integrate the GPU-based implementation of the pair-HMMs forward algorithm into GATK HC. In single-threaded mode, the GPU-based GATK HC implementation is 1.71x faster than the baseline GATK HC implementation. For multi-process mode, a load-balanced multi-process optimization is proposed to ensure a more equal distribution of computation load between different processes. The GPU-based GATK HC implementation achieves up to 2.04x in load-balanced multi-process mode over the baseline GATK HC implementation in non-load-balanced multi-process mode. Next, we additionally integrated the GPU-based implementation of the semi-global alignment algorithm into the GATK HC. Experimental results shown that this implementation is 2.3x faster than the baseline GATK HC implementation in single-thread mode.Computer Engineerin

Towards critical low-temperature relaxation indicators for effective rejuvenation efficiency evaluation of rejuvenator-aged bitumen blends

The relaxation behavior affected by aging and rejuvenation plays a crucial role in its low-temperature cracking potential of bitumen. However, there are limited studies on the relaxation performance of rejuvenated bitumen under different rejuvenation conditions. This paper aims to propose critical indicators to assess the rejuvenation efficiency of low-temperature relaxation performance of various rejuvenated binders. The effects of rejuvenator type/dosage and aging level on relaxation parameters are investigated. The τ50s, t25%, and A are recommended as critical indicators based on their high sensitivities to influence factors and rejuvenation percentage scope. Additionally, molecular dynamic simulation outputs on virgin/aged bitumen and rejuvenators explain the difference in rejuvenation effectiveness of different rejuvenators. The results show that bio-oil rejuvenator exhibits the highest efficiency on regenerating the relaxation performance. All relaxation parameters of aged bitumen can be regenerated by adding rejuvenators. MD simulations reveal that the molecular mobility and free volume ratio of rejuvenators mainly cause the difference in rejuvenation efficiency on the relaxation property between various rejuvenators. The diffusion capacity of rejuvenator shows a more dominant effect on rejuvenation efficiency than fractional free volume.Pavement Engineerin

High-order-helix point spread functions for monocular three-dimensional imaging with superior aberration robustness

An approach for designing purely refractive optical elements that generate engineered, multi-order-helix point spread functions (PSFs) with large peak separation for passive, optical depth measurement is presented. The influence of aberrations on the PSF’s rotation angle, which limits the depth retrieval accuracy, is studied numerically and analytically. It appears that only Zernike modes with an azimuthal index that is an integer multiple of the number of PSF peaks introduce PSF rotation, and hence a depth estimation errors. This implies that high-order-helix designs have superior robustness with respect to aberrations. This is experimentally demonstrated by imaging an extended scene in the presence of severe system aberrations using novel, cost-e cient phase elements based on UV-replication on the wafer-scale.ImPhys/Imaging Physic

Exploring the recovery capacity of recycling agents on atomic-scale energy properties of aged bitumen and their potential correlations with high-temperature rheological performance

This study implements molecular dynamics (MD) simulations to explore the atomic-level energy properties of rejuvenated bitumen, considering the influence of different recycling agent (RA) types, dosages and aging levels of bitumen. Moreover, the potential correlations between energy indices and high-temperature performance of rejuvenated bitumen are explored. Our findings show that recycling agents can effectively reinstate the cohesive energy density (CED) values of aged bitumen, correlating well with their high-temperature rheological properties. The results reveal that the energy parameters of potential energy (UVEP), kinetic energy (UWEK), non-bond energy (EN), total energy (UVET), diagonal energy (UNED), and cross-terms energy (ECT) can reflect the restoration level of recycling agents (RAs) on atomic-level energy characteristics of aged bitumen. Compared to rutting failure temperature (RFT), elastic recovery (R3.2), and creep compliance (Jnr3.2), the zero-shear viscosity (ZSV) greatly correlates with CED. Meanwhile, the UWEK index from MD simulations demonstrates a strong correlation with high-temperature rheological indicators of rejuvenated bitumen. With the rise in UWEK, there is a linear decrease in the RFT, Log(ZSV), and R3.2 values of rejuvenated bitumen. Conversely, the Log(Jnr3.2) exhibits a linear increasing trend. However, the correlation patterns between rheological indicators and either EN or ECT are contingent on the aging degree of bitumen. Based on the correlation coefficient, the UWEK stands out as the primary choice among all energy indices for predicting high-temperature rheological performance of rejuvenated bitumen.Pavement Engineerin

Influence of swelling-degradation degree on rheological properties, thermal pyrolysis kinetics, and emission components of waste crumb rubber modified bitumen

This study investigated the effects of swelling-degradation degree on the rheological properties and thermal pyrolysis behaviors of crumb rubber modified bitumen (CRMB). The equilibrium viscosity of CRMB in 160 ◦Cswelling process is 10.5 Pa·s at 8 h. During the 200℃-degradation procedure, the viscosity increased to a maximum value of 20.58 Pa·s at 7.5 h and gradually reduced to a stable value of 11.09 Pa·s after 35 h. The swelling and degradation processes exhibit the opposite influence on the rheological properties of CRMB. Moreover, the degradation process accelerated the pyrolysis rate of CRMB but hindered the release of toxic gas CO and hydrocarbons.Pavement Engineerin

Balancing the sustainable component of ethylene-vinyl acetate for achieved better compatibility improvement of wax-based warm mix additives in bitumen

The ethylene-vinyl acetate (EVA) polymers are always doped into waxy bitumen to inhibit network of wax crystals in bitumen. However, the compatibility improvement behaviors between wax-based warm mix (WWM) additives and bitumen by EVA are not clear, and the sustainable components of EVA for corresponding WWM additives to achieve better compatibility improvement are also not determined. This paper investigated compatibility improvement behaviors between commonly used WWM additives and bitumen after the addition of EVA to obtain sustainable components of EVA through experimental method of activation energy of viscous flow (AEVF) and density function theory-molecular dynamic (DFT-MD) calculations. The results show that the repulsions between the end of main-chain with highest electronegativity in WWM additives and polar molecules of EVA can alleviate the aggregation behaviors of WWM additives and EVA displays the best and worst compatibility improvements for additives with shortest and longest carbon chains, respectively. The dispersed asphaltenes combined with EVA can form the composite wax inhibitors (WIs) systems to increase diffusion coefficient and reduce percentage increment values of cohesive energy density (CED) to further disrupt ordered degree of WWM additives. On this basis, the sustainable carbon numbers of main-chain for EVA that are slightly less than average carbon numbers of WWM additives will help to better improve the compatibility of WWM additives. This investigation can provide the inspiration on how to choose the sustainable components of EVA to achieve high-efficiency compatibility improvement for corresponding warm mix asphalts (WMAs) with different average carbon numbers.Pavement Engineerin

Use of waste oil/styrene-butadiene-rubber blends as rejuvenators for aged bitumen

This study elaborates the influence of blends formulated by waste oil (WO) and styrene-butadiene rubber (SBR) on thermo-mechanical and chemical compositional characteristics of rejuvenated bitumen. The results show that both WEO (waste engine oil) and WCO (waste cooking oil) can compensate viscous component for reclaimed bitumen, and the effect of WCO is more significant. However, WO-rejuvenated bitumen has considerable drawbacks in terms of temperature susceptibility and flow resistance, but dramatic improvement after being added with SBR has been noticed. Furthermore, the rejuvenation mechanism of WO/SBR blends is revealed by using FTIR tests, which shows that the physical blending mainly determines the rejuvenation mechanism when the WO/SBR blends are used in bitumen. The combination of WO and SBR is beneficial for improving the temperature susceptibility and rutting resistance of rejuvenated bitumen.Accepted Author ManuscriptPavement Engineerin

Toward the long-term aging influence and novel reaction kinetics models of bitumen

This study aimed to explore the long-term aging influence on chemo rheological properties and develop novel consecutive models for the long-term aging reaction kinetics of bitumen. The results revealed that the aging index was significantly dependent on the types of selected parameters. The Zero-order model was suitable to describe the long-term aging reaction kinetics of bitumen based on the oxygen containing functional groups with the reaction rate constants in 0.7–3.3*10−4 (mol L−1·h−1). In the SARA-based consecutive reaction model, the most optimum kinetics model for aromatic fraction was the Third-order reaction model and the corresponding reaction kinetics constant (k1) was 0.02 (mol·L−1)−2(h)−1. The Zero-order model could well fit the generation kinetics of asphaltene molecules with the reaction rate constant k2 of 3.85*10−4 mol·(L·h)−1. Further, the transformation reaction from the resin to asphaltene molecules was the control step of the whole consecutive reaction model. In this study, when one-unit resin fraction was generated, the consumption amount of aromatic fraction was about 2.82 units. Meanwhile, when one-unit resin fraction was consumed, only 0.58-unit asphaltene could be generated. The developed reaction kinetics models could be beneficial to predict the functional groups distribution and SARA fractions in aged bitumen with different aging degrees.Pavement Engineerin