Hydrogen permeability in subsurface

Clean hydrogen is a promising option for reducing carbon dioxide emissions, but it has not yet been used as an energy carrier at the scale required for meeting the net-zero target by 2050. Hydrogen molecules are smaller than nitrogen and methane molecules. Hydrogen, nitrogen, and methane have densities of 0.09 g/L, 1.25 g/L, and 0.71 g/L, respectively, at the standard temperature and pressure. Our knowledge of the geological formations is based on responses to the larger and heavier gases; it is unclear whether we can apply this knowledge to store hydrogen at the required scale.We investigate the single-phase flow of hydrogen in the subsurface and compare it with the single-phase flows of nitrogen and methane. The comparison with nitrogen is helpful because it is used under laboratory conditions. The comparison with methane is also beneficial because engineers understand its behavior under in-situ conditions. We use the Knudsen number (Kn) to determine the flow behaviors under laminar conditions within two domains. The first is a permeable medium representing a conventional gas reservoir, and the second is caprock. Our study shows that the existing knowledge of the first domain's permeability applies to hydrogen flow; however, it is unrealistic for the second domain. The single-phase permeability of the caprock obtained by nitrogen in the laboratory underestimates hydrogen permeability at low pressures (<10 MPa), and the deviation is a non-linear function of pressure. Our study also shows that hydrogen permeability is always larger than methane permeability in the caprock. The difference between the two, controlled by the reservoir pressure, reached 70% in the caprock. The presented results have applications if hydrogen storage in gas reservoirs becomes a reality.     

Study of physical and mechanical properties of polypropylene nanocomposites for food packaging application: Nano-clay modified with iron nanoparticles

Polypropylene (PP) nanocomposites were prepared via melt interaction of clay in a twin screw extruder. The evaluation of PP nanocomposites containing montmorillonite (OMMT) with or without iron nanoparticles modification was studied for food packaging applications. The nanocomposites were investigated by thermal, mechanical, morphological and gas barrier analyses. The X-ray diffraction patterns of all nanocomposites revealed an increment in d-spacing of the OMMT layers and proved the compatibility of neat PP and clay, along with the intercalation and partial exfoliation of the layers. Addition of nanoparticles had reverse effect on the intercalation and exfoliation of the clay to some extent. Transmitting optical and scanning electron microscopy revealed certain homogeneity with uniform distribution of OMMT and nano-particles in the PP matrix. According to the acquired thermal properties, a tendency for the melting temperatures increased with the clay concentration. Also, crystallization temperature and crystallinity decreased with the clay concentration; however, nanoparticles compensated the effect of clay. Despite of no significant change in the ultimate tensile strength and elongation properties were observed in nanocomposites, the yield strength presented a substantial enhancement and the rigidity as well. Melt flow index (MFI) examination revealed decreasing melt viscosity of nanocomposite through increasing OMMT and iron nanoparticles. Besides, OMMT showed a high capacity to improve oxygen and water vapor barrier properties of PP. The use of clay increased the mobility distance of the gas molecules, led to oxygen permeability of neat PP being reduced whereas nanoparticle acted as an active oxygen scavenger and was capable of intercepting and scavenging oxygen by undergoing a chemical reaction with. Migration test also showed no restrictions in the use of nanocomposite films in food packaging.     

Use of biochar-coated polypropylene fibers for carbon sequestration and physical improvement of mortar

Biochar is widely recognized as an effective material for sequestration of carbon dioxide. The possibility of using it as a coating material on polypropylene fibers to improve mechanical properties and permeability mortar is explored in this study. Effectiveness of two types of biochar – fresh biochar and biochar saturated with carbon dioxide prior to application as coating – on compressive and flexural strength, post-cracking behavior and permeability of mortar is studied. The biochar used was derived from mixed wood saw dust by pyrolysis at 300 °C. Experimental results show that application of fresh biochar coating offer significant improvement in compressive strength and flexural strength of mortar. Residual strength and post-cracking ductility of mortar with biochar coated fibers is found to be higher than control samples, although fresh biochar coating offers the best performance. Mortar with polypropylene fibers coated with fresh biochar shows higher impermeability, compared to reference samples and mortar with saturated biochar coated fibers. The findings suggest that biochar coating could be a potential solution to improve properties of fiber reinforced cementitious composites that also promotes waste recycling and carbon sequestration.     

Photon interaction with semiconductor and scintillation detectors

Molten salt is used as primary coolant flowing through graphite moderator channel of a molten salt reactor.Working at high temperature under radiation environment,the pore network structure of nuclear graphite should be well understood.In this paper,X-ray tomography is employed to study the 3D pore structure characteristics of nuclear grades graphite of IG-110,NBG-18 and NG-CT-10,and permeability simulation through geometries are performed.The porosity,number of pores and throats,coordination number and pore surface are obtained.NGCT-10 is of similar microstructure to IG-110,but differs significantly from NBG-18.The absolute permeabilities of IG-110,NG-CT-10 and NBG-18 are 0.064,0.090 and0.106 mD,respectively.This study provides basis for future research on graphite infiltration experiment.     

气藏采收率影响因素研究与启示——以靖边气田A井区为例

以鄂尔多斯盆地靖边气田A井区为例，采用单因素相关分析和数值模拟方法，对比研究了井网控制程度、储层物性及地层废弃压力对气藏采收率影响及其主次关系。结果表明，井网控制程度是影响采收率的首要因素，井网控制程度每增加10%，采收率提高8.5%；渗透率是影响采收率的重要因素，渗透率每增加10%，采收率平均增加6%；废弃压力对采收率亦有较大影响，废弃压力每降低10%，采收率可提高1.6%。三者对采收率影响综合排序为：井网控制程度>储层物性>废弃压力。分析认为，渗透率是储层固有属性，很难从根本改变；而废弃压力受井口外输压力和增压开采成本制约，降低幅度有限。因此，优化井网及增加井网控制程度是提高气藏采收率的有效途径。研究成果具有实践意义，可为改进气田开发方式和提高气藏采收率提供参考。     

Experimental determination of the permeability of engineering textiles: Benchmark II

In this second international permeability benchmark, the in-plane permeability values of a carbon fabric were studied by twelve research groups worldwide. One participant also investigated the deformation of the tested carbon fabric. The aim of this work was to obtain comparable results in order to make a step toward standardization of permeability measurements. Unidirectional injections were thus conducted to determine the unsaturated in-plane permeability tensor of the fabric. Procedures used by participants were specified in the guidelines defined for this benchmark. Participants were asked to use the same values for parameters such as fiber volume fraction, injection pressure and fluid viscosity to minimize sources of scatter. The comparison of the results from each participant was encouraging. The scatter between data obtained while respecting the guidelines was below 25%. However, a higher dispersion was observed when some parameters differed from the recommendations of this exercise.     

Permeability and dynamic elastic moduli of controlled porosity ultra-precision aerostatic structures

Porous ceramic aerostatic bearings enable precise and smooth motion and improved stiffness compared with widely used orifice restrictor bearings. However, the processing techniques so far used are too complex or rely in lowering the sintering temperature to increase fluid flow.     

Microstructure and microwave-frequency electromagnetic properties of Ni0.4Zn0.6Fe2O4/Ba0.6Sr0.4TiO3 composites

(x)Ni_0.4Zn_0.6Fe₂O₄+(1−x)Ba_0.6Sr_0.4TiO₃ composite ceramics with x=0.6, 0.7, 0.8, 0.9 and 1 were synthesized by solid state reaction method. The high dense composites have only two phases, i.e., Ni_0.4Zn_0.6Fe₂O₄ and Ba_0.6Sr_0.4TiO₃. The permittivity ε′ of the composites decreases slightly with the frequency increasing from 3 MHz to 1 GHz. The permittivity ε′′ of the composites also shows a little increase with frequency in the 3 MHz–1 GHz range. The permeability displays a relaxation resonance within the 3 MHz–1 GHz frequency range. The permeability μ′ increases while the cut-off frequency decreases with the Ni_0.4Zn_0.6Fe₂O₄ concentration, obeying the Snoek's law μ_if_r=constant. The permittivity ε′ of the composites decreases with Ni_0.4Zn_0.6Fe₂O₄ concentration. The composites have a relatively higher ε′ than the pure Ni_0.4Zn_0.6Fe₂O₄ at 1–10 GHz. In the frequency range of 1–10 GHz, the magnetic permeability μ′ reaches its maximum and μ′′ shows a minimum for the composite with x=0.6 in all ceramics. The permeability μ′ of the composites decreases with dc magnetic field at 1–10 GHz. The permeability shows a domain wall resonance, and the resonance frequency shifts to high frequency with the dc magnetic field. The permittivity was also influenced by the dc magnetic field due to a magnetodielectric effect.     

多注入轮次提高等流度二元驱采收率的实验研究

针对J16块试验区实施二元驱时,存在注入液在不同渗透性地层中推进速度不均匀、驱油效果变差等问题,开展了多注入轮次提高等流度二元驱采收率的室内实验研究。结果表明:在二元体系的成分和用量相同的条件下,不同注入轮次等流度二元驱采收率不同。实验条件下,四轮次注入时化学驱采出程度最高,达到35.2%,高出一轮次7.49%。多轮次注入二元体系较单轮次注入能够更好的控制含水上升速度,长时间维持较高注入压力,更大限度增强等流度驱油效果。     

储层渗透率对天然气开采的影响研究

随着石油开采量的降低,天然气的需求量便日益增长。为了充分开采气田,需要对气田的地质参数以及地质参数对天然气开采的影响有深入的了解,以提高气田的采收率。主要研究储层渗透率对天然气开采的影响,通过前期调研和数值模拟研究发现,稳产时间和采收率跟渗透率成正比关系,渗透率越大稳产时间越长,采收率越高;此外,随着渗透率的增大,稳产时间和采收率的增幅逐渐减小。因此储层渗透率越大,其对天然气开采的影响也就越小。