Experimental investigations of fracturing fluid flowback and retention under forced imbibition in fossil hydrogen energy development of tight oil based on nuclear magnetic resonance

Experimental works have proved that imbibition under forced pressure (FP, the difference between hydraulic fluid pressure and original pore pressure) has a positive effect on fossil hydrogen energy development in tight oil reservoir. However, the knowledge of the influence of imbibition under forced pressure (forced imbibition, FI) on fracturing fluid flowback and water retention is still limited. In this paper, experiments were designed and conducted to reveal the mechanism of fracturing fluid flowback and water retention under imbibition effect in tight sandstones. As a comparison, unconsolidated sandstones were also investigated in this study. Core samples were divided into two categories: the imbibition ones (treated by imbibition) and the filtration ones (treated by displacement), in accordance with the real oil-water distribution after well shut-in. An imbibition core and a filtration core were stitched together to conduct a flowback experiment. During the experiment, fluid distribution in different pore sizes was monitored continuously by using a low-field nuclear magnetic resonance device. Results show that the flowback recovery in tight sandstones is much lower than that in unconsolidated sandstones due to the difference of pore structure. Meanwhile, forced imbibition leads to higher oil recovery than spontaneous imbibition (SI) in tight sandstones since forced pressure enhances water imbibition. The water imbibed into small-macro and macro pores contributes the major flowback recovery, but the imbibed water in micro pores is rather difficult to displace and finally retains in these pores during the flowback process. Overall, forced imbibition not only enhances oil recovery but also increases water retention, explaining the mechanism of well productivity increase by using the shut-in method in the field. This study can help to clarify the influence of forced imbibition on fracturing fluid flowback and enhancement of fossil hydrogen development, and further provide guidance for flowback designs.     

一种基于单谐次角振动信号的内燃机工作状态监测新方法

分析了内燃机轴承低阶扭振振型特性;提出了单谐次准等差振幅模型。当内燃机轴系满足此条件时,提出一种利用曲轴低谐次扭振信号幅值监测内燃机工作状态的新方法。并以某机车柴油发电机组轴系为对象进行了应用研究,验证了本方法的实用性和诊断准确性。新方法不需要其他结构参数,简便易行,而且准确度高,适用广泛,有较强的工程实用价值。     

SiON／SiN太阳电池双层减反膜的性能研究

报道了用电子回旋共振化学气相沉淀积技术淀积ＳｉＯＮ／ＳｉＮ双层硅太阳电池减反膜的实验研究。用红外吸收谱，俄歇电子谱以及二次离子质谱等实验方法对薄膜的组分，结构２，界面过渡区的特性以及膜层中的氢分布进行了分析，实验表明：在制备减反射膜中，要获得较佳的减反效果，应尽量降低淀积温度，增大微波功率。     

风力机侧向振动稳定性研究

对风力机系统的动态稳定性问题，即风力机侧振与叶轮摆轮的耦合运动，以及由叶片静不平衡引起的响应问题进行了研究。     

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO₂ catalyst doped with Ca and Ni/ZrO₂ were employed in the CO₂ methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO₂ and chemical analysis. The catalytic behavior of these catalysts in the CO₂ methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO₂, the metallic surface area did not change whereas the CO₂ consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca⁺² but also some Ni²⁺ are on the ZrO₂ surface lattice of the Ni/CaZrO₂ catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO₂ methanation rate increases. Moreover, the number of active sites of the CO₂ methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.     

Quantification and statistical significance analysis of group separation in NMR-based metabonomics studies

Currently, no standard metrics are used to quantify cluster separation in PCA or PLS-DA scores plots for metabonomics studies or to determine if cluster separation is statistically significant. Lack of such measures makes it virtually impossible to compare independent or inter-laboratory studies and can lead to confusion in the metabonomics literature when authors putatively identify metabolites distinguishing classes of samples based on visual and qualitative inspection of scores plots that exhibit marginal separation. While previous papers have addressed quantification of cluster separation in PCA scores plots, none have advocated routine use of a quantitative measure of separation that is supported by a standard and rigorous assessment of whether or not the cluster separation is statistically significant. Here quantification and statistical significance of separation of group centroids in PCA and PLS-DA scores plots are considered. The Mahalanobis distance is used to quantify the distance between group centroids, and the two-sample Hotelling's T² test is computed for the data, related to an F-statistic, and then an F-test is applied to determine if the cluster separation is statistically significant. We demonstrate the value of this approach using four datasets containing various degrees of separation, ranging from groups that had no apparent visual cluster separation to groups that had no visual cluster overlap. Widespread adoption of such concrete metrics to quantify and evaluate the statistical significance of PCA and PLS-DA cluster separation would help standardize reporting of metabonomics data.     

Preparation of new proton exchange membranes using sulfonated poly(ether sulfone) modified by octylamine (SPESOS)

Sulfonated poly(arylene ether sulfone) (SPES) has received considerable attention in membrane preparation for proton exchange membrane fuel cell (PEMFC). But such membranes are brittle and difficult to handle in operation. We investigated new membranes using SPES grafted with various degrees of octylamine. Five new materials made from sulfonated polyethersulfone sulfonamide (SPESOS) were synthetized with different grades of grafting. They were made from SPES, with initially an ionic exchange capacity (IEC) of 2.4 meq g⁻¹ (1.3 H⁺ per monomer unit). Pristine SPES with that IEC is water swelling and becomes soluble at 80 °C, its proton conductivity is in the range of 0.1 S cm⁻¹ at room temperature in aqueous H₂SO₄ 1 M, similar to that of Nafion^®. After grafting with various amounts of octylamine, the material is water insoluble; membranes are less brittle and show sufficient ionic conductivity. Proton transport numbers were measured close to 1.