Numerical analysis of the effect of natural microcracks on the supercritical CO2 fracturing crack network of shale rock based on bonded particle models

The problem of predicting the geometric structure of induced fractures is highly complex and significant in the fracturing stimulation of rock reservoirs. In the traditional continuous fracturing models, the mechanical properties of reservoir rock are input as macroscopic quantities. These models neglect the microcracks and discontinuous characteristics of rock, which are important factors influencing the geometric structure of the induced fractures. In this paper, we simulate supercritical CO₂ fracturing based on the bonded particle model to investigate the effect of original natural microcracks on the induced‐fracture network distribution. The microcracks are simulated explicitly as broken bonds that form and coalesce into macroscopic fractures in the supercritical CO₂ fracturing process. A calculation method for the distribution uniformity index (DUI) is proposed. The influence of the total number and DUI of initial microcracks on the mechanical properties of the rock sample is studied. The DUI of the induced fractures of supercritical CO₂ fracturing and hydraulic fracturing for different DUIs of initial microcracks are compared, holding other conditions constant. The sensitivity of the DUI of the induced fractures to that of initial natural microcracks under different horizontal stress ratios is also probed. The numerical results indicate that the distribution of induced fractures of supercritical CO₂ fracturing is more uniform than that of common hydraulic fracturing when the horizontal stress ratio is small.     

BPM授时台至南极长城站短波场强测试分析

本文讨论了在南极长城站收测BPM授时台时号场强的实验数据并和国际广播行政大会推荐的计算方法得到的预测值进行了比较。结果表明,在此条电路上两者较吻合,均方根偏差为6.9dBμv/m,从而在实验上初步验证了FTZ方法的可用性。     

一种新型非基于慢变包络近似的三维有限元束传播法

提出了一种新型非基于慢变包络近似的三维有限元束传播法.该方法相较Hadley所提出的广角束传播法,在分析光信号与光波导之间相互作用时同时考虑了载波和调制波对传输特性的影响,更具一般性且精度更高.通过与已发表的权威文献相比,在相同的计算资源下,精度提高了10%.     

Discrete element simulation of the effect of particle size on the size of fracture process zone in quasi-brittle materials

Experimental tests performed on quasi-brittle materials show that a process zone develops ahead of a crack tip. This zone can affect the strength and the deformation pattern of a structure. A discrete element approach with a softening contact bond model is utilized to simulate the development of the fracture process zone in the three-point bending tests. Samples with different dimensions and particle sizes are generated and tested. It is shown that as the material brittleness decreases, the width of the process zone becomes more dependent on the specimen size. Furthermore, the increase in the particle size, results in increase in the width of the process zone. A dimensional analysis together with the numerical results shows that the width of process zone is a linear function of particle size (radius). This finding is discussed and compared with published experimental data in the literature.     

高稳定高可靠的SFS-Ⅱ型遥测地震台网时间服务设备

ＳＦＳ－Ⅱ遥测地震台网时间服务设备是继国家地震局于７０年代投资研制的“７６８”钟站后,为模拟遥测地震台网研制产投入小批量生产的换代产品。该产品自１９９３年研制完成后,成功地运用在西昌大桥水库,青海花土沟油田,黄河小浪底和李家峡水库等遥测台网记录为中心。其核心心部件：ＳＺＺ－Ｉ型数字钟和ＢＰＭ接收机,先后被成都遥测台网自 遥测台网,丹江水库台网,西藏测台网,隔河岩水库,龙羊峡水库,长江三峡水库前期台