测井技术在石膏矿勘探中的应用

在石膏矿勘探孔中使用聚焦电阻率、密度(长、短源距伽玛伽玛)、岩性密度(散射伽玛能谱———光电吸收截面指数Pe)、中子孔隙度、自然伽玛、声波速度、井径和井斜等测井方法,可以精确划分出石膏矿层的深度、厚度、结构,并能区分出石膏和硬石膏,判定石膏含量。在生产实践中,利用测井方法解释石膏矿层,取得了非常明显的地质效果,为石膏矿勘探开发提供了可靠的依据。     

Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils

In order to investigate the effects of temperature, thickness of soil layer, wetting and drying cycles and soil types on geometrical structure of surface shrinkage cracks in clayey soils, special software Crack Image Analysis System (CIAS) for analyzing shrinkage crack patterns was developed. Eight groups of soil samples were prepared and subjected to drying to crack in laboratory. The number of crack segments and intersections, average crack length, width and aggregate area, crack intensity factor (CIF), and the corresponding probability density functions (PDF) of these parameters were determined by analyzing several crack patterns derived from different experimental conditions. The results show that the soil cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. There is a tendency of crack length, width, aggregate area and their most probable value (MPV) related to the PDF increases with temperature increase. With thicker soil layers, the average crack length, width, aggregate area and CIF are increased, and the main distribution ranges of crack length, width and aggregate area are increased also. When the soil is subjected to multiple wetting–drying cycles, the soil surface generates more irregular and coarse cracks. The number of short and narrow crack segments increases significantly, and the CIF decreases with an increase in wetting–drying cycles. It is also observed that the extent of cracking is directly related to the soil fines fraction and its plasticity index (I_P). The greatest CIF and crack width are observed in the soils with the largest fines fraction and highest I_P. In addition, the ratio of numbers of crack segments to intersections ranges from 1.5 to 2, and cracking mainly takes place in three stages: main-cracks initiation stage; sub-cracks initiation stage; terminal stable stage.