فصلنامه مهندسی معدن
پیاپی 28 (پاییز 1394)

Laser perforating in rocks is a very complex phenomenon that its performance depends on many factors. Since it’s not possible to consider all of these factors in laboratory, numerical modeling is used. In this study, a finite element code (FEM) have been taken to model the thermal and mechanical stresses induced by laser drilling ND:YAG in the hydrocarbon reservoir rock samples. For this purpose the software ABAQUS was used to analyze the thermal and mechanical stresses induced by laser. It is found that Numerical models, show good agreement with the actual observation for holes with diameter of 2 millimeter. In addition, the larger the diameter of the hole is, the vaster the effective zone of stress concentration is. Therefore fracturing occurs in larger zone around the hole.Laser perforating in rocks is a very complex phenomenon that its performance depends on many factors. Since it’s not possible to consider all of these factors in laboratory, numerical modeling is used. In this study, a finite element code (FEM) have been taken to model the thermal and mechanical stresses induced by laser drilling ND:YAG in the hydrocarbon reservoir rock samples. For this purpose the software ABAQUS was used to analyze the thermal and mechanical stresses induced by laser. It is found that Numerical models, show good agreement with the actual observation for holes with diameter of 2 millimeter. In addition, the larger the diameter of the hole is, the vaster the effective zone of stress concentration is. Therefore fracturing occurs in larger zone around the hole.

There have been several statistical methodologies presented for separating anomalous values from background values leading to determination of anomalous areas. These methods range from simple approaches to complex ones and include methods such as Statistical Parameters of Distribution (as a nonstructural method) and U Spatial Statistic (as a structural method). The second group takes the sampling locations and their spatial relation into account for estimating the anomalous areas. The U Spatial Statistic method is one the most important structural methods which by considering the spatial location of the samples and without judging from a geochemical point of view carries out the statistical analysis of the data and separates the subpopulations and determines the anomalous areas. In present study, the surface samples from the Parkam exploration district were used in order to draw a comparison between the capability of two methods of nonstructural methods (Statistical Parameters of Distribution and Gap Statistic) and U Statistic (structural method) in separating anomalous values from background and providing the map of anomaly for grade values of Pb and Zn. Results suggest that the samples indicated by U Statistic and Gap Statistic methods as anomalous are more regular and less dispersed compared to those indicated by the method of Statistical Parameters of Distribution. Both Gap Statistic and U Statistic methods have shown almost similar results for estimating threshold and separation, but U Statistic method is even better than Gap Statistic because the U Statistic method devotes a new value to each sample which can be combined with other methods. Thus the map of prospective areas for Pb and Zn in the exploration district has been prepared using the U Statistic method.

The pivotal role of bubble surface area flux (Sb) and gas hold-up (εg) in flotation columns efficiency has been proved. This paper examines the effect of variables of gas flow rate, feed rate, frother concentration, froth height, particle size and solid percent on gas dispersion parameters (gas hold-up and bubble surface area flux). Test work has been conducted in a column with 10 cm diameter and 400 cm height. Feed to flotation column has been provided by rougher mechanic cell concentrate of Miduk copper complex. Gas hold-up has been measured by pressure difference method and bubble size has been estimated by drift flux analysis. The results of the study reveal that superficial gas velocity and frother rate have a positive impact on bubble surface area flux; however, the increase of pulp solid percent leads to the decrease of Sb. Studies on the gas dispersion parameters in flotation columns show that although gas hold-up decreases due to the improvement of feed flow rate, its effect, in comparison to the air flow rate and frother rate, is negligible. Gas hold-up decreases in collection zone when solid percent increases and this decreasing rate has become more significant when particle size increases. Likewise, by decreasing the froth height, low reduction can be observed in gas hold-up. Finally, a model for prediction of Sb on the basis of εg has been carefully presented by the use of statistical methods.