International Journal of Mining & Geo-Engineering
Volume:46 Issue: 2, Summer and Autumn 2012

Large amounts of hydrocarbon reserves are trapped in naturally fractured reservoirs which are challenging in terms of accurate recovery prediction because of their joint fabric complexity and lithological heterogeneity. Canada, for example, has over 400 billion barrels of crude oil in fractured carbonates in Alberta, most of this being bitumen of viscosity greater than 106 cP in the Grosmont Formation, which has an average porosity of about 13-15%. Thermal methods are the most common exploitation approaches in such viscous oil reservoirs which, in the case of steam injection, are associated with up to 275-300°C temperature changes, leading to considerable thermoelastic expansion. This temperature change, combined with pore pressure changes from injection and production processes, leads to massive effective stress variations in the reservoir and surrounding rocks. The thermally-induced (thermoelastic) stress changes can easily be an order of magnitude greater than the pore pressure effects because of the high intrinsic stiffness of the low porosity limestone and bounding strata. Study of these stress-pressure-temperature effects requires a thermo-hydro-mechanical (THM) coupling approach which considers the simultaneous variation of effective stress, pore pressure, and temperature and their interactions. For example, thermal expansion can lead to significant joint dilation, increasing the macroscopic, joint-dominated transmissivity by an order of magnitude in front of and normal to the thermal front, while reducing it in the direction tangential to the heating front. This leads to strong induced anisotropy of transport processes, which in turn affects the spatial distribution of the heating arising from advective heat transfer.

It is always attempted to reduce the costs of comminution in mineral processing plants. One of the difficulties in size reduction section is not to be designed properly. The key factor to design size reduction units such as crushers and grinding mills, is ore’s work index. The work index, wi, presents the ore grindability, and is used in Bond formula to calculate the required energy. Bond has defined a specific relationship between some parameters which is applied to calculate wi, which are control screen, fine particles produced, feed and product d80. In this research work, a high grade copper sample from Miduk copper concentrator was prepared, and its work index values were experimentally estimated, using different control screens, 600, 425, 212, 150, 106 and 75 microns. The obtained results from the tests showed two different behaviors in fine production. According to these two trends the required models were then defined to present the fine mass calculation using control screen. In next step, an equation was presented in order to calculate Miduk copper ore work index for any size. In addition to verify the model creditability, a test using 300 microns control screen was performed and its result was compared with calculated ones using defined model, which showed a good fit. Finally the experimental and calculated values were compared and their relative error was equal to 4.11% which is an indication of good fit for the results.

The paper is concerned with the hydrogeological appraisal of the proposed mining operations in the Thar lignite field in Sindh, Pakistan. The Thar coalfield covers an area of approximately 9000km2 and contains three lignite seams lying at depth of 130m to 250 m. In the Thar lignite field, the presence of three main aquifers induces pore pressure in the rock mass surrounding the lignite seams and makes high wall slopes potentially unsafe. It is, therefore, necessary to dewater the rock mass before commencing mining excavations. The paper describes the proposed mine dewatering scheme to facilitate depressurising of the rock mass surrounding the mining excavations. Inflow prediction of groundwater to the surface mining excavation was carried out using a SEEP/W finite element software package. The simulation results show that the ground water inflow from the Top aquifer is 114m3/d, from the Intermediate confined aquifer is 141m3/d and from the Bottom confined aquifer is 1.28 x 105 m3 /d. These results were compared with the analytical solutions which indicated that the relative error of estimation of inflow quantities varies from 3.4 % to 6.4%.

In the open-pit mining, one of the first decisions that must be made in production planning stage, after completing the design of final pit limits, is determining of the processing plant cut-off grade. Since this grade has an essential effect on operations, choosing the optimum cut-off grade is of considerable importance. Different goals may be used for determining optimum cut-off grade. One of these goals may be maximizing the output rate (amount of product per year), which is very important, especially from marketing and market share points of view. Objective of this research is determining the optimum cut-off grade of processing plant in order to maximize output rate. For performing this optimization, an Operations Research (OR) model has been developed. The object function of this model is output rate that must be maximized. This model has two operational constraints namely mining and processing restrictions. For solving the model a heuristic method has been developed. Results of research show that the optimum cut-off grade for satisfying pre-stated goal is the balancing grade of mining and processing operations, and maximum production rate is a function of the maximum capacity of processing plant and average grade of ore that according to the above optimum cut-off grade must be sent to the plant.

This paper gives an overview of the difficulties associated with the design of hard rock pillars in South African mines. Recent examples of large scale pillar collapses in South Africa suggest that these were caused by weak partings which traversed the pillars. Currently two different methods are used to determine the strength of pillars, namely, empirical equations derived from back analyses of failed and stable cases and numerical modeling tools using appropriate failure criteria. It is illustrated in the paper that both techniques have their limitations and additional work is required to obtain a better understanding of pillar strength. Empirical methods based on observations of pillar behaviour in a given geotechnical setting are popular and easy to use, but care should be exercised that the results are not inappropriately extrapolated beyond the environment in which they are established. An example is the Hedley and Grant formula (derived for the Canadian uranium mines) that has been used for many years in the South African platinum and chrome mines (albeit with some adaptation of the K-value). Very few collapses have been reported in South Africa for layouts designed using this formula, suggesting that in some cases it might yield estimates of pillar strength that are too conservative. As an alternative, some engineers strongly advocate the use of numerical techniques to determine pillar strength. A close examination unfortunately reveals that these techniques also rely on many assumptions. An area where numerical modeling is invaluable, however, is to determine pillar stresses accurately and to study specific pillar failure mechanisms, such as the influence of weak partings on pillar strength.

Risk-based assessment methods are commonly used at the contaminated sites by hydrocarbon pollutants. This paper presents the results of a two-dimensional finite volume model of reactive transport of biodegradable BTEX which have been developed for the saturated zone of an unconfined aquifer in the Pump station area of Tehran oil refinery, Iran. The model governing equations were numerically solved by modification of a general commercial software called PHOENICS. To reduce costs in general, many input parameters of a model are often approximated based on the used values in the contaminated sites with same conditions. It was not fully recognised the effect of errors in these inputs on modelling outputs. Thus, a sensitivity analysis was carried out to determine the influence of parameters variability on the results of model. For this analysis, the sensitivity of the model to changes in the dispersivity, distribution coefficient, parameters of Monod, Michaelis-Menten, first- and zero- order kinetics modes on the BTEX contaminant plume were examined by performing several simulations. It was found that the model is sensitive to changes in dispersivity and parameters of Michaelis-Menten, first- and zero- order kinetics model. On the other hand, the predictions for plumes assuming Monod kinetics are similar, even if different values for parameterization are chosen. The reason for this insensibility is that degradation is not limited by microbial kinetics in the simulation, but by dispersive mixing. Quantifying the effect of changes in model input parameters on the modelling results is essential when it is desired to recognise which model parameters are more vital on the fate and transport of reactive pollutants. Furthermore, this process can provide an insight into understanding pollutant transportation mechanisms.

Several methods have been developed for gold exploration in the past, among which biological base method is known to be the most efficient with least expenses. This method can also be used for latent gold prospects exploration. In the present study, the possibility of applying Bacillus cereus frequency in soil as a biological marker was investigated for the exploration of latent gold prospecting in Iran. The study was performed on three gold sources in Iran known as Moteh, Zarmehr and Mahallat, however, the major focus was on Mahallat gold reserve. The results of bacterial cultivation showed that no bacteria have been isolated in samples taken from Moteh soil. On the other hand, the presence of bacteria was observed in cultural media which were prepared from the collected samples from Zarmehr and Mahallat. In Mahallat gold reserve the frequency of bacteria was noticeable, particularly in the soils with in-situ fine-grained. In addition, it was seen that when the gold grad increases the bacterial frequency of Bacillus cereus will also increase. Finally, a linear correlation was developed between bacterial frequency and the gold semi-quantified grad. Using this correlation the monitoring of semi-quantified gold grad can be undertaken.