Year:2007 | Volume:41 | Issue:3 (105)|Papers Count:14

Mansuri oil field, which is located at the South-West of Iran, has sand production problem and primary analyses proved the existence of this phenomenon in this field. Generally, there are three methods to evaluate the sand production state which are empirical, numerical, mathematical, and physical. Considering the numerical capability to analyze complex geometries under high stresses condition, FLAC3D, which is a three-dimensional explicit finite-difference program for engineering mechanics computation, was employed to analyze sand production in this field. First, the numerical model was calibrated using designed physical model and then, producing intervals and their perforations were modeled by numeric software. Its results showed that not only end-perforation instability is not the sole dominant mechanism in sand production, but also the effect of adjacent perforations on each other is more important. In this respect, there is an optimum pressure that causes perforations failure and catastrophic sand production. Mansuri field analyses demonstrated that the downhole pressure at its wells is near predicted optimum pressure and producing intervals are going to catastrophically produce sand.

In this paper, first the validity of 3-D DDA is examined by comparing its solution for dynamic block displacement with analytical solution. Displacement of a single block on an inclined plane subjected to a dynamic loading is studied for analytical solution with respect to the frictional resistance offered by the inclined slope. 3-D DDA predicts accurately the analytical displacements. The modification of point-to-face contact constraints is also studied too. In the original 3-D DDA method, block contact constraints are enforced using the penalty method. This approach is quite simple, but may lead to inaccuracies which may be large for small values of the penalty number. The penalty method also creates block contact overlap which violates the physical constraints of the problem. These two limitations are overcome by using the Augmented Lagrangian Method which has been programmed in VC++ and its implementation into the 3-D DDA is presented by an illustrative example. This method has been found to model block contact quite well.

In mining, loading and transportation may cost around 50% of the production expenses. Dispatching is one of the most important and complex problems whose optimization would lead to noticeable saving. Therefore, in order to maximizing the production and, at the same time, controlling the quality of material sent to ore processing plant, transport management system has become one of the interesting subjects for mining managers.Dispatching problem includes two sub-problems, namely allocating trucks and real-time dispatching. Dispatching problems traditionally are solved using Operations Research (OR) models. OR models, commonly, consist of an objective function and some constraints. In dispatching models this objective function may be maximizing trucks utility, maximizing shovels utility, minimizing number of trucks, minimizing waiting time of trucks or shovels, and so on. Loading capacity of shovels, number of shovels and (or) trucks, amount of materials must be transferred, and grade of ore have to be sent to plant are typical examples of constraints for these models. In this study an OR model has been developed for truck allocation and assignment in Sarcheshmeh copper mine based on minimizing the truck number for a particular amount of extraction of ore and waste. Constraints of this model include: limited productivity of shovels, least amount of materials to be produced, range of variability in ore grade, and limited number of trucks. This paper also explains the software that has been developed in MATLAB programming environment for solving the model. Analyzing the results showed that applying the proposed model would lead to 28.5%, equal to more than 10,000 tons per day, of production increase.

With the advent and wide spread use of computers a number of algorithms have been developed to determine the optimum ultimate pit limits in open pit mining. The main objective of these algorithms is to find groups of blocks that should be removed to yield the maximum overall mining profit under specified economic conditions and technological constraints. The most common methods are: Lerchs and Grossmann algorithm based on graph theory, the Korobov algorithm, floating or moving cone method, moving cone II and dynamic programming. Among these, the Lerchs-Grossmann algorithm is the only method that always yields the true optimum pit. The disadvantages of the algorithm are complexity of the method and require more computing time than other methods to find out optimum pit outline. The floating cone approach which does not yield a true optimum pit in some cases is the most popular and simplest method and requires significantly less computing time than any other method to reach a solution. The moving cone II has been developed by Wright to overcome the shortfalls of the floating cone method. In this paper the moving cone II has been evaluated for being as a true optimum open pit design method and also two algorithms has been proposed for modification of this method. For this purpose C++ computer programs have been developed under Windows operating system for these algorithms and their results are compared with the Lerchs and Grossmann method, which is the true optimum open pit design algorithm. The outcomes show that these algorithms are able to produce good results.

Where closely jointed rock masses are encountered in slopes, failure can occur both through the rock mass, as a result of combination of macro and micro jointing, and also through rock substance. Determination of the strength of these rock masses is quite difficult since the size of representative specimens of them is too large for laboratory testing. This difficulty can be overcome by using a non-linear rock mass failure criterion or by back analysis of such slopes. In this paper, a new procedure, and accompanying computer program, is presented for estimation of shear strength parameters, mobilized in slopes cut, in closely jointed rock masses, which obey a non-linear failure criterion, rather than a linear one. In this procedure, the necessary constants to calculate normal stress are dependent to shear strength parameters of the failed rock masses. These parameters can be determined, using a main cross section across the failed slope, without the need for exact value of Geological Strength Index (GSI). In this respect, trials are made with different GSIm and GSIs values, corresponding to various possible combinations of the constant m and s, satisfying the limit equilibrium condition, used in the Hoek & Brown’s failure criterion. The proposed procedure provides a quick check for the GSI obtained from the site investigations. The proposed procedure is used in conjunction with the Morgenstern-Price method of slope analysis, for circular or noncircular slip surfaces. The method outlined in this paper has been satisfactorily applied to Duna landslide, in the right bank of upper dam of Siah Bishe pump-storage, north of Iran.

Dispersed organic matter in the shaly sediments of the siliciclastis Shemshak Formation (Upper Triassic-Middle Jurassic) in the central and eastern Alborz mountains are categorized into three groups including (1) amorphous organic matter, (2) continental organic matter and (3) marine organic matter. Amorphous organic matter dominates in all samples which are predominately derived from degradation of bacteria and phytoplankton remains. Rock-Eval pyrolysis results of the studied shaly samples indicate the presence of hydrogen-depleted organic matter in the Shemshak Formation. According to position of the samples on the Van-Krevelen modified diagram (HI-Tmax), organic matter is considered as altered organic matter group (type IV kerogen in geochemical composition). Organic matter in the studied shales of the Shemshak Formation has experienced high temperature during burial and is now thermally post-mature (average of Tmax is 496oC). Thermal alteration is the main agent of organic matter alteration. Thick marine shales of the Shemshak Formation are rich in altered amorphous organic matter with marine phytoplanktonics origin (degraded type II kerogen). According to geochemical results the studied shales of the Shemshak Formation are classified as poor source rocks (gas-prone), which have mainly entered in gas generation window.

Wave propagation is used as an advanced tool of determining elastic properties of rocks. In spite of being cheap and non destructive tests of rock mechanics, due to its modernity method is not yet replacing the traditional dear and destructive tests. In order to pave ways of replacing this test and making best use of it all effective factors of such method are to be assessed. One fundamental factor affecting the test result is the shape of the specimen tested. The existing standards do not seriously take the sample shape into consideration. It was pointed out elsewhere that in spite of popular taught elastic dynamic properties do vary seriously due to variation of sample shape (height to diameter ratio). As this fact was revealed for limestone in our previous investigation this assessment was extended to other types of rocks for the possibility of true judgment. Therefore, ultrasonic wave propagation tests were conducted on four various rock types with height to diameter ratio of 0.5 to 3. Analyzing of the test results showed that shear wave velocity and elastic dynamic constants are noticeably dependent on sample height/diameter ratio. The variation of height/diameter ratio from 0.5 to 3 caused the variation of shear wave velocity and Poisson’s ratio up to 70%, Elasticity modulus up to 160% and shear modulus up to 200% as follows in details:Variation in shear wave velocity: Limestone, 24%; Siltstone, 70%; Green Tuff, 17% and Granodiorite, 20%.Variation in dynamic elastic modulus: Limestone, 26%; Siltstone, 65%; Green Tuff, 73% and Granodiorite, 33%.Variation in Poisson’s ratio: Limestone, 45%; Siltstone, 160%; Green Tuff, 20% and Granodiorite, 35%.Variation in shear modulus: Limestone, 53%; Siltstone, 200; Green Tuff, 38% and Granodiorite, 45%.It was also observed that the longitudinal wave velocity was not following the height/diameter ratio and showed no specific trend of variation.As seen from the above details, the variation of modulai is much grater for siltstone in compares to the 3 other rocks. It is most likely that this obvious difference is due to inhomogenity of the siltstone texture which causes different behavior in this particular rock.

In present research, chemical leaching of aluminum from red mud, the major waste product of the alkaline extraction of Al from bauxite, was examined. Bauxite is an ore with a high concentration of aluminum compounds. This high aluminum content makes bauxite a useful raw material for the extraction of aluminum. To produce primary aluminum, the aluminum compounds in the bauxite are first dissolved chemically, using caustic soda, in an alumina refinery. This produces aluminum oxide. Red mud, which is a slurry containing natural substances originally present in the bauxite. The ore residues with a residual amount of alkali - is left over from the process. The high concentration of iron compounds gives the waste product its characteristic red color. The amount of red mud produced depends on the aluminum content of the bauxite. Bauxite ores with a high aluminum content result in lower ore residues than bauxite ores with a lower aluminum content from the ore residues, one achieves the optimal conditions for disposal. This is also beneficial in two ways: The caustic soda can be recycled as part of an efficient closed loop system. Apart from remaining traces of alkali, the ore residues do not contain any industrial additives. Thus, red mud is not hazardous waste and can be disposed of in an environmentally neutral manner. In Germany, the mud is pumped through pipes to the plant’s own disposal site, where it is stored. Any caustic soda left behind after sedimentation is directed back to the production process. Natural impervious layers act as a seal for the disposal site to prevent seepage. Groundwater wells are used for control purposes and samples are taken several times a year to check whether any substances from the disposal site have entered the ground-water. Rain-water is pumped off and fed into a wastewater treatment plant. Different methods of red mud disposal are practiced throughout the world but none of them are known to be environmentally innocuous. Sulfuric, nitric, Citric, Oxalic, Gluconic, Malic and Lactic acids were employed individually or as mixtures in chemical leaching experiments. The preheating of red mud and its effect on leaching process has been studied. By using citric and sulfuric acids 78.2% and 93.7% of Al2O3 was extracted while the concentrate of Al2O3 was 12.5 and 14.5 g/l respectively. In case of mixture of acids (citric, oxalic and subsequent H2SO4 addition to reach pH to 1.5), the recovery was 84.6 while 13.5g Al2O3 came into solution. Despite of an impure solution of Al obtained with H2SO4 alone, it may be more efficient and economical due to high concentration extracted Al and high price of organic acids. In other hand, leaching of Al from red mud appears feasible an industrial scale using sulfuric acid. This work will open up a new era to beneficiate red mud through chemical and biotechnological rout in Iran.

A comprehensive investigation was carried out to minimize the cost price of the rock fragmentation process including: drilling, blasting, secondary blasting and separating the large boulders (oversize rocks) while loading, until the optimized fragmentation, powder factor and ratio of burden (B) to blasthole diameter (fh) were achieved by doing several stages of drilling and blasting practically in different mines. The complicated in situ factors control rock fragmentation by blasting, as development of an adequate method for design of drilling and blasting had been a difficult task.  Rock mass parameters affecting the powder factor and B/fh ratio were investigated extensively in different mines and discontinuity plane aperture of rock mass as a new parameter affecting the powder factor and B/fh ratio was also applied. Parameters affecting the rock mass fragmentation were summarized to be discontinuity plane aperture, discontinuity plane spacing, discontinuity plane orientation, rock mass description and unconfined compressive strength of rock material. The quantitative effect of each parameter on B/fh ratio was indicated by a number (rating). The total values of numbers were named “rock fragmentation index” (RFI). The numbers were arranged in a way that RFI was equal to B/fh ratio.  Parameters of RFI and their rating were proposed in a table to use as a new simple method of blasthole pattern design.

Well logs are principal sources of subsurface geological information. They provide significant information on mineralogical composition, texture, sedimentary structures and petrophysical properties such as porosity and permeability. By compiling data from various well logs, one can discriminate sedimentary units with comparable log characteristics. Sedimentary units with similar fluid flow and capacity are named rock type. Rock type determination is the most important task in reservoir characterization of oil bearing formations. Rock type may be determined using different data sets but their definition on the basis of wire line logs is most common. Multivariate cluster analysis (as the best method of data grouping) is one of the most accurate and effective methods in oil bearing reservoir zonation. The method is applied on both detrital and carbonates rocks. This method gets more support by improvements in algorithms and statistics. Proper combination of logs and appropriate algorithm will increase the accuracy, reliability and effect of the method. Similar faces may have different log responses due to diverse factors that affect the logs. Since using statistical methods and procedures are mandatory, in clustering procedure data are grouped with minimum distance and maximum homogeneity. It is obvious that distinct geological parameters can be related to a group of data, which are to be used by geologists for further interpretation. For this calculation, all log readings are considered as "observations" and the used logs as the "values of the observations".There are several ways to compute the distance between objects. The "Standardized Euclidean" distance is used here in form the MATLAB software, because more accurate results are obtained with this procedure. By grouping log data in multidimensional space (equal dimensions with number of logs), each point (reading) can be related to a group of data (rock type). High resolution rock typing with reliable conclusions can be inferred with this procedure using pure mathematical formula in which there is no need to regression equations or trainings. In this method, any geological parameter described from other sources such as cores and thin sections can be related to wells with comparable rock types. The accuracy and reliability of defined rock types can be examined in wells from which suitable cores are available. Results from such a comparison provide a fundamental base for study of wells with poor core and cutting data.Using MATLAB software, this study testifies a new simple method for rock type determination of Asmari Formation in Marun Field. The reliability of the method is examined by correlation of the resultant rock types with those of inferred from cores. Result from such a correlation indicates the reliability of method in rock type determination.