Diversion methods are routinely used in both matrix acidizing and fracturing stimulation treatments. In this study, we focus on one of the classical mechanical diversion methods, ball sealers. Ball sealer diversion is used in cased and perforated wells to divert stimulation fluids by temporarily blocking perforation holes in the casing with rubber-coated balls. This diversion method can be very effective, but there is no general methodology to design ball sealer diversion, or to evaluate its effectiveness from the treating rate and pressure record. Experimental data from an extensive series of full-scale flow experiments conducted by BP were analyzed. One field treatment was analyzed and compared, and a similar trend in seating efficiency was observed. Then, we developed an empirical correlation on the basis of BP experimental data. The correlation enables us to estimate how many ball sealers seat on the perforations. By incorporating this correlation into an acid placement model, we can estimate wormhole penetrations along the wellbore with time. We developed a computer program and studied one hypothetical case to show the usefulness of the ball sealer diversion model.

This study makes a simple model of ball grinder to simulate the dynamics of grinding process. This theoretical analysis of the dynamic characteristics can be used to explain the phenomenon of the Kato¡¦s experiment and it hopes to a useful tool for the design of the ball grinder. The high removal rate is obtained with magnetic fluid grinding when high sliding velocity occurs between the ball and a high rotating drive shaft. When the balls circulation rate breaks away from the shaft speed can be used to predict the onset of skidding. Since the maximum driving friction force is proportional to contact normal force and frictional coefficient, the skidding occurs at the smaller normal force and frictional coefficient. The high viscosity of fluid, the larger fluid drag force is, when overcome the driving force then the skidding occurs. The magnetic gradient is steeper when the width of magnet of the bed is thinner, the effects of supporting stiffness of the floating pad is higher. When the magnetic buoyant force of the ball is larger, the contact normal force is larger, then the removal rate is higher.

A total of 43 Rhizobium leguminosarium bv. trifolii isolates were obtained from soil samples of two ball clover (Trifolium nigrescens) pastures from Iola and Kilgore (Texas) using ball clover as capture plants. The isolates were phenotypically characterized by intrinsic antibiotic resistance (IAR) against a range of concentrations of eight antibiotics, and by the utilization of 95 different carbon sources (BIOLOG system). The rhizobial isolates were also evaluated for their tolerance to salinity, high temperatures and low pH. The isolates showed two different ranges of growth rates: fast-growing (doubling times between 1.4 - 3.7 h) and slow- growing isolates (12.3 - 21.3 h). The numerical analysis of the phenotypic characteristics showed that the 43 isolates could be grouped in 24 different strains. Cluster analysis based on sensitivity responses of IAR, metabolic profiles of BIOLOG and salt, temperature and acidity tolerance levels could distinguish the Rhizobium strains from a Pseudomonas isolate. The analysis also showed that the rhizobial strains isolated from ball clover nodules are different from a commercial R. leguminosarium bv. trifolii strain used as inoculant for this legume.

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Texte remanié de: Diss.--Philologie--Universität Mainz, 1991. / Bibliogr. p. 493-505. Index.

published_or_final_version / Mathematics / Master / Master of Philosophy

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Concern regarding grinding media wear is as old as the invention of the tumbling mill itself. Over the years many techniques have been tried in an attempt to minimize costs associated with grinding. These have included experimentation with different metals, non-metals and different shapes. Through all this, steel grinding balls have proved the most effective media for comminution in tumbling mills. / As old as the tumbling mill is, no accurate technique for estimating the wear of the ball charge has been developed. The mining industry still utilizes the Bond Abrasion test that was developed in the early 1960s. This test which is based solely on the ore properties is inadequate giving a standard deviation in excess of 100%. This can results in high degree of error which for greenfield applications can indicate profitability for non-profitable operations and vice versa. / Peter Radziszewski proposed a decoupled total grinding media wear model that could be used to predict grinding media instead of using the Bond abrasion test. This new model had a standard deviation of 56%, which was a great improvement over the bond abrasion wear estimates. This new model also allowed for the first time, the three wear modes, abrasion, corrosion and impact, responsible for grinding media wear to be quantified. This was an important development as the ability to identify the dominant wear mode in any given operation gives operators a chance to target reduction of wear. The current mining trend is towards exploitation of lower grade ores as the higher grades become depleted. These low-grade ores require finer grinding for the liberation of the value minerals. This in turn means higher ball consumption and higher beneficiation costs. The reduction of ball wear to minimise the overall cost of ore processing operation is going to be a primary concern for all concentrators. / The objective of the research that forms the basis of this thesis was to improve the accuracy of the decoupled grinding media wear model. This was achieved by refining the tests and methodologies used to determine the wear components that make up the decoupled grinding media wear model, performing fundamental testwork to determine a more accurate structure of the decoupled model, and validating this new model. / The new model termed the "modified decoupled grinding media wear model", gives better accuracy in predicting grinding media wear than both the Bond abrasion test and the original decoupled model.