Wells conditions are different in wide range of temperature and depth. Cement slurries in such conditions have to remain pumpable and after setting to stay homogenous in production well life. For cementing operations in wide range of temperature and pressure and to accommodate cement slurries for individual well requirements more than 50 additives are now used for various API classes of cement. Laboratory in NIS -National oil company of Serbia, provides cement analysis of dry cement, tests on cement slurries and cement stone in compliance with methods prescribed by API standard, whereby quality and type of equipment fully meet the requirements. Adaptation of the local cement to the well conditions had already been done by these additives and by numerous tests of pure cement and cement mixtures we developed a palette of typical cement mixtures for cementing oil wells in the south eastern region of the Pannonian basin.
The bucket-wheel dredge “Kovin I” for underwater coal mining with bucket-wheel type UCW-450 has been in operation for over 20 years. Based on analyzing the bucket-wheel dredger performance, productivity, maintenance costs, and reliability, a rational decision was made: to rehabilitate the most essential parts of the dredge, including the bucket wheel and the gearbox. However, the selection and construction of the excavator parts were performed on the ground of available laboratory data for digging resistance. The data itself was determined by the testing methodology that did not include the influence of surrounding water pressure at a certain depth of mining. According to the previous findings, it was necessary to develop a specific research and testing program that would involve appropriate laboratory testing of the geomechanical parameters. These were to represent the influence of hydrostatic water pressure on the working environment—coal. Nevertheless, geomechanical laboratory research tests were initially modified to provide reliable data of cutting resistance, especially in the water under different hydrostatic pressures, fully simulating the “in situ” working conditions of mining, i.e., cutting.
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