Coal particles cleanout which is regarded as the key technology in the operation of coal bed methane (CBM) wells, play an important part in making steady production. In oil wells, Sand cleanout is operated by circulating a liquid or a multiphase fluid into the wellbore to bring sand particles to the surface. Although the sand cleanout operations have been applied successfully in most wells with high efficiency and negligible leakage, it would leak working fluid into coal bed formation, destroy the structure of coal bed and jam the formed channel of gas production. In this paper, a new continuous vacuum cleanout technology has been developed to effectively remove coal particles in CBM wells by employing a jet pump. The Concentric Tubing String (CTS) which is assembled by 3.5 inch tubing and 1.5 inch tubing is also introduced in, because there is no CCT technology in China at the moment. Detailed structure and principle of the coal particles cleanout technology system are described, while a theoretical model is formulated to optimally design the system based on the coal particles settling experimental data and jet pumping theory. It has been shown from field applications that the coal particles cleanout technology makes significant improvements in achieving high efficiency and preventing leakage in CBM wells. Moreover, the new technology reduces the skin damage and increase the production compared to non-vacuum CBM wells.
In view of the characteristic that the bottom pressure of Coalbed Methane Wells (CBM wells) is low and the structure of coal bed could be easily destructed, the author designed a kind of jet pump. The jet pump could improve efficiency of washing bottom-hole coal particle in condition of protecting the structure of coal reservoir. In this paper, we have analyzed the structure of jet pump and working principle; and given the method of calculation the basic parameters of jet pump on the basis of calculating the working efficiency of jet pump from the point of cavitation.
Friction material in the future will be towards the low-noise, low wear debris, no poisoning and environment-friendly trends and direction. This paper describes the friction material formulation filtering and evaluation, and proposes design of the basic idea of friction material formulations. Then the article optimizes design of friction material formulations by means of golden section method and the gray correlation coefficients means. Experimental results show that the method gave by this paper is an effective way to study friction material formulation.
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