According to the 2012s workover treatment statistic in the Hancheng block, the eastern Ordos gas field, the workover caused by pulverized coal accounts for 41.8% of the total, which has seriously affected the continuous and stable drainage. This is one of the main factors which constraint coalbed methane production yield. In this paper, geological factors including the composition of coal petrography, the mechanical strength of coal petrography and coalbody structure destruction and engineering factors including drilling, fracturing and drainage were analyzed to study on the controlling factors on the output of pulverized coal. We conclude that the determinant on output of pulverized coal is the nature of coal seam, however engineering factors cause the output of pulverized coal directly. The root-mean-square amplitude attribute analysis was first used to display the mechanical strength of coal seam. Based on the result, we made the prediction about the possibility of the output of pulverized coal and divided the studying area into four grades. The research on the controlling factors and the prediction of the output of pulverized coal could provide the basis for the prevention and comprehensive treatment of pulverized coal.

Mature oil well temperature logging technique was applied to coalbed methane wells in order to monitor the fracture height and guide the fracturing and drainage. The results show that, after fracture treatment, fracture height was bigger than that of perforated interval, and mainly extended upward. In the case of 11# coal seam in Taiyuan formation of Permian, Upper Palaeozoic, overlying K2 limestone were all cracked through, while in the case of 3# and 5# coal seam in Shanxi formation of Permian, Upper Palaeozoic, overlying sandstone section in some wells was cracked through. In the former case, the fracturing curve shows fracture pressure higher than 27MPa, pump off pressure higher than 20MPa, and high pressure dropping rate over 0.4MPa/min, while the fracture pressure lower than10MPa, pump off pressure lower than 5MPa and low pressure dropping rate that generally under 0.1MPa/min in the latter case. Fracture height is directly influenced by crustal stress of the rock cracked by fractures, and tends to become bigger with the increase of fracture pressure and pump off pressure. To achieve desired results after coalbed methane reservoir stimulation treatment, a restriction of fracture pressure during fracturing process is recommended to control fracture height.

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.