Combined CBM drainage of multiple seams by single well in Enhong block, Yunnan Province

With abundant coalbed methane (CBM) resources, Enhong block in Yunnan Province has trouble in developing CBM due to the multiple-thin coal seams. Based on CBM wells data, this paper focused on the necessity of multi-seam drainage through analyzing the resource abundance and EUR(estimated ultimate recovery), and then came up with some advice for development of Enhong block by referring the fluid mobility of coal seams and CBM development experience in the US. The study shows that the resource is not efficient enough trough drainage of only one seam by single well, which is also the reason of unsatisfactory gas production. On the other hand, the ultimate recovery resources of multiple coal seams are sufficient in Enhong CBM block, paving the way for necessity of multi-seams drainage in every single well. It is wise to drain all coal seams whose thickness are more than 0.5 m with native structure or cataclastic structure. Besides, the low desorption time is beneficial to drainage but the low permeability with intense variety will produce a negative effect on CBM development, which need to be overwhelmed through proper fracturing and drainage methods. Staged fracturing technology is appropriate in Enhong Block which is specialized by its multiple-thin coal seams and weak aquifer between coal-bearing formations, so much more CBM resources can be recovered. In addition, it is important to divide lots of coal seams into groups and drain each group from top to bottom when single vertical well drains multiple coal seams. Moreover, it is necessary to lower liquid level with a slow process when draining water from the coal seams and a high gas production could appear after a long time each coal seam had a reduction of formation pressure.