Study On The CBM Single Well’s Fracturing/drainage Model Of Multi-coalbeds Area

The paper studies on Shaopu and Wenjiaba fields of Bide-santang basin. In terms of mechanical property of coal reservoir, gas-bearing property, reservoir physical property and energy characteristics, the layer field’s change rules and main controlling factors of CBM geologic feature in multi-coalbeds’ unattached gas-bearing system and multi-coalbeds’ united gas-bearing system are clarified. By the methods of physical experiment and numerical simulation, the fracturing methods and technological parameters of different gas-bearing systems under the condition of multiple coal seams are reasonably optimized. The interlayer interference mechanism of CBM production in different gas-bearing systems is also discussed. Besides the fracturing and production orders of CBM single well in multi-coalbeds area is confirmed. Finally, the efficient and orderly exploitation mode of CBM single well in multi-coalbeds area is established.The researches show that Wenjiaba field has the typical characteristics of multi-coalbeds’ uniform gas-bearing system. With the decrease of coal seam, the methane concentration of coal seam presents a weak fluctuating change. The methane content presents a linear increase. The coal reservoir pressure shows a positive correlation with buried depth which has the uniform fluid pressure system. Shaopu field has the typical characteristics of multi-coalbeds’ unattached gas-bearing system. With the decrease of coal seam, the methane concentration and gas content show the fluctuating change. The coal seam is in uncompacted state as a whole, and coal reservoir pressure first increases then decreases with increase of buried depth. Besides the coal reservoir pressure shows a positive correlation with buried depth in the same pressure system.Physical simulational experiment results of hydraulic fracturing show that the fracture pressure of coal rocks shows a negative relation with maximum horizontal principal stress. And the more the horizontal principal stress difference is, the less the fracture pressure is. The fractures of hydraulic fracturing mainly extend in the direction of maximum principal stress. The differences in mechanical properties of rock between coal petrography and roof and floor rock have a certain inhibitory effect on the hydraulic fracture’s extension to roof and floor rock of coal seam. The larger Young modulus of coal is, the more advantageous fracture extension is. The optimize results of multi-layers’ fracturing in CBM single well of multi-coalbeds’ area show that fracturing across gas-bearing systems should be avoided and fractured intervals should be divided by 10 m coal seam spacing. Besides the proper increase of perforated intervals and effective decrease of the thickness of perforated intervals and percentage of perforation contribute to the effect of fracturing reservoir reconstruction. When preposition fluid volume is 40% of fracturing fluid volume and the proppant of smaller particle size and sand process of low sand ratio increased step by step are adopted, proppant concentration is higher in fractures and fracture length and height are supported effectively.The researches of interlayer interference influences of CBM commingling production in multi-coalbeds area show that permeability, coal reservoir pressure gradient, feed flowing capacity of stratum and coal seams’ burial depth difference affect the propagation velocity of reservoir pressure drop. The ratio between critical desorption pressure and reservoir pressure mainly affect the gas breakthrough time and effective desorption area in gas productivity of commingling production. Yet coal thickness has little effect on commingling production.The results of optimizing drainage mode of CBM single well in multi-coalbeds area show that Shaopu field is divided into six gas-bearing systems based on coal reservoir pressure gradient. Bounded by 100 m coal seam span, the coal seams are divided into three coal seam groups in Wenjiaba field. Combining with gas productivity simulation results of each gas-bearing system and coal seam group, the favorable subsystem and coal seam group are screened. According to the level of reservoir pressure, the production orders of each favorable subsystem and coal seam group are confirmed, and the progressive drainage mode is further proposed.Based on the above research results, the efficient fracturing and drainage modes of CBM single well in multi-coalbeds area are finally established.