| The coal-bed methane resource in China is very rich. With the development of the exploration, in recent years it is a tendency to explore the coal-bed methane deeper than1000m. The active water fracturing which is commonly used in CBM, due to the large pumping volume, will cause the reservoir blocking and poor production. Foam fracturing fluid has many advantages to use in the deep CBM, such as low filtration, strong capacity of carrying proppant and easy to flowback. However, the existing foam fracturing liquids can be too hard to break and possible to damage the coal-seam. It is significant to make a research on the foam fracturing fluid which is low damage.In this paper, considering the temperature and pressure of southern QinShui Basin coal-bed reservoir, comparison between N2and CO2, we choose the N2as the gas phase of the fracturing liquid system. Waring Blengder’s method was used to select the foamer, which has the most excellent properties of foam volume and half-life period. Furthermore, we evaluated the effects of the low molecular foam stabilizers and choose the best one to add in the liquid system. In summary, three kind of liquid systems are selected, one contains foamer and stabilizer, the others just have foamer.With the3foam fracturing liquid systems analyzed under high temperature and high pressure, we can get the characteristics of liquid systems, such as volume, half-life period, stability of time, filtration and rheology. It is obvious that the foam fracturing liquid system has many advantages containing large foam volume, long half-life period, strongly ability of carrying proppant, high viscosity and excellent shear performance. Through artificial coal core permeability damage experiments, all the3systems have low damage to the reservoir, and the damage rates are13%～40%, equals to the active water damage.The selected liquid systems have been used in5wells in Qinshui Basin coal-bed reservoir, the effects were better than other wells fractured by active water. |
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