Abstract
In view of the unfavourable conditions created by the “low permeability, low reservoir pressure and low gas saturation” of coal reservoirs in China for coalbed gas production, an autogenous nitrogen fracturing fluid system has been introduced to enhance the permeability of coal reservoirs. By testing the optimized mix ratio of autogenous nitrogen fracturing fluid, the impact of the mix ratio between nitrogen-generating agent and activating agent on reaction rate and gas production has been analyzed and it has been determined that the optimum molar ratio suitable for the fracturing of low-temperature coal reservoir is 2.5:1. By measuring the permeability of coal samples before and after treatment with autogenous nitrogen fracturing fluid, it has been verified that autogenous nitrogen fracturing fluid can increase the coal reservoir permeability, and in addition, the higher the original coal reservoir permeability is, the more significant the permeability increase will be. The test results indicate that when autogenous nitrogen fracturing fluid is used to fracture the coalbed gas reservoir, the permeability of coal reservoir can be effectively improved under its gas expansion and fracture- forming effects. This provides laboratory support to the application of autogenous nitrogen fracturing fluid in hydraulic fracturing.
