Effects of the agglomerated fracturing fluid on the transportation of pulverized coal and its mechanism

During the drainage process, the pulverized coal moves with the carrier fluid in supporting fractures, resulting in the blockage of the fractures and then a decrease in the permeability of the coal reservoir and the conductivity of the supporting fractures. For the purpose of exploring the effects of the properties of the agglomerated fracturing fluid on the transportation of pulverized coal and its mechanism, the coal samples from Urumqi Hedong Mining Area in southern Junggar Basin coalfield are selected as the research object, with distilled water, active water fracturing fluid(1.5%KCl), and agglomeration fracturing fluid(1.5%KCl+0.05%AN) as the carrier fluids. Through the physical simulation experiment of pulverized coal production under the single-phase flow displacement state, the production of pulverized coal and the damage rate of supporting fracture conductivity at the displacement flow rate of 100 mL/min, 200 mL/min, and 300 mL/min are obtained. The results show that when the gas displacement flow rate is 100 mL/min, the cumulative output of pulverized coal of the three carrier fluids all show a linear growth trend, and the damage rate of the fracture conductivity varies within a small range (0.6%-8.1%). At the gas displacement flow rate of 200 mL/min, as the pulverized coal deposits in the supporting fractures, the migration channel shrinks, so that the powder output of each carrier fluid first reaches the maximum value and then decreases. The damage rate of the fracture conductivity of the agglomerated fracturing fluid is low. The difference between the cumulative damage rate of its conductivity and the damage rate of the conductivity of distilled water and active water fracturing fluid are 24.4% and 3.1%, respectively. At the gas displacement flow rate of 300 mL/min, the time when the output of pulverized coal reaches the maximum value is advanced. The fracture conductivity damage rate of the agglomerated fracturing fluid is the lowest, and the difference between the cumulative damage rate of its conductivity and the damage rate of conductivity of distilled water and active water fracturing fluid is 64.8% and 14.9%, respectively. Therefore, with a lower displacement flow rate, the output of pulverized coal is less and the damage rate of conductivity is lower. Through the static settlement experiment and the direct shear experiment, the mechanism of the agglomerated fracturing fluid on the migration of pulverized coal is revealed. During the migration of pulverized coal, by using the agglomerated fracturing fluid, the interface state between the solution and the pulverized coal is changed through the hydrophilic and lipophilic groups of surfactants, and the wettability of the pulverized coal is enhanced, resulting in the aggregation and settlement of pulverized coal particles. By increasing the liquid bridge force, the cohesive force is increased, and the relative movement of the settled coal is inhibited, thereby reducing the number of suspended coal particles. The output of pulverized coal and the damage rate of the conductivity of supporting fractures are effectively reduced, thus reducing the probability of sticking and workover, and realizing effective prevention and control of pulverized coal.