| With the increasing strength of the coal mining, gas disaster accident has beengrowing prominently, which accounts for about80%~90%of the total coal mineaccidents. Hydraulic measures is an effective method for gas control, however, theinvasion of water can cause water locking effect, which is an adverse factor for gasextraction. How to quickly and effectively promote the gas drainage efficiency hasbecome one of the major problems to be solved to realize the sustainable developmentof coal mines.Aiming at the scientific problem of water locking effect in gas extraction, theexperiment method was used in this thesis, from the aspects of experimental researchon surfactant performance and determination of a suitable surfactant, nuclearmagnetic resonance research on liquid retention effect of coal samples under thesaturated solution state, evaluation experiments of surfactant on removing the waterlocking based on centrifugal separation and coal-aqueous phase spontaneousimbibition, which was to explore the feasibility of using the surfactant to removewater locking effect. Adding surfactants in coal seam water injection to remove waterlocking effect was put forward, and some research results were achieved as follows.First of all, the mechanism of water blocking effect was analyzed. Imbibitioneffect produced by capillary and the accumulation of liquid phase were the main tworeasons for the water blocking damage. Physical properties of coal seam, theinterfacial tension of fluid, capillary force, water invasion depth were the importantfactors that influenced water locking effect. Surfactants were adopted to decrease thecapillary force, and the screening criteria was established as followed: reduce thesolution surface tension, increase or remain the contact angle of the solution on thecoal surface, not shrink or close the coal pore, reduce or remain the liquid retentioneffect.Second, the surfactant performance was evaluated the suitable surfactant waschosen. When the surfactant solution achieved the critical micelle concentration, itscorresponding concentration was very small, and different surfactants had differentcritical micelle concentration.The contact angle of the polymer surfactant CMCsolution on the surface of coal samples was larger than water did, while the contactangle of anionic, cationic, nonionic, zwitterionic surfactant solution on the surface ofcoal samples was smaller than water did. When the coal samples were saturated by water, the volume of micropores decreased, which resulted in a larger average porediameter. While the volume of small pores, mesopores, macropores and total poresincreased. The CMC solution could significantly reduce the capillary force, and in thehigher metamorphic degree coals it could change the capillary force from obstructionto motivation in the gas extraction.Third, nuclear magnetic resonance method was used to study the liquid retentioneffect of coal samples. Coal sample saturated by water had a higher irreducible fluidsaturation than saturated by CMC solution, which meant that under the sameconditions, coal samples saturated by CMC solution had less liquid detained. The lessliquid detained, the weaker fluid retention effect was.The relationship between themacropore volume and the irreducible fluid saturation was obtained by fitting usingthe software called Origin. The correlation model was Sl=-1827.11Vm+97.622.Finally, the centrifugal separation and coal-aqueous spontaneous imbibitionexperiment were made to evaluate the effect of the surfactant to remove water lockingeffect. Under the same metamorphic conditions, separating water in unit mass of coalneeded a more powerful centrifugal force than separating CMC solution.Unit mass ofcoal absorbed more water than CMC solution. When the CMC surfactant was used inthe solution, the effect of coal-aqueous spontaneous imbition was slow, and the unitmass of coal sample water quantity-time curve upward trend was more flat, whichmeant that using CMC surfactant had the effect of removing water blocking. |
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