Study on Experiment of Coal Spontaneous Imbibition Considering the Effective Stress
考虑应力作用的煤岩水相自吸实验研究

Hydraulic fracturing is generally applied to improve productivity for the low permeability of the coal seams in China. Fracture fluid has a serious leakoff for considerable nature fractures of coal and can not effectively flow back for strong adsorption capability of coal. The result of these performance leads to permeability impairment and reducing effectiveness of stimulation treatment. This paper studies characteristics and effective stress affecting of coal spontaneous imbibition through water imbibition experiment. The results show that imbibition rate will increase with permeability increasing. Spontaneous imbibition curves can be divided into tow parts of spontaneous imbibition and diffusion\|adsorption. Imbibition rate will decrease nearly one order of magnitude considering effective stress. It indicates that permeability and effective stress are factors affecting water spontaneous imbibition. The paper points out that capillary pressure and attractions between water molecules and coal molecules determines the characteristics of water spontaneous imbibition by analyzing adsorption mechanism and pore structure. The conclusion has some reference significance for evaluation of aqueous phase trapping, optimization of hydraulic fracturing method and fracture fluid design.