考虑应力作用的煤岩水相自吸实验研究

Study on Experiment of Coal Spontaneous Imbibition Considering the Effective Stress

我国煤层气储层渗透率普遍偏低,为达到合理产能需进行压裂改造。煤层气储层裂隙发育导致压裂液滤失严重,强吸附能力使流体得不到有效返排,造成储层损害降低了渗流能力,大大削弱了增产改造的效果。开展了煤岩水相自吸实验,系统研究了煤岩水相自吸特性及应力状态的影响。结果表明,煤样渗透率越高自吸速率越大,自吸曲线可以分为自吸和扩散吸附2段,考虑应力作用自吸速率降低近一个数量级,揭示了煤岩物性和应力条件是煤岩水相自吸的影响因素。通过煤吸附水机理和煤岩孔隙结构分析指出,煤表面与水的相互作用和毛细管压力决定了水的自吸特性。研究获得的认识对煤岩气藏水相圈闭评价、压裂方式优选和压裂液设计具有借鉴意义。

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.