基于等温吸附的页岩水分传输特征研究

研究页岩的水分传输特征至关重要,不仅有助于认识页岩的物理化学性质,而且也有助于评价页岩气的吸附扩散和流动能力.本文设计了页岩的水分传输实验装置,采用美国伍德福德和中国南方龙马溪组页岩为研究对象,开展了不同温度、不同湿度下页岩的水分传输实验,研究了页岩的水分传输特征和影响因素.结果表明,页岩的水分吸附属于II型曲线,包含着单分子层吸附、多分子层吸附和毛细凝聚的过程,GAB模型可用于描述页岩的水分吸附过程;水分吸附随着相对压力的增大而增强,有机碳含量和温度对页岩水分吸附起着增强作用,而方解石会抑制页岩的水分吸附;随着相对压力的增大,页岩的水分扩散系数呈现先增大后减小随后增加的趋势,其系数大约在8.73$times$10$^{ - 9}sim $5.95$times $10$^{ - 8 }$m$^{2}$/s之间;伍德福德页岩的等量吸附热均大于龙马溪页岩的等量吸附热,这与其页岩的成熟度有关.研究结果为认识页岩的物理化学性质和力学性能以及评价页岩气的吸附流动能力提供参考依据. 

STUDY ON MOISTURE TRANSPORT CHARACTERISTICS OF SHALE BASED ON ISOTHERMAL ADSORPTION1)

The study on moisture transport characteristics of shales is critical, which is not only helpful to understand the physical and chemical properties in shales, but also to evaluate the adsorption, diffusion and flow ability of shale gas. In this study, the experimental device of moisture transport in shales was designed and the shale samples from Woodford in USA and Longmaxi Formation in Southern China were used. The moisture transport in shales was carried out at different temperatures and humidities, and the transport characteristics and the effects in shales were investigated. The results indicate that moisture adsorption isotherms of shales belong to type II curve, including the monolayer, multilayer adsorption and capillary condensation, and the GAB model can be used to describe the moisture adsorption process of shale rocks. With the increasing of relative pressure, the moisture adsorption of shales increases. The content of organic carbon and temperature strengthen the moisture adsorption in shales while calcite will inhibit the process. The moisture diffusion coefficient in shales initially increases, then decreases and finally increases with relative pressure, and the value ranges between 8.73$times $10$^{ - 9}$ m$^{2}$/s and 5.95$times $10$^{ - 8 }$ m$^{2}$/s. The isothermal heat of moisture adsorption in Woodford shale is higher than that of Longmaxi Formation, which is related to shale maturity. These results provide some reference basis for understanding the physical and chemical properties in shales and evaluating the adsorption and flow capacity of shale gas.