考虑水蒸气压力的平衡水页岩等温吸附  

Sorption measurements of moisture-equilibrated shale with the consideration of water vapor pressure

作　　者：齐荣荣[1,2] 宁正福[1,2] 王庆[1,2] 张爽 曾彦[1,2] 黄亮[1,2] 杜华明 QI RongRong;NING ZhengFu;WANG Qing;ZHANG Shuang;ZENG Yan;HUANG Liang;DU HuaMing(MOE Key Laboratory of Petroleum Engineering, China University of Petroleum （Beijing）, Beijing 102249, China;State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum （Beijing）, Beijing 102249, China)

机构地区：[1]中国石油大学(北京)石油工程教育部重点实验室,北京102249 [2]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249

出　　处：《中国科学：技术科学》2018年第5期524-536,共13页Scientia Sinica(Technologica)

基　　金：国家自然科学基金项目(批准号:51774298;51274214);教育部科学技术研究重大项目(编号:311008);高等学校博士学科点专项科研基金项目(编号:20120007110.012)资助

摘　　要：基于改进的容积法等温吸附实验装置,分别测量了甲烷在干燥、平衡水条件下的页岩等温吸附曲线,实验温度为303.15,323.15和353.15 K,实验最高压力达20 MPa,实验数据采用修正的Langmuir方程进行拟合.在开展平衡水页岩吸附实验时,考虑了水蒸气压力,认为实验气体为甲烷与水蒸气混合气体,重新计算了混合气体中甲烷吸附量,并从吸附热力学角度阐述考虑水蒸气压力的意义,最后在地层条件下讨论了水蒸气压力对页岩吸附的影响.结果表明,考虑/未考虑水蒸气压力的平衡水页岩Langmuir最大吸附量分别为0.053和0.039 mmol/g,未考虑水蒸气压力的甲烷吸附量被低估26.4%.干燥页岩的等量吸附热为11.6 k J/mol,考虑与不考虑水蒸气压力的平衡水页岩等量吸附热分别为10.7和12.3 k J/mol,由于水分优先吸附于能量较高的吸附位,在水分存在情况下,平衡水页岩对甲烷的等量吸附热应该小于干燥页岩,因此,经水蒸气压力校正后的等量吸附热更加符合热力学一致性.在地层条件下,水蒸气压力对页岩吸附的影响分为两个阶段:(1)浅埋藏阶段(地层深度小于700 m),此阶段由压力梯度主导,压力梯度越大,水蒸气压力对吸附的影响越大;(2)深埋藏阶段(地层深度大于700 m),此阶段由压力梯度和温度梯度同时控制,压力梯度越大,温度梯度越小,水蒸气压力对吸附的影响越大.High-pressure methane sorption isotherms measured at 303.15,323.15 and 353.15 K and pressure up to 20 MPa were measured on dry and moisture-equilibrated shale based on an improved volumetric sorption equipment. The sorption data were fitted by a modified Langmuir equation. Assuming that the experimental gas is the mixture of methane and water vopor in the moisture-equilibrated shale sorption experiment, the sorption capacity of methane accounting for water vapor pressure were recalculated, and the importance of water vapor pressure on shale sorption was discussed basing on thermodynamics of sorption. The results show that the Langmuir maximum sorption capacities of moisture-equilibrated shale with/without consideration of water vapor pressure are 0.053 and0.039 mmol/g, respectively. Methane sorption capacity without consideration of water vapor pressure is underestimated by 26.4%.The isosteric heat of adsorption for dry shale and moisture-equilibrated shale with/without consideration of water vapor pressure are11.6, 10.7 and 12.3 k J/mol, respectively. Since water preferentially occupies the higher energy sites, the presence of moisture is expected to reduce rather than increase the isosteric heat of adsorption. Therefore, the thermodynamic parameter corrected by water is more consistent with thermodynamic consistency. Under the condition of formation, the effect of the water vapor pressure on the sorption of shale can be divided into two stages：（1） shallow burial stage（depth of stratum less than 700 m）, this stage is dominated by the pressure gradient. The greater the pressure gradient, the greater the effect of the water vapor pressure on the sorption of shale;（2）deep burial stage（depth of stratum more than 700 m）, this stage is controlled simultaneously by pressure gradient and temperature gradient. The greater the pressure gradient and the smaller the temperature gradient, the greater the effect of the water vapor pressure on the sorption of shale.

关 键 词：页岩气 吸附 平衡水 水蒸气压力 等量吸附热 

分 类 号：TE311[石油与天然气工程—油气田开发工程]