摘要
准确认识深部条件下气体和水分的赋存状态、相对含量及分布特征,对煤层气高效勘探开发具有重要指导意义。基于理论模型、分子模拟和气水演变分析,明确了煤层中气、水的赋存状态,揭示了气、水动态运聚界限和动态演化过程。考虑煤-水界面作用、水的可动性及赋存状态,煤中水可分为可动水(重力水和毛细水)、束缚水(吸附水、沸石水、结晶水和层间水)、结构水,其中毛细水、重力水和吸附水由孔隙主导,沸石水、结构水、结晶水和层间水由矿物主导。分子模拟结果显示,水分子在0.7 nm孔隙中可以饱和充填,吸附和解吸路径一致,在更大孔隙中出现弱吸附层和自由态。水分子吸附过程表现为单分子含氧基团吸附、单层强吸附、多层弱吸附、水团簇形成和充填孔隙等阶段。甲烷分子在1.5 nm孔隙可存在3层稳定充填吸附,在较大孔隙中(>1.5 nm)即以单层吸附和游离态共存,游离态在介孔及更大孔隙中普遍存在。结合上述吸附-游离气存在界限,改进了游离气和吸附气理论计算公式,为含气量计算提供新思路。深部热成因煤层气是煤大规模生排烃之后的残余气,在排烃过程中发生气驱水和水分蒸发扩散,残余水分为束缚水和结构水,后期无法改变。假定静水压力20 MPa,在0、5、10、15和20 MPa储层压力下,外来水分可入侵最大孔径为7、9、13、27 nm和不侵入。受差异保存条件控制,煤成气除了形成超压和欠压等差异含气系统外,还可能在煤系形成多类型含气模式。上述研究明确了煤层气、水微观赋存机制及形成演化模式,对深部煤层气富集特征及高效开发设计具有指导意义。
Accurately understanding of the occurrence states,relative content,and distribution characteristics of gas-water under deep conditions has important guiding significance for efficient exploration and development of coalbed methane(CBM).Based on the theoretical model,molecular simulation and systematic analysis of gas-water,the occurrence states of gas-water in coal seam is clarified,and the boundary and dynamic evolution process of gas-water dynamic migration and accumulation are revealed.Considering the coal-water interface interaction,the mobility and occurrence states of water,the coalbed water can be divided into movable water(gravity water and capillary water),bound water(adsorbed water,zeolite water,crystallization water and interlayer water)and structural water.The adsorbed water,capillary water and gravity water are dominated by pores,and zeolite water,structural water,crystallization water and interlayer water are dominated by minerals.The molecular simulation results show that water molecules are saturated and filled in 0.7 nm pores,with consistent adsorption and desorption processes,while weak adsorption layers and free states appear in larger pores.The adsorption process of water molecules is manifested in stages:single molecule oxygen-containing group adsorption,monolayer strong adsorption,multi-layer weak adsorption,water clusters formation,and pore filling.Methane molecules stably fill pores(1.5 nm)with 3 layers of adsorption,and coexist in monolayer adsorption and free state in the larger pores(>1.5 nm),resulting in the widespread presence of free state in pores above mesopores.According to the boundary between adsorption and free gas mentioned above,the theoretical calculation formulas for free gas and adsorption gas have been improved to provide new ideas for gas content calculation.Deep thermogenic CBM is the residual gas generated after large-scale hydrocarbon generation and expulsion from coal.During the hydrocarbon expulsion process,the water is driven by methane and the evaporation diffusion process results in a small amount of residual water(bound water and structural water)remaining in the pores,which cannot be changed in the later stage.Assuming a static water pressure of 20 MPa,under reservoir pressures of 0,5,10,15,and 20 MPa,the maximum pore size that external water can invade is 7,9,13,27 nm and non-invasive.Controlled by differential preservation conditions,coal-derived gas not only forms overpressure and under pressure differential gas bearing systems,but also forms multiple types of gas bearing modes in coal measures.The above work has clarified the micro-occurrence mechanism and evolution mode of CBM and water,which has guiding significance for the enrichment characteristics and efficient development design of deep CBM.
作者
李勇
徐立富
刘宇
王子炜
高爽
任慈
LI Yong;XU Lifu;LIU Yu;WANG Ziwei;GAO Shuang;REN Ci(College of Geoscience and Surveying Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China)
出处
《煤田地质与勘探》
EI
CAS
CSCD
北大核心
2024年第2期40-51,共12页
Coal Geology & Exploration
基金
国家自然科学基金项目(42072194,U1910205)。
关键词
深部煤层气
煤层水
分子模拟
游离气
储层压力
deep coalbed methane
coalbed water
molecular simulation
free gas
reservoir pressure
