摘要
煤层气的开采效率受到很多因素影响,煤层开采过程注入的压裂液及煤层中自生的液态水常常会阻碍煤层气的扩散及开采,形成水锁效应,但其成因、机理以及缓解方法仍不完全清楚,也是目前研究的热点。基于大规模、可扩展、可准确反映煤层化学结构的分子模型,通过采用分子动力学方法,在微观尺度模拟了在煤层微孔隙中,甲烷在受到水膜阻碍的情况下,水气两相的流动规律。定量计算了水膜厚度、孔径、储层压力、压差等因素对甲烷及水膜运移速度的影响。结果表明,水的存在会极大地阻碍甲烷的扩散,即造成水锁效应;煤层中的孔径大小及流动压差也会影响甲烷/水的两相流动速率,较大的孔径及较高的压差都有利于甲烷和水的流动。通过对水膜在运移过程中发生的结构变化的分析,对水锁效应出现及消失的规律进行了探究。在大孔径及较厚水膜的条件下,水相可在流动过程中保持完整的连续相,完全封闭煤层中的孔隙,造成水锁效应。而在水膜较薄或孔径较小时,水分子与煤层之间的相互作用力使得水相更容易破裂为多个水分子团簇,并与甲烷气相混合,从而缓解水锁效应。通过纳米尺度的分子模型定量分析了煤层孔径、压差、水膜厚度等因素对水锁效应的影响规律,表明减弱水分子之间并增强水分子与煤层之间的相互作用可能有利于缓解水锁效应。此项研究可以为进一步理解水锁效应机理、提高煤层气开采效率提供启示。
The extraction efficiency of coalbed methane is affected by many factors.Among them,the fracturing fluid injected during coal seam mining and indigenous liquid water in the coal seam often hinder the diffusion and exploitation of coalbed methane,which leads to the water block effect(WBE).The cause,mechanism,and mitigation methods of the WBE are still not completely understood,and are also the topics of current research.This study was based on a large-scale molecular model which accurately reflects the chemical structure of coal,this study used molecular dynamics(MD)methods to simulate the flow patterns of methane and water in the micro-pores of coal seams,considering the hindering effect of water film on methane.The impact of factors such as water film thickness,pore size,reservoir pressure,and pressure difference on the transport velocities of methane and water film has been quantitatively calculated.The results demon-strate that the existence of water will significantly hinder the diffusion of methane and cause WBE.The pore size and pres-sure drop will also affect the two-phase flow speed of methane and water.Larger pore size and higher pressure drop favor the flow of methane and water.Through analyzing the structural changes of the water film during its transportation,the patterns of occurrence and disappearance of WBE was investigated.Under the conditions of larger pore sizes and thicker water films,the water phase can maintain a continuous phase during the flow process,which completely seal the pores in the coal seam,and cause the WBE.On the other hand,when the water film is thin or the pore size is small,the attractive interaction between water molecules and coal seam makes it easier for the water phase to break into multiple water mo-lecular clusters and mix with the methane gas phase,thus alleviating the WBE.Based on the nano-scale molecular models,this study quantitatively investigated the effects of pore sizes,pressures differences,and water film on WBE,showing that reducing the interactions between wat
作者
黄林岗
林凌
罗文嘉
HUANG Lingang;LIN Ling;LUO Wenjia(School of Chemistry and Chemical Engineering,Southwest Petroleum University of China,Chengdu 610500,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2023年第11期4124-4134,共11页
Journal of China Coal Society
基金
油气田应用化学四川省重点实验室开放基金资助项目(YQKF202214)。
关键词
煤层气
分子动力学
水锁效应
煤分子模型
扩散
coalbed gas
molecular dynamics
water blocking effect(WBE)
coal molecular model
diffusion
