不同状态的二氧化碳对煤层气的驱替研究

发布时间：2018-03-27 14:18

  本文选题：煤层气　切入点：超临界二氧化碳　出处：《太原理工大学》2015年硕士论文

【摘要】：煤层气是煤层形成过程中伴生的产物，俗称瓦斯。主要成分与常规天然气相同，都为甲烷气体。众所周知，瓦斯气体的存在对井下作业人员的人身安全以及煤炭资源的财产安全都有重大威胁。瓦斯积聚达到一定浓度，一旦遇到明火就会引起爆炸，会给矿井作业带来巨大的灾难。瓦斯危害一直是困扰我们的一个重大问题。另外，由于煤层气的主要成分与天然气相同，且在煤层中储量丰富，如果能够得以有效利用，我们目前这个资源短缺的现状将会得到巨大改善。所以，如何将煤层气变废为宝，具有很大的现实意义和经济意义。 针对以上情况，本文进行了氦气测煤样渗透率、温度解吸、不同状态下的二氧化碳驱替、驱替前后渗透率测定等试验，系统地研究了煤样的渗透性能及对煤样的驱替或解吸效率。主要的研究内容和结果如下： 1）利用He测煤样弹性阶段、塑性阶段直至断裂破坏整个过程的渗透率，国内煤层大多数是低渗煤层，瓦斯驱替对煤层渗透率有一定的要求，所以在驱替实验前，先进行煤样的渗透率测定实验。实验结果表明：试件在弹性阶段，渗透率基本保持不变，进入塑性阶段后，煤体结构、孔隙及裂隙呈现不规则变形，渗透率出现了较为明显的波动。随着轴向应力进一步增大，试件进入形变强化阶段，在这一过程试件发生了大量而均匀的变形，裂隙通道进一步被打开，渗透率急剧增大。 2）根据温度越高，煤样对气体的吸附能力越差，把含甲烷饱和煤样置于不同温度的水浴中，温度分别设为40℃、60℃、80℃，充分解吸。得出：温度越高，解吸地越快，解吸出来的量也越多。将三个温度下的驱替效率对比得出，在保温阶段，三组实验的解吸效率差距很小，是因为保温阶段，虽然温度高有利于气体解析，但高温同时会导致煤体膨胀，压缩气体运移通道。而在升温阶段由于温度一直在改变，煤体膨胀不均匀，会产生新的裂隙，导致解析效率差距明显。 3）煤样吸附甲烷至饱和，用常规二氧化碳驱替。发现吸附的甲烷量小于进入的二氧化碳量，煤样对二氧化碳的吸附能力大于对甲烷的吸附能力；设定孔隙压分别为7MPa、8MPa，孔隙压越大，驱替完成所需要的时间越短，并且驱替效率越高。在渗透率方面，驱替前的渗透率为0.0125mD，驱替后渗透率变为0.0067mD，渗透率明显变小。所以常规二氧化碳驱替会使煤层渗透性能降低。 4）在亚临界二氧化碳驱替饱和煤样时，，由于CO2临界温度为31.26℃，临界压力为72.9atm。将孔隙压设为7MPa，温度分别设为40℃、60℃、80℃。发现40℃驱替效率最低，且到驱替完全用时最多，80℃驱替的驱替效率最高，但与60℃驱替差距很小。在渗透率方面：驱替后的渗透率为0.01496mD，与驱替前的渗透率0.01126mD相比，渗透率略微变大。所以亚临界二氧化碳驱替会使煤层渗透性能提高，但提高的幅度很小。 5）在超临界二氧化碳驱替时，将孔隙压设为8MPa，温度分别设为40℃、60℃、80℃。在驱替速率和驱替效率方面，与亚临界驱替规律相近，都是40℃最低，80℃最高，且60℃和80℃驱替速率和效率都十分接近。但超临界状态的二氧化碳的驱替速率和效率都优于亚临界状态的二氧化碳。在渗透率方面，驱替前的渗透率为0.01033mD，驱替之后的渗透率为0.01824mD，与驱替前的渗透率相比，渗透率变化很大，所以超临界二氧化碳驱替会使煤层渗透性能大幅提高。
[Abstract]:Coal bed gas is associated with the formation process of coal seam , commonly known as gas . The main component is the same as that of conventional natural gas , it is methane gas . As is well known , the existence of gas gas has serious threat to the personal safety of underground operation personnel and the property safety of coal resources . As the main components of coal bed gas are the same as natural gas , and the reserves are abundant in the coal seam , the present situation of gas shortage will be greatly improved . Therefore , it is of great practical significance and economic significance to change the coal bed gas into treasure .

In view of the above conditions , the permeability , temperature desorption , carbon dioxide displacement and permeability determination of coal samples under different conditions are studied systematically . The permeability properties of coal samples and the displacement or desorption efficiency of coal samples are systematically studied . The main research contents and results are as follows :

1 ) Using He to measure the elastic phase of coal samples , the permeability of the whole process is destroyed by the plastic stage until the fracture , most of the domestic coal seams are low permeability coal seams , and the gas displacement has certain requirements on the permeability of the coal seam . The experimental results show that the permeability of the coal body is basically unchanged after the displacement experiment . The experimental results show that the coal body structure , the pores and the cracks exhibit irregular deformation after the displacement experiment , and the permeability has been obviously fluctuated . As the axial stress increases , the test piece enters the deformation strengthening stage , and the fracture channel is further opened and the permeability increases sharply .

2 ) According to the higher the temperature , the worse the adsorption capacity of the coal sample to the gas , the higher the temperature , the faster the desorption is , the more the desorption efficiency is .

3 ) the coal sample adsorbs methane to saturation , and is driven by conventional carbon dioxide , and the adsorption capacity of the coal sample on the carbon dioxide is larger than that of the incoming carbon dioxide , and the adsorption capacity of the coal sample to the carbon dioxide is larger than that of the methane ;
Setting the pore pressure is 7 MPa , 8 MPa , the greater the pore pressure , the shorter the time required for the completion of displacement and the higher the displacement efficiency . In terms of permeability , the permeability before displacement is 0.0125mD , the permeability after displacement becomes 0.0067mD , the permeability is obviously smaller . Therefore , the conventional carbon dioxide flooding can reduce the permeability of the coal bed .

4 ) At subcritical carbon dioxide displacement saturated coal sample , the critical temperature is 31.26 鈩

本文编号：1671877