注氮气促排煤层甲烷驱替置换效应定量研究

Enhanced Coalbed Methane Recovery(ECMR) , namely promoting recovery of CH4 by CO2 or N2 injection into coalbed , is one of the main methods to improve coalbed methane recovery at present. It is also a new gas treatment technology of eliminating outburst by promoting CH4 emission under the ground. In this project, based on theories and methods of surface chemistry, fluid mechanics, rock mechanics, more systematic experiments for researching dynamic process of CH4 emission by the promoting of N2 will be carried out. A comparatively perfect experimental platform of N2 displacement CH4 will be set up, the evolvement of gas composition, rate of flow, pressure, deformation of the coal, permeability under different gas injection pressure, coal sample payload(crustal stress) and coals could be tracked and tested in real time, thereby achieving dynamic track control of coal variation in the process of injecting , and the single factor such as displacement and replacement also could be studied with quantitative method .This study will provide scientific basis for strengthening gas pre-drainage to prevent outburst in low permeability coal seam, and also lay the theoretical foundation for large-scale application of the new eliminate outburst technology of promoting CH4 emission by injecting N2 .

注气增产法，即向煤层注入CO2或N2以促进CH4回收，是当前提高煤层气采收率的主要方法之一。也是新开发的井下促排CH4消突瓦斯治理技术。本项目基于表面化学、渗流力学、岩石力学等理论和方法对N2促排煤层CH4动态过程开展了较系统的实验。通过搭建功能较为完善的气体驱替煤中CH4的实验平台，能够在不同注气压力和煤样荷载（即地应力）、煤种条件下，实时跟踪和测试气体组分、流量和压力、煤体变形量和渗透率的演化，从而实现对含CH4煤体注入N2过程中煤体变化过程的全程动态跟踪控制及驱替、置换效应单个因素定量化研究。为低透气煤层强化预抽防突提供科学依据，为提出可规模化推广应用的煤层注N2促排甲烷消突新技术奠定理论基础。

煤层瓦斯抽采不但是高瓦斯矿井治理瓦斯超限的基本方法，更是消除和防治煤与瓦斯突出的重要手段。由于受煤层沉积环境、地质变化等因素的影响，我国的高瓦斯矿区煤层渗透性普遍较低，如果不采取其他辅助措施往往很难达到有效预抽煤层瓦斯的目的。采用煤层注气的方法，一方面可以提高煤层中气体渗流速度，另一方面可以降低煤层中瓦斯分压，促进煤层中甲烷解吸，可以起到促排CH4 和消突的作用。井下注N2促排煤层瓦斯主要有驱替、置换两方面效应，为了研究注N2 促排煤层瓦斯过程中驱替和置换效应及其主导作用，利用自研的煤层注气实验装置，进行了单轴应力、分层预压成型条件下煤层注N2 促排瓦斯的模拟实验。对N2置换煤中CH4的置换-驱替效应的单因素贡献进行揭示。.通过进行不同注气压力下（0.6，1.0，1.4MPa）的实验，实验结果表明：注气压力越高，突破时间越短，煤对注入气体的吸附能力越强，突破时间越长。注气压力为0.6MPa时，突破时间为25min；注气压力为1.0MPa，突破时间为15min；当注气压力为1.4MPa时，突破时间为9min，随着注气压力的提高，N2突破时间也在不断缩减，He为不吸附气体，其突破时间更短。.注气过程分三个阶段：第一阶段，注入的N2大部分被煤体吸附，置换效应占主导地位，无驱替作用，第二阶段，N2突破出气口后驱替作用逐渐显现，随着煤体继续吸附N2直至平衡，置换效应开始减弱，驱替效应逐渐增强，表现为大量的N2携载煤中CH4流出腔体，置换和驱替共同作用促排过程，第三阶段，注入的N2大部分流出腔体，只有一小部分滞留腔体被煤体吸附。从注入N2的滞留规律来看，大部分N2都流出腔体体现了驱替效应，且获得了不同注气压力下三个阶段的置换量和驱替量。