煤层气等温吸附/解吸模拟实验技术新进展与应用

Research and Application of In-situ CBM Adsorption/Desorption Simulation

煤岩的吸附/解吸数据是煤层气资源预测、产能评价必需的核心参数,目前常规的等温吸附实验只能获得固定温度下的吸附量和压力之间的关系。如何获得储层条件下准确的等温吸附数据,是煤层气储层实验测试孜孜以求的目标。针对当前煤层气等温吸附测试主要沿用美国专利US5058442/4528550,采用IS-300等温吸附仪,存在测试范围小、破坏样品原始结构及无围压约束等突出问题,创新研制煤层气原位吸附/解吸模拟装置,克服了目前等温吸附测试未考虑地应力影响,不能代表地层真实吸附状态的缺陷。特别是形成非吸附性气体等温吸附实验方法,为变体积自由空间的计算提供参数。该装置的成功研制开发,一方面实现等温吸附装置国产化,另一方面实现高温压条件下煤岩原位吸附模拟技术的从无到有。研究发现,在较高温度和压力时(>85℃,>30MPa),温度对煤吸附能力的影响大于压力的影响。从而证实含气量与埋深关系存在"临界深度",即浅部煤层含气量随埋深增大而增高,在一定埋深达到最大值,超过此埋深之后含气量随埋深进一步增大而趋于降低。

CBM Adsorption/Desorption data are the key parameters to appraise CBM resources and productivity. The current conventional Isotherm adsorption experiment can only provide the relationship between adsorption volume and pressure at a fixed temperature set at the beginning of experiment. How to get the real adsorptiun/desorption data in the in-situ condition become a challenge for the CBM laboratory. To overcome the bottlenecks existing in isothermal CBM adsorption testing which currently adopts the US5058442/4528550 patent and IS-300 in- situ absorption instrument, such as small testing scope, damage of sample＇s original structure, and free from restraint by surrounding pressure, Langfang CBM laboratory created a new CBM adsorption/desorption simulation device that overcomes the shortcoming that the current in-situ adsorption testing does not take into account the influence of stress and cannot reflect the real adsorption status of the formation. Particularly, the method for in-situ adsorption testing of non-adsorptive gas provides the parameters for calculation of variable volume free space. Successful development of this instrument localizes the isothermal adsorption apparatus and creates the in-situ CBM adsorption simulation under the high-temperature condition. The research indicates that the effect of high temperature on CBM adsorption capability is higher than that of pressure under the conditions of high temperature and pressure （〉85℃, 〉30MPa）, thus confirming that a ＂critical depth＂ exists in the relationship between CBM content and buried depth. Namely the CBM content in the shallow layer increases with the rise of buried depth and reaches the maximum value at a certain buried depth. Then the CBM content decreases with the further rise of buried depth after exceeding the certain depth.