页岩含气量测定方法分析与优化

页岩气主要以吸附或游离态赋存于暗色泥页岩或高碳泥页岩层系中,与煤层气在成藏模式、赋存特征、孔裂隙结构、解吸和流动方式、开采技术等方面具有类似性,同属"原地成藏模式"。在页岩气勘探中,含气量的计算多参考煤层气含气量测定标准执行。选取含气量测定具有代表性的页岩样品和煤样实验,分析了页岩气解吸过程特点,并对页岩含气量测定方法提出优化建议。研究表明:页岩含气量测定需要根据提芯时间和暴露时间的长短,选择使用二阶解吸温度或者三阶解吸温度完成解吸;页岩气解吸过程具有解吸温度高、解吸周期短、解吸速率呈现阶段性三个特点;损失气计算受解吸过程中的稳定性影响,最初期解吸数据不符合单分子层解吸理论所分析的变化规律,认为应选用稳定解吸阶段合适的数据点进行计算并修正,保证损失气量数据的准确性。

Analysis and Optimization on Determination Method of Gas Content of the Shale

Shale gas is hosted in the series of strata of the dark shale or high carbon mud shale at the adsorption or free states.There are a lot of similarities with coalbed methane ,such as accumulation mode and exist characteristics,hole fissure structure,desorption and flow regime,mining technology and so on.They all belong to ＂in-situ accumulation mode＂.In the exploration of the shale gas,gas content is calculated according to the determination standard of the coalbcd methane content.Experiment is made using the selected representative samples of shale and coal,and characteristics of shale gas desorption process are analyzed.Optimization proposal of the shale gas content determination is put forward.Research has shown that： during the determination process of the shale gas content,desorption may be finished at two-stage desorption temperature or three-stage desorption temperature according to the interval of core pulling out and exposure duration.There are three characteristics during the desorption process of the shale gas ：high temperature ,short cycle and interval desorption rate.Affected by the desorption process stability in the calculation of loss gas,the initial desorption data does not match the change rule analyzed by monolayer desorption theory.It is suggested that suitable data points at stable desorption stage should be selected to calculate and correct,which will ensure the accuracy of the loss gas data.