地应力地温场中煤层气富集区高精度定量预测的力学方法

High precision and quantitative prediction mechanics method of coalbed methane enrichment area in geo-stress and geothermal field

针对当前我国煤层气富集区预测中预测位置不准、难以定量化描述、精度不高等不足,提出了地应力地温场中煤层气富集区定量预测的力学方法。建立了应力、温度影响下的煤层气压力预测方程、含气量预测方程,预测方程体现了地应力和地温对煤层气压力、含气量、孔隙率的影响,其中,应力和温度通过影响煤层气压力进而影响吸附量,通过影响煤层气压力和孔隙率进而影响游离量,温度还通过影响吸附常数b影响吸附量。以重庆沥鼻峡盐井矿区为研究区,进行了Kaiser声发射原岩应力测试实验、不同温度下的煤体甲烷等温吸附实验和不同埋深的孔隙率测定实验。实验表明,吸附常数a随温度变化不明显,b随温度升高线性减小。以实验为基础,结合现场实测数据和实际地质资料,定量化预测了矿区煤层气含气量分布。以煤层气含量为判别指标,按照富集程度不同,将研究区划分为两级富集区。预测方法克服了以往煤层气富集区预测定性描述、预测不准和精度不高的不足。

Aiming at the shortcomings of inaccurate predicting position,qualitative description and low precision about coalbed methane enrichment region predicting in China,this paper proposed quantitative prediction mechanics method of coalbed methane enrichment region,established prediction equations of gas pressure and coalbed methane（CBM） content influenced by stress and temperature.The equations reflects influence of ground stress and ground temperature on gas pressure,content of CBM and coal porosity.The stress and temperature affects gas pressure and changes gas adsorption content,affects gas pressure and coal porosity and changes gas free content.In addition,temperature affects adsorption parameter b and changes adsorption content.Took Libixia Yanjing mining area in Chongqing as an example,experiments of initial rock stress testing based on Kaiser AE method,methane adsorption testing at different temperatures,coal porosity testing at different depth,were carried out.Adsorption experiment indicates that adsorption parameter a is not obviously changed with temperature,b is linearly reduced with temperature increasing.Based on experiment and geological data,distribution of CBM content was predicted quantitatively.According to the dissimilarity of enrichment degree,the research area was divided into two-level enrichment region by CBM content as index.The prediction method overcomes the shortcomings of qualitative description,error prediction,low precision of CBM predicting.