西山区块煤储层含气性及甲烷碳同位素分布特征

煤层含气性是决定煤层气勘探开发的重要参数，煤层气甲烷碳同位素能有效反映煤层气的赋存条件。根据煤层气井实测含气量数据，剖析了山西沁水盆地煤层含气量分布特征，建立了煤层含气量与煤层埋深、地质构造之间的相关关系和模型，探讨了煤层甲烷碳同位素分布特征及其对含气性分布的指示作用。研究表明:西山区块2号煤层平均含气量6.87 m3/t，8号煤层平均含气量8.4 m3/t，9号煤层平均含气量7.6 m3/t，煤层含气量主要受煤层埋深和构造形态的影响。研究区8号煤层甲烷碳同位素为–65.33‰~–40.94‰，平均–45.88‰，煤层含气量与甲烷碳同位素之间成正相关关系，随着含气量的增加，甲烷碳同位素也逐渐变重。煤层甲烷碳同位素主要受控于煤层气解吸–扩散–运移效应和地下水动力作用等。 

Distribution characteristic of gas content of coal reservoir and its methane carbon isotope in the Xishan block

The gas-bearing properties is an important parameter to determine the exploration and development of coalbed methane(CBM). The methane carbon isotope(δ13C₁) can reflect the reservoir condition of CBM effectively. Based on the date of measured gas content from CBM well, the characteristic of gas content distribution in coalbed was analyzed, and the correlations and models of gas content, the burial depth of coalbed, geological structure were built. The characteristic of δ13C₁ distribution was discussed and it had an indicative function to the distribution of gas-bearing properties. Findings show that, the gas content in the Xishan block is an average of 6.87 m3/t, 8.4 m3/t, 9.6 m3/t in the No.2, 8 and 9 coalbed respectively. The gas content was mainly influenced by burial depth of coalbed and structural configuration. The δ13C₁ value of the No.8 in the study area ranges from -65.33‰ to -40.94‰ and its average is -45.88‰, and there was a positive correlation between coalbed gas content and δ13C₁. δ13C₁ generally is getting heavy with increase of gas content. δ13C₁ is mainly controlled by the coalbed methane desorption-diffusion-transport effect and hydrodynamic condition.