基于不同温压条件等温吸附实验的低煤级储层吸附气含量估算方法

A calculating method of indirelt absorbedgas content of Low-rank Couls based on isothermal adsorption experiments under different temperatures and pressures

为系统分析低煤级煤储层原位吸附气含量,收集了8个样品在25℃和45℃平衡水条件下的等温吸附资料,开展了2个低煤级煤样平衡水条件下等温吸附实验,提出了基于不同温压等温吸附实验的低煤级储层原位吸附气含量预测方法。结果显示:低煤级煤吸附气含量随温度增大而减小,甲烷吸附递减量随压力增加呈指数变化而非线性变化,基于预测方法对海拉尔盆地4煤样和准噶尔盆地南缘阜康矿区F1井钻遇层位原位条件下的吸附气含量进行了估算,结果显示低煤级储层吸附气含量随埋深增加而增加,但增加趋势不明显,与中-高煤级储层吸附气含量随埋深增大变化趋势不同,同时预测结果为F1井实测含气量所验证。本论文成果有助于低煤级储层煤层气的勘探与开发。

In order to systematically analyze the sorption gas content of low-rank coals, methane isothermal adsorption experiments on moisture-equilibrated coals were performed under different temperatures. In total 8 low-rank coal samples＇ methane adsorption experiment data on 25℃ and 45℃ were collected and analyzed while 2 of those were conducted, based on which a indirect adsorbed gas content calculating method was proposed. The results showed that adsorbed gas content in low-rank coals decreased as temperature increased. The relationship between methane adsorption decrement and pressure was not linear over a wide range, but was better described by a logarithmic form. Based on the calculating method, four low-rank coal samples of Hailar Basin in Inner Mongolia and drilled coal seam of F1 well in Fukang mining area of sourthern Junggar Basin were evaluated under in-situ conditions of reservoir temperature and pressure. The results showed that the adsorbed gas content in these low-rank coal reservoir increases but not obviously with increasing burial depth from 600 to 1400m. These characteristics are quite different from that of middle or high rank coal reservoir and the calculating method was validated to be correct by the comparative analysis between calculating results and actual test results of F1 well. Findings in this work are helpful to further understand the adsorbed gas content and improve evaluation of the coalbed methane reserve of low-rank coal reservoirs.