沁水煤层气田高阶煤解吸气碳同位素分馏特征及其意义

沁水盆地是我国煤层气勘探开发的重要有利区,沁水煤层气田位于盆地东南部。对采自沁水煤层气田两口井的煤开展了罐解吸实验。结果表明,该地区煤层气解吸速率很快,96 h后解吸气量都达到了总解吸气量的60%~85%,720 h后解吸过程基本结束;解吸气量大,平均在18 m3/t以上。煤层气解吸过程中甲烷发生碳同位素分馏,δ13C1值变化与解吸率呈良好的线性关系,参考这种正相关关系曲线,定期监视煤层气降压排采过程中甲烷δ13C1值的变化情况,可以大致推测出该地区煤层气解吸率,从而预测煤层气的采出程度。跟踪测试沁水煤层气田A1和A1-3井在试采过程的甲烷δ13C1变化情况,推测现在采出的煤层气可能主要是煤层裂隙中以游离形式存在的煤层气,表明该区煤层气稳产性较好,资源前景广阔。

Characteristics and implications of the carbon isotope fractionation of desorbed coalbed methane in Qinshui coalbed methane field

The Qinshui Basin is an important favorable locale for Coalbed Methane(CBM)exploration and development in China.The Qinshui coalbed methane field was discovered in the southeastern part of the basin.We have carried out an experiment of canister desorption of methane from two fresh coal samples collected from two wells of the field.The experimental results indicate that the coal desorption rate in the area is high,the amount of desorbed gas may reach 60%-85% of the total amount of desorbed gas over 96 hours of desorption,and the whole desorption process was practically ended in 720 hours.The amount of desorbed gas is more than 18 m3/t on average.The fractionation of carbon isotope occurs during the process of canister desorption,and the change in δ13C1 values in methane appears to be linearly related to the desorption rates.According to this linear correlation and regularly monitoring the change in δ13C1 values in the process of coalbed gas production,we can deduce the desorption rates of coalbed methane from the gas field and forecast the recovery percentage and production life.Based on the change in δ13C1 values during the trial production in A1 and A1-3 wells,it is deduced that the produced coal gas probably is mainly free gas coming from fissures in the coal.This demonstrates that the stable yielding quality of CBM is good and the exploration potential of coalbed methane in this basin is high.