基于绝热火焰温度的空气钻井井下燃爆界限预测方法研究

Prediction method of downhole explosion limit in air drilling based on adiabatic flame temperature

为进一步准确、高效预测空气钻井井下燃爆界限,首先基于恒压、恒焓原则下的绝对焓守恒理论,推导出CHO化合物燃烧的绝热火焰温度普适模型,提出使用绝热火焰温度预测空气钻井井下燃爆界限的方法;然后利用高温高压(0.1×10^(6)~10×10^(6)Pa,20~90℃)条件下的甲烷-空气燃爆实验数据,分析燃爆界限预测结果的有效性;最后,以马1-X井为例,提出基于绝热火焰温度预测燃爆界限的钻井现场应用方法。研究结果表明:预测结果与实验结果一致性较高,最大绝对误差为3.84%;随着井深增加,井下燃爆界限范围不断变宽,燃爆上限变化幅度大于燃爆下限;通过摩尔分数与体积流量之间关系,能够使燃爆界限以甲烷产量的形式得以表现。研究结果可实现在钻井现场快速、准确预测燃爆界限,为预防井下燃爆、提高空气钻井安全性提供一定参考。

In order to accurately and efficiently predict the downhole explosion limit of air drilling,based on the absolute enthalpy conservation theory under the principle of constant pressure and constant enthalpy,a universal model of adiabatic flame temperature for CHO compound combustion was derived,and a further method of using the adiabatic flame temperature to predict the downhole explosion limit of air drilling was proposed.The data from high temperature and high pressure(0.1×10^(6)~10×10^(6) Pa,20~90℃)methane-air explosion experiment were used to analyze the effectiveness of the prediction results of explosion limit.Taking Ma 1-X well as an example,the application method in drilling site to predict the explosion limit based on adiabatic flame temperature was introduced.The results show that the prediction results of this method are highly consistent with the experimental results,and the maximum absolute error is 3.84%.As the well depth increases,the range of downhole explosion limit continues to widen,and the variation amplitude of upper limit is larger than that of lower limit.The explosion limit can be expressed in the form of methane production by the relationship between mole fraction and volume flow rate.The prediction method can quickly and accurately predict the explosion limit in the drilling site,and provide some reference significance for preventing the downhole explosion and improving the safety of air drilling.