气体钻井中井眼温度变化及其对注气量的影响

目前关于气体钻井时所需注气量的计算方法均是将环空流体的温度取同一深度的自然地层温度来进行计算，没有考虑井眼内流体与地层进行换热的影响，这必然会带来误差。而且随着井深的增加，这种误差还会相应增大。为此，根据能量守恒原理，建立了考虑井筒流体与地层换热对井筒流体温度影响在内的数学模型，并进行了求解。然后利用求解获得的环空流体温度计算了所需注气量，并将其与按照地层未受干扰温度所得的注气量进行了对比。结果表明，按照自然地层温度所得的注气量偏小，并随着井深的加大该差值会逐渐增大。因此，在进行深井气体钻井作业时需要考虑地层与井眼流体换热的影响来计算井眼流体温度，进而确定出合理的注气量。

HOLE TEMPERATURE VARIATION AND ITS EFFECTS ON GAS INJECTION RATE DURING GAS DRILLING

The currently used methods for calculating gas injection rate during gas drilling all take the temperature of natural formation at the same depth as the temperature of the annulus fluid, without considering the heat exchange occurred between the wellbore fluid and the formation. So the errors are inevitable. What's the worse, the error will become greater by the increase of the well depth. Based on Conservation of Energy Principle, this paper set up a mathematical model taking into consideration the effects on well fluid temperature by heat exchange between the wellbore fluid and the formation, etc. With the solution of annulus fluid temperature obtained from the model, the required gas rate was calculated. By comparing this calculated rate with the rate obtained using formation temperature, this paper found out that the gas injection rate obtained by assuming formation temperature was smaller, and would be much smaller by the increasing depth. Therefore to determine appropriate gas injection rate for gas drilling, this paper suggests the effects of heat exchange between the formation and the wellbore fluid should be taken into consideration when calculating the wellbore fluid temperature.