非稳态注汽条件下井筒热损失计算

在蒸汽吞吐注汽阶段,井口注入参数往往会随时间变化,传统的井筒传热模型没有考虑到这一点,并且在算法上只按井筒深度分段,忽略了注汽时间也需分段.为了准确计算非稳态注汽条件下井筒热损失,首先,利用稳态逐次替换法将非稳态井口注入参数分时间段处理,因而水泥环外缘温度在较短时间内可以视作定值;其次,基于叠加原理对井筒传热模型进行修正,并提出了井筒总热损失表达式;最后,按时间和深度分段求解整个模型.结果表明:即使在相同深度段内,热损失速率也不是定值.因此,某深度段在注汽过程中的总热损失大小应该将各时间段内的热损失叠加.

The calculation of wellbore heat loss under unsteady steam-injection conditions

In the stage of steam stimulation ,the wellhead injection-parameters often change o-ver time during steam injection ,the traditional model for wellbore heat loss failed to consider this factor .Also ,previous work calculated heat loss rate just according to depth step ,ignoring injection-time need to be segmented .In order to accurately calculate the wellbore heat loss under unsteady steam-injection conditions ,firstly ,the unsteady steam-injection parameters were piecewise treated with the method of steady successive substitution ,so the cement/for-mation temperature could be assumed to be constant ;Secondly ,the heat transfer model was modified based on the principle of superposition ,and a total wellbore heat loss formula was put forward ;At last ,the model was solved both as time step and depth step .The results show that the wellbore heat loss rate decreases with injection-time even in the same depth , therefore ,the total heat loss of a certain depth during the w hole injection process is the sum of heat loss in every time step .