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气体钻井过程中钻进参数的改变将引起井内气体的不稳定流动，这种现象在用气体钻井方式打开产层时尤为明显，这些情况用常规气体钻井稳定流动理论不能准确模拟。通过对井内气体不稳定流动的分析，还可以实现钻井过程中的动态地层评价，因此，井内气体不稳定流动也是欠平衡钻井随钻试井理论的重要组成部分。基于可压缩流体不稳定流动理论，文章建立了气体钻井过程中井内瞬态流动的数学模型并提出了模型的数值解法。针对井内水动力体系的复杂特点，文章讨论了定解条件的确定方法。最后将模型应用于伊朗TBK-14井，对开启压风机和增大压风机排量两种情况进行了分析，与现场试验对比表明，数值模拟结果与井内的实际情况一致。

BOREHOLE GAS UNSTEADY FLOW IN THE PROCESS OF GAS DRILLING AND ITS FIELD TEST STUDY

The borehole gas unsteady flow will be caused owing to the variation in drilling parameters in the process of gas drilling and it will be even more obvious when the reservoir is encountered with, which can’t be accurately simulated by the conventional steady flow theory of gas drilling. A dynamic formation evaluation may be also realized through the analysis of borehole gas unsteady flow, so that the analysis is an important component part of well test while drilling theory of underbalance drilling. In the paper, a mathematical model of borehole gas transient flow in the process of gas drilling is set up and a numerical solution method is put forward on the basis of the unsteady flow theory of compressible fluid.In accordance with the complicated characteristics of borehole hydrodynamic system, the initial and boundary conditions are discussed in the paper.Through applying the model to well TBK-14 in Iran and analyzing the borehole gas flow under the two circumstances, i.e.starting compressor and enhacing the displacement of compressor, it was indicated that the numerical simulation result was accordant with the actual situation in the well.