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以多相瞬变流理论为基础，建立了井筒内气液两相流动模型，并对低压欠平衡钻井中注气量对井内压力的影响关系和规律进行计算和分析。计算分析结果表明，注气量对井内压力的影响除与注气量本身大小有关外，还与井深、井眼与钻柱结构尺寸、井内液相流量和性质等因素密切相关。单纯增大注气量并不一定就必然会导致井内压力的降低，这取决于所给条件下构成井筒内气液两相流体的静液压力和流阻间的平衡关系。介绍的模型及方法对确定低压欠平衡钻井过程中各相关参数、地面压缩机组的配置、以及设计方案等有一定指导意义。
Based on the theory of multiphase transient flow, the gas-liquid two-phase flow model in the wellbore was established and the relationship between the gas injection volume and the pressure in the well under low pressure underbalanced drilling was calculated and analyzed. The results of calculation and analysis show that the influence of injection volume on well pressure is closely related to well depth, structure size of wellbore and the flow and nature of liquid in the well except for the size of gas injection itself. Simply increasing the amount of gas injection does not necessarily lead to a decrease in pressure in the well, depending on the equilibrium between the hydrostatic pressure and the flow resistance of the gas-liquid two-phase fluid that forms the wellbore under the given conditions. The introduced models and methods are of guiding significance in determining the relevant parameters of low pressure underbalanced drilling, the configuration of ground compressor units, and the design schemes.