低压及欠平衡钻井中注气量对井内压力的影响

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。

EFFECT OF GAS INJECTION RATE ON BOREHOLE PRESSURE IN UNDERBALANCED DRILLING AT LOW PRESSURE

Based on the theory of multiphase transient flow, a dynamic model with respect to gas/liquid two-phase flow in borehole was developed, it was also calculated and analyzed the effect of gas injection rate on borehole pressure in aerated drilling in this paper. The bottomhole pressure is not only governed by the gas injection rate, but also closely related to some other factors, including the size of wellbore and drill string, physical properties and circulating rate of drilling mud, etc. The results indicate that only increasing the gas injection rate is not certain to result in decreasing the bottomhole pressure, it depends on the balanced relationships between the hydrostatic pressure and flow resistance pressure in the given borehole gas/liquid two-phase fluid. The model and approach may provide some useful help for the different related parameters, the matched compressors, and the design plans in underbalanced drilling.