钻井井喷关井期间井筒压力变化特征

针对目前钻井井喷关井期间井筒压力计算值与实际关井压力差别较大的问题,将关井期间井筒压力变化分为两部分:关井初期地层流体继续侵入井筒的续流部分和气液密度差导致气体滑脱上升部分,从渗流理论和试井理论出发,考虑关井期间井筒内气体和钻井液的压缩性以及井筒的弹性,建立关井期间井筒续流模型;从气液两相流理论出发,考虑关井气体滑脱上升期间气体的膨胀、气体和钻井液压缩性、井筒弹性以及钻井液滤失等因素,建立关井期间气体滑脱模型;然后考虑关井期间井筒续流和气体滑脱综合影响,建立关井期间井筒压力计算模型,并给出基于本模型的气侵关井井筒压力读取方法。结果表明:关井初期井底压力呈指数增加,井底压力大于地层压力之后井底压力呈线性增加;关井初期井筒续流起主导作用,井底压力大于地层压力之后气体滑脱效应起主导作用。

Characteristics of wellbore pressure change during shut-in after blowout

The change of wellbore pressure during the shut-in period after blowout is an important issue for well killing design and affects the wellbore safety. Two main reasons that can cause the wellbore pressure change during the shut-in were accounted, including the wellbore flow after the shut in and the gas slippage due to the density difference between gas and liquid. A wellbore afterflow model was established considering the compressibility of gas and drilling fluid and the elasticity of the wellbore, and a gas slippage model was constructed based on gas-liquid two phase flow principles. It also considered the compressibility of gas and drilling fluid and the filtration of drilling fluid in the wellbore during the shut-in. The results indicate that the bottom hole pressure increases exponentially during the initial period of shut in, but it becomes linearly when the bottom hole pressure is greater than the formation pressure. The afterflow is essential to the bottomhole pressure during the initial shut-in period, while the gas slippage prevails after the bottomhole pressure is greater than the formation pressure.