微流量控制钻井中两相许用钻杆下行速度研究

针对微流量控制钻井中气液两相许用钻杆下行速度问题，考虑气体滑脱、相与环空壁面阻力、回压及井底压差，开展了对不同井深的气液两相许用钻杆下行速度半经验模型的研究，获得了气液两相许用钻杆下行速度的变化规律。当钻杆在气液两相中下行运动时，回压的增大使井筒空隙率减小、气液两相密度增大，加载在井底的有效压力增大，从而使许用钻杆下行速度减小；当井底气侵量增大，此时井底压力小于地层压力，许用钻杆下行速度增大，可借助增大的激动压力消除一部分井底与地层欠压差；当井底安全压差减小，许用钻杆下行速度呈减小趋势。控压钻井中精确计算钻杆许用下行速度，可增大钻井时效。

Research on Allowable Movement Speeds of Downward Drill Pipe in#br#Gasliquid Two Phase in MFC Drilling Operations

For the problems of allowable downward movement speed of drill pipe in gas-mud two phase during MFC drillingoperations，this paper establishes the semi-empirical model for allowable downward movement speeds of drill pipe at differentwell depth by considering gas slippage，resistance between flowing phase and annulus wall，back pressure and pressuredifference in bottom hole. The variation characteristics of allowable downward movement speeds of drill pipe are acquired byadopting the method of computer programming. The results show that when the drill pipe moving downward，increasing backpressure will lead to the decrease of void fraction，increase of gas-liquid two-phase density and effective pressure imposed onthe bottom hole，which will further result in the decrease of allowable downward movement speeds of drill pipe. When thegas influx rate in the bottom hole is increased，the pressure in bottom hole will be reduced to less than the formation pressure.At that time，the allowable downward movement speeds of drill pipe can be increased because the increasing surge pressurecan eliminate a part of pressure difference between bottom hole and formation. The allowable downward movement speeds ofdrill pipe should be decreased with the decrease of safety pressure difference. During the MFC drilling operation，the precisecalculation of allowable downward movement speeds of drill pipe can improve the effectiveness of drilling.