精细控压钻井中环空不稳定流动时间响应分析

Time Response Analysis of Unstable Flow in Annulus Affected by Back Pressure Change

精细控压钻井是井底恒压控压钻井的一种类型,主要通过施加井口回压实时控制井底压力。井口回压的改变会导致钻井液循环经历稳定-不稳定-稳定的过渡,过渡期的响应时间是评价精细控压钻井的一个重要指标。较短的过渡时间可以使井底压力快速恢复平衡,从而提高控压钻井的控压精度。以回压改变后环空钻井液的不稳定流动时间为研究对象,建立了控压响应时间的计算模型。分析了气体体积分数、岩屑体积分数、环空间隙及回压大小等因素对过渡时间的影响规律,分析表明气体体积分数、岩屑体积分数的增大,控压响应时间相应增加;环空间隙、回压的增大,控压响应时间相应减小,其中气体体积分数是影响控压响应时间的主要因素,同时对比分析了弹性控压响应时间计算模型与本文模型之间的差异,得出了在浅井、勘探井的控压钻井中为计算简便而采用的刚性计算模型不仅可以满足计算精度的要求,同时也具有较强的操作性。

As a type of Constant Bottom Hole Pressure(CBHP),fine managed pressure drilling controlled bottom hole pressure in real-time through applying wellhead back pressure.The change of wellhead back pressure would cause drilling fluid circulation to undergo the transition of stable-unstable-stable process,and the response time of transition period was an important indicator to evaluate fine controlled pressure drilling.Shorter transition time could quickly restore the balance of the bottom hole pressure,thereby it could improve the precision of MPD.The transient flow time of drilling fluid in annulus after the change of back pressure was taken as an object of study,a model was established for response time of the managed pressure.The influential law of gas volumetric fraction,cuttings volumetric fraction,annular gap and the size of back pressure on transition time was analyzed.The analysis shows that the with the increases of gas volumetric fraction,cuttings volumetric fraction,response time,annular gap and back pressure,the response time of the controlled pressure decreases,in which the gas volumetric fraction is the main factor influencing the response time of controlled pressure,at the same time I the difference of the elastic control pressure calculation model is contrasted with that of the new model in the study,it is found out that the rigid calculation model used for easy calculation of controlled pressure in shallow and exploration wells is obtained,which can meet the requirements of calculation precision,also it has stronger operation ability.