合理的井底压差设计及应用效果分析

Proper design of bottomhole differential pressure and its application results analysis

钻井施工中，合理的井底压差可以达到提速增效和保护储层的目的。为此，应用计算机仿真系统、岩石破碎学理论研究了不同压差下井底应力场分布及岩石变形状况。结果表明，与正压差相比，在负压差钻井条件下更利于井底岩石破碎，提高机械钻速。但井底压差不能无限制地降低，需要结合具体井位的地质和工程特征，在保证不发生溢流和并壁垮塌的前提下，将井底压差设计在一个合理的范围值内：在渗透性地层钻井时，静液柱压力小于地层孔隙压力时，地层流体将流入井筒，这时设计的最低液柱压力应略高于地层孔隙压力（约0．02MPa）。现场应用表明，井底压差在合理的范围内越小时，机械钻速越高。

Proper bottomhole differential pressure(BHDP)during drilling can help improve the ROP and protect reservoirs.Hereby,this paper,based on the computer simulation system and rock crushing theories,studies the bottomhole stress field distribution and rock deformation mechanism under differential pressures.This study shows that the ROP is improved much more easily by rock crushing under the negative bottomhole differential pressure,in comparison with that under the positive one.However,there is a limit for the BHDP,so its value,in combination with the geological and engineering features of a well,should be designed within a reasonable range under such condition that no overflow or well caving occurs.For drilling through permeable formations,the formation fluid will flow into the wellbore if the hydrostatic pressure gets lower than the formation pore pressure,so the designed minimum hydrostatic pressure should be slightly higher than the formation pore pressure of about 0.02 MPa.Field application shows the lower the BHDP within the proper range,the higher the ROP.