高密度油基钻井液敏感地层变密度控压钻井技术

Application of Variable Density Managed Pressure Drilling Technology with High Density Oil Based Drilling Fluid in Volcanic Rock Sensitive Formation

高密度油基钻井液在小井眼钻井中存在环空循环压耗、抽汲压力、激动压力高等现象,致使压力敏感地层钻井时溢、漏频繁,严重影响作业安全。文章以TF2井149.2 mm井眼火山岩地层钻井为例,针对高密度油基钻井液内摩擦力大和井眼小、井深的特点,分析了在不同工况下井底压力骤变而带来的工程技术风险,提出了变密度控压钻井的技术思路:在不同工况下因循环压耗、抽汲压力、激动压力的变化影响而调整对应的钻井液密度和控制一定的井口压力来实现全作业过程中的井底压力略大于地层压力、保持井筒不溢不漏或微漏的一个状态,确保作业全过程的井控安全。文章对钻进循环、停泵、起钻、下钻4种工况下钻井液密度确定和井口附加压力调节给出了原则和控制条件,并在应用中对TF2井的地层压力、漏失压力、不同工况下的密度值进行了求取。该井应用变密度控压钻井技术,实现了在149.2 mm小井眼中239.83 m的安全进尺,该项技术为类似复杂井的处理积累了宝贵经验。

When high-density oil-based drilling fluids are used for slim hole drilling,such problems as annulus circulation pressure loss,suction pressure and high surge pressure are often encountered,leading to frequent overflow and lost circulation in the volcanic rock sensitive formation which seriously affects drilling safety.Taking Well TF 2 drilled with 149.2mm in volcanic rock formation as an example,aiming at the characteristics of high density of oil based drilling fluid with large friction force and the well is slim hole and deep,the engineering and technical difficulties caused by sudden changes of bottomhole pressure is analyzed under different working conditions.The technical thought of variable managed pressure drilling is put forward.Under different working conditions,the corresponding drilling fluid density is adjusted and the wellhead pressure is controlled to achieve a state in which the bottom hole pressure is slightly greater than the formation pressure to maintain the wellbore without overflow or slight leakage,ensuring the safe well control throughout the whole process of operation.In this paper,the principle and control conditions of drilling fluid density determination and additional wellhead pressure adjustment under four working conditions of drilling cycle,pump stop,tripping out and tripping in are given,and the formation pressure,leakage pressure and density values under different working conditions of Well TF2 are obtained in the application.With the application of variable density managed pressure drilling technology,the well has been safely drilled for 239.83 m footage in the 149.2 mm slim hole and relevant data has been obtained as well.The research results provide valuable experience for the operation in the similar wells.