精细控压钻井重浆帽设计及压力控制方法

Design of heavy grout and pressure control method for fine pressure-control drilling

精细控压钻井是一种主要用于窄密度窗口地层高效、安全钻井的新技术。该技术可精确控制环空压力,实现井底压力恒定。控压起钻过程中,起至预定井深注入重浆帽后进行常规起钻。以往注重浆期间回压控制方法不具备实际操作性,一方面没有考虑钻具内压水眼重浆进入环空造成的影响,设计内容不完善;另一方面没有实时压力控制方法。根据工程实际要求,考虑钻具内压水眼重浆、井眼实际情况、以及地层特性(碳酸盐岩地层可采用近平衡压力控制,硫化氢地层采用略过平衡压力控制),进一步优化井底压力控制。在计算注重浆和井口回压关系时,建立分段实时压力控制曲线,实现起下钻过程中井底压力平稳控制,有效避免停泵期间可能造成的溢流或者漏失,提高钻井安全性及钻井综合效率。

Fine pressure-control drilling is a new technology for efifcient and safety drilling in the stratum with narrow-density windows. The technology enables precise control of annular pressure and realizes constant bottom hole pressure. During pressure-control trip out, drill is lifted to preset well depth, and heavy grout is iflled before conventional trip out. The back pressure control method during the previous heavy grout iflling is not operable.On one hand, the inlfuence of heavy grout from nozzle to annular space by internal pressure of drilling tools is not taken into consideration, thus design contents are incomplete.On the other hand, there is no method for real-time pressure control. Bottom hole pressure control is further optimized according to actual engineering requirements and considerations of heavy grout in nozzle of drilling tools under internal pressure, actual borehole conditions, as well as stratum features (near-balanced pressure control may be adopted for carbonate rock stratum, and slightly-over-balanced pressure control may be adopted for hydrogen sulifde stratum). For calculation of relation between heavy grout iflling and back pressure at wellhead, segmented real-time pressure control curve is established to realize stable control over bottom hole pressure during round trip, effectively avoid possible overlfow or leakage during pump shutdown, and improve drilling safety and overall efifciency.