控压钻井井底气侵停止与否实时判别方法研究

A Real-Time Identification Method for the Bottom hole Gas Invasion State in Managed Pressure Drilling

实时判别井底气侵停止与否是控压钻井井控方法的关键,直接关系到基于立压控制法循环排气或常规关井等后续作业的选取.综合考虑气体运移膨胀和气体溶解的因素,指出出入口流量一致并不等同于井底气侵停止,两者存在时间先后关系.基于快速施加井口回压控制方法,建立了控压钻井井筒与地层耦合的多相变质量流动模型,采用有限差分法迭代求解,模型计算值与实验测量值吻合较好.模拟结果表明,出口流量有无明显拐点是区分出入口流量一致和井底气侵停止时间先后的标志.一旦井底气侵停止,立管压力的二阶导数会迅速降至0点附近且趋于稳定.根据上述参数变化特征,提出了基于出入口流量和立管压力实时监测的井底气侵停止与否实时判别方法.该研究对于完善控压钻井井控理论具有重要的指导意义.

Real-time identification of the bottomhole gas invasion state is the key to well con- trol during managed pressure drilling （ MPD）, which is directly related to the selection of fol- low-up operations involving the gas circulation exhaust based on standpipe pressure control or the conventional shut-in procedure. In view of the factors of gas migration expansion and disso- lution, it is pointed out here that the equilibrium between outlet flow and inlet flow does not di- rectly mean the stop of bottomhole gas invasion, and there is a precedence relationship be- tween them. Based on the rapidly increasing wellhead back pressure control method, an MPD wellbore-formation coupling model for multiphase variable-mass flow was established, and the finite difference method was used to iteratively solve this model. The calculated results agreed well with the experimental measured ones. The simulation results show that the obvious inflex- ion point of the outlet flow is a sign for distinguishing the precedence relationship between the outlet-inlet flow equilibrium and the bottomhole gas invasion stop. Once the bottomhole gas in- vasion stops, the 2nd derivative of the standpipe pressure will quickly drop to near zero and keep stable thereafter. According to the above parameter variation characteristics, a real-time i- dentification method for the bottomhole gas invasion state based on the outlet and inlet flow as well as the real-time monitored standpipe pressure was proposed. This study has guiding signifi- cance for the improvement of the MPD well control theory.