深水钻井增压管线开启判别及参数优化研究

深水钻井过程中钻井液从套管环空返至隔水管段时,由于隔水管段环空尺寸突然增大,钻井液流速降低,携岩效率下降,从而导致钻井事故的产生,而深水区域目的层压力窗口非常小,难以通过增大海上平台钻井泵排量的方法来提高隔水管段携岩效率。鉴于此,基于井筒流动与传热理论,考虑钻井液流变性随温度变化特性,提出了深水钻井增压管线开启判别方法及流程,给出了主井筒内钻井液排量上、下限的计算方法和增压管线排量参数的优化方法。以南海LS-x深水井为例,分析了增压管线开启判别流程及主井筒和隔水管段排量优选计算过程。研究结果表明:深水窄密度窗口目的层一般需要开启增压管线辅助携岩,深水钻井常用的HEM水基钻井液体系在低温下具有较高黏度,有利于隔水管内携岩;增压管线开启后隔水管流动摩阻增大,导致井底ECD略增大,但影响程度非常低,通常情况下增压管线排量在额定排量范围内只需考虑其携岩效率即可。研究成果可为深水钻井水力参数优化和作业安全提供理论参考。

Study on Opening Determining and Parameter Optimization of Booster Line for Deepwater Drilling

During deepwater drilling,when drilling fluid returns from the casing annulus to the riser section,due to the sudden increase of the size of the riser section annulus,the velocity of the drilling fluid decreases and the cutting carrying efficiency decreases,which may lead to drilling accidents.The target layer pressure window in the deep water area is very small,making it difficult to increase the cutting-carrying efficiency of the riser section by increasing the drilling pump displacement on the offshore platform.In view of this,based on the wellbore flow and heat transfer theory,considering the characteristics of the rheology of the drilling fluid with temperature changes,the method and process for determining the opening of the booster line in deepwater drilling are proposed.The calculation method for the upper and lower limits of the drilling fluid flow rate in the main wellbore is given.And the optimization method of the flow rate parameters of the booster line is provided.Taking the South China Sea LS-x deep water well for case study,the process of determining the opening of the booster line and the calculation process of the flow rate optimization of the main wellbore and riser section are analyzed.Studies have shown that the deepwater narrow density window target layer generally needs to open booster line to assist cutting-carrying.The HEM water-based drilling fluid system commonly used in deepwater drilling has higher viscosity at low temperatures,which is preferable to cutting-carrying in the riser.After the booster line is opened,the flow friction in the riser increases,which leads to a slight increase in the bottom hole ECD,but the impact is very low.Generally,as for the flow rate of the booster line within the rated displacement range,only cutting carrying efficiency needs to be considered.The research results can provide a theoretical reference for deepwater drilling hydraulic parameter optimization and operation safety.