起钻中灌浆过程模拟及对井底压力的影响

Simulation of Drilling Fluid Grouting Process during Tripping and its Effect on Bottom Hole Pressure

起钻前向钻具水眼灌入一定体积的高密度钻井液有利于平衡循环压耗和钻井岩屑引起的环空—水眼压差,但同体积高密度钻井液在不同钻具水眼中的高度差异因“U”型管效应会造成水眼—环空中钻井液流动,继而影响现场对溢流、井漏等复杂井况的判断,尤其是在采用复合钻具的深井、超深井中更为突出。文章推导了注入高密度钻井液后复合钻具起钻过程中,在“U”型管效应影响下水眼—环空钻井液体系压力变化过程及流动规律。结果表明,复合钻具起钻过程中,环空灌浆量在整个起钻过程中表现为“正常灌浆—欠灌—多灌—正常灌浆—多灌”五个阶段。灌浆异常量及灌浆异常距离与大、小钻具水眼单位长度容积比值、高密度钻井液与井浆密度差、停泵回压呈正相关关系。理论计算结果能够为钻井现场监测井内压力情况提供指导,尤其是对深井、超深井及时判断井下是否发生溢流、井漏等复杂情况具有重要意义。

Before tripping on the drilling site, it is necessary to pump into the nozzle of the drilling tool with a higher density drilling fluid than the circulating drilling fluid. Higher density drilling fluid can balance the pressure loss and the pressure difference between annulus and nozzle caused by drilling cuttings. However, the height difference of higher density drilling fluid with different volumes in different drilling nozzles will cause the flow of drilling fluid in the nozzle-annular space because of the U-tube effect, which will affect the judgment of complex well conditions such as overflow and lost circulation, especially in the use of compound drilling tools in deep and ultra-deep wells. This paper analyzes the pressure change and flow law of the nozzle-annular drilling fluid system that is affected by the U-tube effect during compound drilling tool tripping operations after pumping higher density drilling fluid. The results show that during the tripping out process of the compound drilling tool, the annulus pumping amount appears as "normal-lack-exceed-normal-exceed pumping" during the whole tripping out process. There is a positive correlation between the abnormal pumping, the ratio of pumping anomaly distance to nozzle volume per unit length of large and small drilling tools, the density difference of higher density drilling fluid and drilling fluid in hole, and the back pressure as pump stopped. The theoretical calculation results can provide guidance for monitoring of pressure in the well, which is especially of great significance for determining the occurrence of overflow and loss and other complex situations in the deep and ultra-deep wells.