井漏失返条件下的吊灌作业安全时间计算方法

Calculation of safe time in "Hang's Mudding-off" technique of circulation loss in return

"吊灌"作业是在井漏失返条件下保持井内压力动态平衡、获得安全作业时间的重要措施。但在实施吊灌作业时,由于反映井筒内环空液面变化规律的动态数模分析方法缺失,不能为工程实践提供吊灌的合理依据,使其基本处于"盲吊"状态。为此,笔者根据"吊灌"技术实际工况,首次采用井筒漏失动态分析方法,建立起吊灌安全作业时间数学模型,给出了多种漏失速率的积分结果,并结合现场实例对计算结果进行了验证。结果表明:(1)利用计算实例对数学模型的可靠性进行检验,计算结果与实际数据高度吻合;(2)适当增加吊灌量可以增加安全作业时间;(3)适当减少吊灌钻井液密度也可以增加安全作业时间。结论认为:该成果可以从根本上解决"吊灌"技术的安全作业时间准确计算问题,对于规避井漏失返条件下的井控安全风险、实现"吊灌"技术优化、降低工程费用等都具有重要意义。

The so-called ＂Hang＇s Mudding-off＂ technique is critical to keeping the dynamic pressure balance and guaranteeing the sufficient safe operation time in wellbore. However, for lack of dynamic mathematical model analysis methods for reflecting the changes of annulus liquid level in the borehole during the ＂Hang＇s Mudding-off＂ operation, the actual operation is basically conducted blindly without reasonable engineering basis. According to the actual conditions, a mathematical model for the safe time of the ＂Hang＇s Mudding-off＂ was, for the first time, built up by using the dynamic borehole leakage analysis method. Then, the integral results of leak-off rates were calculated. Finally, the calculation results were verified by field cases. It is shown that the calculation results are highly accordant with the actual data, indicating the reliability of the mathematical model. The safe operation time can be increased by increasing mud amount or reducing mud density appropriately. With this model, the safe time of ＂Hang＇s Mudding-off＂ operation can be calculated accurately. This research result is of great significance to avoiding well control risk of absorption wells, optimizing the ＂Hang＇s Mudding-off＂ technique and reducing project cost.