基于井筒-地层定压实验的重力置换窗口研究

为了处理重力置换引起的溢漏事故，首先需要了解重力置换发生的条件，分析重力置换窗口，判断井下是否发生重力置换，并采取对应的处理方法。本文通过自主研制的井筒-地层重力置换实验装置，开展气液、液液重力置换临界点实验，基于理论及实验分析，定量计算地层重力置换窗口，并拟合了重力置换窗口临界点压力曲线，拟合公式与实测值误差小于10%。在该实验条件下，当钻井液密度为0.998g/cm3时，气液重力置换窗口为-5800Pa~10.6Pa，液液地层重力置换的窗口为-1192Pa~16.6Pa。结果表明，气液、液液重力置换窗口与流体密度差基本呈线性关系；现场实际井下重力置换窗口远高于此，所以需要在钻进时考虑重力置换窗口的影响。据此，本文提出了预防重力置换发生的方法，以及发生重力置换溢漏事故后对应的处理方法。

Research on gravity displacement window based on wellbore-formation constant pressure experiment

In order to deal with the overflow accident caused by gravity displacement, it is necessary to understand the conditions of gravity displacement, analyze the gravity displacement window to judge whether gravity displacement occurs in the down-hole, and adopt the corresponding treatment method. In this paper, the critical point experiment of gas-liquid gravity displacement was carried out by the self-developed well-formation gravity displacement experimental device. Based on the theory and experimental analysis, the formation gravity displacement window is quantitatively calculated, and the critical point pressure curve of the gravity displacement window is fitted. The error between the fitting formula and the measured value is less than 10%. Under this experimental conditions, when the drilling fluid density is 0.998g/cm3, the gas-liquid gravity displacement window is-5800Pa~10.6Pa, and the liquid-liquid formation gravity displacement window is-1192Pa~16.6Pa. The results show that the gravity density difference between gas and fluid is linear, and the actual gravity displacement window is much higher so that the influence of gravity displacement window should be considered during drilling engineering. In conclusion, the prevention method of gravity displacement and the corresponding treatment method of gravity displacement overflow are put forward.