Abstract
During the period of avoiding typhoon in deep-water drilling, the gas intrusion in the wellbore brings higher risk to the well opening operation. It is very important to improve the accuracy of typhoon avoidance cycle prediction to improve the efficiency of drilling operation and reduce the risk of well control. According to the yield stress characteristics of drilling fluid, the gas migration experiment in the yield stress fluid is carried out in this paper. Based on the experimental results and stress analysis, a prediction model of bubble rising velocity suitable for the yield drilling fluid is established. Considering the rheological properties of drilling fluid and pore characteristics of formation, a prediction model of initial bubble size is established. Combined with the velocity prediction model and bubble size prediction model, the calculation method of typhoon avoidance period is proposed. Through the calculation and analysis, it is found that under the condition of low invasion rate, the formation porosity has little influence on the initial size of bubbles, and the yield stress value of drilling fluid has great influence on the initial size of bubbles. At the same time, the model in this paper makes up for the problem that the prediction value of safe typhoon avoidance period calculated by the previous model is large, and reduces the risk of well opening operation. According to our calculation results, the measures of injecting drilling fluid with low yield stress at the bottom of the well and injecting drilling fluid with high yield stress at the top are put forward, which can effectively increase the safe typhoon avoidance period.
