A New Method to Determine Mud Density in Deflecting Well and its Application

摘要

Because of the inclination of borehole, there is a significant difference about the borehole stability between deflecting and vertical well. Borehole stability has a relationship with not only trajectory of well, including deviation angle and azimuth, but also azimuth of earth stress. This paper will start from stress field of wall of borehole to study borehole stability in inclined well. And with suitable destruction model of wall of borehole, the reasonable dynamic model and determine the safe mud density of deflecting well can be obtained exactly. The new model is used so as to calculate and determine the safe range of mud density in penetration and round - trip operations. Based on the fundamental theories of dynamics, the state of stress in well wall surrounding is discussed in this paper. The expression of main component of stress in the wall of borehole is carried out. According to shear destruction and tensile failure criterions, the models of determining mud density are proposed and the safe range of mud density in round- trip and penetrating operations are calculated in well YH8 of Tarim oilfield.