Study On Wellbore Stability Of Fractured Formation In Xujiaweizi Area

The stability of the borehole wall is the worldwide difficult problem in the well drilling, it can easily cause the borehole wall collapsing, the constriction, the lost circulation, the sticking and the reservoir pollution and some other complex situations or accidents because of the instability of the borehole wall in the well drilling process. Therefore, it is a key to understand and evaluate the complex underground adjacent formation environment correctly and effectively, explore the stability mechanism of the borehole well thoroughly, establish the corresponding prediction theory and the control model, control the instability of the borehole wall during the drilling process effectively, and realize the high quality, safe, highly effective and low costing well drilling.The Xujiaweizi area of Daqing Oil Field has the characteristics of much more deep wells, higher temperature of the bottom hole, better development of the cracks, worse stability of the borehole wall, much more serious collapses and falls of the borehole wall. However, in this area there are many influences that will cause the borehole wall instability, among that, it may cause the drilling fluid leak through microfracture and bedding plane, make the intensity of formation reducing gradually and intensify the borehole wall instability because of the existence of cracks. Firstly, this article analyzed the lithologic characteristic of deep creviced formation and the type of fracture in this area, researched the influence of the stability of the borehole wall from rock fracture in the well drilling. On the base of the laboratory experiment, this article made use of well logging and correlating data to determine the rock mechanics parameter and the crustal stress in this area. In addition, this article researched the influence of the stability of the borehole wall under high temperature and high pressure in this area, established the mathematical theory model which can maintain the borehole wall stable under high temperature and pressure; it also analyzed the weakness formation, the stability of the borehole wall from the level layered rock and fractured formation in this area, and established the corresponding computational mathematics model which can determine reasonable limit of drilling fluid security density effectively. Finally, during the well drilling, it can take the corresponding technical measure to reduce the instability of the borehole wall.