Research About The Relation Between Formation Stresses And Borehole Stability

Borehole stability problem is a complex issue which is a combination of multi-disciplinary knowledge, such as mechanics and chemistry. From the mechanical point of view, the wall mechanics model is established to analyze the force on the well, and verify with finite element simulation.The maximum and minimum horizontal principal stress the wall rock suffered can be measured by the present universal hydraulic fracturing method. Then the vertical stress can be calculated use weight of overlying strata. The mechanical parameters of rock can be get by chamber uniaxial and triaxial test. stress parameters and mechanical parameters measured is the foundation work to stress analysis of rock wall.To select the rock around the shaft area as the object of stress analysis establish mechanical model of vertical well bore which is no casing under the force of rock wall. the stress state surrounding rock wall is analysed, and the pressure and collapse pressure of rock wall is also calculated by elasticity knowledge. Strength criteria is used to judge whether the damage of Wall rock will occur, and to determine the type of damage.Most of the rock in the wall is plastic, and does't break brittlenessly at once when force on it. Analyze the rock by using finite element software named ANSYS, gets the stress distribution strain distribution and the movement of the rock. Then judge that whether the wall is instability or stability,and what kind of damage has occurred,according to trength theory.Predicte the formation stress correlation coefficient in the inversion model by the calculated stress value. It's significant to research the Stability of the wall. inversion formation stress.