Abstract: Many factors can influence stability of well wall in the area of petroleum drilling engineering. Using 3D numeric analysis technology, authors of this paper simulates the influence of fractures on the stability of petroleum well wall. The result indicates that all kinds of fractures have negative influences on the mechanical stability of the walls, however, the degrees of the influence is different from each other correspondingly with the types, attitudes, densities, combination patterns and embedding depth of the fractures, and the general rules are follows: the influence degree of horizontal fractures is higher than inclined fractures, and inclined fractures is higher than perpendicular fractures, i.e., as the dip angle of the fractures increases, the degree of the influence on stability declines; as the number of fractures increases, the degree of the influence on stability declines; as the density of fractures increases, the degree of the influence on stability increases; as the embedding depth increases, the degree of the influence on stability declines.

Key words: fractures, stability, well wall, influence, numerical analysis