Well orientation effect on borehole stability

Using laboratory and field borehole stability data, an empirical correlation of borehole size and stress gradient effects is derived. Using the correlation, the well orientation effect on borehole stability is numerically studied. The study shows that the borehole stability is controlled, under the normal condition, by the largest in-situ stress in the radial borehole direction so that the borehole orientation effect for a horizontal well is not significant if two horizontal stresses are less than the vertical overburden pressure, however, if one horizontal stress is greater than the vertical stress, the orientation significantly affects the borehole stability.