Effect of inclined planar fractures on borehole performance

✍ Scribed by E. Wagner; H. Gaisbauer; H.P. Rossmanith

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 625 KB
• Volume: 44
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(93)90039-u

✦ Synopsis

Excessive borehole pressurization

may cause damage to the borehole with a large possibility of the initiation of new cracks and/or the propagation of minute flaws appearing as surface cracks or embedded cracks in the vicinity of the borehole. When these flaws propagate under the control of the borehole pressure-induced symmetrical radially, rapidly decaying stress field and internal crack face pressure they extend along spatially curved surfaces trying to realign themselves again in a plane, the direction of which is governed by the relative magnitude of the pressures in the borehole and the crack. A 3D-crack propagation algorithm serves for the evaluation of the nucleation possibility of borehole cracks and embedded cracks as a function of the state of stress. Numerical modelling concentrates on a centrally bored cube with an inclined semi-elliptical surface starter crack and an embedded elliptical planar starter crack subjected to various boundary conditions.

The distributions of the stress intensity factors Kl, K2 and K3 along the crack periphery as a function of the pressures and the state of primary stress have been established. Examples for the behaviour of crack initiation and extension due to pressurization are given. An application to high pressure injection in steep boreholes extending from inspection galleries in high arch dams is presented.