Three-dimensional Numerical Models of Drilling Induced Core Fractures

• Author / Creator

  Zhang, Lei

• Drilling-induced fractures in borehole cores have distinct morphologies (e.g., petal, petal-centreline, saddle, and disk) and are produced under pure tensional stress, although most in-situ stresses are compressive. 3D numerical models show that tensile stress concentrations occur near the bottom of a vertical borehole. A new algorithm is developed to trace 3D tensile fractures for a range of crustal stress conditions. In a normal fault regime, fractures change from petal/petal-centreline to saddle to disk with increasing minimum horizontal stress (Sh). In a strike-slip regime, saddle fractures occur, except where Sh is much less than the vertical stress and petal centre-line fractures are found. In a thrust fault regime, saddle and disk fractures occur at low and high Sh, respectively. The results demonstrate that in-situ stress is the dominant control on fracture morphology; variations in Poisson’s ratio and core stub length primarily affect the magnitude of tensile stress.

• Subjects / Keywords

  • Core fracture

• Graduation date

  Fall 2011

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R38D3M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.