Numerical Simulations Of Fracture Propagation And Sealing Implications For Wellbore Strengthening

"To mitigate the small tolerance between pore pressure and fracture gradients an engineering practice referred to as "wellbore strengthening" is conducted to increase the fracture gradient. The method relies on propping and/or sealing the fractures with specially designed materials. Different competing theories exist for physical wellbore strengthening mechanisms which can be categorized into two groups. The first group explains that strengthening happens as a result of increasing wellbore hoop stress when fractures are sealed while the second group emphasis is on fracture tip isolation with suitable materials and enhancing fracture propagation pressure. The numerical models and lab experiments in previous studies have not fully replicated the operational phenomenon of wellbore strengthening. This study presents three-dimensional poro-elastic finite-element simulation's results for hydraulic fracture's initiation, propagation and sealing in the near wellbore region. The main objective of these simulations was to investigate the hypothesis of wellbore hoop stress increases when fractures are wedged and/or sealed during lost circulation control. To further support the numerical simulations' results, relevant field case studies, near wellbore fracture experiments and analytical models were also used. This study demonstrates that fracture sealing is not able to increase wellbore hoop stress more than its ideal state where no fracture exists, however, it helps to restore part or all of the wellbore hoop stress lost during fracture propagation. Field cases reveal the importance of connecting wellbore hoop stress restoration with leak off test's (LOT) interpretation and how wellbore condition can affect initial fracture gradient"--Abstract, leaf iii.