Analysis of Thermally Induced Stresses for Effective Remediation of Lost Circulation Through Drilling Induced Fractures

Abstract

Lost circulation events during drilling are associated with the initiation of new fractures or the reopening of pre-existing fractures from the wellbore. Practices frequently implemented to combat lost circulation, including wellbore strengthening (WBS), are employed by plugging and propping the newly induced and pre-existing fractures to limit further propagation from the wellbore. One observation that was noted is that there is a discrepancy in the performance of lost circulation prevention methods for different temperatures between the fluids used and the surrounding formation. However, it is not yet fully understood how temperature affects pre-existing fractures and newly initiated fractures during these practices. This study discusses how the stress state around fractures is influenced by a change in temperature considering fluid flow into a formation through drilling induced fractures. A finite element analysis with a coupled thermal-hydrologic-mechanical processes simulation was established to demonstrate how the stress redistributes around the fractures while considering fluid invasion and heat transmission. The results of the changing thermal stress around the fractures under various scenarios have been investigated. Included in our analysis is the potential risk of reinitiating fractures. The conclusions from this study indicate that a large temperature difference between the formation rock and fluid flow into the fractures could be a major concern when trying to prevent fracture propagation and control lost circulation events. It could potentially diminish the effect of enhanced hoop stress provided by WBS and fracture plugging by lost circulation materials. Such information is important to facilitate a successful management of lost circulation by taking into accounts the thermal impact of different lost circulation prevention approaches. The results from this paper are particularly important when a large temperature difference exists between circulating fluids and surrounding rock as commonly seen in HPHT and deep water wells.