Finite Element Analysis of Thermally Induced Stresses in the Near-Wellbore Region During Invasion of Mud Into Fractures

Abstract

A severe lost circulation event is usually associated with emanation and propagation of pre-existing or drilling induced fractures from the wellbore. To combat lost circulation and prevent further fracture propagation, a thorough understanding of the stress state in the near-wellbore region with fractures is imperative. However, it is not yet fully understood how temperature variation during the invasion of mud affects pre-existing or newly initiated fractures. A three-dimensional (3D) finite element (FE) analysis was conducted in this study to simulate the transport processes and state of stresses in the near-wellbore region during invasion of mud into fractures. To account for thermal effects, a thermo-poroelasticity model was coupled with flow and heat transfer models in the fractures. This study included a series of sensitivity analyses based on different formation properties and mud loss conditions to delineate the relative importance of different parameters on induced thermal stresses. It also evaluated potential risks of reinitiating fractures under various downhole conditions. The results demonstrate how the stresses redistribute as nonisothermal invasion of mud takes place in fractures. It shows that a temperature difference between the formation rock and the circulating muds can facilitate fracture propagation during invasion of mud. These results due to temperature change can also diminish the enhanced hoop stresses provided by wellbore strengthening (WBS) and other lost circulation prevention methods. Such information is vital to successful lost circulation management. The conclusions of this study are particularly relevant when a substantial temperature difference exists between circulating fluids and surrounding rock, as commonly seen in high-pressure, high-temperature, and deepwater wells.