Finite Element Analysis of Casing Drilling Smearing Effect

Abstract

AbstractCasing while Drilling (CwD) is a new drilling method where the well is drilled and cased simultaneously. Previous field operations of CwD have shown a decrease in drilling non-productive time as well as improvement in controlling lost circulation and wellbore stability. Although advantages of this technology are well noted in the literature, the mechanisms of improvements were not studied comprehensively. In order to study these mechanisms, one has to understand the formation properties, fluid hydraulics, casing dynamics, and how CwD helps in better hydraulic control and results in strengthening effects. In the previous research works, the factors that were widely discussed and results obtained were related to formation properties. However, while considering the stresses in the wellbore, mechanical factors such as the RPM and contact of casing at different positions in wellbore were usually neglected. In furtherance to this study, the importance of plastering mechanism cannot be ignored. This work includes a new insight towards the underlying mechanism of casing-wellbore contact and changes in the near wellbore stresses while casing rotation. The main objective of this study is to investigate the hypothesis of the increase in hoop stress when the casing contacts wellbore with regard to the formation stresses orientations. To accomplish this objective, finite-element analysis has been conducted to simulate several CwD scenarios. The classical equations used to obtain the wellbore stresses include parameters like the far-field stresses, pore pressure, and wellbore geometry. These equations do not consider the effect of casing pipe contact and eccentricity; therefore finite element simulations can be very helpful to investigate these effects. Casing-wellbore contact in both maximum and minimum in-situ stress directions are considered in this study as well as changing contact length. The study of different cases shows the variation of hoop stress, which can be beneficial if properly implemented in CwD operations.