ANALYSIS ON WELLHEAD STABILITY DURING DRILLING OPERATION IN ARCTIC PERMAFROST REGION

The arctic region hold abundant oil & gas resources according to the assessment by United States Geological Survey (USGS) in 2009. While, the thaw of permafrost during drilling operation can lead to the instability of wellhead. A coupled thermal model between wellbore and formation is given considering the latent heat of fusing and migration of water during the thaw of pentrafrost, and the thawed permafrost zone can be estimated. A wellhead stability analysis method considering heat transferred from wellbore is also proposed in this paper. FLAC3D software is applied to analyze the wellhead stability. Some conclusions are made through a case study: Flow in the wellbore delivers heat from deep part of formation to the shallow part of the formation, which leads to the penuafrost thaws. Thawed peturafrost losses most of the shear strength compared to that of the frozen permafrost which leads to the settlement of wellhead. The calculated results using FLAC3D software shows that the wellhead settles as deep as 0.66 m resulting from the permafrost thaw. In addition, the installation of anti-sinking pad is suggested to reduce the wellhead settlement. According to our simulation, the anti-sinking pad with radius of 8 times the wellhead radius is suggested, which can reduce the wellhead settlement to 0.1 m.