TY - JOUR
TI - Wellbore stability analysis in chemically active shale formations
AU - Shi Xiang-Chao
AU - Yang Xu
AU - Meng Ying-Feng
AU - Li Gao
JN - Thermal Science
PY - 2016
VL - 20
IS - 13
SP - 911
EP - 917
PT - Article
AB - Maintaining wellbore stability involves significant challenges when drilling  in low-permeability reactive shale formations. In the present study, a  non-linear thermo-chemo-poroelastic model is provided to investigate the  effect of chemical, thermal, and hydraulic gradients on pore pressure and  stress distributions near the wellbores. The analysis indicates that when the  solute concentration of the drilling mud is higher than that of the formation  fluid, the pore pressure and the effective radial and tangential stresses  decrease, and v. v. Cooling of the lower salinity formation decreases the  pore pressure, radial and tangential stresses. Hole enlargement is the  combined effect of shear and tensile failure when drilling in  high-temperature shale formations. The shear and tensile damage indexes  reveal that hole enlargement occurs in the vicinity of the wellbore at an  early stage of drilling. This study also demonstrates that shale wellbore  stability exhibits a time-delay effect due to changes in the pore pressure  and stress. The delay time computed with consideration of the strength  degradation is far less than that without strength degradation.