Safe Drilling in Chemically Active and Naturally Fractured Source Rocks: Analytical Solution and Case Study

Liu, Chao (Aramco Services Company: Aramco Research Center-Houston) | Han, Yanhui (Aramco Services Company: Aramco Research Center-Houston) | Abousleiman, Younane (PoroMechanics Institute, University of Oklahoma)


The recently formulated theory of dual-porosity dual-permeability porochemoelectroelasticity is applied to derive the analytical solutions for an inclined wellbore drilled through a shale formation, accounting for the effects of natural fractures and shale chemical activity (Liu et al. 2018). With the fully coupling of water, anions, cations flow, stresses, and pore pressure in between shale matrix and fractures, the newly-derived solutions are able to evaluate the relevant stresses and pore pressure around the wellbore.

The analytical solution is applied to study two field cases. The Hoek-Brown failure criterion is employed to evaluate wellbore collapse and mud densities. The two case studies indicate that the analytical solution explains the wellbore failure and is capable of predicting the used safe drilling mudweight. Back analysis on the field data with a sensitivity study is able to estimate the range of the fracture permeability once the matrix permeability is defined.