Abstract:
The relationships between random variables and results of borehole stability model were analyzed by means of Monte-Carlo simulation to figure out the most sensitive factors affecting borehole stability under different stresses and failure criteria. It is indicated that based on the collapse pressure of Mohr-Coulomb criteria, the most sensitive factor in any ground stress field is always the maximum horizontal ground stress. Based on the collapse pressure of Drucker-Prager criteria, the most sensitive factor is pore pressure when the vertical stress is the maximum major stress, and it is the internal friction angle when the vertical stress is the medium or the minimum major stress. The most sensitive factor of formation fracture pressure in any ground stress field is always the minimum horizontal stress. After the most sensitive factors affecting the reliability of borehole stability were defined, the accuracy degree of sensitive factors was improved by taking the measures correspondingly, so that the uncertainty of predicted collapse and fracture pressures is decreased and the reliability of borehole stability is ultimately improved.