Study on Evaluation Method for Wellbore Stability Based on Uncertainty Analysis

Abstract

ABSTRACT The wellbore instability is one of the main complex situations or accidents, which brings great difficulties and risks to the drilling engineering. The existing wellbore stability analysis models mostly ignored the uncertainty of geo-mechanical parameters. The result of geo-mechanical parameters were treated as the fixed values. So there are large errors between the predicted results and the actual underground pressure, which cannot meet the needs of drilling design under complex geological conditions. Therefore, this paper aimed to establish a new method for quantitative evaluation and analysis method for wellbore stability. Firstly, the uncertainty of geo-mechanical parameters were analyzed, the probability distribution of them were obtained. Then the quantitative uncertainty analysis method for fracture and collapse pressure were established based on Monte-Carlo simulation and normal information diffusion. Finally according to the collapse and fracture pressure with credibility, we realized the quantitative evaluation and analysis of wellbore stability. The method established in this paper can provide the scientific basis for evaluation of wellbore stability under complex geological conditions.