Critical evaluation of borehole ovalization analysis against hydrofracturing profiles in argillaceous formations

Abstract

This paper introduces and evaluates the effectiveness of borehole ovalization analysis, a methodology designed to predict the natural stress field by examining deformations in vertical boreholes. The reliability of this approach has undergone rigorous testing across multiple boreholes within soft argillaceous formations, revealing several key observations. First, the results obtained demonstrate a notable correlation with hydrofracturing measurements, enhancing the overall credibility of the methodology. Second, the ratio of horizontal to vertical stress (σH/σh) is found to be contingent on the selected value of the breakout angle (θ), introducing a nuanced variable into the predictive framework. This insight emphasizes the importance of considering breakout angle variability in stress field predictions. Finally, the cohesion of the rock mass emerges as a pivotal factor that significantly influences the estimation of the horizontal stress magnitude (σH). This finding underscores the necessity of accounting for rock mass cohesion when applying borehole ovalization analysis for stress field predictions. Additionally, this paper conducts a meticulous comparative analysis by contrasting its results with findings from three hydrofracturing profiles conducted in distinct boreholes. Through this comparative approach, a more comprehensive understanding of the methodology's strengths and limitations is unveiled, contributing to the ongoing discourse on accurate stress field predictions in subsurface geomechanics.