Numerical simulation and parameter influence analysis of drilling fluid erosion on samples

Abstract:

In geotechnical engineering investigations， obtaining high-quality undisturbed soil samples through drilling is crucial， with the core objective being to minimize sample disturbance. This study addresses the issue of drilling fluid erosion and disturbance on soil samples during the drilling and sampling process. Based on a bottom-hole model of a core bit， numerical simulations were conducted using Fluent software. The research reveals that the erosion of soil samples by drilling fluid advances in a stepwise manner over time， extending from the upper part of the sample toward the bottom， and can be divided into three typical erosion zones. Under varying drilling fluid viscosities and flow rates， the degree of erosion at both the upper and bottom parts of the sample is significantly greater than that in the middle section. Specifically， the erosion range at the upper part expands toward the middle as viscosity and flow rate increase， while the erosion range at the bottom increases with higher flow rates but decreases with higher viscosity. Overall， an increase in soil sample permeability， a reduction in drilling fluid viscosity， and an elevation in flow rate all significantly enhance the erosion effect， with the most severe erosion occurring at the bottom of the sample. This study elucidates the multi-parameter coupled erosion mechanism of the interaction between drilling fluid and soil， providing a quantitative basis for optimizing drilling fluid properties and drilling techniques， which is of great significance for improving the quality of undisturbed soil sampling and the reliability of engineering investigation data.