Stability Analysis in Determining Safety Drilling Fluid Pressure Windows in Ice Drilling Boreholes

Abstract

Borehole stability analysis has been well studied in oil and gas exploration when drilling through rock formations. However, a related analysis of ice borehole stability has never been conducted. This paper proposes an innovative method for estimating the drilling fluid pressure window for safe and sustainable ice drilling, which has never been put forward before. First, stress concentration on a vertical ice borehole wall was calculated, based on the common elastic theory. Then, three failure criteria, the Mogi⁻Coulomb, teardrop, and Derradji-Aouat criteria, were used to predict the stability of the ice borehole for an unbroken borehole wall. At the same time, fracture mechanics were used to analyze the stable critical pressure for a fissured wall. Combining with examples, our discussion shows how factors like temperature, strain rate, ice fracture toughness, ice friction coefficient, and fracture/crack length affect the stability of the borehole wall. The results indicate that the three failure criteria have similar critical pressures for unbroken borehole stability and that a fissured borehole could significantly decrease the safety drilling fluid pressure window and reduce the stability of the borehole. The proposed method enriches the theory of borehole stability and allows drillers to adjust the drilling fluid density validly in ice drilling engineering, for potential energy exploration in polar regions.

Keywords

• borehole stability
• ice drilling
• failure criteria
• fracture mechanics
• safety drilling fluid pressure window