Experiences and Lessons Learned from Designing and Testing of an Air System and a Drilling Fluid Circulation System Adapted for Subglacial Bedrock Sampling in Antarctica

Abstract

Liquid drilling is commonly utilized in sampling of subglacial bedrock in Antarctica. However, this drilling method has relatively low penetration rate compared with air drilling. Additionally, the drilling method may lead to hydraulic fracturing of ice borehole. In this study, a multiprocess drilling system (MPDS) incorporated with different drilling methods, comprising an air system and a drilling-fluid circulation system (DFCS), was developed for sampling the subglacial bedrock in Antarctica. The air system uses a compressor to generate compressed air at a flow rate of 10 Nm3 min−1 and maximum pressure of 1.5 MPa. The compressed air was then dried by a freezing dryer and a desiccant dryer to a dew point of −40°. Before injected into the borehole, the compressed air was cooled to ≤ −5° by an air cooler. The DFCS can pump drilling fluid to the borehole at a flow rate of 100 L min−2 and maximum pressure of 2 MPa. The drilling liquid can be cooled to ≤ −5° by a refrigerating machine and a heat exchanger within DFCS. The ice or rock cuttings are separated by a vibration sieve and a vertical centrifuge. The two systems were integrated into modified 20 ft containers for easy transportation and assembly. Both systems worked with limitations: the failure of the freezing dryer and desiccant dryer led to the breakage of the air cooler in the field, and several problems were found in the drilling-fluid pump, vibration sieve, vertical centrifuge, and circulation tank. This paper presents in detail, the requirements, principles, and design of the air system and DFCS, in addition to the domestic and Antarctic test results. The experiences and learnings gained in this study will contribute to the development of ice and subglacial bedrock drilling technology.