Published December 2020
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The objective of International Ocean Discovery Program (IODP) Expedition 384 was to carry out engineering tests with the goal of improving the chances of success in deep (>1 km) drilling and coring in igneous ocean crust. A wide range of tools and technologies for potential testing were proposed by the Deep Crustal Drilling Engineering Working Group in 2017 based on reports from recent crustal drilling expeditions. The JOIDES Resolution Facility Board further prioritized the testing opportunities in 2018. The top priority of all recommendations was an evaluation of drilling and coring bits because rate of penetration and bit wear and tear are the prevalent issue in deep crustal drilling attempts, and bit failures often require an excessive amount of fishing and hole cleaning time. The plan included drilling in basalt with three different types of drill bits: a tungsten carbide insert (TCI) tricone bit, a polycrystalline diamond compact (PDC) bit, and a more novel TCI/PDC hybrid bit. In addition, a TCI bit was to be paired with an underreamer with expanding cutter blocks instead of extending arms. Finally, a type of rotary core barrel (RCB) PDC coring bit that was acquired for the R/V JOIDES Resolution several years ago but never deployed would also be given a test run.
A second objective was added when additional operating time became available for Expedition 384 as a result of the latest schedule changes. This objective included the assessment and potential improvement of current procedures for advanced piston corer (APC) core orientation.
Expedition 384 began in Kristiansand, Norway, on 20 July 2020. The location for tests was based on various factors, including the JOIDES Resolution's location at the time, our inability to obtain territorial clearance in a short period of time, and a suitable combination of sediment and igneous rock for the drilling and coring operations. IODP Expedition 395, which was postponed due to the COVID-19 pandemic, had proposed sites that were suitable for our testing and offered the opportunity to carry out some serendipitous sampling, logging, and casing work for science.
We first spent 3 days triple coring the top 70 m of sediment at Site U1554 (Proposed Site REYK-6A) to obtain cores for evaluating potential problems with the magnetic core orientation tools and for assessing other potential sources of errors that might explain prior anomalous core orientation results. Comparison of the observed core orientation from magnetic orientation tools to the expected orientation based on the paleomagnetic directions recorded in the cores revealed an 180° misalignment in the assembly of one of the tools. This misalignment appears to have persisted over several years and could explain most of the problems previously noted. The assembly part was fixed, and this problem was eliminated for future expeditions.
We subsequently spent 20 days at Site U1555 (Proposed Site REYK-13A) to test the three types of drill bits, an underreamer, and a coring bit in six holes. The TCI bits were the best performers, the TCI/PDC hybrid bit did not stand up to the harsh formation, and the PDC bit did not get sufficient run time because of a mud motor failure. The cutter block underreamer is not considered able to perform major hole opening in basalt but could be useful for knocking out ledges. The PDC coring bit cut good quality basalt cores at an unacceptably low rate.
In the seventh and final hole (U1555G), we used a regular RCB coring bit to recover the entire 130 m basalt section specified in the Expedition 395 Scientific Prospectus and provided the project team with shipboard data and samples. The basalt section was successfully wireline logged before the logging winch motor failed, which precluded further operations for safety reasons. Additional operations plans in support of Expedition 395, including coring, logging, and casing at Site U1554, had to be canceled, and Expedition 384 ended prematurely on 24 August in Kristiansand.
This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license.