Improvement of well flushing technology during drilling in permafrost

The article presents the research results on flushing of wells during drilling in permafrost. The most effective flushing method is the use of drill fluids added with various antifreeze agents. In order to reduce the time spent on the implementation of this method of well flushing, as well as to prevent thawing and collapse of rocks in unstable intervals of wells, before the addition of antifreeze agents, the drill fluid is cooled down to the desired temperature. To cool drill fluids in summer, a refrigeration machine is used. In winter period, natural cold accumulated by atmospheric air is used for cooling. The drill fluid is cooled by any known method, including simplified approaches without using of complex and energy-consuming compressor refrigeration machines, by air heat exchangers blown with cold air. The proposed method involves the negative temperature mode of flushing and can be used when drilling wells of any purpose, diameter and length in permafrost up to 600 m thick.

Adaptation of the Winkie Drill for subglacial bedrock sampling

The Winkie Drill is an agile, commercially available rock coring system. The U.S. Ice Drilling Program has modified a Winkie Drill for subglacial rock and ice/rock interface coring, as well as drilling and coring access holes through ice. The original gasoline engine was replaced with an electric motor though the two-speed gear reducer and Unipress hand feed system were maintained. Using standard aluminum AW34 drill rod (for 33.5 mm diameter core), the system has a depth capability of 120 m. The drill uses forward fluid circulation in a closed loop system. The drilling fluid is Isopar K, selected for favorable properties in polar environment. When firn or snow is present at the drill site, casing with an inflatable packer can be deployed to contain the drill fluid. The Winkie Drill will operate from sea level to high altitudes and operation results in minimal environmental impact. The drill can be easily and quickly assembled and disassembled in the field by two people. All components can be transported by Twin Otter or helicopter to the field site.

Contesting the evidence for gene expression in lower oceanic crust

Li et al [Nature579, 250–255 (2020)] report microbial gene expression in deep ocean crust, from microbial communities that have concentrations as low as 100 cell per cubic cm. This would be incredible, since that would be the lowest biomass sample ever analyzed for gene expression for a deep biosphere sample by several orders of magnitude. However, I have reanalyzed the data and show that the author’s data are derived from contamination via seawater, humans, human skin associated bacteria, drilling fluid, and molecular reagent kits. The method that the authors used to produce their gene expression data is highly sensitive to DNA contamination, which is the case here. The authors claim that Pseudomonas, a known widespread contaminant in molecular reagent kits, is one of the most active groups in their lower crust samples and base their metabolic analysis on this contaminating organism. Here, I show that the gene expression data are derived from contaminating Pseudomonas (as well as other groups), and I show that the groups claimed as being active in the rock samples are also present in the negative controls at similar or higher relative abundance. For example, methane production in long term incubations was reported but gene expression from methanogens was 10 times higher in the drill fluid negative controls compared to the rock samples, demonstrating that the methane measured is likely derived from methanogen contaminants introduced from the drill fluid. There are no signs of active life here, but lipid biomarkers were found preserved in the rocks. Thus, the authors have sampled a fossilized biosphere, not a living one.

Technical innovations and optimizations for intermediate ice-core drilling operations

The British Antarctic Survey, in collaboration with Laboratoire de Glaciologie et Géophysique de l’Environnement, has in recent years successfully drilled to bedrock on three remote sites around the Antarctic Peninsula. Based on the experience from the multi-season project at Berkner Island (948m depth, 2002–05) we optimized the drill set-up to better suit two subsequent single-season projects at James Ross Island (363m depth, 2008) and Fletcher Promontory (654m depth, 2012). The adaptations, as well as the reasons for them, are discussed in detail and include a drill tent set-up without a trench; drilling without a borehole casing with a relatively low fluid column height; and using a shorter drill. These optimizations were aimed at reducing cargo loads and installation time while maintaining good core quality, productivity and a safe working environment. In addition, we introduce a number of innovations, ranging from a new lightweight cable tensioning device and drill-head design to core storage and protection trays. To minimize the environmental impact, all the drill fluid was successfully recovered at both sites and we describe and evaluate this operation.

Production drilling at WAIS Divide

The deep ice-sheet coring (DISC) drill was used for production ice-core drilling at WAIS Divide in Antarctica for six field seasons between 2007 and 2013. Continuous ice-core samples were obtained between the snow surface and 3405 m depth. During the 2012/13 austral summer, the DISC drill’s newly designed replicate ice-coring system was utilized to collect nearly 285m of additional high-quality core samples at depths of high scientific interest. Annual progress graphs are described, as well as milestones achieved over the course of the project. Drilling operations, challenges encountered, drill fluid usage, drilling results, and the drill crew’s experiences with the DISC drill and replicate coring system during production drilling are described and discussed in detail. Core-processing operations are described briefly, as well as the logistical undertaking of the DISC drill’s deployment to Antarctica.

Deep ice-core drilling performance and experience at NEEM, Greenland

The NEEM deep ice-core drilling in northwest Greenland was completed in summer 2010 after three seasons, which included establishing all drilling infrastructure. Normal drilling operations in the main borehole were declared terminated at 2537.36 m below the surface, when further penetration was stopped by a stone embedded in the ice in the path of the drill head. The design and implementation of the drilling operation strongly resembled the NGRIP drilling program. The NEEM drill was an extended version of the Hans Tausen (HT) drill, with specific modifications to optimize its use with the highly viscous Estisol-240/Coasol drill fluid used at NEEM. Modification to the drill and its performance in the new drilling fluid was largely satisfactory and successful. Throughout the drilling, special consideration was given to the way chips were transported and collected in a new chip chamber, including the consequences of drilling a larger borehole diameter than with previous drill operations that used the HT family of drills. The problems normally associated with warm ice drilling near the base of an ice sheet were largely absent at NEEM.

The investigation and experience of using ESTISOL™ 240 and COASOL™ for ice-core drilling

Continuous good-quality deep ice cores provide excellent scientific data with which to reconstruct a past climate record for >800 ka. At depths starting from ∼100m using an electromechanical drill, a drilling liquid is essential for successful recovery of the very high-quality ice cores demanded by modern scientific analysis techniques (e.g. continuous flow analysis). Finding a suitable drill fluid for use at deep ice-coring drill sites is not an easy task. Temperatures vary greatly not just from site to site, but also at a site where the average mean temperature from surface to bedrock can vary from –55°C to –2.75°C. In the past 60 years, many fluids have been used, with varying degrees of success, but for various reasons are either unavailable, are now considered unsafe and dangerous or are too environmentally damaging to be permitted. Here we report on our pre-season investigation into possible candidate drill fluids, with specific information concerning ESTISOL™ 240 and COASOL™, the rationale behind the redesign of our drill successfully used at NorthGRIP, Greenland, and EPICA DML, Antarctica, the knock-on effect of those changes, and our field experience in Greenland at Flade Isblink in 2006 and at NEEM in 2009–10.

Drill fluid selection for the SUBGLACIOR probe: a review of silicone oil as a drill fluid

As part of the ICE&LASER/SUBGLACIOR projects, an innovative probe called SUBGLACIOR is developed with the aim of perforating the ice sheet down to depths of 3500 m in a single season and continuously measuring in situ the isotopic composition of the meltwater and the methane concentration in trapped gases. Ice chips generated by the electromechanical drilling will be removed from the borehole by circulating a drill fluid. The selection of this drill fluid is important as it will have a major impact on the performance and the environmental evaluation. A literature review of drilling liquids is carried out to select potential fluids for further detailed testing. The selected fluids are varying grades of silicone oils, known as linear polydimethylsiloxanes, and ESTISOL™ 140, an aliphatic ester. The requirements for this project are similar to those for other deep ice-core drilling projects but, due to the embedded analytical system and the speed of drilling, there are some specific considerations. Following extensive testing, we conclude that a silicone fluid with a kinematic viscosity of 3 mm2 s−1 (3 cSt) is ideally suitable and affordable. This evaluation provides new insights into the use of silicone oils as a drill fluid that are of use to the wider ice-core drilling community.

Application of Solid Nitric Deplugging Technology

In order to conquer the disadvantages of conventional acidizing,various special acidizing technology has been developed recent years.For instance, added mud acid into drilling mud is not able to remove the contaminant effectively, especially barium sulphide of drill fluid,however, if added some EDTA into mud acid,this problem can be resolved smoothly.Along with the gradual development of acidizing technology,considering the limitations of mud acid to certain rock and clay,a new acidizing material called nitric powder was developed.When the proportion of nitric acid and hydrochloric acid is 1:3,the mixture will be renamed nitrohydrochloric acid.Nitrohydrochloric acid can dissolve organic material and inanimate matter efficiently,theoretically speaking,this deliquescence may reach 100%，which greatly improved acidizing effect.