2019 Q3 HIGHLIGHTS:
MODULAR DOWNHOLE POSITIONING AND SENSING PLATFORM FOR COILED TUBING DRILLING
MinEx CRC has taken our first steps towards a modular downhole positioning and sensing platform for Coiled Tubing drilling, using 3D printing to fabricate prototypes of the initial design concept.
The capture of downhole positioning and sensing data and delivery of those data to surface in real-time are required to deliver on the MinEx CRC goal of steering a CT drill hole to within 10m of a target at a depth of 1000m.
The modular design of the downhole platform allows multiple fit-for-purpose sensors to be added in series to the bottom hole assembly, with connectivity of power supply, communications and drilling fluid flow between modules. The 3D printed prototypes were fabricated based on designs completed by the Project 2 research team. The prototypes will allow researchers to experiment and make iterative improvements to internal sensor design, component interactions, connections between modules and integration with the bottom hole assembly - prior to manufacturing in the final material.
Our current priority for the downhole platform is a positioning tool. First candidate sensors and circuits for this tool have already been built into the 3D printed prototype and laboratory testing is underway. Our learnings from these tests will inform development of field deployable prototypes, also likely to be fabricated with 3D printers, building toward first field trials using the RoXplorer® CT drilling rig in the second half of 2021.
PROOF-OF-CONCEPT BENCHTOP PROTOTYPE DOWNHOLE GEOCHEMICAL ASSAY TOOL
MinEx CRC have built a proof-of-concept benchtop prototype downhole geochemical assay tool incorporating a laser-induced breakdown spectroscopy (LIBS) sensor.
In order to deliver reliable, accurate and precise multi-element downhole assay in real-time we must overcome challenges related to the downhole environment (high pressures; fast-flowing, turbid drilling fluids; contaminated drill hole walls; and a moving target) and the drilling platform (vibrations; miniaturisation of sensors; compatibility with the bottom hole assembly). The benchtop prototype has been constructed to enable testing of the LIBS sensor against these challenges in a controlled laboratory environment.
The prototype LIBS sensor contains a laser, optical system, and a number of spectrometers as well as a sample chamber. In the first set of experiments, designed to recreate movement of the sensor relative to the drill hole wall during drilling, we have incorporated a moving stage into the sample chamber. Geological samples of different composition can be attached to the moving stage and moved past the sensor at speeds consistent with drilling. The first set of measured samples includes well-characterised marble and granite. Preliminary experiments give geochemical assays which closely match known compositions and clearly distinguish boundaries between the marble and granite samples.
Although these results are promising, our Project 3 team will continue to take a fast-fail approach to the LIBS tool, quickly moving through a series of experiments which could disprove the technology as an option for downhole assay. At each hurdle passed, incremental improvements will be incorporated into the design. Our aim is to make a decision on the viability of a downhole LIBS assay tool by December 2020.
FIBRE-OPTIC DISTRIBUTED ACOUSTIC SENSING (DAS) FOR BORE HOLE SEISMIC APPLICATIONS
MinEx CRC has completed a series of controlled experiments which confirm the promise of fibre-optic Distributed Acoustic Sensing (DAS) for bore hole seismic applications and provide a recommended acquisition design for upcoming field deployments.
As a result of its low cost and ease of deployment, fibre-optic DAS could lead to routine acquisition of bore hole seismic data in the mineral exploration workflow, with profound implications for our understanding of the 3D structure of the subsurface. Before that can happen we need to fully understand the technique and convey it’s benefits to potential end-users. How does the seismic response compare to traditional geophone or hydrophone techniques? What are the optimum acquisition designs and processing methods? How does the seismic response relate to the subsurface geology?
The Project 5 research team has tested a number of fibre-optic cable designs (single mode, multi-mode, helically wound, engineered), in-hole deployment options (free hanging, cemented) and different seismic sources, both active (vibrators, weight drops, shot gun, electromechanical vibrators and sparkers) and passive (earthquakes, ambient noise and drilling noise) and compared the seismic response to conventional bore hole acquisition techniques. The tests were conducted in the 870m deep National Geosequestration Laboratory (NGL) drill hole at Curtin University. The NGL drill hole is well-characterised in terms of rock-types, physical properties and seismic response and is an ideal location to test and calibrate borehole seismic techniques. Our results show that bore hole fibre-optic DAS delivers comparable or better imaging than conventional techniques with higher signal to noise. Best results are achieved when the fibre-optic cable is cemented into the drill hole or (failing that) when using optical fibres that are engineered to give stronger back-scatter properties.
These results will inform the acquisition design of our first field deployments that are planned for late 2019 at MinEx CRC Participant mine sites.
MANTLE-TAPPING CONDUCTIVITY ZONES CONSISTENT WITH LITHOSPHERIC-SCALE METALLOGENIC SYSTEMS
A broadband magnetotellurics (MT) profile across the National Drilling Initiative (NDI) East Tennant Campaign area reveals mantle-tapping conductivity zones consistent with lithospheric-scale metallogenic systems.
The MT data were collected as part of Geoscience Australia’s in-kind contribution to the NDI, which has included acquisition of new geophysical (seismic, airborne electromagnetics), geological and geochronological data and integration with existing drilling data.
MT is a passive geophysical technique which uses natural variations in the Earth’s electric and magnetic fields to measure electrical resistivity in the subsurface. Broadband MT can provide useful information to depths of >50km, to the base of the crust and into the upper mantle. The East Tennant MT survey was planned to map electrical resistivity across crustal-scale features identified in complementary geophysical datasets. The data provide evidence for multiple, steeply-dipping conductive zones which penetrate to mantle depths and connect to the surface along newly-recognised major structures.
Similar features are spatially associated with large ore deposits elsewhere (for example at Olympic Dam) and are thought to be an expression of hydrothermal alteration associated with large metallogenic systems.
The East Tennant area is emerging as an example of effective use of pre-competitive data to characterise the geology and geophysical response of new exploration frontiers in covered parts of Australia. MinEx CRC is using these data to plan the East Tennant drilling campaign, expected to commence in mid-2020, with drill holes designed to target specific geophysical features, test provisional interpretations and provide detailed information for explorers to undertake more effective exploration in the region.
LAKE CARGELLIGO AIRBORNE ELECTROMAGNETIC (AEM) SURVEY
The Cobar – Lake Cargelligo airborne electromagnetic (AEM) Survey, being conducted in September 2019, will provide an important layer of 3D geoscience information ahead of planned National Drilling Initiative (NDI) Cobar drilling campaign.
The AEM survey, being flown by New Resolutions Geophysics, is part of the Geological Survey of New South Wales’ in-kind contribution to the NDI. The completed survey will cover an approximately 300km x 50 km corridor from north of Cobar south towards Rankins Springs.
The AEM technique measures electrical conductivity of the subsurface by applying a primary magnetic field, generated from an airborne transmitter, which induces electrical currents in the ground. These currents generate a secondary magnetic field which can be measured by a receiver on the same airborne platform. The Cobar – Lake Cargelligo survey will be collected by a helicopter AEM platform and will be flown at a height of 60 m, with the transmitter and receiver suspended 30 m below, along east-west lines that are 2.5 to 5 km apart. The flight lines are designed to avoid populated areas, buildings, towers, stock concentrations and steep terrain. The data will be used to map the natural electrical properties of rocks and soils to a depth of around 400 metres, which can then be used to identify groundwater resources and electrically conductive (or resistive) anomalies that may be associated with buried mineral deposits.
The AEM survey is an important component of the pre-competitive data being collected in advance of the MinEx CRC Cobar drilling campaign, due to take place in 2022 and 2023. The combination of drilling and co-located geophysical data is intended to inform and de-risk exploration in this undercover exploration frontier.