David Bamford, Director at IMMER Ltd

Fellow Geophysicists!

I think that nowadays we are all aware of what a UAV, aka a ‘drone’, is; as geophysicists they offer us great advantages in data collection onshore for oil & gas exploration and mining geophysics, and environmental surveys.

In this short article I will outline some of the key measurement technologies that we can deploy but first let’s consider the general argument in favour of UAVs.

Why UAVs?

It’s a commonplace that surveying with UAVs is quicker and cheaper than with “walkers”. As Coptrz tell us:

"Turn a 2-week Survey into a 2-day Project": 

In addition, provided they are ATEX-compliant, UAVs can survey very large areas that it could be hazardous for humans to enter, for example parts of gas terminals, refineries etc.

My favourite ‘survey unit’ is a football/soccer pitch which is typically 100 x 70 metres.

A quadcopter UAV flying at 2 metres/sec and executing a raster scan survey with lines 2 metres apart would take roughly 30-35 minutes to complete the task. So perfect for smaller sites such as drilling locations, landfills, anaerobic digesters and so on.

But some sites are much bigger - for example, both the Grain LNG regas terminal and the Stanlow Oil refinery cover ~600 acres or roughly 300 football pitches. Here a faster flying fixed wing UAV would be more appropriate if coverage of the whole site was needed.

This article by the Survey of India is a short summary of the types of UAV and the planning of drone operations:
https://www.linkedin.com/pulse/drone-based-mapping-survey-india-transforming-large-scale-06gac

The critical factor with regard to the sensors a UAV can carry is their weight. Here are some that are ‘good to go’ today:

• Magnetometers 
• Gamma Ray Spectrometers
• Thermal imagers (Infra Red)
• Hyperspectral (VNIR, SWIR - best described as ‘emerging’)
• TDLAS
• Electromagnetics (limited but VLF available)
• GPR
• LiDAR

Gravity, especially Gravity Gradiometry, lies in the future!

Applications in Onshore Oil & Gas Exploration

Especially in the USA, exploratory surveys to detect the presence of near surface anomalies caused by the microseepage of petroleum are well known.

The basic ideas are:

1. Hydrocarbons, chiefly methane through pentane, migrate upwards from source rocks and reservoirs to the surface
2. When upward-migrating light hydrocarbons reach near-surface oxidizing conditions, aerobic hydrocarbon-oxidizing bacteria consume methane (and other light hydrocarbons) and decrease oxygen in pore waters.
3. With this development of anaerobic conditions, the activity of sulphate-reducing bacteria results in sulphate ion reduction and oxidation of organic carbon to produce reduced sulphur species and bicarbonate ion.
4. Highly reactive reduced sulphur species can then combine with iron to form iron sulphides and oxides. Iron sulphide can be in the form of pyrite, marcasite, magnetite, pyrrhotite, greigite, or maghemite.
5. As a result of bacterial sulphate reduction, sulphate ion concentration is decreased. In addition, bicarbonate is added to pore waters, raising pH and thus promoting precipitation of isotopically light, pore-filling carbonate cements.

There are several choices as to the detection/measurement technology::

Direct detection of hydrocarbons:

1. Surface/near surface geochemistry:

Indirect detection of effects of hydrocarbons:

2. Geophysical measurements, detecting ‘unusual’ minerals:

a. Magnetic
b. Electrical
c. Gamma Ray

3. Observation of changes in rock colours, eg whitening of red beds.

4. Impact on vegetation:

a. Reflectivity
b. ‘Health/Stress’

Direct detection (1) is sometimes termed Passive Geochemistry - see for example, https://www.findingpetroleum.com/event/Passive-surface-geochemistry-to-map-hydrocarbons-and-assess-CO2-storage-sites/06a40.aspx

Geophysical measurements (2) have traditionally been the domain of "walkers" but it is easy to see how UAVs can play an important role - ‘2-day surveys instead of 2-week projects’.

Spotting the impact on rock colours and vegetation (3 and 4) is more likely the domain of higher-flying aircraft or satellites.

I’m sure some will regard this topic as occupying but a small corner of our world of Geophysics - compared with the attractions of seismic reflection (3D, 4D, OBNs, FWI etc) - but I’d like to highlight the potential to integrate satellite, UAV and “walker” technologies required in this small corner.

Applications in Onshore Minerals Exploration

I thought very hard about using AI to write a learned-looking piece on the technologies deployed in mineral exploration but discovered I didn’t need to as Kayuza Okada said all that needs to be said in his 2022 paper “Breakthrough technologies for minerals exploration” which you can find here: - a far better summary than anything I (or AI!) could deliver.

I offer his comments on UAVs (and USVs):

“Unmanned survey platforms are an evolving technology area. Although it is unclear what the next technology breakthrough for mineral exploration will be, advanced maneuvering control technology and the technology to operate multiple unmanned platforms simultaneously will be the keys to increasing the use of automation to reduce the cost of labor-intensive exploration.”

Applications in Emissions Monitoring & Measurement

Again, the increasingly recognised necessity for this topic is the integration of satellite, aircraft/UAV and “walker” borne sensors, with methane emissions being the main target.

In the U.K., the UAV application sees Big Sky Theory Ltd (BST: https://www.bigskytheory.co.uk/launch-locate )leading the charge, specializing in advanced drone operations and airborne intelligence, particularly for detecting fugitive methane emissions in the energy and waste sectors. BST use specialized drone technology for environmental monitoring and autonomous data collection - autonomous flight, terrain following, and electro-optical/infrared (EO/IR) sensor integration - with support from Innovate UK and the National Physical Laboratory. Operates the "Launch & Locate" programme for methane emissions mapping. They have secured multiple Innovate UK grants for drone development.

Summary

Some time ago, I went down memory lane to summarise what I had heard and what I knew of the evolution of the seismic technology that completely underpins our efforts to explore for oil & gas - from the first steps offshore in the early 1940s - click here to view.

Truly a triumph of Geophysics and Geophysicists!

As Geophysicists, I recommend that we now take hold of the idea that UAVs are not just for delivering parcels or medical supplies but can deliver more and better data about the Earth, the Environment, Emissions… Everything in fact.

KeyFacts Energy: Commentary