Navigating multiple acres of dense, thorny brush on foot is a difficult task, even for native wildlife. For technicians hired to locate buried oil and gas wells on a future solar project site, the task would be daunting without first clearing the brush – a potentially expensive process.
Since much of the overgrown survey areas could not readily be crossed on foot, a more practical approach was needed – namely, hovering over it. Unmanned aerial vehicles (UAVs), commonly called drones, can do more than capture spectacular aerial photographs. UAVs are becoming an increasingly important tool for inspecting towers, building facades (and other areas normally requiring lifting equipment or scaffolding), preparing high-resolution orthophotography, measuring the volumes of stockpiles, assessing avian habitat, detecting storage vessel leaks, and creating digital surface models. UAVs are becoming our “feet” when we can’t easily get boots on the ground!
With the recent improvements in drone and equipment technology, evaluation of areas and items that were otherwise impractical are now possible. These improvements include increased payload capacities and battery life, precision lightweight equipment including light detecting and ranging (LiDAR) and infrared/thermal cameras, as well as magnetic, electromagnetic, and ground penetrating radar (GPR) instruments. On this project, these 21st-century flying machines helped our team deliver more accurate data than could have been gathered on foot, collected quickly without the need for disturbing the land.
Our client requested the magnetic survey during the early planning stages of their project so that the solar equipment infrastructure could be separated from any abandoned underground oil and gas well casings at the site. This approach was intended to help minimize the need for design changes, change orders, and/or remedial action if otherwise unidentified oil and gas wells were encountered during construction.
Fortunately, the oil and gas drilling activity on the property wasn’t entirely undocumented. The team reviewed oil and gas permit records, as well as historical aerial photographs, to prepare GIS-based maps showing suspected well locations to be surveyed. This information helped our technicians prepare precise UAV flight plans consisting of 200-foot by-200-foot areas over the suspected or permitted well location coordinates. Survey areas were drawn in ArcGIS and other GIS software, which was imported into the flight mission control software to create flight plans for each survey.
The surveys were laid out precisely, with 21 parallel transects spaced 10 feet apart and were flown from 10 to 60 feet above ground level. With the magnetometer attached to the UAV, the vehicle flew at speeds of 10 to 30 feet per second. This enabled the team to perform each survey in 10 minutes or less. Performing the same work on foot on an area with only minimal vegetation or after being cleared would have taken about two hours. Mobilizing the required heavy equipment and clearing the work areas with a brush mulcher would have cost thousands of dollars.
The magnetometer instrument collected 200 magnetic readings per second along with the geographic coordinates using a GPS data logger. Utilizing the GPS-enabled flight control software allowed the UAV to maintain flight path and altitude, even on windy days. The precise GPS and rapid data collection rates helped maintain the accuracy of the data gathered by the airborne magnetometer at rapid survey speeds.
The data recorded by the instrument helped our team successfully identify the location of underground well casings. The geographic coordinates of the areas with high magnetic field readings were noted and the location was staked.
Combining the capabilities of the heavy-duty UAV, flight mission control software, and lightweight, high-sensitivity magnetic instrumentation transformed a potentially complicated project into a complete success. The client received the data they needed to safely build infrastructure for their solar project, while saving thousands by not having to clear brush from hundreds of acres of land. The technology also allowed our team to do the job safely and more efficiently. The project earned a 2020 EBJ Business Achievement award for Project Merit from the Environmental Business Journal. This project proved that we can fly over the earth to discover what’s beneath the surface!
Jim Major, P.G., is a professional geophysicist and FAA licensed UAS pilot in the San Antonio, Texas office. He is the South Texas geophysical services group leader and is responsible for managing and conducting geophysical projects across Texas.