Satellite imagery and oil-well production data shows an association between decades of oil activity and the ‘alarming rates’ of land movement. The study’s findings match those of research conducted in the years following the 4.8 magnitude earthquake that shook East Texas in 2012.
Researchers from Southern Methodist University (SMU) looked at a 4,000 square-mile (over 10,359km) area of the production-heavy West Texas Permian Basin using images made public by the European Space Agency. In one location the ground had shifted as much as 40 inches (101.6 cm) in less than three years. Sink holes have long been a feature of the area, with a 2016 SMU report raising concerns that two of the largest sink holes are continuing to grow. That report was also based on satellite data.
“The ground movement we’re seeing is not normal. The ground doesn’t typically do this without some cause,” said geophysicist Zhong Lu, professor in the Roy M. Huffington Department of Earth Sciences at SMU and an expert in satellite radar imagery analysis.
“These hazards represent a danger to residents, roads, railroads, levees, dams, and oil and gas pipelines, as well as potential pollution of ground water,” Lu said. “Proactive, continuous detailed monitoring from space is critical to secure the safety of people and property.”
Despite the limited scope of the study, its authors are confident that the effects of fluid injection extend beyond those of the sites studied. Co-author of the study and research scientist at SMU, Jin-Woo Kim, commented that the area had been ‘punctured like a pin cushion’ by oil wells since the 1940s.
Fluid injection includes the use of waste salt water and CO2 flooding to enhance oil recovery. The scientists found that ground movement coincided with rates of nearby injection activity and the volume of injected fluid. Fresh water leaking into disused wells and dissolving the salt formations inside also contributes to this process.
A statement from SMU said that this research was the first to identify signals of small-scale ground deformation by using large datasets spanning years and then adding supplementary information. Using a technology called ‘interferometric synthetic aperture radar’ (InSAR), the scientists can detect changes that aren’t visible to the naked eye and can capture information on ground deformation to an accuracy of sub-inches or better, they say.
In a 2016, study by Stanford University researchers showed that a 4.8 magnitude earthquake in Texas was caused by the ‘high-volume’ fluid injection used in oil operations. The study also used InSAR to analyse the relationship between human and geological activity, identifying deep-well injection sites as the trigger for the earthquake. The scientists emphasised that a better understanding of local geology was necessary to manage the effects of oil operations on the land.
In a press release from SMU, Jin-Woo Kim said that, while the correlation between fluid injection and ground movement could be coincidental, the possibility that human activity is responsible cannot be discounted and highlighted the need to monitor the area: “Our efforts to continuously monitor West Texas with this advanced satellite technique can help sustain safe, ongoing oil production.”