Oil drilling may have caused small earthquake in Surrey, research suggests

A series of more than 100 small earthquakes in Surrey in 2018 and 2019 may have been caused by oil drilling from nearby wells, a new study by UCL researchers suggests. It was done.

Earthquakes that occurred in Newdigate and surrounding areas between April 2018 and early 2019 have been recorded with magnitudes between 1.34 and 3.18 and have been associated with cracks in walls and ceilings and other damage to homes. There were also reports of houses and beds shaking. .

Geologists disagree over whether these earthquakes could have been caused by drilling at Hawley’s Horse Hill well, about 5 to 10 kilometers away.

Previously, some researchers have argued that earthquake patterns are not consistent with oil extraction and that increases in seismic activity do not immediately follow periods of increased extraction.

The study, published in Geological Magazine, ran more than 1 million simulations estimating the frequency of earthquakes based on the timing and amount of oil extraction, and found that the model’s predictions were largely in line with what happened. This suggests a link between oil drilling and earthquakes. .

Lead author Dr Matthew Fox (UCL Geosciences) said: ‘Our study suggests that there is a link between earthquakes and oil drilling at Horse Hill, but it is unlikely that this link is due to chance. “We can’t rule it out. We need more research to understand.” If this is cause and effect, however, our findings indicate that oil drilling may have caused the earthquake. ”

Oil drilling at Horse Hill was halted in October after planning permission was canceled in a landmark court case. A Supreme Court judge has ruled that the Surry County Council should have considered all of the project’s climate impacts before approving it.

However, another project to carry out exploratory oil drilling in Balcombe, West Sussex, has received parliamentary approval. This is the subject of a legal challenge by residents’ groups, and the case is due to be heard by the Court of Appeal in January 2025.

Extracting oil changes the pressure of the fluid within the rock from which the oil is extracted. This pressure change can spread tens of kilometers underground and intersect with faults (shear fractures between two blocks of rock). The rate at which this pressure change occurs is determined by the rock’s permeability (how quickly liquid passes through the rock).

Because faults are often subject to large strains, even small changes in stress can cause rapid movement of rocks, potentially triggering earthquakes.

In a new study, researchers used a mathematical model to predict the number of earthquakes that could occur based on the amount of oil extracted, taking into account two different rock types from which the oil was extracted. did.

Because much of the important information is unknown (for example, how long is the time lag between the extraction of oil and the occurrence of an earthquake?), the researchers used Bayesian machine learning tools to randomly calculate unknown parameters such as time lag. Changed.

Based on the work of the late Dr Rob Westerway, a geologist at the University of Glasgow, the researchers were able to explain oil extraction by switching between two different rock types, with Portland Rock on the one hand and Portland Rock on the other. It was a million times more permeable than Kimmeridge rock. This means the time lag between extraction and a potential earthquake can be a matter of days instead of weeks.

Although the earthquakes started just before oil drilling began, researchers believe these earthquakes may have been caused by preparatory work, such as checking the pressure within the well, thereby causing similar pressure changes from underground. He said it was possible that the damage had spread to the fault line.

Researchers said the situation was complicated by the fact that seismometers (instruments that detect ground vibrations) were installed in the area only after the first major earthquake occurred. Minor earthquakes that may have occurred before these devices were installed were not recorded. This highlights the need for detailed seismic monitoring before oil drilling begins at proposed construction sites.

Co-author Professor Philip Meredith (UCL Geosciences) said: “Our study highlights the importance of monitoring seismic activity in potential oil extraction areas before oil extraction begins. “Caution should be the pronoun. There’s no point in saying we won’t do it.” Potential problems may arise.

“These earthquakes were unusual events, as there had been no significant seismic activity in Surrey for decades. However, unusual events occur in nature, so the timing in relation to oil drilling may have been a coincidence. cannot be excluded.”