Sinkholes have occasionally popped up in and around oil patches for decades, added Lu. He said that’s especially true among older wells, where pipes have degraded, old crews did not know how to best drill to prevent subsurface issues and operators flushed oil reservoirs full of water in efforts to eek more hydrocarbons out of the earth.
While it’s difficult to draw a definitive cause for every sinkhole, oil and gas wells can provide a new avenue for fresh water to work its way deep into the ground, interacting with layers of salt and other soluble materials that can break down and cause the ground above it to become weak and ultimately give way, Lu and Paine said.
In Daisetta, the land on which the new sinkhole sits has been the center of a slew of lawsuits, with attorneys for the city and local residents claiming that the oil field service company that once called the plot home injected more wastewater into the ground beneath it than its permits allowed, eating away at the salt dome beneath it and causing the earth to cave in.
Those lawsuits, filed after the first nearly 500-foot-wide and up-to-75-foot-deep sink hole formed there in 2008, were dismissed by judges citing circumstantial evidence. Neither attorneys for the city of Daisetta nor attorneys representing DeLoach Vacuum Service/DeLoach Oil & Gas Waste Well, the now defunct oil field services company, responded to requests for comment. The Texas Oil & Gas Association also did not respond to request for comment.
“It’s really difficult to prove a cause and effect for sinkhole formation in places like that,” said Paine. “Any evidence is buried in the depths of the sinkhole and are not accessible for people to find out.”
Even so, there are other well-documented cases of sinkholes cratering around old oil wells.
Take Hendrick Well No. 10-A — a 2,559-foot-deep West Texas well that produced oil from 1928 to 1951 but had been inactive since March 1964, according to the UT Austin’s Bureau of Economic Geology. On June 3, 1980, the ground beneath that unused well cracked open to create a hole nearly eight stories deep and about the length of a football field in diameter. It became known as the Wink Sink, named after a tiny town nearby.
Two decades later, a second sinkhole formed about a mile south of the first Wink Sink. This time, the hole surrounded the Gulf WS-8 well, a water supply well drilled 3,582 feet deep that produced an estimated 800 million barrels of water that was ultimately injected into oil wells to try to push more hydrocarbons out of the earth.
That sinkhole, Wink Sink 2, has grown into an oval shape ranging from two to nearly three football fields across.
Even though both Wink Sinks surround old wells used for oil and gas activities, scientists have been reluctant to definitively draw a definitive link between their formation and the old oil wells.
Lu said there are layers of salt beneath the ground there, some as thick as 100 feet, which are part of a larger geologic area known as the Salado Formation.
“If you want to take oil or gas out [of the ground], you have to pass through that layer,” he said.
But once oil drilling is over, water can work its way into the ground through the same pathways producers sucked the oil out, Lu said.
He said the process is similar to the dissolving of a teaspoon of salt when water is poured over it. That can also happen if enough water seeps into massive layers of salt buried beneath the earth.
Studies from UT Austin found that Wink Sink 1 formed when unsaturated water flowed to the salt layer of that formation, causing it to collapse. But those studies did not conclude whether the damaging water came from induced fractures caused by oil drilling, the borehole from the well itself or natural causes.
Analysis is similarly inconclusive about what caused the sinkholes in Daisetta, although the issue is similar.
Daisetta sits atop what is known as a salt dome, which is formed when columns of salt rise toward the surface because they’re made of lower-density material than the rocks above it, Paine said. The salt is closer to the surface in salt domes than in other places, but that also means water can leach into those layers more quickly and easily, causing them to dissolve and potentially create salt domes.
But it’s much harder to place blame on why the salt dissolved, especially when it’s so close to the surface in places like Daisetta, Paine said. There are sinkholes around wells that provide a conduit for water to get to the salt and dissolve it, he said.
