24 October 2019
Saltwater seep signals subsurface issues in Oklahoma
Investigations continue to determine the cause of a high-TDS saltwater seepage in Oklahoma’s main oil & gas region
Oklahoma Corporation Commission (OCC) officials have yet to identify the source of saltwater seepage reported on July 1 on the border between Blaine and Kingfisher counties. The water has been bubbling to the surface of a wheat field at a rate of 68-70 bbl/d.
OCC spokesman Matt Skinner told Water in Oil that the plugging of three of Devon Energy’s non-producing wells located 905-3,340 feet away had no impact on saltwater flows. This meant officials were able to rule out that the water might be coming through well casing and migrating to the surface.
As a next step, officials requested a 30-day shut-in of four saltwater disposal wells (SWDs) located within 3 miles of the seep. No decrease in seepage was detected after the period ending on October 22, and third-party consultants hired by the OCC recommended extending the shut-in for another 15 days.
“If we see the purge drop and we see pressures come down at our other pressure reading points, then we're obviously on the right track. At that point, we will have narrowed it down to one or a combination those four wells,” Skinner explained.
The SWDs operated by Continental Resources, H2OK and S&S Star Operating are all injecting into Permian- or Virgilian-age rock about 5,600-6,600 feet deep.
Water sampled at the surface has 301,000 ppm of total dissolved solids (TDS), which is a likely indication that it originated in the deep Mississippian Formation, Oklahoma Geological Survey hydrogeologist Kyle Murray told Water in Oil. Samples from the nearby disposal wells show much lower TDS levels of around 70,000-90,000 ppm, suggesting the injected water was produced from a much shallower area.
Skinner stressed however that the formation of specific interest was the Permian and that, for now, the OCC has stopped permitting new disposal into the formation within an 11,000-square-mile area.
Saltwater seeps in Oklahoma are not unheard of, but this one is unique in that officials haven’t been able to quickly and easily identify a source, Skinner said.
According to Murray, subsurface faulting may have played a role in the seep. In the months leading up to the discovery, more than 30 seismic events of 0.8-2.4ML were registered in the area. The quakes that Murray plotted formed a line through the area of investigation, strongly indicating the presence of a fault.
“The only way you get water to move vertically from Mississippian or Permian to the surface is if you have a zone of weakness,” Murray explained. “This apparent fault is a potential pathway and it actually goes through the area where two of those disposal wells are.”
Another possibility is that the fault is a conduit between a naturally occurring pocket of water and the surface. In that scenario, the water would have to be coming from as deep as the Mississippian, where TDS levels can be very high, Murray said.
The OCC’s Induced Seismicity Department is investigating and monitoring seismicity in the general area; however, those investigations are separate from the seep issue.
For the time being, the saltwater is being diverted into a ditch and trucked daily to a commercial SWD about 4.5 miles away. Skinner said the extent of damage to the farmland cannot be assessed until the flows stop and that groundwater has so far not been affected.