Insufficient distance between wellbores caused a vertical oil well to leak fluids after hydraulic fracturing of a nearby horizontal well last January in Red Deer County, Alta., an investigation by the Alberta Energy Resources Conservation Board has determined.
In addition to allowing the horizontal wellbore to be closer than allowed by its own protocols, the operator, Midway Energy Ltd., didn’t notify the vertical well’s operator, Wild Stream Exploration Inc., about the frac job. If it had known about the operation, Wild Stream might have been able to prepare equipment for the pressure surge that occurred when its well came into communication with the fractured well, ERCB said.
Partly because no violation of provincial regulations occurred, the agency took no enforcement action.
In a Dec. 12 report, ERCB said the wellbores are 129 m apart at their closest point—less than the 135 m minimum distance indicated by Midway protocols. Modeling projected the fracture half-length at 90 m, and the protocols call for well spacing of at least 1.5 times the half-length.
Because the planned fracture stimulation size was too great for the separation distance, communication between the wells occurred within the formation both wells targeted at about 1,850 m below surface, ERCB said. Formation and frac fluids from Midway’s horizontal well flowed to surface through Wild Stream’s vertical well on Jan. 13.
Frozen ground prevented much of the fluid from seeping below the surface, ERCB said. Cleanup was mostly complete within 72 hr.
The area potentially affected by initial release of an estimated 75 cu m of fluid was about 225 m by 200 m. Vacuum trucks recovered about 68 cu m of diesel-based frac and formation fluids, some of which had flowed down a hillside and pooled in a natural depression off the lease.
Samples from eight water wells within 1,300 m of the spill site showed no elevated levels of hydrocarbons, nitrate, or nitrite. Water and soil testing and other remediation operations continue under the jurisdiction of Alberta Environment and Sustainable Resource Development.
Through casing integrity and cement integrity logging, ERCB determined that wellbore integrity met its regulatory requirements.
The agency said communication between wells didn’t occur until about 1 hr and 45 min after the frac job, so no significant decrease in pressure was observed at the Midway well during the operation.
Increased pressure and flow rates in the Wild Stream vertical well caused surface components, which weren’t rated for hydraulic fracturing, to fail.
ERCB said the second, third, fourth, and fifth frac stages of the horizontal hole are closest to the bottomhole location of the Wild Stream well. It said one of the last three stages was most likely to have established communication with the vertical well.
Despite damage to valves and piping, Wild Stream wellhead components maintained integrity and were able to shut in the release.
ERCB said the main leak occurred in a 1-in. fuel supply line feeding back to the pumpjack engine and walking-beam compressor coming from the casing side of the wellhead.
Responses deemed appropriate
ERCB said both companies responded to the incident appropriately.
“The incident did not impact any member of the public, wildlife, livestock, groundwater, or surface water bodies,” it said.
The agency said Midway wasn’t required by regulations to notify Wild Stream of its frac operations. If it had provided notification, ERCB said, Wild Stream could have taken steps to prevent the release or limit its effects.
Failure by Midway to follow its protocol on well spacing might have prompted an enforcement action, but ERCB decided not to take that step.
“This is a unique situation in that the incident itself is a very uncommon occurrence and did not, in the ERCB’s opinion, result from or indicate an ongoing systemic deficiency in the operations of either licensee involved.”
In addition, both companies have been taken over by other operators since the incident, the agency said.