Reflecting a growing caution in the oil/natural gas sector to temblors, the Colorado Oil and Gas Conservation Commission (COGCC) has ordered changes in a wastewater injection site in Weld County, asserting that actions at the location are deemed to be potentially related to nearby low-level seismic activity.

COGCC has authorized resumption on Friday of limited injections at lower pressures and volumes, along with continued seismic monitoring. “We are proceeding with great care and will be tracking activities at this site closely,” said COGCC Director Matt Lepore. “We’re moving slowly and deliberately as we determine the [long-term] right course for this location.”

The resumption of limited injection activity will be reviewed on an ongoing basis and may be halted if seismic events within a 2.5-mile radius of the well occur at or above a magnitude of 2.5 or greater, COGCC officials said.

Separately, COGCC officials confirmed that past injection volumes by operator NGL Water Solutions DJ LLC are being investigated for potential violations of permitted volumes that could result in financial penalties. “The matter remains under investigation, and any further information on possible enforcement would be contained in a notice of alleged violation from the agency,” a COGCC spokesperson said.

The latest move follows a 20-day halt in disposal operations by NGL Water Solutions on June 23 (see Shale Daily, June 26). Ongoing monitoring by University of Colorado (CU) seismologists picked up additional evidence of low-level seismic activity near the injection site.

Since the original shutdown, seismic activity has continued around the well, but it has been at a lower energy level, according to the CU researchers. With approval and oversight by COGCC, NGL has made adjustments in the well that are expected to mitigate the potential for future seismic events.

COGCC now is requiring NGL Water Solutions to make changes in its well and adjust its disposal activities. The state agency has been working with the operator and a team of (CU) researchers to determine “whether deep injection at the site may be tied to the recent seismic activity detected within the general vicinity,” a COGCC spokesperson said.

Following an original quake May 31 that was initially classified as 3.4 magnitude and since reduced to 3.2, the CU researchers picked up a 2.6-magnitude earthquake June 23, and COGCC has further analyzed data from the university team’s local network of instruments.

CU geophysics professor Anne Sheehan and some graduate students are maintaining and monitoring five seismic measuring devices around the original May 31 temblor’s epicenter (see Shale Daily, June 12).

Based on flow rate tests by NGL, a high permeability zone was identified near the bottom of the injection well. This created a preferred pathway for the wastewater, so the operator has plugged the basement of the well from 10,360 feet to 10,770 feet of depth, sealing off the pathway and increasing the distance between the injection zone and the basement rock, COGCC’s spokesperson said.

With the resumption of limited activity, NGL will be permitted to inject an initial maximum rate of 5,000 b/d of wastewater with 1,521 psi, and after 20 days the maximum injection rate may be increased to 7,500 b/d at the same pressure.