Arkansas regulators Wednesday afternoon established a permanent moratorium area for any new drilling wastewater injection wells in an area of the Fayetteville Shale where four such wells are thought to have contributed to earthquakes.

The Arkansas Oil and Gas Commission (AOGC) also ordered the shut in of one injection well in the area. The operators of three other injection wells slated for closure had already agreed to plug them before the hearing. The move does not affect natural gas drilling, but drillers that had been using those wells for disposal will have to truck their wastewater to one of roughly 730 other disposal wells in the state.

“There was enough plausible evidence to show a connection and a relationship between disposal operations in this particular area of Arkansas and the seismic activity which occurred last summer and up through earlier this year,” AOGC Executive Director Larry Bengal told NGI’s Shale Daily.

Earlier this year Oklahoma City-based Chesapeake Operating Inc. and Little Rock, AR-based Clarita Operating LLC agreed to halt drilling waste injection activities at two disposal wells while the potential link with earthquakes was examined (see Shale Daily, March 8) [BHP Billiton Petroleum LLC later acquired the Chesapeake assets as part of a larger Fayetteville acquisition (see Shale Daily, April 4)].

Shortly after waste injections at the wells had ceased, the earthquake swarm that had plagued the region died down (see Shale Daily, March 17). “You can definitely see a marked difference, especially in the larger events, the 2.5 or greater,” Arkansas Geological Survey’s Scott Ausbrooks, geohazards supervisor, said at the time. In June the permanent shut in of four injection wells in the region was proposed along with the moratorium area (see Shale Daily, June 23).

The moratorium extends about five miles on either side of two centerlines extending northeast to southwest through the Guy-Greenbrier earthquake swarm and the historic Enola earthquake swarm, from north of Greers Ferry Lake to the Arkansas River.

Bengal said following the earthquake activity in the region a new fault was discovered that was unknown when the disposal wells were drilled. “It’s a deeper fault trend that extends down to the basement rock,” he said. “The basement rock is where many of the earthquakes were occurring. That’s where the principal rock stress is that the injection wells potentially triggered.”

Areas outside of the injection well moratorium area will be monitored more closely going forward, and further restrictions on injection wells are possible, Bengal said. “[In] the areas outside the moratorium we will be proposing additional regulations in the permitting process for disposal wells to supply seismic information as well as maybe establishing setbacks from those wells to try to determine if there is in fact outside the moratorium area that same trend that could result in the occurrence of seismicity related to disposal wells. If that is the case, the moratorium area — at least on a well by well basis — could expand.”

The operator that had contested the closure of its well is Deep-Six Water Disposal Services, which is a unit of Oklahoma City-based Hurst Oil Investments Inc. The company has the option of appealing the order, which requires the well to be plugged by Sept. 1.