Earthquakes linked to oil and gas activity are in the news. A recent study in Ohio linked a rash of small earthquakes to fracing of wells in the area. Earthquakes in Oklahoma have increased tenfold since 2009. A swarm of small earthquakes hit the Dallas-Fort Worth area recently. The US Geological Survey is raising its evaluation of earthquake hazard risk in Texas as a result.
In Texas, the spate of small earthquakes is tentatively tied to injection wells rather than fracing of new wells. The theory is that the injected water lubricates lithologic layers, allowing them to slip and causing quakes.
The Environmental Protection Agency estimates that there are 144,000 Class II injection wells in the US. The RRC has permitted more than 50,000 Class II injection wells in Texas since the 1930’s. These injection wells are used to dispose of water and waste produced from wells, both that from the fracing process and water produced with oil and gas in the production phase. Many oil wells produce hundreds of barrels of water for each barrel of oil produced. Without injection wells, the Texas oil and gas industry would screech to a halt.
In response to the increased seismic activity in Texas, the Texas Railroad Commission hired its own seismologist
and proposed new rules for those applying for permits to drill disposal
wells. The RRC’s proposed rules originally were drafted to require applications for injection well permits to provide a calculation of the estimated “five pounds per square inch, 10-year pressure front boundary,” as a way to determine whether or not the well would likely cause seismic activity in the area. When water is injected into a formation underground, it increases the pressure in the formation, and that pressure spreads through the formation over time. The five-psi, 10-year pressure front is the distance from the injection well to which pressures will increase by five psi if the well is operated at the permitted rate and pressure over a 10-year period.
The RRC published the proposed rule for comments and received 36 comments, including comments from the Environmental Defense Fund, the Sierra Club, the Texas Alliance of Energy Producers, some groundwater conservation districts, the EPA, the US Geological Survey, and Chevron USA. In response to comments, the RRC changed its proposed rule. Instead of requiring the five-psi, 10-year pressure front study, the RRC will require each applicant to provide copy of a USGS map showing all recorded seismic events within 9 kilometers of the proposed well location (about 6.1 miles). The pressure-front study will be required “only in certain limited circumstances where additional information is necessary to demonstrate that fluids will be confined if the well is to be located in an area where conditions exist that may increase the risk that fluids will not be confined to the injection interval.”
The original proposed rule also said that the RRC could modify, suspend or terminate a permit “if injection is suspected of or shown to be causing seismic activity.” The final rule modifies this language to read “if injection is likely to be or determined to be causing seismic activity.”
The RRC’s discussion of comments, and the final rule, can be found here. rrc earthquake rule.pdf