Statistical analysis of compliance violations for natural gas wells in Pennsylvania

Regulatory inspection and violation reports provide insight into the impact of natural gas extraction on the surrounding environment, human health, and public safety. Inspection reports for natural gas wells in Pennsylvania were collected from the Pennsylvania DEP Compliance Report from 2000 to 2014. Analysis of 215,444 inspection records for 70,043 conventional and unconventional wells was conducted in order to compare the odds of violations occurring under different circumstances. Logistic regression models were used to estimate the probability of violations occurring for both conventional and unconventional wells. When inspected, conventional wells had 40% higher odds of having a violation. However, unconventional wells had higher odds for environmental violations related to waste discharge as well as cementing and casing failures. Large operators had 40% lower odds of having any violation than smaller operators. While larger operators had fewer violations, a few of the largest companies had rates of violation much higher than the average for all operators, with some reaching violation rates as high as 1 in 4 active wells. A well also has a higher chance of being in violation if it is in the first year (85%) or second year (109%) since its spud date.