“Frac hits” sounds a little bit like a “best of album”, maybe a “best of album” for the oil and gas industry. But no, frac hits are something the oil and gas industry doesn’t want. Why? Because when a frac hit occurs then it means the horizontal fractures produced during hydraulic fracturing of a well have either intersected a nearby (offset) well or the fractures that were produced by hydraulic fracturing in a nearby well. How does an oil and gas operator know there has been a frac hit? Well the operator of the nearby well is going to be sure to let them know, because it often reduces the production of oil and gas and raises the pressure in the wellbore of their well. It can also introduce hydraulic fracturing fluid into a nearby well, which then may travel up the borehole and spill out on the surface. An increase in pressure, as well as the extension of fractures into the rock formation around a nearby well, can also damage the casing and cement. Cemented casing protects overlying rock formations from oil and gas coming up the sides of the well and possibly getting into groundwater. So a frac hit is not particularly popular in the oil and gas industry.

Frac hits occur more often when oil and gas wells are located close together. The Environmental Protection Agency in their December 16, 2016 report –“Hydraulic Fracturing for Oil and Gas: Impacts from the Hydraulic Fracturing Water Cycle on Drinking Water Resources in the U.S.” – states most frac hits occur when wells are less than 1100 feet from one another. But frac hits have also occurred in oil and gas wells up to 8422 feet away from a well being hydraulically fractured. That’s over a mile away.

Most frac hits are located in areas where the oil and gas rock formation is shallow, because predominantly horizontal fractures are formed. Deeper rock formations develop predominantly vertical fractures. Rock formations at depth are under greater vertical pressure from the overlying rock formations, which results in more upward extension of fractures. Shallower formations don’t have much in the way of vertical pressure from overlying rock, so they fracture outward or horizontally.

Just like producing oil and gas wells, nearby abandoned wells can be affected by hydraulic fracturing. Abandoned wells are old wells which are no longer used. They may have been plugged with cement. Other wells were often just left with open boreholes. It depends on the wells age and what the state regulations required at the time of abandonment. For example and according to EPA:  Pennsylvania’s abandonment regulations for oil and gas wells were not issued until 1957. The state’s records show there were 176,000 oil and gas wells abandoned prior to 1957. I was surprised at the number of wells. You never think of Pennsylvania as being a major oil and gas state, even though the first oil and gas well in the United States was drilled there. In fact, the state’s records show that around 300,000 oil and gas wells were drilled in Pennsylvania prior to 1957. So only a little over 100,000 wells would have been properly plugged under state regulations. These old abandoned wells are sometimes near the new wells being drilled today in Pennsylvania. Old wells, even when they were plugged with cement, are probably now deteriorating. Nothing lasts forever, especially cement and steel casing.  So if one of these old deteriorating or open borehole wells is intersected by new hydraulically induced fractures, then some interesting things can occur. For example EPA cites an abandoned well in Tioga County, Pennsylvania which received a frac hit as a result of a newly drilled gas well being hydraulically fractured. The abandoned well produced a 30 foot geyser of brine for more than a week.

So how do frac hits affect water resources? Although not a major pathway for gas or contaminants to enter drinking water zones, EPA’s research shows frac hits are a potential concern in areas where shallow oil and gas is being developed, producing wells and abandoned wells are abundant, and a groundwater source is being actively used by households. In addition, if surface spills from frac hits occur then contamination of nearby surface waters and shallow groundwater may also be a concern.