Aeromagnetic surveys for the location of undocumented orphaned wells

The U.S. Department of Energy's National Energy Technology Laboratory (NETL) conducted research to field test the ability of airborne methods to locate existing wells quickly and accurately with minimal landowner impact. Helicopter surveys with two boom-mounted atomic magnetometers were used to locate wells at two oil fields in Wyoming and at four large oil and gas producing areas in Pennsylvania. At the two Wyoming oil fields, the helicopter magnetic survey identified 91%–96% of the wells located by exhaustive ground search. A different validation was used for the thickly forested Pennsylvania flight areas where well picks from the helicopter magnetic survey were used to direct the ground search to potential well locations for verification. The number and location of verified well locations were then compared to well records in the state database. For the oldest wells (circa 1860–1880), the number of wells in the state database exceeded the number of wells identified by the helicopter magnetic survey because many early wells had wood casing (nonmagnetic). For wells drilled between 1880 and 1950, the helicopter surveys found two to five undocumented wells for each well in the state database. The best results were achieved at a gas storage field where wells were drilled after 1950. There, 98% of the wells located by the helicopter magnetic survey were documented. In 2017, NETL used an atomic magnetometer on a small uncrewed aircraft system (sUAS) to refly an area previously flown with a crewed helicopter. The magnetic map from the sUAS survey was equal to that obtained with a crewed helicopter. High-resolution topographic images developed from sUAS LiDAR surveys were found to be helpful in locating very early wells with wood casing. When the wood casing decayed, soil subsided into the well void, leaving a circular depression that is easily recognized in high-resolution LiDAR imagery.