The Commonwealth of Pennsylvania now requires that operators identify existing wells within a 1000-ft-wide buffer zone surrounding unconventional wells that will be hydraulically fractured. This is to mitigate for the concern that fluids and gas from the hydraulically fractured well might communicate with undocumented and possibly unplugged wells that are the legacy of Pennsylvania's early oil and gas history. The rule requires that operators consult state well databases, company records, historic maps and photos, and the recollection of landowners to identify active wells, inactive wells, orphan wells, abandoned wells, and plugged and abandoned wells that are located within the 1000-ft.-wide buffer area. Adhering to these guidelines will provide a nearly complete inventory of wells drilled after 1955, when the state recorded well locations as part of the permitting process. However, helicopter magnetic surveys have shown that these methods identify less than 40﹪ of the wells drilled prior to 1955. This paper describes research by the National Energy Technology Laboratory (NETL) to develop low-cost, drone-based airborne surveys to locate existing wells. NETL's approach uses drone magnetic surveys to locate wells with steel casing and high-resolution drone LiDAR surveys to locate wells with nonmagnetic casing (wood or cast iron) or wells where casing has been removed.
Pennsylvania has a 150-year history of oil and gas production-the longest of any state- and this enduring activity has resulted in the drilling of more than 300,000 recorded wells (Dilmore and others, 2015). However, undocumented wells likely exist because innumerable wells were drilled during Pennsylvania's intense early oil and gas history when incomplete records were kept of well locations. The concern is that early wells are likely to be ineffectively sealed because there were no laws that required effective plugging when the wells were abandoned. Now, many undocumented and unplugged wells are thought to be in areas of emerging shale gas and shale oil development where open wellbores might provide a pathway for undesired upward migration of fluids and gas from hydraulically fractured reservoirs. Because of this concern, Pennsylvania regulators now require operators to locate the surface and bottom hole locations of existing wells (active, inactive, orphaned, abandoned, and plugged and abandoned wells) having well bore paths within 1,000 feet measured horizontally from the vertical well bore and 1,000 feet measured horizontally from the surface above the entire length of a horizontal well bore (Commonwealth of Pennsylvania 25 PA Code, 2016). Currently, regulations require that operators search well databases and historical records, and formally question landowners to determine if wells exist within the 1000-ft.-wide buffer zone. Prior research by the National Energy Technology Laboratory (NETL) has shown that while well databases are nearly complete for wells drilled after 1955 (when well locations started being recorded as part of the permitting process), the location record for earlier wells was less complete, containing less than 40 percent of the wells that could be located by airborne magnetic surveys. (Sams and others, 2017). Augmenting state well location data with historical records (farm line maps, old publications, historic air photos, company records, etc.) improves, but still does not provide a complete inventory of existing wells. Airborne magnetic surveys are the current gold standard for locating existing wells with steel casing, particularly older wells, which tend to have a strong magnetic signature (Hammack and others, 2016). However, airborne magnetic surveys are expensive and cannot detect wells where:
the casing has been removed or
the casing is non-magnetic (wood) or weakly magnetic (cast iron).
This paper seeks to reduce the cost of airborne magnetic surveys with the use of new, light-weight atomic magnetometers deployed on small unmanned aerial vehicles (sUAV). High-resolution drone Light Detection and Ranging (LiDAR) surveys are used to limit the ground search area (target) for wells with no casing or non-magnetic casing by looking for the topographic footprint of the well site.
