Confusion exists as to whether a well should be designated a gas storage well or an observation well. It's exact "true" state may depend on whether the well is being used to input and withdraw gas at any given moment. Operators commonly turn these wells "on and off" depending on their needs. In a sense, the well is a gas storage well when gas is flowing through it, and is an observation well when gas is not flowing.
Historically, the permitting of these wells appears to have changed, further clouding this distinction. In the past, permits were issued for either "gas storage" or for "observation" wells, the latter commonly known as "gas storage observation" wells. More recently, wells drilled for either "gas storage" or solely for observation have both been permitted as "gas storage or observation" wells. This lumping may avoid some procedural problems, however, it offers less information about the wells. In keeping with the earlier categories, which may give a more helpful picture of the reservoir geometry, the IGS attempts to report and keep up with whether a well is considered a "gas storage" well, or an "observation" well.
Caution. The PDMS user should be aware of potential errors that may result from this approach, and may want to search for more information about the "true" nature of any of these wells.
As a rough guide, one might assume that wells which are closely grouped together within the interior of a gas storage field are likely to be gas storage wells and not observation wells. Wells which fall around the outside edge of a group of gas storage wells are somewhat more likely to be maintained for observation of the reservoir boundary area. Wells that are separated by some considerable distance from closely grouped wells in a gas storage field are most likely observation wells, used to detect migration of gas from the reservoir.