Eastern Section Meeting

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A Case Study of the Successful Utilization of Isotopic Fingerprinting in Plugging Artesian Flow at an Orphan Gas Well in Southern Ontario


In the 150 years of oil and gas activities In Ontario, many thousands of wells have been left in unplugged condition. Such wells are potential conduits for migration of sulphur water, hydrocarbons, and brines to other subsurface formations or to the surface. Under the Ontario Abandoned Works Program, over 300 high risk former oil and gas wells have been plugged and abandoned. There is often limited or no information available for wells selected for plugging, including depth and details on well construction. There is often no cement behind the casings or the casings have been removed. Casings are also often severely corroded and may collapse in the wellbore, making attempts to re-enter the well for plugging time-consuming and expensive. Some wells exhibit artesian flow of large volumes of sulphur water at the surface, sometimes accompanied by natural gas, and pose unique challenges for successful plugging. In partnership with the University of Western Ontario a geochemical tool was recently developed to identify the geological formations which are the source of leaking fluids. The tool utilizes isotopic fingerprints in combination with geological and hydrogeological mapping. This data is used to determine the geological source of the water and then establish a strategy to permanently isolate it. The tool can reduce the costs of plugging by optimizing the design of the plugging operation. A case study is presented for two derelict gas wells where isotopic fingerprinting has been recently successfully used in the plugging of two former gas wells with artesian flows of sulphur water exceeding 500 gal/min. The tool was used to guide the design of a program for wellbore control and cementing to isolate the flow within the source formation. This significantly reduced the time and costs for successful plugging operations.