Risk assessment through feature, event, and process for repurposing suspended oil and gas wells for geothermal purposes

Many countries have set the goal of net zero carbon emission and are diverting their energy source towards renewables. In that respect, geothermal energy is a continuous renewable energy source that is not affected by any metrological conditions. However, geothermal energy is not used to its full potential, and at present, less than 1 % of renewable energy is produced by geothermal sources. One of the biggest reasons that hinder its adoption is the cost of drilling and completion associated with the geothermal well, which almost takes 50 % of the project budget. Therefore, it is important that, where possible (with conducive geothermal conditions), conventional oil and gas wells that are old or temporarily suspended should be retrofitted into geothermal wells. In this way, the initial cost of the geothermal project can be reduced, which is mainly due to the drilling operations. However, before repurposing old retired wells, conducting a proper risk assessment is important to avoid any well integrity issues in the long run. Therefore, this paper presents a concept of accessing the risk using Feature, Event, and Process (FEP) that have been integrated with the interaction matrix, incident potential matrix (IPM), and cause-effect plot diagram. This risk assessment technique identifies the well components that might be susceptible to failure, and remedial work should be conducted on such elements. However, geothermal wells have no specific FEPs; hence, the FEPs from CCS wells have been used, which have their limitation when used for geothermal systems. Nonetheless, to show the feasibility of this approach in assessing the risk, two case studies of the fictitious tubingless geothermal well are presented in this paper.