Quantitative assessment approach to assess benefits of subsurface safety valves and tubing and packer systems in depleted reservoir and aquifer gas storage wells

Abstract

The Battelle Memorial Institute, Sandia National Laboratory, and Nova Northstar LLC, jointly carried out two projects, sponsored by the Pipeline and Hazardous Materials Safety Administration, assessing the roles of subsurface safety valves and tubing and packer systems in depleted reservoir or aquifer wells used for underground gas storage. The assessment was based on the American Petroleum Institute 581 method and on the storage well-specific model created by the 2017 Joint Industry Task Force organized by the UGS industry in response to the Aliso Canyon gas leak. The model was expanded to capture the specific functionalities of safety valves and tubing and packers, as well as to account for workover risk associated with monitoring and maintenance of such devices. The main conclusion of the two projects is that the application of safety valves and/or tubing and packer systems can reduce risk in some, but not all, gas storage wells. Gas storage wells with low initial risk, as measured by a likelihood of a loss of control event and by a projected consequence of such event, would generally not benefit from installation of new safety systems. In fact, the risk may be increased due to risk of more frequent and more complex workover operations or due to deliverability impairments. For some wells, the initial risk is such that the application of a safety valve or a tubing and packer can substantially decrease risk, specifically reduce consequences of loss of control events. Wells with inherent or initial risk, particularly driven by high likelihood of failure, would see risk reduced by the application of a safety valve or a tubing and packer, however, remaining risk are unacceptably high. An effective way to assess the applicability of these safety devices is to apply quantitative risk models, specifically models that evaluate probabilities/likelihood and consequence of accidents. • Broader use of quantitative risk models should be promoted in the UGS industry. • Tubing and packer systems can reduce risk in some but not all gas storage wells. • Sub surface safety valves can reduce risk in some but not all gas storage wells. • Workover risk should be included in the overall risk model. • Human factors may substantially affect the risk assessment.