Abstract
Management of hydrate risk is a challenging problem in gas-condensate production systems. A "no inhibitor, no production" operational strategy is the norm due to the insufficiency of real-time knowledge of process conditions and hydrate kinetics in the field. This implies both lost-production costs and inadequate risk awareness. Recent advances in hydrate kinetics modeling in gas-dominated systems, based on fundamental research at the University of Western Australia (UWA), however, provide an opportunity for increased operational efficiencies and safety. This paper presents progress made in a joint-industry project (JIP) towards an integrated, real-time flow assurance model incorporating hydrate kinetics.
This JIP leveraged existing data from UWA -- including flowloopmeasurements and the modelling of hydrate growth and transport mechanisms -- to achieve the integration of a hydrate kinetics model with an existing, field-proven multiphase flow simulator. This paper discusses the modeling, validation against experimental data, and the testing against historical data from a field system underhydrate-free and hydrating conditions.
The model showed good agreement for multiphase flow prediction of laboratory experiments. Trends of pressure drop dependence on various flow parameters agreed as well. For field data of a large gas-condensate pipeline, the model correctly predicted when hydrates form and when they are absent. These simulations, further, revealed the sensitivity of overall hydrate holdup and distribution to several parameters, including ambient temperature, holdup profiles, water droplet entrainment, and the strength of hydrate-wall adhesion. Since number of these parameters are subjected to underlying uncertainties in field conditions, a viable hydrate monitoring/prediction tool ought to be based on ensembles of simulations (an analogy might be drawn to hurricane track prediction). This is particularly true for predicting the location of the hydrate blockage and the time-to-remediation.
Currently, there is little modeling support to help manage hydrate risk in gas-condensate production operations without recourse to overly conservative strategies, such as overdosing. This model represents the first steps towards an online tool that can be integrated into digital twins of such fields. Such a tool will help optimize inhibitor consumption, reduce lost production costs, and provide early warning of hydrate blockage hazard. Potential end-user savings, from inhibitor consumption alone, are estimated at USD 500M in capital expenditure and USD 50M per annum in operational expenditure, for a typical moderate to large development.
