A Novel Technique for Monitoring Hydrate Safety Margin

Abstract

Great concerns with flow assurance issues have been raised by the oil and gas industry, while the industry is increasingly moving to deepwater reservoirs. Gas hydrate blockages are one of the most common risks for the long distance offshore gas and oil production transport pipelines. Various types of hydrate inhibitors are usually deployed to ensure unimpeded flow of hydrocarbons. At present hydrate inhibitors are injected at the upstream of the pipelines according to approximate assessment of the flowing conditions including the produced water cut and the hydrate phase boundary that is determined based on the worst temperature and pressure conditions, without any means of monitoring the actual degree of inhibition along the pipeline. A novel technique has been developed to optimize the injection of hydrate inhibitors by monitoring the actual hydrate safety margin (i.e., degree of inhibition), which makes it possible to reduce unnecessary cost and potential impact on the environment. It measures the acoustic velocity and electrical conductivity of downstream aqueous samples and then determines both the inhibitor concentration and salt concentration through a trained artificial neural network. The hydrate phase boundary, hence the hydrate safety margin, are finally determined by an integrated in-house thermodynamic model using the determined salt and inhibitor concentrations. Its performance has been intensively evaluated using synthetic samples and real produced water samples by the authors and some oil & gas and service companies. This communication reports the success in development of the hydrate inhibition monitoring system. Results of the evaluation demonstrate that the system can be used for different inhibition systems including methanol-salt systems, mono ethylene glycol- salt systems, and kinetic hydrate inhibitor-salt systems with an acceptable measurement accuracy.