Avoiding gas hydrate problems in deepwater operations

Long distance tiebacks and transportation of unprocessed wellstreams could have significant impact on the economics of many marginal and deepwater oil fields. Flow assurance can be of great importance in these systems, where high pressures, low temperatures, and long residence times for fluids could result in gas hydrate problems. However, for such systems the traditional techniques, such as insulation, heating, and injection of thermodynamic inhibitors, may be insufficiently effective and overly expensive. Alternative technologies, such as, injection of low dosage hydrate inhibitors (kinetic and anti-agglomerate inhibitors) subsea water separation and making use of the natural inhibition effect of oil and formation water, are receiving considerable attention. In this paper, the developments in the testing and applications of low dosage hydrate kinetic inhibitors, subsea separation techniques and hydrate inhibition in oil systems to avoid hydrate problems in deepwater operations are discussed. The testing methods for evaluating these techniques and some experimental results are presented. In the evaluation and testing, a conventional stirred tank rig (kinetics rig) and a new glass micromodel rig have been deployed. The glass micromodel has been applied to visually observe gas hydrate formation in water and oil systems, investigating hydrate morphology and tendency for agglomeration and blockage. The kinetics rig is used to upscale the micromodel results, and measure the induction times, rate of gas hydrate formation, and assess transportability of gas hydrate slurries. Experiments were conducted using several North Sea light oils.