(728c) Efficient Assessment of Gas Hydrate Formation Probability Using the HPS-Alta

Natural gas hydrates are ice like solids which are stable at temperatures and pressures typical of subsea oil and gas flowlines. As oil and gas production moves towards deeper water, complete hydrate avoidance becomes more challenging to realize economically. Although hydrate nucleation is stochastic, in principle it should be possible to apply results from experimentally-verified hydrate-specific nucleation theory to predict hydrate formation probability during production, thereby enabling a transition to risk-based hydrate management strategies. Representative experimental nucleation data is however traditionally challenging to obtain in an efficient manner given the need to measure a large number of formation events to properly characterise the stochasticity.

To address such challenges, we have developed a high pressure stirred automated lag time apparatus (HPS-ALTA) in which thermoelectric Peltier elements are used to rapidly transition system conditions from outside to within the hydrate equilibrium region. The fast ramp rates possible in this apparatus are also influenced by each cell’s relatively low thermal mass. Together, these factors enable efficient measurement of large numbers of hydrate formation events under shear, subsequently allowing for the determination of smooth formation probability distributions. The use of pressure-based rather than optical hydrate detection enables the detection of hydrate formation in opaque mixtures (e.g. water-oil emulsions).

In this presentation, we will demonstrate the use of the HPS-ALTA for efficient assessment of hydrate formation probability, both under relatively fast temperature ramping (enabling efficient determination of subcooling distributions) and at constant temperature (enabling extraction of induction time distributions). We will cover both (a) practical aspects related to the use of this apparatus and (b) example datasets showing how the HPS-ALTA can be used to efficiently screen (e.g.) inhibitor chemicals or, alternatively, provide data which can be compared with theoretical predictions for hydrate formation. For example, with regards to the former, we demonstrate the critical role played by shear in the HPS-ALTA in overcoming what would otherwise be severe mass transfer limitations both in gas-water and gas-water-oil systems. Importantly, such limitations can affect both formation onset and early-stage hydrate growth and thus are critical to characterise. We will also compare experimental data from conventional HPS-ALTA cells with that obtained in a visual HPS-ALTA cell, the latter allowing direct observation of the hydrate phase (film versus slurry) at different shear rates. We will then show how the HPS-ALTA can be used to explore how the presence of liquid hydrocarbons and/or inhibitor chemicals influence hydrate formation probability and early-stage growth.