Hydrate Deposition Mechanisms on Pipe Walls

Abstract

Abstract As the oil and gas industry moves towards offshore developments in deeper waters, the risk management of plugging pipelines due to hydrate formation increases in difficulty, which may lead to operation/safety hazards (Sloan, 2005). To tackle this challenge, the flow assurance community requires predictive tools to account for hydrate formation in flowlines (Zerpaet al., 2011). Although significant knowledge has been gained from mechanistic models for hydrate plug formation, there are still components missing for a comprehensive model, such as hydrate deposition on pipeline walls. Currently, field and flowloop data suggest the need to include and quantify hydrate deposition in the hydrate formation model (Lachanceet al., 2012). Agglomeration of hydrate particles by itself cannot account for large pressure drop observed during hydrate formation. Because hydrate deposition is difficult to decouple from other hydrate related phenomena (e.g., agglomeration), little to no research has previously been done addressing this phenomenon, particularly in gas-liquid systems. This paper details the initial effort to study hydrate deposition mechanism as part of a DeepStar funded project (CTR11203). Here, we present results that provide insight into hydrate deposition mechanisms based on experimental investigations designed to isolate this phenomenon from other hydrate issues. We have identified that water (hydrate former) reaches the deposition surface by direct contact of water with the surface, by condensation of water on the cold surface, and finally by liquid capillarity. Once the water reaches the deposition surface hydrate deposits form. We have also found that the rate of hydrate deposition increases by decreasing the surface temperature and these results are repeatable. We have shown that hydrate deposition on pipe walls is a key component for hydrate plug formation. The understanding gained with this investigation contributes to the efforts of the flow assurance community to develop a comprehensive hydrate formation model that could account for all the risks pertinent to hydrate formation in multiphase flow systems.