Challenges in Hydrate Plug Prevention in Pipelines Seen Over the Lifetime of a Field

When the oil and gas industry explores subsea resources in remote areas and at high water depths, it is important to have advanced simulation tools available in order to assess the risks associated with these expensive projects. A major issue is whether hydrates will form when the hydrocarbons are transported to shore in subsea pipelines, since the formation of a hydrate plug might shut down a pipeline for an extended period of time, leading to severe losses. The industry practices a conservative approach to hydrate plug prevention, which is the addition of inhibitors to ensure that hydrates cannot form under pipeline pressure and temperature conditions. The addition of inhibitors to subsea pipelines is environmentally unfriendly and also a very costly procedure. Recent efforts has therefore focused on developing models for the hydrate formation rate (hydrate kinetics models), which can help determine how fast hydrates might form a plug in a pipeline, and whether the amount of inhibitor can be reduced without increasing the risk of hydrate plug formation. The main variables determining whether hydrate plugs form in a pipeline are: 1) the ratio of hydrocarbons to water, 2) the composition of the hydrocarbons, 3) the flowrates/flow regimes in the pipeline, 4) the amount of inhibitor in the system. Over the lifetime of a field, all 4 variables will change, and so will the challenge of hydrate plug prevention. This paper will examine the prevention of hydrate plugs in a pipeline, seen from a hydrate kinetics point of view. Different scenarios that can occur over the lifetime of a field will be investigated. Exemplified through a subsea field development, a pipeline simulator that considers hydrate formation in a pipeline is used to carry out a study to shed light on the most important issues to consider as conditions change. The information gained from this study can be used to cut down on inhibitor dosage, or possibly completely remove the need for inhibitor.