Method for assessing the hydrate formation from a mixture of natural gas flows of varying degrees of moisture content

Abstract

The article deals with the issues of assessing the conditions of hydrate formation when mixing natural gas flows of various standards. An urgent problem of operation, especially of offshore subsea gas pipelines, is the prediction of the time, place and expected intensity of hydrate formation. Depending on the changing operating mode of the gas pipeline, dispatch service specialists must be able to adjust the process control tactics on their own, as quickly as possible. The predisposition of a particular gas pipeline to hydrate is also important for the dispatching service. Changes in the volumes of gas entering the region under consideration from different sources, due to the constant change in gas production, create the need to mix gases of different standards and pump them into subsea gas pipeline. To avoid hydrate formation, it is important to predict the thermobaric conditions that will be formed in the gas pipeline by considering the characteristics such as a volume in the mixture and the moisture content of the gas. The processes of hydrate formation proceed quickly and if the beginning of the process is overlooked, the problem of significant or complete blockage of the gas pipeline might appear. The paper gives a systematization of the risk of hydrate formation depending on several infrastructural factors – the presence of a preliminary gas drying system and a system for starting and receiving cleaning pistons. A method is proposed for estimating the moisture content and dew point temperature of a natural gas mixture by the condition and the proportion of primary flows. It has been shown that the addition of a small volume of undried gas to the main dried gas significantly increases the risk of hydrate formation. A formula is given for calculations for a mixture of multiple natural gas flows. The advantage of this method is the quick calculations, and the absence of the need for huge mathematical calculations and laboratory studies. This is an important element in the activities of the dispatch service, limited by a lack of time in the process of preventing hydrate formation.