Gas pipelines want to provide transportation flexibility to meet demand, but are always focused on operational safety, reliability, system integrity, and environmental issues. Transportation networks need to ensure the components of gas are acceptable for delivery to end users. Local distribution companies want to meet customer demand and have no existing capacity to remove or extract hydrocarbons from their system. This paper introduces a method for calculating hydrate formation and the phase transfer between gas and liquid to allow the user to know how much liquid exists in a pipeline and the appropriate pigging scenario for the liquid fallout. The paper focuses on determining pigging and how the gas transfers to liquid and the amount of liquid hold up that occurs in the pipeline. Using these mathematical models and algorithms can allow an operator to know the correct timing for pipeline inspection and where in the pipeline system liquid is building up for potential safety monitoring.

Introduction and Background

Cleaning a pipeline during operation is a maintenance procedure that needs to be done on a regular predetermined frequency using pigs adequately designed for the proper cleaning application. The pigging operation will almost always increase the flow efficiency and reduce operating expenses. In pipelines that have low flow conditions it is more prevalent to see an increase in the collection of free water in the bottom of the pipeline, even in crude oil lines. In low flow conditions you need a mechanical means (pigs) to remove both the solids and liquids that collect in the bottom of the pipeline to help prevent the process of internal corrosion. When a pipeline goes online 100% efficiency cannot be expected, but a routine pigging can keep a pipeline operating at 90 – 95 percent capacity. A pigging requires manual labor and adds cost to the pipeline. An algorithm is needed to estimate the amount of liquid in a pipeline at any given moment and allow the user to know that it is time to pig the pipeline to help alleviate the issues of free water or condensate that is staying in the pipeline. Previous papers have already gone over how the simulation flow and gas condensation work in a gas pipeline. Below is the mathematical procedure to estimate the liquid hold up along with the amount of piggable liquid that is in the pipeline to give a better time to pig a pipeline.

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