A New Method to Detect Blockage in Gas Pipelines
Authors: Kegang Ling , Xingru Wu , Zheng Shen 
Published: September 2015

Because of its efficiency, cleanliness, and reliability, natural gas is an important sector in global energy consumption. It supplies nearly one-fourth of all energy used in United States and is expected to increase 50% within the next 20 years. More gas delivery infrastructure is being constructed to meet the transportation requirement of the ever increasing demand of natural gas. At the same time, the existing gas infrastructure is aging. Ensuring natural gas infrastructure reliability is one of the critical needs for the energy sector. Operators prefer to capitalize on the transportation capacity of these old pipeline systems to reduce the cost for building new pipelines. This makes the blockage become a highly risky factor because a small blockage can cause operating pressure to exceed the safety specification. Therefore, the reliable and timely detection of the blockage of gas pipeline is critical to ensure the reliability of the natural gas infrastructure.

To design proper pigging tools, it is important to detect where the blockages are and their sizes. Physical inspection and mathematical model simulation are used to identify blockage in gas pipeline. Generally, the physical method can result in an accurate detection of location and size of the blockage at the expense of production shut-down and high cost/long time to run the physical detection, which is a very expensive measure in long-distant gas pipeline. The mathematical simulation detects blockage through numerical modeling, which could give a quick evaluation at a much lower cost but with higher uncertainties. Our literature review indicated that a simple, practical, and reliable method to detect blockage without a recorded inlet or outlet pressure is highly demanded.

In this study, we developed multi-rate tests method to detect blockage in gas pipeline. By conducting multi-rate tests, the location and size of blockage can be evaluated. The new method can be applied in the conditions of no measured inlet or outlet pressure, which have not been investigated before. It is worth locating blockage under these conditions because as oil and gas exploration and production move to harsh environment, no pressure gauge installed at the inlet or outlet of pipeline can be common in the fields. Even for the onshore fields or fields with easy access, pressure is not transferred to center office in real-time. In addition, the metering equipment and pressure gauges installed in the pipeline may be out of work. Therefore, our method provides a practical, quick and low computational cost approach to estimate blockage corresponding to these conditions.

The blockages in one pipeline and parallel/looped pipelines were evaluated in this project using the proposed method. Considering that most of complicated pipeline systems under operation can be decomposed into the basic units such as one pipeline and parallel/looped pipelines, the proposed model can realistically and feasibly identify blockage in a complex pipeline network. Furthermore, existing studies assumed single blockage in the pipeline, which limits the application of available models because the detection will be misleading if there are more than one blockage in the pipeline. To fill this gap we developed a model to differentiate single-blockage scenario from multi-blockage scenarios based on multi-rate tests. The identification is critical because it guides the blockage detection to the right direction.