Both in designing hydrocarbon pipeline transportation systems as well as in response planning, it is of importance to be able to accurately estimate the total outflow rate from a pipeline rupture. In response planning this will have a direct impact on the mobilization of people and equipment, for example the number of vessels with oil collecting capabilities that have to be mobilized for an offshore pipeline rupture. To be able to simulate the fluid flow out of a pipeline rupture, a full transient multiphase model is required. Several effects have to be included in the model. This will typically include thermodynamic fluid properties as functions of temperature and pressure, the surrounding pressure, pipeline insulation, wall friction and multi-phase flow regime transitions. The size of the rupture or leak will also influence the total oil release as well as the transient behavior of the rupture; i.e. the maximum initial rate and the time before the system is stabilized. Typically for a small rupture or leak the release rate is dependent on the critical mass flow rate through the opening, but for a large rupture or total break of a pipeline the rate will be restricted by the wall friction inside the pipeline. Modeling techniques for the simulation of pipeline ruptures are discussed and examples of simulation of rupture of live crude transportation pipelines are presented. The effect of the operational conditions in the system is also discussed including the influence of time delay for shut down as well as the effect of a network of pipelines.
In recent years, the annual loss associated with the cost of accidents in the petroleum industry has been increasing. On average, there is one pipeline accident every day resulting in millions of gallons of hazardous material are spilled to the environment every year. For offshore pipelines, the cleanup can be extremely difficult and the consequences to the environment might be severe. The main causes of pipeline ruptures and leaks are corrosion (both internal and external), construction damage, weld failures, incorrect operation, and third party damage like ship Page 2 anchors and bottom trawls. Volumes of hydrocarbons lost due to failure are either determined from metered production information where possible, or estimated by computer models. As a spill may have occurred quite some time before it is detected, obtaining an accurate volume can be difficult. Leak detection systems that are based on volumetric flow measurements together with pressure/temperature measurements will easily detect a full rupture and close the valves and isolating the pipeline, but for small leaks, this could be more difficult and take time to detect.
To be able to predict the fluid release rate out of a pipeline due to a leak or rupture, several parameters must be known, and the most important parameter (in addition to the total pipeline volume and pressure) is the fluid composition.
