Strategies for Isothermal, Real-Time, Transient Pipeline Models in Shut-In Conditions

Onshore, liquid pipelines are often modeled with isothermal models. Ignoring thermal effects is justified because thermal effects are of secondary importance and because the data, such as burial depth, soil thermal conductivity, soil heat capacity, and soil density, required to accurately predict thermal behavior in buried pipelines is not known accurately. In addition, run speeds are faster for isothermal models than for rigorous thermal models, which is particularly important in real-time models. One condition where thermal effects become important is when a pipeline is shut-in. Pumps increase the temperature of the fluid, so the fluid temperature is, on average, greater than ambient temperature. When a pipeline is shut-in, the temperature decreases causing a corresponding decrease in pressure. Since an isothermal model does not account for this behavior, the decreasing pressure can be misinterpreted as a leak. This paper discusses a strategy for correcting the model to properly account for the behavior in shut-in conditions. The strategy is applied to real-time pipeline models using Synergi Pipeline Simulator (SPS), although the method is applicable to any isothermal model.