An existing 20″ pipeline system is being modified to operate in a batching mode to integrate the production of a new field. Two dismissible crude oils will be pumped in a specific batching scheduled to minimize the mixing volume and avoid further contamination of the highest quality oil. The fluids to be carried by the pipelines are primarily crude oils with density differences of approximately 15% and dynamic viscosity ratios up to 12.5. Both the transient response and steady-state analysis are being performed for each of the two pipelines and the entire system to determine its operating constraints and estimate the batch volume to be received at the end facility. The conducted analysis estimates the contaminated interface volume in this pipeline segment for various pipeline operating conditions. Determination of blending interface was calculated by using a pipeline simulation approach. From the pipeline modeling, it was observed that the mixing interface is slightly larger when the lighter oil batch is followed by the heavy oil. In addition, results indicated a similar mixing trending of the two fluids when the batching cycle is modified. One of the critical parameters in the calculations is the dispersion coefficient that is linear dependent of the molecular diffusion coefficient. Thus, a parametric analysis was included in the estimation of the volumes for both cases, since an exact diffusion coefficient value was not available for these types of crude oils. The pipeline modeling results provided a good estimate of the volume interface. The mixing volumes calculated by this approach are not only relevant for the operational stand point of view of the pipeline, but they are good indicators for the economic feasibility of the pipeline operation and project expansion. Thus, this study presents results from the pipeline modeling and covers the basic parameters that will affect a batching operation of two different fluids.
The oil transport system under consideration is composed of an existing 84 miles of 20″ diameter pipeline connecting Oil Center "A" (OCA) to a refinery facility. In addition, a 20″ diameter pipeline that runs from another Oil Center "B" (OCB) ties into the OCA pipeline at a node junction. Therefore, from the node junction to the refinery facility, both systems share a common 20″ pipeline that travels approximately 73 miles through a relatively downhill terrain. The two oil centers are managed by different operators, and they provide oil with different characteristics. Therefore, the operation of the system is based on a batch transport philosophy. The design batch transport system has been performed by flow rate control at oil centers and pressure control at the refinery receiving facility. However, a production increase is anticipated from OCA. Thus, the transport philosophy has been modified to adjust this increment of capacity. The proposed operating method is based on pressure control at the oil center. The targeted production will vary from 4,300 GPM to 3,700 GPM at the light crude oil center, OCA, while OCB was scheduled to maintain a constant rate of approximately 1,500 GPM.
