When crude oil temperature drops below the wax appearance temperature, the high molecular weight paraffin components crystallize and precipitate from the oil. In a pipeline, this often leads to the formation of gels, which can be deposited onto the cold pipeline inner walls to form a solid wax phase. Wax deposition can severely reduce flow rate, and can even cause total blockage of a pipeline. As on-shore oil fields are being rapidly depleted, oil wells are drilled further offshore in deep water, which require longdistance sub-sea pipelines to transport crude oil on-shore. Wax deposition becomes much more severe and extensive for such operations due to very low ocean floor temperatures. A fundamental understanding of the mechanisms of wax deposition and aging (hardening) is essential for the optimal design and implementation of various wax removal techniques. Modeling wax formation and deposition in the presence of strong flow, heat and mass transfer in a pipeline poses a significant challenge due to the complicated couplings among various physical effects occurring at diverse length scales. There is still considerable uncertainty on the wax deposition mechanisms in a pipeline. The exact nature of the wax precipitation, growth, and the evolution of the gel layer microstructure and their effects on the wax deposition are poorly understood at best. The proposed research presents a comprehensive study of the wax deposition phenomenon in a pipeline employing multi-scale numerical simulations as well as laboratory experiments. The proposed research is the first of its kind that couples the microstructure evolution in the gel layer at the micro and the meso scales with the flow of the bulk liquid at the macro-scale. The microstructure evolution of the growing gel layer has never been studied quantitatively before. Our strategy is to simulate the growing microstructure from wax precipitation particulates in the presence of flow and heat transfer. The successful modeling of the microstructure evolution provides accurate information on the wax content and thus the aging process of the wax. This multi-scale approach can realistically reflect the physical phenomena occurring at diverse length scales in wax deposition, as well as other multiphase multi-component precipitation and solidification problems. The companion experiments to be carried out at our collaborators laboratory at China University of Petroleum will exam and analyze the morphology of the gel layer using a Cross- Polarizing Microscope (CPM) and wax composition using a Differential Scanning Calorimeter (DSC). These experimental results will be used to validate the simulations.
|Effective start/end date||9/1/09 → 8/31/13|
- National Science Foundation (NSF): $325,000.00