Crude oil samples were collected from three-buried gathering lines of Cambay Basin and were characterized in Drilling Cementation and Stimulation (DCS) Research Center, PDPU for their hydrodynamic (Viscosity, Density) and thermal (Specific heat, thermal conductivity) properties along with solubility curve (WAT, pour point and precipitation curve) at Gujarat Energy Research Management Institute (GERMI), PDPU. Theoretical wax mass fluxes for four available wax deposition models were computed using the characterized properties of crude oil samples. Field wax mass fluxes were computed based on field data obtained from the gathering lines and were compared with the theoretical wax mass fluxes. The field data for both 2 km and 5 km long 8 inch ID gathering lines indicated that the crude oil in these pipelines was flowing under laminar flow regime, while for 25km 8 inch ID gathering line it indicated a turbulent flow condition. This leads us to conclude that the presumption of only turbulent flow condition prevails is a myth; both laminar and turbulent flow conditions can occur. Furthermore, a wax mass flux analysis revealed that field wax mass fluxes for gathering lines with laminar flow regime (Re = 200 to 2300) is in good agreement with Film Mass Transfer (FMT) model, while the predictions from Equilibrium Model (EM) and Matzain models are in good agreement with the field data of gathering line with turbulent flow condition (Re = 5400). These agreements are because, for laminar flow case Chilton-Colburn analogy (no-precipitation case) is satisfied which means no precipitation occurs in the mass transfer boundary layer and large amount of wax is deposited radially in the pipe. While, for turbulent flow conditions, the concentration profile is dependent on temperature profile and complete precipitation or instantaneous precipitation occurs in the mass transfer boundary layer. In our study, we made every attempt to obtain reliable field data for comparison with the existing models. The four unique field cases presented here would be useful to researchers in validating their models. In addition, it made us realize that wax deposition is not only an offshore flow assurance problem but also a major flow assurance problem for onshore operations.

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