Review of wax sedimentations prediction models for crude-oil transportation pipelines

Wax sedimentation in pipelines is a severe crude oil production and transportation challenge.Pipeline surface roughness is experienced at the early stages of the problem;with time,the effective pipe cross-sectional area is reduced due to pipeline wax plugging,causing pumping pressure increase,equipment failures,and blockages,resulting in unnecessary downtime costs and pipeline abandonments in the worst situation.This paper reviews mathematical and experimental loops models used for pipeline solid wax predictions and calculations as functions of pressure,temperature,and fluid composition;by assessing model's Assumptions,strengths and weaknesses.It is found that most mathematical models applied molecular-diffusion mechanisms in modeling and neglected shear effects;which resulted in wax over-prediction.Experimental loop was time-consuming due to mounting and dismounting of test section during wax deposition measurements;our modification has included sensor-integration to detect,measure,and analyze wax deposition;Reliable wax predictions models are essential to properly design pipelines and adopt cost-effective strategies for wax deposition prevention,control,and removal.

Investigation of adsorption behaviors of paraffin waxes on iron, iron oxide, and iron Ⅲ oxide pipeline's internal surfaces using adsorption locator model

Wax deposition in pipelines leads to pressure drop,reduced effective cross-sectional area,and blockages.Although mathematical models and experimental loops were used to model wax precipitation on pipeline surfaces,its prediction at molecular levels is not fully recognized.Molecular dynamics is another powerful approach that can predict wax precipitation at the molecular level.This paper uses molecular dynamics simulations with the adsorption locator model found in Material Studio Software to investigate the adsorption behaviors of Icosane-C20H42,Docosane-C22H46,and Tetracosane-C24H50 paraffin waxes on the Fe,FeO,and Fe2O3 pipeline internal surfaces.Modeling is performed by varying temperature values and validated with experimental data.It was found that as the temperature altered,the adsorption energies,probability energy distribution and adsorption density field on the surfaces also changed;on the other hand,the energetic analysis results showed adsorption energies increase with carbon numbers increase due to its larger surface contacting areas and lower aspect ratio,which resulted in stronger interaction with the surfaces.Further,paraffin waxes showed to adsorb easily on Fe surfaces than oxide surfaces.At temperatures below Wax Appearance Temperature(WAT)on both simulations and experiments showed wax deposition.The lower adsorption energy capacity observed on the Fe2O3 pipeline surface confirms it's vitality and suitability for crude oil transportation pipelines surface lining material.