Study On The Mechanism Of Fouling And Wax Formation In FRP Oil Casing

In order to enhance the cost efficiency and safety of pipeline, the glass fiber reinforced plastics (GFRP) pipeline are extensively applied to tubing and casing. However, the lack of scaling and wax deposition mechanism on GFRP under oilfield conditions causes the common misunderstanding of scaling and wax deposition mechanism in oil and gas industries, which results in inappropriate selection of pipeline and unreasonable operation parameters.In this paper, the scaling and wax deposition experiments of GFRP and 13Cr tubing were carried out under the actual oilfield conditions. (1) The produced water quality, oil properties and the components of scale on tubing were analyzed, then prepare the diesel-wax mixtures based on the oil properties. (2) The formation water and prepared diesel-wax mixtures were used as reaction medium, the scaling and wax deposition experiments for different surface roughness of GFRP and 13Cr tubing were carried out, then the corresponding weight gain were obtained. (3) The effect of temperature, pressure, time, surface roughness and material type of pipeline on scaling and wax deposition principle was analyzed from the macroscopic view. (4) On the other hand, the specimens were analyzed by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray Diffraction (XRD), Optical Contact Angle measurement (OCA), combining with the principle of weight gain, the scaling and wax deposition mechanism on GFRP was revealed. (5) On the basis of the east square method, the prediction of scaling and wax were established by fitting the weight gain.The scaling and wax deposition mechanism on GFRP and the prediction as shown:(1) The components of scale on specimens are similar with tubing; the scaling experiments showed that scaling is increasing with temperature rising, and 35? is the critical temperature of scaling; the scaling under atmospheric pressure is apparently higher than that of 5.0MPa; the effect of temperature on scaling is stronger than that of pressure; the trend of scaling with time is unstable, and the scale grain generated in the early stage is harder than that of the late stage; the scaling has positive relation with the surface area, rather than the surface roughness; GFRP has better anti-scaling property than 13Cr tubing.(2) The similar diesel-wax mixtures were prepared, which could be validated with crude oil samples in future investigation; the wax deposition experiments indicated that wax deposition is decreasing with temperature falling; the wax deposition under atmospheric pressure is apparently higher than that of 3.5MPa; the effect of temperature on wax deposition is stronger than that of pressure; the wax deposition has positive relation with the surface area, rather than the surface roughness; the wax grain on GFRP is harder than that of 13Cr; GFRP has better anti-wax deposition property than 13Cr tubing.(3) The prediction of scaling and wax deposition were established.This study was carried out to provide an improved understanding of the scaling and wax deposition under the oilfield conditions. Meanwhile, the results of this study provide the theoretical foundation for selection of pipeline, and the program of scale and wax removal and inhibition.