Influence Of Polymer Pour Point Depressants On Wax Deposition Characteristics Of Waxy Oil

Wax deposition generally exists in crude oil pipeline.The research on wax deposition has been a hotspot in the field of oil and gas storage and transportation,and it is of great importance to the safe and economical operation of oil pipeline.In this paper,the effects of the polyoctadecylacrylate?POA?and polyethylene-vinyl acetate?EVA?pour point depressants on the wax deposition of 10 wt%model waxy oil was investigated with the aid of an in-house wax deposition device,DSC test,HTGC/FT-IR analysis,and microscopic observation.The results showed that the wax deposition formed by pure waxy oil?without POA?is homogeneous,while adding a small amount of POA?50²00 ppm?triggers the formation of heterogeneous wax deposits along the radial direction.The structure of the outer-layer deposit is porous with relatively lower WAT and wax content than the inner-layer deposit.When the POA concentration increases further??400 ppm?,the formed wax deposit structure closely adheres to the wax deposition barrel and becomes more compact with the same WAT and wax content along the radial direction.With the increase of POA concentration,the precipitated wax crystals become more compact,which favors the formation of thinner but more compact wax deposits with relatively high WAT,wax content and critical carbon number?CCN?.Compared with the non-added oil samples,the critical carbon number of the wax deposition formed by treated oil sample increases from C₂₄ to C₂₅.With the increase of deposition time,the content of the n-alkanes?above the CCN?in the wax deposition gradually increased,while the content of the n-alkanes?below the CCN?in the wax deposition gradually decreased,which indicated that the addition of the POA accelerates the aging rate of wax deposition.The addition of EVA also leads to the formation of heterogeneous wax deposition structure,but the influence of EVA on the wax deposition is different from that of POA.The result shows that?a?the structure of outer-layer wax deposit is hard flake,and the structure strength is larger;the structure of inner-layer wax deposit is porous with more liquid oil bound in it.?b?The WAT and wax content of the outer-layer wax deposit is always much higher than that of inner-layer wax deposit.With the increase of the concentration of EVA in the oil sample?50⁴00ppm?,wax deposition shows little change on the macroscopic appearance.?c?The thickness of the wax layer gradually becomes thinner with the increase of EVA concentration,and the wax deposition inhibition rate of EVA is slightly lower than that of POA with the same additive concentration.?d?After the addition of EVA in the waxy oil,the WATs of the formed wax deposits increase greatly with increasing the EVA concentration.However,the average increase of wax content in the wax deposition is smaller than that of POA.The synergistic effect of pour point depressants and asphaltene on the wax deposition was investigated.The results showed that adding PPDs and asphaltene in the model waxy oil greatly modifies the morphology of precipitated wax crystals,thus greatly changing the wax deposition behavior of the oil and reduce the gel point of waxy oil.Under the synergistic effect of PPDs and asphaltene,the deposition rate of waxy oil decreases more greatly and the aging rate of wax deposition is faster.When the concentration of POA in the oil sample reaches 400ppm,the synergistic effect is different from that of the POA alone.The wax content of the inner-layer wax deposit is higher than that of the outer-layer wax deposit,and the wax deposit is heterogeneous.Under the synergistic effect of EVA and asphaltene,the wax content of the inner-layer wax deposit is always higher than that of the outer-layer wax deposit,which is contrary to the effect of EVA alone.In the study of the experimental conditions on the wax deposition,it was found that the deposition rate decreases with the increase of temperature difference of waxy oil and deposition barrel,oil temperature and spinning speed of oil sample barrel;the aging rate of wax deposit gradually increases with the increase of temperature difference of waxy oil and deposition barrel,oil temperature and spinning speed of oil sample barrel.