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The precipitation of wax crystals in water-in-crude-oil emulsion impairs the safety and economy of multiphase transportation in oil fields. At present, there are different opinions on the precipita...

In this paper, a novel ethylene-vinyl acetate copolymer (EVA)/amino-functionalized polymethylsilsesquioxane (PAMSQ) composite wax inhibitor (WI) was prepared through melt blending, and the rheological and wax depositing properties of the doped crude oil were studied. The EVA/PAMSQ composite can strongly crystallize with wax molecules and trigger the formation of compact wax flocs, which greatly improve the rheological properties of crude: compared to the pure EVA at the same dosage, the composite can further decrease the gel point and apparent viscosity (25 °C) by 14.6 °C and 92.0%, respectively. The wax deposition can also be inhibited by adding the composite: adding EVA inhibits the mass of the wax deposit at 24 h by 62.3%, and this number is suppressed by 77.9% after adding the EVA/PAMSQ composite, but the wax molecule diffusion is accelerated and the wax content in the wax deposit rises because of the improved crude oil rheological characteristics. Here, we develop the gel structure theory to consider the wax deposition process affected by the WI. Adding the WI contributes little to the wax precipitation temperature but decreases the gel structural strength of the oil a lot, and thus, the oil near the pipe wall can only form the wax deposit with a higher wax content to resist the pipe wall shearing. Therefore, the crude oil added EVA/PAMSQ composite possesses not only the lowest wax deposit rate and the highest aging rate but also the highest wax content in the wax deposit.

In the crude oil production, comb-like octadecyl acrylate (OA) polymers are usually added into the well as flow improver, causing the existence of OA polymers in the produced fluid. OA polymers and...

Paraffins cause many issues during the production and transportation of crude oils. To date, there is abundant research on the rheological properties of crude oils after paraffin crystallization an...

Asphaltenes are natural pour point depressants, and the effect of asphaltene polarity on the low-temperature rheology of waxy oils has been well studied. In this paper, the influence of asphaltene ...

For the pipeline transportation of waxy crude oil, pour point depressants (PPDs) have been developed and used to improve its flowability at low temperature. As supercritical CO2 (scCO2) flooding becomes a common technique to improve oilfield recovery, how the sensitivity of PPD changes due to the degassed crude oil treated by CO2 should be studied. In this work, the effect of scCO2 extraction on the performance of EVA in improving the flowability of Changqing degassed crude oil is investigated by means of a self-developed scCO2 treating equipment, SARA/HTGC analysis, SEM analysis, pour point test, rheological measurement, asphaltene precipitation test, particle size analysis, DSC test, and microscopic observation. The results show that without EVA addition, scCO2 extraction aggravates the flowability of the crude oil at low temperature. The scCO2 extraction extracts light components from asphaltene aggregates causing asphaltenes to precipitate, which inhibits the asphaltenes on playing a role as the natur...

The influence of thermal treatment temperature on the flowability and wax deposition characteristics of Changqing waxy crude oil was researched in detail through pour point/rheological tests, a cylindrical Couette wax deposition experimental device, DSC analyses, asphaltenes stability tests, and microscopic observations. It is found that the flowability of the crude oil can be greatly improved through increasing the thermal treatment temperature. Meanwhile, the wax deposition rate of the crude oil can be outstandingly inhibited with the increase of thermal treatment temperature from 50 to 70 °C. Moreover, the flow regime can also influence the wax deposition characteristics. Under cold flow regime (22 °C/12 °C), the structure of formed wax deposits is homogeneous while the aging of the wax deposits is not obvious. Under hot flow regime (30 °C/20 °C), the aging of the wax deposits is obvious, but a heterogeneous two-layer structure exists in the formed wax deposits at the thermal treatment temperatures 50 ...

In CO2 flooding, the dissolution of CO2 in produced fluid may change the stability of crude oil emulsion, thereby affecting the design/operation of the gathering pipeline and oil–water separation. The purpose of this study is to investigate the stability change of crude oil emulsion and its mechanisms after the dissolution of CO2. The stability of the CO2-dissolved crude oil emulsions is determined with a self-made apparatus. The mechanisms of the stability change are uncovered from interfacial properties and bulk viscosity. It is found that the stability of the crude oil emulsions is visibly reduced with an increasing dissolved quantity of CO2. This is partly attributed to the fact that dissolved-state CO2 can lessen the interfacial dilational modulus and increase the loss angle markedly, thus lowering the structural strength and elasticity of the interface. Meanwhile, the dissolution of CO2 in crude oil can reduce its viscosity, resulting in easier collision of droplets. In view of these experimental re...

In part 1 (10.1021/acs.energyfuels.7b03657), the synergistic effect of ethylene–vinyl acetate copolymer (EVA) pour point depressant (PPD) and rensin-stabilized asphaltenes on improving the flowability of synthetic waxy oil has been verified. This paper is a continuous work studying the effect of the asphaltene content (0.01–3 wt %) on the synergistic effect between EVA PPD and resin-stabilized asphaltenes. The results showed that, in the absence of EVA and with the increase of the asphaltene content, the precipitated wax crystals of the waxy oil tend to grow gradually from initial big needle-like to smaller and more regular (spherical-like) particles with a larger amount; therefore, adding aphaltenes can only decrease the apparent viscosity of waxy oil at the temperature range slightly lower than the wax precipitation temperature (WPT) (the precipitated wax crystal amount is low), and the temperature range is broadened by increasing the asphaltene content. When the temperature is decreased far below the W...

Both polymeric pour point depressants (PPDs) and asphaltenes can improve the flowability of waxy oils. However, the effect of polymeric PPDs together with asphaltenes on the flowability of waxy oils is not clear. In this paper, the synergistic effect of ethylene–vinyl acetate (EVA) PPD (100 ppm) and resin-stabilized asphaltenes (0.75 wt %) on the flow behavior of model waxy oils (10–20 wt % wax content) was investigated through rheological tests, DSC analysis, microscopic observation, and asphaltenes precipitation tests. The results showed that the asphaltenes disperse well in the xylene/mineral oil solvent as small aggregates (around 550 nm) with the aid of resins. The EVA or asphaltenes alone moderately improve the flow behavior of waxy oils by changing the wax crystals’ morphology from long and needlelike to a large, radial pattern or fine particles, respectively. The wax precipitation temperatures (WPTs) of waxy oils are also slightly decreased by adding EVA or asphaltenes, meaning that the cocrystall...

In real crude-oil pipelines, the formed wax deposits could be heterogeneous along the radial or axial directions. However, studies on this aspect are scarce. In this paper, the effect of the polyoctadecyl acrylate (POA) wax inhibitor on the wax deposition of 10 wt % model waxy oil was investigated with the aid of an in-house wax deposition device, differential scanning calorimetry test, high-temperature gas chromatography–Fourier transform infrared analysis, and microscopic observation. The results showed that adding POA in the model waxy oil greatly modifies the morphology of precipitated wax crystals, thus greatly changing the wax deposition behavior of the oil. For oil sample 1 (without POA), the precipitated wax crystals (needle-like) more easily form porous network structures, causing the formation of a thick and porous wax deposit with relatively low WAT, wax conten,t and critical carbon number (CCN). With the increase of POA concentration (oil samples 2–5), the precipitated wax crystals become more...

The W/O emulsion formed by waxy crude oil tends to gelatinize under low-temperature gathering conditions, which may harm the flow assurance of multiphase transportation. This study mainly focused on the wax-precipitating gelation process of crude oil emulsions, and the structural differences of the emulsions with different water fractions at their gelation temperatures (GTs). First, the changes of wax appearance temperature (WAT) and precipitated wax amount at GT with variable water cut were investigated by DSC. Then, the specific structural properties of these different water cut emulsions at their own GTs were investigated by viscoelastic, yielding behavior, and structural breakdown experiments. On these bases, the gelation mechanism of a waxy crude oil emulsion was deduced. The WAT of a waxy crude oil emulsion was found to rise, evidently with the addition of dispersed water, verifying that water droplets provide necessary nucleation sites for paraffins and thus make them more prone to precipitate. Whe...

Polar moieties of the conventional polymeric pour point depressants (PPDs) greatly influence the PPDs’ performance on waxy crude oil. However, the influencing mechanism of the polar moieties on the PPD’s performance is not clear. In this paper, four poly(octadecyl acrylate-vinyl acetate) (POA-VA) PPDs with different VA molar fractions were first synthesized; then, the performance of the four PPDs on Dingbian waxy crude oil was investigated by experiments and mesoscopic dynamic simulation. The experimental results show that the crystallization ability of the PPDs deteriorates with increasing VA molar fraction, while the performance of the PPDs first increases and then decreases with the increase of VA molar fraction. At a moderate VA fraction 25 mol %, the PPD-3 shows the best performance in decreasing the WAT, pour point, and viscosity of the crude oil. The simulation results correlate well with the experimental data and confirm that (a) the addition of the PPDs inhibits the transformation of wax molecule...

In this work, we investigated the development of asphaltenes-triggered two-layer wax deposit with deposition time using an in-house wax deposition device, DSC, HTGC, SARA, and microscopic observation. For the pure waxy oil (Waxy Oil A), the formed wax deposit is a homogeneous and loose waxy oil gel. The wax deposit mass is relatively high and increases with increasing deposition time, while the wax appearance temperature (WAT), wax content, and ΔW of the wax deposit are relatively low and increase slowly with increasing deposition time. The critical carbon number (CCN) of the wax deposit is C24. The precipitated wax crystals (needlelike) in the wax deposit are liable to form a continuous network structure, which is adverse for the diffusion of wax molecules. The presence of asphaltenes in the pure waxy oil (Waxy Oils B–D) causes the formation of a two-layer wax deposit, which can be clearly characterized by the significant difference of structural strength. Different from the outer-layer wax deposit, the ...