Behavior Of Waxy Crude Oil Research Articles

Insights into pour point depressants: a brief review of their impact on the behavior of waxy crude oil

Insights into pour point depressants: a brief review of their impact on the behavior of waxy crude oil

Effect of a novel type of water-in-oil nanocomposite viscosity improver on rheological properties of crude oil

The waxy crude oil was routinely transported by means of adding pour point depressants (PPD), which can significantly improve the flow behavior of waxy crude oil. In this study, the physical properties of crude oil were first characterized. Subsequently, a novel variety of W/O nanoemulsion was prepared based on water in an EVA/toluene solution at a 3:1 proportion, and evaluated as a viscosity improver. It was found by virtue of the laser particle size analyzer that the EVA emulsion reaches the nano-scale. EVA nanoemulsion can present a behavior similar to nanocomposite PPD, and form a denser and regular structure with wax crystals via heterogeneous nucleation. Compared with conventional EVA, EVA nanoemulsion further reduces the oil viscosity, gel point and yield value by 52.8%, 0.05 °C and 29.6%. In addition, the impact of particle size of EVA nanoemulsion on the rheology of crude oil was discussed. In combination with DSC curve and POM, the action mechanism of EVA nanoemulsion on crude oil was analyzed.

Application of Rheo-optic In Situ Measurement Technology to Study Waxy Crude Oil Rheology

The micromechanism of waxy crude oil gelling is the interaction between wax crystals to form a certain intensity flocculation structure, which significantly increases the cost of production and transmission. In this paper, rheo-optic in situ measurement technology is applied to the rheological study of waxy crude oil for the first time and also to the rheological response of typical waxy crude oil to thermal history, the micromechanism of shear-thinning, and the dynamic behavior of wax crystal. Through the new experimental technique and analysis method, it is found that two types of wax crystals can be formed under certain thermal historical conditions, which have opposite performances in microscopic morphology, mechanic properties, and flocculation tendency, and the change of its proportion in crude oil is the root cause of the initial cooling temperature affecting the fluency of waxed crude oil. It was found that the microscopic behavior of waxy crude oil with the increase of shear rate went through the following whole process: the waxy crude oil system changes from static to dynamic, the wax crystal flocculation network undergoes deformation, cracks, and ruptures, and wax crystal aggregates break, small aggregates orient along the flow field, and small aggregates continues to deform and break. When the shear rate is below 5 s–1, the crack of the flocculation structure plays a leading role. It is only after the shear rate exceeds 5 s–1 that the deformation of the wax crystal and its flocs begins to function. Furthermore, according to the microscopic images of the wax crystals motion sequence, the micromorphology of different types of flocs and the dynamic behaviors under shearing are systematically analyzed by dynamic micro-object capture technology.

Study on microstructure wax evolution behavior of waxy crude oil during cooling

The microcosmic characteristics of wax evolution of waxy crude-oil directly affect the heat transfer process of crude-oil. A microscopic experiment was carried out on the wax deposit process of waxy crude-oil by polarized light microscopy. The phase change characteristics of wax crystals during wax deposit process were analyzed, and the process of wax crystal precipitation was quantitatively analyzed by the image analysis software ImageProPlus. The results show that the wax deposit process mainly includes wax crystal nucleation, growth and bonding, which together lead to the formation of wax crystal network. The sample oil particle number and the wax crystal area fraction curves have inflection points at 41 ? and 38?, respectively, which are caused by different carbon number alkane content and wax crystal bonding. By analyzing the particle size and particle area curves, it is known that nucleation precipitation and growth are alternately dominant in the early stage of wax crystal growth. Through the wax roundness study, it is found that the growth of wax crystals in the early stage is mainly in the longitudinal direction, and the growth in the late stage is not directional. According to the phase change process of wax crystal, it is proposed that the temperature of the crude-oil with porous media grid structure is coalescence point. By using the position point tracking of wax crystal and analysis of the variation characteristics of microscopic parameters, the coalescence point temperature of the sample crude-oil in this experiment is 38?.

Effects of 4-vinylbenzyl trioctylphosphonium- bentonite containing poly(octadecylacrylate-co-1-vinyldodecanoate) pour point depressants on the cold flow characteristics of waxy crude oil

Wax crystals networks of paraffinic crude oil are a result of cooling processes that greatly affect the macroscopic properties of wax oil, which in turn affect the rheological behavior of waxy crude oil. Therefore, it is very important to study the effect of the formation of these crystals on the rheological properties of wax oil by considering the inhibition of the formation of these crystals. This research paper aims to study the impact of polymer nanocomposite on the pour point of paraffinic crude oil and to determine the rhetorical properties of paraffin oil treated with a polymer containing nano-layered bentonite material. Firstly, the bentonite clay (BT) was treated with a 4-vinylbenzyl trioctylphosphonium chloride monomer (VTOP) to turn the clay surface from hydrophilic to lipophilic clay (VTOP-BT) and consequently facilitate its incorporation into the octadecylacrylate-co-vinyldodecanoate copolymer.A series of the poly(octadecylacrylate-co-1-vinyldodecanoate-co-VTOP-BT) nanocomposites with different ratios of VTOP-BT (0.5–3%) was prepared using radical solution polymerization and described using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, high-resolution transmission microscopy, and proton nuclear magnetic resonance (1H NMR). The collected results from the effect of the additives on crude oil have demonstrated that polymers nanocomposites have a significant impact in reducing the viscosity of wax crude oil compared to poly(octadecylacrylate-co-vinyldodecanoate). By using a dose of 1500 ppm of poly(octadecylacrylate-co-vinyldodecanoate-co-VTOP-BT) nanocomposite that contains 1% VTOP-BT, the pour point decreased from 27 to −3 °C (i.e., 30 °C). By the same token, the long-term stability measurement, the polymer nanocomposite slowed excellent behavior compared to virgin polymer.

The effect of physical properties on the gelation behavior of waxy crude oil during shutdown

In this paper, the effect of different viscosity and specific heat capacity on the gelation behavior of waxy crude oil was studied. The additional specific heat capacity method and the momentum source term method are used for numerical simulation. Grey correlation analysis method was used to quantitatively express the correlation degree of viscosity and specific heat capacity on average flow velocity, temperature drop rate and the ratio of gelled oil area to total area. The results show that the influence of viscosity on the gelation behavior of waxy crude oil is greater than that of specific heat capacity. When the viscosity of crude oil is large, natural convection is weaker and the temperature drop rate is smaller, which retards the development of the gelation behavior of crude oil. For crude oil with larger heat capacity, the temperature drop rate is smaller and the natural convection is slightly stronger, but the temperature drop rate has a great influence on the gelation behavior of crude oil, making it develop slowly. The influence of both viscosity and specific heat capacity on gelation behavior is limited.

Influence of Heavy Organics Composition on Wax Properties and Flow Behavior of Waxy Crude Oils

Paraffinic crude oils are desirable because of their high content of saturated hydrocarbons but may present handling challenges due to crystallization of high molecular weight paraffin at low temperatures. The prediction of wax properties and behavior of waxy crude oil is important in order to adopt appropriate mitigative measures to forestall flow assurance problems associated with wax crystallization and deposition. Accurate predictive models are limited mainly by the sheer complexity of crude oil composition. Result of analysis of saturates, aromatics, resins and asphaltene content of crude oils (SARA) has been used as a simple tool to predict and interpret crude oil properties and behavior but has been found inadequate in predicting wax instability. In this paper, we report on the use of SARA analysis and paraffin distribution data to interpret the wax properties and flow behavior of Niger-Delta crude oils. The crude oil properties determined include wax content, asphaltene and resin content by gravimetry, pour point, wax appearance temperature by cross-polarized microscopy and paraffin carbon number distribution of whole oil and wax precipitate by GC-FID. Asphaltene and resin content were found to influence the oil pour point, while saturates content, paraffin carbon number of crystallizing waxes and wax content control its low-temperature flow properties.

Features of very heavy crude oil transportation

The paper discusses the features of very heavy crude oil transportation in pipelines as exemplified by foreign transportation techniques. Special focus is given on the processes of rheologically complex behavior of waxy crude oils.

Pressure Effect on the Rheological Behavior of Waxy Crude Oil with Comb-Type Copolymers Bearing Azobenzene Pendant

In this work, a pressure responsive poly(α-octadecene-co-maleic acid azobenzene amide) (Azo-MAC) was synthesized and able to enhance the flowability of waxy crude oil with asphaltenes significantly under high pressure. High-pressure UV–vis spectrometer was used to characterize its pressure response under pressures. The onset temperature and enthalpy during wax crystallization of Liaohe waxy crude oil under various pressures were determined by using high-pressure differential scanning calorimeter. The viscosity and yield stress were measured by high-pressure rheometer. On the basis of our experimental data, a mechanism was propounded that the conformation transformation from cis to trans of azobenzene groups in Azo-MAC at enhanced pressure may destroy the assembly of asphaltenes, disturb the crystallization of paraffins and thus improve the flowability of oils. Azo-MAC should be an ideal additive for exploitation and transportation of oils under high pressure.

Spreading of waxy oils on calm water

The objective of this paper is to provide a simple extension of the much-used gravity spreading model for oil on calm water to account for the spreading behavior of waxy crude oils in cold waters – including the observed retardation and eventual termination of spreading at certain oil film thicknesses. This peculiar behavior is not predicted by traditional spreading models for oil on calm water (i.e. viscous-gravity spreading models), but may occur due to non-Newtonian oil properties caused by precipitation of wax at low temperatures. To clarify the spreading behavior of such oils, SINTEF has conducted a series of laboratory experiments with a range of waxy oil mixtures. The present paper contains analyses of data from these experiments, including favorable comparisons with calculations by a proposed improved surface spreading model.

A new experimental investigation on upgrading of waxy crude oils by methacrylate polymers

Several methods have been used to reduce problems caused by wax precipitation during the production and/or transportation of waxy crude oil. Polymers are used to improve pour point and rheological behavior of waxy crude oils. In this work, the influence of the polymer inhibitors such as methacrylate polymers, as wax inhibitor, with different range of molecular weight and alkyl side chain carbons on the rheological behavior and pour point of two Iranian waxy crude oils were evaluated. Two Iranian waxy crude oils were selected on the basis of wax and asphaltene contents. The rheological behavior of these crude oils in absence and in presence of methacrylate polymer was studied. The rheological data cover the temperature range of–1 to 12°C. The results indicated that the performance of methacrylate polymer was dependent on the molecular weight, alkyl side chain carbons and the asphaltene content of crude oil. Methacrylate polymers with longer alkyl side chains than 18 carbons would perform best as wax inhibitors in two cases. Also, for crude oil with low asphaltene, higher molecular weight methacrylate polymer is the best flow improver and lower molecular weight methacrylate polymer showed good efficiency for crude oil with high asphaltene content.

Settling and re‐entrainment of wax particles in near‐gelling systems

Under near‐gelling conditions, the precipitated wax particles can settle down due to gravity and form a bed at the bottom of the pipeline. During restart, the settled waxy bed can increase the pressure drop significantly, and the necessity for pigging and/or addition of chemicals has to be determined to re‐entrain settled wax particles. A laboratory‐scale flow loop, first of its kind, has been built and used to understand the settling and re‐entrainment behavior. The experimental results confirmed the settling of precipitated wax in a pipe under quiescent conditions when the oil temperature falls between wax appearance temperature and pour point. During restart, complete re‐entrainment was attained after reaching a critical flow rate. Solid transport models were able to predict reasonably good results in agreement with experiments. This work emphasizes the importance of understanding the behavior of waxy crude oil during production shutdown and design appropriate startup strategies. © 2017 American Institute of Chemical Engineers AIChE J, 64: 765–772, 2018

Performance improvement of the ethylene-vinyl acetate copolymer (EVA) pour point depressant by small dosages of the polymethylsilsesquioxane (PMSQ) microsphere: An experimental study

In a previous work, the addition of the polymethylsilsesquioxane (PMSQ) microsphere (50–400ppm) can improve the flow behavior of waxy crude oil through the spacial hindrance effect. However, the flow improving efficiency of the neat PMSQ microsphere is not as good as the traditional polymeric pour point depressants (PPDs). In this paper, the effect of the ethylene-vinyl acetate copolymer (EVA2806) PPD together with the PMSQ microsphere (with the size around 2µm) on the flow behavior of a typical waxy crude oil was investigated. The results show that adding 50ppm EVA PPD can greatly improve the flow behavior of the oil. The neat PMSQ microsphere cannot improve the flow behavior of the oil at small dosages (≤10ppm), but can significantly improve the performance of the EVA PPD. The gelation point, G′, G″, transient apparent viscosity and yield stress of the oil decrease further after adding both 50ppm EVA and a small amount of the PMSQ microsphere (≤10ppm). The best flow improving efficiency is found at 50ppm EVA+2.5ppm PMSQ. The addition of the PMSQ microsphere has little influence on the WAT and precipitated wax crystal amount of the oil doped with EVA, but outstandingly changes the morphology of the precipitated wax crystals into larger and more compact flocs. The adsorption tests show that the EVA molecules can adsorb and concentrate on the PMSQ microsphere, thus causing the formation of the EVA/PMSQ composite particles. The composite particles can act as nucleation templates for the wax precipitation, resulting in larger and more compact wax microstructures and then further improving the flow behavior of the oil. The PMSQ microsphere dosage and the amount of EVA PPD adsorbed on the microsphere obviously influence the performance of the composite particle with the best performance at 50ppm EVA+2.5ppm PMSQ. The findings mentioned above provide a new way to improve the performance of polymeric PPDs efficiently.

Oil dispersible polymethylsilsesquioxane (PMSQ) microspheres improve the flow behavior of waxy crude oil through spacial hindrance effect

Application of nanocomposite pour point depressants to improve the rheology of waxy crude oil is a novel and efficient technique and receives much attention. However, the effects of nano and microparticles alone on the rheology of waxy crude oil are unclear up to now. In this paper, monodispersed PMSQ microspheres with different sizes (200nm–10µm) were successfully synthesized through a two-step sol-gel route. Then the effect of the PMSQ microspheres on the flow behavior of two typical waxy crude oils was studied. The results showed that the PMSQ microspheres disperse well in oil phase as single spheres. A small dosage of the PMSQ microspheres significantly decreases the gelation point, elastic modulus G′, viscous modulus G″, apparent viscosity and yield stress of the two oil samples, indicating that the PMSQ microspheres improve the flow behavior of waxy crude oil at temperatures below the wax appearance temperature. The flow improving efficiency of the PMSQ microspheres is greatly influenced by the size and dosage of the microspheres. Moreover, adding PMSQ microspheres in the oil samples also inhibits asphaltenes precipitation because the PMSQ microspheres are capable of adsorbing part of the asphaltenes. However, the PMSQ microspheres have little influence on the exothermic character and microstructure of the two oil samples. Similar tests on a model waxy oil further confirmed that the PMSQ microspheres cannot participate in wax precipitation process and change the morphology of precipitated wax crystals, but can impede the interactions of the precipitated wax crystals through spacial hindrance effect, which inhibits the development of wax crystal network structure and thus improves the flow behavior of the oil. This mechanism brings a new way to improve the flow behavior of waxy crude oil and favors the development of new-generation flow improvers based on nano or microparticles.

Measurement and Prediction of Time-independent and Time-dependent Rheological Behavior of Waxy Crude Oil

Wax deposition phenomenon changes the rheological behavior of waxy crude oil completely. In the current work, the rheological time-dependent and time-independent behaviors of waxy crude oil samples are studied and flow curve and compliance function are measured for the oil samples with various wax contents at different temperatures. A decrease in temperature and an increase in wax content lead to an increase in the viscosity and yield stress but a significant drop in compliance function. A modified Burger model is developed to predict the behavior of the compliance function and a modified Casson model is used to predict the flow curve of the waxy crude oil samples within a vast range of wax contents and temperatures. The proposed Burger and Casson models match with experimental results with R2 of 99.7% and 97.33% respectively.

CHARACTERIZATION AND EVALUATION OF WAXY CRUDE OIL FLOW

Part of the oil found in the Brazilian subsoil has a high wax content, which makes its flow process difficult at low temperatures because of the increase in the viscosity of the fluid. This paper studied the flow behavior of waxy crude oil under variation in the temperature of the external environment of the flow, the volumetric flow rate of the oil and the emulsified water content of the oil. The results were compared with those obtained for a non-waxy crude oil that had similar rheological properties at temperatures above the wax appearance temperature (WAT). The proposed tests were based on the experimental design technique, and the behavior of the fluids was evaluated based on the pressure variation generated by the flow.

Experimental study and a proposed new approach for thermodynamic modeling of wax precipitation in crude oil using a PC-SAFT model

A powerful method is necessary for thermodynamic modeling of wax phase behavior in crude oils, such as the perturbed-chain statistical associating fluid theory (PC-SAFT). In this work, a new approach based on the wax appearance temperature of crude oil was proposed to estimate PC-SAFT parameters in thermodynamic modeling of wax precipitation from crude oil. The proposed approach was verified using experimental data obtained in this work and also with those reported in the literature. In order to compare the performance of the PC-SAFT model with previous models, the wax precipitation experimental data were correlated using previous models such as the solid solution model and multi-solid phase model. The results showed that the PC-SAFT model can correlate more accurately the wax precipitation experimental data of crude oil than the previous models, with an absolute average deviation less than 0.4 %. Also, a series of dynamic experiments were carried out to determine the rheological behavior of waxy crude oil in the absence and presence of a flow improver such as ethylene–vinyl acetate copolymer. It was found that the apparent viscosity of waxy crude oil decreased with increasing shear rate. Also, the results showed that the performance of flow improver was dependent on its molecular weight.

Real-time monitoring and measurement of wax deposition in pipelines via non-invasive electrical capacitance tomography

Tomographic analysis of the behavior of waxy crude oil in pipelines is important to permit appropriate corrective actions to be taken to remediate the wax deposit layer before pipelines are entirely plugged. In this study, a non-invasive/non-intrusive electrical capacitance tomography (ECT) system has been applied to provide real-time visualization of the formation of paraffin waxes and to measure the amount of wax fraction from the Malay Basin waxy crude oil sample under the static condition. Analogous expressions to estimate the wax fraction of the waxy crude oil across the temperatures range of 30–50 °C was obtained by using Otsu’s and Kuo’s threshold algorithms. Otsu’s method suggested that the wax fraction can be estimated by the correlation coefficient while Kuo’s method provides a similar correlation with . These correlations show good agreements with the results which are obtained from the conventional weighting method. This study suggested that Kuo’s threshold algorithm is more promising when integrated into the ECT system compared to Otsu’s algorithm because the former provides higher accuracy wax fraction measurement results below the wax appearance temperature for waxy crude oil. This study is significant because it serves as a preliminary investigation for the application of ECT in the oil and gas industry for online measurement and detection of wax fraction without causing disturbance to the process flow.

Fast degradation and viscosity reduction of waxy crude oil and model waxy crude oil using Bacillus subtilis

Abstract Microbial degradation of waxy crude oil provides efficient, economical and environment friendly solution to enhance the waxy crude oil production from mature brownfield crude oil reservoirs, addressing flow assurance challenges during transportation, and on-shore and off-shore oil-spill remedies. This study systematically investigates the utilization of thermophilic Bacillus subtilis for the degradation of waxy crude oil obtained from the oilfield and model crude oil prepared by various higher molecular weight waxes suitable for high temperature applications. The influence of microorganism to improve the flow behavior of waxy crude oil has been analyzed by means of viscosity and compositional degradation. The degradation and reduction in the viscosity of crude oil at various temperatures have been analyzed. More than 95% of degradation has been observed in 15 days for both the crude oil samples at 50 °C. The simple nutrient and microorganism combination and the high activity of enzymes aided to get utmost and faster degradation of the crude oil. This study will be useful to employ the thermophilic bacteria for various oilfield applications.

Estimation of gas void formation in statically cooled waxy crude oil using online capacitance measurement

Waxy crude oil is one of the massively produced petroleum reserves in the oil and gas industry. It possesses two different natures at different conditions. At a temperature above its wax appearance temperature it functions as a Newtonian fluid. Moreover, when it flows in a subsea environment where the temperature drops, the occurrence of non-Newtonian fluid would appear. However, it is mandatory to prevent the pipelines from building up with the solid wax layer, or else a strong paraffinic gel structure would plug the flow of the waxy crude oil. This gel accumulation results in the emergence of thermal shrinkage where gas voids consequently occur. A Malay Basin waxy crude oil has used for this study to investigate the gas void formation in statically cooled waxy crude oil using an online Electrical Capacitance Tomography (ECT) measurement. This paper has been focused on the development of a non-invasive, non-intrusive approach for the visualization of waxy crude oil by applying the ECT system. The online inspection of the behavior of waxy crude oil is important so that the appropriate action can be taken during the gas void formation within a gelled crude oil. An experimental study was conducted on a 1.18in. circular flow loop rig at distinct temperatures to assess the behavior and formation of gas voids formed due to thermal shrinkage. A capacitance sensor with dual planes consisting of eight electrodes per plane was installed on the rig to capture the images and measure the raw capacitance. Gas voids within a range of 8–14% were observed within the gelled crude oil based on different cooling temperatures. It has been found from the analysis that the gas voids follow an increasing trend with a decrease in temperature and cooling rate.