Flow Of Waxy Crude Oils Research Articles

Application of Bio-Derived Alternatives for the Assured Flow of Waxy Crude Oil: A Review

High molecular weight paraffin/wax precipitates in the solution of crude oil when the surrounding temperature falls below the wax appearance temperature, which causes the problem of wax deposition in pipelines. To enhance the rheology of the crude oil and lessen wax deposition, pour point depressants (PPDs) and flow enhancers were utilized. These substances change the wax crystals’ morphology, reducing crystal interlocking and preventing wax agglomeration from facilitating wax dispersion. However, recent research prompted a further investigation to improve the performance of conventional polymeric PPD and to address wax accumulation in a safe and environmentally responsible way. This is because of their poor performance at high shearing, expensive preparations, limited biodegradability, and toxicity. The primary objective of this study is to provide a thorough summary of current studies on the use of seed oil extracts rich in unsaturated fatty acids as an alternative for polymeric PPD. Important studies on the use of nanoparticles to improve the performance of conventional PPD, as well as strategies put into place to overcome issues with nanoparticle application, are also highlighted. Finally, an outlook of potential research ideas to develop pour point depressants is provided.

Influence of Poly (benzyl oleate-co-maleic anhydride) Pour Point Depressant with Di-Stearyl Amine on Waxy Crude Oil

An important problem for the oil industry is the deposition of paraffin on pipelines during the transit of crude oil and restart processes at low temperature. In this regard, the need for suitable methods of wax deposition has attracted substantial attention. Therefore, pour point depressants (PPDs) are considered a critical processing aid to modify the paraffin crystallization and improve the flow of waxy crude oil. The effect of pendants in comb-type copolymers on the ability of crude oil to flow in the cold is examined in the current study. Such PPDs were first created by the free radical polymerization of maleic anhydride with benzyl oleate to create the poly (benzyl oleate-co-maleic anhydride). The resultant copolymer was then aminated with alkyl amine (stearyl amine) (C18H39N) to form pendant alkyl amine chains. The esterified copolymers were structurally characterized by Fourier Transform Infrared, X-ray diffraction spectral analysis, and scanning electron microscopy. Moreover, the potential interactions between PPD and waxes were investigated by using differential scanning calorimetry, X-ray diffraction, and light microscopy. The obtained PPDs, which are effective at a dose of 2000 ppm, were able to reduce the pour point by up to 3 °C. The viscosity and yield stress of the petroleum waxy crude oil were revealed by rheometer.

Effect of Amla Fruit (Phyllanthus emblica) Extract in Flow Assurance of Indian Waxy Crude Oil

SummaryWax present in crude oil starts to precipitate during flow through the pipeline below the wax appearance temperature (WAT). The phenomenon creates problems during transportation such as choking in pipeline, pumping pressure, etc. Pour-point depressants (PPDs), wax inhibitors, and other additives are used to remediate wax deposition problems. This paper focuses on the application of a natural extract from Amla fruit (Phyllanthus emblica) in Indian waxy crude oil (WCO) to improve flow behavior and wax deposition rate with varying properties such as temperature, time, and dosage. The result has been compared with commercial additives procured from Deva Drill Tech, India. The extraction procedure was conducted with Amla fruit skin (P. emblica) and with ethanol as a solvent. After the addition of 800-ppm Amla extract, the pour point was reduced by 9°C, and the viscosity was decreased by up to 98% at 50°C. This is due to the interaction and bond formation between synthesized PPD and wax molecules. As a result, less pumping power is required for efficient flow. The thixotropic area was reduced from 164 750 to 134 852 Pa·s after the addition of 800 ppm of synthesized additives. Viscoelastic behavior improved significantly after the addition of Amla extract and commercial additives. This will diminish considerably the energy required to restart the flow of WCO. Morphological changes confirm that more smaller and diffused wax particles were created from large wax agglomerates. The derived PPD is much more effective compared with a commercial one, is more environmentally friendly, and no special attention is required for the pretreatment of PPD-treated crude oil, which ultimately will reduce the project cost.

Three-dimensional numerical simulation of heat transfer and flow of waxy crude oil in inclined pipe

The purpose of this study is to obtain the heat transfer and flow law of waxy crude oil in the inclined pipeline and to provide theoretical guidance for the safe operation of the pipeline. In this paper, three-dimensional numerical simulation of pipes with inclination angles of 0°, 25 °and 45 °is carried out by using CFD software. The temperature and velocity fields of waxy crude oil and the cooling gelation law of crude oil are basically the same in different cases. Affected by the initial temperature field of shutdown, the average temperature of horizontal pipeline decreases gradually along the flow direction of pipeline. The inclined pipe is mainly affected by the natural convection caused by gravity, and the temperature decreases gradually along the downward direction of the inclination of the pipe. The inclination angle of the pipe increases to 45°, the temperature difference between the highest and lowest points of the pipe increases to 5.012 °C, and the liquid volume fraction increases by 1.6%. Among them, the low-lying pipe section is more likely to cause pipeline blockage.

A non-isothermal approach to evaluate the impact of the cooling stage on the startup flow of waxy crude oils

Waxy crude oils submitted to low temperatures at quiescent conditions turn into a gel with a corresponding yield stress. Thus, a higher pressure drop is needed to restart, leading to a flow assurance issue. Generally, this problem is tackled by considering the material at rest, with a given state and an imposed pressure drop. In the present work, we investigate how the cooling process after a shutdown impacts the problem. We emulate a stoppage of short duration so that the cooling after the shutdown stage does not lead to a condition of uniform temperature. The temperature-dependent rheology of the material is such that the crude oil shows viscoplastic behavior only below the gelation temperature. The early stages of the process, before and during the shutdown, resulting in a heterogeneous gel, which serves as an initial condition for the restart stage. We perform 2D non-isothermal simulations in a pipe considering three stages, namely (i) normal operation conditions; (ii) cooling stage at rest after stoppage; (iii) restart by an imposed pressure drop. Particular emphasis is given to the role of the plastic number ( P l ) and the duration of the cooling after the shutdown stage. A comparison with the corresponding homogeneous condition is also made. The results show that higher values of P l and higher waiting times in the cooling after the shutdown stage lead to conditions less prone to restart. Only cooling times of short duration lead to restart in the same conditions as the normal operation ones. The pressure drop necessary for a restart is an increasing function of the cooling time. • We examine the restart problem of a waxy crude oil modeled as a viscoplastic material. • The rheological properties are dependent on the temperature. • The previous stages like normal flow and cooling after shutdown are considered. • Heterogeneous initial conditions at the restart are obtained for different cooling times. • Comparisons between heterogeneous and homogeneous conditions show the importance of previous stages.

Application of Novel Fruit Extract for Flow Assurance of Indian Field Waxy Crude Oil

Summary This research article deals with the application of shikakai fruit (Senegalia rugata) extract (SE) used as a novel bio-additive for improving flow properties of waxy crude oil (WCO) to reduce pumping cost during pipeline transportation. SE was synthesized using solvent extraction method, which is one of the most common economic extraction processes. Bio-additive was characterized by Fourier transform infrared spectroscopy (FTIR) spectroscopy, carbon, hydrogen, nitrogen, sulfur (CHNS) analysis, gas chromatography-mass gas chromatography-mass spectroscopy (GC-MS), differential light scattering, and thermogravimetric analysis (TGA). Pour point of WCO was decreased by 12°C due to addition of 1,000 ppm of SE on crude oil. Viscosity of WCO reduced significantly after addition of a bio-additive. It was found that viscosity of SE beneficiated crude oil (1,000 ppm dosage) at 30°C is less than that of pure crude at 50°C. So, addition of SE may be an alternative of heating during flow of WCO. Microscopic studies confirm that wax and other solid particles become smaller and more dispersive so that the particles are not able to come closer and form a three-dimensional network. Consequently, flow becomes easier and pumping cost gets reduced. Experimental data related to viscosity better fitted with Casson model and Bingham model before addition of SE depict that significant yield stress is required to restart the flow of crude oil. Due to the addition of SE, yield stress was deceased significantly and crude oil beneficiated with bio-additive tends to behave like a Newtonian fluid. This article also investigates wax deposition through laboratory-designed wax depositional setup. The wax deposition of crude oil after addition of 1,000 ppm SE was comparatively 56 and 75% lower than untreated crude oil when deposition studies were performed for 2 and 4 hours, respectively, at 25°C. Wax crystals of SE-treated crude oil decreased in diameter and disoriented the particles, preventing the formation of three-dimensional networks so that crude oil can easily flow through pipelines. Considering the efficacy of extracted bio-additive and its cost effectiveness, the same can be applied for flow assurance of WCO through pipelines even at very low temperatures.

Flow pattern, pressure drop and inclination analysis on liquid-liquid two phase flow of waxy crude oil in pipelines using PIPESIM

Produced water is a water that comes out with the crude oil during the production of the well. It contains non-soluble and soluble oil or organics, dissolved and suspended solids with different chemicals used during production process. Thus, it must be properly accounted as it affects the economical productivity of crude oil and separation efficiency as a result of stubborn emulsions between crude oil and water. Thus, a simulation study was conducted using PIPESIM to predict the flow pattern and pressure drop of waxy crude oil and water flow in horizontal and inclined pipelines (i.e., -15° from horizontal). In this simulation study, water cuts were ranging from 0% to 90% while the flow rates were ranging from 2.03 to 16.21 cm3/s. The study comprised fluid modelling, physical modelling and running the simulation with the most suitable multiphase flow correlation in PIPESIM. This simulation study used the waxy crude oil has 16.15% of wax content and simulation was performed at 30°C. The validity of the simulation results was accomplished by comparing the published findings. There were only two types of flow patterns that can be identified by PIPESIM; stratified wavy and dispersed flow. The investigations proved that pressure drop was greatly influenced by flow rates and flow patterns. By decreasing the inclination angle, the boundary between the stratified and dispersed flow regimes shifted to the upper left of the flow pattern map while showing a higher pressure drop than horizontal pipeline due to the combined effect of pressure difference and gravity. The simulation results can be used as a platform for better understanding on more complex cases of gas, oil and water concurrent flow in pipelines.

Numerical investigation on the flow and heat transfer characteristics of waxy crude oil during the tubular heating

In industrial practice, tubular heating is known as an effective technology to ensure the security storage of waxy crude oil in the tank. Insights of the thermal and flow behaviors during the tubular heating is a key aspect to optimize the strategy of this heating technology, in order to reduce the cost. In this study the physical and mathematical models representing the heat transfer and flow of waxy crude oil during tubular heating are established. The additional specific heat capacity and momentum source terms methods are employed to address the changing physical properties related to the paraffin crystallization and dissolution. The FVM, PISO and fully implicit first order temporal differentiation algorithms are used to perform the numerical simulation. Our outcomes show that the thermal process during tubular heating can be divided into four phases: ①Local thermal response phase, ②Thermal diffusion phase, ③Global thermal response phase, ④Elimination of gelled oil phase. The initial thermal influence range is inhibited by the thermal condition and solid-like gelled waxy crude oil formed after cooling. The plume flow takes great effects of transferring the heat from the tubes to crude oil and accelerating the phase transition, and finally facilitates the oil temperature uniform increasing in most parts of the tank. Whereas the gelled crude oils in the corner between the sidewall and base wall have the strongest solid-like character and lowest temperature. A low temperature layer keeps covering the base wall. At the top wall, the center region between the sidewall and center of the tank is long time occupied by gelled oil. The proportion of solid-like gelled crude oil keeps decreasing with a small slope value following a linear relationship with heating time. A pronounced phase change of waxy crude oil from the transition state into the pure liquid is observed. The minimum temperature value decreases in the initial heating period, and then steeply increases to an approximate plateau value. The fluctuations of the heating powers are observed indicating the transient thermal convections around the tubes. The heat loss power is lowest at the base wall and nearly unchanged. The heat loss power at top wall and sidewall are significantly influenced by heating tubes and depend on the wall temperature.

A Novel Method for Characterizing the Aggregation of Wax Crystals and An Improvement in Wax Deposition Modeling

Abstract The aggregation behavior and the subsequent deposition behavior of wax crystals own undesirable effects on the production and transportation of waxy crude oil. The understanding and prediction of these behaviors are essential to ensure economic and uninterrupted flow of waxy crude oil when the oil temperature decreases below the wax appearance temperature (WAT). In this paper, a novel method of fractal dimensional analysis was introduced to elucidate the aggregation behavior of wax crystals in different shear flow fields. The fractal methodology for characterizing wax crystal aggregation was then developed, and a blanket algorithm was introduced to compute the fractal dimension of the aggregated wax crystals. Considering the flow characteristics of waxy crude oil in a pipeline can be correlated with the shearing stress work, a modified wax deposition model focusing on shearing energy analysis was established. The results indicate that a quantitative interpretation of the wax crystal aggregation behavior can be realized using the fractal methodology. The aggregation behavior of the wax crystals is closely related to the temperature and shearing experienced by the waxy crude oil. The aggregation behavior will be intensified with decreasing temperature and shearing effect, and a wider fractal dimension distribution appears at lower temperatures when the same shear rate range is used. Furthermore, the improved model provides a method for discussing the effects of the operating conditions on wax deposition. The average relative deviation between the improved model prediction results and experimental results from the literature is 3.01–5.32%.

Novel Approach for Improving the Flow of Waxy Crude Oil Using Thermochemical Fluids: Experimental and Simulation Study.

This article focuses on the flow assurance of waxy crude oil using an environmentally benign and cost-effective approach involving thermochemical reaction. The study incorporates experimental and simulation works to evaluate heat and pressure generation potentials and heat transfer efficiency of the thermochemical fluids. Experimental results reveal that at the concentration (1 M) of thermochemical fluid (TCF) ranging between 14 and 33% v/wt of the waxy oil, sufficient heat could be generated to raise the temperature of the oil significantly above the pour point (48 °C). In addition, from the bench-top treatment of a damaged tubing, it was observed that more than 95% of the deposited wax could be removed using the thermochemical solutions. Subsequently, a large-scale application of the technology in a long-distance flow assurance of waxy crude oil was confirmed through process simulation. Ultimately, the simulation results revealed the capacity of the method to improve the temperature and pressure profiles of the pipe flow system, and most significantly, to remove wax deposition up to 98%.

Startup flow of yield-stress non-thixotropic and thixotropic materials in a tube

An experimental study of the flow of yield stress materials was conducted. The main goal was to understand the relationship between the minimum axial pressure gradient required for the onset of motion and the rheological properties. The sought-for application is the startup flow of waxy crude oils in subsea pipelines. We examined two types of yield stress materials, namely a non-thixotropic acrylic polymer solution and a layered silicate suspension which presents thixotropic properties. We observed that for both materials the measured minimum axial pressure gradient was in good agreement with the prediction of a simple force balance. On the other hand, a puzzling fact is observed in the oil industry, namely that the just mentioned force balance result grossly overestimates the minimum axial pressure gradient for the case of gelled waxy crude oils. One often evoked explanation is the thixotropic behavior of the gelled crude, but the present results serve to falsify it.

Gas void formation in statically cooled waxy crude oil

If a gel is formed when the flow of waxy crude oil within a pipeline is stopped for a period of time, the required restart pressure may be high and the line is costly to operate. The conventional method of predicting the restart pressure for gelled crude oil assumes a constant yield stress across and along the pipe section; this often leads to excessive over sizing of pump and piping system. Many researches highlighted that the presence of gas voids upon cooling of waxy crude may have an impact on the yield stress of gelled crude. This paper describes the use of Magnetic Resonance Imaging (MRI) to investigate the formation behaviour of gas voids within a gelled crude oil sample from a field in the South China Sea. Scanning of gelled crude at selected temperatures was performed following cooling in the circular pipe section within an experimental flow loop rig. Gas voids within the range of 7–12% were observed in the gelled samples resulted from different cooling temperatures and cooling rates. The cooling temperature and cooling rates were observed to influence significantly the location and volume of gas voids formed within the gelled samples. Higher cooling rates resulted in higher volume of gas voids close to pipe wall while lower cooling rates resulted in more gas voids located around core of the pipe.

Mathematical Models for Waxy Crude Oils

In this paper we review a series of mathematical models formulated for the flow of waxy crude oils, that is, of mineral oils with a high content of paraffinic hydrocarbons (with the generic name of waxes) which may be dissolved or segregated as solid crystals at sufficiently low temperatures. The flow takes place in a laboratory test loop. The crystals have a tendency to form aggregates, producing a gel-like structure. The resulting product can be modeled as a Bingham fluid, but its rheological parameters (yield stress and viscosity) depend on the amount and state of the segregated phase, whose evolution is in turn influenced by the flow. Of course temperature plays a key role. Wax can form a solid deposit at the pipe wall, reducing the pipe radius and this phenomenon is also taken into account. The models presented have a different degree of complexity, depending on which phenomena they include. In presenting each of them we discuss their expected range of validity.

Some new results on the flow of waxy crude oils in a loop

Some new results on the flow of waxy crude oils in a loop

Some mathematical models for the flow of waxy crude oils

We present some recent models describing the flow of mineral oils with a high content of paraffin at temperature below the cloud point (i.e. the crystallization temperature of paraffin) and more specifically below the pour point at which the crystals aggregate and the oil takes a jel-like structure. From the rheological point of view such a system can be modelled as a Bingham fluid whose parameters evolve according to the volume fraction of crystallized paraffin and the aggregation degree of crystals. The problem is not studied in its full generality since a number of different situations can arise presenting various degrees of complexity. Therefore many questions remain open for further research.

Obstruction of Pipelines During the Flow of Waxy Crude Oils

When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gradient is established, which causes mass transfer of the solute to occur toward the tube wall. The solute precipitates off the solution in the neighborhood of the wall, and adheres perfectly to it. The deposited mass gradually obstructs the conduit, affecting the pressure and flow fields. A simple model is presented that gives the thickness of the deposited layer as a function of axial position and time. The liquid solution is assumed to behave according to the Herschel-Bulkley rheological model. Results are presented in the form of time evolution of axial distributions of pressure, temperature, layer thickness, global heat transfer coefficient and Reynolds number.