Search Results (19)

During the pipeline transport of high-wax crude oil, paraffin precipitation often results in deposit formation, and a thorough investigation into the issue of wax deposition is crucial for ensuring the safe operation and economic benefits of the pipeline. This work critically reviews the latest research progress focusing on the mechanisms, the factors influencing it, and the kinetic models used to describe it. Although research on single-phase crude oil wax deposition has made certain progress both domestically and internationally, existing studies have limitations in terms of the diversity of crude oil types. In previous studies, the types of crude oil used to explore influencing factors were relatively singular. When modeling, the diversity of crude oil properties was not fully considered, leading to a lack of general applicability of the established models across different types of crude oil. To overcome this limitation, future research should place greater emphasis on the diversity of crude oil properties. Specifically, it is necessary to collect and analyze wax deposition data from a wider variety of crude oils and delve into the mechanisms by which different crude oil properties influence the wax deposition process. Therefore, future research needs to further take into account the diversity of crude oil properties and establish kinetic models that are quantitatively correlated with these properties. This will contribute to more accurate prediction and assessment of wax deposition risks during pipeline transportation for various types of crude oil, thereby providing robust assurance for the safe operation of pipelines. Full article

Fallen leaves and their decomposition directly deposit leaf wax n-alkanes into sediments, which can be used to identify local flora. These n-alkanes are important for studying past vegetation and climate, but their distribution in sediments must be known. Aeolian sand n-alkanes are particularly important for understanding paleoclimates in arid regions, despite the challenges of extraction due to their extremely low abundance. To investigate the preservation of plant leaf wax n-alkanes in deserts, we analyzed n-alkanes in aeolian sands from the Northern Ulan Buh Desert (UBD), China, and compared them to the surrounding vegetation. We calculated the total n-alkane concentration (ΣALK), average chain length (ACL_21–35), and carbon preference index (CPI_21–35). In the Northern UBD, aeolian sand n-alkanes have lower ΣALK, indicating microbial degradation. The eastern aeolian sand has lower CPI_21–35 and ACL_21–35 than the adjacent vegetation, whereas the western sand values are consistent with the plants, likely due to the transport of plant-derived materials by wind and water from the nearby mountains. Our study shows that sedimentary n-alkane signatures are not only determined by local vegetation but also influenced by environmental factors like temperature and precipitation. Additionally, local deposition processes play a significant role in determining the properties of these n-alkanes. Full article

The well productivity of high-waxy reservoirs is highly influenced by temperature changes. A decrease in temperature can cause the precipitation of wax from the crude oil, leading to a decrease in the formation’s drainage capacity and a drop in oil production. In this study, the wax precipitation of crude oil is characterized by rheological properties tests and differential scanning calorimetry (DSC) thermal analysis. The wax damage characteristics of cores and the relative permeability curves at different temperatures were investigated through coreflood experiments. Furthermore, nanoemulsion is selected as a chemical agent for injection fluid. The nuclear magnetic resonance (NMR) scanning technique is used to investigate the effects of oil recovery enhancement at different pores by increasing temperature and adding nanoemulsion. By comparing the changes in T₂ spectra and the distribution pattern of residual oil before and after liquid injection, the results have shown that both increasing temperature and adding nanoemulsion have a significant effect on oil recovery. The improvement of micropores is less pronounced compared to macropores. The produced oil mainly comes from the large pores. When the temperature is lower than the crude oil dewaxing point temperature, there is a serious dewaxing plugging phenomenon in the pores. Additionally, by observing the pattern of residual oil distribution at the end of the NMR online drive, it is hereby classified into wax deposition retention type, weak water washing retention type, and immobilized type, each with its own distinct characteristics. Wettability alteration and interfacial tension reduction can help to improve the drainage capacity of high-wax oil reservoirs, which is the main mechanism of nanoemulsion for enhanced oil recovery. These findings are highly valuable for enhancing the comprehension of the impact of highly waxed crude oils on drainage capacity and the ultimate oil recovery rate, particularly in relation to wax precipitation deposition. Full article

The problem of wax deposition widely exists in offshore oil fields; waxing of the oil tubing will lead to a reduction in the cross-sectional area of the flow and, in serious cases, the flow path will be blocked, causing the well to stop production. In order to cope with this problem, a thermal dynamic wax removal method has emerged in recent years that utilizes hot nitrogen gas circulation between the oil tube and annulus to raise the temperature of the oil tube to achieve the purpose of wax removal and plug removal and is quick and easy to operate. Unlike conventional wellbore temperature calculation methods, the wellbore temperature field under hot nitrogen circulation conditions is influenced both by the reservoir temperature gradient and the hot nitrogen injection temperature, injection pressure, and injection rate. In this paper, a temperature calculation model for a wellbore considering both annulus injection temperature and tubing temperature and their interactions is modeled, which can consider the effects of different hot nitrogen injection temperatures, injection rates, and injection pressures. The model is used to calculate the temperature distribution for different injection parameters in order to ensure that the tubing temperature is higher than the wax precipitation temperature and that the annulus temperature is not higher than the maximum temperature resistance of the rubber in the packer. The study provides a design method for wax removal and plug removal with hot nitrogen gas circulation. Full article

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. Full article

The precipitation of asphaltene and waxes occurs when crude oil characteristics change as a consequence of pressure, temperature variations, and/or chemical modifications, etc. The costs associated with the cleaning of deposition on the production equipment and the loss of profit opportunities can go beyond hundreds of millions of USD. Thus, there is a strong incentive to search for ways to mitigate deposit formation during the crude production process. A light crude bottom hole fluid sample from a deep well with an asphaltene deposition problem was analyzed in the laboratory. Basic data on density, viscosity, bubble point, GOR, and asphaltene onset pressure were measured at a PVT laboratory. Asphaltene characterization, as a prescreening for appropriate inhibitors, has been conducted using asphaltene phase diagrams (APD). The APD generated from two developed software programs in both Matlab and Excel codes were favorably compared with the phase behavior of other oil samples available in the literature and has shown to be an excellent match. Various test methods were used to demonstrate the asphaltene instability of the oil samples. Eleven chemical inhibitors from five global companies were screened for testing to inhibit the precipitation. The optimum concentration and the amount of reduction in precipitation were determined for all of these chemicals to identify the most suitable chemicals. Finally, some recommendations are given for the field application of chemicals. Full article

In the oil and gas industry, wax formation and deposition are common problems, particularly during production and transportation. To better understand the expected behaviour of a given waxy crude oil and consequently select the best solution to prevent wax deposition, it is vital to conduct laboratory tests or numerical simulations to model its performance. For a Brazilian oil field, the phase behaviour of 17 crude oils was modelled using Multiflash software. To tune the model, laboratory tests were used, including true boiling point curves and viscosity tests. This study followed two stages: the first allowed characterization of the wax appearance temperature (WAT) and determination of the expected precipitation curves for these crude samples, and the second stage was evaluation of the impact on wax precipitation after the addition of methane (CH₄), carbon dioxide (CO₂) or fatty acid (CH₃(CH₂)_nCOOH). Results showed that WAT varied between 47.5 °C and 51.6 °C for these crude oil samples at atmospheric pressure, considering the differential scanning calorimetry (DSC) method. Furthermore, the percentage of wax mass formed varied between 13.3% and 18.3%. By adding the aforementioned chemicals as an inhibitor, it is possible to observe a reduction in the paraffin precipitation tendency. Inhibition was compared in terms of effectiveness between the chemicals studied, and it was concluded that adding myristic acid (C14:0), oleic acid (C18:1), palmitic acid (C16:0), or lauric acid (C12:0) was the most effective in reducing the WAT value. In fact, when adding 25% mole fraction, CH₄ and CO₂ can reduce the WAT value by up to 4%, but the results are strongly dependent on the fluid pressure. Myristic acid was the most effective in reducing the WAT value by up to 5%, and the results were less pressure dependent. Full article

The Dabei deep high-pressure condensate gas field occupies the paramount position in the Tarim Oilfield in China, the exploration and developments of which have been progressing. Since the initial development, the wax deposition and plugging in the wellbore and gathering pipeline have been the most bothering issues, resulting in the reduction or even shutdown of condensate gas well production. Therefore, the wax appearance temperature of Dabei condensate oil was studied using the capillary viscometer, differential scanning calorimetry (DSC), and polarizing microscope observation. The wax content was tested by using the DSC and crystallization separation test method. Finally, the wax appearance temperatures of degassed condensate oil and equilibrium condensate oil under different pressures were tested. Experimental results show that the wax appearance temperature measured by polarizing microscope observation was higher than that measured by the DSC and capillary viscometer, the lag of which can be recorded as the cloud point. The wax appearance temperature measured by polarizing microscope observation is of high accuracy. Secondly, the DSC method is not sufficient for measuring wax precipitation at low temperatures, showing a lower wax content than the crystallization separation test method. Thus, the wax content of Dabei condensate oil can be better measured by using the crystallization separation test method. Additionally, the wax precipitation law of equilibrium condensate oil is opposite to that of degassed condensate oil. The wax appearance temperature of equilibrium condensate oil increases as the pressure decreases. The results of wax appearance temperature of equilibrium condensate oil provide a useful and quick index to judge the potential risk of wax precipitation in the Tarim Oilfield, which can provide an efficient strategy for the development of waxy condensate gas reservoirs and the optimization of wax prevention and treatment technology. Full article

Deposition of wax is considered one of the most significant culprits in transporting petroleum crude oils, particularly at low temperatures. When lowering pressure and temperature during the flow of crude oil, the micelle structure of the crude oil is destabilized, allowing oil viscosity to increase and precipitating paraffin (wax) in the well tubulars and pipeline, which increase the complexity of this culprit. These deposited substances can lead to the plugging of production and flow lines, causing a decline in oil production and, subsequently, bulk economic risks for the oil companies. Hence, various approaches have been commercially employed to prevent or remediate wax deposition. However, further research is still going on to develop more efficient techniques. These techniques can be categorized into chemical, physical, and biological ones and hybridized or combined techniques that apply one or more of these techniques. This review focused on all these technologies and the advantages and disadvantages of these technologies. Full article

There has been a large amount of experience in recent decades in the use of magnetic fields on reservoir fluids. This paper discusses the effect of a magnetic field on wax precipitation. An analytical model is developed to quantify the wax deposition rate on the tubing surface during the magnetic treatment of reservoir oil. It has been established that the passage of the oil flow through a non-uniform magnetic field causes a high-intensity electric field for a sufficiently long period of time, the effect of which decreases the solubility of wax in oil, increases the intensity of wax precipitation in oil, and reduces the wax deposition on the tubing surface. The model accounts for the fact that the wax deposits present on the tubing surface are a highly efficient heat insulator that changes the temperature regime of the flow and the temperature of the tubing wall. This circumstance changes the rate of deposits but does not make these deposits less harmful to wells’ operation. A method for calculating the equilibrium wax concentration and changing the solubility of wax in oil under a constant electric field has been developed. We show that the effect of magnetic treatments on wax deposition rises with the increase in the concentration of asphaltenes in the oil and water cut. Full article

Condensate oil is increasingly valued as the high-quality conventional hydrocarbon resources generally decline. The efficient development of condensate oil, however, has always been a world problem; massive condensate oil will be retained in reservoirs in case of improper exploitation process, resulting in a significant resource waste and economic loss. One of the problems closely related to enhancing condensate oil recovery is wax precipitation and deposition in wellbore. Therefore, it is vital to investigate the characterization methods for the wax precipitation and deposition behavior in wellbores. The current status of research on modelling characterization methods, experimental characterization methods and molecular dynamics representation of wax precipitation and deposition behavior is reviewed in this paper; the applicability and limitation of modeling and experiment studies for characterizing wax precipitation and deposition of condensate oil in the wellbore are critically summarized and discussed. Moreover, the molecular dynamics simulation technique characterizes wax precipitation and deposition behavior from the micro scale, which makes up for the deficiencies of macroscopic experiment, enriches the investigation of wax precipitation and deposition, and provides important guidance and reference value for the development of unconventional hydrocarbon exploitation processes. Full article

One of the main problems in the oil industry is the fallout of asphaltene–resin–paraffin deposits (ARPDs) during oil production and transportation. The formation of organic deposits leads to reduced equipment life and reduced production. Currently, there is no single methodology for the numerical simulation of the ARPD dropout process. The aim of our work was to obtain a correlation dependence characterizing the rate of wax growth over time for oils in the Perm Krai, depending on temperature, pressure, and speed conditions. Experimental data for 20 oil samples were obtained using a Wax Flow Loop installation that simulates fluid movement in tubing. The developed correlation was tested in 154 wells. The results of numerical modeling of the paraffin precipitation process made it possible to correct the inter-treatment period of scraping for 109 wells (71%), indicating the high accuracy of the developed approach. Full article

A high content of asphaltene and wax in crude oil leads to difficulties in the recovery and transportation of crude oil due to the precipitation of asphaltenes and the deposition of waxes. Comb-like polymers were found to be capable of inhibiting the aggregation of asphaltenes and crystallization of waxes. In this work, comb-like bipolymers of α-olefins/ultra-long chain (C18, C22 and C28) alkyl acrylate were synthesized and characterized by FT-IR and ¹H NMR spectra. The results show that, for a model oil containing asphaltene, the initial precipitation point (IPP) of asphaltene was prolonged by UV, and the asphaltene particle size was reduced after adding the biopolymers, as revealed by dynamitic light scattering (DLS). The bipolymer containing the longer alkyl chain had a better asphaltene inhibition effect. However, DSC and rheological results show that the wax appearance temperature (WAT) of the typical high asphaltene and high wax content of crude oil was obviously reduced by adding bipolymers with shorter alkyl chains. The bipolymer (TDA2024-22) with a mediate alkyl chain (C22) reduced the viscosity and thixotropy of the crude oil by a much larger margin than others. Compared with the previously synthesized bipolymer with phenyl pendant (PDV-A-18), TDA2024-22 exhibited a better performance. Therefore, bipolymers with appropriate alkyl side chains can act as not only the asphaltene inhibitors but also wax inhibitors for high asphaltene and wax content of crude oil, which has great potential applications in the oil fields. Full article

Wax precipitation and deposition are serious flow assurance problems. Wax precipitation is investigated simultaneously using centrifugation and high-temperature gas chromatography (C-HTGC) to obtain the amount and component distribution of precipitated wax in artificial waxy oil and diesel at different temperatures. However, the conventional C-HTGC method gives upper measurements of the amount of precipitated wax, as it ignores wax dissolved in crude oil in the centrifugal cake. A modified C-HTGC method was developed to obtain the precipitated solid fraction of crude oil, based on the mass balances of the non-crystallized fraction of the centrifuged cake. The weight, percent and carbon number distribution of precipitated solid wax crystals at different temperatures of artificial oil and 0# diesel were obtained. It was found that wax precipitation characteristics are affected by many factors, including the carbon number distribution of the oil, the sensitivity of alkane crystallization to temperature and the temperature of the waxy oil solution. The average carbon number of alkanes in precipitated wax crystals decreases with the decrease in temperature. The distribution of alkanes in solid wax crystals is roughly the same as that in 0# diesel but slightly heavier than in diesel. Alkanes with high carbon numbers precipitate simultaneously with those with low carbon numbers. Full article

The Shunbei crude oil pipeline is prepared to use the unheated transportation process to transport waxy crudes. However, the wax formation in the pipeline is unknown. In order to predict the wax deposition of the pipeline, the physical property experiment of Shunbei crude oil was carried out through field sampling. The density, freezing point, hydrocarbon composition, and viscosity–temperature characteristics of crude oil are obtained. The cloud point and wax precipitation characteristics of the crude oil were obtained using the differential scanning calorimetry (DSC) thermal analysis method. Then, the wax deposition rate of the pipeline was predicted by two methods: OLGA software and wax deposition kinetic model. Finally, the optimal pigging cycle of the pipeline was calculated on this basis. The results show that: Shunbei crude oil is a light crude oil with low wax content, a low freezing point, and a high cloud point. Comparing the OLGA simulation results with the calculation results of the Huang Qiyu model, the development trend of wax deposition along the pipeline was the same under different working conditions. The relative error of the maximum wax layer thickness was 6%, proving that it is feasible for OLGA to simulate wax deposition in long-distance crude oil pipelines. Affected by the wax precipitation characteristics of Shunbei crude oil, there was a peak of wax precipitation between the pipeline section where crude oil temperature was 9.31–13.31 °C and the recommended pigging cycle at the lowest throughput was 34 days in winter and 51 days in spring and autumn. Full article