Advancements in crude wax deposition management: An overview of chemical, physical, and microbial methods

Introduction

The wax in crude oil usually contains of a variety of light and intermediary hydrocarbons (Paraffins, aromatics, naphthenes) and extra heavy organic compounds, including resins, The experimental approach focused on assessing the cold flow technology's effectiveness in reducing wax deposition. (Bruno et al. 2008) [10] . Wax deposition leads to blocks pipelines and reduces its inner diameter (Figure 1) therefore; the cost of petroleum production increases gradually (Patowary et al. 2016) [33] . Wax is mainly composed of long straight chain of hydrocarbons called poly-hydrocarbons that are aromatic organic compounds consists of carbons and hydrogen and multiple aromatic rings. Several types of crude oil all over the world rapid deposition property because of it has high viscosity and it also contain paraffin wax content up to 32.5% (Rehan et al. 2016) [36] . According various investigations it has been observed that the basic reasons behind wax deposition in the pipelines are change in temperature, higher viscosity and presence of higher percentage of wax content (Lonje et al. 2022) [28] . Since long, several researchers have done lots of work on preventing the prevention of crude wax deposition in the pipelines. This includes several physical, chemical and mechanical processes but these approaches are not cost effective, moreover, leads to secondary pollution (Hamida and Babadagli 2007) [19] . Therefore, use of viable and cost effective technique may result in solving this problem. This technique is based on exploitation of microbe's activity on petro-hydrocarbons, it has been found that microorganisms degrade this heavy organic compound and utilize it as a carbon and energy sources for its growth. Due to production of extra cellular enzymes and metabolic activities of microorganisms they can digest this heavy oil by enzymatic mechanisms (Sousa et al. 2019) [40] . Various types of microbial enzymes are responsible for the degradation of paraffin wax, which will be discussed afterwards in the article. Number of methods are used for detection and identifying the crude wax deposition inside the wells like low production and slow transfer process. Consideration of this problem, there is needed to propose an appropriate and cost effective technique for the removal of crude wax from the wells. Microbial technique is a proved in previous research, is appropriate and effective alternative method in contrast of conventional methods for the prevention and elimination of the wax deposition (Adlan et al. 2020) [2] . The idea about basic characteristics of the paraffin wax degrading bacteria is they must be facultative anaerobic (Working in the presence or absence of oxygen), environmentally safe, no slime forming and not genetically altered and non-pathogenic (Sadeghazad et al. 2003; Kiyingi et al. 2022) [37,26] . Before the discussion about removal and preventive phenomenon, firstly thrash out what are different reasons behind the deposition of waxy crude oil in well-bore, reservoir and pipelines. There are some basic few sources behind crude wax deposition are given below: Sources of crude wax deposition a) Alteration occurring in the temperature, pressure and gas content during the process. b) High viscosity characteristic. Therefore, high molecular weight heavy hydrocarbon loss their solubility in the system and gets precipitated out of the mixture. Crude oil has one of the demerit, it can immediate changes its physical and chemical properties according to changes in the temperature and pressure of the system (Kiyingi et al. 2022) [26] .

Types of crude wax

Crude oil waxes are basically classified into two groups; paraffin wax and microcrystalline wax. They are present in petroleum residue and distillates containing straight chain of hydrocarbons (Kiyingi et al. 2022) [26] .

Paraffin wax

It consists of a complex mixture of hydrocarbons with the general properties like non-reactive, colourless, non-toxic, good water barrier and burning fuel. Paraffin waxes have clearly defined crystal structure and tendency to be brittle and hard. The melting point of paraffin wax is between 120º-160º F (Tiwari et al. 2014) [41] .

Microcrystalline wax

It is produced from the combination of distillates and residues of oil. Microcrystalline waxes have less-defined crystalline structure, higher viscosity and dark in colour. Sometime also called micro wax, they are soft and tacky to being hard and brittle according to their compositional balance (Kiyingi et al. 2022) [26] .

Problem caused by the wax deposition

In transportation pipelines, deposited wax build-up and causes higher pressure drops and decreases transfer capacity. In storage tanks, these deposits reduce storage capacity. In upstream operations, wax formation around the wellbore decreases permeability, negatively affecting well performance. In most cases, acidizing hasn't proven effective under typical operating conditions. Other conventional methods, including chemical, thermal, and mechanical approaches, also have limitations, similar to methanol-based treatments (Alnaimat et al. 2019) [4] . Additionally, the low purity of crude oil during distillation often leaves behind impurities like clay and sea waste from the drilling process, which contributes to wax formation during transportation. Here are some few problems caused by wax deposition in the pipelines and reservoirs in brief given below.

Low flow rate:

In transportation pipe lines, waxy crude oil deposition in the wells develops greater drops and smaller transfer capacities. Low flow rate means a huge loss in the production of crude oil. Wax appears thicker and thicker makes the flow area smaller with time going by persuade the transportation capacity and operation safety of the pipelines.

It is because it can increase the pressure; blocking area and can cause leakage.

Losses storage capacity:

In storage tanks, crude wax deposited on to the walls and bottom, resulting into the occupation of storage tanks area which leads to the loss of tank storage capacities (Alnaimat et al. 2019) [4] .

Methods for crude wax control are as follows

There are numerous conventional methods used for the prevention and control of wax deposition.

Thermal methods

Earlier, hot oiling methods were used for dissolving waxy crude oil. In this method hot oil was pumped between casing and tubing, where it returns to the tubing with dissolved wax. Nowadays, several electrical heating methods are used like heat tracing, steam tracing, insulation Parman et al.

2013) [32] and many more methods that have given below:

Electric downhole heaters: Use of electrical heating for wax prevention purposes is done in two different ways: insertion of electrical cable through flexible line and use of internal steel layer on electricity conductor. Thermo electric cables are installed on the inner side of the well and the paraffin sediment is melted through electro thermal function or it is never formed. The effect of this method is very prominent but it is not formally used because of its high cost.

ii) Heat tracing: It consists of pipeline with insulation and active heating inserted inside wells. There are two types of active heating methods one is electric and other one is circulation of hot fluid.

iii) Steam tracing: It is done to maintain higher temperature to reduce product viscosity (Oskouei et al. 2005) [31] .

Mechanical Methods

Numerous mechanical methods are implemented in few past years for the crude wax management; few of them are as follows:

Wire line scrapping This is a relatively new tool to remove paraffin's from tubing of flowing wells. The weight of scraper varies from 1lb to 5 lb and is of a diameter slightly less than that of tubing into which it runs. These are placed in the wells by means of a lubricator and allowed to fall in the bottom of the tubing or to a stop or pinned collar placed just above normal paraffin zone. When the well is opened, the scrapper is propelled to the top of hole then it enters the lubricator and remains there until the well is shut in. Either a gate or spring latch is provided for retention of the scraper on the surface (Sausa et al. 2019) [40] .

Automatic tube scrapping

This is a relatively new tool to remove paraffin's from tubing of flowing wells. The weight of scraper varies from 1lb to 5 lb and is of a diameter slightly less than that of tubing into which it runs. These are placed in the wells by means of a lubricator and allowed to fall in the bottom of the tubing or to a stop or pinned collar placed just above normal paraffin zone. When the well is opened, the scrapper is propelled to the top of hole then it enters the lubricator and remains there until the well is shut in. Either a gate or spring latch is provided for retention of the scraper on the surface (Tiwari et al. 2014) [41] .

Pigging

Pipe pigging technology has been in existence for many years because of its low cost in comparison to replacement of pipelines. Pigging is also considered to be the most convenient method to assess the internal condition of an operating pipeline (Shamari et al. 2012) [38] . Soon after placing in service, the flow efficiency of pipelines decreases. It is easily noticeable by lower flow rates, increased operating pressure, higher fuel bills, undesirable product and pig wear.

Chemical methods

Chemical injection along with system design can increase the production capacity of the system. Factors considered while using a chemical method includes its suitability in terms of risk to personnel, material compatibility, environment profile, availability, cost and impact on process facilities (Gentili 2005) [17] . Maximum value can be achieved in minimum capital expenditure by using proper chemical injection techniques and procedures (Willmon et al. 2006) [44] . Chemical methods include surfactants, dispersants, solvents and wax crystal modifiers. Solvent dissolve only a fixed amount of paraffin.

Pour point depressants

Paraffin consists molecular species of linear chains of carbon containing 14 or more carbon atoms. These species, known as waxy substances, can lead to oil pumping issues at low temperatures. The pour point temperature is the lowest temperature at which crude oil can flow when cooled under specific conditions. At lower temperatures, wax tends to form crystals with a lattice-like structure (Boucetta et al. 2022) [9] . To address this issue, pour point depressants are used. Also known as paraffin inhibitors or flow improvers, these substances are polyesters of fatty acids. Essentially, they are polymers with a paraffinic segment that cocrystallizes with the wax and a polar component that restricts the degree of co-crystallization. These depressants modify the size and shape of the wax crystals, preventing the formation of large crystals. They achieve this by either adsorbing onto the surface of newly formed crystals or cocrystallizing with the precipitating wax. In this way, pour point depressants work by adhering to the surface of growing wax crystals. (Niijjaawan et al. 2010) [30] .

Paraffin Dispersants

These are surfactants which keep the already formed paraffin crystals from agglomerating into a mass with enough weight to fall out of the solution and get deposited.

Water soluble Detergents play a crucial role in breaking down asphaltenes and paraffins while also aiding in the separation of oil from water. Additionally, they form a protective layer on the surface of equipment, which helps prevent future deposits. The action of detergents is based on their ability to neutralize the forces that cause paraffin particles to clump together. Dispersants, on the other hand, have a unique structure: one end of the molecule attaches to the paraffin, while the other end dissolves either in oil or water, depending on the phase where the paraffin needs to be dispersed (Craddock et al., 2007) [13] . These dispersants are typically made from substances such as sulfonates, alkyl phenol derivatives, ketones, and terpenes. They are versatile, functioning both in removing existing deposits and in preventing new ones. Their application can vary; they might be used in batches, continuously, or injected directly into the matrix (Dobbs, 1999) [15] . Solvent combined with dispersants can prolong the period of re-deposition. They can be used in deep water where pipeline plugging is always problematic.

Winterized Paraffin Crystal Modifier

This method employs a combination of solvated and nonsolvated mixtures of various paraffin crystal modifiers, including maleic olefin esters, polymeric acrylate and methacrylate esters, as well as ethylene vinyl acetate polymers and copolymers (Joutey et al., 2013) [24] . The objective is to create a stable solid suspension of these active crystal modifiers within a non-solvent liquid matrix (Becker, 2001) [7] . Specialized wax dissolvers, when used in tailored treatments, have proven effective in enhancing the removal of wax deposits from pipe walls and preventing future accumulation. The application of wax dissolvers changes the physical properties of pig waxes, facilitating the removal of hydrocarbon deposits. These chemical injection strategies significantly improve the cleaning process, allowing for more accurate data collection during intelligent pigging operations.

Various factors affect the success of using a solvent. Some of these are type of paraffin, quantity of paraffin, solvent used, contact time and temperature (Chen and Zhong 2019) [11] .

Emulsion Method

It considers addition of surfactants to endorse emulsification which can reduce the tendency for wax deposition. It uses surfactants to form an (Oil in water) emulsion from produced fluids in the well bore and to wet the steel surfaces with water film which does not allow adherence of wax (Karamalidis et al. 2010) [25] . Emulsion can cause lower interfacial tension and greater shear rate that lead to reduced paraffin deposition (Amin et al, 2007) [5] . Emulsification method inhibits the deposition of higher molecular weight paraffin components. They reduce total amount of wax and leave a softer wax (Ahn et al, 2005) [3] . This enhances well productivity and operational efficiency while minimizing the need for regular removal of paraffin build-up.

Thermo Chemical Methods

In this technique exothermic reaction between a blend of solvent and other active compound forms chemical which is a concentrated solution of an extremely effective paraffin wax dispersant in a hydrocarbon solvent and act as dispersant that tends to change the morphology of wax from crystalline to amorphous (Ibrahim et al., 2005) [22] . The two pack system is injected simultaneously through production tubing into the well bore. Injection of two pack chemicals and post flush is carried out using pumps, tanks, tubing to mix two pack chemicals in production tubing. Minimum soaking period required after chemical injection is 12 hours (Hidayat and Turjaman 2016) [20] . Upon mixing, both components will produce heat and reaction product. Reaction product is powerful paraffin dispersant that prevent re-deposition after temperature returns to normal (Mineki et al. 2015) [29] . The salts formed act as excellent wax dispersing agents. Heat generated is generally adequate to melt organic deposits. Organic acids used mainly include alkyl substituted analogs of benzene sulphonic acids and naphthalene sulphonic acid (Becker et al, 2001) [7] .

Magnetic Methods

In this method, oil is made to pass through the powerful magnets. Basic mechanism is that when crude oil flows through magnetizer, the wax is set on the action of magnetic field and an electronic circumference is generated in the molecule of wax and a cyclic magnetic field is generated in this electronic circumflex. It disturbs and deteriorates the orientation of the momentary magnetic pole in the wax molecule and weakens the chromatic dispersion to inhibit the growing and coagulation of wax crystals and to prevent the paraffin precipitation in oil wells. The wax molecules get paralyzed and orient them in direction of flow thus inhibiting their ability to migrate to the walls to deposit. The device utilizing magnetic fields are called magnetic fluid conditioners or stabilizers (Ahn et al, 2005) [3] .

Microbial Treatment

The microbial treatment based on the activity of naturally occurring selected and isolated bacteria has proved to be an effective technique to the conventional chemical methods in preventing and removing wax deposition in oil field facilities and pipelines. These techniques use gas, acid, surfactant and alcohol producing bacteria to remove blocking type hydrocarbons. Micro-organism involved with microbial treatment of crude oil are mostly facultative, live, naturally occurring and are anaerobic, non-pathogenic, contains no sulphate reducing bacteria or slime forming bacteria and are environmentally safe (Willmon et al., 2006) [44] . Various bacterial activities were found to have the ability of producing bio surfactant in the form of biological molecules (Oskouei et al., 2005) [31] . These bio surfactants possessing higher surface activities were capable of reducing surface and interfacial tension at interface between liquids and solids. It can control paraffin deposition by reducing the length of paraffin molecule and producing by products that acts as surfactant and paraffin solvent (Etoumi, 2007) [16] . In this method cultured microbes are injected into a well bore to produce chemicals that inhibit wax precipitation to break down the produced wax. These methods provide continuous wax remedial solution rather than a temporary one. Thus, biological wax removal methods are quite effective, economically viable and warrant further study (Binks et al, 2015) [8] . This method has some drawbacks. Microbes are imported from abroad and the price is very high and application in oilfield is inconvenient since the oil well is required to be neatly washed before adding bacterium into it (Guerreiro et al. 2012) [18] . Microbes require water to survive and cannot tolerate high temperature. So, this method was limited to wells that produce water and have bottom hole temperature below 200̊ F (Kovrigin and Kukharchuk 2016) [27] .

Recent developments in microbial methods

Microbes can produce various fermentation products, including carbon dioxide, methane, nitrogen, and biosurfactants. The effectiveness of wax removal is influenced by factors such as the concentration of the injected bacteria, the size of the bacterial culture plug, incubation time, and the level of residual oil saturation. Biosurfactants, whether added externally or produced in situ, play a key role in emulsifying oil and helping detach it from wax, making them highly promising for microbial wax remediation (See Table 1). These biosurfactants also reduce the viscosity of heavy crude oil, which makes it easier to pump. Pseudomonas sp. DG2 has shown a strong ability to degrade paraffin and efficiently remove wax. The lipopeptide biosurfactant produced by this strain has excellent emulsifying properties and can significantly lower the oil-water interfacial tension. Biosurfactant extracted from Bacillus sp. G6 is highly stable at high temperature upto 100 °C so it can be appropriate choice for the elimination of wax deposition (Rawat et al. 2024) [35 ] .

Pseudomonas aeruginosa (N2), a strain isolated from the formation water in the Bi-304 block of the Henan Oilfield, has been identified as a highly efficient producer of rhamnolipids, a type of biosurfactant. This biosurfactant demonstrates strong surface activity and remains stable across a wide range of pH levels (5-12), temperatures (15-80 °C), and salinity (0-32 g/L NaCl). On the other hand, Bacillus licheniformis (KB18), which was isolated from petroleum-contaminated soil, does not have the ability to produce biosurfactants. Pseudomonas aeruginosa Biodegradation of wax components Smith et al. 2019 [39] 2.

Bacillus subtilis Production of biosurfactants to disperse wax Johnson et al. 2020 [23] 3.

Rhodococcus erythropolis

Wax ester formulation and emulsification Kiyingi et al. 2022 [26] 4.

Acinetobacter calcoaceticus Enzymatic degradation of long chain alkanes Lonje and Liu 2022 [28] 5.

Alcanvorax borkumensis Alkane hydroxylase production for wax breakdown Theyab M A 2021 [45] 6.

Candida tropicalis Yeast mediated wax conversion Liang et al. 2016 [46] 7.

Micrococcus luteus Surface mediated wax solublization Kiyingi et al. 2022 [26] 8.

Pseudomonas fluorescence Produces extracellular polymeric substances Kiyingi et al. 2022 [26] Bio surfactant from the thermo-and halo tolerant species, Bacillus licheniformis isolates and thermo tolerant Bacillus subtilis strains have been tested for with various levels of success in reservoirs and in laboratory simulations (Adedeji et al. 2022) [1] . Pipelines wax deposition is a critical problem in oil pipelines transportation and its severity increases in offshore pipelines. Wax deposition occurs when paraffin components in crude oil precipitate and deposit on the cold pipelines wall, when the inner wall temperature falls below the cloud point temperature or wax appearance temperature. Different wax deposition techniques were reported it includes chemical application, mechanical, thermal method, magnetic method, bacterial method, application of ultrasonic waves, laser technology, piezoelectric method, cold flow technology etc. In the worst cases, when no of such techniques is feasible to be used, production must be stopped in order to cut and replace the plugged portion of the line (Kiyingi et al. 2022) [26] . Microbial method has been proposed as an attractive and encouraging technique to tackle the wax deposition problem. Microbes have the ability to absorb wax, are able to remove effectively wax deposits or at least reduce the deposition over a certain time period (Figure 2). Applications of micro-organisms is a popular technique because they are non-pathogenic, non-carcinogenic, and non-combustibles and are environmentally safe (Patowary et al. 2016) [33] . Kiyingi et al. (2022) [26] conducted a study to evaluate the ability of three bacterial species-Pseudomonas aeruginosa, Bacillus subtilis, and Acinetobacter lwoffi-isolated from petroleum-contaminated water and soil to break down crude oil. They tested the effectiveness of these bacteria both individually and in combination as a mixed bacterial consortium, using capillary gas chromatography to measure the biodegradation of crude oil. [21] . All reported methods for crude wax removal have their own advantages and disadvantage depend on their mechanism of treatment and action. The advantages and disadvantage of different methods including chemical, physical, thermal and biological and their application proven yet or not is represented below in Table 2. 2.

Chemical dispersant Reduces the viscosity of wax

Can cause secondary deposits Proven Willmon and Edwards 2006 [44] 3.

Thermal treatment Immediate wax removal Energy intensive Proven Parman et al. 2013 [32] 4.

Mechanical pigging

Effective at removing large deposites Can damage pipelines Proven Wang W, Huang Q (2014 [43] 5. Biosurfactant Biodegradable and ecofriendly High production cost Not yet Rawat et al. 2024 [35] 6. Enzymatic degradation Specific and effective wax breakdown Enzyme stability issues Not yet Johnson, A., et al.

(2020) [23] 7. Microbial degradation Sustainable and low cost Slow process and maintenance required Not yet Patowary et al. 2016 [33] 8.

Hot oil circulation Effect for immediate wax remove

Requires continuous heating Proven Bahadori (2014) [6]

Conclusion

In crude oil production and transportation pipelines, wax deposits cause greater pressure drops and reduce transfer capacity. In storage tanks, these deposits lead to a loss of storage space. In upstream operations, deposits can decrease permeability near the wellbore, which negatively impacts well performance. Traditional acidizing methods haven't proven effective in these situations, and other conventional approaches whether chemical, thermal, or mechanical come with significant drawbacks, such as secondary pollution, high costs, pipeline damage, and the risk of re-deposition of crude wax.

In some studies, bio-treatment methods have been explored to address paraffin deposits. Tests have shown that biosurfactant-producing species can alter the wettability of stainless steel, making it water-wet, and reduce the surface tension between water and stainless steel by forming an emulsion. This process is crucial for preventing paraffin buildup. Bacterial treatment has been found to remove up to 79.0% of paraffin deposits.

Conflict of Interest

Authors declare that there is no conflict of interest in this review article.

Contribution: GR

Original draft and conceptualization and design, Review and editing,

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