7.+Solutions

=Overview =
 * General method: addition of crystal modifiers change the crystal structure of paraffin deposits, thereby lowering the sum of its aggregate interactive forces
 * Solvated wax/kerosene mixtures can then be treated to cause even greater rheological improvement and cause significant reductions in fluid viscosities
 * The effectiveness of the applied solution greatly depends on the type of aggregate forming waxes that are present in the oil
 * The choice of which crystal modifier is key to the success of the treatment.

=Possible Solutions = Asphaltene and paraffin deposition in production wells, pipelines and surface facilities has been a significant problem with large economic repercussions when ignored (Ramirez-Jaramillio et al. 2005). As such, various remedies have been suggested to overcome deposition of paraffin wax and asphaltene in pipelines. These include preheating the crude, using special heating-cooling treatment cycles, and controlling thermal conditioning to maximize the natural pour-point depressing effect of resin and asphaltene present in the crude (Hemant et al. 2008). In addition there are applications of microwaves, ultrasound irradiation, magnetic fields, lining and coating pipelines with fiber-reinforced plastics to reduce the wettability of paraffin with the wall of the pipe, and covering the inner wall surfaces with polypropylene (Hemant et al. 2008).

1. Pour-Point Depressant (Crystal Modifiers)
Pour-point depressants (PPDs) are designed to be cost-effective methods to improve cold-flow properties of crude and other fuel oils to remain primarily as a fluid (Wang et al. 1999). PPDs accomplish this task by modifying the size and shape of wax crystals and inhibit the formation of large wax crystal lattices (Wang et al. 1999). Wang, Flamberg, and Kikabhai determined that PPDs typically have three components (Wang et al. 1999):


 * 1) A wax-like paraffinic part composed primarily of linear alkyl chains of 14 to 25 carbon atoms long, which co-crystallizes with the oil’s wax-forming components
 * 2) A polar component to limit the degree of co-crystallization
 * 3) A primary component composed of polymers which, when attached to the wax crystal, will sterically hinder growth of large crystals



Figure 1: PPD Chemical Structure (Hemant et al. 2008)

Generally, the polar component of the additive creates the barrier to the formation of the interlocking crystal wax network (Wang et al. 1999). As a result, the altered shape and smaller size of the wax crystals reduce the formation of the interlocking networks and reduces the pour point (Hemant et al. 2008).

Mechanism
<span style="font-family: Arial,Helvetica,sans-serif;">The mechanism to prevent agglomeration primarily involves the structure of the PPDs to disrupt the crystal habit of wax crystals (Hemant et al. 2008).The structures involved in this process are: the pendant chains to co-crystallize with the wax and the polar end groups which are responsible for disrupting the orthorhombic crystal structure into a compact pyramidal form (Hemant et al. 2008).This process prevents the crystals from agglomerating and forming a gel-like structure to deposit on the pipeline surface (Hemant et al. 2008).

<span style="font-family: Arial,Helvetica,sans-serif;"> <span style="font-family: Arial,Helvetica,sans-serif;">Figure 2: PPD Inhibition mechanism of wax modification. 2a) Chemical structure of wax 2b) Crystal shape of wax structure 2c) Crystal structure of growing wax lattice 2d) Polymeric Additive with wax-like components 2e) Co-crystallization of wax and PPD 2f) sterically hindered wax structure (Wang et al. 1999)

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<span style="font-family: Arial,Helvetica,sans-serif;">Figure 3: Prevention mechanism of interlocking wax crystals by polymer additives. a) nucleating site interaction (red) to asphaltene and wax molecules (blue) b) Polar component of additive (green) hinder co-crystallization of asphaltenes and wax (Hemant et al. 2008)

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<span style="font-family: Arial,Helvetica,sans-serif;">Figure 4: Pictomicrographs of Waxes of KS and ND crude oils. A) KS crude without additive, B) KS crude with additive, C) ND crude without additive D) ND crude with additive (Hemant et al. 2008)

<span style="font-family: Arial,Helvetica,sans-serif;">The efficacy of the additive generally depends on the rheological properties on the crude oil (Hemant et al. 2008). As such, crude containing comparable amount of asphaltenes may not react in the same manner as paraffin predominate crudes (Hemant et al. 2008). Asphaltenes in crude behave as a natural PPD, and can hinder the growth of wax crystals by attaching to the surface of the wax crystals (Herman et al. 2008). So, incorporating an additive into the crude can diminish the interaction between the additive and the wax crystals resulting in a poor performance of the PPD (Hermant et al. 2008). By the experimental data collected by Hermant et al., a single PPD cannot effectively depress the pour point of all types of crudes (2008) (Wang et al. 1999). Specifically tailored PPDs must be designed to match the crude’s paraffin chain length and composition to participate efficiently in the crystallization of wax crystals to depress the pour point (Wang et al. 1999).

<span style="font-family: Arial,Helvetica,sans-serif;">2. Trichloroethylene - Xylene binary system
<span style="font-family: Arial,Helvetica,sans-serif;">Xylene-based PPDs form structures with segments that interact with the developing wax crystals to inhibit crystal formation (Bello et al. 2005). A specific xylene based PPD which exhibits a substantial effect as a pour-point depressant is trichloroethylene-xylene (TEX) binary system (Bello et al .2006).This additive utilizes one or more postulated mechanisms including nucleation, adsorption,[| co-crystallization]and improved wax solubility in the reduction of large wax crystals (Bello et al .2006). The trichloroethylene compound contains an ionic pair of electrons which facilitates greater adsorption of the inhibitor molecules onto the wax crystal networks and prevents the interlocking of the wax network (Bello et al. 2005).

<span style="font-family: Arial,Helvetica,sans-serif;">The TEX binary system has the ability to form a stable suspension in crude oil, which results in the inhibition of wax crystal formation. (Bello et al. 2005). As a result, this additive has a greater application on various different crudes and a tremendous economic benefit in the inhibition of wax-crystal formation (Bello et al. 2006).

<span style="font-family: Arial,Helvetica,sans-serif;">3. Sulphur Trioxide
<span style="font-family: Arial,Helvetica,sans-serif;">It is known that while the precipitation and formation of paraffins and asphaltenes is at the core of the fouling problem, it is the accumulation of such compounds that affects the flow characteristics of fluids in pipelines. The cause of such accumulation is attributed to irregularities of, or specific physical properties of, the inner surface of the pipeline (Charles and Marcinew 1986).

<span style="font-family: Arial,Helvetica,sans-serif;">Theory and Application
<span style="font-family: Arial,Helvetica,sans-serif;">After the inside surface of the pipeline is thoroughly washed, it is treated with sulphur trioxide to create a strongly water-wet surface (Goncharenko et al. 1978). It is important to note that the "highly" water-wet properties of the material are only observed on the inner surface of the steel. This highly hydrophilic surface creates a thin layer of water that is held close to the surface (Bernadiner 1993) and prevents any already formed paraffins or asphaltenes from accumulating on the surface.

<span style="font-family: Arial,Helvetica,sans-serif;">Another method of application is the introduction of an aqueous solution containing dissolved sulphur trioxide to the pipeline (Bernadiner 1993). The dual responsibilities this solution has is as a surface cleaner of the pipeline's interior and a wetting agent to create the lubricating layer of water on the inner surface of the pipeline(Bernadiner 1993). Work has been done regarding surfactants to accomplish the cleaning job the solution must accomplish. Also, these surfactants can act to emulsify the oil and water in the production line, thus lowering the rate of formation of paraffin deposits (Bernadiner 1993).

<span style="font-family: Arial,Helvetica,sans-serif;">Practice
<span style="font-family: Arial,Helvetica,sans-serif;">While this method is not generally accepted by industry it has, experimentally, yielded very promising results. It has been shown that success (prevention of paraffin accumulation) can be achieved with less than 10% water content (Bernadiner 1993) in the pipeline fluid. This makes it a good candidate for future study of application.

<span style="font-family: Arial,Helvetica,sans-serif;">4. Surfactants
<span style="font-family: Arial,Helvetica,sans-serif;">Surfactants are employed in pipelines to discourage the formation of paraffins in favourable amounts. The use of surfactants is an accepted method for dealing with flow problems caused by paraffins and asphaltene fouling (Bernadiner 1993) and is often employed in drilling operations (Bernadiner 1993) as well.

<span style="font-family: Arial,Helvetica,sans-serif;">Mechanism
<span style="font-family: Arial,Helvetica,sans-serif;">The general surfactant includes the following components (Wasan 2009):
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Hydrophilic section ("water-loving")
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">Hydrophobic section (repelled by water), which may also be lipophilic (dissolves in oils and non-polar solvents)

<span style="font-family: Arial,Helvetica,sans-serif;"> <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Figure 5:Structure of a surfactant <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif;">(Wasan Laboratory [date unknown])

<span style="font-family: Arial,Helvetica,sans-serif;">These two parts of the surfactant molecule act in concert to encapsulate paraffin droplets (Wasan 2009) (in the case of usage in pipelines) and keep them emulsified in the product stream. This trapping of small clusters of paraffin is achieved by the strong dipole-dipole interaction between the hydrophilic (polar) end of the surfactant molecule and any water in the product stream (Wikipedia Article: Emulsion...[updated 2010]). The surfactant molecule is oriented by these forces such that it forms a barrier between any paraffin and any water in the product stream (Wikipedia Article: Emulsion...[updated 2010]), which inhibits the accumulation of paraffin in the pipeline.

<span style="font-family: Arial,Helvetica,sans-serif;">Pigging
<span style="font-family: Arial,Helvetica,sans-serif;">Pigging, is a process by which deposits on the interior wall of a pipeline (namely paraffins and asphaltenes) are removed by running a 'pig' through the pipeline that physically removes them from the pipeline walls (PPSA 2010). Pigging is inherently a remedial technique.

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Figure 6: Manual insertion of a pig into a pipeline (Engineering News [date unknown]).

<span style="font-family: Arial,Helvetica,sans-serif;">Mechanism
<span style="font-family: Arial,Helvetica,sans-serif;">The technique employs the use of a 'pig', which is a snug fitting pipeline insert, that is launched from a position upstream in the pipeline and is later retrieved downstream. The pig is moved through the pipeline via the production pressure. Pigs that are used for pipeline cleaning are generally made of a hard plastic (PPSA 2010) and often incorporate some type of brushing mechanism on the outside, such as wire bristles. This design also allows for small changes in the pipeline diameter without loss of pig effectiveness (PPSA 2010). <span style="font-family: Arial,Helvetica,sans-serif;">

**<span style="font-family: Arial,Helvetica,sans-serif;">Disadvantages **
<span style="font-family: Arial,Helvetica,sans-serif;">There are a few disadvantages to pigging that do not make it a viable solution to all pipeline deposition control <span style="font-family: Arial,Helvetica,sans-serif;">applications.
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">As the pig must be inserted and removed from the pipeline manually, production is often interrupted (PPSA 2010)(be it only for a relatively small amount of time).
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">Human contact with the pig is considered to dangerous to some degree.
 * 3) <span style="font-family: Arial,Helvetica,sans-serif;">As pigging is the removal of already formed deposits, it does little to actually solve the problem of paraffin and asphaltene deposition.

**<span style="font-family: Arial,Helvetica,sans-serif;">﻿Hot Oiling **
<span style="font-family: Arial,Helvetica,sans-serif;">This method of paraffin deposition remediation involves the circulation of a stream of hot fluid (often oil) through process lines with the intention to dissolve and dislodge any accumulated deposits (Charles and Marcinew 1986). Hot oiling works on the premise that heavier waxes have a lower solubility at lower temperatures. Since deposition tends to occur in areas of higher temperature variance (Charles and Marcinew 1986), this method also works to effectively prevent temperature variation (Charles and Marcinew 1986), to a certain degree.

**<span style="font-family: Arial,Helvetica,sans-serif;">Solvent Soaks **
<span style="font-family: Arial,Helvetica,sans-serif;">Though the name may imply the sole use of solvents, a solvent soak is simply an advanced method of hot oiling utilizing chemical, as well as thermal dissolution and remove of deposited paraffins (Charles and Marcinew 1986). Similar to hot oiling, solvents are circulated through well tubing and process pipelines to dissolve any paraffins which have been deposited (Charles and Marcinew 1986). Solvents are used because they effectively work to decompose paraffins (being relatively large hydrocarbons) into smaller hydrocarbons that are more soluble in the oil (Charles and Marcinew 1986).

<span style="font-family: Arial,Helvetica,sans-serif;">Surfactants are often used in tandem with solvent soaking to prevent the re-formation of paraffins from the newly created lighter hydrocarbons. Surfactants accomplish this by decreasing inter facial tension between paraffins and other stream materials (Bernadiner et al. 1993) thus discouraging accumulation and, indeed, the formation of paraffin deposits.

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