Phoenix Chemical Corp.
Removal by Mechanical Means
This is the oldest method known for the removal of heavy hydrocarbon deposits. It is done by mechanically scraping the tubing. For line cleanup, soluble or insoluble pigs are used. The pigs remove a portion of the wax as they travel through the lines.
Mechanical removal of deposits and the disposal of those deposits is a cumbersome operation. Furthermore, while this method may be effective for cleaning the tubing and lines, it is not effective in removing hydrocarbon deposits that may be present at the formation.
Removal by Hot Fluid
Another old method of removing hydrocarbon deposits is through the use of hot oil, hot water or steam. This is performed by circulating the hot fluid to remove the deposits from the well conduit, or by injection into the formation to open up the plugged areas.
This method works by melting the hydrocarbon deposits. Therefore, it is important to insure that the melted hydrocarbons are not deposited in the formation. Melted hydrocarbons often deposit in the formation when the hot oil introduced into the formation is saturated with melted paraffin and asphaltene, and the formation temperature is lower than the cloud point of the hot oil.
Under these circumstances precipitation will occur and consequently cause permeability reduction and damage to the formation. When hot fluid treatment is used, the hot fluid should be injected down the annulus and up the tubing (not vise versa).
It is also recommended that crystal modifiers or solvency enhancer chemicals be added to the hot oil. This will help suspend the heavy hydrocarbons in the hot oil and hinder its precipitation out of the hot oil, thus decreasing the chance of damage to the formation, and enhancing the solubility effects of the hot oil.
Use of Solvents
Solvents are the most popular methods of hydrocarbon removal. Some of the excellent solvents are Carbon Disulfide, Chlorinated Solvents, Benzene, Xylene and Toluene.
Carbon Disulfide is one of the best known solvents for the removal of waxy deposits; however, it is extremely dangerous to handle, and its use is banned in most countries. It is explosive, with a flash point of -22°F (-30° C) and autoignition temperature of 212°F (100°C). It is also very poisonous.
Chlorinated solvents are excellent solvents, but they damage the catalyst used in the refinery process and are considered a fire and health hazard. Therefore, their minimal detection in any crude oil leads to the rejection of that crude by the refineries.
Benzene is an excellent solvent; however, it is extremely flammable and is a carcinogenic compound (Cancer causing compounds).
Xylene and Toluene are also excellent solvents; however, they quickly reach their saturation point, thus large quantities are often required.
When solvents come in contact with the deposits, they dissolve the heavy hydrocarbon deposits until the solvents reach their saturation level. If the solvents are not removed from the well promptly after their saturation level is reached, then some of the dissolved paraffin will precipitate out of solution (recrystallize). Sometimes recrystallization leads to a worse clogging problem than what was present prior to the treatment, due to the agglomeration of deposits in areas that did not previously have any deposits. Therefore, solvents should be handled with caution and removed promptly after treatment.
Use of Dispersants
Dispersants are also popular chemicals for the removal of paraffin deposits. The dispersants do not dissolve paraffin but disperse it in the oil or water through surfactant action. Dispersants are usually added to crude oil or to water before they are circulated.
Use of Crystal Modifiers and Inhibitors:
Crystal modifiers and inhibitors are a class of chemicals which attack the nucleating agents of the hydrocarbon deposit and break them down to prevent the agglomeration of paraffin crystals. This is done by keeping the nucleating agents in solution.
The asphaltene particles are usually the nucleating agents. By keeping them in solution, the agglomeration of paraffins will be hindered. In order for crystal modifiers to be effective they have to be continuously present in the crude. Therefore, crystal modifiers are usually continuously injected into the well, or they may be squeezed far inside the formation to prolong their presence and time release into the crude.