Ever since paraffin-based crude oils were introduced, accumulated paraffin or asphaltenes in the casing in well bores and flow lines has detracted from overall well production, by inhibiting crude oil flow. Each year, wells – thousands of them – experience such substantial production losses (as a result of paraffin or asphaltenes buildup) that they are abandoned altogether. Though millions of research dollars have been invested to develop better methods for preventing or removing the paraffin deposits, as yet, no universal solution has been found.
Results vary from success to complete failure, as the process of discovery is essentially one of trial and error. One reason for this is that controlling paraffin is hampered by the uncertainty of the composition of the deposit, in large part due to variances in molecular structure among paraffin-based crude oils. For example, the physical characteristics of the waxes will vary from the bottom to the top of the buildup (i.e., the deposit may be soft and flocculent, in the upper tubing sections, yet generally of uniform composition, where temperature and pressure remain relatively constant).
To fully remediate paraffin buildup, an operator has several options.
– Hot Oiling
– Coiled Tubing
– Continuous Application of Heat
– Hot Water
– Batch Treatments
– Continuous Treatments
– Chemical – Wax Solvents/Dispersants
– Combination Treatments with Mechanical or Thermal Techniques
Mechanical removal of paraffin
Using wireline cutting tools and flowline scrapers are the oldest methods of removing wax deposits. The cost of scraping is on par with that of deploying thermal techniques. One advantage of scraping is that some scraping systems will support paraffin cleaning concurrent with oil production, enabling operators to keep production levels up. In either case, cleanings must be scheduled at frequent enough intervals or it could lead to more labor-intensive methods being required and, in some instances, they will not be successful. Ideally, scrapings are scheduled regularly enough that the tool will be able to clean the well within one – three passes, at most.
Though well established, scraping techniques are not without disadvantages. In some instances, this method can result in large chunks of scraped paraffin settling in flowlines or surface equipment causing blockage. Additionally, metal on metal typically roughens the tubing wall and encourages more deposits, bacterial growth, and corrosion.
Thermal removal of wax
Melting paraffin deposits has been in use almost as long as scraping. Though the technique is relatively simple, the cost low, and results immediate, if the requisite time and temperature requirements are not fully recognized, operators can expect treatments to be inadequate, and possibly result in extensive well service operations.
Heat and Hot Water
The use of heat for removal of paraffin in pipelines is impractical. Because of the location of buried lines, and the variance in temperature as hot oil, hot water, or steam move along the pipe, it is not unlikely that crystalline waxes may be dislodged and flow with the melted waxes and if treating ceases before all the wax has been displaced, which can be difficult to determine, substantial sections of line totally or partially plugged and require further cleaning.
In-situ heat generating techniques
Though successful in certain situations, these patented processes pose certain hazards associated, such as potential corrosion, rapid pressurization, and fire.
Chemical remediation techniques and prevention of wax deposition
Depending on the degree of blockage, chemical solvents and dispersants may also be effective in removing blockage from wells and flowlines and can significantly reduce the need for remediation and lower operating costs, but are often used in conjunction with the mechanical and thermal techniques, rather than as a standalone solution.
Oil Well Stimulation
Oil well stimulation solutions vary by producer and include plant-based materials, domestically grown, that offer a fully biodegradable alternative to acid stimulation or traditional solvents. These solutions are designed to break down paraffin or asphaltenes and remove buildup from the well. In the event of the condensate blockage, they can disperse water blockages. Oil well stimulants can be custom formulated to suit either paraffin or asphaltene and their application can take on different forms. Unlike acids or solvents, these solutions do not degrade the oil or require neutralizing an acid agent.