Water-wet surfaces are known to be an important factor in a mechanism of paraffin inhibition. Previous attempts to create these surfaces with chemical coatings or plastic-lined tubing have met with limited success. A patented process 1 has been developed that overcomes the problems previously associated with obtaining long-lasting, strongly water-wet surfaces downhole. This process generates heat within the tubing, converts paraffin into a water-dispersible resude and super cleans the surface of the rods and tubing. The resulting effect is a hydrophilic surface on all wellbore production equipment. This environment reduces the adhesive force of the paraffin to the rod and/or tubing surface and allows the precipitated paraffin to be produced out of the well.
Hydrophilic surfaces are difficult to create and maintain in a producing oil well. Two different approaches to wettablity alteration are available. One is to treat the produced fluids with dispersants so the paraffin crystals can no longer adhere to one another. This method is highly dependent upon the chemistry of the hydrocarbons and the reliability of the application mode to properly dispense the treatment chemical.
The other approach is to treat the downhole goods so they become water-loving and retard adhesion. Tubing that has been internally coated with plastic above ground is one method. Silicate coatings and various other chemicals have been applied in situ in an attempt to create an even, nonadhesive surface.
Plastic coatings are subject to rapid abrasion and may not hold up for extended periods of time. Chemical treatments are subject to application in less than ideal circumstances. Oil coatings and residual paraffins are difficult to remove. Without an extremely clean surface on which to adhere, most coatings either never take hold or are rapidly washed or worn away.
A solution to these problems is a treatment that can super clean oily surfaces downhole and that does not depend on a coating to maintain a water-wet environment. Since this treatment is applied directly to the tubular goods, the application effectiveness can be readily monitored. Also, our experience to date indicates the composition of the oil is not critical to the process.
It was theorized that sulfur trioxide, in liquid and/or vapor form, would be able to accomplish the tasks of cleaning and creating a water-wet surface.
Cleaning of the oily surfaces downhole was a primary concern in this application of sulfur trioxide. It was found that tremendous heat was generated when the treatment chemical came in contact with water or hydrocarbons. This heat appears to be necessary for complete removal of hardened paraffin deposits. Without sufficient heat, only the surface of in-situ deposits is sulfonated. The stability of the treated deposit could then affect the longevity of the treatment.