Preventing and removing wax deposition inside vertical wells: a review

Wax deposition is one of the most challenging flow assurance issues in oil production processes. The related problems span from reservoirs to refineries, but their consequences can be particularly challenging when the affected area is difficult to reach, such as producing wells. The wax deposition in the areas adjoining the bore, the bore face, the tubing string and the pump is the result of the cooling effect, which occurs when the oil flows from the high-pressure reservoir into the wellbore to the surface. During the depressurization the oil expands, and the heat is drawn from the oil. The temperature loss induces crystallization of the wax and the subsequent plugging of the well. In this case, wax deposition leads to the decrease of well flow rates and eventually causes total blockage. This paper sums up the main technologies applied to prevent or remediate the wax deposition formed inside the wells. A comprehensive review was presented, and the main advantages and disadvantages of these techniques were highlighted. For instance, the mechanical removal is still a widely used technique for solving wax problems inside wells, despite being a costly procedure; heating is another frequent used technique, but it can cause formation damage; bacterial treatments still require further studies on site conditions; changing the operational conditions may be undesirable due to other management field circumstances; coating and insulating materials generally are not fully efficient, being required to implement complementary techniques; cold flow was only tested in pipelines and it was not applicable to wells; finally WIT, electric and magnetic field or oscillatory motion are practical applications that have not been fully proven yet.