Study on the precipitation regular of asphaltene in gas injection well

Objective This paper aims to solve the problem of asphaltene deposition blocking wellbore in the process of gas injection production of crude oil in Donghe block.

Methods Based on light scattering theories and using a high pressure/high temperature solid deposition test device, the effects of temperature, pressure, gas-oil ratio and other factors on the precipitation behavior of asphaltenes were tested.

Results Temperature increase improves the solubility of the asphaltene in the crude oil and promotes the stability of the crude oil. Under isothermal pressure depletion conditions, asphaltenes gradually precipitate and reach maximum precipitation near the bubble point pressure with the descend of pressure. In other words, the risk of asphaltene deposition is highest when near the bubble point pressure. The bubble point pressure of DH-1 well corresponds to the well depth of 2 140 m, which is close to the actual blocked position at 1 969 m in production well. Therefore, the bubble point pressure can be used to predict the plugging location in oil wells. The higher the amount of dissolved gas, the higher the onset asphaltene precipitation pressure, and thus the larger the asphaltene precipitation pressure range the more likely asphaltene deposits to occur in deeper well sections.

Conclusion The research reveals the asphaltene precipitation law during gas injection, which has an important guiding role in prevention and control of asphaltene precipitation in gas injection wells.