Natural Gas Industry B (Feb 2022)
Asphaltene precipitation trend and controlling its deposition mechanism
Abstract
The B oilfield is a large integrated oilfield in the Middle East. Asphaltene precipitates from crude oil and deposits on solid surfaces, affording considerable blockages of the formation, wellbore, and production equipment. To fully understand the asphaltene precipitation trend and deposition mechanism deeply, and solve the abovementioned problems in the B oilfield, fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, and isothermal depressurization experiments (IDEs) have been conducted to predict the asphaltene precipitation trend of an oil sample. According to the experiments, the saturate, aromatic, resin, and asphaltene ratios were 5.6%, 37.4%, 33.1%, and 15.9%, respectively. The calculated colloidal instability index reached 0.88, indicating a risk of asphaltene precipitation. Based on IDEs, asphaltene precipitation was observed in the view cell window at 3196, 3545, and 3750 psi at different temperatures. Furthermore, the asphaltene deposition mechanism was studied on a string surface at the microscale based on molecular simulations and control measures were proposed. According to the simulations, the deposition process is found to be spontaneous. Asphaltene molecules were self-assembled and formed nanoaggregates in the form of a π–π conjugation. They were deposited parallelly on the string with a “face-to-face” pattern. When the simulation temperature reached 325 K, asphaltene deposition reached the maximum under the simulation conditions. Compared with omitting dispersants, the average distance between the asphaltene molecules and string mass center improved and the energy of the system had considerably lowered after adding dispersants, implying that dispersants can effectively weaken the asphaltene deposition process. This paper provides some suggestions for preventing and removing blockages of electric pumps caused by asphaltene deposition.
