How Do Methane, Carbon Dioxide or Fatty Acids Affect Waxy Crude Oils?

Abstract

In the oil and gas industry, wax formation and deposition are common problems, particularly during production and transportation. To better understand the expected behaviour of a given waxy crude oil and consequently select the best solution to prevent wax deposition, it is vital to conduct laboratory tests or numerical simulations to model its performance. For a Brazilian oil field, the phase behaviour of 17 crude oils was modelled using Multiflash software. To tune the model, laboratory tests were used, including true boiling point curves and viscosity tests. This study followed two stages: the first allowed characterization of the wax appearance temperature (WAT) and determination of the expected precipitation curves for these crude samples, and the second stage was evaluation of the impact on wax precipitation after the addition of methane (CH4), carbon dioxide (CO2) or fatty acid (CH3(CH2)nCOOH). Results showed that WAT varied between 47.5 °C and 51.6 °C for these crude oil samples at atmospheric pressure, considering the differential scanning calorimetry (DSC) method. Furthermore, the percentage of wax mass formed varied between 13.3% and 18.3%. By adding the aforementioned chemicals as an inhibitor, it is possible to observe a reduction in the paraffin precipitation tendency. Inhibition was compared in terms of effectiveness between the chemicals studied, and it was concluded that adding myristic acid (C14:0), oleic acid (C18:1), palmitic acid (C16:0), or lauric acid (C12:0) was the most effective in reducing the WAT value. In fact, when adding 25% mole fraction, CH4 and CO2 can reduce the WAT value by up to 4%, but the results are strongly dependent on the fluid pressure. Myristic acid was the most effective in reducing the WAT value by up to 5%, and the results were less pressure dependent.