Catalytic Role of Various Clay Minerals on Low-Temperature Oxidation during the Air Injection Process in Light Oil Reservoirs

High-pressure air injection (HPAI) is a potential enhanced oil recovery (EOR) technique for exploiting low-permeability hydrocarbon reservoirs with light oil. During this process, low-temperature oxidation (LTO) reactions between crude oil and injected air mainly occurred. However, the impact of different clay minerals on the low-temperature oxidation characteristics of light crude oil has rarely been investigated. In this work, a series of static low-temperature oxidation experiments were performed under the conditions of three clay minerals, i.e., kaolinite, chlorite, and montmorillonite, and different mineral concentrations. Increasing the clay concentration from 5 to 10% further enhances the LTO reaction, and the oxidation rate increases from 1.02 to 1.8 times that of the blank sample, with the higher enhancement generally observed at 10% loading. The results reveal that clay minerals have a positive effect in accelerating the oxidation rate at the stage of low-temperature oxidation, while chlorite shows the best catalytic effect, owing to its excellent ion exchange capacity. Moreover, the LTO process leads to the production of oxygenated hydrocarbons, CO, and CO₂, corresponding to an increase of the resin and asphaltene relative content in crude oil. Under the temperature of the anomalistic point, the viscosity of crude oil increases by 120 to 220 mPa·s due to the production of resin. Nevertheless, at the stratum temperature of 70 °C, the viscosity uplift is only 0-4 mPa·s due to the volatilization of light hydrocarbons. The results demonstrated here will support the enhancement of unconventional hydrocarbon recovery and offer crucial guidance in optimizing HPAI techniques in light oil reservoirs.