Low-temperature combustion behavior of crude oils in porous media under air flow condition for in-situ combustion (ISC) process

A porous medium thermo-effect cell (PMTEC) was developed to fast characterize the combustion of crude oils in porous media in air flow for air injection enhanced oil recovery (EOR) process. We described how PMTEC works and employed it to investigate the combustion behavior of seven crude oils including two light oils, two medium oils, two heavy oils, and one extra heavy oil. The results showed that, except the two light oils, the others exhibited a strong low-temperature combustion (LTC) phenomenon at about 270-280 degrees C with a high temperature increase to approximately 700 degrees C and the release of CO2 and CO gaseous products. This LTC behavior was compared with the widely documented oxidation behavior in air injection process including low-temperature oxidation (LTO) and high-temperature oxidation (HTO) characterized by high-pressure differential scanning calorimetry (HP-DSC). It turned out that the LTC occurred in PMTEC was different from the LTO or HTO observed from HP-DSC experiments. In addition, this LTC can propagate in porous media with air flow, which was detected by a newly developed optical fibre technology instead of traditional thermal couples. Furthermore, the effect of copper stearate, iron stearate, nickel stearate, and cobalt stearate as oil-soluble catalysts on the LTC was investigated. Copper stearate showed the best catalytic effect. It significantly shifted onset and peak temperatures into lower temperature from 278 and 287 degrees C to 227 and 237 degrees C, respectively, exhibiting a great potential in catalyzing crude oils combustion in ISC process. The catalytic effect of these four catalysts is in turn: copper > iron > cobalt > nickel.