Research On Low-temperature Oxidation Process Of Heavy Oil Under Simulated Thermal Recovery Temperature Environment

Air-assisted-steam huff and puff technology is a high efficient mining technique for the later stage of steam stimulation and steam flooding.The main operation is to inject a proper amount of air and catalyst before the steam injection,and the injected air reacts with the crude oil in the reservoir with the assist of catalyst.The mechanism of EOR is mainly to increase the formation pressure and pressurize for cleanup,and also has the auxiliary effect of reducing viscosity,gravity displacement and enlarging the heating cavity.In this paper,two different kinds of heavy oil were studied for the low temperature catalytic oxidation process in different reservoir temperature.In the temperature range of 80??260?,temperature gradient is 20?,a series of low temperature oxidation(low temperature catalytic oxidation)experiments was carried out.After the reaction,the composition of the tail gas,the viscosity,the acid value and the SARA composition of the oxidation oil were analyzed,and a series of regular cognition of heavy oil catalytic oxidation at low temperature was obtained.It was found that the oxidation stage of heavy oil could be divided into two stages,first stage was oxidized viscosity enhancing process,and the second stage is oxidative decomposition process.From the analysis of the current experimental results,the viscosity increasing effect of heavy oil was notable when the temperature was below 200?,once the temperature exceeded 240??260?,heavy oil cracking occurred in the certain temperature range,the viscosity and acid value were reduced to some extent,accompanied by the content of light components in heavy oil increased,the content of heavy components decreased,thus improving properties of heavy crude oil.In the process of heavy oil oxidation with the presence of transition metal salt catalyst,heavy oxygen consumption capacity increased,catalyst could also reduce the oxidative cracking reaction activation energy.In the process of oxidative cracking,the catalyst also inhibited the increasing of asphaltene content,which made the viscosity of the catalytic oxidation of heavy oil lower than that of non-catalytic oxidation heavy oil.A series of steam/air co-injection experiments with different injection ratio at different temperatures were carried out.The optimal injection and production plan has been found by comparing the degree of oil recovery and water content,and analyzing the oil samples at different stages,the effect of low temperature oxidation process of heavy oil on recovery after air injection was also clarified.The experimental results show that,in the air/steam co-injection single pipe experiments,the best air/steam ratio was "40%air+60%steam",and the final recovery factor was 23.96%higher than that of the steam flooding experiment under the same temperature.At the same time,the SARA analysis of the produced oil at different stages along the displacement process shows that the composition of SARA is basically unchanged compared with the raw oil before the gas breakthrough.After the gas breakthrough,the content of light component,especially the saturates content increased gradually by 0.25%?26.70%.Meanwhile,the asphaltene content increased by 0.36%?7.67%and the resins content decreased by 1.95%?27.39%.Further analysis of residual oil samples in sand filled pipe showed that asphaltene increased significantly compared with raw oil,and the content of resins and aromatics decreased significantly,but the saturation fraction also increased significantly.In the air/steam co-injection double pipe experiment,with high and viscosity increased effect was contributing to the profile control.The high viscosity crude oil plug after oxidation is replaced by injected gas,forming effective plugging in high permeability zone,improving the utilization of unexploited crude oil at low permeability zone,and ultimately improving the comprehensive recovery level.The SARA analysis is similar to the single tube experiment.The whole displacement process is accompanied by the in-situ upgrading effect of heavy oil,which makes the physical property of the extracted oil improve.