Study on the Variation Rule of Produced Oil Components during CO2 Flooding in Low Permeability Reservoirs

Abstract

CO2 flooding has been widely studied and applied to improve oil recovery from low permeability reservoirs. Both the experimental results and the oilfield production data indicate that produced oil components (POC) will vary during CO2 flooding in low permeability reservoirs. However, the present researches fail to explain the variation reason and rule. In this study, the physical model of the POC variation during CO2 flooding in low permeability reservoir was established, and the variation reason and rule were defined. To verify the correctness of the physical model, the interaction rule of the oil-CO2 system was studied by related experiments. The numerical model, including 34 components, was established based on the precise experiments matching, and simulated the POC variation during CO2 flooding in low permeability reservoir at different inter-well reservoir characteristics. The POC monitoring data of the CO2 flooding pilot test area in northeastern China were analyzed, and the POC variation rule during the oilfield production was obtained. The research results indicated that the existence of the inter-well channeling-path and the permeability difference between matrix and channeling-path are the main reasons for the POC variation during CO2 flooding in low permeability reservoirs. The POC variation rules are not the same at different inter-well reservoir characteristics. For the low permeability reservoirs with homogeneous inter-well reservoir, the variation of the light hydrocarbon content in POC increases initially followed by a decrease, while the variation of the heavy hydrocarbon content in POC is completely opposite. The carbon number of the most abundant component in POC will gradually increase. For the low permeability reservoirs with the channeling-path existing in the inter-well reservoir, the variation rule of the light hydrocarbon content in POC is increase-decrease-increase-decrease, while the variation rule of the heavy hydrocarbon content in POC is completely opposite. The carbon number variation rule of the most abundant component in POC is increase-decrease-increase.