Abstract
In order to enhance oil recovery in low and ultra-low permeability layer, both of the numerical simulation and physical model experiment have been researched. First, the dynamic distribution of CO1 and N1 in the oil and gas phase in the CO2-N2 compound flooding process was numerically simulated by using the long slim-tube model. The results show that the CO2 slug should have at least 0.3 PV to prevent the impact of N2 channeling effectively. Second, under the experimental conditions of complete miscibility of CO2-crude oil, the two types of natural cores including low and ultra-low permeability, respectively, are used for experimental study on oil displacement. The results confirm that CO2-N2 compound flooding with 0.3 PV CO2 pre-slug can achieve a good result. Finally, a five-point well pattern element model is established by CMG. The recovery and the gas cost of per ton of oil are calculated respectively for CO2-N2 compound flooding and full CO2 flooding at 300 m well spacing of low and ultra-low permeability layer. According to the simulation results, the optimal CO2 pre-slug size in CO2-N2 compound flooding under the condition of low and ultra-low permeability layer five-point well pattern is 0.4 PV.
Highlights
Most of low permeability and ultra-low permeability layers can not be effectively developed by water flooding
By using reservoir numerical simulation technology, the CO2 flooding simulation calculation under non-darcy flow condition[10] was carried out, etc., and the CO2 miscible flooding scheme and development mode were optimized[11].These studies provide a theoretical basis for CO2 flooding technology
The dynamic distribution of hydrocarbon phase during displacement shows that too small CO2 slug cannot prevent the impact of N2 channeling on the miscible flooding, and the CO2 slug should have at least 0.3 PV to effectively prevent the impact of N2 channeling
Summary
Most of low permeability and ultra-low permeability layers can not be effectively developed by water flooding. Scholars at home and abroad have done a lot of researches and experiments on CO2 flooding Basic theories such as factors affecting CO2 flooding efficiency[1], miscible flooding mechanism[2,3], flow in a porous medium characteristics of CO2 flooding[4], and determination of near-miscible flooding region[5] have been explored. The long core physical model experiment of CO2 miscible flooding[8], the CO2 flooding experiment of ultra-low permeability-tight reservoir and so on[9] were carried out in laboratory. Numerical simulation and physical model experiments of CO2-N2 compound flooding in low permeability and ultra-low permeability reservoir are carried out. The size of CO2 pre-slug in CO2-N2 compound flooding is optimized to improve the oil recovery
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