The Effect And Mechanism Of CO₂ Huff-n-puff On Enhanced Oil Recovery In Tight Conglomerate Reservoirs

Tight conglomerate reservoirs have low permeability and strong heterogeneity,resulting in a poor water injection development effects.CO₂ huff-n-puff has the advantages of reducing the viscosity of crude oil,improving the fluidity of crude oil,and quickly replenishing the formation pressure.The thesis carried out related research,such as CO₂ huff-n-puff physical simulation experiments in tight conglomerate reservoirs,and revealed the enhanced oil recovery effect and oil-increasing mechanism of CO₂ huff-n-puff in M oilfield conglomerate reservoirs.The study of CO₂-formation water-conglomerate interaction shows that with the increase of interaction time and CO₂ pressure,the more severe the rock surface dissolution.This increases permeability to some extent,but as the reaction continues,the clay particles from dissolution can clog pores and damage the formation.In the experimental temperature range used in this study,no phenomenon of blocking the pores and damaging the rock formation was found.The MMP,minimum miscibility pressure,of crude oil and CO₂ in the formation is 28.5 MPa,measured by the thin tube experiment.Through CMG-Win Prop and the principle of pressure equivalent substitution,the MMP was reduced to 12.025 MPa,and the experimental pressure of the physical model was reduced from 53 MPa to 23 MPa.The rationality of the equivalent substitution is verified by the Grashof number,indicating that the simulated oil can be used to carry out CO₂huff-n-puff physical simulation experiments,which can well guide the experimental results under high formation pressure.The indoor physical model experiment shows that the lower the depletion mining degree is,the better the CO₂ huff-n-puff is to enhance the recovery factor,up to 10.06%.With the increase in CO₂ injection rate and soaking time,the recovery first increased and then decreased.There was an optimum gas injection rate（0.75 PV）and soaking time（10h）,and the highest recovery was 11.07%.This thesis has important guiding significance for CO₂ huff-n-puff to enhance oil recovery in tight conglomerate reservoirs.