Experiments Of Gas Injection Huff-and-puff In Fracturedvuggy Reservoirs

The fractured-vuggy carbonate reservoirs in Tahe oilfield are dominated by large caves,dissolved pores and fractures,have complex connection between pores and caves,and strong heterogeneity.After completion of bottom water drive or water flooding,there are still a few kinds of remaining oil,such as attic oil,interwell oil et al.As one of the main methods to improve oil recovery,the gas injection huff and puff can improve the development by supplying formation energy,dissolving and reducing viscosity,gas cap and bottom water synergy.In this paper,the influence of injected gas medium on the physical properties of crude oil was tested by PVT,3D physical model based on geological data is used to simulate the process of water injection and oil displacement and the process of gas injection.The effects of three kinds of gas media?N₂,CO₂,N₂:CO₂=1:1?on the remaining oil under the presence of two kinds of viscosity?1094.5mPa·s and 23.6mPa·s?were investigated.On the basis of analyzing the dynamic characteristics of gas injection huff and puff production,the influence of different gas injection medium on the recovery of light/heavy oil reservoir is studied.In addition,the effects of gas injection huff and puff on different degree of increase in high,middle and low positions were investigated.At last,the dynamic production and production mechanism of gas injection huff and puff are studied by using two-dimensional visualization model.The PVT experimental results show that N₂,CO₂,composite gas medium injection can change the oil bubble point pressure,density and oil volume factor,the greater crude oil dissolved gas,the higher the bubble pressure.The 3D model of physical simulation experiments show that gas injection huff and puff can control bottom water,and improve the recovery of 7.55%²8.22%,effect to heavy oil is better than that of thin oil,effect of N₂,CO₂ is better than composite gas,effect to top part is better than that of the lower part.Two dimensional model huff and puff experiments show that gas medium has the effect of supplying formation energy and gravitational differentiation can help form secondary gas cap,control bottom water,and replace attic oil,monadnock oil,oil film.The results can provide reference for the design of gas injection huff and puff in the fractured-vuggy carbonate reservoir.