A Experimental Study On Lower Permeability Reservoirs CO₂ Immisscible Drive

Recently, the reserve volume of low permeability reservoirs accounts for as highly as 60 to 70 percent of identified geologic reserve. As a result, low permeability reservoirs will be the main resource foundation of enhancing production during a very period. But the low permeability reservoir's small pore throat, its poor physical property, its strong inhomogeneity, its having threshold pressure, its slight absorbing capacity, its slow oil well inject water development effective, its water content promotes suddenly, all of which leads to difficult inject water development. CO2 drive is not affected by the reservoir temperature or the degree of mineralization, with its advantages such as its wide applicable scope, its low cost of driving, and its remarkable recovery ratio enhancement and so on. It is quite effective to low permeability reservoirs and the special type reservoir in particular,therefore, it becomes one kind of enhancing oil recovery that is praised highly at home and abroad.In view of Daqing Long Hupao the oil field catwalk oil layer concrete reservoir conditions, CO2 immisscible drive experimental studies on the extremely low permeability reservoirs are carried. Using the physical analogue the method, the simulated P.V.T of the initial oil in place,the P.V.T of the initial oil in place and the phase change rule after CO2 injection, the characters of permeability ratio curve determination of CO2 drive, the property change of the rock after CO2 injection are studied. Core drives experiments are carried and the mechanism of immisscible drive is analyzed. The result shows that For the high platform oil layer, its interstitial oil saturation of water drive is high, the end point of aqueous phase permeability is high, two-phase region is small, the water saturated of isotonic curve is high, breakthrough early , water content the watery rises quickly. The injection capacity of CO2 drive is far more than that of water drive, and it's over 618 times larger. While the rock permeability increases, the rock wettability hydrophilicity enhances. As the CO2 injection rate increases, high pressure natural parameter and the phase state of the initial oil in place changes, the solution gas-oil ratio of initial oil in place, the saturation pressure elevates, the initial oil in place volume factor, the shrinkage, compacting factor, the average coefficient of solubility, the expansion coefficient increase, the viscosity, the density reduce. As the pressure of CO2 drive increases, gas breakthrough time, the recovery ratio when gas breakthrough, the final recovery ratio and trade the oil rate increase, CO2 injectivity enhances, the production gas-to-oil ratio increases, the CO2- oil interfacial tension reduces. The lower the rock permeability is, the better the effectiveness of displacement characteristics of CO2 drive is. Consequently CO2 drive is fit for the high platform oil layer.