Gas Injection To Enhance Oil Recovery In Fractured-vuggy Reservoir

Fractured-vuggy reservoir occupies a very important position in the oil and gas resources in the world. This kind of reservoir has strong heterogeneity and its fluid distribution is complex. Multi-scale and connection diversity of fracture and cavern itself caused difficulties in the development. In recent years, with continuous developing fractured-vuggy reservoir in tahe oilfield, a certain understanding of development has been achieved. In the early stage of developing Tahe Oilfield, water injection for oil and unit water injection alleviate the situation of the reservoir production decline, but in the later stage of development, the effect of water injection for oil deteriorates, water cut rises too fast and "attic oil" remaining in the high parts of the cave is difficult to be produced. Water flooding only is difficult to meet the development needs. Oil recovery of reservoir can be enhanced by gas injection through mechanism of gravity differentiation, recovering formation pressure, reducing the oil viscosity to improve effect of reservoir development to further enhance oil recovery.The content of this paper is mainly from the Sinopec Northwest Petroleum bureau. After reading a large number of related literature, according to the similarity criterion,on the basis of the distribution law of reservoir, this paper gives a design for full diameter fracture cave physical model and gas injection for oil in single well model which resists high temperature and high pressure. Using this experimental device, the indoor nitrogen injection for oil experiment is completed. And paper analyzes which way is the most beneficial to the development of reservoir. The mainly completed content in this paper are as follows:1、The effect of bottom water, gas injection method and reservoir oil volume on oil recovery in the single well model. The results show that when the bottom water is plentiful available, bottom water flooding energy can be used to flood oil, for sufficient bottom water reservoir when gas injection rounds are the same recovery rate under gas injection is higher than without bottom water; For bottom water reservoir experiments use the pure gas injection, water alternating gas (WAG) injection and gas-water mixed injection three ways," attic oil" remaining in the upper part of the single well after the bottom water drive which is difficult to produce, can be out partly by gas injection, control the speed of bottom water coning, finally it is concluded that with sufficient bottom water effect of pure gas injection is best; When the reservoir oil volume is large effect is more pronounced with gas injection method.2、Oil displacement experiments of fractured-vuggy physical model and the influence of nitrogen displacement, gas injection rate, oil viscosity and gas injection method on the oil recovery are mainly studied. Studies show that after water flooding, part of oil remains in fractured-vuggy physical model, after gas injection the liquid flow conditions can be improved, further improving the recovery rate; Choosing gas injection rate will affect the final recovery percentage, and an optimum injection rate exists allowing gas to enter the cracks and fully mix with crude oil without premature gas breakthrough; the influence of different gas injection methods on recovery under heterogeneous condition is also compared.