Study On The Change Of Crude Oil Properties In Gas-injection Reservoir

The fracture-pore carbonate reservoir is characterized by network reservoir,with cavity as the main accumulating space and fracture as the connection channel. Tahe Oilfield is of strong heterogeneous carbonate reservoir, various flow way co-exist, and exploration and development is very difficult. Because of the high salinity of formation water and high temperature of the reservoir, the methods such as polymer flooding, three element composite, microbial method, thermal recovery and EOR technology which have been successfully used in sandstone reservoir, can’t be directly used for cave type carbonate reservoir in Tahe oilfield seam. The development of reservoir fracture leads to the high risk of using chemical method.Gas injection is an effective method for enhancing oil recovery. It not only can maintain the formation pressure, but also can effectively improve the recovery rate for the gas injection process in a fractured reservoir. Mine gas injection test statistics show that there are three factors including reservoir characteristics, fluid properties and dynamic parameters affect gas injection results. The different characteristics of the reservoir have different requirements for gas injection and gas source. This thesis focuses on the domestic and foreign gas injection to enhanced oil recovery based on the present situation and development tendency of research, through the research on cave type reservoir characteristics and gas injection before the formation oil properties and phase behavior of different types of gas injection,the comprehensive analysis of improving oil recovery mechanism,identified as the Tahe oil field gas injection was applied to study nitrogen and hydrocarbon gas. Through laboratory experiments, we know the effects of different gases on the characteristics of formation fluid pressure. And in the different gas injection conditions, we know the change rule of fluid properties. What’s more, we put forward the corresponding solutions. After water injection for fractured reservoir, we do gas injection simulation experiment in the indoor. Firstly, we have an analysis of the feasibility of gas injection for enhancing oil recovery. Secondly, compared with the gas injection flooding development methods, in order to improve the recovery rate of provide the basis for scheme selection.The results show that volume coefficient of crude oil increases, the expansion coefficient increased, the viscosity decreased, the density decreased after gas injection. At the same gas injection pressure, gas solubility is much higher than the amount of nitrogen dissolved. When they are the same injection rate, the range-ability of oil property was similar. In Consideration of the source and cost, nitrogen has the rich sources and low cost. What’s more, it is easy for post-processing. In immiscible flooding or gravity function mechanism flooding, Nitrogen for crude oil light component extraction ability is lower than that of the natural gas. So Nitrogen has advantages for gas injection in a fractured reservoir. Due to gravity difference and viscosity difference, it is easier to form gravity differentiation phenomenon so as to achieve the purpose of oil displacement. The results also show that if nitrogen injection has oxygen, it will lead that oil saturation pressure rise, volume coefficient and expansion coefficient of the crude oil was decreased, the viscosity of the crude oil rise. It is bad for gas injection, and it will bring hidden dangers in the production.