Study On Mechanism Of Gravity Stabilized Air Injection And Reservoir Simulation

Gas injection(including air,nitrogen,carbon dioxide,etc.)is an effective method to improve the oil recovery of low permeability reservoirs.Air injection and nitrogen injection are available in the case that the sources of natural gas and CO2 are limited.Compared with nitrogen,air injection flooding technology has the advantages of low cost and thermal effects.Especially for low permeability reservoir with great formation dip and thick oil layer,gravity stabilized Air Injection technology has great advantages.In this paper,a garavity stablized air injection reservoir simulation model which includes three phases and nine components is built on the reservoir conditions of Qi-131 block which is located in Liaohe oil field.The mechanism of air flooding to enhance oil recovery includes: oxygen is consumed and heat is released in the process of low temperature oxidation of crude oil.As a result,the temperature of the reservoir rises.Gas flooding plays the most important role in the process of enhancing oil recovery,followed by the thermal effect.Swelling of the injected gas also helps to improve oil recovery,but contributes a little.The difference between oil and gas gravity is helpful to raise the oil recovery and the larger the formation dip is,the better the gravity stabilized effect is.Sensitivity studies have been carried out to provide reference for preliminary reservoir project design,including formation dip,gas injection rate and sedimentation type.The real reservoir simulation model of Qi-131 block is established,and history match is conducted.Though analyzing laboratory experiment results,studying successful field cases,carrying out reservoir simulation and theoretical calculation,the way of developing the target block is demonstrated.For Qi-131 reservoirs,high temperature oxidation is difficult to form and be stable.The difference between HTO and LTO is very small in terms of EOR.In the same time,the thermal effect of "fire flooding" contributes a little in flooding.In addition,high-temperature oxidation process is complicated and requires high-duty device,so considering the actual situation of in the Qi-131 block,low-temperature oxidation mode is recommended.Injection schemes of Qi-131 block is designed and optimized.FQGD well pattern is the best well pattern.The most optimal gas injection rate of a well is 30000m3/d.Besides,simulation results show that there are three production wells which produce oxygen.It is suggested that if the oxygen concentration rises to the threshold of explosion,relevant measures should be taken.