PHASE IDENTIFICATION AND SATURATION DETERMINATION IN CARBON DIOXIDE FLOODING OF WATER FLOODED CHALK USING X-RAY COMPUTED TOMOGRAPHY

摘要

As an effective method to cope with green-house gas emission,and to enhance oil recovery,injection of carbon dioxide(CO2) into water flooded petroleum reservoirs has obtained increasing attention.In the laboratory studies,identification of different phases and determination of their saturations by use of X-ray computed tomography(CT) is the key problem to visualize flow and to get insight into the mechanisms of CO2 injection. The flooding process is essentially three-phase,and involves interaction between oil, water and CO2(mutual solubility,change of acidity,swelling of the oil,etc.).The purpose of our study is to investigate experimentally the possibility and potential problems of identifying different phases and quantifying their saturations during CO2 flooding.Laboratory experiments on injection of CO2 into chalk cores from the Danish North Sea,saturated with Isopar-L petroleum mixture and distilled water,with various combinations of dopants,have been carried out under the pressures varying in the low to medium range.The experiments utilized CT imaging to visualize the in-situ saturations of the fluids.An optimization method was suggested for the image data analysis,in order to correct the out-of-range data due to low energy level scanning and inhomogeneity of chalk.During experiments,strong adsorption of some dopant on the chalk cores was observed.Sensitivity of chalk to different dopants is discussed.Based on recorded data during CO2 flooding,as well as on the image data and production profiles of the different phases,the detailed data analysis was conducted.The key factors for the successful application of the X-ray computed tomography to the multiphase flows in a chalk rock were identified.The necessary conditions for successful experiments are suggested.