A NEW EVALUATION METHOD OF CO₂ GAS BASED ON THE DIFFERENCE OF HYDROCARBON COMPONENTS BY GAS LOGGING: A CASE STUDY IN THE ENPING DEPRESSION

Influenced by gas properties, reservoir lithology, reservoir physical properties and other factors, conventional logging methods are not efficient enough for both qualitative identification and quantitative evaluation of CO₂ gas. Taking the Enping depression as a case, based on the characteristics of hydrocarbon components in the oil layer, CO₂ gas layer and CO₂ oil layer, this paper, using the field gas logging data together with formation testing data and cable pumping sample data, creatively proposed some explanation charts for qualitative identification and quantitative evaluation of CO₂ based on the difference in hydrocarbon components in gas log. ① An effective qualitative identification chart is established for CO₂ gas reservoir, selecting C₁% and (C₃+C₄+C₅)/C₁ as the characteristic parameters of hydrocarbon components from gas log. ② A quantitative relationship between the CO₂ content and the C₁% of the reservoir is established with the data from gas log for quantitative calculation of the CO₂ content in the exploration stage. The method is applied for 3 fluorescence display layers in 2 exploration wells recently completed, and the interpretation coincidence rate reaches 100%. It has solved the problem of CO₂ qualitative identification and quantitative evaluation in the exploration stage, and also provided a strong technical support for the rapid decision-making of exploration and development operations.