Modeling CO2 Injection Including Diffusion in a Fractured-Chalk Experiment with Initial Water Saturation

摘要

This paper presents a modeling study of CO2 injection in chalk core base on data reported by Darvish (2007). The experiment consisted of a vertically-oriented 60 cm long chalk outcrop core initially saturated with live reservoir oil at 130o C and 300 bar. After saturating the core with oil and water by displacement, a small fracture volume surrounding the core was created by heating solid Wood’s metal that originally filled the volume between the core and core holder. CO2 was then injected for 20 days. The experiment was performed at a pressure above the minimum miscibility pressure (MMP), as defined by a traditional 1D multi-contact displacement process. Our modeling was conducted with a compositional reservoir simulator. The 2-dimensional r-z model used fine grid for the core matrix and surrounding fracture. The match of reported oil and water production data gave a high degree of confidence in the model. Mass fractions of components measured periodically during the experiment were also matched. Our modeling study indicates that gravity drainage is affecting the displacement process but mass transfer including vaporization, condensation and molecular diffusion has a significant impact on recovery performance for CO2 injection in the Darvish experiment. Another observation made in our study was the strong influence of surface separator temperature on surface oil production. CO2 injection rate and initial water saturation effects were investigated by comparing this experiment with similar experiments where CO was injected at lower rates, and tests with no initial water saturation.