Pressure characteristics in CO2 flooding experiments

In the initial period of CO2 flooding, formation pressures of reservoirs do not increase noticeably. Physical simulation experiments were designed to study this phenomenon. In the 1-D infill-sand model, it was found that, under the same pressure conditions, the densities of distilled water, salt water and crude oil increased with CO2 dissolution, and then reached stability. By the volume decrease calculation of the liquid and the distilled water dissolution experiment, it was confirmed that the effects of CO2 dissolved in oil and water are the main reasons for any pressure decrease. In the 2-D sand plate model, injection pressure also decreased. By analyzing production PV (pore volume) and injection PV curves, it was found that the main reason for the pressure decrease is that the injected CO2 can flow into the minute pores that are unavailable to oil and water, and comparatively speaking, dissolution of CO2 can be neglected. The result is also proven by porosity calculations and CO2 flooding experiments using different production control methods and by using carbonate cores.