Simulation of CO2 Huff ‘n’ Puff Using Relative Permeability Hysteresis

ABSTRACT The CO2 Huff-Puff technique is becoming an attractive technique to stimulate a large variety of wells. This paper presents a new approach to the simulation of this technique, using the concept of relative permeability hysteresis. A newly developed software was used for the study. It is made of a general purpose compositional simulator system that displays numerous specific features arranged in a modular structure. For increased efficiency, numerical models adapted to given problems, can be automatically generated from this system. In the present study, a model was generated to include among other options the kr, Pc hysteresis and to simulate the Huff–Puff process. This study is mainly focused on low productivity reservoir for which CO2 stimulation could represent a viable alternative to being shut down. First the case of a watered out light oil reservoir was investigated. The model was validated by successfully history –matching production data from a typical huff–puff cycle. A performance prediction was performed for additional cycles and parametric runs on amounts of injected CO2 were performed. Then the case of a heavy oil reservoir with no water production was studied. A successful history match of three consecutive stimulation cycles was obtained. However it was found necessary to introduce a rate of gas dissolution in heavy oil, which is more representative of the physical phenomena. A performance prediction was conducted for additional cycles; and a number of parametric runs were performed. The results show that for heavy oil, gas injectivity and oil productivity may increase with the number of cycles in an unlimited medium,higher final oil productivity is obtained with short cycles than with long ones,the influence of up to 25% hydrocarbon gas in the CO2 is limited. Finally it appears that in both types of reservoirs, the relative permeability hysteresis is the main cause for incremental oil production. Oil viscosity plays a major role with the heavy oil only, as would normally be expected.