Experimental and dimensional analysis of CO₂-assisted gravity drainage in low permeability dip reservoirs of east China

ABSTRACT

In this paper, we attempted to analyze the experimental results about different CO₂ injection rates affect the oil recovery and pressure gradient in low permeability dip reservoirs. For these experiments, a special core holder was designed to load a core of 100 cm long and 2.5 cm in diameter; furthermore, it could have different dip angles to simulate gravity segregation condition. Different CO₂ injection rate was chosen to analyze how affect the frontal speed of CO₂ plume, oil recovery, and CO₂ sequestration. The results show CO₂ storage efficiency could be greatly enhanced about 20% by decreasing the injection rates from 0.4 to 0.05 mL/min in dip system. Nevertheless, the ultimate oil recovery will achieve to be 63% when CO₂ injection rate drop to 0.1 mL/min, further reduction of injection rate to 0.05 mL/min will lead to lower recovery 58.1% and higher CO₂ storage efficiency 64.7%. We found there was a huge pressure loss in the middle of core when injection rate is too slow, it is beneficial to CO₂ storage efficiency. The dimensionless number N_vp that we proposed take pressure changes and displacing front velocity into account, which has a better correlation with oil recovery compared to capillary and gravity dimensionless numbers. Analyzing the results suggest that conducting reasonable CO₂ injection rate, monitoring pressure changes along with flooding process may be dominated factors to CO₂-assisted gravity drainage in low permeability dip reservoirs.

KEYWORDS:

• CO₂-assisted gravity drainage
• dip reservoir
• low permeability
• stable oil-gas interface
• CO₂ injection rate

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Acknowledgments

The authors want to acknowledge all the colleagues of Sinopec Petroleum Exploration and Production Research Institute, Enhanced Oil Recovery Technology laboratory, Beijing, China.

Additional information

Funding

The work was supported by National Key Technology Research and Development Program of China during the 13th Five-Year plan (2016ZX05048003).