Enhancing tight oil recovery using CO2 huff and puff injection: An experimental study of the influencing factors

A series of core flooding tests were conducted using a specially-designed matrix?fracture model to assess the performance of CO2 huff and puff (?huff-n-puff?) injection with respect to the enhanced oil recovery (EOR) of tight oil. Four key influencing factors were taken into consideration: number of huff-n-puff cycles, matrix permeability, matrix size, and gas type. The results imply that CO2 huff-n-puff injection is capable of effectively recovering tight matrix oil, and there is an optimal cycle regime for such huff-n-puff processes which depends on matrix permeability, matrix size, etc. As the permeability of the matrix is less than 30.0 md, the effectiveness of CO2 huff-n-puff is significantly weakened as the permeability decreases, indicating the great difficulty encountered when developing tight oil reservoirs. Above this value, such effect diminishes. As the matrix size increases, oil recovery using CO2 huff-n-puff decreases and the effect is more obvious when the permeability is low. But, in general, matrix size has a weaker effect on EOR than permeability. Natural gas is a promising albeit less effective alternative when CO2 is unavailable.