Recovery efficiency and characteristics of long core by CO₂ flooding in low permeability sandstone reservoirs

¹ School of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
² School of Petroleum Engineering, China University of Petroleum, Beijing 102249, China

^* ttli@xsyu.edu.cn

Abstract

CO₂ flooding is an economical and efficient enhanced oil recovery technology, however, it is difficult for conventional short core experiments to provide accurate parameters for the later on-site optimization scheme. In this paper, on the basis of long core flooding experiments and applying NMR technology, we quantitatively evaluated the recovery efficiency and remaining oil distribution characteristics by CO₂ in low-permeability sandstone reservoirs from a microscopic perspective, and explored the potential of CO₂ flooding in low-permeability sandstone reservoirs. Results showed that with the CO₂ injection pressure increase, the recovery efficiency of the long core increased and the ultimate recovery was 65.3%. Recovery efficiency of short cores at the inlet, middle and outlet decreases successively, but the change range was not large, and all of them are around the recovery efficiency of long core. In addition, at low injection pressure, almost all CO₂ went into the larger pores to replace oil. As increased pressure, the oil started to be produced from the smaller pores, but at 22 MPa, the recovery efficiency in larger pores (76.88%-83.38%) was still higher than that of smaller pores (68.73%-72.74%). Which provided a guide for optimizing the CO₂ enhanced oil recovery method in the field.