Study on the Difference in CO2 and Air Injection in the Fracture/Matrix Dual Medium of Continental Shale Reservoirs

Chunmiao Ma; Fengqi Tan; Jianhua Qin; Ninghong Jia; Xiankun Li; Yuqian Jing; Ruihai Jiang

doi:10.1021/acsomega.3c02216

Study on the Difference in CO₂ and Air Injection in the Fracture/Matrix Dual Medium of Continental Shale Reservoirs

ACS Omega. 2023 May 25;8(22):20020-20030. doi: 10.1021/acsomega.3c02216. eCollection 2023 Jun 6.

Authors

Chunmiao Ma^{1

2}, Fengqi Tan^{1

2}, Jianhua Qin³, Ninghong Jia⁴, Xiankun Li^{1

2}, Yuqian Jing^{1

2}, Ruihai Jiang^{1

2}

Affiliations

¹ College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory Computational Geodynamics, Chinese Academy of Sciences, Beijing 100049, China.
³ Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834000, China.
⁴ Research Institute of Petroleum Exploration and Development, Beijing 100000, China.

Abstract

To clarify the impact of different displacement media on the enhanced oil recovery of continental shale and realize the efficient and reasonable development of shale reservoirs, this paper takes the continental shale of the Lucaogou Formation in the Jimusar Sag in the Junggar Basin (China, Xinjiang) as the research object and uses real cores to build the fracture/matrix dual-medium model. Computerized tomography (CT) scanning is used to visually compare and analyze the influence of fracture/matrix dual-medium and single-matrix medium seepage systems on oil production characteristics and clarify the difference between air and CO₂ in enhancing the oil recovery of continental shale reservoirs. Through a comprehensive analysis of the production parameters, the whole oil displacement process can be divided into three stages: the oil-rich and gas-poor stage, oil and gas coproduction stage, and gas-rich and oil-poor stage. Shale oil production follows the rule of fractures first and matrix second. However, for CO₂ injection, after the crude oil in the fractures is recovered, the oil in the matrix migrates to the fractures under the action of CO₂ dissolution and extraction. Overall, the oil displacement effect of CO₂ is better than that of air, resulting in a 5.42% higher final recovery factor. Additionally, fractures can increase the permeability of the reservoir, which can greatly enhance oil recovery in the early oil displacement process. However, as the amount of injected gas increases, its impact gradually decreases, and ultimately, it is consistent with the recovery of nonfractured shale, which can achieve nearly the same development effect.