Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (6): 1333-1338.doi: 10.11743/ogg20190617

• Methods and Technologies • Previous Articles     Next Articles

Mechanism of shale oil mobilization under CO2 injection

Zhao Qingmin1,2,3, Lun Zengmin1,2,3, Zhang Xiaoqing4, Lang Dongjiang1,2,3, Wang Haitao1,2,3   

  1. 1. State Energy Center for Shale Oil Research and Development, Beijing 100083, China;
    2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China;
    3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;
    4. Dagang Oilfield Company, PetroChina, Tianjin 300280, China
  • Received:2019-02-18 Revised:2019-05-13 Online:2019-12-28 Published:2019-10-15

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Abstract: CO2 injection may be the most effective method to enhance shale oil recovery due to its good injectivity and miscibility with crude oil.However,unlike conventional reservoirs,shale reservoirs usually feature fractures and micro/nano-scale pores,and thus whether CO2 can enter micro/nano-scale pores to mobilize oil inside is the key to a successful CO2-EOR in shale reservoirs.Therefore,a CO2-EOR experiment was carried out to find out the features and mechanism of oil mobilization in the micro/nano-scale pores of shales by means of nuclear magnetic resonance (NMR).In addition,effects of total exposure time and times of exposure on recovery performance were also investigated.Both NMR T2 spectrum and images indicate that oil in all shale pores can be effectively mobilized by CO2 injection.The recovery factor is 32.63% for the first shale oil -CO2 contact.The production rate is correlated to the exposure time:an initial fast-increa-sing stage followed by a declining stage hereafter.The CO2 diffusion is the main mechanism driving the CO2-EOR in shale reservoirs.In conclusion,the study has proven that CO2 injection serves to effectively enhance shale oil recovery,which may provide an analogy to the effective development of continental shale oil elsewhere.

Key words: micro/nano-scale pore, fracture, nuclear magnetic resonance (NMR), diffusion, CO2, shale oil, enhanced oil recovery (EOR)

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