Xinjiang Petroleum Geology ›› 2025, Vol. 46 ›› Issue (1): 114-120.doi: 10.7657/XJPG20250114

• APPLICATION OF TECHNOLOGY • Previous Articles     Next Articles

Laboratory Experiments and Field Tests of CO2 Near-Miscible Flooding for Medium-Viscosity Oil in NJH Block, Santanghu Oilfield

ZHANG Qi1a(), ZHU Yongxian2, HAN Tianhui1b   

  1. 1. PetroChina Tuha Oilfield Company, a.Research Institute of Exploration and Development; b. Development Department, Hami, Xinjiang 839000, China
    2. Tuha Oilfield Company, PetroChina, Hami, Xinjiang 839000, China
  • Received:2024-07-01 Revised:2024-08-25 Online:2025-02-01 Published:2025-01-24

Abstract:

The NJH block of the Santanghu oilfield features sandstone reservoirs containing medium-viscosity oil, with crude oil viscosity of 20.8 mPa·s. The reservoir is at medium water cut stage, with a predicted waterflood recovery factor of 22.70%, leaving a limited potential for further enhanced oil recovery. To figure out an applicable enhanced oil recovery (EOR) technique, laboratory experiments and field test were conducted on CO2 near-miscible flooding for medium-viscosity oil to understand the mass transfer patterns and EOR mechanisms of this technique, thereby determining its feasibility. The research results show that the front of the CO2 flooding mainly plays a swelling effect, and the rear exerts a stronger extraction effect than the front. Reducing the viscosity and improving the remaining oil displacement efficiency are the main stimulation mechanisms. The viscosity of surface crude oil reduced by 55%, the content of C2-C15 components increased by 18.3%, and the displacement efficiency improved by 4.6 times. Permeability ratio is found to be the primary factor influencing swept volume, with a permeability ratio of 6, leading to a recovery factor of only 13.84% in low-permeability layers. During the field test, the cumulative injected gas volume is 2.66×104 t, cumulative oil production is 0.78×104 t, and oil exchange ratio is 0.29, confirming a promising application of CO2 near-miscible flooding for medium-viscosity oil.

Key words: Santanghu oilfield, NJH block, medium-viscosity oil, CO2 flooding, near-miscible flooding, enhanced oil recovery, field test

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