Petroleum Reservoir Evaluation and Development ›› 2022, Vol. 12 ›› Issue (5): 784-793.doi: 10.13809/j.cnki.cn32-1825/te.2022.05.010

• Methodological and Theory • Previous Articles     Next Articles

Variation of crude oil properties with multi-cycle CO2 huff-n-puff of horizontal wells in ultra-low permeability reservoir

LIAO Songlin1(),XIA Yang2,CUI Yinan1,LIU Fangzhi1,CAO Shengjiang1,TANG Yong3   

  1. 1. Sinopec East China Oil and Gas Company, Taizhou, Jiangsu 225300, China
    2. The 5th Oil Production Plant of PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710000, China
    3. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China
  • Received:2021-06-21 Online:2022-10-26 Published:2022-09-27


CO2 huff-n-puff after fracturing of horizontal wells can effectively improve the properties of crude oil and increase the oil recovery of ultra-low permeability reservoirs. Combined with the geology and fluid characteristics of a typical ultra-low permeability reservoir, Block H, the mechanism of multi-cycle CO2 injection in horizontal wells and the variation of crude oil properties in ultra-low permeability reservoirs are studied by means of laboratory experiment and numerical simulation. The results show that after CO2 injection, the saturated pressure of crude oil increases, the volume expands, the viscosity decreases, and the system becomes lighter. And the main action mechanism of different stages of CO2 huff-n-puff are different: in the injection stage, the main mechanism is to supplement the formation energy, dissolve in crude oil, and reduce the crude oil viscosity; in the soaking and the initial stage of production, the main mechanism is to reduce the crude oil viscosity and expand the scope of CO2; in the middle and late period of well opening production, the light hydrocarbons and a small amount of intermediate component hydrocarbons in the oil phase are extracted. The CO2 content in oil phases at different distances in the reservoir is analyzed by the method of fixed time and fixed point, and it is deduced that the lateral sweep radius of CO2 injection along the fracture in H block is 24~40 m. With the increase of the huff-n-puff cycle, the increase of molar content of CO2 in the oil phase decreased from 451 times in the first cycle to 0.44 times in the third cycle. The dissolved amount of injected CO2 in crude oil decreases relatively, and the effect on the properties of crude oil also gradually decreases. The above research provides a new analysis method for understanding the mechanism of CO2 huff-n-puff, and provides some theoretical support for further popularizing the multi-cycle CO2 huff-n-puff technology of horizontal wells in ultra-low permeability reservoirs.

Key words: ultra-low permeability reservoir, CO2 multi-cycle huff-n-puff, crude oil properties, component change, numerical simulation

CLC Number: 

  • TE341