Xinjiang Petroleum Geology ›› 2022, Vol. 43 ›› Issue (1): 42-47.doi: 10.7657/XJPG20220106

• RESERVOIR ENGINEERING • Previous Articles     Next Articles

Effect of CO2 Pre-Pad in Volume Fracturing of Conglomerate Reservoirs in Mahu Sag, Junggar Basin

YI Yonggang1(), HUANG Kexiang2, LI Jie1, MOU Shanbo3, YU Huiyong1, MOU Jianye2(), ZHANG Shicheng2   

  1. 1. Research Institute of Engineering Technology, Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834000, China
    2. School of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
    3. Xinjiang Zhengtong Petroleum and Natural Gas Co., Ltd., Karamay, Xinjiang 834000, China
  • Received:2021-07-07 Revised:2021-08-09 Online:2022-02-01 Published:2022-01-24
  • Contact: MOU Jianye E-mail:yiyg@petrochina.com.cn;moujianye@cup.edu.cn

Abstract:

The conglomerate reservoirs in the Mahu sag of Junggar basin are tight and the reservoir fluid has a poor flow capacity, resulting in rapid decline and unsteady production. Although the effect of CO2 pre-pad fracturing is better than that of hydraulic fracturing, no systematic study has been carried out on how CO2 affects the crude oil and reservoir rocks in Mahu sag. In this study, the displacement ability of CO2 aqueous solution, the dissolution of core minerals and the changes in core porosity and permeability are analyzed. It is found that in the Mahu conglomerate reservoirs, the crude oil displacing rate by CO2 aqueous solution is higher than that by pure CO2 or water. The Mahu conglomerate reservoir has a higher carbonate content, so CO2 aqueous solution can play a stronger dissolution role and increase the porosity and permeability of the reservoir. Experimental results show that the porosity has increased by 27% on average, and the permeability has increased by 110% on average. The injected CO2 aqueous solution prefers dissolving calcite first, then dolomite and last chlorite. Mineral dissolution mainly occurs in the first 5 days, and then becomes less after 5 days.

Key words: Mahu sag, conglomerate reservoir, CO2, crude oil displacement, dissolution, porosity, permeability, mineral composition

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