Journal of Southwest Petroleum University(Science & Technology Edition) ›› 2023, Vol. 45 ›› Issue (4): 121-132.DOI: 10.11885/j.issn.1674-5086.2021.10.16.01

• OIL AND GAS ENGINEERING • Previous Articles     Next Articles

Experimental Evaluation on the Cement Sheath Integrity of Unconventional Oil and Gas Well During Large-scale Hydraulic Fracturing

GUAN Zhigang1, DENG Kuanhai2, WU Yanxian1, LIN Zhiwei1, LIN Yuanhua2   

  1. 1. Research Institute of Petroleum Engineering, Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834099, China;
    2. National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China
  • Received:2021-10-16 Online:2023-08-10 Published:2023-07-18

Abstract: Large-scale hydraulic fracturing of unconventional oil and gas wells will put the cement sheath in an extreme service environment, which is easily lead to the failure of the cement sheath barrier. The key to avoid the failure of the cement barrier is to investigate and understand failure mechanism of cement sheath under the alternating pressure induced by fracturing. Therefore, a self-developed experimental device is used to simulate the wellbore environment to carry out the physical test and evaluation of the sealing performance and interface mechanical performance of the full-scale“production casing- normal/high cement sheathintermediate casing” under alternating pressure. The sealing performance and interface mechanical performance of cement sheath were characterized by the number of seal failure cycles and interfacial bond strength, and the sealing performance results of ordinary cement sheath under four alternating pressures(0↗30↘0, 0↗50↘0, 0↗60↘0, 0↗70↘0 MPa) and high strength cement sheath under five alternating pressures(0↗30↘0, 0↗50↘0, 0↗60↘0, 0↗70↘0 and 0↗80↘0 MPa) are obtained. The influence of alternating pressure peak and cycles times on cement sheath integrity is analyzed, the failure mechanism and process of cement sheath integrity under alternating pressure are revealed, and the correlation between cement sheath sealing performance and interface mechanical performance is clarified. It is found that the sealing/channeling resistance and interface mechanical properties of high-strength cement sheath are obviously better than those of ordinary cement sheath. The results can provide an important basis for the optimization of cement slurry system and fracturing construction parameters in unconventional oil and gas wells.

Key words: alternating pressure, cement sheath integrity, full-scale test, unconventional oil and gas well, large-scale hydraulic fracturing

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