Issue 45

Q.-C. Li et alii, Frattura ed Integrità Strutturale, 45 (2018) 86-99; DOI: 10.3221/IGF-ESIS.45.07 86 Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs Qing-Chao Li, Yuan-Fang Cheng, Qiang Li School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China. B16020053@s.upc.edu.cn http://orcid.or/ 0000-0001-7373-4046 yfcheng@upc.edu.cn http://orcid.org/0000-0001-7181-9919 Fu-ling Wang College of Science, China University of Petroleum (East China), Qingdao, Shandong 266580, China. Chuang Zhang, Chuan-liang Yan School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China. A BSTRACT . The global reserves of natural gas hydrates are extremely abundant, but hydrate reservoirs are usually clayey silt hydrate reservoirs with low strength, and borehole collapse is a key issue during the drilling operation. In the present work, both the investigation method and the finite element model that used for investigating borehole collapse in hydrate- bearing sediment are developed, and the superiority of the investigation method developed herein is also analyzed. The results show that changes in temperature and/or pore pressure do not necessarily lead to the hydrate dissociation. Hydrate dissociation occurs only when both temperature and pore pressure satisfy the conditions of hydrate dissociation. Moreover, the applicability of the investigation method developed herein is verified by comparing the equivalent plastic strains obtained by the coupled model developed in this paper and the simplified model respectively. In addition, the simplified model overestimates the extent of the wellbore collapse for the drilling operation in hydrate-bearing sediments. All these results demonstrate that both the investigation method and the finite element model can be used for borehole stability simulation in hydrate-bearing sediments. K EYWORDS . Hydrate-bearing sediments; Hydrate dissociation; Wellbore instability; Borehole collapse; Finite element analysis. Citation: Li, Q. C., Cheng, Y. F., Li, Q., Wang, F. L., Wei, J., Ding, J. P., Zhang, H. W., Song, B. J., Zhang, C., Yan, C. L., Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs, Frattura ed Integrità Strutturale, 45 (2018) 86- 99. Received: 19.05.2018 Accepted: 25.05.2018 Published: 01.07.2018 Copyright: © 2018 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION atural gas hydrates are crystalline structures formed by natural gases (mainly methane, generally more than 96%) and pure water under the conditions of low temperature and high pressure [1-3]. More and more attention has been paid to methane hydrate development from hydrate-bearing sediments in deep water for its clean property N