Title: Wellbore stability analysis of fractured formations based on Hoek-Brown failure criterion

Authors: Tianshou Ma; Zixin Yang; Ping Chen

Addresses: State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China ' State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China ' State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China

Abstract: The borehole stability is a key factor to ensure the success of drilling in deep fractured formations. However, the analysis method of wellbore stability, which is based on the single plane of weakness theory, is difficult to apply in actual engineering due to the difficulty in determining the occurrence and mechanical parameters of weak planes. Thus, an analytical method was proposed using the Hoek-Brown (H-B) criterion to predict the wellbore stability for fractured formations. The effects of the pore pressure propagation, in-situ stress, and wellbore pressure had been involved. The results show that the critical mud weight (CMW) calculated using H-B criterion is higher than the Mohr-Coulomb. The stability of the borehole in case 3 (reverse faulting) was poorer than case 1 (normal faulting) and case 2 (strike-slip faulting). The unstable zones and CMW gradually increase with time, due to the increase in pore pressure. The filter cake, which has low permeability, plays an important role in maintaining the stability of the wellbore in fractured formations. This method could help to improve the evaluation of wellbore stability for fractured formations. [Received: February 14, 2015; Accepted: May 3, 2016]

Keywords: wellbore stability; collapse pressure; critical mud weight; CMW; failure criteria; Hoek-Brown; Mohr-Coulomb.

DOI: 10.1504/IJOGCT.2018.089934

International Journal of Oil, Gas and Coal Technology, 2018 Vol.17 No.2, pp.143 - 171

Available online: 26 Jan 2018 *

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