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Borehole stability in naturally fractured rocks with drilling mud intrusion and associated fracture strength weakening:A coupled DFN-DEM approach

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1565-1581页

作者： Yaoran Wei Yongcun Feng Zhenlai Tan Tianyu Yang Xiaorong Li Zhiyue Dai Jingen Deng College of Petroleum Engineering China University of Petroleum (Beijing)Beijing102249China State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum (Beijing)Beijing102249China College of Safety and Ocean Engineering China University of PetroleumBeijing102249China

Borehole instability in naturally fractured rocks poses significant challenges to *** mud invades the surrounding formations through natural fractures under the difference between the wellbore pressure(P w)and pore pressure(P p)during drilling,which may cause wellbore ***,the weakening of fracture strength due to mud intrusion is not considered in most existing borehole stability analyses,which may yield significant errors and misleading *** addition,only limited factors were analyzed,and the fracture distribution was *** this paper,the impacts of mud intrusion and associated fracture strength weakening on borehole stability in fractured rocks under both isotropic and anisotropic stress states are investigated using a coupled DEM(distinct element method)and DFN(discrete fracture network)*** provides estimates of the effect of fracture strength weakening,wellbore pressure,in situ stresses,and sealing efficiency on borehole *** results show that mud intrusion and weakening of fracture strength can damage the *** is demonstrated by the large displacement around the borehole,shear displacement on natural fractures,and the generation of fracture at shear *** intrusion reduces the shear strength of the fracture surface and leads to shear failure,which explains that the increase in mud weight may worsen borehole stability during overbalanced drilling in fractured formations.A higher in situ stress anisotropy exerts a significant influence on the mechanism of shear failure distribution around the ***,the effect of sealing natural fractures on maintaining borehole stability is verified in this study,and the increase in sealing efficiency reduces the radial invasion distance of drilling *** study provides a directly quantitative prediction method of borehole instability in naturally fractured formations,which can consider the discrete fracture network,mud intrusion,and as

关键词： Borehole stability naturally fractured rocks Weakening of fracture strength Discrete fracture network Distinct element method

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Investigation of mechanical properties of fractured marbles by uniaxial compression tests

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Journal of Rock Mechanics and Geotechnical Engineering 2011年第4期3卷 302-313页

作者： Hepine Xie Jianliang Pei Jianping Zuo Ru Zhang State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Chengdu 610065 China College of Hydraulic and Hydroelectric Engineering Sichuan University Chengdu 610065 China Institute of Rock Mechanics and Fractals School of Mechanics and Civil Engineering China University of Mining and Technology Beijing 100083 China

Uniaxial compression tests （UCTs） on 34 naturally fractured marble samples taken from the transportation tunnels of Jinping I1 hydropower station were carried out using the MTS815 Flex test GT rock testing system. Rockburst proneness index WET is determined for the marble samples with the UCTs. According to the number, size and spatial structure characteristics of the internal natural fractures of the marble samples, fractures are basically divided into 4 types, namely, single fracture, parallel fracture, intersectant fracture and mixed fracture. The mechanical properties of naturally fractured rocks （4 types） are analyzed and compared with those of intact rock samples （without natural fractures）. Experimental results indicate that failure characteristics of fractured rocks are appreciably controlled by fracture distribution or fracture patterns. In comparison with intact rocks, the failure of fractured marbles is a locally progressive failure process and finally rocks fail abruptly. Statistically, the uniaxial compressive strengths （UCSs） of rocks with single, parallel, intersectant and mixed fractures are 0.72, 0.69, 0.59 and 0.46 times those of the intact rocks, respectively. However, the elastic modulus of the fractured Yantang marbles is generally not different from that of intact rocks. But the elastic moduli of Baishan marble with single, intersectant and mixed fractures are 0.61, 0.62 and 0.45 times those of intact rocks, respectively. Experimental results also indicate that WEt of fractured marbles is generally smaller than that of intact marbles, which implies that rockburst intensity of fractured marble in field may be controlled to some extent. In addition, the bearing capacity of surrounding rocks is also reduced, thus the surrounding rocks should be supported or reinforced timely according to practical conditions.

关键词： rock mechanics naturally fractured rocks deformation and failure of rocks rock strength

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